Severe Thunderstorm Warning 63, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
955 AM CDT FRI APR 30 2010

.UPDATE...
LINE OF SHOWERS AND THUNDERSTORMS PUSHING NORTHWARD INTO SOUTH
CENTRAL IOWA...WITH LIMITED INSTABILITY. THEREFORE HAVE SEEN A
GENERAL WEAKENING TREND IN STORMS AS THEY MOVE INTO THE STATE FROM
MISSOURI. LATEST MODELS SUGGESTING INSTABILITY TO INCREASE ACROSS
THE SOUTHEASTERN CWA...WITH DECENT SHEAR IN PLACE BOTH IN THE LOW
LEVELS AND DEEP LAYER SHEAR. THEREFORE SEVERE THREAT STILL IN PLACE
ACROSS THE SOUTHEASTERN/EXTREME EASTERN CWA. SHORTWAVE MOVING INTO
THE CENTRAL KANSAS EXPECTED TO BE THE MAIN SOURCE OF LIFT WITH THIS
ACTIVITY...WITH EXPECTED INITIATION INTO THE EARLY AFTERNOON TO MID
AFTERNOON HOURS. ACTIVITY SHOULD MOVE QUICKLY EAST...AND LOCAL WRF
RUNS SUGGEST AROUND A 3 HOUR PERIOD OF ACTIVITY ACROSS OUR
SOUTHEASTERN CWA BEFORE ACTIVITY PUSHES EASTWARD OUT OF THE AREA.
THEREFORE HAVE ADJUSTED SOME OF THE POPS TO REFLECT THE LATEST
THOUGHTS...AND ADJUSTED TEMPERATURES TO ACCOUNT FOR COOLER TEMPS
ACROSS WESTERN IOWA AND WARMER TEMPS ACROSS THE SOUTHEAST.

.SHORT TERM /TODAY/...
ONGOING CONVECTION WILL DIMINISH A BIT THIS MORNING WITH PLENTY OF
DEBRIS CLOUDS ON THE WAY FOR TODAY. THE FRONT CONTINUES TO HANG UP
WITH THE NEARLY PARALLEL FLOW AND WILL NOT MAKE MUCH MORE HEADWAY
EAST UNTIL THE STRONGER UPPER LEVEL JET MAX NOW ROUNDING THE 4
CORNERS AREA CATCHES UP WITH THE SFC WAVE OVER OK/KS AND RAPIDLY
MOVES THIS FEATURE NORTHEAST...DEEPENING IT BY SAT MORNING OVER
SOUTHERN CANADA TO A 982 MB LOW. WILL BE LEANING WITH THE GEM/EURO
FOR BOTH SHORT TERM AND EXTENDED FCST TODAY AS THE GFS CONTINUES TO
HAVE PROBLEMS WITH THIS SYSTEM AND NAM ONLY SLIGHTLY BETTER. AS THE
SFC LOW TRACKS NEARLY DUE NORTH...SOUTHERLY SFC FLOW WILL INCREASE
DURING THE DAY TO 20 TO 35 MPH OVER THE EAST...INCREASING DEW POINTS
AHEAD OF THE FRONT TO THE LOWER 60S EAST. UPPER LEVEL WIND FIELDS
LOOK TO BE INCREASING MORE SO JUST TO THE EAST OF I35 DURING THE
AFTERNOON HOURS. MODELS HAVE CLOUD COVER AND SOME SHOWERS HOLDING ON
DURING THE DAY. DAYTIME HEATING TO INCREASE MLCAPE DURING THE
AFTERNOON. PROVIDED WE GET SOME SUNSHINE TODAY EAST...NARROW AXIS OF
600 TO 1000 J/KG RIBBON OF CAPE WILL BUILD EAST NORTHEAST JUST ALONG
THE BOUNDARY DURING THE AFTERNOON AND EARLY EVENING. LOOKING AT THE
PROGS FOR TODAY...STORMS SHOULD BEGIN TO INTENSIFY IN THE EARLY
AFTERNOON HOURS AROUND I35 AND STRENGTHEN AS THEY MOVE INTO EASTERN
IA. THUS...THE BEST CHANCES FOR SEVERE WILL LIE JUST ALONG AND EAST
OF THE I35 CORRIDOR. WINDS...HAIL...AND A FEW TORNADOES WILL BE
POSSIBLE IF SOME OF THE SUPERCELLS CAN BECOME DISCRETE. OTHERWISE
DURING THE LATER PORTION OF THE AFTERNOON HOURS...NAM SOUNDINGS NEAR
KOTM SHOW BETTER TURNING AT LOWER LEVELS ALONG WITH LARGER CAPE
VALUES AND SOUNDINGS A BIT MORE STABLE OVER CENTRAL AND WESTERN
AREAS. HIGHS TODAY VERY DEPENDENT ON SOME INSOLATION. GIVEN WARM
READINGS NOW...EVEN A 10 TO 15 DEGREE RISE IN TEMP WILL GET THE
REGION INTO THE 70S THIS AFTERNOON.

