Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 251738
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1238 PM CDT MON AUG 25 2014

.SHORT TERM /TODAY/...
ISSUED AT 403 AM CDT MON AUG 25 2014

WIDELY SCATTERED THUNDERSTORMS HAVE DEVELOPED AGAIN EARLY THIS
MORNING...INITIATED BY A WEAK IMPULSE MOVING OVERHEAD AND A MODEST
LOW LEVEL JET TAKING ADVANTAGE OF THE UNSTABLE ENVIRONMENT
SURROUNDING A DECAYING FRONTAL ZONE CREEPING ACROSS THE AREA. EXPECT
THIS FRONT TO STALL IN A SOUTHWEST TO NORTHEAST ORIENTATION ACROSS
IOWA TODAY...PROVIDING RELATIVELY COOLER WEATHER IN THE NORTHWEST
BUT MAINTAINING HOT AND HUMID CONDITIONS IN THE CENTRAL AND
SOUTHEAST SECTIONS. WITHIN THIS ENVIRONMENT A FEW STORMS WILL LIKELY
PERSIST PAST SUNRISE INTO THE MID MORNING HOURS...BUT SHOULD THEN
DISSIPATE WITH WARM TEMPERATURES ALOFT BUILDING OVER THE AREA DURING
THE DAY. ADDITIONAL STORMS WILL DEVELOP AGAIN TONIGHT UNDER SIMILAR
CONDITIONS...BUT SHOULD MAINLY BE AFTER 00Z WITH JUST SOME 20 TO 30
POPS INTRODUCED LATE THIS AFTERNOON/EVENING IN THE PEAK HEATING
HOURS. OTHER THAN CONVECTIVE CONCERNS...INCREASED TEMPERATURES A BIT
FOR TODAY GIVEN THE EXPECTED STALLING LOCATION OF THE FRONT AND
PROPENSITY FOR HEATING AND MOISTURE POOLING ALONG SUCH BOUNDARIES AT
THIS TIME OF YEAR. EXPECT HEAT INDEX VALUES WILL ONCE AGAIN TOP OUT
AROUND 100 DEGREES FROM ROUGHLY THE DES MOINES METRO SOUTHWARD AND
EASTWARD...SO NO HEADLINES ARE ANTICIPATED AT THIS TIME.

.LONG TERM /TONIGHT THROUGH SUNDAY/...
ISSUED AT 403 AM CDT MON AUG 25 2014

NUMEROUS ROUNDS OF THUNDERSTORMS STILL ON TAP THROUGH AT LEAST
THURSDAY. EACH OF THE NEXT THREE NIGHTS WILL CONTAIN THE POTENTIAL
FOR HEAVY RAINFALL WITH THE PRIMARY RISK ALONG AND NORTH OF
INTERSTATE 80 DURING THE PERIOD. A COLD FRONT OVER NORTHWEST IOWA
WILL DROP SLOWLY SOUTH THROUGH THE STATE INTO TONIGHT AS HIGH
PRESSURE SETTLES SOUTH INTO THE DAKOTAS. THE BOUNDARY IS QUITE
SHALLOW NEAR THE SFC AND WILL BE OVERRUN BY MOISTURE ADVECTION
OVERNIGHT AS THE SUB TROPICAL HIGH TO THE SOUTH WRAPS GULF
MOISTURE WITH SOME MONSOONAL CONTRIBUTION INTO THE STATE. STRONG
FORCING WILL BE IN PLACE OVER NORTHERN AND CENTRAL IOWA GENERALLY
BETWEEN HIGHWAYS 18 AND 30 DUE TO SEVERAL KINEMATIC AND
THERMODYNAMIC FACTORS. THE RIGHT ENTRANCE OF THE UPPER JET WILL
BRING GOOD UPPER LEVEL DIVERGENCE IN ADDITION TO A SHORT WAVE
PASSING THROUGH THE MID LEVELS. CONCURRENTLY STRONG THETA-E
ADVECTION WILL BE FOCUSED ACROSS THE AREA. DEEP LAYER SHEAR OF 25
TO 35 KTS WILL SUPPORT GOOD STORM ORGANIZATION AND STORM MOTIONS
WILL BE EAST TO NORTHEAST AROUND 20 KTS AND PARALLEL TO THE
INSTABILITY AXIS RESULTING IN TRAINING CELLS. WILL HAVE THE
POTENTIAL FOR A FEW SEVERE STORMS BUT THE GREATER THREAT WILL BE
HEAVY RAINFALL WITH CONDITIONS FAVORABLE FOR EFFICIENT RAINFALL
PRODUCING STORMS.

