SPC AC 210550
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1150 PM CST THU DEC 20 2007
VALID 221200Z - 231200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
PROGRESSIVE MID/UPPER LEVEL WAVE TRAIN TO PERSIST OVER NORTH AMERICA
INTO THE WEEKEND WITH LARGE SCALE TROUGH AMPLIFICATION LIKELY ACROSS
THE CNTRL CONUS THROUGH SATURDAY. AS ONE VIGOROUS SRN BRANCH IMPULSE
MOVES OFF THE SOUTHEAST U.S. COAST THROUGH TODAY...ANOTHER STRONG
SYSTEM IS ALREADY MOVING INTO THE SOUTHWEST/FOUR CORNERS. THIS NEXT
DISTURBANCE IS FORECAST TO EJECT NEWD FROM THE SRN PLAINS DURING
SATURDAY...EVENTUALLY MERGING WITH ITS NRN BRANCH REFLECTION...NOW
DEVELOPING SEWD ACROSS THE CANADIAN ROCKIES. THE RESULTING
DEEP-LAYER CYCLONE IS FORECAST TO ENCOMPASS MUCH OF THE UPPER MS
VALLEY/GREAT LAKES AREAS BY EARLY SUNDAY.
PRIOR TO SIGNIFICANT DEEPENING OF THE GREAT LAKES CYCLONE...STRONG
DYNAMIC FORCING FOR ASCENT WILL ACCOMPANY THE SRN BRANCH IMPULSE
OVER THE SRN PLAINS. THIS FORCING WILL CONTRIBUTE TO CYCLOGENESIS
ALONG THE COLD FRONT OVER TX/OK AREA BY EARLY SATURDAY. RESULTING
SURFACE LOW WILL TRACK NEWD FROM AR TO THE MIDWEST THROUGH SATURDAY
NIGHT SUSTAINED BY STRENGTHENING 100KT 500MB JET STREAK AND POTENT
MID LEVEL HEIGHT FALLS. TRAILING COLD FRONT WILL SWEEP RAPIDLY EAST
FROM THE LOWER MS VALLEY TO THE TN VALLEY/DEEP SOUTH THROUGH
DAYBREAK SUNDAY.
...ARKLATEX ACROSS LOWER MS VALLEY...
NWRN GULF CONTINUES TO UNDERGO ONLY GRADUAL COOL SEASON MODIFICATION
DUE TO SERIES OF RECENT WEAK FRONTAL PASSAGES. MOST RECENT ANALYSIS
INDICATES 0.5-1C POSITIVE SST ANOMALY WITH LOW 60F SURFACE DEWPOINTS
CURRENTLY RESIDING WITHIN 50-100 MILES OF THE COAST. DESPITE
RELATIVELY SHORT RECOVERY TIME IN THE WAKE OF MOST RECENT SHORT WAVE
PASSAGE...IT APPEARS REASONABLE TO EXPECT AT LEAST LOW 60S F
DEWPOINTS WILL BE TRANSPORTED NWD/INLAND AHEAD OF THE NEXT FRONTAL
SYSTEM FORECAST TO APPROACH THE AREA LATE SATURDAY.
RESULTING WEAK WARM SECTOR DESTABILIZATION /MUCAPE 200-400 J PER KG/
MAY FIRST BE REALIZED BY INCREASING CONVECTION ROOTED ABOVE A STABLE
BOUNDARY LAYER...FROM THE ARKLATEX NEWD INTO AR AND THE OZARKS.
POTENT FORCING AND EFFECTIVE SHEAR ACROSS THESE AREAS MAY ACT TO
OVERCOME LACK OF GREATER INSTABILITY TO SUPPORT FAST-MOVING ISOLATED
TSTMS EMBEDDED WITHIN AN EXPANDING STRATIFORM RAIN SHIELD FROM AR TO
TN THROUGH SATURDAY NIGHT. A LOW PROBABILITY OF MARGINALLY SEVERE
HAIL/GUSTY WINDS MAY ACCOMPANY A COUPLE OF THE STRONGER STORM
UPDRAFTS/DOWNDRAFTS.
FARTHER SOUTH...FROM SRN AR ACROSS LA/MS...LARGE SCALE FORCING WILL
BE MORE LIMITED AS DPVA/STRONGER HEIGHT FALLS REMAIN NORTH OF THE
REGION. HOWEVER...LOW LEVEL FRONTAL CIRCULATION SHOULD BE SUFFICIENT
TO INITIATE A NARROW SQUALL LINE IN WEAKLY UNSTABLE REGIME. GIVEN
FAST TRANSLATION OF THE MID/UPPER LEVEL SYSTEM AND STRONG VERTICAL
SHEAR...A FEW FAST-MOVING LINE SEGMENTS CAPABLE OF DAMAGING WINDS
APPEAR POSSIBLE. OVERALL SEVERE POTENTIAL CURRENTLY APPEARS LIMITED
GIVEN WEAK FORCING/INSTABILITY ADVERTISED IN LATEST GUIDANCE.
THUS...ONLY LOW /5 PERCENT/ SEVERE PROBABILITIES ARE WARRANTED AT
THIS TIME.
..CARBIN.. 12/21/2007
CLICK TO GET WUUS02 PTSDY2 PRODUCT
NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z
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