1. Doppler radar. God only knows what it means
Doppler radar? God only knows what it means! We will all know after we take the MSC Radar Course though.

2. For God's sake, we had to wait 25 years for Doppler… I pray it won't be that long to get Dual Polarized!

3. Cold Fronts - Outline You are wondering…
Cold Front Basics
Conceptual Models
Conventional Radar Signatures
Doppler Signatures
Conveyor Belt Conceptual Model (CBCM)
Summary
I would like the participants to have access to this presentation so that they can play it again at their own leisure. There is a lot of information here. This first presentation cannot make you an expert although it is intended to encourage you to practice. The “hidden” slides are important but had to be cut to make it even remotely possible to achieve the time limit allotted to this presentation.
Within this presentation there is a strong emphasis on operational conceptual models and how the remote sensing data being investigated might be used to assess which conceptual model best applies in a particular situation. As a result there is significant effort made to describe and explain the relevance of each conceptual model. As a result this presentation does not simply display multiple examples of cold front in radar imagery. It is intended to be much more. I hope that you enjoy it.
You will notice an “end” link in the lower right hand corner of the last several pages. This link will allow me to jump to the end and wrap up the presentation should we run out of time. It is more important to cover the material well than to cover it all poorly.
Phil Chadwick
Biography
Phil Chadwick is an operational meteorologist turned researcher and instructor. Phil the Forecaster has been a meteorologist with Environment Canada since The last five years associated with COMET, have been a career highlight. Phil specializes in the analysis and diagnosis of severe weather using remote sensing (one doesn't want to get too close). You may want to see a tornado before you die but not just before you die! Satellite and radar meteorology are his personal favourites.
Phil’s research includes extensive papers on performance measurement and severe weather climatology, Visual Basic programming and of course, remote sensing. Most of this research can be found on the NorLat website under “case studies”. Simply Google “NorLat”.
Phil is first and foremost an operational meteorologist who believes that the analysis and diagnosis of the real atmosphere is an important way to advance the science. Admittedly, Phil has concentrated on satellite meteorology and has been branded as a satellite meteorologist throughout his career. Radar meteorology is very important as well but there is always satellite data available at great spatial and temporal resolutions to bring to bear on the analysis and diagnosis concern of the day – the “problem du jour”. Some of Phil’s radar meteorology applications appear for the first time in this radar course. Finally, Phil strongly believes that meteorology and science must be fun and that the human has an important if not essentially vital role in the provision of quality service.
S. Petterssen's classic 1956 text: Weather Analysis and Forecasting, Vol. 1, Motion and Motion Systems, McGraw-Hill, Ch. 11 (Fronts and frontogenesis) , pp. 189 ff.:
...let the term FRONTAL SURFACE denote a sloping surface or zone of transition separating two air masses of different density. Similarly, the term FRONT will denote the intersection of the frontal surface with a chart. In these definitions the emphasis is upon the SLOPING arrangement of a DENSITY contrast.
You are wondering…
“How Can I fill an hour with radar cold fronts?”
phil

4. The Classic Cold Front
S. Petterssen's 1956 text: Weather Analysis and Forecasting, Vol. 1, Motion and Motion Systems, pp. 189
...let the term FRONTAL SURFACE denote a sloping surface or zone of transition separating two air masses of different density. Similarly, the term FRONT will denote the intersection of the frontal surface with a chart. In these definitions the emphasis is upon the SLOPING arrangement of a DENSITY contrast.
The cold front is really a three-dimensional surface. It is a pity that the understanding often ends as a line drawn where this 3-D surface intersects with the ground.
The mixing zone is behind the surface front and under the frontal surface

5. The Classic Cold Front – Conventional Radar
Typically heavy precipitation near surface front
Precipitation typically convective
Other things to consider include:
Precipitation Type
Bright banding
Attenuation
Anomalous Propagation
Beam Blocking
Radar Dome Wetting
Non-meteorological targets
etc
Sometimes precipitation before and after cold front
Sometimes precipitation after cold front
Sometimes precipitation before and after cold front
Sometimes precipitation before cold front
The heavy precipitation is at and immediately following this sharp and linear cold front.
Take home message – conventional radar data shows the precipitation distribution and character and much more.
From Conventional Data do we really know where the cold front is?
Take Home Message (THM):
Conventional radar for precipitation distribution, character, phase & more

6. The Classic Cold Front – Doppler Radar
Strong Cold Advection
– beam above ANA front
Weak Warm Advection
– beam in mixing zone or above frontal surface to here
Strong Cold Advection
– beam likely under frontal surface to here
Strong Cold Advection in PBL behind
Cold front – No frictional Ekmann Spiral
Slope of 1/50 cold front = 1.1o
Winds back above surface
The cold front is very much a complicated three dimensional structure. The slope of the front is not necessarily constant and is certainly not uniform.
The Doppler radar signal is also variable and can be angled less than or more than the slope of the front making interpretation extremely challenging.
This slide is intended to illustrate how challenging the Doppler radar analysis and diagnosis of cold frontal characteristics can be. It is typically sufficient operationally to just determine:
Whether the front is anabatic or katabatic
Frontal speed
Thermal advections
Thermal advection trends
Stability and stability trends
Slope of 1/200 warm front = 0.3o
Vertical Discontinuity (Cold Advection) at 250 m SE of radar
Vertical Discontinuity (Cold ) at 700 m NW of radar … Frontal Slope … ???????
SE of radar SWLY winds veer slightly with height… in Warm Sector
NW of radar SWLY winds veer slightly and then back strongly with height…
NW of radar a 1.5 degree beam follows a slope of about 1:40 meaning…
Take Home Message (THM): Doppler radar for winds, VWS, front location,
slope, advections, stability… do you know where your beam is ?.. complicated
the 1.5 degree beam might switch above or below the cold frontal surface .

