Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 232012
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
312 PM CDT WED JUL 23 2014

.SHORT TERM /TONIGHT/...
ISSUED AT 242 PM CDT WED JUL 23 2014

HIGH PRESSURE WILL CONTINUE TO PUSH SOUTHEAST INTO GREAT LAKES
REGION OVERNIGHT. THIS WILL HELP TO KEEP CONDITIONS DRY THROUGHOUT
THE OVERNIGHT...WITH CLOUDS MOSTLY DECREASING AFTER SUNSET. AS HIGH
PUSHES EAST WINDS WILL BECOME MORE SOUTHERLY LATE IN THE
PERIOD...WITH INCREASE WAA ACROSS THE WEST. HAVE WARMED LOWS SLIGHTLY
GIVEN AMOUNT OF WARMING IN THE AFTERNOON AND WAA AND INCREASING
CLOUDS...ESPECIALLY IN THE WEST. APPROACHING SYSTEM WILL REACH
WESTERN IOWA BY EARLY MORNING...THOUGH BEST FORCING DOES NOT ARRIVE
INTO CWA UNTIL AFTER 12Z. GIVEN RELATIVELY DRY CONDITIONS...HAVE
THEREFORE OPTED FOR A DRY FORECAST THROUGH THE PERIOD...THOUGH MAY
BE TOO DRY IN THE WEST IN THE EARLY MORNING HOURS.

.LONG TERM /THURSDAY THROUGH WEDNESDAY/...
ISSUED AT 242 PM CDT WED JUL 23 2014

THURSDAY THROUGH FRIDAY NIGHT...
SURFACE HIGH TO PROPAGATE EAST OF IOWA BY LATE THURSDAY MORNING.
CWA TO RETURN TO SOUTHERLY FLOW...BUT HIGH SHOULD BE CLOSE ENOUGH
TO HOLD MORE NOTABLE WARM AIR ADVECTION OFF UNTIL FRI. 700 MB
TEMPS FCST TO BE NEAR +11C WHICH WOULD CAP OFF MOST
CONVECTION...ESPECIALLY EAST OF I-35. ADDITIONAL PROBLEM THURSDAY
IN THE DMX CWA WILL BE A NOTABLE LACK OF MOISTURE. SFC TROUGH TO
PASS THROUGH THE DAKOTAS AND INTO SOUTHERN MINNESOTA/NORTHERN IOWA
THURSDAY AND THURSDAY NIGHT. STRONG SOUTHWESTERLY WINDS OF 40 TO
45 KTS AT 850 MB WILL SUPPORT DECENT SLUG OF MOISTURE TRANSPORT
INTO WESTERN IOWA BY 06Z AND INTERSTATE 35 BY 12Z...BRINGING PWAT
VALUES UP TO +1 TO +2 STD DEV. TIGHT GRADIENT OF THETA-E ADVECTION
TO MOVE ACROSS CWA FROM WEST TO EAST. CAPE VALUES FRI MORNING NOT
SIGNIFICANT SO NO SVR WEATHER THREAT. FORECAST SOUNDINGS SHOW
DECENT WARM CLOUD DEPTH...SO EXPECT DECENT PRECIPITATION
EFFICIENCY. SHEAR PROFILE SUFFICIENT TO SUSTAIN STORMS AS THEY
PROPAGATE EASTWARD...PUSHING EAST OF THE CWA BY 18Z. FORECAST
ISSUE WILL BE IF THERE WILL BE AFTERNOON CONVECTION ASSOCIATED
WITH DAYTIME HEATING. MODELS SHOWING AXIS OF MOISTURE CONVERGENCE
ORIENTED N-S TO MOVE ACROSS CWA DURING THE DAY. HOWEVER...H850
TEMPS PUSHING +25C AND H750 MB TEMPS PUSHING +15C WILL CREATE
FORMIDABLE CAP. BEST FORCING TO BE EAST OF CWA WITH MORNING
SYSTEM. WITH NO APPARENT TRIGGERS OR FORCING MECHANISMS TO HELP
BREAK CAP...SO WILL CONFINE FRIDAY PM POPS TO EASTERN PARTS OF
CWA. REGARDLESS OF POPS...AM CONFIDENT THAT HEAT INDEX VALUES WILL
RANGE FROM 95 TO 105 FOR CENTRAL TO SOUTHWESTERN PARTS OF CWA.

SATURDAY THROUGH WEDNESDAY...AN UNSEASONABLY STRONG UPPER TROUGH IS
FORECAST TO BE ALONG THE US/CANADIAN BORDER AT 12Z SATURDAY. THE
12Z MODELS ARE IN DECENT AGREEMENT WITH THE OVERALL THEME OF
AMPLIFYING THE UPPER TROUGH OVER THE GREAT LAKES AND EASTERN US AND
A RIDGE OVER THE WESTERN CONUS. UNSEASONABLY COOL AIR WILL
DOMINATE THE WEATHER PATTER OVER IOWA FROM SUNDAY THROUGH THE
EXTENDED. TEMPERATURES IN FORECAST MAY NOT CAPTURE THE COOLEST
TEMPERATURES AND WILL NEED TO BE ADJUSTED. THERE WILL BE A FEW
PRECIPITATION CHANCES DURING THIS TIME FRAME...BUT THE WEATHER
SHOULD BE MAINLY DRY. SURFACE RIDGE SHOULD BE EAST OF IOWA BY
WEDNESDAY AND TEMPERATURES WILL LIKELY WARM BEYOND THE FORECAST
PERIOD.

&&

.AVIATION...23/18Z
ISSUED AT 1223 PM CDT WED JUL 23 2014

CONDITIONS WILL REMAIN VFR THROUGH PERIOD...WINDS WILL SHIFT TO
THE SOUTH AHEAD OF APPROACHING SYSTEM. MAY SEE TSRA/VCTS AT
WESTERN AND NORTHERN SITES...KFOD/KMCW...NEAR END OF PERIOD AND
BEYOND PERIOD.


&&

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

$$

SHORT TERM...AWB
LONG TERM...KOTENBERG/JOHNSON
AVIATION...AWB


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