SPC AC 151630
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1130 AM CDT SAT AUG 15 2009
VALID 151630Z - 161200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF THE
CENTRAL/NRN PLAINS...
...THERE IS A SLGT RISK OF SVR TSTMS OVER THE FAR NERN MN AREA...
...SYNOPSIS...
UNSEASONABLY STRONG UPPER TROUGH...LOCATED OVER THE NRN
ROCKIES/GREAT BASIN REGION IS FORECAST TO MOVE EWD INTO NRN/CENTRAL
PLAINS BY SUNDAY MORNING. MAIN FOCUS FOR SEVERE THUNDERSTORM
DEVELOPMENT IS EXPECTED TO BE IN ASSOCIATION WITH A STRONG SHORTWAVE
TROUGH AND 50-60 KT JET MAX LIFTING ENEWD FROM SRN ID/NWRN UT INTO
WRN SD BY DAYBREAK SUNDAY. BAROCLINICITY WILL STRENGTHEN ALONG
FRONTAL BOUNDARY FROM THE CENTRAL DAKOTAS INTO ERN CO...AS IT SHIFTS
EWD THROUGH THE PERIOD INTO THE UPPER MS VALLEY AND THROUGH THE
CENTRAL/NRN PLAINS.
...UPPER MS VALLEY...
CONSIDERABLE CLOUDS/PCPN FROM ERN NEB/WRN IA NWD TO THE CANADIAN
BORDER WERE ASSOCIATED WITH AN ELONGATED TROUGH ALOFT CONTAINING
SEVERAL EMBEDDED SMALL SCALE CIRCULATIONS. THICKER CLOUDS WILL
BE MAINTAINED INTO THE AFTERNOON HOURS ACROSS MUCH OF THIS REGION
AND REDUCE THE THREAT FOR SEVERE STORMS...DUE TO THE MAINTENANCE OF
A COOLER/MORE STABLE BOUNDARY LAYER. HOWEVER...AHEAD OF THE UPPER
TROUGH...ESPECIALLY ACROSS NERN MN...TEMPERATURES WILL WARM INTO THE
LOWER TO MID 80S...WHICH WOULD RESULT IN MLCAPE VALUES AROUND 1000
J/KG. THIS INSTABILITY COMBINED WITH UPPER TROUGH FORCING AND 30-35
KT DEEP LAYER SHEAR WOULD BE SUPPORTIVE OF A FEW SEVERE STORMS.
INCREASING LOW LEVEL JET SPEEDS AND PRESENCE OF E-W ORIENTED WARM
FRONT IN NERN MN SUGGEST LOW LEVEL SHEAR MAY BE STRONG ENOUGH FOR
ISOLATED TORNADOES AND WIND DAMAGE.
...CENTRAL PLAINS...
LARGE SCALE ASCENT ASSOCIATED WITH SHORTWAVE TROUGH AND UPSLOPE
BOUNDARY LAYER WINDS SHOULD RESULT IN VIGOROUS STORM DEVELOPMENT
NEAR THE ERN WY/NERN CO HIGHER TERRAIN BY LATE AFTERNOON. THE ELY
SURFACE WINDS ARE EXPECTED TO ADVECT 50+ DEGREE DEWPOINTS WWD TO THE
HIGHER TERRAIN AND WITH TEMPERATURES WARMING TOWARD 80F...MODERATE
INSTABILITY SHOULD DEVELOP. APPROACHING SPEED MAX WILL INCREASE THE
EFFECTIVE SHEAR INTO THE 40-50 KT RANGE...SUPPORTIVE OF SUPERCELLS
AND SMALL LINES. LOW LEVEL SPEED AND DIRECTIONAL SHEAR MAY SUPPORT A
TORNADO OR TWO INTO THE EARLY EVENING HOURS...THOUGH LARGE HAIL AND
ISOLATED DAMAGING WITHIN LINE SEGMENTS SHOULD BE THE PRIMARY SEVERE
THREATS. AS LOW LEVEL JET INCREASES THIS EVENING...STORMS SHOULD
CONSOLIDATE INTO 1 OR 2 MCS/S WITH SEVERE WIND BECOMING THE GREATER
THREAT DURING THE EVENING HOURS.
...FL PENINSULA...
A TROPICAL WAVE WAS MOVING THROUGH THE REGION AND HAS ENHANCED
THUNDERSTORM ACTIVITY NEAR THE FL KEYS THIS MORNING. WITH
HEATING...STORMS SHOULD BECOME MORE WIDESPREAD ACROSS THE FL
PENINSULA. ALTHOUGH WIND PROFILES ARE NOT PARTICULARLY STRONG AND
MOSTLY ELY THROUGH THE TROPOSPHERE...THE MOIST BOUNDARY LAYER AND
STRONG INSTABILITY COULD RESULT IN VERY BRIEF TORNADO OR TWO OR A
SEVERE WIND GUST AS STORMS INTERACT WITH STORM-INDUCED OUTFLOW
BOUNDARIES.
..IMY/SMITH.. 08/15/2009
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 2000Z
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