7. The Classic Cold Front Conventional and Doppler Radar
The conventional display of a cold front is dramatically different from the Doppler display. Both reveal valuable information about
3-D Precipitation rate/intensity
3-D Precipitation type
3-D precipitation trends
Cold frontal characteristics of speed, stability and trends in speed and stability
Surface front ahead of elevated front
They are very different …
They both have valuable information…
Take Home Message (THM):
Conventional and Doppler radar allow analysis and diagnosis of real WX

8. The Classic Cold Front Cold Warm
Circulation and deformation occur at every level in the atmosphere. The surface cold front is JUST One.
Think of the cold frontal surface and the deformation zone/skin as a surface separating air masses.
Cold C
Warm
The cold front is really a three-dimensional surface. It is a pity that the understanding often ends as a line drawn where this 3-D surface intersects with the ground.

9. Radar Viewing
Cold
The radar viewing is actually a 3-D display as well. As already presented, the radar beam does not always go where you think it goes.
This makes the observation of another 3-D phenomenon particularly challenging presenting lots of opportunities for confusion.
Radar Interpretation of the Cold Frontal Discontinuity is Complex
3D of Radar Measurement and 3D of the Cold Frontal Surface

10. Anabatic and Katabatic Cold Fronts
Green for “GO”
Red for “Stop”
Frontogenesis
Ana
Jet axis & dry intrusion parallel the frontal cloud band to form a sharp rear cloud edge
Zero vorticity line parallels/near sharp back cloud edge
Clouds and precipitation:
along and behind the cold front
Associated with cold advection – mdt to strong
Active
Kata
Jet axis crosses frontal cloud band
Zero vorticity line crosses front - higher cloud poleward & lower clouds equatorward
Clouds and precipitation:
ahead of cold front
Associated with warm advection – or weakening cold advection
Frontolysis
Knot active
Expect any backing flow to be generally anabatic in nature.
Expect any veering flow to be generally katabatic in nature.
Expecting a cyclonic, backing flow to be anabatic.
Expect any anticyclonic, veering flow to be generally katabatic in nature.
Diagnosing Frontal Type – Anabatic or Katabatic?
Equivalent thickness Gradient zone of equivalent thickness:
Ana Cold Front: within the cloud band
Kata Cold Front: behind the cloud band
Thermal front parameter (TFP) The maximum of TFP accompanies the cloud band:
Ana Cold Front: within the leading area of the cloud band
Kata Cold Front: within the rear area of the cloud band
Temperature advection There is relatively weak warm advection ahead of the Cold Front, and pronounced cold advection behind it.
Ana Cold Front: cloudiness usually lies within CA, TA=0 ahead of cloud band
Kata Cold Front: cloudiness usually lies within WA, TA=0 within the cloud band
Positive vorticity advection (PVA) in upper levels PVA maxima can be found near the rear edge of the cloud band indicating the propagation of the upper level trough and/or the approach of a jet streak (see Front Intensification By Jet Crossing ).
Isotachs at 300 hPa
Ana Cold Front: the jet runs behind the cloud band and parallel to it. The jet crosses the frontal system in the area of the occlusion point. The front is on the anticyclonic side of the jet.
Kata Cold Front: the jet crosses the Cold Front at a sharp angle; according to the jet crossing point the cloud band can be on the anticyclonic or cyclonic side of the jet.
As already mentioned, there are similarities between Kata Cold Fronts and Split Fronts (see Split Front ). The main difference is the orientation between jet and front: in the case of a Split Front the jet approaches from the rear nearly at right angles.
Shear vorticity at 300 hPa Zero line of the shear vorticity:
Ana Cold Front: the zero line is close to and parallel to the rear cloud edge
Kata Cold Front: the zero line crosses the Cold Front; usually it accompanies the transition of the lower cloud tops on the cyclonic side to higher tops on the anticyclonic side of the front.
Ascent
Descent
JET

11. Active or Anabatic Cold front
Ascent
Frontal
Speed
Winds above front
slower
Anabatic Front – Frontogenesis
One only needs to apply the equation of continuity to explain the impact of a backing wind in the warm air above the cold frontal surface.
If the wind backs above the cold frontal surface, then that wind is less than than the forward speed of the cold front. The air is convergent at this height and air must be ascending through continuity. Such a cold front with backing winds above the frontal surface must be anabatic.
According to the conveyor belt theory:
The frontal cloud band and precipitation are related to an ascending Warm Conveyor Belt, which has a rearward component relative to the movement of the front, causing the frontal cloud band and precipitation to appear behind the surface front.
Parallel to the warm conveyor belt there is a dry stream (dry intrusion). The sharp rear cloud edge of frontal cloudiness marks the transition between the two relative streams.
Winds back with height above the cold front to the left of the COL
Backing winds mean unstable - Active Green for “Go”

