Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 282340
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
640 PM CDT SUN SEP 28 2014

.SHORT TERM /TONIGHT/...
ISSUED AT 324 PM CDT SUN SEP 28 2014

CU FIELD WILL DISSIPATE AS DAYTIME HEATING SUBSIDES WITH GENERALLY
CLEAR CONDITIONS FOR MOST OF THE NIGHT. SURFACE BOUNDARY ACRS THE
DAKOTAS AND MN WILL SAG TO NEAR THE IA/MN BORDER BY DAYBREAK AS
SHORTWAVE PROGRESSES ACROSS SOUTHERN CANADA. THE BULK OF FORCING
WILL REMAIN WELL NORTH OF IOWA ALONG WITH THE BEST THREAT OF
PRECIPITATION. OTHERWISE...DECENT RADIATIONAL COOLING WILL OCCUR
AS SURFACE WINDS WILL BE LIGHT AND VARIABLE. WILL LIKELY SEE SOME
DECENT GROUND FOG ONCE AGAIN...ESPECIALLY IN FAVORED LOW LYING
AREAS AND RIVER VALLEYS AND HAVE INCLUDED IN THE FORECAST.

.LONG TERM /MONDAY THROUGH SUNDAY/...
ISSUED AT 324 PM CDT SUN SEP 28 2014

NO SIGNIFICANT CHANGES IN LONG TERM FORECAST THINKING TODAY. THE
MILD AND MOSTLY DRY WEATHER WILL LAST FOR ANOTHER DAY OR
TWO...FOLLOWED BY A CLOUDY AND WET PERIOD THEN MUCH COOLER WEATHER
TO END THE WEEK. ON MONDAY MID LEVEL RIDGING WILL BE UNDERCUT BY A
DYING COOL FRONT SAGGING DOWN FROM MINNESOTA INTO NORTHERN IOWA.
THIS WILL RESULT IN A FEW SHOWERS AND STORMS ACROSS OUR NORTH LATE
MONDAY...WHILE IN THE CENTRAL AND SOUTHERN SECTIONS SUNNY AND WARM
WEATHER WILL CONTINUE WITH TEMPERATURES RISING INTO THE LOW TO MID
80S IN RESPLENDENT SUNSHINE. THE FRONTAL BOUNDARY WILL STALL
ACROSS NORTHERN IOWA MONDAY EVENING...THEN BECOME WASHED OUT AND
RETROGRADE AS IT IS BRIDGE BY A SURFACE HIGH PRESSURE AREA
BUILDING ACROSS WISCONSIN AND ILLINOIS AND TURNING OUR LOW LEVEL
FLOW TO EAST THEN SOUTHEAST.

MEANWHILE ON MONDAY A LARGE 500 MB TROUGH WILL BE MOVING SLOWLY
ACROSS THE ROCKIES...AS ANOTHER LARGE TROUGH FOLLOWING ON ITS
HEELS IN THE NORTHERN STREAM COMES ASHORE OVER THE BRITISH
COLUMBIA COAST. THE LEADING TROUGH WILL MOVE OVER THE HIGH PLAINS
ON MONDAY NIGHT WITH THE PRIMARY LOBE OF VORTICITY CLOSING OFF
OVER WESTERN NEBRASKA AND SOUTH DAKOTA BY TUESDAY MORNING...THEN
SHOOTING NORTHWARD OVER THE DAKOTAS AND INTO MINNESOTA ON TUESDAY
AND TUESDAY NIGHT. BEHIND THIS INITIAL SYSTEM GENERAL 500 MB
TROUGHINESS WILL GRADUALLY OVERSPREAD THE CENTRAL U.S. AND
IOWA FOR THE REMAINDER OF THE WEEK.

THE INITIAL SYSTEM ON TUESDAY WILL GENERATE SHOWERS AND
THUNDERSTORMS MAINLY ACROSS WESTERN IOWA TUESDAY AFTERNOON AND
EVENING...WHICH SHOULD BLEED EASTWARD AND FADE OUT EARLY TUESDAY
NIGHT BEFORE ADDITIONAL DEVELOPMENT OCCURS LATE TUESDAY NIGHT
THROUGH WEDNESDAY WITH A SECOND IMPULSE ROUNDING THE TROUGH. THERE
IS SOME MARGINAL SEVERE WEATHER THREAT INITIALLY IN OUR
NORTHWESTERN COUNTIES BUT IT IS A NARROW WINDOW OF OPPORTUNITY
BEFORE THE FORCING ASSOCIATED WITH THE MID LEVEL LOW DEPARTS...AND
EVEN THESE CONDITIONS WILL BE MORE FAVORABLE UP TOWARD THE SIOUX
FALLS AREA. AT THE SURFACE...WINDS WILL REMAIN GENERALLY FROM THE
SOUTHEAST FROM TUESDAY INTO THURSDAY AS THE SYNOPTIC BOUNDARY
ATTENDING THE BROAD 500 MB TROUGH LINES UP WELL TO OUR NORTHWEST.
THIS BOUNDARY WILL FINALLY PUSH THROUGH IOWA SOMETIME AROUND
FRIDAY CONCURRENT WITH A SHARPER 500 MB SHORTWAVE...CLEARING
THINGS OUT AFTER THE 36 TO 48 HOURS OF EXTENDED POPS BUT ALSO
BRINGING MUCH COOLER TEMPERATURES FROM FRIDAY THROUGH THE WEEKEND.
THE COOLER AIR WILL BE REINFORCED BY THE FINAL SHOTS OF 500 MB
ENERGY MOVING OVERHEAD AROUND EARLY FRIDAY AND PERHAPS FRIDAY
NIGHT...BUT THESE TRAILING IMPULSES WILL BE DRIER WITH VERY
LIMITED ATMOSPHERIC MOISTURE AND LITTLE TO NO RAINFALL IS EXPECTED
DURING THAT TIME FRAME.

&&

.AVIATION...29/00Z
ISSUED AT 636 PM CDT SUN SEP 28 2014

OVERNIGHT FOG REMAINS THE PRIMARY RESTRICTION POTENTIAL THROUGH
THE PERIOD. AGAIN LOCAL IFR OR LOWER CONDITIONS MAY OCCUR. SOME
UNCERTAINTY ON POTENTIAL CIGS BY MONDAY AFTERNOON AS A BOUNDARY
NEARS THE AREA. SOME INDICATIONS THAT CIGS BELOW 3 KFT MAY OCCUR
AFTER 18Z.

&&

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

$$

SHORT TERM...COGIL
LONG TERM...LEE
AVIATION...DONAVON



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