Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 212346
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
646 PM CDT THU AUG 21 2014

.SHORT TERM /TONIGHT/...
ISSUED AT 351 PM CDT THU AUG 21 2014

YET ANOTHER MESSY FORECAST FOR TONIGHT. CURRENTLY A SHORTWAVE IS
EXITING IOWA AND THE ASSOCIATED FORCING WITH IT HAS PUSHED INTO
ILLINOIS. ANY CONVECTION IS WANING AND WILL BE ALL BUT GONE IN AN
HOUR OR TWO. CLOUDS ARE CLEARING FAST AND THE SUNNY SKIES ARE
ALLOWING FOR CLOUDS TO CLEAR OR AT LEAST LIFT AND WE ARE HEATING
UP...HOWEVER IT MAY BE LATE ENOUGH THAT HIGHS WILL REMAIN CLOSE TO
THE GOING FORECAST. NOT REALLY LOOKING FOR ANY STORMS THIS EARLY
EVENING AS THERE WILL BE LITTLE TO FOCUS ON...UNTIL THE LOW LEVEL
JET INCREASES. HOWEVER...THE LATEST SPC SWODY1 STILL KEEPS A
SLIGHT RISK ACROSS MOST OF THE CWA. CANNOT SAY I AGREE TOTALLY
WITH IT BUT IT IS NOT OUT OF THE REALM OF POSSIBILITY EITHER.
THEIR THOUGHT IS THAT WITH CLEARING WILL COME DESTABILIZATION AND
ADDITIONAL STORM DEVELOPMENT WHICH WILL SINK INTO FAR NORTHERN
IOWA THIS EVENING/TONIGHT. THE 4KM NSSL DOES IN FACT SHOW THIS
SCENARIO BUT THE HOPWRF...HRRR...AND NAM 12 FAIL TO MATERIALIZE
ANY REAL CONVECTION UNTIL LATER TONIGHT WHEN A SHORTWAVE DRIVES A
FRONTAL BOUNDARY INTO US AS A LOW LEVEL JET FOCUSES ACROSS
SOUTHEAST IOWA.

MY ASSESSMENT IS THAT LATER THIS EVENING/TONIGHT ANOTHER SHORTWAVE
WILL CROSS IOWA FLATTENING THE UPPER RIDGE A BIT COINCIDENT WITH
THE LOW LEVEL JET WHICH WILL FOCUS INTO SOUTHERN/SOUTHEAST IOWA.
THERE IS ABUNDANT MOISTURE IN PLACE AND SOME WEAK THETA-E
ADVECTION AND FORCING MOVES INTO SOUTHERN IOWA AS WELL SO IF ALL
THIS COMES TOGETHER...LATER THIS EVENING THROUGH A FAIR PORTION OF
THE OVERNIGHT WE SHOULD SEE REDEVELOPMENT OF THUNDERSTORMS ACROSS
THE SOUTHERN/SOUTHEAST THIRD OR SO OF THE FORECAST AREA.

ADDING TO THIS WILL BE A SURFACE LOW OVER WESTERN MINNESOTA THAT
WILL MOVE EAST SOUTHEAST TONIGHT AS THE SHORTWAVE PUSHES ACROSS...
DRAGGING A FRONTAL BOUNDARY ALONG WITH IT.  BY 12Z THE FRONTAL
BOUNDARY WILL LIE SOMEWHERE NEAR A LINE FROM WATERLOO TO OMAHA.
PRETTY MUCH KEPT POPS CONFINED TO ALONG AND SOUTH OF THIS BOUNDARY
WITH THE BEST POPS FURTHER SOUTH ALONG THE MO BORDER. NORTH OF
THIS BOUNDARY THE LOW LEVEL MOISTURE WILL STILL RESIDE AND
PATCHY FOG WILL DEVELOP. VISIBILITIES COULD BE AS LOW AS A MILE OR
SO AND IT WILL BE POSSIBLE ACROSS A FAIRLY EXPANSIVE AREA...ENOUGH
TO WARRANT MENTION IN THE ZONES. PATCHY FOG IS POSSIBLE
ELSEWHERE...SOUTH OF THE BOUNDARY AS WELL BUT IT ISN`T AS CLEAR
CUT AS NORTH OF THE BOUNDARY. GIVEN THE POSSIBILITY OF
REDEVELOPMENT ACROSS THE NORTH I DID CARRY VERY LOW POPS ACROSS
FAR FAR NORTH FOR A COUPLE OF HOURS MID TO LATE EVENING BUT KEPT
HIGHER POPS SOUTH/SOUTHEAST.

