Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 282322
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
522 PM CST FRI NOV 28 2014

.SHORT TERM /TONIGHT/...
ISSUED AT 340 PM CST FRI NOV 28 2014

SHARP WARM FRONT HAS SET UP ALONG THE SRN EDGE OF THE SNOW PACK
EXTENDING FROM NORTH OF KOFK-KDSM-KSTL. WARM FRONT WILL CONTINUE
TO PROGRESS NORTH TONIGHT. THE MAIN FORECAST PROBLEM FOR TONIGHT
IS WHAT TO DO W.R.T. FOG. MOISTURE IS SLOW TO WORK INTO THE
SYSTEM...BUT LOW 30S DEW POINTS ARE MOVING INTO NRN MO AND FAR
SRN IA WHICH SHOULD LEAD TO FOG OVER THE SNOWFIELD. BOUNDARY LAYER
WINDS ARE HIGH ENOUGH THAT THERE IS A DECENT CHANCE THAT WE WILL
SEE STRATUS INSTEAD OF MORE DENSE FOG. THOUGH I PLAYED WIDESPREAD
FOG...I DID NOT THINK THE FOG WOULD BECOME WIDESPREAD DENSE...BUT
RATHER DEVELOP INTO MORE OF A STRATUS DECK. TEMPS WILL NOT FALL
MUCH TONIGHT WITH STRONG WAA IN PLACE.

.LONG TERM /SATURDAY THROUGH FRIDAY/...
ISSUED AT 340 PM CST FRI NOV 28 2014

CONCERNS ARE NOT SIGNIFICANT THROUGH THE PERIOD...BUT INCLUDE FOG
EARLY...TEMPS AND PRECIP TRENDS LATE. IMMEDIATE QUESTION WILL BE
EXTENT OF FOG AT ONSET. NAM AND OTHER HI RES NMM CORE MODELS APPEAR
TO HAVE OVERINITIALIZED SNOW COVER AND HOLD ONTO IT TOO LONG AS
WELL. HOPWRF AND NCEP WRF/ARW SEEM TO HAVE A BETTER HANDLE AND POINT
TOWARD HIGHER CONFIDENCE IN NERN SECTIONS...WHICH MAKES SENSE
CONSIDERING CURRENT LOW TEMP/DEWPOINT SPREADS THERE. SREF HITS
THINGS HARD AND MORE WIDESPREAD...BUT NMM MEMBERS MAY BE OVER
INFLUENCING THINGS. THUS WILL KEEP AREAS OF FOG WORDING NE THIRD
FOR A BIT. FOG/STRATUS PROGRESSION WILL HAVE A BIG IMPACT ON TEMPS
TOMORROW TOO. WARM FRONT BISECTING IA NW-SE AT 20Z WILL HAVE
LIFTED TO AT LEAST THE IA/MN BORDER TRYING TO PUSH ENTIRE STATE
INTO THE WARM SECTOR. NAM AND ASSOCIATED MOS IS TOO COOL...ECMWF
MOS TOO WARM...SO BLEND OF GFS AND ECMWF MOS MAY BE THE BEST BLEND
OR AT LEAST REDUCE ERRORS THE MOST. THIS RESULTS IN WARM SECTOR
HIGHS A DEGREE OR SO WARMER THAN PREVIOUS. WOULD NOT BE SURPRISED
TO SEE A FEW 60F READINGS.

STAYED ABOVE MOS AGAIN SAT NIGHT WITH OVERZEALOUS MODEL SNOW
COVER INFLUENCES PERSISTING. FOG WILL LIKELY NOT BE AS BAD AS
TONIGHT...BUT SHALLOW MOISTURE TRANSPORT OVER MOIST COOL SOILS MAY
LEAD TO PATCHY FOG AHEAD OF COLD FRONT TRAVERSING IA. FRONT SHOULD
BE EXITING SERN SECTIONS BY 12Z WITH TEMPS STEADY OR SLOWING
FALLING THROUGH SUN. RAW MODEL TEMPS SEEM A LITTLE HIGH
CONSIDERING SOURCE REGION OVER THE SNOW COVER AND STRENGTH OF THE
ARCTIC HIGH...1040MB PLUS OVER SIOUXLAND. THUS HAVE LOWERED HIGHS
CLOSER TO MOS...AT LEAST THE WARM END.

THIS ARCTIC SURGE WILL NOT LAST LONG HOWEVER WITH RETURN FLOW
STARTING AGAIN MON NIGHT. TEMPS...ESPECIALLY TUE...WILL NEED TO
BE WATCHED IN THIS PERIOD AS THEY MAY END UP WARMER AND A BIT
CLOSER TO NORMAL. FORCING WITH LONG WAVE TROUGH PASSAGE TUE WILL
BRUSH NRN IA BUT FORECAST WILL STAY DRY DUE TO LACK OF SUFFICIENT
MOISTURE. ATTENTION WILL THEN TURN UPSTREAM TO EVOLUTION OF TROUGH
OFF CA COAST. MODELS ARE STILL HAVING DIFFICULTY COMING TO ANY RUN
TO RUN CONTINUITY...AND IT MAY BE AWHILE BEFORE THAT OCCURS
CONSIDERING MULTIPLE SHORT WAVES AND TROUGH DOES NOT REACH RAOB
NETWORK UNTIL EARLY NEXT WEEK AT THE EARLIEST. ECMWF IS BECOMING A
BIT STRONGER AND EMPHASIZING MORE NRN SHORT WAVE WHILE THE GFS IS
IN PIECES THROUGH THE MID MS VALLEY. TIME AND LOCATION WILL REMAIN
IN QUESTION BUT FEEL CONFIDENT AT LEAST PATCHY LIGHT PRECIP WILL
OCCUR SOMETIME WED NIGHT-THU NIGHT SO HAVE KEPT SLIGHTS THU-THU
NIGHT FOR NOW. WHATEVER OCCURS WILL NOT BE ENOUGH FOR 36 HOURS
WORTH OF PRECIP.

&&

.AVIATION...29/00Z
ISSUED AT 522 PM CST FRI NOV 28 2014

MAIN ISSUE TONIGHT IS FOG DEVELOPMENT...WITH INCREASING LOW LEVEL
MOISTURE. FOR NOW EXPECT NORTHERN TAF SITES TO BE HIT THE HARDEST
AND HAVE POSSIBLE LIFR/IFR VSBYS AND CIGS BY THE LATE NIGHT HOURS
INTO EARLY SATURDAY. SOUTHERLY FLOW EXPECTED MORE FOR SATURDAY
WITH ANY FOG EXPECTED TO BURN OFF BY MID MORNING.

&&

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

&&

$$

SHORT TERM...MS
LONG TERM...SMALL
AVIATION...BEERENDS



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