SPC AC 070558
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1258 AM CDT MON JUL 07 2008
VALID 071200Z - 081200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM PARTS OF THE NRN/CENTRAL
PLAINS EWD TO THE UPPER MS VALLEY/WRN GREAT LAKES REGION...
...SYNOPSIS...
A SHORT WAVE TROUGH...CURRENTLY CROSSING THE NRN ROCKIES PER WATER
VAPOR IMAGERY...IS EXPECTED TO AMPLIFY AS IT PROGRESSES EWD THROUGH
THE NRN PLAINS TO UPPER GREAT LAKES REGION THIS FORECAST PERIOD.
WEAKER IMPULSE WILL PRECEDE THIS NRN STREAM TROUGH...AND TRACK FROM
NEB ACROSS THE UPPER MS VALLEY TO GREAT LAKES THIS AFTERNOON AND
EVENING. MEANWHILE...THE LINGERING UPPER TROUGH IN THE EAST WILL
MOVE SLOWLY EWD ACROSS NC/VA.
...SRN MN/IA TO WRN GREAT LAKES...
SURFACE BOUNDARY IS EXPECTED TO BE LOCATED GENERALLY E-W FROM WI/IL
BORDER WWD INTO NEB AT 12Z THIS MORNING. THE IA PORTION OF THIS
BOUNDARY SHOULD SHIFT N TOWARD THE MN BORDER IN RESPONSE TO HEIGHT
FALLS WITH THE APPROACHING NRN STREAM TROUGH. DESPITE GENERALLY
WEAK TO MODEST MID LEVEL LAPSE RATES...A VERY MOIST AIR MASS
RESIDING ON EITHER SIDE OF THE SURFACE BOUNDARY /DEWPOINTS IN THE
UPPER 60S TO LOWER 70S/ WILL RESULT IN MODERATE INSTABILITY FROM IA
INTO SERN MN TO CENTRAL/SRN WI AND NRN IL. GREATEST INSTABILITY
/MLCAPE 2000-2500 J/KG/ WILL BE FOUND OVER IA...S OF THE BOUNDARY...
WHERE SURFACE HEATING SHOULD BE GREATER.
WSWLY MID LEVEL WINDS OVER THE UPPER MS VALLEY WILL INCREASE TO
40-50 KT IN RESPONSE TO THE AMPLIFYING SHORT WAVE TROUGH. ASCENT
ATTENDANT TO THE NEB IMPULSE AND ANY SURFACE HEATING WITHIN A WEAKLY
CAPPED AIR MASS IN THE VICINITY OF THE E-W SURFACE BOUNDARY SHOULD
SUPPORT TSTM DEVELOPMENT BY EARLY AFTERNOON ALONG THIS FRONT.
INCREASING DEEP LAYER SHEAR WILL SUPPORT ORGANIZED STORMS WITH THIS
ACTIVITY RESULTING IN A HAIL/WIND THREAT. A SWLY LLJ EXTENDING FROM
OK/KS TO UPPER MS VALLEY WILL STRENGTHEN THIS AFTERNOON INTO THE
EVENING...WITH LOW LEVEL SHEAR EXPECTED TO INCREASE FROM NRN IA/SRN
MN INTO WRN WI BY LATE AFTERNOON. THUS...ACTIVITY OCCURRING ACROSS
THIS AREA SHOULD HAVE AN INCREASED TORNADO POTENTIAL.
MODELS REMAIN FAIRLY CONSISTENT INDICATING AN MCS SHOULD EVOLVE THIS
EVENING OVER THE SERN/E-CENTRAL MN AND WRN WI AREA...AND THEN
PROCEED ENEWD ACROSS MUCH OF WI INTO PARTS OF UPPER MI...AND
POTENTIALLY LOWER MI LATE TONIGHT. STRENGTHENING WIND FIELDS WITH
THE AMPLIFYING UPPER TROUGH SUGGEST DAMAGING WINDS WILL BECOME THE
PRIMARY THREAT WITH THIS MCS...ESPECIALLY THROUGH MUCH OF THE
EVENING.
...NEB/WRN KS/ERN CO...
A SURFACE TROUGH EXTENDING FROM NEB INTO NWRN KS TO ERN CO WILL BE A
FOCUS OF NEW TSTM DEVELOPMENT THIS AFTERNOON. STRONG SURFACE
HEATING BENEATH A PLUME OF STEEP MID LEVEL LAPSE RATES WILL SUPPORT
A CORRIDOR OF MODERATE INSTABILITY ALONG THE EXTENT OF THE SURFACE
TROUGH. THE COMBINATION OF SURFACE HEATING AND ASCENT ATTENDANT TO
A COUPLE OF WEAK IMPULSES TRAVERSING THIS REGION SHOULD WEAKEN THE
CAP BY AFTERNOON PROMOTING TSTM DEVELOPMENT. A DECREASE IN STRONGER
MID LEVEL FLOW/SHEAR VALUES WITH SWD EXTENT FROM NEB WILL TEND TO
CONFINE THE POTENTIAL FOR ORGANIZED STORMS TO THE NEB/NWRN-NRN KS
PORTION OF THE SURFACE TROUGH. STRONG WIND GUSTS AND HAIL WILL BE
THE PRIMARY THREATS.
...DAKOTAS...
ONGOING CLUSTER OF TSTMS EXTENDING FROM WRN SD INTO CENTRAL ND
SHOULD PROGRESS EWD TODAY...WITH SURFACE HEATING EXPECTED IN THE
WAKE OF THIS MORNING ACTIVITY OVER WRN/CENTRAL DAKOTAS. THIS
COMBINED WITH COOLING MID LEVEL TEMPERATURES/STEEPENING LAPSE RATES
SPREADING EWD WITH THE NRN STREAM TROUGH SHOULD RESULT IN MODERATE
INSTABILITY ALONG A COLD FRONT MOVING EWD THROUGH THIS REGION.
FORCING FOR ASCENT WITH THE UPPER TROUGH AND ALONG THE FRONT ARE
EXPECTED TO SUPPORT NEW TSTM DEVELOPMENT BY EARLY-MID AFTERNOON.
STRONG DEEP LAYER SHEAR WILL PROMOTE STORM ORGANIZATION...WITH
SUPERCELLS POSSIBLE. HAIL AND STRONG WIND GUSTS WILL BE THE MAIN
THREATS WITH THIS ACTIVITY...WHICH SHOULD TEND TO WEAKEN THIS
EVENING AS IT SPREADS EWD INTO THE ERN DAKOTAS AS THE BOUNDARY LAYER
STABILIZES.
..PETERS/HURLBUT.. 07/07/2008
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