Severe Thunderstorm Warning 28, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
323 PM CDT TUE APR 6 2010

.SHORT TERM.../THIS AFTERNOON AND EVENING/
SFC LOW PRESSURE NOW CENTERED NEAR RED OAK WITH VERY DYNAMIC FLOW
ONGOING AROUND IT. STILL MONITORING SEVERE WX POTENTIAL FOR THIS
AFTERNOON AND EARLY EVENING AND MORE PARTICULARLY THE TORNADIC
THREAT. A SMALL TORNADIC SWEET SPOT IS EXPECTED NEAR THE TRIPLE
POINT WHERE BEST POTENTIAL FOR BACKING FLOW EXISTS AND EFFECTIVE
SRH VALUES OF 200-300 M2/S2. FARTHER SOUTH...STRONG SOUTHWEST FLOW
SHOULD LIMIT TORNADIC ACTIVITY HOWEVER VERY LARGE HAIL AND
DAMAGING WIND GUSTS OVER 70 MPH ARE POSSIBLE. GIVEN SUCH DYNAMIC
FLOW...ANY TORNADO THAT DOES DEVELOP COULD BE QUITE STRONG NEAR
THE WARM FRONT. EXPECT THE WARM FRONT TO REGRESS BACK TO THE
SOUTHEAST WITH SUPERCELLS POSSIBLY CROSSING THE BOUNDARY AS THIS
OCCURS AND MOVING INTO INCREASED SRH VALUES WHICH WOULD ENHANCE
LOW LEVEL ROTATION. BUNKERS RIGHT MOVING SUPERCELL MOVEMENT OF 45
TO 55 KT MEANS THEY WILL BE MOVING QUITE QUICKLY.

PRIMARY FORECAST CHALLENGE WILL BE THUNDERSTORM INITIATION TIME.
STRONG DIFFERENTIAL HEATING IS TAKING PLACE OVER CENTRAL IOWA WITH
THE TEMPERATURE AT DSM NOW AT 80 DEGREES...66 AT AMW AND LOWER 50S
TO THE NORTH. TO THE WEST...CLOSED UPPER LOW PRESSURE OVER NORTHEAST
COLORADO WILL CONTINUE TO SHIFT EAST AND ENHANCE SW FLOW ALOFT.
SHORTWAVE ENERGY TO THE SOUTHWEST WILL ARRIVE LATE THIS AFTERNOON
AND SHOULD PROVIDE ENOUGH KINEMATIC FORCING TO PROVIDE A TRIGGER FOR
THUNDERSTORM DEVELOPMENT IF THE BOUNDARY ITSELF IS NOT SUFFICIENT.
QUASI-DRYLINE OVER SW IA MAY TRIGGER SRN CONVECTION EARLIER. STORMS
WILL MOVE EAST OF THE AREA BY MID EVENING THEN STRONG CYCLONIC FLOW
WITH NORTHEAST WINDS OF 20G35KTS IS LIKELY AND MAY BE BORDERLINE
WIND ADVISORY CRITERIA. LINGERING SHOWERS ARE ALSO LIKELY.

.LONG TERM.../WEDNESDAY THROUGH TUESDAY/
MAIN FORECAST CONCERN IS WITH LINGERING RAIN AND THUNDERSTORM
CHANCES DURING THE DAY WEDNESDAY AND WITH ACTIVE WEATHER PATTERN
SETTING UP EARLY NEXT WEEK. MODELS ARE IN GOOD AGREEMENT THROUGH
THE WEEKEND...SO LEANED TOWARD A BLEND OF THE GFS/ECMWF DURING THE
WEEKEND AND SREF/NAM FOR WEDNESDAY INTO FRIDAY.

UPPER LEVEL LOW AND 500 MB TROUGH MOVE ACROSS THE STATE DURING THE
DAY TOMORROW AND FINALLY MOVE FAR ENOUGH EAST BY 00Z THURSDAY TO
DECREASE POPS ACROSS THE NORTHWEST DURING THE AFTERNOON WEDNESDAY.
KEPT WITH LIKELY POPS ACROSS CENTRAL TO EASTERN PORTIONS OF THE CWA
THROUGH MUCH OF THE DAY WEDNESDAY. FAIRLY STRONG CAA WITH 850MB
WINDS AT 30 TO 40KTS LOOK TO MIX DOWN TO THE SURFACE AND WILL
PROVIDE A WINDY AND BRISK DAY. DROPPED TEMPS SLIGHTLY ACROSS THE
STATE FOR HIGHS WITH REGARDS TO THE RAIN AND WINDY CONDITIONS ON
WEDNESDAY. SURFACE HIGH PRESSURE AND UPPER RIDGE BEGIN TO BUILD
INTO THE REGION BY THURSDAY NIGHT BEHIND OF A WEAK VORT MAX THAT
CUTS ACROSS THE STATE DURING THE DAY THURSDAY. THIS VORT MAX HAS
LIMITED MOISTURE AND MAINLY BRINGS SOME MID LEVEL CLOUDS ATOP THE
MIXED LAYER. MIXED LAYER WINDS ARE AROUND 25 KTS ON THURSDAY...SO
NOT EXPECTING AS WINDY CONDITIONS AS WEDNESDAY BUT STILL LOOKS TO
BE FAIRLY BREEZY.

