VALID 041200Z – 051200Z

…NO SVR TSTM AREAS FORECAST…

…SYNOPSIS…
HIGHLY AMPLIFIED UPPER-AIR PATTERN WILL PERSIST ACROSS
CONUS…CENTERED UPON QUASISTATIONARY TROUGHING FROM LS SSWWD ACROSS
MO TO WRN GULF OF MEXICO. EMBEDDED MID-UPPER LOW — NOW EVIDENT IN
MOISTURE CHANNEL IMAGERY OVER KS/MO BORDER REGION — SHOULD FILL
VERY SLIGHTLY WHILE DRIFTING VERY SLOWLY EWD OR NEWD ACROSS WRN MO
THROUGH PERIOD. MEANWHILE…LARGE BERMUDA-HIGH REGIME WILL REMAIN
ANCHORED OVER ATLC. FARTHER W…PERSISTENT ANTICYCLONE INITIALLY
OVER NV SHOULD BE SHUNTED SOMEWHAT SEWD ACROSS AZ…AS HEIGHTS FALL
OVER NWRN CONUS IN ADVANCE OF TROUGH NOW OFFSHORE BC.

AT SFC…REMNANTS OF OLD BAROCLINIC ZONE FROM LOWER GREAT LAKES TO
SRN MS DELTA REGION WILL BECOME MORE DIFFUSE…AS ASSOCIATED THETAE
GRADIENT LOOSENS AND RICH MOISTURE TO ITS E BEGINS TO SHIFT SLOWLY
WWD OVER MS VALLEY AND S TX. WRN SEGMENT OF WEAK COLD FRONT — NOW
OVER EXTREME NWRN ND AND ERN MT — SHOULD STALL OVER
S-CENTRAL/W-CENTRAL MT AS LEE TROUGHING OCCURS IN ADVANCE OF PAC
SHORTWAVE.

…ERN CONUS…
BUILDING OF HEIGHTS OVER ATLC WILL TIGHTEN GRADIENT ALOFT BETWEEN
CENTRAL CONUS TROUGHING AND ATLC ANTICYCLONE…RESULTING IN BROAD
FETCH OF SLIGHTLY STRENGTHENING/DEEP-TROPOSPHERIC FLOW WITH
SUBSTANTIAL SLY COMPONENT FROM NRN GULF ACROSS SRN APPALACHIANS TO
OH VALLEY. MOIST PLUME WILL BECOME SWLY TO WLY ACROSS LOWER GREAT
LAKES AND PORTIONS NEW ENGLAND. EMBEDDED WITHIN THIS
REGIME…SCATTERED TSTMS ARE EXPECTED THROUGHOUT PERIOD. AS
REFLECTED IN ENHANCED TSTM FCST…COVERAGE LIKELY WILL BE MORE
NUMEROUS AND DENSELY CLUSTERED ON MESOBETA SCALE DURING DAYTIME…AS
POCKETS OF SUBTLE DIABATIC HEATING OCCUR IN CLOUD/PRECIP BREAKS.
DAMAGING GUSTS MAY OCCUR FROM PRECIP-LOADING ENHANCED OUTFLOW IN
MOST INTENSE CELLS VIRTUALLY ANYWHERE WITHIN THIS CORRIDOR…WHILE
ISOLATED LARGE HAIL IS MORE PROBABLE FROM CENTRAL APPALACHIANS
REGION NEWD.

LOW-LEVEL SHEAR SHOULD BE RELATIVELY MAXIMIZED GENERALLY BETWEEN
04/18Z-05/06Z BENEATH 35-45 LLJ ACROSS PORTIONS E-CENTRAL GULF
COAST…GA/AL AND NWD TOWARD PORTIONS WV/OH/PA. FCST SOUNDINGS SHOW
ENLARGED 0-1 KM AGL HODOGRAPHS…THOUGH SHEAR VECTORS ASSUME
NEGATIVE VALUES FROM 850-500 MB. NONETHELESS…FAVORABLE LOW-LEVEL
WIND PROFILES COMBINED WITH VERY MOIST/LOW-LCL AIR MASS SUPPORTS
CONDITIONAL POTENTIAL. WITHIN RELATED CORRIDOR OF MRGL
UNCONDITIONAL PROBABILITIES…MESOSCALE FOCI FOR RELATIVELY ENHANCED
SRH/VORTICITY AND POSSIBLE CATEGORICAL ENHANCEMENT OF TORNADO RISK
ARE UNCERTAIN ATTM.

…SWRN CONUS…
ALTHOUGH MIDLEVEL WINDS SHOULD BE SOMEWHAT WEAKER THAN PREVIOUS
DAY…ANOTHER ROUND OF WIDELY SCATTERED TO SCATTERED AFTN TSTMS
SHOULD DEVELOP OVER PORTIONS NM AND MOVE SWD TO SWWD. POTENTIAL
EXISTS FOR ISOLATED HAIL NEAR SVR LEVELS AND A FEW DAMAGING
GUSTS…AS ACTIVITY MOVES ATOP WELL-MIXED SUBCLOUD LAYERS UNDERLYING
MLCAPE 1000-1500 J/KG…LOCALLY HIGHER. OVER 180 DEG OF VEERING
WITH HEIGHT IS FCST…WITH SLYS/SELYS AT SFC BENEATH NLY TO NNELY
FLOW AROUND UPPER 1/3 OF CAPE LAYER. EFFECTIVE SHEAR MAGNITUDES
40-45 KT THEREFORE ARE EVIDENT IN FCST SOUNDINGS DESPITE WEAK
LOW-MIDDLE LEVEL SPEEDS. POTENTIAL SHOULD DIMINISH MARKEDLY AFTER
ABOUT 04Z…AS AIR MASS STABILIZES FROM COMBINATION OF SFC DIABATIC
COOLING AND MAXIMIZED COVERAGE OF CONVECTIVE OUTFLOWS.

…MT…
ISOLATED TO WIDELY SCATTERED TSTMS SHOULD DEVELOP INVOF FRONTAL
ZONE…AND OVER SRN/WRN PORTIONS OF AREA…ALONG HIGHER TERRAIN. SFC
DEW POINTS RANGING FROM LOW 50S TO MID 60S F WILL UNDERLIE
MODERATELY STEEP MIDLEVEL LAPSE RATES…COMBINING WITH INSOLATION TO
YIELD MLCAPE IN 500-1500 J/KG RANGE. THOUGH WEAK LOW-LEVEL WINDS
ARE FCST OVER MOST OF THIS AREA…250-500 MB LAYER FLOW WILL BE
SUFFICIENT TO CONTRIBUTE TO AROUND 30-40 KT EFFECTIVE SHEAR
MAGNITUDES IN SUPPORT OF A FEW ORGANIZED TSTMS. MAIN CONCERN IS
HAIL/GUSTS NEAR SVR LIMITS BETWEEN MID-AFTN AND EARLY EVENING.

..EDWARDS.. 07/04/2013