SWODY2
SPC AC 211729
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1229 PM CDT FRI OCT 21 2011
VALID 221200Z - 231200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
A BROAD LONGWAVE TROUGH CURRENTLY LOCATED FROM THE ROCKIES TO THE
EAST COAST WILL AMPLIFY/DEEPEN OVER THE ERN STATES ON SATURDAY
BETWEEN A STRONG WRN ATLANTIC RIDGE AND A RIDGE BUILDING EWD INTO
THE GREAT BASIN FOUR CORNERS REGION. A COUPLE OF PACIFIC SHORTWAVE
TROUGHS MOVING INTO THE SRN PLAINS AND UPPER MIDWEST WILL BE THE
IMPETUS FOR CONVECTIVE DEVELOPMENT...WITH THE FORMER BEING MORE
LIKELY FOR TSTMS AND SOME SEVERE WEATHER THREAT.
...OK/TX/ARKLATEX...
SLY LOW LEVEL MOISTURE RETURN WILL CONTINUE ON SATURDAY AS MASS
FIELDS CONTINUE TO RESPOND TO A SHORTWAVE TROUGH DIGGING SEWD FROM
WY/NRN CO AND ACROSS THE CENTRAL/SRN PLAINS. A WARM FRONT EXPECTED
TO RESIDE FROM W-E OVER NRN TX AT 12Z SATURDAY IS FORECAST TO MOVE
NWD INTO SRN OK THIS FORECAST PERIOD...WITH THIS BOUNDARY BEING A
FOCUS FOR CONVECTIVE DEVELOPMENT FROM MID-LATE SATURDAY AFTERNOON
AND SPREADING ESEWD SATURDAY NIGHT. SURFACE HEATING COMBINED WITH
STEEPENING MIDLEVEL LAPSE RATES/COOLING TEMPERATURES ALOFT ARE
EXPECTED TO SUPPORT MUCAPE OF 500-1000 J/KG. THE TIMING OF THE
WY/CO TROUGH INTO THE SRN PLAINS DURING THE MID-LATE AFTERNOON
SUGGESTS TSTMS SHOULD INITIALLY FORM OVER SRN OK/N TX...WITH
ACTIVITY MOVING TOWARD THE ARKLATEX SATURDAY NIGHT AS THE SLY LLJ
VEERS TO SWLY-WLY WITH THE PASSAGE OF THE SHORTWAVE TROUGH. THE
COMBINATION OF MARGINAL INSTABILITY AND SOME UVVS SUGGEST THE
COVERAGE OF STRONGER STORMS SHOULD REMAIN LOWER THAN A CATEGORICAL
SLIGHT RISK. HOWEVER...GIVEN THE STEEPENING MIDLEVEL LAPSE RATES
AND VERTICALLY VEERING WINDS/EFFECTIVE BULK SHEAR TO AROUND 45
KT...ISOLATED LARGE HAIL AND STRONG WIND GUSTS WILL BE A THREAT WITH
THE MORE PERSISTENT UPDRAFTS AND ACTIVITY THAT HAS DEVIANT STORM
MOTIONS.
...FAR ERN ND/NRN MN...
A SHORTWAVE TROUGH...CURRENTLY APPROACHING BRITISH COLUMBIA PER
WATER VAPOR IMAGERY...WILL AMPLIFY ESEWD FROM ALBERTA ON SATURDAY
REACHING CENTRAL/SRN MANITOBA AND ADJACENT ONTARIO/NRN MN BY 12Z
SUNDAY. AN ATTENDANT TRAILING COLD FRONT IS EXPECTED TO MOVE
QUICKLY EWD FROM THE NRN HIGH PLAINS TO ERN MN AND WRN LAKE SUPERIOR
BY THE END OF THE PERIOD. MOISTURE RETURN AHEAD OF THE WIND SHIFT
IS EXPECTED TO BE QUITE MARGINAL. HOWEVER...FORECAST SOUNDINGS DO
SUGGEST COOLING MIDLEVEL TEMPERATURES/STEEPENING LAPSE RATES
SATURDAY NIGHT...MAINLY ACROSS NRN MN...WILL AID IN VERY WEAK
INSTABILITY ROOTED AROUND 800-850 MB. STRONGER FORCING ALOFT IS
FORECAST TO REMAIN ACROSS SRN CANADA...THOUGH SOME UVVS GLANCING
THIS REGION AND EQUILIBRIUM TEMPERATURES BECOMING COLD ENOUGH FOR
CHARGE SEPARATION MAY SUPPORT A STRIKE OR TWO EMBEDDED WITHIN A BAND
OF SHOWERS FORMING ALONG THE ADVANCING COLD FRONT. LOW COVERAGE OF
EXPECTED TSTMS CONTINUES TO PRECLUDE THE INCLUSION OF A GENERAL TSTM
AREA.
..PETERS.. 10/21/2011
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