Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 141750
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1250 PM CDT SUN SEP 14 2014

.UPDATE...
ISSUED AT 1121 AM CDT SUN SEP 14 2014

ALREADY HAD SOME RESPONSE TO RETURN FLOW WITH EHANCED H850-H700
FRONTOGENESIS OVER NORTHERN NEBRASKA AS MOISTURE FED INTO THE
ISENTROPIC LIFT ZONE WITH SW FLOW ALOFT. RADAR SHOWED MID LEVEL
RETURNS NOT QUITE YET STRONG ENOUGH TO PRODUCE ANY RAINFALL AT THE
SFC BY 15Z...THAT AND DRY COLUMN OVER THE REGION SHOULD CONTINUE
TO SLOWLY GIVE WAY TO PRECIP LATE THIS AFTERNOON AND EVENING
ACROSS THE NORTH. CLOUDS OVER THE NORTH CONTINUE TO HINDER WARMING
WHILE THE SOUTH IS WARMING MORE QUICKLY DUE TO INCREASED
INSOLATION. THUS...HAVE MODIFIED AFTERNOON HIGHS BY WARMING SOUTH
CONSERVATIVELY INTO THE LOWER 70S...AND COOLED THE NORTH BY 3 OR
SO DEGREES. EXPECTING THAT THE AREA WILL BE GENERALLY PARTLY SUNNY
TO MOSTLY CLOUDY BY 23-00Z THIS EVENING. COLUMN DRY ENOUGH THAT
LITTLE IF ANY PRECIP EXPECTED THROUGH THE AFTERNOON HOURS
TODAY...EVEN WITH UPPER LEVEL RETURNS ACROSS NORTHEAST NEBRASKA AT
THIS TIME.

&&

.SHORT TERM /TODAY/...
ISSUED AT 314 AM CDT SUN SEP 14 2014

LITTLE SENSIBLE WEATHER OF CONCERN TODAY. MID CLOUDS ARE ADVANCING
THROUGH IA EARLY THIS MORNING IN ZONE OF WARM/THETA-E ADVECTION
AHEAD OF WEAK MO VALLEY SHORT WAVE NOTED IN SUBTLE WATER VAPOR
DARKENING. THERE HAS BEEN NO PRECIPITATION HOWEVER. MID LEVEL
FORCING WILL GRADUALLY INCREASE AS MT JET SEGMENT AND UPSTREAM
ALBERTA SHORT WAVE DROP INTO THE BASE OF NRN CONUS MEAN TROUGH.
MOISTURE WILL BE LIMITED THOUGH SO DO NOT EXPECT ANY PRECIP UNTIL
BEYOND THIS PERIOD WHEN ANOTHER ROUND OF THETA-E ADVECTION ARRIVES
AND STABILITY LOWERS.

WEAK SLY FLOW AND 0-2KM WARM ADVECTION SHOULD HELP TEMPS REBOUND
TODAY. SOUNDINGS SUGGEST WARMER GFS MOS TEMPS ARE MORE REALISTIC.

.LONG TERM /TONIGHT THROUGH SATURDAY/...
ISSUED AT 314 AM CDT SUN SEP 14 2014

RAIN CHANCES WILL RETURN TONIGHT AS A LOBE OF VORTICITY SWINGS
THROUGH THE BROAD CYCLONIC FLOW ALOFT. ON THE LEADING FLANK OF
THIS SHORTWAVE A BROAD REGION OF VERTICAL FORCING WILL SPREAD OVER
THE AREA LATE TONIGHT...ESPECIALLY AFTER MIDNIGHT...AND INTO
MONDAY MORNING BEFORE THE WAVE MOVES THROUGH COINCIDENT WITH A
SURFACE TROUGH. DESPITE A RELATIVE LACK OF INSTABILITY OR LOW
LEVEL FORCING...THE UPPER LEVEL SUPPORT IS SUFFICIENT TO WARRANT
60 TO 80 POPS ACROSS MOST OF THE AREA LATE TONIGHT AND EARLY
MONDAY MORNING THOUGH FORECAST AMOUNTS ARE PRETTY LIGHT AND NO
REAL IMPACTS ARE ANTICIPATED.

