SWODY2
SPC AC 261730
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1230 PM CDT THU MAY 26 2011
VALID 271200Z - 281200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS NRN VA/MD...CENTRAL/ERN
PA TO NEW ENGLAND...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS CENTRAL/ERN OK INTO WRN
AR AND SWRN MO...
...SYNOPSIS...
BROAD UPPER TROUGHING IS PROGGED TO EVOLVE OVER THE ERN PACIFIC AND
WESTERN U.S...AS A STRONG UPPER JET PROGRESSES INLAND. DOWNSTREAM
RIDGING ACROSS THE PLAINS WILL ADVANCE EWD TO ALONG AND EAST OF THE
MS VALLEY...AS THE EXIT REGION OF THE PACIFIC UPPER JET NOSES EAST
OF THE ROCKIES.
DOWNSTREAM...MODELS REMAIN CONSISTENT SHOWING THE REMNANT UPPER
TROUGHING OVER THE ERN STATES SPLITTING ON FRIDAY...WITH AN
INCREASINGLY SHEARED NRN PORTION LIFTING NEWD WITHIN STRONGER FLOW
AROUND THE NWRN PERIPHERY OF RIDGING CENTERED OFF THE NORTH ATLANTIC
COAST. WITHIN A WEAKER FLOW REGIME...THE SRN PORTION IS FORECAST TO
TURN SEWD ACROSS THE SOUTH ATLANTIC COAST STATES.
...PARTS OF THE NRN MID ATLANTIC COAST STATES INTO NEW ENGLAND...
MODELS SUGGEST MODERATE INSTABILITY AND SUFFICIENT DEEP LAYER SHEAR
WILL EXIST FARTHER SEWD ON FRIDAY. THUS...THE SLIGHT RISK AREA HAS
BEEN EXPANDED TO INCLUDE MORE OF NRN VA...CENTRAL AND NRN MD...AND
MUCH OF SERN PA.
12Z MODELS CONTINUE TO REMAIN WEAKER WITH THE STRENGTH OF THE
LOWER/MID TROPOSPHERIC FLOW FIELDS ON THE WRN/NRN PERIPHERY OF THE
ATLANTIC RIDGING. HOWEVER...DEEP LAYER SHEAR IS STILL PROGGED TO BE
STRONG AND SUPPORTIVE OF ORGANIZED CONVECTIVE DEVELOPMENT AS A
SEASONABLY MOIST BOUNDARY LAYER DESTABILIZES WITH HEATING...FROM
ALONG AND IN LEE OF THE NORTH CENTRAL APPALACHIANS THROUGH WRN/SRN
NEW ENGLAND. RELATIVELY STEEP MID-LEVEL LAPSE RATES WILL CONTRIBUTE
TO MLCAPE ON THE ORDER OF 1000-2000 J/KG...WHILE FORCING ASSOCIATED
WITH THE SHEARING IMPULSE IS EXPECTED TO BE SUFFICIENT TO SUPPORT
STORM DEVELOPMENT. ADDITIONAL FORCING FOR ASCENT APPEARS POSSIBLE
AS A COMPACT SHORTWAVE TROUGH...CURRENTLY TRACKING EWD ALONG THE
CENTRAL GULF COAST PER WATER VAPOR IMAGERY...TRACKS NEWD ACROSS VA
TO ERN PA FRIDAY AFTERNOON. SOME STORMS MAY TAKE ON SUPERCELLULAR
STRUCTURE WITH AN ENHANCED RISK FOR LARGE HAIL... WHICH APPEARS TO
BE THE PRIMARY SEVERE THREAT...THOUGH CONSOLIDATING STORM CLUSTERS
MAY BE ABLE TO GENERATE STRONG WIND GUSTS. A TORNADO THREAT CANNOT
BE RULED OUT...GIVEN INCREASING LOW LEVEL SHEAR AS A SSWLY LLJ
STRENGTHENS SOME /35-40 KT/ LATE FRIDAY AFTERNOON/EVENING FROM VA/MD
TO THE HUDSON VALLEY/WRN NEW ENGLAND.
...S CNTRL PLAINS AND OZARK PLATEAU...
LATEST MODELS SUGGEST ONLY MINOR ADJUSTMENTS WERE NEEDED TO THE LOW
SEVERE PROBABILITIES /5 PERCENT/ ACROSS THE WRN EXTENT OF THIS
THREAT AREA. BENEATH MODEST AND DIFLUENT WEST NORTHWESTERLY
MID/UPPER FLOW...SUBSTANTIVE LOW-LEVEL MOISTENING IS EXPECTED EAST
OF A WEAK SURFACE LOW...AND ALONG A DEVELOPING WARM FRONT... ACROSS
THE SOUTH CENTRAL PLAINS FRIDAY. THIS SHOULD YIELD MODERATE CAPE
/MLCAPE 1000-2000 J PER KG/ ACROSS THE SLIGHT RISK AREA IN THE
PRESENCE OF STEEP LAPSE RATES. MID/UPPER FORCING FOR CONVECTIVE
DEVELOPMENT REMAINS UNCLEAR...AND COULD BE WEAK...BUT STRENGTHENING
WARM ADVECTION NEAR A 30-50 KT SLY LLJ MAY BE SUFFICIENT TO SUPPORT
SCATTERED STORMS...ESPECIALLY FOR FRIDAY NIGHT. HOWEVER...FORECAST
SOUNDINGS SUGGEST STRONG SURFACE HEATING AND THE LOW LEVEL WAA MAY
PROVE SUFFICIENT TO BREACH THE WARM EML/CAP OVER THE SRN EXTENT OF
THE SLIGHT RISK AREA FRIDAY AFTERNOON. A FEW MODELS SUGGEST THIS
POTENTIAL WITH SOME OF THIS ACTIVITY BEING BOUNDARY LAYER BASED...
INITIATING PRIOR TO NIGHTFALL OVER PARTS OF CENTRAL AND ERN OK...
WHERE VERTICAL SHEAR WILL BE SUFFICIENT FOR SUPERCELLS.
...ERN/SRN GA INTO ADJACENT NRN FL...
LOW SEVERE PROBABILITIES /5 PERCENT/ HAVE BEEN EXTENDED SWD TO
INCLUDE THIS REGION. ALTHOUGH GENERALLY WEAK FORCING FOR ASCENT IS
FORECAST WITH THE SRN EXTENT OF THE SPLIT FLOW REGIME...30 KT WNWLY
MIDLEVEL WINDS AND SOME BACKING OF LOW LEVEL FLOW SHOULD RESULT IN
EFFECTIVE BULK SHEAR OF 25-35 KT. THESE FACTORS COMBINED WITH
MIDLEVEL LAPSE RATES APPROACHING 7 C/KM AND MLCAPE 1000-2000 J/KG
SUGGEST PRIMARILY DIURNALLY-DRIVEN MULTICELLS AND A POTENTIAL
SUPERCELL OR TWO. WEAK FORCING SHOULD LIMIT THE COVERAGE OF
STRONGER ACTIVITY.
..PETERS.. 05/26/2011
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