12. Inactive or Katabatic Cold Front
Knot active
Descent
Frontal
Speed
Winds above front
faster
Katabatic Front - Frontolysis
One only needs to apply the equation of continuity to explain the impact of a veering wind in the warm air above the cold frontal surface.
If the wind veers above the cold frontal surface, then that wind is stronger than the forward speed of the cold front. The air is divergent at this height and air must be descending to fill the void through continuity. Such a cold front with veering winds above the frontal surface must be katabatic.
According to classical theory:
The ascent of warm air is restricted by dry descending air originating from behind the front and, consequently, dissipating the higher clouds.
The main zones of cloudiness and precipitation appear in front of the surface front.
According to the conveyor belt theory:
The ascending Warm Conveyor Belt is overrun by the dry intrusion.
The dry air originates from upper levels of the troposphere or even from the lower levels of the stratosphere, and crosses the Cold Front from behind.
The warm conveyor belt acquires a component which is inclined forwards relative to the movement of the Cold Front. Therefore, frontal clouds and precipitation tend to lie ahead of the surface front.
The cloud tops in the area of the dry air stream are relatively low, whereas on the leading edge of this area the cloud tops are higher. This area indicates the so-called upper Cold Front.
The air mass which is advected by the dry intrusion is colder than the air within the warm conveyor belt. The intrusion cools air above and, later, also ahead of the Cold Front. Furthermore, the air of the upper relative stream has lower equivalent potential temperature. The result is the development of a conditionally unstable layer close to the leading edge of the frontal cloud band. This can be observed as a transformation of layered clouds into convective ones.
Winds veer with height above the cold front to the right of the COL
Veering winds mean stable - Knot active Red for “Stop”

13. Anabatic and Katabatic Cold Fronts
Active
Knot active
WX After
WX Before
Warm Conveyor Belt
Warm Conveyor Belt
Of course, the conceptual models are taken to the extreme in the placement of the clouds and weather.
There are a lot of similarities between Kata Cold Fronts and Split Fronts (see Split Front ). The main difference is the orientation between the jet and the front.
It is generally considered that a Kata Cold Front evolves from an Ana Cold Front. As baroclinic disturbances often develop over the Atlantic, the newly developed Ana Fronts can mainly be found there, whereas older, continental fronts are mostly Kata type. Another reason for the spatial differences might be that the lower parts of the front are decelerated due to the friction of the continent, while the upper parts continue with higher speed.
From my Buddies at ZAMG

14. Split Cold Front Conceptual Model
WCB (Warm Conveyor Belt)
Jet streak and positive vorticity advection (PVA) at a large acute angle
Dry above the low level cloud band and a strong gradient between the two cloud bands at different heights.
Left of jet fronts tend to be ANA in character.
Right of jet fronts tend to be KATA in character
Warm Conveyor Belt
Jet Streak
Definition: A Split Front is accompanied by a cyclonically curved cloud band, which, contrary to a classical Cold Front (see Cold Front ), contains a distinct double banded structure with cold cloud top temperatures at the leading edge and warmer cloud top temperatures at the rear edge:
In the thick cloud band at the leading part of the Split Front VIS signals are white to grey, IR and WV signals are white, representing a thick, multilayered cloud band;
In the low cloud band at the rear part of the Split Front VIS signals are white, IR signals are dark grey to grey and WV signals are either black (if one is using the Meteosat 8 WV 6.2 µm , which shows higher level water vapour) representing a low cloud band with very dry air above or fairly white/light grey if the Meteosat 8 WV 7.3 µm representing the lower atmosphere is used;
In the ideal case the boundary between both cloud bands is marked by a sharp gradient of IR and WV pixel values. In reality only a gradual change of IR and WV grey shades exists;
Some features of a life cycle can be observed:
often EC shaped cellular cloudiness develops within and above the low cloud band on the cyclonic side of the jet axis;
in the WV imagery a black area sometimes develops on the anticyclonic part of the jet axis over the low cloud band of the front, indicating sinking dry air connected with relative streams (see Meteorological physical background);
in a multilayered leading cloud band the higher cloud fibres are shifted downstream and the high and low cloud bands become decoupled.
Note: In literature (especially US) the name Split front has been used in relation to an upper level Cold Front. This is comparable to "Frontal delay by mountains" and "Decoupling of cloud layers at different heights" in this manual (see Orographic Effects on Frontal Cloud ).
Temperature advection (WA) = WCB (Warm Conveyor Belt): The ridge of WA is superimposed on the high level cloudiness representing the warm air rising on the upper level warm frontal surface.
Jet streak and positive vorticity advection (PVA): A jet streak approaches the cloud band at a large acute angle accompanied by a PVA maximum in the left exit region.
Humidity: Very dry values in the upper and middle troposphere above the low level cloud band and a strong gradient between the two cloud bands at different heights can be observed.
Relative streams and isentropic potential vorticity (IPV): Typical configuration of relative streams as described in Meteorological physical background, IPV anomaly on relevant isentropic surfaces indicating stratospheric air.                                                                   
Warm Conveyor Belt
Warm Conveyor Belt

