Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 221142
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
642 AM CDT TUE JUL 22 2014

...UPDATED AVIATION DISCUSSION...

.SHORT TERM /TODAY/...
ISSUED AT 339 AM CDT TUE JUL 22 2014

.TODAY...ANOTHER HOT AND VERY HUMID DAY TODAY WITH SURFACE DEW
POINTS WELL INTO THE 70S AND MAXIMUM TEMPERATURES FORECAST TO RISE
WELL INTO THE 90S ACROSS MUCH OF CENTRAL IOWA. SEVERAL LOCATIONS IN
THE SOUTHERN HALF OF THE FORECAST AREA WILL LIKELY SEE HEAT INDEX
VALUES FROM 105-110 BY THIS AFTERNOON. WENT A DEGREE OR TWO ABOVE
THE NAM12/ECMWF FOR MAXIMUM TEMPERATURES TODAY AS THEY HAVE HAD A
BETTER HANDLE ON THE TEMPERATURES.

WEAK CONVECTION TRYING TO DEVELOP OVER WESTERN IOWA BUT IS
IMMEDIATELY HITTING THE VERY STRONG CAP IN PLACE AND NOT ABLE TO
STRENGTHEN AND SUSTAIN THEMSELVES. HAVE SLIGHT POPS GOING THROUGH
11Z TO HANDLE THE ISOLATED CONVECTION BUT NOT ANTICIPATING ANYTHING
LONG LIVED.

COLD FRONT LOOKS TO PUSH ACROSS THE STATE THIS AFTERNOON AND SHOULD
CLEAR IOWA BY 00Z WEDNESDAY. WITH THE AFOREMENTIONED CAP IN PLACE
(+16C 700MB TEMPERATURES)...NOT EXPECTING MUCH TO DEVELOP UNTIL
AFTER 21Z OVER SOUTHERN IOWA. THERE IS A TREMENDOUS AMOUNT OF CAPE
VALUES THIS AFTERNOON AS IT RANGES FROM 4000 TO 6000 J/KG IN
SOUTHERN IOWA. HOWEVER...THE LOW LEVEL SHEAR IS MINIMAL AND THE 0-
6KM IS WEAK AS WELL IN SOUTHERN IOWA. NOT A LOT OF CONFIDENCE WITH
MUCH...IF ANYTHING...BREAKING THROUGH THE CAP THIS AFTERNOON.
HOWEVER ON THE OTHER SIDE OF THE COIN...NOT A LOT OF CONFIDENCE IT
WILL BE COMPLETELY DRY ACROSS SOUTHERN IOWA THIS AFTERNOON. SO LEFT
SLIGHT TO LOW CHANCE POPS GOING AFTER 21Z AS MAY SEE A COUPLE
ISOLATED STORMS PERCOLATE WITH THE AMOUNT OF INSTABILITY PRESENT
AHEAD OF THE FRONT.  FIND SUPPLEMENTAL AFD IMAGES ON OUR LATEST BLOG
POST: NWS.WEATHER.GOV/BLOG/NWSDESMOINES/

