Severe Thunderstorm Warning 5, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
640 AM CDT FRI APR 2 2010

...UPDATED FOR 12Z AVIATION DISCUSSION...

.SHORT TERM /TODAY/...
SYSTEM TO MOVE ACRS STATE TODAY AND IS MORE PROGRESSIVE THAN LAST
NIGHTS RUNS.  HAVE ALREADY SEEN SOME SHOWER ACTIVITY FARTHER WEST
OVERNIGHT AHEAD OF THIS BOUNDARY BUT THE MAJORITY OF THIS PCPN DIED
RATHER QUICKLY AS ANY WEAK INSTABILITY WAS QUICKLY EXHAUSTED.  AS
THE FRONT APPROACHES THIS MORNING...MODELS INDICATE SOME ADDITIONAL
MOISTURE STREAMING NORTHWARD WITH A NARROW CORRIDOR OF WEAK
INSTABILITY MOVING INTO THE STATE.  EXPECT TO SEE SOME SCT TO NMRS
SHOWERS AND A FEW THUNDERSTORMS INCREASE AHEAD OF THE BOUNDARY
THROUGH THE DAY AS THE MOISTURE DEEPENS IN ADVANCE OF THE FRONT.
AREAL COVERAGE WILL LIKELY EXPAND DUE TO THE INCREASING MOISTURE
WITH TIME...THEREFORE HAVE HIGHEST POPS IN THE EAST BY AFTERNOON.
INSTABILITY REMAINS RATHER WEAK SO DONT ANTICIPATE SEVERE WEATHER
ALTHOUGH MAY SEE SOME ISOLATED HAIL BY AFTERNOON WITH PEAK HEATING.
TEMPERATURES PROBLEMATIC WITH MOS GUIDANCE TOO LOW AS TEMPS ALREADY
NEAR OR AT SUGGESTED HIGHS.  HAVE GONE HIGHER THAN GUIDANCE...
ESPECIALLY IN THE EAST WHERE THE FRONT ARRIVES LATER IN THE DAY.
THEN HAVE APPLIED AN NON-DIURNAL CURVE TO TEMPERATURES AS FRONT
PASSES THROUGH THE STATE.  GIVEN THE MORE PROGRESSIVE NATURE...DONT
ANTICIPATE HUGE HYDRO ISSUES AT THIS TIME WITH HEADLINES NOT NEEDED
AT THIS POINT.

.LONG TERM /TONIGHT THROUGH THURSDAY/...
SYSTEM TO IMPACT THE AREA TODAY INTO TONIGHT...MUCH MORE PROGRESSIVE
WITH MODELS IN GOOD AGREEMENT THAN IT HAS BEEN IN PREVIOUS DAYS AS
UPPER LOW NOT QUITE AS DEEP AND REMAINING MORE OF AN OPEN WAVE AS IT
LIFTS NORTHWARD THROUGH THE CENTRAL/NORTHERN US. SFC LOW ALREADY
EXPECTED TO BE INTO SRN CANADA/NRN MN BY 06Z SATURDAY...THEREFORE
EXPECT INITIAL LINE OF PRECIPITATION TO BE THROUGH THE CWA BY LATE
EVENING. HAVE REMOVED POPS FOR LATE TONIGHT WITH THE FASTER
PROGRESSION OF THIS WAVE...WITH WRAP AROUND AREA OF PRECIP EXPECTED
TO MOVE TO THE NORTH OF THE CWA. WEAK DISTURBANCE TO MOVE THROUGH
LATE SATURDAY AFTERNOON...BUT MOISTURE IS SCARCE SO INCREASED SOME
CLOUDS BUT KEPT THE FORECAST DRY. ZONAL FLOW CONTINUES WITH WAA BACK
INTO THE CWA SUNDAY...THEN SOUTHWESTERLY FLOW TO DEVELOP AGAIN
TOWARD EARLY NEXT WEEK AS ANOTHER UPPER LEVEL WAVE DIGS INTO THE
WESTERN US. SFC LOW DEVELOPING ACROSS THE CENTRAL PLAINS BY LATE
MONDAY INTO MONDAY NIGHT...WITH AN ASSOCIATED WARM FRONT PUSHING
NORTH ACROSS THE CWA. GFS/EC IN SOME DISAGREEMENT ON THE TIMING WITH
THIS SYSTEM. GFS CONTINUES TO BE MORE PROGRESSIVE...PUSHING THE
SYSTEM INTO THE GREAT LAKES BY EARLY WEDNESDAY...WITH THE EC KEEPING
THE WAVE BACK OUT ACROSS THE CENTRAL PLAINS. WILL HAVE TO MONITOR
FOR BETTER CERTAINTY WITH THE TIMING...BUT EITHER WAY...LOOKS LIKE A
SCENARIO FOR DECENT CHANCES FOR THUNDER/POSSIBLY EVEN SOME ISOLATED
SEVERE. SFC TO SLIDE ACROSS THE CWA TUESDAY...SO EXPECT CWA TO
REMAIN IN THE WARM SECTOR WITH DECENT INSTABILITY INTO TUESDAY
EVENING. COLD FRONT TO MOVE THROUGH BY LATE TUESDAY NIGHT...WITH
CHANCES FOR THUNDER DIMINISHING INTO WEDNESDAY. HAVE CONTINUED WITH
CHANCE POPS ACROSS THE CWA FOR MONDAY NIGHT INTO WEDNESDAY AS THIS
SYSTEM PROGRESSES THROUGH THE REGION.