15. Split Cold Front Conceptual Model
Upper flow, jet streak and positive vorticity advection (PVA) cross front at large angle
Split Cold Front Conceptual Model
Dry above the low level cloud band with strong gradient between the two cloud bands - very different cloud top heights
Copied from This material is excellent and aside from shortening it and precise – ing the main points, I can’t add anything. The point of this PowerPoint would be to get some actual satellite examples and illustrate the satellite signatures.
The conceptual model of a Split Front is strongly connected with jet streaks and sinking of very dry stratospheric air. The initial stage of a Split Front generally is an Anabatic Cold Front type. In contrast to the Ana Cold Front, the warm conveyor belt is overrun aloft by the relative stream of the dry intrusion, which transports very dry air. This process takes place as the warm air ascends ahead of the surface cold front with a forward component relative to the frontal system.
Looking at the situation on isentropic surfaces, the meteorological process which leads to the typical appearance of a Split Front in the satellite images can be explained as follows: together with a jet streak approaching the frontal cloud band, dry stratospheric air is advected on the cyclonic side, and dry but tropospheric air on the anticyclonic side of the jet axis. Both air streams are sinking at this stage of development. Relative streams on the isentropic surface are parallel to the jet axis within the jet streak but show a characteristic splitting in the exit region into a northwards oriented and a southwards oriented component. While the southern branch is still sinking, the northern branch is rising again. During an interaction of jet streak and frontal cloud band this configuration of relative streams causes a dissolution of cloudiness from above and the Split Front character appears.
There are proposals to classify the rear edge of the low cloud band as surface and the rear edge of the high cloud band as upper level front. Between these frontal surfaces a shallow moist zone remains. A characteristic feature of the upper level front is that in most cases this frontal surface is a moisture boundary and not a thermal boundary (see Typical appearance in vertical cross section).
In connection with the approaching jet streak a PVA maximum in the left exit region may be superimposed on the low cloud band of the Split Front. Within this area the development of the above mentioned EC-like cloudiness can often be observed (see Front Intensification By Jet Crossing - Cloud structure in satellite image ).
Typical configuration of relative streams with IPV anomaly on relevant isentropic surfaces indicating stratospheric air

16. Split Front in Theta Coordinates
Typical configuration of relative streams with IPV anomaly on relevant isentropic surfaces indicating stratospheric air.

17. Split Front and the PV Maximum
PVA maximum crossing surface cold front in left exit of jet streak

18. Split Front and the Wind Maximum
Jet streak approaching split front

19. Split Front Weather
Cellular on radar
Ana
Upper Front
Tie these ideas into the convective turbulence concepts.
Kata
Upper Front
Take Home Message (THM): With split front most WX with upper cold front – still apply ANA, KATA ideas.

20. Transitional Cold Fronts
Applying the Deformation Zone Conceptual Model
Ana
Green for “GO”
Ascent
Warm
Cold
Descent
cyclonic
anticyclonic C
Descent
Warm
Warm
The deformation zone is actually a three dimensional skin that enclose an air mass characterized by a small range in potential temperature. Air mass enclosed by these deformation zone skins shuffle around and compete with one another for space on the planet.
The intersection of an air mass with the earth’s surface is a front. If the colder potential temperature air mass is retreating, the associated front is a warm front. If the colder potential temperature air mass is advancing, the associated front is a cold front. It is that simple. The front is a two dimensional representation of the air mass intersection with the ground or any level for that matter. A deformation zone (for air masses) is a two dimensional representation of the air mass intersection with a level. A surface front is simply a deformation zone at the surface. A front at any level is simply a deformation zone at that same level.
The importance of this is that we can apply the deformation zone conceptual model to the frontal conceptual model. The resulting characteristics, analysis and diagnosis tools are very powerful, meteorological tools. In particular, they are very insightful in the characteristics of anabatic and katabatic fronts. These insights are summarized in the accompanying slide. The fact that these conceptual models are all internally consistent lends credibility into the process and the assertions above.
anticyclonic
Ascent
Kata
Red for “STOP”
cyclonic

21. Transitional Cold Fronts
Ana
Related to weather…
Ascent
Descent C
Descent
Kata
This is the pattern typically seen in satellite imagery of cold front.
Ascent
Take Home Message (THM):
Deformation Zone Conceptual Model consistent with Ana and Kata CM’s

22. Transitional Cold Fronts
Applying the Deformation Zone Conceptual Model
Ana
This is the pattern typically seen in satellite imagery of cold front – a specific example.
Kata
to Ana and Kata Cold Fronts CM’s. Highly Idealized but…
a useful Conceptual Model that can assist…

23. Split Front and the Upper Deformation Zone
Ana
Ascent
Descent
Ana
Warm Conveyor Belt
Text that goes with these images copied from the previous notes page. I bet COMET could make them more artistic.
With a jet streak approaching the frontal cloud band, dry stratospheric air is advected on the cyclonic side, and dry but tropospheric air on the anticyclonic side of the jet axis. Both air streams are sinking at this stage of development. Relative streams on the isentropic surface are parallel to the jet axis within the jet streak but show a characteristic splitting in the exit region into a northwards oriented and a southwards oriented component. While the southern branch is still sinking, the northern branch is rising again.
Copied from More background information
In the ideal case the isentropes of the equivalent potential temperature show two frontal crowding zones, an upper level front and a surface front. Both crowding zones have Cold Front - like inclinations. While the upper level front is connected to the high leading cloud band, the surface front represents the low-level cloudiness at the back side of the frontal system. Whereas the crowding zone of the surface front is strongly pronounced, the crowding zone of the upper level front is mostly weak. Therefore the upper level front is not characterized as a thermal boundary but rather as a moisture boundary (see Meteorological physical background). The field of temperature advection shows often pronounced WA in front of and above the upper level frontal zone, which is connected with the upper level cloudiness. CA, typical for Cold Fronts, is situated below the surface front.
The most characteristic feature of the humidity distribution is a dry area in higher levels between the two frontal zones. High values of humidity can be found in front of the frontal zones.
In the case of superimposed EC cloudiness a distinct isotach and PVA maximum can be found above the surface front at approximately 300 hPan (see Front Intensification By Jet Crossing - Typical appearance in vertical cross section ).
According to the distribution of humidity the satellite signals in IR and WV images show the highest pixel values in front of the upper level front and, if existing, within the EC - like cloud part. At the backside of the upper level front the VIS signals are usually higher while IR and WV signals are much lower than in front of the upper level front (see Cloud structure in satellite image).
Compare also the chapter Cloud structure in satellite image, where the cross section is indicated in the image. In contrast to the ideal case the surface cold front has a superadiabatic layer in the lower levels of the troposphere. The upper level Cold Front is well developed. The distribution of humidity shows the described insertion of drier air between the two frontal zones. The IR and WV images show the pronounced decrease of temperature from the low to the high cloud part.
02 September 1995/12.00 UTC - Meteosat IR image; position of vertical cross section indicated
Kata
Apply to both surface and upper cold fronts
Warm Conveyor Belt
Kata

