SWODY2
SPC AC 131641
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1141 AM CDT SUN MAY 13 2007
VALID 141200Z - 151200Z
..THERE IS A SLGT RISK OF SVR TSTMS FROM THE UPPER GREAT LAKES SWWD
INTO THE CNTRL HIGH PLAINS...
..SYNOPSIS...
MAIN BELT OF POLAR WESTERLIES WILL REMAIN CONFINED TO CANADA AND THE
NRN TIER OF STATES WITH THE PRIMARY FEATURE OF INTEREST BEING
AMPLIFYING SHORT WAVE TROUGH WHICH WILL TRANSLATE FROM THE NRN HIGH
PLAINS EWD INTO THE UPPER MS/MID MO VALLEYS BY 15/12Z. IN THE
LOW-LEVELS...ATTENDANT SURFACE LOW INITIALLY OVER ERN ND IS FORECAST
TO DEVELOP ENEWD INTO THE UP OF MI/LAKE SUPERIOR BY MONDAY EVENING
WHILE TRAILING COLD FRONT PUSHES SEWD THROUGH THE DAKOTAS AND CNTRL
HIGH PLAINS.
..UPPER GREAT LAKES SWWD INTO ERN CO...
DESPITE MODEST BOUNDARY LAYER MOISTURE /DEWPOINTS IN THE MID 50S TO
LOWER 60S/ THE DEVELOPMENT OF STEEP LOW TO MID-LEVEL LAPSE RATES
WILL CONTRIBUTE TO A MODERATELY UNSTABLE AIR MASS BY AFTERNOON AHEAD
OF COLD FRONT WITH MLCAPES INCREASING TO 1500-2000 J/KG. FORCING
FOR ASCENT AHEAD OF APPROACHING UPPER TROUGH AND STRONG FRONTAL
CONVERGENCE SHOULD SUPPORT AN INCREASE IN SURFACE-BASED STORM
DEVELOPMENT BY MID/LATE AFTERNOON FROM THE MN ARROWHEAD SWWD THROUGH
ERN SD...CNTRL NEB AND ERN CO.
DEEP LAYER VERTICAL SHEAR /EFFECTIVE BULK SHEAR OF 40-50 KT/ WILL BE
STRONGEST OVER NRN PORTIONS OF SLIGHT RISK AREA IN ASSOCIATION WITH
BELT OF STRONGER MID-LEVEL FLOW ALONG THE INTERNATIONAL BORDER.
HERE...A FEW SUPERCELLS AND/OR BOWING STRUCTURES WILL WE POSSIBLE
WITH A THREAT OF A FEW TORNADOES...DAMAGING WINDS AND LARGE HAIL.
VERTICAL SHEAR WILL TEND TO DECREASE WITH SWD EXTENT ALONG FRONTAL
ZONE WITH MULTICELLULAR CLUSTERS LIKELY BEING THE DOMINANT
CONVECTIVE MODE. STILL...THE STEEP LAPSE RATES AND RESULTANT
MODERATE INSTABILITY WILL BE SUPPORTIVE OF LARGE HAIL AND DAMAGING
WINDS WITH THE MORE INTENSE STORMS.
..WRN CO INTO SRN WY...
BOUNDARY LAYER WILL BE RELATIVELY DRY WITH DEWPOINTS IN THE
30S...PERHAPS LOWER 40S. HOWEVER...THE PRESENCE OF STEEP LAPSE
RATES WILL COMPENSATE...CONTRIBUTING TO THE DEVELOPMENT OF AFTERNOON
MLCAPES OF 500-1000 J/KG. DEEP LAYER VERTICAL SHEAR WILL BE
SLIGHTLY STRONGER THAN LOCATIONS FARTHER TO THE E OVER THE FRONT
RANGE OWING TO THE PRESENCE OF 30-35 KT MID-LEVEL FLOW ALONG SRN
PERIPHERY OF UPPER TROUGH MOVING THROUGH THE NRN HIGH PLAINS. AS
SUCH...POTENTIAL FOR A FEW ORGANIZED STORMS WILL EXIST AHEAD OF COLD
FRONT WITH SOME THREAT OF ISOLATED LARGE HAIL AND LOCALLY STRONG
WIND GUSTS.
..ELSEWHERE...
A WARM AND MOIST LOW-LEVEL AIR MASS IS EXPECTED TO EXIST ALONG SWRN
PERIPHERY OF SURFACE RIDGE AXIS OVER THE LOWER MS VALLEY WITH
POCKETS OF MODERATE INSTABILITY /MLCAPES OF 1000-2000 J PER KG/
DEVELOPING BY AFTERNOON. LATEST MODEL GUIDANCE SUGGESTS THAT A WEAK
IMPULSE TRANSLATING WWD/NWWD MAY PROVIDE THE FOCUS FOR A
CONCENTRATED AREA OF TSTMS OVER PARTS OF SRN MS...LA INTO ERN TX
MONDAY AFTERNOON...A FEW OF WHICH COULD BE BRIEFLY SEVERE.
FINALLY...ISOLATED SEVERE STORMS WILL ONCE AGAIN BE POSSIBLE OVER
CNTRL/SRN PORTIONS OF THE FL PENINSULA MONDAY AFTERNOON INTO
EVENING. AN ELY BOUNDARY LAYER FLOW REGIME IS FORECAST TO BECOME
ESTABLISHED ACROSS THE AREA...LIKELY ENHANCING CONVERGENCE ALONG WRN
PENINSULA SEA BREEZE. THIS ELY LOW-LEVEL FLOW WILL COEXIST BENEATH
MODEST HIGH LEVEL WLY WINDS /30-50 KT AT 7-10 KM AGL/ SUGGESTING
THAT SOME POTENTIAL WILL EXIST FOR STORM ORGANIZATION WITH A THREAT
OF ISOLATED DAMAGING WINDS AND PERHAPS SOME HAIL.
.MEAD.. 05/13/2007
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