&&

.AVIATION...
02/12Z...COLD FRONT WILL PASS THROUGH IOWA TODAY WITH SHOWERS AND A
FEW ISOLATED THUNDERSTORMS ASSOCIATED WITH ITS PASSAGE.  CONDITIONS
WILL PRIMARILY REMAIN VFR ALTHOUGH MVFR TO ISOLATED IFR CONDITIONS
CAN BE EXPECTED IN AND NEAR THE SHOWERS THAT DO DEVELOP.  SFC WINDS
WILL INITIALLY BE SOUTH FOR ALL TAF SITES BUT BECOME MORE SW TO
WESTERLY BEHIND THE FRONT WITH TIME.  DRIER AIR WILL PUSH INTO THE
STATE TONIGHT WITH DECREASING CLOUDS AND UNRESTRICTED VSBYS.

&&

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

&&

SHORT TERM...COGIL
LONG TERM...BEERENDS
AVIATION...COGIL

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
455 AM CDT FRI APR 2 2010

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-081>086-
092>097-031000-
EMMET-KOSSUTH-WINNEBAGO-WORTH-PALO ALTO-HANCOCK-CERRO GORDO-
POCAHONTAS-HUMBOLDT-WRIGHT-FRANKLIN-BUTLER-BREMER-SAC-CALHOUN-
WEBSTER-HAMILTON-HARDIN-GRUNDY-BLACK HAWK-CRAWFORD-CARROLL-GREENE-
BOONE-STORY-MARSHALL-TAMA-AUDUBON-GUTHRIE-DALLAS-POLK-JASPER-
POWESHIEK-CASS-ADAIR-MADISON-WARREN-MARION-MAHASKA-ADAMS-UNION-
CLARKE-LUCAS-MONROE-WAPELLO-TAYLOR-RINGGOLD-DECATUR-WAYNE-APPANOOSE-
DAVIS-
455 AM CDT FRI APR 2 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...TODAY AND TONIGHT

ISOLATED NON SEVERE THUNDERSTORMS ARE EXPECTED TO SPREAD EASTWARD
ACROSS THE CWA TODAY INTO THIS EVENING. LOCALLY HEAVY RAINFALL IS
POSSIBLE THIS AFTERNOON INTO EARLY EVENING.

RIVER FLOOD WARNINGS FOR MINOR TO MODERATE FLOODING REMAIN IN
EFFECT THROUGHOUT PORTIONS OF THE DES MOINES RIVER BASIN. PLEASE
SEE OUR WEBSITE AT WEATHER.GOV/DESMOINES FOR MORE DETAILS.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

CHANCES OF THUNDERSTORMS BEGIN MONDAY ACROSS THE AREA...AND
CONTINUE THROUGH WEDNESDAY NIGHT. HOWEVER...THE PREDICTABILITY OF
SEVERE STORMS IS TOO LOW AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NEEDED TODAY OR TONIGHT.

MJB

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