Mid-latitude Cyclones and Weather Forecasting AT351 Lab 9 March 26, 2008

Mid-latitude (Extratropical) Cyclone  A cyclone (area of low pressure) in the middle (35°-70°) latitudes  Important for global heat transport  Help to redistribute energy between the tropics (equator) and the poles  Often associated with significant weather events  Described by the Polar Front Theory  Form on boundaries between warm and cold air  Polar front is the boundary between polar cell and Ferrel cell  Cold Polar air meeting warm tropical air

Features of a Mid-latitude Cyclone  Deep low pressure area with attached cold and warm fronts  Often an occlusion forms, the triple point lending to the formation of severe weather  Precipitation associated with the cold and warm fronts organizes in typical “comma cloud” structure

Stages in Wave Cyclone Development Polar Front -->

Polar Front Theory  Initially, there is a stationary front that acts as the boundary separating cold, continental polar air from warm, maritime tropical air  Winds blow parallel to this front on either side  Flow around the highs

Cyclogenesis  A wave forms on the front due to a shortwave disturbance  Frontal Wave  Incipient Cyclone  The front develops a "kink" where the wave is developing  Precipitation will begin to develop along the front  Overrunning and lifting Central Pressure

Strengthening  The cyclonic circulation around the low becomes more defined  The central pressure intensifies  The cold front and warm front have more organized motion  Cyclone usually pushed east or northeast by the winds aloft

Mature Cyclone  The cold front catches up with the warm front and an occlusion forms  Where does the energy to do all of this come from?  The cyclone is at its strongest at this point  Severe weather often develops near the “triple point”  Note: Precipitation in 3 locations

Dissipation  The occlusion grows with time  Eventually, the occlusion is so great that the supply of warm, moist air into the low is cut off  Cold air on both sides  When this happens, the system starts to dissipate

Family of Cyclones

Strengthening  A low pressure area’s strength is defined by how low the pressure is  Hence, all a low needs to strengthen is for its pressure to drop in the center  How might that happen?

Strengthening Low  We know that for the pressure to drop, air must leave the column  It isn’t leaving at the surface, because the wind is spiraling inward  Therefore, it must leave at the upper levels  Rising motion will cause this

What is this showing? What do the dashed lines represent?

Long Waves vs Short Waves  Uneven heating causes troughs and ridges to form around the globe  An almost constant ring of trough/ridge patterns exist, called longwaves  The Polar Vortex  Waves usually move west-east, but can sometimes appear to move westward  Called retrograde motion  Within these longwaves, disturbances exist called shortwaves  Shortwaves deepen in longwave troughs  Shortwaves weaken in longwave ridges  Shortwaves move faster (generally)

Long Waves

Short Waves

Interaction with Upper Levels  Previous model for cyclone development only includes surface characteristics – but what happens higher up can determine what happens below  Remember this picture?  Turns out that divergence aloft can help to remove mass from a column, hence lowering the surface pressure even more

Interaction with Upper Levels  Downstream of an upper level trough, the air tends to diverge  If a surface low is located slightly downstream of an upper level trough, the divergence will be located above the low and help to intensify it

Mid-latitude Cyclones : The Upper Level  A 500 mb trough moves into place directly above a surface stationary front  If a shortwave trough moves into the main flow, the flow pattern is disturbed  As the 500 mb trough deepens, the associated upper level divergence strengthens, helping to intensify the surface low  Stronger winds aloft force the upper level trough to move eastward faster, and eventually it becomes located above the surface low  When the surface and upper level low are “stacked”, convergence at both levels starts to “fill” the low pressure area, weakening the cyclone

Another Example – Jet Streaks  A jet streak is an area within a jet stream that has the highest wind speeds  Typically jet streaks are thought of as made up of four quadrants – separated by left and right, entrance and exit  The right entrance region and the left exit region both contain divergence (aloft) and so they promote the development of surface low pressure systems  Due to shifts in the Coriolis Force brought about by acceleration of the wind

