SPC AC 130529
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1229 AM CDT THU MAY 13 2010
VALID 141200Z - 151200Z
...THERE IS A SLGT RISK OF SVR TSTMS FRI AFTN AND EVE ACROSS PARTS
OF THE TN VALLEY/CUMBERLAND PLATEAU...AND CNTRL/SRN APPALACHIANS
INTO THE MID ATLANTIC COAST....
...THERE IS A SLGT RISK OF SVR TSTMS FRI AFTN AND EVE ACROSS PARTS
OF THE SRN HIGH PLAINS...
...SYNOPSIS...
MODELS CONTINUE TO INDICATE THAT REMNANTS OF A SIGNIFICANT UPPER
LOW/TROUGH WILL LIFT INTO THE UPPER GREAT LAKES REGION BY 12Z
FRIDAY. THE SYSTEM IS THEN PROGGED TO TURN EASTWARD...AND GRADUALLY
SOUTHEASTWARD...ACCELERATING TOWARD THE NORTH ATLANTIC COAST LATE
FRIDAY/FRIDAY NIGHT...WITHIN A CONFLUENT REGIME TO THE WEST AND
SOUTH OF AN UPPER LOW OVER THE CANADIAN MARITIMES. AS THIS
OCCURS...SUBTROPICAL RIDGING APPEARS LIKELY TO FLATTEN ACROSS THE
LOWER OHIO/TENNESSEE VALLEYS INTO THE MID ATLANTIC COAST...WHILE THE
HIGH CENTER WEAKENS AND SHIFTS EASTWARD...AWAY FROM SOUTH ATLANTIC
COASTAL AREAS.
A COLD FRONT ASSOCIATED WITH THE NORTHEASTERN IMPULSE IS EXPECTED TO
SHIFT SOUTHEAST OF THE LOWER GREAT LAKES AND OHIO VALLEY INTO THE
MID ATLANTIC COAST AND TENNESSEE VALLEY. HOWEVER...THIS FEATURE
WILL LIKELY WEAKEN AND STALL ACROSS THE SOUTHERN PLAINS...BEFORE
BEGINNING TO RETREAT NORTHWARD LATE IN THE PERIOD ...AS A
SIGNIFICANT PORTION OF LINGERING UPPER TROUGHING OVER THE SOUTHWEST
GRADUALLY ADVANCES EASTWARD TOWARD THE SOUTHERN ROCKIES.
IN RESPONSE TO THE EVOLVING PATTERN...A RETURN FLOW OFF THE GULF OF
MEXICO IS EXPECTED TO CONTINUE INTO THE RIO GRANDE VALLEY AND
SOUTHERN PLAINS...WHILE MOISTURE INFLUX TO THE EAST BECOMES CUT-
OFF. HOWEVER...RESIDUAL LOW-LEVEL MOISTURE ALONG AND SOUTH OF THE
LENGTH OF THE FRONTAL ZONE WILL LIKELY REMAIN SUPPORTIVE OF
WIDESPREAD CONVECTIVE DEVELOPMENT DURING THIS PERIOD...PROBABLY
INCLUDING AT LEAST A FEW SEVERE THUNDERSTORMS.
...OHIO/TENNESSEE VALLEYS EASTWARD TO MID ATLANTIC COAST...
THE MOST SUBSTANTIAL SURFACE HEATING AND DESTABILIZATION...WHICH
COULD BECOME MODERATE TO STRONG BY FRIDAY AFTERNOON...IS EXPECTED
ACROSS PARTS OF THE TENNESSEE VALLEY/CUMBERLAND PLATEAU...AND AREAS
TO THE LEE OF THE SOUTHERN/CENTRAL APPALACHIANS. THIS MAY REMAIN
SOUTH OF THE MORE SUBSTANTIVE MID-LEVEL HEIGHT FALLS...AT LEAST
THROUGH THE DAYTIME HOURS...BUT MODELS ARE SUGGESTIVE THAT
INHIBITION WILL WEAKEN SUFFICIENTLY FOR CONSIDERABLE THUNDERSTORM
ACTIVITY ACROSS MUCH OF THE REGION DURING THE MID/LATE AFTERNOON
HOURS. ON THE SOUTHERN FRINGE OF THE STRONGER WESTERLIES...30-50 KT
500 MB FLOW WILL PROBABLY ENHANCE STORM DEVELOPMENT IN THE PRESENCE
OF MIXED LAYER CAPE GENERALLY ON THE ORDER OF 1500-2000 J/KG. A FEW
SEVERE STORMS/STORM CLUSTERS ARE POSSIBLE...WITH THE RISK FOR
DAMAGING WINDS AND LARGE HAIL.
...SOUTHERN HIGH PLAINS...
SOUTH OF THE STALLING FRONT...MID-LEVEL LAPSE RATES ARE EXPECTED TO
REMAIN STEEP IN CLOSE PROXIMITY TO THE SOUTHERN ROCKIES/ MEXICAN
PLATEAU REGION. MODELS ARE SUGGESTIVE THAT CONSIDERABLE SURFACE
HEATING WILL ALSO CONTRIBUTE TO STEEPENING LOW-LEVEL LAPSE RATES
ACROSS SOUTHEAST NEW MEXICO AND SOUTHWEST TEXAS INTO THE PECOS
VALLEY...PERHAPS PARTS OF THE TEXAS SOUTH PLAINS...WHERE MOIST
LOW-LEVEL UPSLOPE FLOW IS PROGGED TO CONTRIBUTE TO MODERATE
INSTABILITY. AIDED BY DIVERGENT UPPER FLOW DOWNSTREAM OF THE
APPROACHING UPPER TROUGH...THIS SHOULD BE SUFFICIENT FOR SCATTERED
LATE AFTERNOON AND EVENING STORMS. BENEATH A BELT OF 30-40 KT
SOUTHWESTERLY 500 MB FLOW NOSING OUT OF NORTHERN MEXICO...VERTICAL
SHEAR WILL BE SUFFICIENT FOR SUPERCELLS CAPABLE OF PRODUCING LARGE
HAIL...LOCALIZED STRONG SURFACE GUSTS...PERHAPS AN ISOLATED TORNADO
OR TWO.
..KERR.. 05/13/2010
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NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z
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