SWODY1
SPC AC 230556
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1256 AM CDT WED APR 23 2008
VALID 231200Z - 241200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS MUCH OF THE SRN PLAINS
NWD THROUGH THE CENTRAL/NRN HIGH PLAINS...
...SYNOPSIS...
UPPER FLOW PATTERN IS EXPECTED TO BECOME MORE AMPLIFIED OVER THE
LOWER 48 STATES TODAY AS A DEEP TROUGH MOVES INLAND TO THE WRN U.S.
AND A DOWNSTREAM RIDGE SHIFTS EWD EXTENDING FROM THE CENTRAL GULF
COAST STATES TO THE UPPER OH VALLEY/CENTRAL APPALACHIANS BY 12Z
THURSDAY. SEVERAL MID LEVEL SHORT WAVE TROUGHS ATTENDANT TO THE WRN
LONGWAVE TROUGH AND EMBEDDED WITHIN SRN STREAM JET ARE FORECAST TO
TRANSLATE INTO THE PLAINS...SUPPORTING WIDESPREAD CONVECTIVE
DEVELOPMENT THIS FORECAST PERIOD. IN THE LOW LEVELS...SURFACE
CYCLOGENESIS IS EXPECTED OVER ERN WY THIS AFTERNOON WITH A LEE
TROUGH/DRY LINE EXTENDING SWD THROUGH THE HIGH PLAINS IN RESPONSE TO
APPROACHING WRN TROUGH. A SURFACE BOUNDARY IS EXPECTED TO STALL
EARLY IN THE PERIOD FROM SD INTO CENTRAL MN...AND THEN RETREAT NWD
INTO ND/NRN MN THIS EVENING IN RESPONSE TO STRENGTHENING LOW LEVEL
WINDS AS WY LOW/MID LEVEL TROUGH TRACK NEWD. FARTHER S...A WARM
FRONT THIS MORNING RESIDING FROM THE TX PANHANDLE INTO OK SHOULD
SPREAD NWD...BUT BECOME DIFFUSE AS A BROAD LLJ DEVELOPS ACROSS THE
PLAINS ADVECTING MOISTURE NWD THROUGH THE WARM SECTOR..
IN THE NORTHEAST...AN UPPER TROUGH...CURRENTLY LOCATED OVER THE
UPPER GREAT LAKES/NRN ONTARIO...WILL TRACK EWD BREAKING DOWN THE NRN
EXTENT OF THE ERN RIDGE OVER QUEBEC INTO THE LOWER GREAT LAKES AND
NEW ENGLAND. A COLD FRONT ATTENDANT TO THIS SYSTEM WILL MOVE SEWD
THROUGH THE LOWER GREAT LAKES REGION...REACHING ERN ME TO NRN VA BY
12Z THURSDAY.
...SRN PLAINS...
A LEAD SRN STREAM SHORT WAVE TROUGH/SPEED MAX SHOULD BE LOCATED OVER
FAR W TX AT 12Z TODAY AND MOVE EWD INTO W TX BY 18Z AND REACH
OK/ARKLATEX REGION TOWARD 24/00Z...WITH A SECOND IMPULSE...
CURRENTLY APPROACHING SRN CA/NRN BAJA...REACHING W TX REGION BY LATE
THIS AFTERNOON. A MOIST/MODERATELY UNSTABLE AIR MASS CURRENTLY
EXISTS ACROSS MUCH OF THE SRN PLAINS. ASCENT AHEAD OF THE LEAD SRN
STREAM IMPULSE SHOULD BE AIDING IN ONGOING TSTMS AT 12Z TODAY ACROSS
PARTS OF W TX INTO THE TX PANHANDLE/WRN OK. DEGREE OF INSTABILITY
AND 40-50 KT EFFECTIVE BULK SHEAR IN THIS REGION WILL RESULT IN A
HAIL THREAT WITH THIS EARLY ACTIVITY. AS THIS LEAD SYSTEM
TRANSLATES EWD INTO THE SRN PLAINS...ADDITIONAL TSTM DEVELOPMENT IS
LIKELY TO SPREAD ACROSS MUCH OF OK AND N TX. STEEP LAPSE RATES WILL
MAINTAIN A MODERATELY UNSTABLE AIR MASS OVER THE SRN PLAINS WITH
30-40 KT OF EFFECTIVE SHEAR SUPPORTING A THREAT FOR HAIL AND
DAMAGING WIND GUSTS.
ALTHOUGH SOME UNCERTAINTY EXISTS WITH DEGREE TO WHICH BOUNDARY LAYER
CAN DESTABILIZE ACROSS W/NW TX IN WAKE OF MORNING TSTMS... ASCENT
ATTENDANT TO SRN CA/NRN BAJA TROUGH REACHING THIS REGION BY LATE
AFTERNOON WILL MAINTAIN HEIGHT FALLS WITH NEW TSTM DEVELOPMENT
POSSIBLE. 50 KT WSWLY MID LEVEL WINDS ACROSS THE SRN PLAINS WILL
SUSTAIN STRONG EFFECTIVE BULK SHEAR FOR SUPERCELL STRUCTURES.
PRESENT INDICATIONS SUGGEST THIS LATE AFTERNOON CONVECTIVE
INITIATION SHOULD OCCUR ACROSS NW TX BETWEEN THE SRN TX PANHANDLE TO
EAST OF MAF TO ABI. GIVEN DEGREE OF INSTABILITY/DEEP LAYER
SHEAR...HAIL...SOME VERY LARGE HAIL...AND TORNADOES WILL BE
POSSIBLE. THIS ACTIVITY SHOULD THEN DEVELOP ENEWD ACROSS N TX/SRN
OK AS THIS LATTER SHORT WAVE TROUGH MOVES INTO THE SRN PLAINS WITH
AN ATTENDANT THREAT FOR HAIL/DAMAGING WINDS.