.LONG TERM /TONIGHT THROUGH MONDAY/...
ISSUED AT 339 AM CDT TUE JUL 22 2014

THE COLD FRONT MOVING SOUTH TODAY WILL CONTINUE TO PUSH SOUTH OF THE
REGION BETWEEN 00Z AND 06Z WEDNESDAY.  MODELS ARE AT ODDS WITH ANY
RESIDUAL CONVECTION ACROSS THE SOUTH DURING THIS TIME. THOUGH GFS
SHOWS H700 TEMPERATURES COOLING ENOUGH TO FIRE CONVECTION ALONG THE
H850 COOL FRONT...GEM/NAM/EURO ALL SUGGEST THAT TEMPS ALOFT WILL
CONTINUE TOO WARM TO MAINTAIN MUCH OF ANY CONVECTION DURING THE
OVERNIGHT HOURS OVER OUR AREA IN THE SOUTH. WITH LITTLE CONVERGENCE
EXPECTED ALONG THE SFC BOUNDARY AND ALOFT...EXPECT THAT THE
CONSENSUS OF CONVECTION ENDING EARLY WILL HOLD FOR TONIGHT. AS
COOLER AIR ARRIVES...H850 TEMPS BACK OFF FROM CURRENT VALUES OF 22
TO 26C THIS EVENING AND BY 12Z WED WILL HAVE FALLEN BACK TO 11C
NORTH TO NEAR 18C ALONG THE SOUTHERN BORDER. WITH PERSISTENT
NORTHEAST WINDS OVERNIGHT...COOLER AIR SHOULD HAVE LITTLE TROUBLE
REPLACING THE HOT/HUMID CONDITIONS LEFT OVER IN THE EVENING HOURS.
MOST OF THE AREA SHOULD DROP BACK DOWN INTO THE 60S WITH THE
EXCEPTION OF DES MOINES...WHICH WILL BE STILL INFLUENCED BY THE HEAT
ISLAND EFFECT THROUGH THE NIGHT AND MAY HOLD TO NEAR 70. AS THE
COOLER AND DRIER AIR MOVES IN FOR WEDNESDAY...THE ENTIRE AREA SHOULD
ENJOY A PLEASANT DAY WITH FAIR WX CLOUDS AND LIGHT NORTHEAST
BREEZES. AS HIGH PRESSURE BUILDS ACROSS THE REGION...DRY WEATHER
WILL CONTINUE FOR WED NIGHT AND THURSDAY EAST. OVER THE
WEST...THURSDAY THE H500 UPPER LEVEL RIDGE WILL BEGIN TO REBUILD
TOWARD IOWA WITH ANOTHER PUSH OF WARM AIR ADVECTION. THIS SHOULD
RESULT IN AN AREA OF SHOWERS AND THUNDERSTORMS ACROSS THE NORTHERN
PLAINS...HEADING SOUTHEAST INTO WESTERN IOWA BY THURSDAY MORNING.
GENERALLY...THE MODELS ARE IN AGREEMENT WITH THE COMPLEX OF STORMS
WEAKENING AS IT MAKES ITS WAY EAST THURSDAY BOTH FROM A STANDPOINT
OF WEAKENING LOW LEVEL JET DURING THE MORNING AND THE SFC HIGH STILL
TO THE EAST. THE GFS IS A BIT MORE AGGRESSIVE IN KEEPING THE AREA
GOING ACROSS CENTRAL IOWA...BUT WILL NOT LEAN TOWARD THAT SOLUTION.
BY THURSDAY NIGHT LOW PRESSURE WILL DEEPEN ACROSS THE WESTERN
PLAINS...WITH FORCING INCREASING OVERNIGHT ACROSS THE REGION. THIS
WILL RESULT IN A MUCH BETTER CHANCE FOR SHOWERS AND THUNDERSTORMS
REGION WIDE THURSDAY NIGHT INTO FRIDAY MORNING...BUT ESPECIALLY OVER
THE NORTHEAST. LATER IN THE DAY ON FRIDAY ADDITIONAL THUNDERSTORMS
SHOULD DEVELOP ALONG A WARM FRONT AND LEADING EDGE H700 CAP...
EXPANDING DURING THE NIGHT OVER THE EAST. MODELS CONTINUE TO
STRUGGLE WITH THE EVOLUTION OF THE SYSTEM FOR THURSDAY AND FRIDAY
AND ARE LEANING TOWARD A RAPID RETURN OF WARM CONDITIONS ACROSS THE
SOUTH BY FRIDAY AFTERNOON. THE EURO IS PUSHING HIGHS ACROSS THE
SOUTH INTO THE LOW 90S FRIDAY...BUT WILL WAIT FOR ANOTHER MODEL RUN
BEFORE MAKING ANY SIGNIFICANT CHANGES.  BY THURSDAY AFTERNOON AND
NIGHT INSTABILITY WILL BE ON THE INCREASE AND BULK SHEAR/WIND FIELDS
ALSO INCREASING OVERNIGHT INTO FRIDAY MORNING. WITH THAT...THERE MAY
BE AN INCREASED CHANCE FOR SOME SEVERE WEATHER OVER THE AREA.
FOLLOWING THE PASSAGE OF THE SYSTEM FRIDAY AND FRIDAY NIGHT...A
PLEASANT DAY IS EXPECTED ON SATURDAY IN THE WAKE OF THE STORM. BY
THE END OF THE WEEKEND SUNDAY INTO MONDAY...THE PASSAGE OF A
STRONGER COLD FRONT FROM CANADA WILL USHER IN MUCH COOLER AIR AS
WELL AS A CHANCE FOR SOME SCT THUNDERSTORMS. FOR NOW THERE IS SOME
UNCERTAINTY WITH THE TIMING OF THE FRONT...THOUGH THE CURRENT
CONSENSUS IS FOR THE FRONT TO PASS THROUGH THE AREA SUNDAY
AFTERNOON. FOLLOWING THE FRONT...HIGHS ARE LIKELY TO FALL BACK INTO
THE 70S TO NEAR 80S WITH LOWS IN THE 50S TO LOWER 60S FOR MONDAY AND
TUESDAY.

&&

.AVIATION...22/12Z
ISSUED AT 638 AM CDT TUE JUL 22 2014

WEAK ISOLATED THUNDERSTORM MOVING INTO POLK COUNTY MAY SKIRT JUST
NORTH OF DSM AIRPORT THIS MORNING AND HAVE VCTS MENTIONED ATTM.
HAVE MVFR VIS AT MCW DUE TO FOG IMPROVING BY 13Z...BUT MAY LINGER
AS LATE AS 14Z. OTHERWISE...EXPECTING VFR CONDITIONS THE REMAINDER
OF THE TAF PERIOD WITH SOME ISOLATED CONVECTION AT OTM LATE THIS
AFTERNOON. LOW CONFIDENCE WITH ANY DEVELOPMENT AND LEFT TAF DRY
ATTM.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
HEAT ADVISORY UNTIL 7 PM CDT THIS EVENING FOR ADAIR-ADAMS-
APPANOOSE-AUDUBON-BLACK HAWK-BOONE-BREMER-BUTLER-CALHOUN-CARROLL-
CASS-CERRO GORDO-CLARKE-CRAWFORD-DALLAS-DAVIS-DECATUR-EMMET-
FRANKLIN-GREENE-GRUNDY-GUTHRIE-HAMILTON-HANCOCK-HARDIN-HUMBOLDT-
JASPER-KOSSUTH-LUCAS-MADISON-MAHASKA-MARION-MARSHALL-MONROE-PALO
ALTO-POCAHONTAS-POLK-POWESHIEK-RINGGOLD-SAC-STORY-TAMA-TAYLOR-
UNION-WAPELLO-WARREN-WAYNE-WEBSTER-WINNEBAGO-WORTH-WRIGHT.

&&

$$

SHORT TERM...PODRAZIK
LONG TERM...REV
AVIATION...PODRAZIK


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