ON MONDAY A SURFACE HIGH PRESSURE AREA WILL BUILD IN QUICKLY FROM
THE NORTHWEST...RESULTING IN RAPID CLEARING DURING THE AFTERNOON
AND COOLER AIR MOVING IN BY MONDAY EVENING. AS WINDS GO LIGHT WITH
CLEAR SKIES MONDAY NIGHT TEMPERATURES WILL FALL RAPIDLY AFTER
DARK...BUT MINIMUM TEMPERATURES WILL BE LIMITED BY SOMEWHAT HIGHER
DEWPOINTS AND WARMER TEMPERATURES ALOFT THAN WERE PRESENT DURING
THE FRIDAY NIGHT/SATURDAY MORNING RADIATIVE COOLING EVENT. THUS
MONDAY NIGHT LOWS ARE STILL HELD IN THE UPPER 30S TO LOWER 40S AND
NO REAL FROST THREAT IS ANTICIPATED.

THE COOL SURFACE HIGH WILL MOVE OFF TO THE EAST AND SOUTHEAST ON
TUESDAY...WITH STEADILY MODERATING TEMPERATURES AND DRY WEATHER
THE RULE THROUGH THURSDAY GIVEN SOUTHEASTERLY LOW LEVEL FLOW
BENEATH NORTHWESTERLY FLOW ALOFT. MEANWHILE A LARGE 500 MB RIDGE
WILL BUILD ALONG THE ROCKIES AND HIGH PLAINS...EVENTUALLY MOVING
OVER IOWA AND OFF TO THE EAST AROUND FRIDAY AS A LONGWAVE TROUGH
FROM THE WEST COAST ADVANCES TOWARD THE MIDWEST. THERE MAY BE A
WINDOW OF OPPORTUNITY FOR SOME SHOWERS AND STORMS AROUND THE TOP
OF THE RIDGE ACROSS NORTHERN IOWA THURSDAY NIGHT/FRIDAY...BUT A
MUCH MORE LIKELY RAIN CHANCE WILL COME WITH THE PASSAGE OF THE
LONGWAVE TROUGH ON FRIDAY NIGHT/SATURDAY. AT THIS TIME THE DETAILS
OF THIS EVOLUTION AND ANY SEMBLANCE OF CONFIDENCE IN TIMING REMAIN
UNCLEAR...BUT HAVE INCLUDED CHANCE POPS FOR THE LATTER PERIOD AS
SOMEWHERE AROUND THE FIRST HALF OF NEXT WEEKEND WE SHOULD SEE A
ROUND OF SHOWERS AND STORMS WITH THE TROUGH PASSAGE.

&&

.AVIATION...14/18Z
ISSUED AT 1250 PM CDT SUN SEP 14 2014

MAIN CONCERNS OVERNIGHT WILL BE LOWER CIGS AND CHANCES FOR PRECIP.
2 MAIN AREAS OF FORCING...UPPER LEVEL BOUNDARY ACROSS THE NORTH
AND WEAK WARM FRONT/INVERTED TROUGH ACROSS THE SOUTH WILL COMBINE
FOR LIGHT RAIN SHOWERS AND LOWERING CIGS TO MVFR AFT 08Z TO 15Z AS
THE BOUNDARIES PUSH THROUGH. TOWARD THE END OF THE PERIOD
EXPECTING SOME IMPROVEMENT AS FRONTS SLIDE EAST AND NORTHERLY
WINDS INCREASE WITH SLIGHTLY DRIER AIR RETURNING TO THE REGION.
/REV

&&

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

$$

UPDATE...REV
SHORT TERM...SMALL
LONG TERM...LEE
AVIATION...REV


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