24. Conventional Radar What kind of cold front?
Anabatic - Ana Front - Active - WX After Front
Katabatic - Kata Front - Knot Active - WX Before Front
Placement of clouds and weather relative to cold front
This is the pattern typically seen in satellite imagery of cold front – another specific example.
What kind of cold front?

25. Doppler Radar Anabatic - Ana Front - Active - WX After Front
Katabatic - Kata Front - Knot Active - WX Before Front
Placement of clouds and weather relative to cold front
Wind direction – depends on viewing perspective
Usually sharp change in wind direction
Usually sharp change in radial wind component
Discontinuity on Doppler
Discontinuity along a range ring or radial ?
Discontinuity = line
Anabatic - Ana Front - Active - WX After Front
Katabatic - Kata Front - Knot Active - WX Before Front
Placement of clouds and weather relative to cold front
Wind direction – depends on viewing perspective
Usually sharp change in wind direction
Usually sharp change in radial wind component
Discontinuity on Doppler.
Discontinuity along a range ring or radial ?
Not along a range ring

26. Doppler – Cold Front Approaching Radar
Assuming there is widespread precipitation!
What Doppler Sectors?
What Doppler Colours? Where?
Doppler – Cold Front Approaching Radar
Anabatic Precipitation Distribution?
Katabatic Precipitation Distribution?
Ana - main zone of cloudiness and precipitation after the surface front.
Kata - main zones of cloudiness and precipitation before the surface front.

27. Doppler – Cold Front Past Radar
Assuming there is widespread precipitation!
What Doppler Sectors?
What Doppler Colours? Where?
Doppler – Cold Front Past Radar
Anabatic Precipitation Distribution?
Katabatic Precipitation Distribution?
Ana - main zone of cloudiness and precipitation after the surface front.
Kata - main zones of cloudiness and precipitation before the surface front.

28. Doppler – Cold Front Approaching Radar
Is it simple? Yes No
Doppler – Cold Front Approaching Radar
Depends where the Doppler Radar is…
Relative to the pattern…

29. Doppler – Cold Front Past Radar
Is it simple? Yes No
Doppler – Cold Front Past Radar
Depends where the Doppler Radar is…
Relative to the pattern…

30. ? Overshooting Anabatic or Katabatic Cold Front
Ontario Example
? Overshooting
Fuzzy Isodop disconnected at Front
Veering Isodop = Warm Advection
All of these categorical classifications are like every generalization, never completely correct. Classifications like generalizations can however, be useful and thus are acceptable statements.
Disconnnect not along ring = spatial (not vertical)
Notice: the west of cold front
Isodop backs with respect to the radar &
Isodop itself veers (slightly) with height…
Cold Advection
Stabilization

31. Anabatic or Katabatic Cold Front
3 hours later
Anabatic or Katabatic Cold Front
Ontario Example
1.4 km
Above Cold Frontal
Surface?
1.6 km
Stay flexible
Ongoing
Analysis and
Diagnosis is
Vital…
With a radar angle of 0.5o and a radial range from the radar of about 100 km, the elevation above the radar elevation is 1.4 km. This occurs at 80 km WNW of the cold front.
The typical height above ground behind a cold front with a slope of 1:50, would be 1.6 km at 80 km behind the cold front.
This slide is intended to illustrate the thought processes that can be employed to analyze and diagnose a Doppler radar display of a cold front.
0.5o radar elevation at 100 km radial from the radar has beam at 1.4 km
Height of 1:50 cold front 80 km WNW of surface front is 1.6 km…
The Radar is probably sampling the warm air above the cold frontal
surface which must have a shallower slope closer to 1:60

32. Anabatic or Katabatic Cold Front
Nova Scotia Example
140 km
Spatial Discontinuity does NOT FOLLOW Range rings
Front climbs 3 km in 140 km giving frontal slope of 1:45. ANA steeper than average.
Backing above ANA front also consistent.
This example is meant to highlight that the PPI characteristics of Doppler along the three dimensional cone makes interpretation challenging. The Doppler cone can intersect the three dimensional frontal surface multiple times thus making interpretation very challenging indeed.
Nil Isodop Veering
Isodop Backing – Cold Advection
Isodop Backing – Cold Advection
Isodop Veering – Warm Advection
Where is the front intercepted aloft?
1.5 km Or is front higher? Backing at 3.0km characteristic of Anabatic Front

33. Lesson here – Doppler behind a cold front is tricky!
Nova Scotia Example
Lesson here – Doppler behind a cold front is tricky!
Above
Ana
Front
Scale Exaggerated
In Mixing
Zone
In Frontal
Cold
Advection
1.5 deg
On Average this cold front not as steep as 1.5 o
Except at the leading edge.
This example is meant to highlight that the PPI characteristics of Doppler along the three dimensional cone makes interpretation challenging. The Doppler cone can intersect the three dimensional frontal surface multiple times thus making interpretation very challenging indeed.
1.5 Degree Elevation Angle = 1:38 slope
Estimated frontal slope = 1:45 (not quite as steep)
ANA steeper than average (1:50)
Backing above ANA front also consistent.

