1. Mid-Latitude Cyclone Development
BFB: 10/20/2015 Zach Hiris & Phil Pascerelli

2. Purpose of Mid-Latitude Cyclones
What is the role of mid-latitude cyclones in the atmosphere?
Balance the temperature gradient
Gradient forms because heating is never equal in the atmosphere
If it was, we’d never see the weather we have each day!
Strong gradients can produce very strong mid-latitude cyclones!

3. Characteristics Cold Core Lows
Strengthen with height
Warm Air Advection prevalent near most precipitation
Creates lift needed for precip
Heaviest Snow
“Always to the left of the low” -Dr. Ballentine. Why?
Deformation!
Winds converge on one axis and diverge on another- creates lift!

4. 2 3 1 1 Formation Where do these cyclones tend to form in the CONUS?
Eastern Seaboard/Gulf of Mexico
Heating effects of diabatic and latent heating (Gulf Stream interaction)
Lee side of the Rockies
Due to stretching effects
Alberta Canada region
Known for “Alberta Clippers” and Miller B storms- more on this later! 3 2 1 1

5. Ingredients Needed Divergence! Vorticity Baroclinic Zones
Where upper level winds are diffluent (spreading apart)
Leads to low level convergence
Vorticity
“Spin” in the atmosphere
Part of the reason the Lee side of the Rockies sees cyclogenesis
Baroclinic Zones
Heating differences- think frontal zones, strong temperature boundaries (Gulf Stream)

6. Upper Level Troughs
Mid-latitude cyclones are often associated with 500mb “troughs”, or areas of lower heights
Depending on the orientation of the trough, this can indicate strengthening, weakening, etc.
Also indicate diffluence/confluence, among other things (i.e. upper level lift)

7. Positive Tilt vs. Negative Tilt
Positive tilted troughs indicate that a low pressure system has not yet reached maturity or is weakening
Typically don’t produce significant weather
Negatively tilted troughs
Most commonly produce sigificant weather
Indicates low pressure has reached maturity
Also is a sign of differential advection- low level WAA below mid/upper level CAA
Increasing instability!

8. Positive vs. Negative Tilt

9. Common Storm Tracks Rockies Cyclones Gulf of Mexico/East Coast
Panhandle Hook
Tracks through Ohio Valley or further south
Great Lakes Cutter
Cuts west of the Great Lakes- commonly produce severe weather East of the Mississippi
Gulf of Mexico/East Coast
Miller A
Classic winter storm track for I-95 corridor
Miller B
Technically different versions - depending on the definition these storms also originate from Alberta, Canada

10. L L L Cyclone Tracks Great Lakes Cutter Panhandle Hook
Miller B “Transfers”
Miller A “Nor’Easter” L

11. Winter Storms
Storms from Fall to Spring are typically stronger than in the summer. Why?
The temperature gradient/jet stream is stronger!
Stronger thermal gradient- more rapid cyclogenesis
Stronger storms = Stronger lift = Heavy snow!
Must know what to look for for where a storm is tracking!
Where will the snow develop?

12. Winter Storm Forecasting
Tips to producing a successful winter storm forecast (rain/snow/ice)
Know the track of the low
Use Dr. B’s rule for determining where snow is most likely to occur
Keep in mind what’s happening in the upper levels- where’s the baroclinic zone, PVA?
Thermal Profiles
Must know the thermal profiles of every level- let BUFKIT/Skew-T’s be your friend!
Identify less obvious features- Warm Air Advection, Cold Air Damming, etc.
Magic temperatures for Dendritic growth (DGZ): -16 to -12C
Deeper DGZ- better snow rates and heavier snow

13. Cyclone Forecasting- Archive (GHD 2011)
Things to look for…
500mb Heights/Vorticity
Look at the trough and its orientation- where it’s tracking
Where is the PVA?
700mb Humidity & 850mb Temps/Humidity
Where is the moisture? Thermal gradient (aka baroclinic zone?)- Where is the low going?
Surface Maps
Where does the actual low track in relation to these?

14. Cyclone Forecasting- Archived Case (GHD 2011)

15. Example of Cyclone Forecasting- GFS
Look for lower 500mb heights- where is the upper level low developing?
Is there confluence ahead of the storm track?
Confluence- Upper Level air coming together- convergence in the upper atmosphere tends to deflect cyclones away
Where are the areas of vorticity- where is it heading?
Positive Vorticity Advection (PVA)- where the PVA is, the surface low usually follows
Where is the best place diffluence (divergence)?
Important to know the features above the surface
Knowing where the storm tracks in relation to these gives you the storm track!

16. GFS Example- Images

17. Famous Mid-Latitude Cyclones (March 1993)
One of the strongest mid-latitude cyclone observed in the United States
The low rapidly intensified at a rate of 17 hPa in 12 hours in the Gulf of Mexico
A pressure of 961 hPa recorded in White Plains, New York
Weather models forecast the storm accurately five days out.
One inch of snow was observed along the Gulf Coast, 42.9 inches of snow recorded in Syracuse, New York
Birmingham, Alabama recorded 13 inches of snow and a low temperature of -16.7°C (2°F)

18. March 1993- Triple Phaser Can be referred to as a “Triple Phaser”
All 3 portions of the jet stream (Arctic, Polar, Subtropical) combined over the eastern U.S. coast
Led to massive strengthening

19. Famous Mid-Latitude Cyclones (March 1993)

20. Famous Mid-Latitude Cyclones (Oct. 2010)
Also known as the “Octo-bomb”
Known as the most intense extratropical cyclone in U.S. history (beats out Blizzard of 1978) with a recorded pressure of 952mb
The low rapidly intensified (bombed out) over the Northern Plains
Wind gusts of up to 70mph were recorded from the strong pressure gradient
Produced significant severe weather
One of only 3 days in October the SPC highlighted a “High Risk”
Oct. 26th produced 57 tornado reports, 339 wind reports

21. Famous Mid-Latitude Cyclones (oct. 2010)