SWODY1
SPC AC 060507
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1207 AM CDT SAT OCT 06 2007
VALID 061200Z - 071200Z
..THERE IS A SLGT RISK OF SVR TSTMS PORTIONS CENTRAL HIGH PLAINS TO
WRN MN/ERN ND...
..SYNOPSIS...
HIGHLY AMPLIFIED SYNOPTIC PATTERN WILL CHARACTERIZE MID/UPPER LEVELS
THROUGH PERIOD...ANCHORED BY BROAD ANTICYCLONE CENTERED OVER OH
VALLEY...AND STRONG WRN CONUS TROUGH. PRIMARY MID/UPPER CYCLONE --
INITIALLY EVIDENT IN MOISTURE CHANNEL IMAGERY OVER NV -- SHOULD
EJECT NEWD OVER N-CENTRAL ROCKIES THIS PERIOD. ALTHOUGH SOME MINOR
TRACK DIFFERENCES ARE EVIDENT AMONGST OPERATIONAL AND SREF GUIDANCE
PACKAGES...CONSENSUS FCST APPEARS REASONABLE FOR LOW MOVING NEWD
ACROSS WY TO NRN HIGH PLAINS BY 7/12Z...WITH POSITIVELY TILTED
TROUGH TRAILING SWWD ACROSS AZ AND NRN BAJA AT THAT TIME. BROAD AND
STRONG FETCH OF SSWLY FLOW ALOFT WILL PRECEDE TROUGH...E.G. 90-125
KT JET AT 250 MB AND 60-90 KT AT 500 MB...FROM NERN AZ ACROSS
CENTRAL CO TO NWRN SD AT 7/00Z. WEAK SHORTWAVE PERTURBATION -- NOW
INDICATED OVER MN -- SHOULD MOVE THROUGH MEAN RIDGE POSITION OVER LS
AROUND DAYBREAK THEN ESEWD ACROSS SERN ONT AND NEW ENGLAND.
AT SFC...CYCLONE NOW OVER WY SHOULD MOVE NEWD OVER SERN ND AND
WEAKEN SOMEWHAT...BUT STILL MAINTAIN FRONTAL-WAVE CHARACTERISTICS
FROM SERN ND ACROSS NRN MN DURING 7/00Z-7/12Z TIME FRAME. TRAILING
COLD FRONT SHOULD MOVE EWD OUT OF CENTRAL/NRN ROCKIES AND ACROSS
DAKOTAS/ERN WY AND CENTRAL HIGH PLAINS. BY END OF PERIOD...THIS
FRONT SHOULD LIE FROM BOUNDARY WATERS REGION OF NRN MN SSWWD ACROSS
SIOUX-LAND AREA...S-CENTRAL NEB AND EXTREME WRN KS. SECONDARY/WAVE
LOW MAY FORM ALONG FRONT BY 7/00Z INVOF CO/NEB BORDER...BEFORE
BECOMING DIFFUSE AMIDST EWD FRONTAL SURGE. MEANWHILE...WARM FRONT
NOW OVER SRN SD AND CENTRAL MN SHOULD DRIFT NWD INTO N-CENTRAL MN
AND SERN ND.
..CENTRAL/NRN PLAINS...UPPER MIDWEST...
COLD FRONTAL ZONE SHOULD BE PRIMARY FOCUS FOR ORGANIZED CONVECTIVE
POTENTIAL THIS PERIOD...WITH SOME HAIL AND DAMAGING GUSTS POSSIBLE
PRIMARILY FROM AFTERNOON THROUGH EVENING. DEEP-LAYER VERTICAL SHEAR
PROFILES INVOF COLD FRONT ZONE WILL BE FAVORABLE FOR SUPERCELLS
BENEATH ERN EDGE OF AFOREMENTIONED 500 MB FLOW BELT. MOST ENLARGED
LOW LEVEL HODOGRAPHS ARE EXPECTED OVER PORTIONS ERN DAKOTAS/WRN MN
-- INVOF FRONTAL-WAVE LOW AND EWD ALONG WARM FRONT WHERE ASSOCIATED
ISALLOBARIC FORCING WILL ENHANCE/BACK LOW LEVEL WINDS. FOR HOWEVER
LONG THAT STORMS CAN DEVELOP AND REMAIN RELATIVELY DISCRETE OVER
LATTER REGION...LARGE HAIL AND DAMAGING GUSTS ARE POSSIBLE ALONG
WITH CONDITIONAL TORNADO RISK..LATTER BEING MAXIMIZED IN ZONE OF
200-400 J/KG OF 0-3 KM SRH. SECONDARY AREA OF ENHANCED LOW LEVEL
SHEAR -- E OF CENTRAL HIGH PLAINS FRONTAL-WAVE LOW -- ALSO MAY
SUPPORT SUPERCELL DEVELOPMENT...ESPECIALLY IF CAPPING IN THIS AREA
CAN MAINTAIN RELATIVELY DISCRETE/TAIL-END STORMS AS INDICATED BY
SOME MODELS AND BY FCST SOUNDINGS.
