Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 230457
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1157 PM CDT MON SEP 22 2014

.SHORT TERM /TONIGHT/...
ISSUED AT 354 PM CDT MON SEP 22 2014

SURFACE HIGH PRESSURE WILL SLOWLY SHIFT EAST TONIGHT INTO
TUESDAY MORNING AND PROVIDE SOME LIGHT RETURN FLOW OVERNIGHT. MID-
LEVEL THETA-E ADVECTION AHEAD OF WEAK SHORTWAVE SLOWLY MOVING ACROSS
NEBRASKA/SOUTH DAKOTA WILL PROVIDE AN INCREASE IN CLOUD COVER PAST
06Z OVER WESTERN IOWA. LEANED TOWARD THE COOLER NAM12/SREF FOR LOW
TEMPERATURES TONIGHT...ALTHOUGH WITH THE WEAK RETURN FLOW AND
INCREASING CLOUDS OVER THE WEST...MAY SEE A FEW FAR WESTERN AREAS
WITH A NON-DIURNAL TEMP TREND. HAVE PATCHY FOG MENTIONED ACROSS THE
NORTHEAST WHERE RADIATIONAL COOLING LOOKS TO SET UP CLOSER TO THE
CENTER OF THE HIGH PRESSURE.

.LONG TERM /TUESDAY THROUGH MONDAY/...
ISSUED AT 354 PM CDT MON SEP 22 2014

LITTLE SENSIBLE WEATHER OF CONCERN THROUGH THE PERIOD OUTSIDE OF A
WINDOW FOR PRECIP INTO MIDWEEK. UPPER LOW DRIFTING THROUGH ROCKIES
RIDGE WILL LIKELY BRING SCATTERED WEAK CONVECTION TO IA FROM LATE
TUE TO LATE WED.  DO NOT EXPECT WIDESPREAD PRECIP...MUCH LIKE WHAT
IS CURRENTLY OCCURRING UPSTREAM...WITH  WEAK TO MODERATE FORCING
AND WEAK INSTABILITY. THIS SHOULD GRADUALLY DRIFT W TO E THROUGH
IA TUE WITH FORCING AND MOISTURE INITIALLY BASED 3KM AND ABOVE.
AIRMASS WILL START QUITE DRY BELOW. HOWEVER THERMODYNAMIC
FORCING...MAINLY THETA-E ADVECTION WITH INCREASED
MOISTURE...SHOULD LOWER CIGS TUE NIGHT INTO WED. BY LATE WED THE
FORCING AND MOISTURE APPEARS TO BE MAINLY AT OR BELOW 3KM...AND
REMAINS WEAK...SO THERE IS NEVER REALLY ANY GOOD PHASING OF
FORCING AND MOISTURE WITH ANY DEPTH. LITTLE BAROCLINICITY OR WARM
ADVECTION EITHER BASED ON 305/310K ISENT SURFACES.

BY THU THE UPPER LEVEL RIDGE WILL CONTINUE TO BUILD FROM THE ROCKIES
INTO THE NRN PLAINS AND S CENTRAL CANADIAN PROVINCES DIMINISHING
FORCING AND MOISTURE INTO IA AS UPPER WAVE FINALLY MOVES AWAY.
HEIGHTS AND TEMPS WILL BE VERY ANOMALOUS NORTH OF IA WITH EXTREME Z
AND T CLIMO PERCENTILES IN THOSE LOCATIONS AS THERMAL RIDGE BUILDS
TO OUR NORTH. FARTHER SOUTH THOSE VALUES WILL NOT BE AS EXTREME
OR ATYPICAL WITH OUR WEATHER DRY AND TEMPS NORMAL TO ABOVE NORMAL
IN SUSTAINED SOMEWHAT WEAK SLY/SELY LOW LEVEL FLOW. A SRN STREAM
WAVE DOES LIFT FROM THE FAR SRN PLAINS INTO THE OH VALLEY LATE IN
THE PERIOD...BUT APPEARS TOO FAR SOUTH DO TO MUCH HERE.

&&

.AVIATION...23/06Z
ISSUED AT 1153 PM CDT MON SEP 22 2014

HIGH PRESSURE TO EAST OF IA WILL CONTINUE TO MOVE AWAY AS UPPER
LOW OVER THE NRN ROCKIES AND NORTHERN HIGH PLAINS MOVES EAST
TOWARD IA. AREA OF SHOWERS AND LOWER CLOUDS TO THE WEST WILL
ADVANCE INTO THE WESTERN TAF SITES BY 06Z/24...BUT THE EAST WILL
REMAIN DRY. VFR CONDITIONS THROUGHOUT THE TAF PERIOD OTHER THAN
SOME PATCHY FOG IN THE KOTM AREA AROUND SUNRISE.

OUTLOOK...UPPER LOW WILL CONTINUE EAST WITH UNSETTLED WEATHER AND
AREAS OF MVFR CONDITIONS WED AND WED NIGHT. IMPROVEMENT IS
EXPECTED THURSDAY AND  FRIDAY WITH HIGH PRESSURE BUILDING INTO
THE AREA.

&&

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

$$

SHORT TERM...PODRAZIK
LONG TERM...SMALL
AVIATION...MS SEP 14


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