Weather Forecasting - Qualitative  Most information for a qualitative forecast can be seen on a simple weather map  If you see a low pressure area that has been moving eastward towards Colorado, what type of weather might you expect?  If a cold front is moving southward through Wyoming, what would you expect the temperature to do?  If it’s going to be cloudy tomorrow, will it be warmer or colder than it was today?  Often the best forecast is persistence: if it’s warm and sunny today, and it was warm and sunny yesterday, the odds are pretty good that it will be warm and sunny tomorrow (unless you know something else)

Weather Forecasting - Quantitative  In order to predict specific quantities in a forecast (temperature, humidity, rainfall) we rely on computer models  Numerical weather prediction (NWP) uses a system of equations that describes the behavior of the atmosphere  NWP model uses the current state of the atmosphere as its initial condition and steps through a small time step, recalculating every number for each step until the forecast time is reached

Initialization  A computer model has a set of equations in it that dictate what will happen based on what we already know  Takes the actual initial conditions and applies the equations to create a picture of the weather 5 minutes from now  Calls that prediction the “new data” and runs another 5 minutes  Repeats until you get the desired forecast (12 hours, 24 hours, etc)

MOS  The output from a model can be shown in the form of Model Output Statistics (MOS)  MOS is a summary of the predicted condition of the atmosphere at each forecast time  MOS is often called “model guidance”, because forecasters will use the generated numbers as a guide to make their forecast  MOS isn’t perfect though, and forecasting takes some intuition

What models produce output for use in MOS? See UCAR website.  The Eta Model: runs forward 84 hours  The GFS (Global Forecasting System) model runs forward for 10 days.  Combines the old “Aviation” and “Medium-Range Forecast” (MRF) models  The NGM (Nested Grid Model): an older model that is largely replaced by the Eta although it has a high quality climatological dataset for use in MOS.

The premise behind MOS  The (preceding) models produce output describing the weather over No. America and vicinity at grid points or in “wave space”.  Conditions for this time of year at a specific city may have occurred similarly in the historic past (i.e., old climate data are used).  Forecasts of current conditions can be made for a city using the current model output and based on the historic weather outcomes.

Downfalls of MOS  There isn’t just one model that is used for NWP  Multiple models are used that have differences in resolution and in the equations used and assumptions made  The models never agree on everything  A good forecaster will look at multiple model predictions and have a feel for which model performs the best under certain circumstances

So why aren’t forecasts always right?  Observations aren’t good enough!  A model is only as good as its initial conditions  Even having an observation for every square meter of the planet would leave out smaller details…and we don’t have even close to that many observations  Computers aren’t fast enough!  In order to truly create a perfect forecast, one would have to use the exact equations on a really, really small spatial scale  In order to create a model that will create a 12 hour forecast in less than 12 hours, we must approximate certain parts of equations and run the model on a grid with spacing of multiple kilometers  ~1.2 million grid points x thousands of calculations > 1 Billion calculations per time step  More than 1 Quadrillion calculations per time step at 1 meter resolution (10 12 )  More than 4 Quadrillion calculations to simulate 12 hours  Forces us to make approximations to the equations that govern the atmosphere  Little bit of error added at each time step  Chaos reigns supreme!  Ever heard of the butterfly effect? It’s more than just a movie

Chaos Theory  Also known as the “Butterfly Effect”, coined by Dr. Edward Lorenz in the 60’s (he’s still teaching at MIT)  Basically says that even the most insignificant change to initial conditions will magnify into drastic changes  The smallest disturbance will eventually grow into a large difference – this limits the range of forecasts to just a few days  Even if the initial conditions and computing power were perfect, chaos theory would limit us to a reasonable range of about 2 weeks  Computers cannot possibly predict the movement of a butterfly, or how hard you step on the gas pedal

So How far have we come?  100 years ago we just looked to the west.  The first attempt at numerical weather prediction by Lewis Fry Richardson was done by hand.  On a WWI battlefield as part of an ambulance unit in Northern France  Just wanted to predict the pressure change over the next six hours  Calculation took him six weeks!  And he was off by over 140 mb…