MAIN CONCERNS/UNCERTAINTIES PRECLUDING LARGER SVR PROBABILITIES ATTM
ARE THREEFOLD AND INTERRELATED --
1. GEOMETRY/MODE OF CONVECTION -- WITH FORCING BOUNDARY LYING
LARGELY PARALLEL TO MIDLEVEL AND MEAN FLOW VECTORS. THIS INDICATES
POTENTIAL FOR QUICK TRANSITION AWAY FROM DISCRETE STORMS TO
LINEAR...MESSY AND INTERFERENCE-PRONE CONVECTIVE PATTERN.
2. STRONGEST LARGE SCALE ASCENT ALOFT SHOULD REMAIN BEHIND SFC COLD
FRONT.
3. LARGE PROPORTION OF CONVECTION MAY DEVELOP AND/OR MOVE BEHIND SFC
COLD FRONT. DIURNAL/SFC-BASED DEVELOPMENT IS POSSIBLE ALONG FRONT
GIVEN FAVORABLY STG WARM SECTOR INSOLATION AND MOISTURE...AS
EXPECTED. HOWEVER...MEAN WIND VECTORS PARALLEL TO FCST FRONTAL
ORIENTATION INDICATE ANY MOTION OF BOUNDARY WILL YIELD ANAFRONTAL
REGIME...AND THAT INITIALLY SFC-BASED TSTMS DEVELOPING ALONG FRONT
MAY GO BEHIND IT. SEVERAL PROGS ALSO INDICATE AREAS OF CONVECTIVE
PRECIP DISTINCTLY W OF BOUNDARY FROM SERN WY/NEB PANHANDLE NEWD.
..UPPER GREAT LAKES...
WIDELY SCATTERED TSTMS MAY DEVELOP E OF STRONGEST CAPPING...IN ZONE
OF FAVORABLY MOIST LOW LEVEL AIR MASS AND WAA. ISOLATED LARGE HAIL
AND STG/DAMAGING GUSTS ARE POSSIBLE...PARTICULARLY DURING AFTERNOON
AND EARLY EVENING. FCST SOUNDINGS SUGGEST 60S F SFC DEW POINTS
SUPPORTING 1000-1500 J/KG MLCAPES. THIS SHOULD BE ACCOMPANIED BY
ENOUGH VEERING WITH HEIGHT -- FROM WSW OR SW FLOW AT SFC TO WNWLY
ALOFT -- TO YIELD ENLARGED 0-3 KM HODOGRAPHS. DEEP-LAYER SHEAR WILL
BE WEAK TO MRGL -- E.G. 30-35 KT EFFECTIVE SHEAR OVER MUCH OF
REGION. WEAK SUBSIDENCE ALOFT ACCOMPANYING DNVA MAY OCCUR BEHIND
SHORTWAVE TROUGH...AND INVOF SYNOPTIC SCALE RIDGE.
HOWEVER...ASSOCIATED MIDLEVEL STABILIZATION IS NOT EVIDENT IN MODEL
FCST SOUNDINGS...INDICATING THAT EFFECT WILL BE MORE THAN
COUNTERBALANCED BY ENHANCEMENT TO LARGE SCALE ASCENT ASSOCIATED WITH
LOW LEVEL WAA.
ERN-MOST EXTENSION OF THIS REGIME AND/OR SEPARATE AREA OF SIMILAR
CONVECTIVE POTENTIAL MAY REACH ACROSS INTERVENING PORTIONS ONT
TOWARD NRN NY...AHEAD OF SHORTWAVE TROUGH. HOWEVER...SVR POTENTIAL
THAT FAR E APPEARS TOO CONDITIONAL/MRGL ATTM TO WARRANT AOA
5-PERCENT PROBABILITY LINE.
.EDWARDS/BRIGHT.. 10/06/2007
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