SPC AC 041958
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0258 PM CDT TUE MAY 04 2010
VALID 042000Z - 051200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER A PORTION OF THE NERN
U.S....
...THERE IS A SLGT RISK OF SVR TSTMS FROM PARTS OF NRN IA...SERN MN
AND WI...
...IA THROUGH SERN MN AND WI...
OCCLUDED FRONT EXTENDS SEWD THROUGH MN THEN AS A COLD FRONT FROM SRN
MN THROUGH NWRN IA INTO SRN NEB. WARM FRONT STRETCHES SEWD THROUGH
CNTRL WI. DIABATIC WARMING IS DESTABILIZING THE PRE-FRONTAL WARM
SECTOR. HOWEVER...LOW LEVEL MOISTURE IS LIMITED WITH DEWPOINTS
MOSTLY IN THE 40S...AND THERE HAS BEEN A TENDENCY FOR DEWPOINTS TO
MIX DOWN INTO THE 30S JUST AHEAD OF FRONT ACROSS PARTS OF NWRN IA.
AS A RESULT MLCAPE WILL GENERALLY NOT EXCEED 500 J/KG...WITH THE
GREATER INSTABILITY EXPECTED ACROSS WI WHERE LESS MIXING WILL OCCUR
IN VICINITY OF THE WARM FRONT AND WHERE TEMPERATURES ALOFT ARE
SLIGHTLY COOLER. STORMS WILL LIKELY DEVELOP THIS AFTERNOON IN IA
ALONG THE SEWD MOVING COLD FRONT AS WELL AS FARTHER NE ACROSS WI
WITHIN ZONE OF LOW-LEVEL ISENTROPIC LIFT AND WARM ADVECTION.
VERTICAL SHEAR WILL SUPPORT ORGANIZED STORMS STRUCTURES INCLUDING
BOWING LINE SEGMENTS AND SUPERCELLS. ISOLATED DAMAGING WIND AND
LARGE HAIL ARE THE MAIN THREATS.
...NERN STATES...
CLUSTER OF STORMS MOVING THROUGH THE NERN U.S. WILL CONTINUE TO POSE
A THREAT OF ISOLATED DAMAGING WIND NEXT COUPLE HOURS.
..DIAL.. 05/04/2010
.PREV DISCUSSION... /ISSUED 1127 AM CDT TUE MAY 04 2010/
...UPPER MIDWEST...
MORNING WATER VAPOR LOOPS SHOW AN UPPER LOW OVER
MT/SASKATCHEWAN...WITH A SHORTWAVE TROUGH PASSING THROUGH THE BASE
OF THE LOW ACROSS THE DAKOTAS. THIS FEATURE WILL ROTATE INTO
MN/IA/WI LATER THIS EVENING HELPING TO INITIATE SCATTERED
THUNDERSTORMS. MOISTURE IS INITIALLY VERY LIMITED WITH DEWPOINTS
GENERALLY IN THE 40S. HOWEVER...RAPID NORTHWARD TRANSPORT OF 50S
DEWPOINTS OVER MO/IL ALONG WITH SHALLOW MIXING ACROSS PARTS OF WI/MN
WILL LIKELY LEAD TO AT LEAST POCKETS OF MID 50S DEWPOINTS ACROSS THE
RISK AREA...ALONG WITH MLCAPE VALUES AROUND 1000 J/KG. LOW AND MID
LEVEL LAPSE RATES ARE VERY STEEP...PROMOTING VIGOROUS UPDRAFTS
CAPABLE OF HAIL AND DAMAGING WINDS THROUGH THE EVENING. VERTICAL
SHEAR PROFILES WILL BE QUITE FAVORABLE FOR SUPERCELLS AND BRIEF
TORNADOES ACROSS WI AROUND 00Z...ALTHOUGH THE LOW DEWPOINT VALUES
AND RATHER HIGH LCL VALUES WILL TEND BE LIMITING FACTORS TO THE
TORNADO RISK.
...NORTHEAST...
A RATHER STRONG SHORTWAVE TROUGH IS PROGRESSING EASTWARD ACROSS THE
EASTERN GREAT LAKES. STEEP LAPSE RATES AND COOL TEMPERATURES ALOFT
WILL HELP OFFSET MEAGER LOW LEVEL MOISTURE AND CONTINUE TO PROMOTE
THE DEVELOPMENT OF SCATTERED THUNDERSTORMS AHEAD OF THE TROUGH.
GIVEN TRENDS THUS FAR AND AREAL COVERAGE OF STRONGER CELLS...HAVE
OPTED TO INTRODUCE A SLIGHT RISK OVER PARTS OF EASTERN NY AND
WESTERN NEW ENGLAND TO ACCOUNT FOR INCREASING RISK OF LOCALLY
DAMAGING WINDS.
...SOUTHEAST...
BAND OF SHOWERS AND THUNDERSTORMS CONTINUES ALONG/AHEAD OF THE
SURFACE FRONT FROM WESTERN FL INTO GA/SC. AMPLE LOW LEVEL MOISTURE
AND MODERATE INSTABILITY WILL HELP TO MAINTAIN A FEW STRONG CORES IN
THIS ACTIVITY THROUGH THE DAY AS STORMS APPROACH THE SC/GA/NORTHEAST
FL COAST. VERTICAL SHEAR PROFILES ARE SUFFICIENT FOR SOME STORM
ROTATION WITH BOW/LEWP STRUCTURES POSSIBLE. ISOLATED GUSTY/DAMAGING
WINDS OR A BRIEF TORNADO APPEAR TO BE THE MAIN THREATS.
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z
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