Richardson’s Forecast Factory

How far have we come?  In 1937, the US started using weather balloons.  It wasn’t until WWII that the existence of a jet stream was confirmed.  In 1948, ENIAC was put together by John von Neumann in a 30 by 50 room.  In April 1950, the first 24-hr forecast was attempted.  Took more than 24 hours due to breakdowns  8 years later, forecasts began to show signs of skill.  As it stands today, we can have a great deal of faith in a weather forecast out to about 3 days.  Just 30 years ago, we could only do 2 days  Beyond that, the accuracy drops dramatically  If you see a 15 day forecast…don’t believe it

Improvements  As computers improve and we can run better models, we may be able to extend the range to 4 or 5 days in our lifetimes  Better numerical techniques  Fewer approximations  Better measurements  Better understanding of interactions with other systems  However, because of chaos, and that sensitive dependence on initial conditions it is unlikely that we will ever go much farther than that

Station Name – Artesia, NMDate and Time the Model was run

Decoding MOS – Max and Min Temperature KMIA AVN MOS GUIDANCE 9/04/ UTC KMIA AVN MOS GUIDANCE 9/04/ UTC DT /SEPT 4 /SEPT 5 /SEPT 6 / DT /SEPT 4 /SEPT 5 /SEPT 6 / HR HR X/N X/N TMP TMP DPT DPT CLD BK BK BK OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV BK CLD BK BK BK OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV BK WDR WDR WSP WSP P P P P Q Q Q Q T06 33/ 0 64/ 0 21/ 0 19/ 0 42/ 0 80/ 0 37/ 0 37/ 0 39/ 0 22/ 0 T06 33/ 0 64/ 0 21/ 0 19/ 0 42/ 0 80/ 0 37/ 0 37/ 0 39/ 0 22/ 0 T12 66/ 0 42/ 0 93/ 0 58/ 0 66/ 0 T12 66/ 0 42/ 0 93/ 0 58/ 0 66/ 0 CIG CIG VIS VIS OBV N N N N N N N N N N N N N N N N N N N N N OBV N N N N N N N N N N N N N N N N N N N N N

Decoding MOS – 3 hourly temperature forecasts KMIA AVN MOS GUIDANCE 9/04/ UTC KMIA AVN MOS GUIDANCE 9/04/ UTC DT /SEPT 4 /SEPT 5 /SEPT 6 / DT /SEPT 4 /SEPT 5 /SEPT 6 / HR HR X/N X/N TMP TMP DPT DPT CLD BK BK BK OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV BK CLD BK BK BK OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV BK WDR WDR WSP WSP P P P P Q Q Q Q T06 33/ 0 64/ 0 21/ 0 19/ 0 42/ 0 80/ 0 37/ 0 37/ 0 39/ 0 22/ 0 T06 33/ 0 64/ 0 21/ 0 19/ 0 42/ 0 80/ 0 37/ 0 37/ 0 39/ 0 22/ 0 T12 66/ 0 42/ 0 93/ 0 58/ 0 66/ 0 T12 66/ 0 42/ 0 93/ 0 58/ 0 66/ 0 CIG CIG VIS VIS OBV N N N N N N N N N N N N N N N N N N N N N OBV N N N N N N N N N N N N N N N N N N N N N

Decoding MOS – Cloud Cover KMIA AVN MOS GUIDANCE 9/04/ UTC KMIA AVN MOS GUIDANCE 9/04/ UTC DT /SEPT 4 /SEPT 5 /SEPT 6 / DT /SEPT 4 /SEPT 5 /SEPT 6 / HR HR X/N X/N TMP TMP DPT DPT CLD BK BK BK OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV BK CLD BK BK BK OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV BK WDR WDR WSP WSP P P P P Q Q Q Q T06 33/ 0 64/ 0 21/ 0 19/ 0 42/ 0 80/ 0 37/ 0 37/ 0 39/ 0 22/ 0 T06 33/ 0 64/ 0 21/ 0 19/ 0 42/ 0 80/ 0 37/ 0 37/ 0 39/ 0 22/ 0 T12 66/ 0 42/ 0 93/ 0 58/ 0 66/ 0 T12 66/ 0 42/ 0 93/ 0 58/ 0 66/ 0 CIG CIG VIS VIS OBV N N N N N N N N N N N N N N N N N N N N N OBV N N N N N N N N N N N N N N N N N N N N N