34. Anabatic or Katabatic Cold Front
Another Cold front
Anabatic or Katabatic Cold Front
WSO
Southwestern Ontario
0120Z Dec 23, 2006
CAPPI 1.5 km
Rain rate
Cut a cross-section
Once again, these categorical classifications are like every generalization, never completely correct. Classifications like generalizations can however, be useful.
Applying Conceptual Models to patterns is
fundamental to operational meteorology.

35. You can almost see the subsidence… Vertical Cross-Section
The same Cold front
Katabatic
You can almost see the subsidence…
Vertical Cross-Section
WSO
Southwest Ontario
0120Z Dec 23, 2006
Rain rate
GEM temps contoured; T0 orange; Tw0, Tw2, Tw5 in blues
Descent
The precipitation definitely precedes the katabatic cold front in this example. SW
GEM cold front NE

36. Cold sector Isodop almost backs… counter clockwise
The same Cold front
Cold sector Isodop almost backs… counter clockwise
Warm sector Isodop veers… clockwise
WSO
Southwestern Ontario
0120Z Dec 23, 2006
-0.09° Radial Velocity
Cold Advection over Warm Advection ? Destabilization – Isodop backs with range/height ?
Is it real?
Yes, it is real – but SO weak & where relative to frontal surface?

37. Cold sector Isodop veers… clockwise ???
The same Cold front
2 hours later
Not much of a COLD front
Cold sector Isodop veers… clockwise ???
WSO
Southwestern Ontario
0320Z Dec 23, 2006
-0.09° Radial Velocity
One must not be complacent when attempting to analyze and diagnose Doppler radar data. There are many variables to consider.
But wait… this makes no sense…
-0.09o = near surface= frictional Ekmann Spiral

38. Cold front
WSO
Southwestern Ontario
0320Z Dec 23, 2006
VAD
The lesson here – look at all data for evidence & a solution
Isodop and Winds back with height
As they should behind a cold front!
Always look for supplemental and confirming information. The more pieces of evidence that one can obtain to support a conclusion, the more likely the conclusion is indeed correct. This applies to everything in life and not just meteorology.

39. Most pcpn is out ahead of cold front
The same Cold front
2 hours later
Anabatic or Katabatic Cold Front
2 hours later…
still Katabatic
WSO
Southwestern Ontario
0320Z Dec 23, 2006
CAPPI 1.5 km Rain rate
Most pcpn is out ahead of cold front

40. The Conveyor Belt Conceptual Model
Cold Front Conceptual Models
With a Radar Emphasis
R = Right of the Col
C = Centered on the Col
L = Left of the Col
End

41. The Conveyor Belt Conceptual Model
Think in 3-D
End

42. Think in 3-D NLY Flows Sinking Isentropically
Radar Signatures Relative to the Conveyor Belts
NLY Flows Sinking Isentropically
SLY Flows Rising Isentropically
All circulations in the atmosphere are three dimensional with skins that are always stretching and deforming. We can use two dimensional deformation zones to represent these circulations and air mass boundaries. Fronts are in fact deformation zones. Anabatic and katabatic fronts can be characterized by the by using the deformation zone concepts.
The centre of a conveyor belt circulation is the col of the associated deformation zone. The strongest portion of any circulation tends to be in the centre and this is also identified by the col. These circulations tilt at different levels in the atmosphere and the tilt can be characterized by the tilt of the line joining all of the cols. The tilt of this col line perpendicular to the front gives the frontal slope. The tilt of the col line either toward the north or south tells about the dynamics of the circulations.
For a cold front in the northern hemisphere if this tilt is toward the north, the circulation is also from the north. The associated cold advection would likely make this a strong cold front. If the tilt is toward the south, the associated cold advection is likely to be weak.
Active weather is likely to be on the cyclonic side of the col while inactive weather is likely to be on the anticyclonic side of the col.
Think in 3-D
End

