SWODY1
SPC AC 121921
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0121 PM CST WED DEC 12 2007
VALID 122000Z - 131200Z
..NO SVR TSTM AREAS FORECAST...
..SYNOPSIS...
IN THE MORE ZONAL NORTHERN BRANCH OF THE SPLIT BELT OF POLAR
WESTERLIES EMANATING FROM THE NORTHERN PACIFIC...A VIGOROUS SHORT
WAVE TROUGH IS IN THE PROCESS DIGGING TO THE SOUTHEAST OF THE
CANADIAN/NORTHERN U.S. ROCKIES. THIS FEATURE HAS CONTRIBUTED TO THE
NORTHEASTWARD ACCELERATION OF A SIGNIFICANT IMPULSE OUT OF THE
SOUTHWESTERN U.S. SOUTHERN BRANCH TROUGH.
THE MID-LEVEL CIRCULATION ASSOCIATED WITH THE LATTER SYSTEM IS IN
THE PROCESS OF WEAKENING OVER THE SOUTHERN ROCKIES...AND WILL LIKELY
BECOME INCREASINGLY SHEARED AS IT LIFTS ACROSS THE SOUTH CENTRAL
PLAINS INTO THE MIDDLE MISSISSIPPI VALLEY LATER TODAY THROUGH 12Z
THURSDAY. THIS IS FORECAST TO OCCUR AS THE NORTHERN IMPULSE TURNS
EAST SOUTHEASTWARD INTO THE UPPER MISSISSIPPI VALLEY. BUT...THE
ASSOCIATED FORCING IS EXPECTED TO CONTRIBUTE TO MORE SUBSTANTIAL
DEVELOPMENT OF A LOW AMPLITUDE SURFACE FRONTAL WAVE LIFTING OUT OF
THE LOWER MISSISSIPPI VALLEY...INTO PARTS OF THE MIDDLE/UPPER OHIO
VALLEY BY EARLY THURSDAY.
..EASTERN TEXAS THROUGH THE OHIO VALLEY...
THE SOUTHEASTERN STATES SUBTROPICAL RIDGE IS SLOWLY BEGINNING TO
WEAKEN. BUT...A RELATIVELY WARM MID-LEVEL ENVIRONMENT ASSOCIATED
WITH IT IS CAPPING THE MOIST BOUNDARY LAYER TO THE SOUTHEAST OF
SURFACE FRONT ADVANCING ACROSS WESTERN GULF COASTAL AREAS...AND
TOWARD THE EASTERN GULF STATES/UPPER TENNESSEE VALLEY/CENTRAL
APPALACHIANS.
CONSIDERABLE INHIBITION EXISTS EVEN TO THE IMMEDIATE COOL SIDE OF
THE SURFACE FRONT...FROM CENTRAL/EASTERN TEXAS THROUGH THE LOWER
OHIO VALLEY...WHERE AN ELEVATED MOIST LAYER LINGERS ABOVE THE
FRONTAL INVERSION. BUT...ENHANCED ISENTROPIC ASCENT AHEAD OF THE
SOUTHERN BRANCH IMPULSE HAS BEEN SUFFICIENT TO SUPPORT SCATTERED
ONGOING STORMS ACROSS PARTS OF NORTHERN TEXAS. THE CONVECTION IS
MOSTLY BASED IN THE 850-700 MB LAYER...WITH ONLY VERY WEAK CAPE ON
THE ORDER OF A COUPLE HUNDRED J/KG AT BEST. SO...STORMS ARE
EXPECTED TO REMAIN WEAK...AND MAY NEVER BECOME PARTICULARLY
WIDESPREAD. HOWEVER...ACTIVITY PROBABLY WILL CONTINUE TO GRADUALLY
DEVELOP EAST NORTHEASTWARD ACROSS THE ARKLATEX REGION AND PARTS OF
THE LOWER OHIO/TENNESSEE VALLEYS THROUGH THE REMAINDER OF THE
PERIOD. BY OR SHORTLY AFTER 12Z THURSDAY...SOME INCREASE IN
COVERAGE COULD ACCOMPANY THE DEVELOPING FRONTAL WAVE ACROSS THE
UPPER OHIO VALLEY/CENTRAL APPALACHIANS.
..SOUTHERN ROCKIES...
WEAK DESTABILIZATION HAS OCCURRED BENEATH THE MID-LEVEL COLD CORE OF
THE SOUTHERN BRANCH IMPULSE. WHILE AN ISOLATED THUNDERSTORM APPEARS
POSSIBLE...MAINLY NEAR THE SACRAMENTO MOUNTAINS OF SOUTH CENTRAL NEW
MEXICO...NEARLY NEGLIGIBLE CONVECTIVE POTENTIAL IS EXPECTED TO
DIMINISH BY LATE AFTERNOON AS UPPER SYSTEM LIFTS INTO THE SOUTH
CENTRAL PLAINS.
.KERR.. 12/12/2007
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