Decoding MOS - Cloud Cover  CL = Clear, no clouds  SC = Scattered, between clear and the sky ½ filled with clouds  BK = Broken, between sky ½ filled with clouds and totally cloudy  OV = Overcast, sky filled with clouds

Decoding MOS – Winds KMIA AVN MOS GUIDANCE 9/04/ UTC KMIA AVN MOS GUIDANCE 9/04/ UTC DT /SEPT 4 /SEPT 5 /SEPT 6 / DT /SEPT 4 /SEPT 5 /SEPT 6 / HR HR X/N X/N TMP TMP DPT DPT CLD BK BK BK OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV BK CLD BK BK BK OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV BK WDR WDR WSP WSP P P P P Q Q Q Q T06 33/ 0 64/ 0 21/ 0 19/ 0 42/ 0 80/ 0 37/ 0 37/ 0 39/ 0 22/ 0 T06 33/ 0 64/ 0 21/ 0 19/ 0 42/ 0 80/ 0 37/ 0 37/ 0 39/ 0 22/ 0 T12 66/ 0 42/ 0 93/ 0 58/ 0 66/ 0 T12 66/ 0 42/ 0 93/ 0 58/ 0 66/ 0 CIG CIG VIS VIS OBV N N N N N N N N N N N N N N N N N N N N N OBV N N N N N N N N N N N N N N N N N N N N N

Meteorology Wind Direction 000 = From the North 270 = From the West 090 = From the East 180 = From the South

Decoding MOS – Chance of measurable precipitation KMIA AVN MOS GUIDANCE 9/04/ UTC KMIA AVN MOS GUIDANCE 9/04/ UTC DT /SEPT 4 /SEPT 5 /SEPT 6 / DT /SEPT 4 /SEPT 5 /SEPT 6 / HR HR X/N X/N TMP TMP DPT DPT CLD BK BK BK OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV BK CLD BK BK BK OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV BK WDR WDR WSP WSP P P P P Q Q Q Q T06 33/ 0 64/ 0 21/ 0 19/ 0 42/ 0 80/ 0 37/ 0 37/ 0 39/ 0 22/ 0 T06 33/ 0 64/ 0 21/ 0 19/ 0 42/ 0 80/ 0 37/ 0 37/ 0 39/ 0 22/ 0 T12 66/ 0 42/ 0 93/ 0 58/ 0 66/ 0 T12 66/ 0 42/ 0 93/ 0 58/ 0 66/ 0 CIG CIG VIS VIS OBV N N N N N N N N N N N N N N N N N N N N N OBV N N N N N N N N N N N N N N N N N N N N N

Decoding MOS – Quantitative Precipitation Forecast KMIA AVN MOS GUIDANCE 9/04/ UTC KMIA AVN MOS GUIDANCE 9/04/ UTC DT /SEPT 4 /SEPT 5 /SEPT 6 / DT /SEPT 4 /SEPT 5 /SEPT 6 / HR HR X/N X/N TMP TMP DPT DPT CLD BK BK BK OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV BK CLD BK BK BK OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV BK WDR WDR WSP WSP P P P P Q Q Q Q T06 33/ 0 64/ 0 21/ 0 19/ 0 42/ 0 80/ 0 37/ 0 37/ 0 39/ 0 22/ 0 T06 33/ 0 64/ 0 21/ 0 19/ 0 42/ 0 80/ 0 37/ 0 37/ 0 39/ 0 22/ 0 T12 66/ 0 42/ 0 93/ 0 58/ 0 66/ 0 T12 66/ 0 42/ 0 93/ 0 58/ 0 66/ 0 CIG CIG VIS VIS OBV N N N N N N N N N N N N N N N N N N N N N OBV N N N N N N N N N N N N N N N N N N N N N T06, T12: probability of thunderstorms / severe t-storms over 6, 12h

