DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 270615
SWODY1
SPC AC 270613

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0113 AM CDT FRI APR 27 2007

VALID 271200Z - 281200Z

..THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE MID ATLANTIC
STATES...

..THERE IS A SLGT RISK OF SVR TSTMS FOR PORTIONS OF OK AND NORTHERN
TX...

..SYNOPSIS...
INITIAL UPPER LOW OVER THE WESTERN GREAT LAKES IS FORECAST TO
WEAKEN/LIFT NORTHEASTWARD INTO EASTERN CANADA TODAY...WHILE SEVERAL
TRAILING SHORTWAVE IMPULSES CROSSING THE PLAINS AND TENNESSEE
VALLEY/MID ATLANTIC STATES REINFORCE AN EVOLVING BROAD UPPER TROUGH
OVER THE EASTERN THIRD OF THE COUNTRY. IN THE WEST...BROAD UPPER
RIDGE WILL AMPLIFY OVER MUCH OF THE WESTERN STATES BENEATH STRONG
PACIFIC JET NOSING INTO THE PACIFIC NORTHWEST/WESTERN CANADA.

..MID ATLANTIC STATES THROUGH EARLY EVENING...
PRIMARY COLD FRONT WILL PUSH EASTWARD FROM THE SPINE OF THE
APPALACHIANS TOWARD THE MID ATLANTIC SEABOARD THROUGH EARLY EVENING.
AHEAD OF THE FRONT...POCKETS OF STRONGER DAYTIME HEATING AND
DEWPOINTS IN THE 60S F WILL CONTRIBUTE TO AMPLE INSTABILITY FOR
SCATTERED STRONG/SEVERE STORMS FROM LATE MORNING THROUGH EARLY
EVENING...ESPECIALLY FROM THE DELMARVA VICINITY TO THE
PIEDMONT/COASTAL AREAS OF THE CAROLINAS. NAM/NAMKF FORECAST
SOUNDINGS SUGGEST MLCAPE VALUES OF 750-1000 J/KG IN THE AMBIENT WARM
SECTOR. VERTICAL SHEAR PROFILES WILL SUPPORT THE EVOLUTION OF SOME
SEMI-DISCRETE AND/OR LINE EMBEDDED SUPERCELLS...WITH LARGE
HAIL/DAMAGING WINDS AND A FEW TORNADOES POSSIBLE.

..OK AND WESTERN/NORTHERN TX THIS AFTERNOON/EVENING...
WITH SHORTWAVE TROUGH EXPECTED TO CROSS THE SOUTH CENTRAL PLAINS
TODAY...ASSOCIATED LARGE SCALE ASCENT IS EXPECTED TO LEAD TO
INCREASING THUNDERSTORM COVERAGE ACROSS MUCH OF OK AND PORTIONS OF
NORTHERN/WESTERN TX THROUGH THE AFTERNOON HOURS. IN THE WAKE OF THE
EAST COAST UPPER TROUGH/COLD FRONT...MODEST BOUNDARY MOISTURE WILL
GRADUALLY RETURN NORTHWESTWARD ACROSS TX/OK AROUND SURFACE HIGH
CENTERED OVER THE ARKLATEX. ALTHOUGH SURFACE DEWPOINTS WILL
GENERALLY BE LIMITED TO THE MIDDLE 50S F OR LESS...AFTERNOON HEATING
WILL LEAD TO MODEST CONVECTIVE INSTABILITY WITH MLCAPES UP TO 1000
J/KG. FORECAST SOUNDINGS DEPICT STRONGLY VEERING WIND PROFILES WITH
EFFECTIVE BULK SHEAR GREATER THAN 40 KT...SUPPORTIVE OF SOME
SUPERCELLS WITH A RISK OF LARGE HAIL AND STRONG WIND GUSTS.

.GUYER/CARBIN.. 04/27/2007

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