Tuesday, September 11, 2007

DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 110601
SWODY1
SPC AC 110558

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1258 AM CDT TUE SEP 11 2007

VALID 111200Z - 121200Z

..NO SVR TSTM AREAS FORECAST...

..SYNOPSIS...

DYNAMIC LARGE-SCALE PATTERN IS FORECAST ACROSS NERN QUARTER OF THE
NATION AS DIGGING MID AND UPPER-LEVEL JET STREAKS CONTRIBUTE TO
CONSIDERABLE INTENSIFICATION OF UPPER TROUGH OVER THE LOWER GREAT
LAKES INTO NEW ENGLAND. IN THE LOW LEVELS...SURFACE LOW ASSOCIATED
WITH THIS SYSTEM IS FORECAST TO DEEPEN AS IT DEVELOPS NEWD FROM SWRN
ONTARIO INTO CNTRL QUEBEC. TRAILING STRONG COLD FRONT WILL PUSH EWD
THROUGH THE UPPER OH VALLEY AND LOWER GREAT LAKES TODAY...AND
EVENTUALLY THROUGH NEW ENGLAND AND THE MID ATLANTIC COAST TONIGHT.

..NORTHEAST...

COMPLEX LARGE-SCALE PATTERN IS EXPECTED TODAY OWING TO THE PRESENCE
OF MULTIPLE SURFACE BOUNDARIES AND THE EARLY ARRIVAL OF A WEAKER
SHORT WAVE THAT WILL PRECEDE PRIMARY UPPER SYSTEM. IT APPEARS THAT
THE MOST VIGOROUS CONVECTIVE DEVELOPMENT WILL BE FOCUSED LATER TODAY
ALONG SLOW-MOVING FRONTAL BOUNDARY EXTENDING FROM THE LOWER HUDSON
VALLEY SWWD THROUGH THE DELMARVA...AS WELL AS ALONG MORE PROGRESSIVE
COLD FRONT PUSHING EWD THROUGH NY/PA...EVENTUALLY INTO NEW ENGLAND.

LATEST MODEL GUIDANCE SUGGESTS THAT CLOUDS/PRECIPITATION ASSOCIATED
WITH WEAKER LEAD IMPULSE MAY TEND TO LIMIT AIR MASS DESTABILIZATION
WITHIN SYSTEM WARM SECTOR TODAY. HOWEVER CURRENT SURFACE
OBSERVATIONS AND GPS IPW DATA SHOW THE PRESENCE OF A MOIST
ENVIRONMENT WHICH SHOULD BE MAINTAINED AS SWLY LLJ INCREASES TO
30-40 KT. THIS MOISTURE COUPLED WITH SOME DIABATIC HEATING AND
INCREASING HEIGHT FALLS SHOULD CONTRIBUTE AT LEAST A MARGINALLY
UNSTABLE THERMODYNAMIC ENVIRONMENT WITH SBCAPES OF 500-700 J/KG.

VERTICAL SHEAR WILL CONCURRENTLY STRENGTHEN AS MID AND HIGH-LEVEL
JET STREAKS PROPAGATE EWD INTO THE LOWER GREAT LAKES WITH SUFFICIENT
DEEP LAYER VERTICAL SHEAR FOR SUPERCELLS AND BOWING LINE SEGMENTS
CAPABLE OF DAMAGING WINDS...SOME HAIL AND PERHAPS A BRIEF TORNADO.
CONSIDERABLE UNCERTAINTY STILL EXISTS WITH REGARD TO THE DEGREE AND
DISTRIBUTION OF CONVECTIVE INSTABILITY LATER TODAY ACROSS SYSTEM
WARM SECTOR. THEREFORE...ONLY LOW SEVERE PROBABILITIES WILL BE
MAINTAINED ATTM.

..NRN LOWER MI...

PROXIMITY OF COLD UPPER TROUGH WILL RESULT IN THE DEVELOPMENT OF
STEEP LAPSE RATES AND WEAK CONVECTIVE INSTABILITY AHEAD OF STRONG
COLD FRONT MOVING THROUGH THE REGION TODAY. MESOSCALE FORCING ALONG
COLD FRONT SHOULD SUPPORT A LOW-TOPPED CONVECTIVE LINE OR CLUSTERS
OF TSTMS THIS AFTERNOON WITH THE POTENTIAL FOR SOME MARGINALLY
SEVERE HAIL AND STRONG WIND GUSTS.

..AZ/NM...

DIURNAL TSTMS ARE EXPECTED TO DEVELOP THIS AFTERNOON OVER THE
COMPLEX TERRAIN WITHIN A STEEP LAPSE RATE ENVIRONMENT WITH SBCAPES
OF 500-800 J/KG. FORECAST SOUNDINGS SUGGEST THAT VERTICAL SHEAR
WILL REMAIN RELATIVELY WEAK...THOUGH THE STEEP LAPSE RATES SHOULD
SUPPORT A FEW STRONG UPDRAFTS CAPABLE OF HAIL AND/OR LOCALLY
DAMAGING WIND GUSTS THROUGH THIS EVENING.

.MEAD/JEWELL.. 09/11/2007

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