Decoding MOS – Precip. Amount  0 = no precipitation  1 = 0.01 to 0.09 inches  2 = 0.10 to 0.24 inches  3 = 0.25 to 0.49 inches  4 = 0.50 to 0.99 inches  5 = 1.00 to 1.99 inches  6 = 2.00 inches or greater

Decoding MOS – Local forecast KMIA AVN MOS GUIDANCE 9/04/ UTC KMIA AVN MOS GUIDANCE 9/04/ UTC DT /SEPT 4 /SEPT 5 /SEPT 6 / DT /SEPT 4 /SEPT 5 /SEPT 6 / HR HR X/N X/N TMP TMP DPT DPT CLD BK BK BK OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV BK CLD BK BK BK OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV BK WDR WDR WSP WSP P P P P Q Q Q Q High Temperature: 89F Low Temperature: 77F Precipitation Category: Cat-4

Decoding MOS – Zone Forecast KMIA AVN MOS GUIDANCE 9/04/ UTC KMIA AVN MOS GUIDANCE 9/04/ UTC DT /SEPT 4 /SEPT 5 /SEPT 6 / DT /SEPT 4 /SEPT 5 /SEPT 6 / HR HR X/N X/N TMP TMP DPT DPT CLD BK BK BK OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV BK CLD BK BK BK OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV BK WDR WDR WSP WSP P P P P Q Q Q Q T06 33/ 0 64/ 0 21/ 0 19/ 0 42/ 0 80/ 0 37/ 0 37/ 0 39/ 0 22/ 0 T06 33/ 0 64/ 0 21/ 0 19/ 0 42/ 0 80/ 0 37/ 0 37/ 0 39/ 0 22/ 0 T12 66/ 0 42/ 0 93/ 0 58/ 0 66/ 0 T12 66/ 0 42/ 0 93/ 0 58/ 0 66/ 0 Tonight: Mostly cloudy with scattered showers and thunderstorms. Lows in the mid 70s. Light southeast winds. Chance of rain 30%. Tomorrow: Mostly cloudy with scattered to numerous showers and thunderstorms. Highs near 90. Light southwest winds. Chance of rain 70%. Tomorrow Night: Mostly cloudy with scattered showers and thunderstorms. Lows in the mid 70s. Light southwest winds. Chance of rain 70%.

MOS on the web  s.php s.php s.php

Introduction  July 1996: USA changes to a more international system for meteorological data reporting: METAR/TAF. Replaced surface airways code.  METAR: A routine aviation weather report  SPECI: non-routine wx reports  TAF: Aerodrome (airport) forecasts

METAR Observations Example METAR Report METAR KABC Z AUTO 21016G24KT 180V240 1SM R11/P6000FT -RA BR BKN015 0VC025 06/04 A2990 RMK A02 PK WND 20032/25 WSHFT 1715 VIS 3/4V1 1/2 VIS 3/4 RWY11 RAB07 CIG 013V017 CIG 017 RWY11 PRESFR SLP125 POOO3 6OOO9 T TSNO $ KABC - ICAO STATION (location) IDENTIFIER Four character ICAO location identifier. K = USA; PA = Alaska; PH = Hawaii Z - DATE/TIME All dates and times in UTC using a 24-hour clock; two-digit date and four-digit time; always appended with Z to indicate UTC. AUTO REPORT MODIFIER AUTO: Indicates a fully automated report with no human intervention. It is removed when an observer logs on to the system. COR: Indicates a corrected observation. No modifier indicates human observer or automated system with human logged on for oversight functions.