43. DCB rises isentropically as it curls cyclonically northward
Vertical Deformation Zone Distribution and the CBCM Summary Left of the Col C
CCB C
DCB rises isentropically as it curls cyclonically northward
Located in the dry slot of the comma head
Winds back with height above the cold frontal surface
The cold frontal slope is steeper than the average 1:50
Cold front is likely Anabatic C C
DCB
Left of COL DCB
DCB C
Back C
DCB
Typical distributions of the conveyor belts and the associated deformation zones. Recall from the satellite palette that the deformation zone is actually a cross-section of the deformation sheath that encases an isentropic flow. Similarly, the vorticity centres depicted in the deformation zone conceptual model are actually vortex tubes that also slope in the vertical along with the deformation sheath.
The Warm Conveyor Belt (DCB) typically rises isentropically with poleward (both northeasterly and northwesterly) motion and time. The DCB is shown with no vertical wind shift but typically it veers with height which is consistent with warm air advection.
The Cold Conveyor Belt (CCB) typically sinks isentropically with equatorward (southwesterly) motion and time. The CCB typically backs with height which is consistent with cold air advection.
The Dry Conveyor Belt (DCB) typically sinks isentropically with equatorward (southeasterly) motion and time. In the “dry slot” of the comma pattern, the DCB is typically rising isentropically with poleward (northeasterly) motion and time. The DCB typically veers with height with the approaching upper ridge.
The flow Equatorward of the conveyor belt system has not been typically described but is the remains of the dry conveyor belt caught up in the upper ridge circulation. (Chadwick has described it in unpublished work.) This circulation is dry and subsiding with poleward (northwesterly) motion and time. The portion of the flow that turns southwesterly dry rises with equatorward (southwesterly) motion and time. This portion of the CCB typically veers with height which is consistent with warm air advection west of the upper ridge.
The slope of the isentropic surfaces can be inferred from the overlap of the deformation zones. The slope of the isentropic surfaces can also be used to analyze instability. Isentropically speaking, sinking cold air and rising warm air converts thermal energy into kinetic energy. The vertical motions of dry air is not so simple isentropically speaking – have to ponder this!
The introduction of isentropic thinking to NinJo will make the investigation of these concepts much easier.
End

44. Cold Frontal Conceptual Models
Anabatic Cold Front
Cloud pattern
Anabatic - Ana Front - Active WX After Front A B
End

45. DCB sinks isentropically as it curls anticyclonically southward
Vertical Deformation Zone Distribution and the CBM Summary Right of the Col C
CCB C
DCB sinks isentropically as it curls anticyclonically southward
Located along the equatorward tip of the comma tail
Winds veer with height above the cold frontal surface
The cold frontal slope is more shallow than the average 1:50
Cold front is likely Katabatic C C
DCB
DCB C
Right of COL DCB C
DCB
Typical distributions of the conveyor belts and the associated deformation zones. Recall from the satellite palette that the deformation zone is actually a cross-section of the deformation sheath that encases an isentropic flow. Similarly, the vorticity centres depicted in the deformation zone conceptual model are actually vortex tubes that also slope in the vertical along with the deformation sheath.
The Warm Conveyor Belt (DCB) typically rises isentropically with poleward (both northeasterly and northwesterly) motion and time. The DCB is shown with no vertical wind shift but typically it veers with height which is consistent with warm air advection.
The Cold Conveyor Belt (CCB) typically sinks isentropically with equatorward (southwesterly) motion and time. The CCB typically backs with height which is consistent with cold air advection.
The Dry Conveyor Belt (DCB) typically sinks isentropically with equatorward (southeasterly) motion and time. In the “dry slot” of the comma pattern, the DCB is typically rising isentropically with poleward (northeasterly) motion and time. The DCB typically veers with height with the approaching upper ridge.
The flow Equatorward of the conveyor belt system has not been typically described but is the remains of the dry conveyor belt caught up in the upper ridge circulation. (Chadwick has described it in unpublished work.) This circulation is dry and subsiding with poleward (northwesterly) motion and time. The portion of the flow that turns southwesterly dry rises with equatorward (southwesterly) motion and time. This portion of the CCB typically veers with height which is consistent with warm air advection west of the upper ridge.
The slope of the isentropic surfaces can be inferred from the overlap of the deformation zones. The slope of the isentropic surfaces can also be used to analyze instability. Isentropically speaking, sinking cold air and rising warm air converts thermal energy into kinetic energy. The vertical motions of dry air is not so simple isentropically speaking – have to ponder this!
The introduction of isentropic thinking to NinJo will make the investigation of these concepts much easier.
Veer
End

46. Cold Frontal Conceptual Models
Katabatic Cold Front
Cloud pattern
Katabatic - Kata Front - Knot Active WX Before Front A B
End

47. Behind the Cold Front Conceptual Models
Left of the Col looking across the flow B A
DCB
WCB oriented for
more frontal lift
Deep Instability
And moisture
likely
Mixing Zone
CCB
More frontal
Lift with backing
Surface
Cold Front
WCB A B
Cold air in Cold Conveyor Belt (CCB) deep & moist.
Notes:
All descriptive terms are intended to be comparative between the various conveyor belts in the Conveyor Belt Conceptual Model.
All quantities are intended to be the average or typical values
The DCB tends to rise isentropically turning cyclonically
Typically in the dry slot of the comma pattern
Winds typically back with height above the cold frontal surface
The cold frontal slope is steeper than the average 1:50
Cold front is likely Anabatic
Precipitation returns will be limited in extent
Precipitation will tend to be very cellular
This results in an incomplete display of the Doppler wind field in particular
Precipitation will be extensive for acceptable radar depiction of the features
Warm Conveyor Belt (WCB) very deep, warm, moist and rising isentropically
CCB approximately horizontal or rising slightly and moving southeastward
CCB backs with strong cold advection
WCB just ahead of cold front backs with significant VWS
Frontal slope is steeper than the typical 1:50
Significant backing above the frontal zone – anabatic cold front
End

