VALID 041300Z – 051200Z

…NO SVR TSTM AREAS FORECAST…

…SYNOPSIS…
PATTERN WILL REMAIN AMPLIFIED ACROSS THE LWR 48 THROUGH EARLY
FRI…BUT THERE WILL BE SOME CHANGES. THE GRT BASIN RIDGE SHOULD
CONTINUE TO RETREAT SWD AS A SERIES OF IMPULSES IN THE WLYS LOWER
HEIGHTS ACROSS SW CANADA AND THE PACIFIC NW. FARTHER E…EXPECT
CNTRL U.S. UPR TROUGH/LOW TO GRADUALLY WEAKEN WHILE REMAINING NEARLY
STNRY OR DRIFTING SLIGHTLY E. AT THE SAME TIME…SATELLITE INDICATES
THAT RETROGRESSION OF THE WRN ATLANTIC RIDGE HAS ENDED. THE SYSTEM
WILL…HOWEVER…REMAIN STRONG AND MAINTAIN EXISTING TIGHT HEIGHT
GRADIENT ACROSS THE ERN U.S.

AT LWR LVLS…WEAK FRONT/INVERTED TROUGH FROM THE CNTRL GULF CST TO
THE MID-OH VLY SHOULD BECOME INCREASINGLY DIFFUSE TODAY AS WEAK LOW
PRESSURE NOW IN THE N CNTRL GULF ADVANCES NNE ALONG IT.
ELSEWHERE…ERN PART OF COLD FRONT OVER THE NRN PLNS SHOULD WEAKEN
WHILE WRN PART STALLS OVER SRN/WRN MT IN RESPONSE TO LEE TROUGHING
AHEAD OF APPROACHING PACIFIC SHORTWAVE IMPULSE.

…ERN GULF CST NNE TO LWR GRT LKS/NORTHEAST TODAY…
SEASONABLY STRONG HEIGHT GRADIENT WILL PERSIST ALONG AN ARC FROM THE
NERN GULF OF MEXICO NNE ALONG THE APPALACHIANS INTO THE UPR OH
VLY…LWR GRT LKS…AND THE NORTHEAST THROUGH TNGT. COINCIDENT WITH
THIS FLOW WILL BE A PLUME OF DEEP…MOISTURE-RICH AIR….WITH PW AOA
2 INCHES FROM ERN KY SWD TO THE GULF…AND AROUND 1.75 INCHES FROM
OH INTO NEW ENGLAND.

WITH WIDESPREAD CLOUD COVER/SHOWERS ALREADY IN PLACE FROM MUCH OF OH
SSW TO THE ERN GULF CST…SFC HEATING WILL BE MINIMAL. BUT GIVEN
MOISTURE-RICH ENVIRONMENT AND STRONG MEAN FLOW…SETUP COULD YIELD
OCCASIONAL POCKETS OF LOW-TOPPED CONVECTION/STORMS POSING A RISK FOR
ISOLD PRECIP-ENHANCED WIND GUSTS. AND…GIVEN FRICTIONALLY-DRIVEN
BACKING OF LOW-LVL FLOW…A RISK ALSO WILL EXIST FOR ISOLD
TORNADOES. THIS RISK MAY BE GREATEST OVER THE FL PANHANDLE AND CSTL
BEND…WHERE THE GREATEST LOW-LVL BUOYANCY SHOULD EXIST AND WHERE
APPROACH OF WEAK SFC WAVE FROM THE N CNTRL GULF WILL MAXIMIZE SELY
LOW-LVL WINDS.

SATELLITE SUGGESTS THAT SFC HEATING WILL BE SOMEWHAT GREATER FARTHER
NE…FROM WV AND WRN MD NEWD THROUGH PA/NY INTO NEW ENGLAND.
ANTICYCLONIC NATURE OF LARGE-SCALE FLOW WILL KEEP FORCING FOR ASCENT
LIMITED…AND LOW-LVL FLOW WILL BE WEAK. BUT SUBSTANTIAL /30-40 KT/
DEEP…SWLY MID-LVL WINDS IN THE PRESENCE OF EVEN MODERATE SFC
HEATING COULD PROMOTE THE DEVELOPMENT OF ISOLD SMALL-SCALE BOWING
SEGMENTS WITH LOCALLY DMGG WIND AND PERHAPS A TORNADO. SUCH A THREAT
SHOULD BE GREATEST WITH ANY SUSTAINED STORMS THAT DO
FORM…ESPECIALLY FROM UPSTATE NY INTO ME THIS AFTN THROUGH EARLY
TNGT.

…SW U.S. THIS AFTN/EVE…
SWD SHIFT OF GRT BASIN RIDGE INTO AZ WILL RESULT IN DIMINISHED NLY
FLOW OVER THE SRN RCKYS AND FOUR CORNERS REGION RELATIVE TO RECENT
DAYS…WITH MINIMAL CHANGE IN MOISTURE. NEVERTHELESS…SFC
HEATING/TERRAIN CIRCULATIONS SHOULD FOSTER ANOTHER ROUND OF
SCTD STRONG TO LOCALLY SVR AFTN/EVE STORMS OVER THE HIGHER
ELEVATIONS OF NM AND THE AZ RIM COUNTRY. AS THESE STORMS
MOVE/DEVELOP MAINLY S OR SWWD…POTENTIAL WILL EXIST FOR
ISOLD HAIL AND A FEW DMGG WIND GUSTS GIVEN 1000-1500 J/KG MLCAPE
AMIDST A DEEP…WELL-MIXED BOUNDARY LAYER. THE STRONGEST/MOST
SUSTAINED STORMS SHOULD OCCUR OVER CNTRL/SRN NM AND PERHAPS FAR W
TX…WHERE 20+ KT NLY 500 MB FLOW WILL CONTRIBUTE TO
35+ KT DEEP SHEAR.

…MT THIS AFTN/EVE…
ISOLD TO WDLY SCTD TSTMS SHOULD FORM NEAR STALLED FRONT OVER SRN/WRN
MT THIS AFTN…AND OVER THE HIGHER TERRAIN. WITH SFC DEW POINTS
MAINLY IN THE UPR 50S TO MID 60S F AND MODERATELY STEEP MID-LVL
LAPSE RATES…SFC HEATING SHOULD YIELD 500-1500 J/KG MLCAPE. LOW-LVL
WINDS WILL REMAIN WEAK…BUT 30+ KT WLY 500 MB FLOW WILL PROVIDE
AMPLE DEEP SHEAR FOR ORGANIZED/SUSTAINED STORMS. LARGE-SCALE FORCING
WILL BE MODEST EVEN AFTER ARRIVAL OF LEAD UPR IMPULSE /NOW IN WA/
INTO W CNTRL MT LATE IN THE DAY. WHILE STORM COVERAGE LIKELY WILL
REMAIN LIMITED…A CONDITIONAL RISK FOR SVR HAIL/WIND WILL
EXIST…ESPECIALLY FROM MID-LATE AFTN THROUGH EARLY EVE.

..CORFIDI/MOSIER.. 07/04/2013