METAR Observations Example METAR Report METAR KABC Z AUTO 21016G24KT 180V240 1SM R11/P6000FT -RA BR BKN015 0VC025 06/04 A2990 RMK A02 PK WND 20032/25 WSHFT 1715 VIS 3/4V1 1/2 VIS 3/4 RWY11 RAB07 CIG 013V017 CIG 017 RWY11 PRESFR SLP125 POOO3 6OOO9 T TSNO $ 21016G24KT - WIND DIRECTION AND SPEED Direction in degrees from true north (first three digits); next two digits: speed in whole knots; if needed, include character as: Gusts (character) followed by maximum observed speed; always appended with KT to indicate knots; 00000KT for calm 180V240 - if direction varies by 60 o or more and speed greater than 6 knots, a Variable wind direction group is reported, otherwise omitted. If wind direction is variable and speed 6 knots or less, replace wind direction with VRB followed by wind speed in knots. 1SM VISIBILITY Prevailing visibility in statute miles and fractions with space between whole miles and fractions; always appended with SM to indicate statute miles (5280 feet); values <1/4SM reported as M1/4SM.

Runway Visual Range (RVR)  R11/P6000ft: runway 11has 6000 ft visibility. [Others: R11R or R11L or R11C]  P: RVR is higher than the sensor reported  M: RVR less than sensor (not illustrated here)  V: RVR Variable. Example: R06L/2000V4000ft for runway 6 left

METAR Observations Example METAR Report METAR KABC Z AUTO 21016G24KT 180V240 1SM R11/P6000FT –RA BR BKN015 0VC025 06/04 A2990 RMK A02 PK WND 20032/25 WSHFT 1715 VIS 3/4V1 1/2 VIS 3/4 RWY11 RAB07 CIG 013V017 CIG 017 RWY11 PRESFR SLP125 POOO3 6OOO9 T TSNO $ -RA BR – Current WEATHER PHENOMENA - Intensity or Proximity “-” Light, “no sign” Moderate, “+” Heavy, VC Vicinity - Precipitation: DZ Drizzle, IC Ice Crystals, UP Unknown in automated observations, RA Rain, PL Ice pellets, SN Snow, GR Hail, SG Snow grains GS Small hail/snow pellets; SH showers; TS thunderstorm - Obscuration: BR Mist (< or = 5/8SM), SA Sand, FU Smoke, HZ Haze, VA Volcanic Ash, PY Spray, DU Widespread Dust - Other: SQ Squall, FC Funnel Cloud, SS Sandstorm, +FC Tornado/ Waterspout, DS Duststorm, PO Well developed dust/sand whirls.

METAR Observations Example METAR Report METAR KABC Z AUTO 21016G24KT 180V240 1SM R11/P6000FT –RA BR BKN015 0VC025 06/04 A2990 RMK A02 PK WND 20032/25 WSHFT 1715 VIS 3/4V1 1/2 VIS 3/4 RWY11 RAB07 CIG 013V017 CIG 017 RWY11 PRESFR SLP125 POOO3 6OOO9 T TSNO $ BKN015 OVC025 - SKY CONDITION. Cloud amount and height: CLR (In automated METAR reports only, no clouds detected below feet.); (Human Observers: clear is SKC) Sky CLeaR 0/8; FEW 1/8- 2/8; SCattered 3/8-4/8; BroKeN 5/8-7/8; OVerCast 8/8; 3-digit height of base in hundreds of feet; followed by Towering CUmulus or CumulonimBus if present. More than 1 layer may be reported. 06/04 - TEMPERATURE/DEW POINT. Each is reported in whole degrees Celsius using two digits; values are separated by a slash; sub-zero values are prefixed with an M (minus).