IF THE MORNING ACTIVITY IS NOT AS EXTENSIVE IN COVERAGE AS CURRENTLY
EXPECTED...THEN MUCH STRONGER INSTABILITY WILL BE POSSIBLE ACROSS
PARTS OF THE SRN PLAINS WITH THE POTENTIAL FOR AN UPGRADE TO A
MODERATE RISK.
...CENTRAL AND NRN PLAINS...
A SHORT WAVE TROUGH...CURRENTLY MOVING INLAND OVER NRN CA PER WATER
VAPOR IMAGERY...IS FORECAST TO TRACK NEWD WITHIN BAND OF STRONG SWLY
MID-UPPER LEVEL FLOW REACHING WY BY 24/00Z AND THEN INTO THE NRN
PLAINS TONIGHT. STEEP MID LEVEL LAPSE RATES /8-9 C/KM/ WILL SPREAD
EWD ACROSS THE CENTRAL/NRN HIGH PLAINS ATOP WRN EXTENT OF MOISTURE
RETURN...RESULTING IN A NARROW CORRIDOR OF MODERATE INSTABILITY
/MLCAPE 1000-1500 J/KG/. THIS INSTABILITY WILL EXTEND ALONG AND E
OF DRY LINE FROM ERN WY/SWRN SD SURFACE LOW SWD THROUGH ERN CO/WRN
KS TO SRN HIGH PLAINS. WEAK HEIGHT FALLS ACROSS THIS REGION DURING
THE AFTERNOON COMBINED WITH DIFFLUENT AND DIVERGENT UPPER FLOW IS
EXPECTED TO AID THE DEVELOPMENT OF SCATTERED TSTMS. A STRONGLY
SHEARED ENVIRONMENT AND MODERATE INSTABILITY WILL SUPPORT ISOLATED
SUPERCELLS CAPABLE OF PRODUCING VERY LARGE HAIL/LOCALLY DAMAGING
WIND GUSTS AND...PERHAPS...BRIEF TORNADOES.
STRENGTHENING SLY LLJ OVER NEB TO ERN DAKOTAS/MN TONIGHT WILL
SUPPORT INCREASING LOW LEVEL WAA AND THE LIKELIHOOD FOR AFTERNOON
ACTIVITY TO DEVELOP AND EXPAND NEWD ACROSS THE DAKOTAS TO MN AFTER
DARK. ALTHOUGH BOUNDARY LAYER WILL TEND TO STABILIZE WITH LOSS OF
DAY TIME HEATING...ELEVATED INSTABILITY AND MODEST EFFECTIVE BULK
SHEAR SHOULD SUPPORT A THREAT FOR ISOLATED HAIL AS STORMS SPREAD
NEWD OVERNIGHT.
...ARKLATEX REGION NWD TO IA...
SURFACE HEATING WITHIN A MOIST AIR MASS EXTENDING FROM THE LOWER MS
VALLEY TO LOWER MO VALLEY TODAY SHOULD SUPPORT MODERATE INSTABILITY
AGAIN TODAY ACROSS THIS REGION. MODELS SUGGEST TSTMS WILL BE
POSSIBLE ACROSS THIS REGION ALONG ERN EXTENT OF EML WHERE THE CAP
SHOULD BE WEAKER. ENHANCED LOW LEVEL CONVERGENCE IN VICINITY OF
LEFT OVER OUTFLOW BOUNDARIES FROM TUESDAY CONVECTIVE CLUSTERS MAY
PROVIDE A FOCUS FOR THIS ACTIVITY. WEAK TO MODEST DEEP LAYER SHEAR
SHOULD LIMIT THE SEVERE WEATHER THREAT WITH ISOLATED HAIL/STRONGER
WIND GUSTS POSSIBLE.
ASCENT ATTENDANT TO LEAD SRN STREAM IMPULSE AND WAA ALONG
STRENGTHENING LLJ FROM NERN TX TO IA THIS EVENING IS EXPECTED TO
SUPPORT AN EXTENSIVE ZONE OF EVENING/OVERNIGHT TSTM DEVELOPMENT FROM
THE ARKLATEX REGION TO IA. ISOLATED HAIL/STRONG WIND GUSTS WILL BE
POSSIBLE WITH THIS ACTIVITY.
...UPSTATE NY SWWD TO NWRN PA/NERN OH...
WNWLY MID LEVEL WINDS ARE EXPECTED TO INCREASE ACROSS THIS REGION
TODAY AS ONTARIO UPPER TROUGH MOVES EWD. SURFACE DEWPOINTS IN THE
LOWER 50S...CURRENTLY LOCATED ACROSS THE SRN GREAT LAKES REGION...
ARE EXPECTED TO ADVECT NEWD AHEAD OF TRAILING COLD FRONT INTO THE
LOWER GREAT LAKES /NERN OH TO WRN AND UPSTATE NY/. ALTHOUGH MID
LEVEL LAPSE RATES SHOULD BE WEAK...THIS LOW LEVEL MOISTURE AND
SURFACE HEATING SUGGEST INSTABILITY SHOULD BE SUFFICIENT FOR A FEW
STRONGER STORMS. ISOLATED HAIL AND STRONG WIND GUSTS WILL BE THE
PRIMARY THREATS.
..PETERS/JEWELL.. 04/23/2008
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