Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 240937
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
337 AM CST TUE FEB 24 2015

.SHORT TERM /TODAY/...
ISSUED AT 336 AM CST TUE FEB 24 2015

MAIN CONCERN TODAY WILL BE TEMPS AND WIND. NRN MN SHORT WAVE HAS
DRIVEN SOME MID LEVEL CLOUDINESS INTO NRN IA BUT ANY ASSOCIATED
PRECIP SHOULD BE RELEGATED TO MN AND WI. ATTENDANT SURFACE TROUGH
WILL ENTER NRN IA THIS MORNING...EXITING SERN FORECAST AREA DURING
THE AFTERNOON. ALTHOUGH TRAILING COLD FRONT AND ADVECTION WILL NOT
REACH NRN IA UNTIL LATE IN THE AFTERNOON...FRM/MCW BUFR SOUNDINGS
DEPICT MIXING TO JUST SHY OF 1KM AFTER INITIAL TROUGH PASSAGE.  AVG
OF MEAN MIXED LAYER WIND AND WIND AT TOP OF MIXED LAYER SUGGESTS
PEAK GUSTS INTO THE MID 30S /KTS/ FOR A FEW HOURS NORTH...18-20Z OR
SO.  NO HEADLINE HOWEVER WITH BOTH SUSTAINED WINDS AND GUSTS BELOW
ADVISORY CRITERIA /26-39KTS/.

HIGH TEMPS ARE EITHER AT OR JUST ABOVE PREVIOUS FORECAST. RECENT
WARM UP EVENTS WITH STRONG WINDS HAVE SUGGESTED AT OR ABOVE THE WARM
END OF THE RAW MODEL AND MOS GUIDANCE SUITE IS APPROPRIATE.

.LONG TERM /TONIGHT THROUGH MONDAY/...
ISSUED AT 336 AM CST TUE FEB 24 2015

A FAIRLY WEAK HIGH PRESSURE RIDGE WILL SLIDE BY TO OUR NORTHEAST
TONIGHT...BUT BY EARLY WEDNESDAY MORNING WINDS WILL ALREADY BE
SWINGING AROUND TO EASTERLY WITH INCREASING CLOUDS AHEAD OF AN
APPROACHING STORM SYSTEM. THIS WILL COME IN THE FORM OF A STEADILY
DEEPENING 500 MB TROUGH SWINGING DOWN FROM CANADA OVER MINNESOTA
AND DAKOTAS ON WEDNESDAY...THEN REACHING IOWA BY WEDNESDAY NIGHT
AND SUBSEQUENTLY STRETCHING OUT OVERHEAD AS THE PARENT 500 MB LOW
CURRENTLY ANCHORED OVER HUDSON BAY FINALLY KICKS OUT EASTWARD. AT
THE SURFACE...A LOW PRESSURE SYSTEM DEVELOPING BENEATH THE
FORWARD FLANK OF THE 500 MB TROUGH WILL MOVE SOUTHEASTWARD FROM
NEBRASKA INTO KANSAS AND MISSOURI ON WEDNESDAY AND WEDNESDAY
NIGHT. THE ZONE OF WARM AIR ADVECTION ALONG THE NORTHEASTERN
HEMISPHERE OF THIS LOW PRESSURE CENTER WILL RESIDE BENEATH A
REGION OF BROAD ASCENT ASSOCIATED WITH THE APPROACHING 500 MB
TROUGH...RESULTING IN A WIDE SWATH OF SNOWFALL ACROSS MUCH OF IOWA
FROM NORTHWEST TO SOUTHEAST ON WEDNESDAY AND WEDNESDAY NIGHT.
FORECAST SOUNDINGS REVEAL DEEP SATURATION PARTICULARLY DURING THE
DAY ON WEDNESDAY...AND WHILE MOST OF THE CLOUD LAYER RESIDES
BENEATH THE DENDRITIC GROWTH ZONE ROUGHLY IN THE -10 TO -6
LAYER...THE FORCING AT THE TOP OF THE CLOUD LAYER AND WITHIN THE
DGZ IS PRETTY IMPRESSIVE. HAVE CONTINUED THE TREND OF INCREASING
SNOWFALL AMOUNTS ACROSS THE AREA AND WOULD NOT BE SURPRISED IF
THERE IS A BAND OF FIVE PLUS INCHES...HOWEVER THE FORECAST
CONTINUES TO BE CONSTRAINED BY UNCERTAINTY REGARDING THE TRACK OF
THE LOW AND AFOREMENTIONED SNOW BAND. THE ECMWF CONTINUES TO TAKE
IT FURTHER NORTHEAST...ROUGHLY FROM EMMETSBURG TO
OSKALOOSA...WHILE MOST OF THE REMAINING GUIDANCE IS MORE FROM
DENISON TO OTTUMWA OR THEREABOUTS. GIVEN THESE UNCERTAINTIES AND
THE MARGINAL AMOUNTS CURRENTLY FORECAST HAVE NOT ISSUED ANY
HEADLINES AT THIS TIME...BUT THESE WILL BE STRONGLY CONSIDERED
LATER TODAY AS THE STORM ENTERS THE 24-HOUR FORECAST WINDOW AND
SHORT RANGE MODEL GUIDANCE HOPEFULLY COMES TO A BETTER CONSENSUS
ON THE SNOW TRACK.