METAR Observations Example METAR Report METAR KABC Z AUTO 21016G24KT 180V240 1SM R11/P6000FT –RA BR BKN015 0VC025 06/04 A2990 RMK A02 PK WND 20032/25 WSHFT 1715 VIS 3/4V1 1/2 VIS 3/4 RWY11 RAB07 CIG 013V017 CIG 017 RWY11 PRESFR SLP125 POOO3 6OOO9 T TSNO $ A2990 ALTIMETER. Altimeter setting (in U.S. reports) is always prefixed with an A indicating inches of mercury; reported using four digits: tens, units, tenths, and hundredths. RMK REMARKS IDENTIFIER. Remarks includes clarifying or augmenting data concerning elements in the body of the METAR, additive coded data and maintenance data. AO2 TYPE OF AUTOMATED STATION. AO1; automated station without a precipitation discriminator. AO2; automated station with precipitation discriminator.

METAR Observations Example METAR Report METAR KABC Z AUTO 21016G24KT 180V240 1SM R11/P6000FT –RA BR BKN015 0VC025 06/04 A2990 RMK A02 PK WND 20032/25 WSHFT 1715 VIS 3/4V1 1/2 VIS 3/4 RWY11 RAB07 CIG 013V017 CIG 017 RWY11 PRESFR SLP125 POOO3 6OOO9 T TSNO $ PK WND 20032/25 - PEAK WIND. PK WND dddff(F)/(hh)mm; direction in degrees, speed in whole knots, time in minutes after the hour. Only minutes after the hour is included if the hour can be inferred from the report. WSHFT WIND SHIFT. WSHFT followed by hours and minutes of occurrence. The term FROPA may be entered after the time if it is reasonably certain that the wind shift was a result of a frontal passage.

METAR Observations Example METAR Report METAR KABC Z AUTO 21016G24KT 180V240 1SM R11/P6000FT –RA BR BKN015 0VC025 06/04 A2990 RMK A02 PK WND 20032/25 WSHFT 1715 VIS 3/4V1 1/2 VIS 3/4 RWY11 RAB07 CIG 013V017 CIG 017 RWY11 PRESFR SLP125 POOO3 6OOO9 T TSNO $ P HOURLY PRECIPITATION AMOUNTPrrrr; in tens, units, tenths and hundredths of an inch since last regular hourly METAR. A trace is reported as P AND 6-HOUR PRECIPITATION AMOUNT. 6RRRR; precipitation amount, including water equivalent, to nearest 0.01 inches for past 6 hours reported in 00, 06, 12, and 18 UTC observations and for past 3 hours in 03, 09, 15, and 21 UTC observations. A trace is **** Not on this report - 24-HOUR PRECIPITATION AMOUNT. 7****; precipitation amount to nearest 0.01 inches for past 24 hours reported in 12 UTC observation; e.g., indicates 0.15 inches of precipitation for past 24 hours.

METAR Observations Example METAR Report METAR KABC Z AUTO 21016G24KT 180V240 1SM R11/P6000FT –RA BR BKN015 0VC025 06/04 A2990 RMK A02 PK WND 20032/25 WSHFT 1715 VIS 3/4V1 1/2 VIS 3/4 RWY11 RAB07 CIG 013V017 CIG 017 RWY11 PRESFR SLP125 POOO3 6OOO9 T TSNO $ T HOURLY TEMPERATURE AND DEW POINT. TsnTaTaTa snT'aT'aT'a; reported to nearest tenth of o C; sn: 1 if temperature or dew point below 0 o C and 0 if temperature/dew point 0 o C or higher HOUR MAXIMUM TEMPERATURE. 1snTxTxTx; maximum temperature for past 6 hours reported to nearest tenth of degree Celsius; reported on 00, 06, 12, 18 UTC reports; sn = 1 if temperature below 0 o C and 0 if temperature 0 o C or higher HOUR MINIMUM TEMPERATURE. 2snTnTnTn; minimum temperature for past 6 hours reported to nearest tenth of degree Celsius; reported on 00, 06, 12, 18 UTC reports; sn = 1 if temperature below 0 o C and 0 if temperature 0 o C or higher.

For you slackers out there…  Metar decoders:  sion/swometardecoder.html sion/swometardecoder.html sion/swometardecoder.html 

Ultra-cool METAR Displays  www-frd.fsl.noaa.gov/mab/metar   Click on Java applets large version