FRIDAY AND SATURDAY LOOK TO BE DRY AND MILD WITH UPPER RIDGE
BUILDING INTO THE REGION.  WARMING TREND BEGINS FRIDAY AND
CONTINUES SATURDAY AND SUNDAY AS UPPER RIDGE PUSHES EAST AND ALLOWS
FOR SOUTHWEST FLOW TO DEVELOP ACROSS THE AREA.  WARMED HIGHS ON
SATURDAY WITH THE WAA AND CLEAR SKIES.

A WEAK SHORTWAVE ENTERS THE REGION SUNDAY NIGHT INTO MONDAY.  BOTH
GFS/ECMWF ARE IN GOOD AGREEMENT WITH THIS SYSTEM AND BUMPED POPS UP
ACROSS THE CWA DURING THE AFOREMENTIONED TIME FRAME.  DEEP TROUGH
DEVELOPMENTS ACROSS THE WESTERN CONUS EARLY NEXT WEEK AND EJECTS
EASTWARD IN THE CENTRAL PLAINS AND MIDWEST BY LATE TUESDAY INTO
WEDNESDAY. KEPT WITH CURRENT MENTION OF POPS ACROSS THE CWA MONDAY
NIGHT THROUGH TUESDAY NIGHT.

&&

.AVIATION...
06/18Z...SHARP FRONTAL BOUNDARY IS IN PLACE OVER CENTRAL IOWA AND
WILL SHIFT EAST OF THE TAF SITES BY MID EVENING. IFR/LIFR CONDITIONS
WILL REMAIN OVER NORTHERN IA THROUGH MUCH OF THE NIGHT BEFORE CIGS
BEGIN TO LIFT WED MORNING. STRONG THUNDERSTORMS ARE POSSIBLE
VICINITY OF KDSM/KOTM THROUGH EARLY EVENING. GUSTY NORTHEAST WINDS
WILL DEVELOP OVERNIGHT WITH GUSTS TO 35 KTS POSSIBLE.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...TORNADO WATCH 57 IN EFFECT UNTIL
10 PM CDT THIS EVENING FOR CENTRAL TO EAST CENTRAL IOWA.

&&

SHORT TERM...DONAVON
LONG TERM...PODRAZIK
AVIATION...DONAVON

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
231 PM CDT TUE APR 6 2010

IAZ026>028-036>039-046>050-057>062-070>075-081>086-092>097-071945-
FRANKLIN-BUTLER-BREMER-HAMILTON-HARDIN-GRUNDY-BLACK HAWK-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-
231 PM CDT TUE APR 6 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...THIS AFTERNOON AND TONIGHT

SEVERE STORMS ARE EXPECTED TO DEVELOP THIS AFTERNOON AND INTO THE
EARLY EVENING HOURS. THE THREAT FOR DISCRETE TORNADIC SUPERCELLS
CONTINUES TO INCREASE ACROSS THE AREA. THE GREATEST THREAT FOR A
FEW STRONG TORNADOES EXIST ESPECIALLY ALONG THE HIGHWAY 30 AND
INTERSTATE 80 CORRIDORS EAST OF A JEFFERSON TO STUART LINE. THIS
COULD BECOME A PARTICULARLY DANGEROUS SITUATION.

THESE STORMS WILL ALSO BE CAPABLE OF VERY LARGE HAIL TO THE SIZE
OF BASEBALLS AND STRAIGHT LINE WIND GUSTS UP TO 80 MPH. LOCALIZED
VERY HEAVY RAIN IS ALSO POSSIBLE.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

ISOLATED NON-SEVERE THUNDERSTORMS ARE POSSIBLE EAST OF INTERSTATE
35 ON WEDNESDAY. ANOTHER ROUND OF THUNDERSTORMS IS EXPECTED ON
MONDAY. AT THIS TIME IT IS TOO EARLY TO DETERMINE SEVERITY OF
THESE STORMS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS LIKELY BETWEEN 4 PM AND 10 PM THIS AFTERNOON
AND EVENING.

IAZ004>007-015>017-023>025-033>035-044-045-071945-
EMMET-KOSSUTH-WINNEBAGO-WORTH-PALO ALTO-HANCOCK-CERRO GORDO-
POCAHONTAS-HUMBOLDT-WRIGHT-SAC-CALHOUN-WEBSTER-CRAWFORD-CARROLL-
231 PM CDT TUE APR 6 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...THIS AFTERNOON AND TONIGHT

SCATTERED THUNDERSTORMS ARE POSSIBLE THROUGH TONIGHT...SOME MAY
BECOME SEVERE AT TIMES. THE MAIN THREAT LOOKS TO BE HAIL UP TO THE
SIZE OF QUARTERS WITH WIND GUSTS UP TO 60 MPH AT TIMES.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

ISOLATED NON-SEVERE THUNDERSTORMS ARE POSSIBLE EAST OF INTERSTATE
35 ON WEDNESDAY. ANOTHER ROUND OF THUNDERSTORMS IS EXPECTED ON
MONDAY. AT THIS TIME IT IS TOO EARLY TO DETERMINE SEVERITY OF
THESE STORMS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS POSSIBLE THROUGH THIS EVENING.

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
530 PM CDT TUE APR 06 2010

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0524 PM     HAIL             KNOXVILLE               41.32N 93.10W
04/06/2010  E1.00 INCH       MARION             IA   FIRE DEPT/RESCUE

            NW CORNER OF KNOXVILLE

&&

AW

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
543 PM CDT TUE APR 06 2010

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0515 PM     HAIL             CEDAR FALLS             42.52N 92.45W
04/06/2010  E1.75 INCH       BLACK HAWK         IA   TRAINED SPOTTER

            INTERSECTION OF 6TH AND MAIN

&&

JB