Re: Severe Weather Discussion - October '09
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1223 PM CDT WED OCT 07 2009
VALID 081200Z - 091200Z
...THERE IS A SLGT RISK OF SVR TSTMS THU AFT AND EVE ACROSS PARTS OF
THE SRN PLAINS INTO THE OZARK PLATEAU...
...SYNOPSIS...
MODELS INDICATE THAT A MERGER OF SPLIT POLAR STREAMS WILL OCCUR
DURING THIS FORECAST PERIOD...DOWNSTREAM OF AN ELONGATED DIGGING
NORTHERN BRANCH LOW/TROUGH ACROSS THE CANADIAN PRAIRIES...AND
NORTHWEST OF A BUILDING SUBTROPICAL RIDGE OVER THE SOUTHEASTERN U.S.
AND WESTERN ATLANTIC. THIS IS EXPECTED TO RESULT IN AN
INTENSIFYING...BROADLY ANTICYCLONIC HIGH LEVEL JET CORE ACROSS THE
UPPER MISSISSIPPI VALLEY AND UPPER GREAT LAKES REGION INTO
SOUTHEASTERN CANADA. AS A VIGOROUS SHORT WAVE IMPULSE DIGS AROUND
THE SOUTHWESTERN PERIPHERY OF THE CANADIAN TROUGH...AN INCREASINGLY
SHEARED SOUTHERN BRANCH CLOSED LOW/TROUGH IS PROGGED TO LIFT OUT OF
THE FOUR CORNERS STATES INTO THE CENTRAL/SOUTHERN PLAINS BY LATE
THURSDAY NIGHT OR EARLY FRIDAY. ALTHOUGH VARIABILITY EXISTS AMONG
THE GUIDANCE...IT SEEMS PROBABLE THAT FORCING DOWNSTREAM OF THIS
LATTER FEATURE WILL SUPPORT THE EVOLUTION OF A SIGNIFICANT WAVE
ALONG A DEVELOPING SURFACE FRONT ACROSS PARTS OF THE SOUTH CENTRAL
PLAINS AND OZARK PLATEAU INTO THE LOWER OHIO VALLEY. THIS LIKELY
WILL BE PRECEDED BY A STRONG RETURN FLOW OF MOISTURE FROM THE
WESTERN GULF COAST REGION /WHERE SURFACE DEW POINTS ARE NOW IN THE
UPPER 70S AND PRECIPITABLE WATER VALUES ARE IN EXCESS OF 2
INCHES/...ON A 40-50+ KT SOUTHERLY 850 MB JET. ASSOCIATED
DESTABILIZATION AND LARGE-SCALE FORCING FOR UPWARD VERTICAL MOTION
ARE EXPECTED TO CONTRIBUTE TO INCREASING CONVECTIVE POTENTIAL FROM
PARTS OF THE SOUTHERN PLAINS INTO THE MIDDLE MISSISSIPPI AND OHIO
VALLEYS.
...SRN PLAINS INTO MID MS/LWR OH VALLEYS...
AGEOSTROPHIC FORCING IN THE RIGHT ENTRANCE REGION OF THE HIGH LEVEL
JET IS EXPECTED TO SUPPORT AN EVOLVING CONVECTIVE BAND WITHIN AN
ELEVATED WARM ADVECTION REGIME TO THE NORTH OF A DEVELOPING SURFACE
FRONT BY 12Z THURSDAY...FROM PARTS OF NORTHERN OKLAHOMA AND
SOUTHERN/EASTERN KANSAS INTO NORTHERN/CENTRAL MISSOURI. ACTIVITY
MAY EXTEND WITHIN A LOW-LEVEL CONFLUENT ZONE ...TO THE WEST OF THE
LOW-LEVEL JET AXIS...SOUTH OF THE WARM FRONT INTO WESTERN
OKLAHOMA...AND PROBABLY WILL PERSIST THROUGH MUCH OF THE DAY...WITH
ONLY A SLOW EASTWARD PROGRESSION.
TO THE SOUTHEAST OF THIS CONVECTION...IN THE DEVELOPING WARM SECTOR
ACROSS PARTS OF NORTHERN TEXAS AND EASTERN OKLAHOMA INTO SOUTHWEST
MISSOURI...DAYTIME HEATING IS STILL UNCERTAIN DUE TO THE POSSIBLE
PRESENCE OF CONSIDERABLE CLOUD COVER ASSOCIATED WITH THE RETURNING
MOISTURE. BUT...THIS ENVIRONMENT SEEMS LIKELY TO REMAIN
PRECIPITATION FREE...WITH SURFACE DEW POINTS RISING INTO THE 70S.
GUIDANCE GENERALLY SUGGESTS THAT THIS WILL CONTRIBUTE TO MIXED LAYER
CAPE IN EXCESS OF 1000 J/KG BY LATE AFTERNOON.
THIS DESTABILIZATION...COUPLED WITH STRENGTHENING FORCING ASSOCIATED
WITH THE IMPULSE EMERGING FROM THE SOUTHWEST...SHOULD BE SUFFICIENT
TO INITIATE VIGOROUS STORM DEVELOPMENT PRIOR TO NIGHTFALL. IN THE
PRESENCE OF A MODERATELY STRONG AND SHEARED DEEP LAYER SOUTHWESTERLY
MEAN FLOW...SEVERE STORMS ARE LIKELY. UPSCALE GROWTH INTO AT LEAST
A BROKEN SQUALL LINE IS EXPECTED... BUT DISCRETE STORM DEVELOPMENT
MAY PERSIST NEAR/JUST AHEAD AND TO THE SOUTH SOUTHWEST OF THE
PRE-FRONTAL BAND THROUGH THE EVENING HOURS. GIVEN THE SIZE OF THE
HODOGRAPHS NEAR/BELOW THE LOW-LEVEL JET AXIS...WITH SUBSTANTIAL
CLOCKWISE CURVATURE...HIGH BOUNDARY LAYER MOISTURE CONTENT AND
HUMIDITY WILL PROVIDE A FAVORABLE ENVIRONMENT FOR TORNADOES IN
ISOLATED CELLS...AND PERHAPS WITHIN THE SQUALL LINE.
OTHERWISE...DAMAGING WIND GUSTS AND HAIL WILL ALSO BE
POSSIBLE...BEFORE ACTIVITY WEAKENS AS BOUNDARY LAYER INSTABILITY
WANES ACROSS THE OZARK PLATEAU OVERNIGHT.
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Originally Posted by venture79
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