AS THE LOW PRESSURE SYSTEM AND ASSOCIATED SNOWFALL MOVE OFF TO THE
SOUTHEAST ON WEDNESDAY NIGHT AND THURSDAY A LARGE CANADIAN HIGH
PRESSURE AREA WILL BUILD ACROSS THE MIDWESTERN U.S. AND DIRECTLY
OVER IOWA BY AROUND FRIDAY MORNING. THIS WILL LEAD TO YET ANOTHER
SURGE OF COLD WEATHER FOR OUR FORECAST AREA DURING THE LATTER HALF
OF THE WORK WEEK. WIND CHILL HEADLINES MAY BE WARRANTED AT SOME
POINT...ESPECIALLY IF THE FRESH SNOW PACK FROM THE WEDNESDAY
SYSTEM ALLOWS TEMPERATURES TO FALL FURTHER THAN CURRENTLY
ANTICIPATED LATER IN THE WEEK.

AS MENTIONED ABOVE...THE 500 MB TROUGH REACHING IOWA BY THURSDAY
MORNING WILL BECOME STRETCHED OUT LATER IN THE WEEK...BETWEEN THE
RAPIDLY DEPARTING HUDSON BAY LOW AND A LOW ATTEMPTING TO CUT OFF
OVER THE SOUTHWESTERN U.S. THIS SOUTHWESTERN TROUGH WILL PLACE
IOWA BENEATH SOUTHWESTERLY FLOW FROM THIS WEEKEND INTO NEXT WEEK.
THE GFS AND ECMWF HAVE BEEN PERSISTENT IN THEIR ATTEMPTS TO SPIT
OUT A 500 MB IMPULSE MOVING FROM THE WEST COAST TO OUR REGION OVER
THE WEEKEND...HOWEVER THERE HAS BEEN CONSIDERABLE VARIABILITY IN
THE TIMING AND INTENSITY OF THIS IMPULSE. IN ANY EVENT SUCH A
SYSTEM WILL LIKELY BE REFLECTED BY AN INVERTED SURFACE PRESSURE
TROUGH AND LARGE SWATH OF SNOW DEVELOPING OVER THE MIDWEST...WITH
MOST PROGNOSTIC GUIDANCE PAINTING THIS PRECIPITATION ACROSS
KANSAS...MISSOURI...AND ABOUT THE SOUTHEAST HALF OF IOWA. THIS
SEEMS REASONABLE GIVEN THE ORIENTATION OF THE SYSTEM AND HAVE
INCREASED POPS TO LIKELY ACROSS THE SOUTHEAST HALF OR SO OF OUR
FORECAST AREA...THOUGH THE AMOUNT OF SNOW ACCUMULATION THAT MAY BE
EXPECTED REMAINS VERY MUCH UP IN THE AIR FOR NOW.

&&

.AVIATION...24/06Z
ISSUED AT 1139 PM CST MON FEB 23 2015

VFR CONDITIONS WILL CONTINUE TO PREVAIL TONIGHT. CIGS WILL LOWER
TOWARD MORNING WITH POTENTIAL FOR A PERIOD OF MVFR AS A COLD FRONT
PASSES THROUGH IN THE MORNING. GUSTY NORTHWEST WINDS WILL DEVELOP
WITH THE FRONTAL PASSAGE WITH GUSTS IN EXCESS OF 35 KTS POSSIBLE.
WINDS WILL DIMINISH LATE AFTERNOON INTO EARLY EVENING.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...SMALL
LONG TERM...LEE
AVIATION...DONAVON



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