Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 181557
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1057 AM CDT MON AUG 18 2014

.UPDATE...
ISSUED AT 1055 AM CDT MON AUG 18 2014

UPDATE WILL BE COMING OUT SHORTLY FOR TIMING CHANGES...DELAYS...ON
THE ONSET OF CONVECTION TODAY.

UPDATE ISSUED AT 533 AM CDT MON AUG 18 2014

CURRENT TRENDS SHOWING THAT LEFTOVER CONVECTIVE SYSTEM OVER
SOUTHWEST IOWA CONTINUES TO WEAKEN AND SPINNING UP ONLY A FEW
SHOWERS. HAVE UPDATED ZONES TO REFLECT LESSENING CHANCES FOR
SHOWERS/STORMS THIS MORNING WITH MORE OF THE FOCUS FOR THIS
AFTERNOON OVER THE NORTH AS EARLIER FORECAST. NO OTHER CHANGES.
/REV

&&

.SHORT TERM /TODAY/...
ISSUED AT 410 AM CDT MON AUG 18 2014

FORECAST TODAY POSES A FEW CHALLENGES. EARLY MORNING FOG/VSBY
SOUTHEAST SHOULD BEGIN TO IMPROVE TOWARD SUNRISE AS HIGH CLOUDS
BEGIN TO MOVE ACROSS THE AREA. CONVECTION OVERNIGHT FOCUSED MAINLY
OVER FAR NORTHERN IOWA WITH WEAK VORT MAX AND BOUNDARY AIDING IN
SLOW MOVING TRAINING STORMS AND LOCALLY HEAVY RAINFALL...RADAR
ESTIMATES UP TO 3 TO 4 INCHES. SUBJECTIVE SFC ANALYSIS SHOWS ANOTHER
WEAK SURFACE WAVE AND FRONT OVER NORTHEAST NEBRASKA WITH MAIN
NORTHERN STREAM SHORTWAVE OVER THE EASTERN DAKOTAS. THE NEBRASKA
SYSTEM SHOULD HELP TO INITIATE SOME SHOWERS AND THUNDERSTORMS THIS
MORNING WEST INTO CENTRAL/NORTH CENTRAL IOWA DURING THE DAY AS 305K
SFC SHOWS MOISTURE TRANSPORT AND UPGLIDE INCREASING IN THIS AREA
DURING THIS TIME. BY MID AFTERNOON UPSTREAM WAVE AND MODEST
WESTERLIES BEGIN TO INCREASE FORCING ACROSS NORTHERN AND NORTHEAST
SECTIONS. THIS COMBINED WITH DAYTIME HEATING WILL PUSH MLCAPE VALUES
TO 1500 TO 2000 J/KG NORTHEAST TO NEARLY 2500 J/KG CENTRAL. THREAT
FOR SEVERE STORMS WILL INCREASE DURING THE MID TO LATE AFTERNOON FOR
MOST OF CENTRAL IOWA MAINLY FOR WIND AND HAIL.  THOUGH PRECIPITABLE
WATER VALUES REMAIN QUITE HIGH TODAY NEAR 1.5 INCHES AND WARM CLOUD
DEPTHS ARE NEAR 10 TO 12KFT...STORMS SHOULD BE FAIRLY PROGRESSIVE.
EVEN WITH THAT SAID...COULD SEE SOME LOCATIONS GET A VERY QUICK 1 TO
2 INCHES OF RAIN IN SOME OF THE HEAVIER STORMS. HIGHS WILL REACH THE
80S REGION WIDE WITH DEW POINTS IN THE LOWER 70S MAKING FOR A
MORE SUMMER LIKE AFTERNOON.

