Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 261958
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
258 PM CDT SAT JUL 26 2014

.SHORT TERM /TONIGHT THOUGH MONDAY/
... ISSUED AT 223 PM CDT SAT JUL 26 2014

WATER VAPOR IMAGERY WAS SHOWING ADVERTISED UPPER TROUGH OVER THE
NORTHERN PLAINS AND SOUTH CENTRAL CANADA MOVING SOUTHEAST TOWARDS TO
THE GREAT LAKES THIS AFTERNOON.  THUNDERSTORMS OVER EASTERN NEBRASKA
EARLY THIS AFTERNOON WERE MOVING AND DEVELOPING SOUTH INTO
INSTABILITY GRADIENT.  AT THE SURFACE...A STATIONARY FRONT EXTENDED
FROM EASTERN NEBRASKA EAST THROUGH FAR SOUTHERN IOWA AT 18Z.  THE
IMMEDIATE FORECAST CONCERN IS THUNDERSTORMS THIS EVENING AND THEIR
IMPACTS. THE AIRMASS OVER CENTRAL AND NORTH CENTRAL IOWA WAS
RELATIVELY STABLE EARLY THIS AFTERNOON WITH AN AREA OF DRY AIR AT
850 MB COUPLED WITH LIGHT NORTHEAST FLOW CENTERED OVER THE STATE
ACCORDING TO THE SPC MESO PAGE. THE POCKET OF DRY AIR IS
COINCIDENT WITH A SMALL SURFACE HIGH OVER NORTHERN IOWA AT 18Z.
SHORT RANGE MESOSCALE MODELS ALONG WITH 12Z NAM/GFS ALL SUGGEST
VERY LITTLE ACTIVITY THIS EVENING. CONVECTION OVER NEBRASKA SHOULD
CONTINUE TO FEED INTO UNSTABLE AIR OVER SOUTHEAST NEBRASKA AND
NORTHERN MISSOURI LATE THIS AFTERNOON. THE AIRMASS OVER SOUTH
CENTRAL IOWA SHOULD DESTABALIZE ALONG A LOW-LEVEL MOISTURE AXIS
NEAR THE IOWA AND MISSOURI BORDER. AT THIS POINT...THE BEST CHANCE
FOR THUNDERSTORMS APPEARS TO BE SOUTHERN IOWA...CLOSE TO THE
MISSOURI BORDER. MUCH OF CENTRAL AND NORTHERN IOWA WILL LIKELY BE
DRY. AS THE VIGOROUS UPPER TROUGH...FOR LATE JULY...MOVES
SOUTHEAST TONIGHT...THE ASSOCIATED COLD FRONT WILL SWEEP ACROSS
IOWA. THE FRONT WILL CLEAN OUT ALL MESOSCALE BOUNDARIES AND IT
WILL USHER IN COOLER AND DRIER AIR.

MODELS ARE IN GOOD AGREEMENT WITH THE MASS FORECAST FIELDS SUNDAY
AND MONDAY CARVING OUT A DEEP UPPER TROUGH OVER THE EASTERN CONUS.
BIG STORY FOR IOWA WILL BE UNSEASONABLY COOL AIR OVER THE STATE. 850
MB TEMPERATURES ARE FORECAST FROM 8-12 DEGREES C ACCORDING TO THE
12Z GFS WHICH APPEARS REASONABLE.  KEPT MENTION OF SHOWER ACTIVITY
IN THE NORTHEAST SUNDAY AFTERNOON...OTHERWISE IT SHOULD BE DRY AND
UNSEASONABLY COOL SUNDAY AND MONDAY.

.LONG TERM /TUESDAY THROUGH SATURDAY/
... ISSUED AT 223 PM CDT SAT JUL 26 2014

EASTERN CONUS UPPER TROUGH REMAINS IN PLACE THROUGH THE EXTENDED
WITH THE 500 MB UPPER RIDGE CENTERED OVER THE ROCKIES. AT THE
SURFACE...A LARGE SURFACE RIDGE REMAINS IN PLACE THROUGH THE
PERIOD. LATE IN THE FORECAST PERIOD...THE 12Z ECMWF/GFS RETROGRADE THE
UPPER LOW ENOUGH TO SUPPORT A SMALL CHANCE OF SHOWERS.
OTHERWISE...DRY AND CONTINUED BELOW NORMAL TEMPERATURES.

&&

.AVIATION...26/18Z
ISSUED AT 1235 PM CDT SAT JUL 26 2014

NOTABLE CHANGES SINCE 12Z TAF. IN THE SHORT TERM...TSRA OVER NW
IOWA. THESE STORMS WILL MOVE EAST AND IMPACT KFOD AND KMCW FOR
NEXT FEW HOURS. FOR LATER THIS AFTERNOON AND EVENING...BOUNDARY
LOCATED IN NORTHERN MO WILL MOVE NORTHWARD INTO SOUTHERN IA. THIS
BOUNDARY WILL BE FOCUS FOR SEVERE WX THREAT...WITH DAMAGING WINDS
PRIMARY THREAT...LARGE HAIL SECONDARY THREAT. DROPPED TS FROM
KDSM TAFS AS IT APPEARS STORMS SHOULD STAY SOUTH OF METRO AREA.
LEFT TSRA IN KOTM TAFS...BUT STORMS MAY STAY SOUTH OF KOTM AS
WELL. WILL...OF COURSE...BE MONITORING AND UPDATING THROUGHOUT
DAY. SKC AND LIGHT WINDS BEHIND THIS SYSTEM FOR OVERNIGHT.


&&

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

$$

SHORT TERM...JOHNSON
LONG TERM...JOHNSON
AVIATION...KOTENBERG



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