Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 311122
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
622 AM CDT THU JUL 31 2014

.SHORT TERM /TODAY/...
ISSUED AT 308 AM CDT THU JUL 31 2014

SFC HIGH PRESSURE IS RIDGED THROUGH IOWA EARLY THIS MORNING. A FEW
POCKETS OF FOG HAVE DEVELOP MAINLY OVER FAR NORTHERN AND INTO
WESTERN IOWA. THE FOG LIKELY WILL INCREASE IN AREAL COVERAGE OVER
THE NEXT FEW HOURS BUT SHOULD NOT BECOME WIDESPREAD AND THEN BURN
OFF QUICKLY AFTER SUNRISE. AN UPPER PV ANOMALY  AND ASSOCIATE MID
LEVEL SHORT WAVE ARE CURRENTLY MOVING SOUTH/SOUTHEAST THROUGH
EASTERN NORTH DAKOTA AND NORTHWEST MINNESOTA. THIS SYSTEM HELPED
GENERATE A FEW THUNDERSTORMS NEAR THE CANADIAN BORDER WEDNESDAY
AFTERNOON. DIURNAL HEATING TODAY IS EXPECTED TO STEEP LOW TO MID
LEVEL LAPSE RATES OVER NORTHERN IOWA BY THE AFTERNOON ESPECIALLY
WITH A WEDGE OF COOL 700 MB TEMPERATURES NEAR ZERO C. SURFACE BASED
CAPES OVER 1000 J/KG ARE LIKELY BY THE AFTERNOON. WHILE NO FORCING
MECHANISMS WILL BE PRESENT NEAR SURFACE...THE ATMOSPHERE WILL BECOME
STATICALLY UNSTABLE BY THIS AFTERNOON. THE AFOREMENTIONED UPPER
LEVEL SYSTEM SHOULD BRING ENOUGH KINEMATICS TO FORCE ENOUGH
VERTICAL ASCENT FOR A FEW THUNDERSTORMS TO DEVELOP. THE
COMBINATION OF LOW MELTING LEVELS NEAR 11 KFT AND GOOD HAIL CAPE
IN THE -10 TO -20 C RANGE MAY LEAD TO A STORM OR TWO PRODUCING
PENNY TO QUARTER SIZED HAIL. TEMPERATURES TODAY WILL BE SIMILAR TO
WEDNESDAY. EXPECT SCT TO BKN CUMULUS TO DEVELOP BY THIS AFTERNOON
CENTRAL AND NORTH.

.LONG TERM /TONIGHT THROUGH WEDNESDAY/...
ISSUED AT 308 AM CDT THU JUL 31 2014

THE MILD AND QUIET WEATHER EXPERIENCED OVER THE LAST SEVERAL DAYS
WILL HOLD THROUGH THE END OF THE WEEK...BUT CHANGES ARE ON WAY IN
THE EXTENDED FORECAST PERIOD WITH A MORE ACTIVE WEATHER PATTERN
SETTING UP NEXT WEEK.

FROM TONIGHT THROUGH SATURDAY IOWA WILL REMAIN BENEATH THE
SOUTHWESTERN PERIPHERY OF CYCLONIC FLOW ALOFT AROUND AN EASTERN
U.S. TROUGH. AT THE SURFACE WE WILL CONTINUE TO BE DOMINATED BY
HIGH PRESSURE WITH LIGHT WINDS AND RELATIVELY DRY WEATHER. A FEW
SHOWERS OR THUNDERSTORMS WILL BE POSSIBLE THIS EVENING AND THEN
AGAIN ON FRIDAY AFTERNOON BUT ANY STORMS THAT DO DEVELOP WILL BE
VERY ISOLATED AND OF LITTLE TO NO IMPACT. MEANWHILE TEMPERATURES
WILL CONTINUE TO WARM BY A DEGREE OR PERHAPS TWO EACH
DAY...REMAINING NEAR OR BELOW NORMAL OVERALL WITH RELATIVE
HUMIDITY LOWER THAN IS TYPICAL AT THIS TIME OF YEAR. OVERALL THE
NEXT SEVERAL DAYS WILL SEE NO DISCERNIBLE CHANGE IN SENSIBLE
WEATHER FROM THAT THAT HAS PREVAILED DURING THE WEEK UP TO THIS
POINT.