.LONG TERM /TONIGHT THROUGH SUNDAY/...
ISSUED AT 410 AM CDT MON AUG 18 2014

IMPRESSIVE SHORT WAVE CURRENTLY MOVING INTO NORTH DAKOTA WILL
BE ENTERING NORTHERN IA BY 00Z. SFC LOW PRESSURE MOVING ACROSS
MINNESOTA WILL DRAG A BOUNDARY ACROSS THE STATE THROUGH THE
EVENING AND WILL BRING A THREAT FOR THUNDERSTORMS. THE SPC DAY 1
SLIGHT RISK AREA LOOKS ON TARGET WITH MAINLY A HAIL AND DAMAGING
WIND THREAT. THE UPPER WAVE WILL CLOSE OFF AS IT SHIFTS EAST INTO
THE WESTERN GREAT LAKES REGION ON TUESDAY. EXPECT THE AREA TO
REMAIN DRY TUESDAY WITH THE FAR NORTHEAST REMAINING JUST SOUTHWEST
OF THE PRIMARY CYCLONIC FLOW AND SHOWER THREAT REGION.

ANOTHER UPPER LOW WILL DROP INTO SOUTHERN CALIFORNIA LATE TUESDAY
AND INTO WEDNESDAY WHILE A SUBTROPICAL HIGH BEGINS TO LIFT NORTH
INTO THE SOUTHEAST US. THIS WILL CREATE SOUTHWEST FLOW INTO THE
REGION WITH GOOD MOISTURE ADVECTION STREAMING NORTH ALREADY BY
LATE TUESDAY NIGHT. THUNDERSTORMS CHANCES WILL LIFT INTO THE FAR
SOUTHWEST BY EARLY WEDNESDAY MORNING HOWEVER THE THREAT WILL
DIMINISH DURING THE DAY TUESDAY AS WARM 850 MB AIR OVERSPREADS THE
AREA AND A CAP ARRIVING. THE NEXT SHORT WAVE ARRIVES WEDNESDAY
NIGHT AND WILL BRING RENEWED CHANCES FOR THUNDERSTORMS TO MAINLY
THE NORTH. PWAT VALUES NEAR 2 INCHES AND WARM CLOUD DEPTHS IN
EXCESS OF 14 KFT WILL AGAIN BE IN PLACE LEADING TO EFFICIENT RAIN
PRODUCING STORMS.

THE SUBTROPICAL HIGH LIFTS FURTHER NORTH INTO THE SOUTHERN PLAINS
TOWARD THE END OF THE WEEK. SOME LOW POPS LINGER THROUGH THURSDAY
AND FRIDAY BUT GENERALLY IT WILL BE MAINLY DRY...HOT AND HUMID
WITH HIGHS POTENTIAL PUSHING INTO THE 90S. THE LONG WAVE TROUGH
ACROSS THE NORTHWESTERN CONUS WILL SHIFT EAST OVER THE WEEKEND AND
WILL PUSH A BOUNDARY INTO THE STATE AT THE END OF THE PERIOD
BRINGING COOLER CONDITIONS AND ANOTHER CHANCE FOR THUNDERSTORMS.

&&

.AVIATION...18/12Z
ISSUED AT 653 AM CDT MON AUG 18 2014

LIFR FOG CONTINUES OVER THE SOUTHEAST AT KOTM BUT SHOULD BEGIN TO
IMPROVE BY 13-15Z WITH SUNRISE. OLD CONVECTIVE COMPLEX OVER
SOUTHWEST IA/NORTHERN MO CONTINUES TO DRIFT EAST WITH LITTLE
IMPACT. MESO/SYNOPTIC MODELS IN BETTER AGREEMENT WITH ARRIVAL OF
FORCING WITH NORTHERN STREAM SHORTWAVE...WITH MOST OF THE
CONVECTION TO BE FOCUSED ACROSS THE NORTH AND DEVELOPING TOWARD
17-19Z AND CONTINUING TO 22-23Z. MVFR CONDITIONS MAY ACCOMPANY THE
STORMS THIS AFTERNOON AND AGAIN THIS EVENING. SOME UNCERTAINTY ON
EXACT TIMING AND COVERAGE TODAY AND THIS EVENING SO HAVE INCLUDED
VICINITY WORDING FOR NOW. A COLD FRONT TRAILING THE SYSTEM MAY
BRING A WEAKER...SECOND ROUND OF CONVECTION BETWEEN 00Z AND 04Z
ACROSS THE REGION. /REV


&&

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

$$

UPDATE...MS AUG 14
SHORT TERM...REV
LONG TERM...DONAVON
AVIATION...REV



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