Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 121740
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1240 PM CDT FRI SEP 12 2014

.SHORT TERM /TODAY/...
ISSUED AT 333 AM CDT FRI SEP 12 2014

PRECIP AND TEMP TRENDS WILL BE THE PRIMARY CONCERNS TODAY.  RIGHT
ENTRANCE REGION DIVERGENCE OF STRONG 120KT JET FROM MO VALLEY INTO
SERN CANADA CONTINUES TO ENHANCE BROAD SWATH OF PRECIP FROM NE/KS
INTO THE NWRN HALF OF IA.  FORCING IS MAINLY KINEMATIC AND MID LEVEL
BASED DRIVEN BY DIVERGENCE AND DPVA...AND ALTHOUGH THERE IS LITTLE
TO NO THETA-E ADVECTION BELOW 3KM...THERE DOES APPEAR TO BE FAIRLY
HIGH BASED FRONTOGENETICAL FORCING AND RESPONSE.  ENHANCED SW-NE
PRECIP BANDS LINE UP FAIRLY NICELY WITH RAP H7/H5 FN DIVERGENCE AND
LOWER STATIC STABILITY NOTED BY SLIGHTLY NEGATIVE EPV IN THE SAME
LAYER. HIGH RES MODEL PRECIP DEPICTIONS ARE IN QUITE GOOD AGREEMENT
BUT LOOK SLOW AT THE MOMENT SUGGESTING PRECIP WILL MAINLY BE IN THE
MORNING...AND CERTAINLY BE EXITING TO THE EAST 21Z-00Z.

TEMPS WILL BE PROBLEMATIC WITH EXTREMELY ANOMALOUS AIRMASS JUST
UPSTREAM. BOTH THE NAEFS CLIMATOLOGICAL AND GEFS M-CLIMATE
PERCENTILES ARE IN THEIR LOWEST AND HIGHEST RESPECTIVE 1 PERCENT FOR
TEMPS AND MSLP. THIS COLD AIRMASS COMBINED WITH PRECIP WILL RESULT
IN LITTLE TEMP REBOUND TODAY AND SOME NON-DIURNAL TRENDS WITH HIGHS
NO BETTER THAN THE LOWER 50S.  ALTHOUGH NOT IN THE FORECAST...WOULD
NOT BE SURPRISED TO SEE A FEW SPOTS STRUGGLE TO REACH 50F. THESE
HIGHS WOULD AGAIN BREAK MIN MAX RECORDS WHICH RANGE FROM 53-56F AT
MASON CITY...WATERLOO...DES MOINES AND OTTUMWA.

.LONG TERM /TONIGHT THROUGH THURSDAY/...
ISSUED AT 333 AM CDT FRI SEP 12 2014

LITTLE CHANGES TO THE GOING FORECAST AS MODELS REMAIN IN AGREEMENT
BOTH FROM RUN TO RUN AND AMONG EACH OTHER. LARGE AREA OF HIGH
PRESSURE TO BUILD INTO THE STATE TONIGHT WITH DRY CONDITIONS AND
CLEARING SKIES. VERY COLD AIR FOR THIS TIME OF YEAR TO REMAIN IN
PLACE ACROSS THE REGION...WITH H85 TEMPS AROUND 0C TONIGHT AND ONLY
WARMING TO AROUND +5C THROUGH THE WEEKEND. WITH THE COOL AIR AND
HIGH PRESSURE IN PLACE TONIGHT...CLEAR SKIES AND LIGHT WINDS
TEMPERATURES EXPECTED TO DROP OFF QUITE A BIT. HOWEVER THE TEMPS MAY
BE TEMPERED SOME BY THE LINGERING MOISTURE FROM ALL THE RAIN THE
PAST FEW DAYS AND ADDITIONAL RAIN TODAY...WHICH LEADS TO BEING
SOMEWHAT HESITANT ON POTENTIAL FOR FROST FORMATION AS WELL.
THEREFORE STUCK WITH LOWS IN THE MID TO UPPER 30S AND SOME PATCHY
FROST WORDING ACROSS THE WEST/NORTH WHERE COOLEST TEMPS EXPECTED.

HIGH PRESSURE TO DOMINATE OVER THE WEEKEND...WITH TEMPS GRADUALLY
WARMING A BIT. OTHERWISE NEXT CHANCE FOR PRECIPITATION AS ANOTHER
WEAK UPPER LEVEL WAVE AND ASSOCIATED COLD FRONT DROPS THROUGH THE
REGION. ANOTHER LARGE AREA OF HIGH PRESSURE TO THEN BUILD INTO THE
CENTRAL US FOR MUCH OF NEXT WEEK. THERMAL PROFILES WARM SOME WHICH
SHOULD ALLOW TEMPERATURES TO CREEP BACK INTO THE 70S BY WEDNESDAY
INTO THURSDAY. A LARGER UPPER LEVEL WAVE THEN LOOKS TO DIG INTO THE
CENTRAL US BY NEXT FRIDAY INTO THE WEEKEND WHICH SHOULD BRING
ADDITIONAL CHANCES FOR PRECIPITATION TO MUCH OF THE AREA. EVEN WITH
THE WARMING BY THE END OF THE FORECAST PERIOD...TEMPERATURES WILL
REMAIN WELL BELOW THE SEASONAL AVERAGES THROUGH MUCH OF NEXT WEEK.

&&

.AVIATION...12/18Z
ISSUED AT 1232 PM CDT FRI SEP 12 2014

NEXT 6 OR SO HOURS IS WINDOW OF MAIN WEATHER AS TAF SITES HOVER IN
MVFR CEILINGS. AFTER 02Z...ALL SITES BECOMING SKC...WITH CALM WINDS
THROUGH SUNRISE SATURDAY MORNING AS HIGH PRESSURE TO BLAST AWAY
CLOUDS AND PUT ALL TAF SITES INTO VFR. FOR THE REST OF
TODAY...BAND OF SHOWERS TO CONTINUE MOVING EASTWARD. NO REASON FOR
PRECIP TO INTENSIFY AND/OR PRODUCE TS...SO HAVE LEFT THUNDER OUT
OF TAFS AND HAVE NOT REDUCED VSBYS BELOW 6SM.

&&

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

$$

SHORT TERM...SMALL
LONG TERM...BEERENDS
AVIATION...KOTENBERG


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