48. Behind the Cold Front Conceptual Models
Centered on the Col looking across the flow. A
WCB oriented for
moderate frontal lift
DCB B
Common area
for deep
instability
Mixing Zone
CCB
Surface
Cold Front
WCB A B
Cold air in Cold Conveyor Belt (CCB) moderately deep & moderately moist.
Notes:
All descriptive terms are intended to be comparative between the various conveyor belts in the Conveyor Belt Conceptual Model.
All quantities are intended to be the average or typical values
This is the portion of the DCB pointing directly at the col in the associated deformation zone.
It is almost a straight line flow separating cyclonic curvature to the left (poleward) from anticyclonic curvature to the right (equatorward)
There is typically a dry delta pattern just upstream from the col location
The cold frontal slope is likely to be close to the average 1:50
Cold front is neither Katabatic or Anabatic
Precipitation will be spotty for radar depiction of the features
Warm Conveyor Belt (WCB) moderately deep, warm, moist and rising isentropically
CCB approximately horizontal and moving isentropically southward
CCB nearly straight with nil or weakening cold advection
WCB just ahead of cold front nearly straight with nil VWS
Frontal slope is near the typical 1:50
Nil VWS above the frontal zone – neither ana or katabatic cold front
End

49. Behind the Cold Front Conceptual Models
Right of the Col looking across the flow.
DCB A
WCB oriented for
less frontal lift B
Mixing Zone
Less frontal
Lift with veering
Surface
Cold Front
WCB
CCB
Chance of
deep instability A B
Cold air in Cold Conveyor Belt (CCB) shallow & dry.
Notes:
All descriptive terms are intended to be comparative between the various conveyor belts in the Conveyor Belt Conceptual Model.
All quantities are intended to be the average or typical values
Cold air in Cold Conveyor Belt (CCB) shallow & dry.
Precipitation will be lacking for radar depiction of the features
Warm Conveyor Belt (WCB) is shallow, warm, moderately moist and rising isentropically
CCB sinks isentropically southwestward
CCB veers with height consistent with weakening cold advection ~ warm advection
WCB just ahead of cold front also typically veers with height
Frontal slope is more shallow than the typical 1:50
Veering winds above the frontal zone indicative of katabatic cold front
Precipitation will be lacking for radar depiction of the features
Warm Conveyor Belt (WCB) is shallow, warm, moderately moist and rising isentropically
CCB sinks isentropically southwestward
CCB veers with height consistent with weakening cold advection ~ warm advection
WCB just ahead of cold front also typically veers with height
Frontal slope is more shallow than the typical 1:50
Veering winds above the frontal zone indicative of katabatic cold front
End

50. DCB to the Left of the Col - Doppler
The Cold Left Wing Climb Conceptual Model
DCB in dry slot is typically ascending and backing
Steeper frontal slope will be evident.
Within the CCB – Cold Advection:
Cold advection backing probably overpowers the Ekman spiral veering. Beaked eagle.
Mixing layer
Cold frontal surface o
Dry CB
Within the DCB:
West of radar backing, cold advection, Anabatic cold front
East of radar nil VWS or possibly weaker backing
DCB to the Left of the Col - Doppler
Stoop
To bend or sag downward.
To lower or debase oneself.
To descend from a superior position; condescend.
To yield; submit.
To swoop down, as a bird in pursuing its prey.
Right Wing
Left Wing C
End

51. The Cold Left Wing Climb CM
Anabatic !
This cold front is oriented NNE-SSW.
The Cold Left Wing Climb CM
The heavy precipitation is at and immediately following the sharp and linear cold front.
End

52. DCB Centred on the Col The Cold Screaming Eagle CM
DCB in this portion of dry slot may ascend but nil VWS A B
Within the CCB – Cold Advection:
Cold advection probably overpowers the Ekman spiral signature. Beaked eagle
Mixing layer
Cold frontal surface o
Right Wing
Left Wing
Dry CB
Within the DCB:
Nil VWS C
DCB Centred on the Col - The Cold Screaming Eagle CM
– These are exploratory estimates until we discover a good example.
Stoop
To bend or sag downward.
To lower or debase oneself.
To descend from a superior position; condescend.
To yield; submit.
To swoop down, as a bird in pursuing its prey.
End

53. DCB Right of the Col The Cold Left Wing Dive CM
The eagles left wing is folded forward as if it is about to turn to the right and swoop down. That is what this part of the DCB does.
The right wing is still fully extended to catch the lift of the WCB. C A
Within the CCB – Cold Advection:
Cold advection probably overpowers the Ekman spiral signature. Beaked eagle B
Mixing layer
Cold frontal surface o
Right Wing
Left Wing
Dry CB
Within the DCB:
Winds veer with range/height to the west
Katabatic cold front
DCB Right of the Col - The Cold Left Wing Dive CM – These are exploratory estimates until we discover a good example.
Stoop
To bend or sag downward.
To lower or debase oneself.
To descend from a superior position; condescend.
To yield; submit.
To swoop down, as a bird in pursuing its prey.
End

54. Cold Fronts - Outline Keep Looking UP! Thank you for your attention!
Cold Front Basics
Conceptual Models
Conventional Radar Signatures
Doppler Signatures
Conveyor Belt Conceptual Model (CBCM)
Summary
Keep Looking UP!
I hope that you had fun…
Phil Chadwick
Thank you for your attention!
Remote sensing is your Friend!
Take Home Message (THM):
Radar is useful to analyze and diagnosis cold fronts … Doppler is tricky!

55. Radar Analysis and Diagnosis of Cold Fronts
One Final Take Home Message (THM):
Expect any cyclonic, backing flow to be anabatic.
Expect any anticyclonic, veering flow to be katabatic.
Southerly flows typically rise isentropically.
Northerly flows typically sink isentropically.