LATE ON SATURDAY THE AFOREMENTIONED EASTERN U.S. TROUGH WILL BEGIN
TO PROGRESS EASTWARD...ALLOWING A DEEP LAYER RIDGE ACROSS THE
WESTERN U.S. TO BUILD MORE OVER THE MIDWEST AND PLACING IOWA
BENEATH THE NORTHEASTERN PERIPHERY OF ITS INFLUENCE. THIS WILL
LEAD TO WARMER TEMPERATURES AND A GRADUAL RETURN OF HIGHER
HUMIDITY FROM SUNDAY THROUGH MONDAY AND INTO TUESDAY...BUT WILL
ALSO PLACE OUR AREA NEAR THE SO CALLED RING OF FIRE AS IMPULSES
MOVING THROUGH THE WEST NORTHWEST FLOW ALOFT OVERTOP THE RIDGE AND
PROVIDE THUNDERSTORM CHANCES ESPECIALLY ACROSS OUR NORTHERN AND
NORTHEASTERN COUNTIES BY TUESDAY. MEANWHILE...A LARGE BUT
RELATIVELY WEEK LOW PRESSURE TROUGH WILL COME ASHORE OVER SOUTHERN
CALIFORNIA EARLY NEXT WEEK AND GRADUALLY PROGRESS
NORTHEASTWARD...ERODING THE WESTERN U.S. RIDGE AND PUSHING
INEXORABLY TOWARD THE MIDWEST. IT WILL THEN BE ABSORBED AND PHASED
INTO A NORTHERN STREAM WAVE APPROACHING FROM CANADA AROUND TUESDAY
NIGHT AND WEDNESDAY AS IT MOVES ACROSS IOWA. PROVIDING THAT THE
TIMING OF THIS PHASING REMAINS ON TRACK...THE SYNOPTIC SET UP WILL
FAVOR THE BEST CHANCE FOR WIDESPREAD RAINS WE HAVE SEEN IN WEEKS.
FROM TUESDAY NIGHT THROUGH WEDNESDAY NIGHT HAVE INCREASED POPS TO
40 TO 50 PERCENT ACROSS MOST OF THE AREA...AND THEY MAY NEED TO BE
PUSHED HIGHER IF CONFIDENCE IN TIMING CONTINUES TO INCREASE. THE
OVERALL SCENARIO DOES NOT APPEAR PARTICULARLY FAVORABLE FOR SEVERE
WEATHER ALTHOUGH IT IS ALWAYS A POSSIBILITY AT THIS TIME OF
YEAR...BUT THE BIGGER STORY IF THIS SYSTEM PANS OUT WILL BE THE
BENEFICIAL RAINS THAT IT WILL BRING TO LAWNS...GARDENERS...AND
AGRICULTURAL INTERESTS ALIKE. STAY TUNED FOR UPDATES IN THE COMING
DAYS AS THIS TIME FRAME IS STILL NEARLY A WEEK OUT AND CHANGES ARE
ENTIRELY POSSIBLE.

&&

.AVIATION...31/12Z
ISSUED AT 622 AM CDT THU JUL 31 2014

LOCALIZED FOG WILL DIMINISH QUICKLY THIS MORNING. VFR CONDITIONS
ARE FORECAST FOR MUCH OF TODAY HOWEVER THERE IS THE POTENTIAL FOR
ISOLATED THUNDERSTORMS THIS AFTERNOON ALONG WITH CIGS BLO 3 KFT
OVER THE NORTHERN SITES. LOCALIZED FOG MAY RETURN AGAIN TONIGHT

&&

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

&&

$$

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



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