.LONG TERM /FRIDAY THROUGH THURSDAY/...
ISSUED AT 351 PM CDT THU AUG 21 2014

FORECAST REMAINED FOCUSED ON CONTINUED HOT AND HUMID CONDITIONS
AND THUNDERSTORM CHANCES OVER THE WEEKEND. LEANED TOWARD THE
DRIER...AND THUS WARMER NAM/ECMWF THROUGH THE WEEKEND.

FRIDAY THROUGH SUNDAY...OVERNIGHT CONVECTION WILL LINGER ACROSS
THE SOUTH PAST 12Z FRIDAY BEFORE PEAK HEATING IN CONJUNCTION WITH
A WEAK SHORTWAVE RIDING ALONG THE UPPER RIDGE BY THE LATE
AFTERNOON AND EVENING HOURS FRIDAY. MUCH OF THE FORECAST AREA
REMAINS CAPPED THROUGH 20Z FRIDAY AND PULLED BACK THE RE-DEVELOP
UNTIL THEN. MAINLY EXPECTING ISOLATED CONVECTION LATE TOMORROW
AFTERNOON INTO THE EVENING BEFORE THE MAIN SURFACE LOW AND
ASSOCIATED WARM FRONT TRANSITION ACROSS THE STATE. A LITTLE BETTER
ORGANIZED FOCUS BY SATURDAY MORNING AS THE WARM FRONT BULGES INTO
NORTHERN IOWA BY 12Z SATURDAY AND COINCIDES WITH A DECENT SLUG OF
THETA-E ADVECTION AND QG FORCING IN THIS AREA. HAVE LIKELY POPS
12-18Z SATURDAY BEFORE CONVECTION SHOULD MOVE INTO MINNESOTA BY
THE AFTERNOON. SEVERE POTENTIAL TOMORROW INTO SATURDAY ARE LIKELY
LIMITED WITH LACK OF SIGNIFICANT SHEAR PRESENT.

TWEAKED UP MAX TEMPS ON SATURDAY AND SUNDAY WITH THE WAA AND GOOD
MIXING BOTH DAYS. HEAT INDEX VALUES ACROSS THE CENTRAL AND
SOUTHERN SECTIONS OF THE FORECAST AREA LOOK TO TOP 100 EACH
AFTERNOON BUT STILL BELOW ADVISORY CRITERIA ATTM. ON
FRIDAY...ALTHOUGH SOUTHERN IOWA HEAT INDEX VALUES NEAR
CRITERIA...WITH THE MORNING CONVECTION AND LINGERING CLOUD COVER
MAY INHIBIT THE MAX TEMPS AND THUS LOW CONFIDENCE WITH ANY
HEADLINES ATTM.

MONDAY THROUGH THURSDAY...LARGE UPPER LEVEL RIDGE HOLDS IN PLACE
OVER THE SOUTHEAST PORTION OF THE COUNTRY AND KEEPS WESTERN TO
NORTHERN IOWA IN THE RING OF FIRE. A FEW ADDITIONAL SHORTWAVES
RIDE ATOP THE RIDGE SUNDAY NIGHT THROUGH TUESDAY NIGHT BEFORE A
DECENT COLD FRONT PUSHES ACROSS THE REGION WEDNESDAY. TWEAKED UP
MAX TEMPS ON WEDNESDAY WITH GOOD WAA AHEAD OF THE FRONT.
OTHERWISE...DRY AND COOLER LATE NEXT WEEK.

&&

.AVIATION...22/00Z
ISSUED AT 637 PM CDT THU AUG 21 2014

WINDS WILL LESSEN OVERNIGHT...WITH LIGHT WINDS AND AMPLE LOW LEVEL
MOISTURE WILL SEE BR/FG AT SITES NEAR 12Z...AND HAVE TRENDED
VISIBILITIES AND CEILINGS DOWN TO MVFR AND IFR...THOUGH MAY DROP
LOWER AT TIMES. IN ADDITION...ADDITIONAL ROUNDS OF TSRA/SHRA MAY
AFFECT SOUTHERN SITES NEAR 12Z...KDSM/KOTM...WITH CEILINGS AND
VISIBILITIES REDUCING TO MVFR OR LOWER WITH TSRA. WINDS WILL
REMAIN LIGHT THROUGH REMAINDER OF PERIOD WITH CONDITIONS RETURNING
TO VFR BEYOND 12Z.

&&

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

&&

$$

SHORT TERM...FAB
LONG TERM...PODRAZIK
AVIATION...AWB


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