Severe Thunderstorm Warning 76, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
340 PM CDT TUE MAY 13 2003

MAIN FORECAST CHALLENGE WILL BE IN THE SHORT TERM WITH AN ACTUAL DRY
SPELL STILL POSSIBLE LATE THIS WEEK INTO VERY EARLY NEXT WEEK.
MODELS FAIRLY CLOSE ON LARGER SCALE FEATURES THAT WOULD AFFECT OUR
WEATHER AND HAVE OVERALL USED A MODEL BLEND.

VIGOROUS SHORT WAVE TROUGH TO MOVE ACROSS THE NORTHERN PLAINS THIS
EVENING AND INTO IA WEDNESDAY. STRONG DEEP LAYERED QG FORCING THIS
AFTERNOON THROUGH 06Z ACROSS THE AREA. MODELS HAVE OVERFORECAST THE
AMOUNT OF LOW LEVEL MOISTURE RETURN UP THE MO RIVER VALLEY INTO
WESTERN IA. STILL A DECENT AREA OF LOW LEVEL CONVERGENCE AND DEEPER
LAYERED CAPE TO OUR WEST WILL SUPPORT THE CONTINUATION OF STRONG
STORMS W OF THE CWA THROUGH THE AFTERNOON AND VERY EARLY EVENING.
OUR AREA DOES HAVE SOME ELEVATED INSTABILITY COUPLED WITH MODEST
MOISTURE TRANSPORT AND MODERATE SPEED SHEAR WHICH WILL SUPPORT AN
MCS TYPE SYSTEM MOVING ACROSS THE CWA THIS EVENING AND EARLY
OVERNIGHT. I SUSPECT THE SYSTEM WILL WEAKEN AS IT MOVES E INTO IA AS
ALL MODELS DIMINISH THE ELEVATED INSTABILITY BY 06Z. NORTHERN ZONES
WILL HAVE BEST SHOT FOR PCPN SUPPORTED BY STRONG KINEMATIC FORCING
AND UPPER DIVERGENCE. THE PCPN AREA SHOULD SWEEP E AND NE OF OUR
AREA BY LATE TONIGHT WITH MAINLY DRY CONDITIONS EXPECTED THROUGH
MOST OF THE MORNING. AS THE UPPER LOW DROPS SE OVER IA WEDS...THERE
SHOULD BE ADDITIONAL SHOWERS THAT MOVE S OVER THE AREA DURING MAINLY
THE AFTERNOON AND EVENING. WILL END ALL POPS BY MIDNIGHT THURS.

AREA WILL THEN REMAIN UNDER WEAK UPPER RIDGING LATE IN THE WEEK AND
DURING THE WEEKEND. LOOKS LIKE MOST CONVECTIVE ACTIVITY WILL BE
CONFINED TO THE CENTRAL AND NORTHERN PLAINS. NEXT FRONTAL BOUNDARY
LOOKS TO MOVE INTO IA TUESDAY WHICH WILL BRING OUR NEXT CHANCE FOR
RAIN. TIL THEN...LOW LEVEL SE FLOW AND MODERATE H850 TEMPS WILL KEEP
TEMPS NEAR SEASONAL NORMS.

.DSM...NONE

JAW

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-081>086-
092>097-141100-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
540 AM CDT TUE MAY 13 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR CENTRAL IOWA.

.DAY ONE...TODAY AND TONIGHT

LOW PRESSURE WILL DEVELOP ACROSS THE PLAINS TODAY AND MOVE INTO THE
MID MISSOURI RIVER VALLEY BY THIS EVENING.  THUNDERSTORMS ARE
EXPECTED TO DEVELOP AHEAD OF THE LOW ACROSS WESTERN IOWA BY MID TO
LATE AFTERNOON.  ENOUGH INSTABILITY IS EXPECTED TO BE PRESENT TO
PRODUCE SOME SEVERE STORMS.  THE PRIMARY THREAT WILL BE FROM LARGE
HAIL AND DAMAGING WINDS.

BY TONIGHT...THE THUNDERSTORMS ARE EXPECTED TO FORM INTO A LARGE
COMPLEX AND MOVE EAST ACROSS MUCH OF CENTRAL IOWA.  SOME SCATTERED
SEVERE WEATHER IS EXPECTED WITH THE STORMS...AGAIN THE MAIN THREAT
BEING FROM LARGE HAIL AND DAMAGING WINDS.  IN ADDITION...MOISTURE
RACING NORTH INTO THE SYSTEM WILL PRODUCE HEAVY RAINFALL...PRIMARILY
ACROSS NORTHERN IOWA.  RAINFALL FROM ONE TO ONE AND A HALF INCHES IS
POSSIBLE WITH LOCALIZED HIGHER AMOUNTS.  CONTINUE TO MONITOR THE
WEATHER FOR ADDITIONAL UPDATES ON THIS APPROACHING SYSTEM.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE EXPECTED ON
WEDNESDAY...ESPECIALLY BY AFTERNOON AS DAYTIME HEATING DESTABILIZES
THE ATMOSPHERE.  HOWEVER...NO SEVERE WEATHER IS EXPECTED AT THIS
TIME.  RELATIVELY TRANQUIL WEATHER IS THEN FORECAST FOR THE
REMAINDER OF THE OUTLOOK PERIOD.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED WEST OF INTERSTATE 35 BY MID TO
LATE AFTERNOON AND ACROSS ALL OF CENTRAL IOWA OVERNIGHT.

&&

MORE INFORMATION CAN BE OBTAINED AT WWW.CRH.NOAA.GOV/DMX (ALL LOWER CASE).

COGIL