Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 162345
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
645 PM CDT TUE SEP 16 2014

.SHORT TERM /TONIGHT/...
ISSUED AT 314 PM CDT TUE SEP 16 2014

SURFACE HIGH CENTERED IN WEST CENTRAL ILLINOIS WILL GRADUALLY
SHIFT EASTWARD OVERNIGHT. RETURN SOUTHERLY FLOW HAS ALREADY SET
IN ACROSS WESTERN IOWA WHERE DEWPOINTS HAVE BEEN STEADILY CLIMBING
ALL DAY. LOW STRATOCUMULUS DECK FROM SOUTH CENTRAL NEBRASKA INTO
EASTERN SOUTH DAKOTA IS ASSOCIATED WITH A WEDGE OF THETA-E
ADVECTION LIFTING NORTHEASTWARD ON THE BACKSIDE OF THE HIGH.
EXTRAPOLATION OF THE CLOUD SHIELD BRINGS IT INTO THE WESTERN CWA
BY 03Z AND DES MOINES BY 06Z...WHICH MATCHES WELL WITH MODEL
GUIDANCE WITH RESPECT TO THE THETA-E ADVECTION BAND. INCREASED
CLOUD COVER OVERNIGHT FROM WEST TO EAST WITH PARTLY TO MOSTLY
CLOUDY WORDING THROUGHOUT THE CWA. OVERNIGHT LOWS WILL BE THE
BIGGEST QUESTION AND ARE DEPENDENT ON THE TIMING OF THE CLOUDS.
GIVEN THE RATE THAT TEMPERATURES DROPPED OFF LAST NIGHT AND THE
TIMING OF THE CLOUDS...EXPECT A QUICK BUT SHORT- LIVED DROP IN
TEMPERATURES FROM 00-06Z FOLLOWED BY A NEAR STEADY STATE TREND
AFTER 06Z. DROPPED MIN TEMPS THE LOWEST IN THE EAST WHERE SKIES
WILL REMAIN CLEAR THE LONGEST. ALMOST ALL OF THE HIGH RESOLUTION
GUIDANCE TAKES ANY ATTENDANT PRECIPITATION TO THE SOUTH OF IOWA
WITH THE BETTER 925-700MB MOISTURE TRANSPORT BETWEEN 09-12Z
TONIGHT...BUT STILL CANNOT RULE OUT A STRAY SHOWER OR STORM IN
THIS TIMEFRAME AND THUS RETAINED SLIGHT CHANCE WORDING IN THE FAR
SW CWA.

.LONG TERM /WEDNESDAY THROUGH TUESDAY/...
ISSUED AT 314 PM CDT TUE SEP 16 2014

MAIN FORECAST CONCERN DEALT WITH GRADUAL WARMING TREND THROUGH
THE END OF THE WORK WEEK AND PRECIPITATION CHANCES THURSDAYNIGHT
THROUGH SATURDAY.

WEDNESDAY...WEAK MID-LEVEL SHORTWAVE AND ASSOCIATED THETA-E
ADVECTION SHOULD QUICKLY EXIT THE STATE BY 15Z WEDNESDAY IF NOT
SOONER. KEPT SLIGHT POPS GOING ACROSS THE FAR SOUTHWEST 12-15Z
WEDNESDAY.

THURSDAY INTO FRIDAY...INCREASED CLOUD COVER THURSDAY ACROSS THE
WEST-NORTHWEST AS A WEAK SHORTWAVE AND THETA-E ADVECTION ENTER
THE WESTERN EDGES OF IOWA BY THE AFTERNOON. STILL PLENTY OF DRY
AIR UNTIL THE BETTER SLUG OF THETA-E ADVECTION AND BETTER LARGE
SCALE FORCING MOVE ACROSS NORTHERN IOWA OVERNIGHT INTO FRIDAY
MORNING. KEPT WITH CHANCE POPS ACROSS THE NORTH DURING THE
AFOREMENTIONED TIME FRAME. ALSO...WAA BEGINS LATE THURSDAY NIGHT
INTO EARLY FRIDAY MORNING AND HAVE MENTION OF NON-DIURNAL
TEMPERATURE TREND...MAINLY ACROSS WESTERN IOWA. INCREASED WINDS
ON FRIDAY WITH GOOD MIXING AND DECENT PRESSURE GRADIENT
DEVELOPING AHEAD OF COLD FRONT. AS A RESULT...TWEAKED MAX TEMPS
UP SLIGHTLY...ESPECIALLY WITH THE WARMER START FRIDAY MORNING.

FRIDAY NIGHT THROUGH SATURDAY...MUCH STRONGER MOISTURE TRANSPORT
DEVELOPS FRIDAY NIGHT INTO SATURDAY MORNING AHEAD OF A SHARP COLD
FRONT TO PUSH THROUGH BY SATURDAY. KEPT WITH LIKELY POPS AS EXTENDED
MODELS ARE IN DECENT AGREEMENT WITH THE OVERALL TIMING AND LOCATION
OF THE FRONT/PRECIP FRIDAY NIGHT INTO SATURDAY. HEAVY RAIN LOOKS
POSSIBLE...BUT LOW CONFIDENCE WITH THE REMNANTS OF ODILE MAKES IT
THIS FAR NORTH AS THE 12Z MODEL RUNS KEEP IT SOUTH OF THE AREA.

SUNDAY THROUGH TUESDAY...NO MAJOR CONCERNS DURING THIS PERIOD AS
LARGE SURFACE HIGH AND UPPER LEVEL RIDGE BUILD INTO THE STATE SUNDAY
AND INTO EARLY NEXT WEEK.

&&

.AVIATION...17/00Z
ISSUED AT 645 PM CDT TUE SEP 16 2014

MAINLY VFR CIGS EXPECTED OVERNIGHT AS LOW/MID CLOUD DECK SPREADS IN
FROM THE WEST.  THERE IS A CHANCE FOR BRIEF MVFR CONDITIONS BETWEEN
09Z AND 12Z.  A DISTURBANCE WILL CLIP SW IA AND THERE MAY BE AN
ISOLD SHOWER OR THUNDERSTORM AROUND BUT NONE ARE EXPECTED CLOSE
ENOUGH TO A TAF LOCATION TO MENTION.  LIGHT SOUTH TO SOUTHWEST SFC
WIND WILL BECOME SOUTHEAST EARLY WEDNESDAY MORNING.

&&

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

&&

$$

SHORT TERM...SKOW
LONG TERM...PODRAZIK
AVIATION...FAB


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