SWODY2
SPC AC 041717
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1217 PM CDT THU OCT 04 2007
VALID 051200Z - 061200Z
..THERE IS A SLGT RISK OF SVR TSTMS FROM PARTS OF THE NRN PLAINS
EWD INTO THE UPPER GREAT LAKES...
..SYNOPSIS...
LARGE UPPER TROUGH CURRENTLY EVOLVING ALONG THE PACIFIC COAST IS
FORECAST TO UNDERGO FURTHER AMPLIFICATION DURING THE DAY TWO PERIOD
AS IT SLOWLY PROGRESSES EWD THROUGH THE WRN STATES. AS THIS
OCCURS...DOWNSTREAM RIDGE WILL ALSO INTENSIFY...MOST NOTABLY FROM
HUDSON BAY INTO THE UPPER GREAT LAKES. IN THE LOW LEVELS...A BROAD
AREA OF LOW PRESSURE FROM THE GREAT BASIN EWD INTO THE CNTRL HIGH
PLAINS WILL GRADUALLY CONSOLIDATE INTO A SURFACE LOW OVER WY WITH
THIS FEATURE DEVELOPING EWD INTO WRN SD BY SATURDAY MORNING.
ATTENDANT WARM FRONT WILL SLOWLY LIFT NWD THROUGH THE DAKOTAS...MN
AND WI...WHILE LEE TROUGH IS MAINTAINED OVER THE CNTRL/SRN HIGH
PLAINS. FARTHER TO THE W...PACIFIC COLD FRONT WILL PUSH EWD THROUGH
THE GREAT BASIN INTO CNTRL ROCKIES.
..NRN PLAINS EWD INTO UPPER GREAT LAKES...
CLUSTERS OF ELEVATED TSTMS /SOME POSSIBLY SEVERE/ ARE EXPECTED TO BE
ONGOING FRIDAY MORNING NEAR AND TO THE N OF SURFACE WARM FRONT OVER
ERN SD...MN AND WI. WAA/ISENTROPIC ASCENT FOCUSED ALONG THE NOSE OF
A PERSISTENT...SLY/SWLY LLJ WILL BE THE PRIMARY MECHANISM SUSTAINING
THESE STORMS WITHIN AN ENVIRONMENT OF MODEST INSTABILITY AND
VERTICAL SHEAR /I.E. MUCAPES OF 1000-1500 J PER KG AND EFFECTIVE
BULK SHEARS OF 30-35 KT/. THE LLJ AND ASSOCIATED FORCING MECHANISMS
WILL PERSIST THROUGH MUCH OF THE PERIOD...WITH MULTIPLE EPISODES OF
ELEVATED...SEVERE STORMS POSSIBLE TO THE N OF RETREATING WARM
FRONT...MAINLY OVER ERN ND EWD ACROSS MN INTO PARTS OF WI. FORECAST
SOUNDINGS INDICATE STRENGTHENING CLOUD- BEARING SHEAR FRIDAY INTO
FRIDAY NIGHT WITH AN INCREASING THREAT OF A FEW SUPERCELLS CAPABLE
OF MAINLY LARGE HAIL.
THE PROSPECTS OF ANY SURFACE-BASED STORM DEVELOPMENT ALONG THE WARM
FRONT ARE QUITE UNCERTAIN AND LATEST MODEL GUIDANCE WOULD SUGGEST
ONLY A VERY LOW PROBABILITY OF INITIATION AND SUSTENANCE. THE
PRIMARY LIMITING FACTOR APPEARS TO BE THE PRESENCE OF A LOWER TO
MID-TROPOSPHERIC CAPPING INVERSION WHICH IS EXPECTED TO BE
MAINTAINED BY BUILDING HEIGHTS DOWNSTREAM FROM WRN U.S. TROUGH.
INDEED...BOTH THE THERMODYNAMIC AND KINEMATIC ENVIRONMENT WILL BE
QUITE SUPPORTIVE OF TORNADIC SUPERCELLS GIVEN THE RATHER STRONG LOW
AND DEEP LAYER SHEAR AND MODERATE CONVECTIVE INSTABILITY.
HOWEVER...GIVEN THE ABOVEMENTIONED CONCERNS...SEVERE PROBABILITIES
HAVE BEEN LOWERED.
..ERN UT/NWRN CO/SWRN WY...
A STRONGLY SHEARED ENVIRONMENT IS EXPECTED TO DEVELOP ACROSS THE
REGION FRIDAY OWING TO THE PROXIMITY OF 70-80 KT MID-LEVEL JET
STREAK DEVELOPING DOWNSTREAM FROM UPPER TROUGH AXIS. CLOUDS AND
PRECIPITATION WILL LIKELY LIMIT THE DEGREE OF AIR MASS
DESTABILIZATION AHEAD OF SURFACE COLD FRONT...HOWEVER FORECAST
SOUNDINGS DO SUGGEST THAT AT LEAST MARGINAL INSTABILITY /MLCAPES OF
200-500 J PER KG/ WILL DEVELOP BY AFTERNOON. THE STRONG VERTICAL
SHEAR AND INCREASED DEEP LAYER FORCING FOR ASCENT MAY BE SUFFICIENT
TO SUPPORT A COUPLE STRONG TO SEVERE STORMS WITH THE PRIMARY THREATS
BEING DAMAGING WIND GUSTS AND SOME HAIL.
.MEAD.. 10/04/2007
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