.LONG TERM /TONIGHT THROUGH THURSDAY/...
QUIETER WEATHER RETURNS...WITH ONE THE MAIN LOW REMAINING WRAPPED UP
OVER NORTHERN MN AND SOUTHERN CANADA. ANOTHER SFC LOW WILL TRACK
JUST TO THE EAST OF IOWA SAT NIGHT AND SUNDAY...ALLOWING FOR AN AREA
OF SHOWERS TO JUST GRAZE THE SOUTHEAST SECTIONS INTO EARLY SUNDAY.
MODELS ARE SHOWING A WEAK FEATURE IN THE WESTERLIES ARRIVING ON
MONDAY WHICH MAY BRING SOME SCT SHOWERS AS WELL. TEMPS DURING THE
PERIOD WILL REMAIN MILD...BUT NOT AS WARM AS THE PAST FEW DAYS.
OVERNIGHT LOWS WILL DIP INTO THE LOWER 40S SAT NIGHT THROUGH SUNDAY
NIGHT BEFORE EVERYONE WARMS UP. A STRONGER WAVE WILL ARRIVE BY
TUESDAY AND SIGNIFICANT WARMING WILL OCCUR WITH HIGHS BACK IN THE
MID 70S AND LOWS IN THE 40S AND 50S. THE GFS IS QUICK TO PULL COOLER
AIR BACK DOWN INTO THE REGION ON WED...TOO FAST...AND WILL AGAIN
LEAN TOWARD THE GEM/EURO WHICH KEEPS THE REGION MILDER THROUGH MID
TO LATE WEEK WITH A MORE ZONAL UPPER LEVEL WIND REGIME.

&&

.AVIATION...
30/12Z...COMPLEX WX STTN WITH SFC BNDRY EXTENDING FRM SWRN MN...THRU
WRN IA...INTO ERN KS THIS MRNG.  FEELING IS SCNDRY TROF LAGGING TO
THE WEST WILL TAKE OVER WITH NET EFFECT BEING A JUMP WEST WITH LEAD
FNTL BNDRY.  SCT SHRA ERY THIS MRNG WILL BREAK UP.  NEW CONVECTION
WILL DEVELOP AS SCNDRY BNDRY...NOW SERN SD INTO CNTRL KS...MOVS EWD.
SCT-BKN LINE OF TSRA LKLY TO DVLP OVER WRN IA...AND BECOME MORE
ORGANIZED EAST OF KDSM-KMCW LN BY 19Z OR SO...PASSING EAST OF THE
TAF SITES BY 00Z.  AFT FRONT MOVS THRU...WNDS WILL BCM LGT SWLY WITH
VFR CONDS AND AC CIGS.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE

&&

UPDATE...BEERENDS
SHORT TERM/LONG TERM...REV
AVIATION...MS APR 10

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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE DES MOINES IA
855 AM CDT FRI APR 30 2010

IAZ083-084-093>095-301500-
CLARKE-DECATUR-LUCAS-RINGGOLD-WAYNE-
855 AM CDT FRI APR 30 2010

AT 850 AM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED AN
AREA OF STRONG TO SEVERE THUNDERSTORMS OVER HARRISON COUNTY...MOVING
NORTHEAST AT 60 MPH.

SEVERE SIZED HAIL AND DAMANGING WINDS ARE POSSIBLE FROM THESE STORMS.

THE STORMS WILL MOVE INTO SOUTHEAST IOWA BY 915 AM AND THEN RACE
NORTHEAST REACHING THE I80 CORRIDOR EAST OF DES MOINES BY 1100 AM.

THESE STORMS MAY REQUIRE WARNINGS THIS MORNING IN SOUTHEAST IOWA.

JOHNSON

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