THE AREA OF HIGH PRESSURE WILL MOVE ACROSS MINNESOTA ON TUESDAY
AND SHOULD HELP BRING SOME STABILITY TO IOWA. THE MOISTURE WILL
BEGIN TO SURGE BACK NORTHWARD QUICKLY TUESDAY NIGHT WITH ANOTHER
ROUND OF THUNDERSTORMS AND THE POTENTIAL FOR ANOTHER BAND OF HEAVY
RAIN IN THE AFOREMENTIONED AREA. THE THREAT FOR THUNDERSTORMS WILL
CONTINUE WEDNESDAY THROUGH EARLY THURSDAY AS THE AREA OF HIGH
PRESSURE SHIFTS TOWARDS THE WESTERN GREAT LAKES AND AN AREA OF LOW
PRESSURE MOVES INTO KANSAS AND NEBRASKA. THIS WILL KEEP THE STRONG
MOISTURE ADVECTION INTO THE STATE. PWATS WILL MAX WEDNESDAY NIGHT
INTO THURSDAY NEAR 2 INCHES. THE PRIMARY CONCERN FOR ALL OF THESE
EVENTS IS 2 OR 3 OF THESE EVENTS WILL CROSS OVER THE SAME AREAS
AND MAY RESULT IN SIGNIFICANT HYDROLOGY IMPACTS BEFORE THIS SYSTEM
FINALLY DEPARTS LATE IN THE WEEK. EXPECT FLASH FLOOD HEADLINES
WILL BE NEEDED AT SOME POINT.

MODEL GUIDANCE IS FINALLY CONSISTENT WITH THE SLOWER MOVEMENT OF
THE WESTERN UPPER LOW WITH IT OPENING UP AND TRACKING TOWARD THE
AREA LATE IN THE WEEK. THIS WILL KEEP PRECIPITATION CHANCE OVER
IOWA THROUGH SATURDAY FOLLOWED BY A PREDOMINATELY ZONAL FLOW.
TEMPERATURES THROUGH THE WEEK WILL BE DEPENDENT ON CLOUD COVER
AND BOUNDARY LOCATION WITH GENERALLY COOL CONDITIONS NORTH AND
GRADUALLY COOLING CONDITIONS SOUTH.

&&

.AVIATION...25/18Z
ISSUED AT 1226 PM CDT MON AUG 25 2014

COLD FRONT ACROSS THE CWA WILL MAKE SLOW PROGRESS SOUTHEAST BEFORE
STALLING OUT SOUTHEAST OF THE STATE. WARM AIR IS EXPECTED TO
OVERRUN THE FRONT TONIGHT WITH AN AREA OF THUNDERSTORMS FORMING
ACROSS THE TAF SITES. THE MOST FAVORED AREA NOW APPEARS TO BE THE
SOUTH HALF TO TWO THIRDS OF THE STATE. THUNDERSTORMS WILL BE OUT
OF THE AREA BY 12.

OUTLOOK...SEVERAL UPPER AIR DISTURBANCES WILL MOVE ACROSS THE AREA
BRINGING PERIODIC THUNDERSTORM ACTIVITY FOR THE NEXT SEVERAL
DAYS.

&&

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

$$

SHORT TERM...LEE
LONG TERM...DONAVON
AVIATION...MS AUG 14


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