Wednesday, September 22, 2010

DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 221627
SWODY1
SPC AC 221625

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1125 AM CDT WED SEP 22 2010

VALID 221630Z - 231200Z

...THERE IS A SLGT RISK OF SVR TSTMS OVER PORTIONS OF THE NRN AND
CNTRL PLAINS INTO UPPER MIDWEST...

...THERE IS A SLGT RISK OF SVR TSTMS OVER CNTRL/SRN NEW ENGLAND INTO
THE MID ATLANTIC STATES...

...NRN/CNTRL PLAINS INTO THE UPPER MIDWEST...

ELEVATED...STRONG TO SEVERE TSTMS IN PROGRESS THIS MORNING OVER NERN
NEB/SERN SD ARE EXPECTED TO MOVE/DEVELOP EWD/NEWD TODAY INTO
CNTRL/SRN MN/NRN IA IN ADVANCE OF MIDLEVEL IMPULSE TRANSLATING ENEWD
ACROSS SD/NEB. FORCING ASSOCIATED WITH THIS FEATURE COUPLED WITH AN
ENHANCED ZONE OF WARM THERMAL AND MOISTURE ADVECTIONS ALONG SSWLY
LLJ STRENGTHENING TO 40-50 KT WILL SUSTAIN AN ENVIRONMENT
CHARACTERIZED BY MUCAPE OF 1500-3000 J/KG --REF. 12Z OAX/LBF
SOUNDINGS-- AND SUFFICIENT CLOUD-BEARING SHEAR TO SUPPORT SUPERCELLS
CAPABLE OF MAINLY LARGE HAIL TO THE N OF RETREATING WARM FRONT.

WITHIN SYSTEM WARM SECTOR...THE COMBINATION OF STRONG DAYTIME
HEATING...BOUNDARY LAYER DEW POINTS IN THE 60S TO AROUND 70F AND
STEEP LAPSE RATES WILL CONTRIBUTE TO A MODERATELY UNSTABLE...BUT
CAPPED AIR MASS WITH MLCAPE INCREASING TO 1500-2500 J/KG. GIVEN THE
EARLY ENEWD PROGRESSION OF ABOVE-MENTIONED SHORT WAVE TROUGH ALONG
NRN EXTENSION OF THE DEVELOPING WARM SECTOR OVER NEB/IA...THERE IS
SOME UNCERTAINTY AS TO HOW SURFACE-BASED... DIURNALLY-ENHANCED TSTM
ACTIVITY WILL EVOLVE. CURRENT THINKING IS THAT PERHAPS THE SWD
EXTENSION OF PERSISTENT...ELEVATED TSTM COMPLEX WILL BECOME
PROGRESSIVELY MORE SURFACE-BASED AS SYNOPTIC WARM FRONT RETREATS NWD
THROUGH NEB/IA TOWARD THE SD/MN BORDERS.

ANY STORMS THAT CAN BECOME ROOTED IN THE BOUNDARY LAYER WILL
EXPERIENCE A MOIST AND STRONGLY SHEARED LOWER-TROPOSPHERIC
ENVIRONMENT INVOF OF WARM FRONT WHERE A FEW TORNADOES WILL BE
POSSIBLE IN ADDITION TO LARGE HAIL AND DAMAGING WIND GUSTS.
ADDITIONAL...DIURNALLY-ENHANCED STORMS WILL BE POSSIBLE IN ADVANCE
OF DEEPENING LEE CYCLONE OVER WRN NEB WHERE ENVIRONMENT WILL ALSO BE
SUPPORTIVE OF SUPERCELLS CAPABLE OF LARGE HAIL...DAMAGING WINDS AND
PERHAPS A COUPLE TORNADOES.

STRONG/SEVERE TSTMS ARE EXPECTED TO CONTINUE OVERNIGHT...PERHAPS
EXPANDING IN AREAL COVERAGE...IN ASSOCIATION WITH NEXT SIGNIFICANT
SHORT WAVE TROUGH WHICH WILL EMERGE FROM THE CNTRL HIGH PLAINS IN
ADVANCE OF GREAT BASIN LARGE-SCALE TROUGH. LARGE HAIL AND STRONG
WIND GUSTS WILL BE THE PRIMARY HAZARDS WITH THE MOST INTENSE STORMS.


...CNTRL/SRN NEW ENGLAND INTO THE MID ATLANTIC STATES...

12Z UPPER-AIR ANALYSIS AND MORNING WATER VAPOR IMAGERY INDICATE A
SHORT WAVE TROUGH OVER THE LOWER GREAT LAKES AND UPPER OH VALLEY
WILL PROGRESS EWD TODAY IN TANDEM WITH SURFACE COLD FRONT THROUGH
THE REGION. WHILE THE AMBIENT PRE-FRONTAL AIR MASS IS NOT OVERLY
MOIST...VISIBLE SATELLITE IMAGERY SUGGESTS THAT STRONG DIABATIC
HEATING SHOULD OCCUR...CONTRIBUTING TO STEEPENING LAPSE RATES AND
MLCAPE VALUES INCREASING TO 1000-1500 J/KG. FORCING FOR ASCENT
ASSOCIATED WITH SHORT WAVE TROUGH AND FRONTAL UPLIFT SHOULD FOSTER
SCATTERED TSTM DEVELOPMENT BY AFTERNOON ALONG/AHEAD OF COLD FRONT
OVER CNTRL/ERN PARTS OF NY/PA WITH ADDITIONAL...MORE ISOLATED STORM
FORMATION SWD ALONG LEE TROUGH SITUATED OVER THE PIEDMONT.

FORECAST SOUNDINGS INDICATE STRENGTHENING WSWLY/WLY TROPOSPHERIC
FLOW WITH THE APPROACH OF THE SHORT WAVE TROUGH WITH SETUP BECOMING
INCREASINGLY FAVORABLE OF BOWING LINE SEGMENTS CAPABLE OF MAINLY
DAMAGING WIND GUSTS THROUGH THIS EVENING. VERTICAL SHEAR IS
EXPECTED TO DIMINISH WITH SWD EXTENT ALONG THE LEE TROUGH...THOUGH
THERMODYNAMIC ENVIRONMENT WILL STILL BE SUPPORTIVE OF LOCALLY STRONG
WINDS.

...ERN GREAT BASIN...

LARGE-SCALE FORCING FOR ASCENT IS FORECAST TO STEADILY STRENGTHEN
OVER THE REGION TODAY IN ADVANCE OF LARGE-SCALE TROUGH PROGRESSING
EWD THROUGH CA/NV AND THE LOWER CO VALLEY. AT THE SAME
TIME...INTENSIFYING SURFACE CYCLONE OVER WRN UT WILL BEGIN TO DRAW
THE NRN EXTENSION OF GULF OF CA MOISTURE SURGE CURRENTLY OBSERVED
OVER CNTRL/SRN AZ INTO THE AREA...SUPPORTING MODEST AIR MASS
DESTABILIZATION THROUGH THE DIURNAL HEATING CYCLE. GIVEN THE
CONCURRENT INCREASE IN VERTICAL SHEAR AND DYNAMIC FORCING FOR
ASCENT...SETUP WILL FAVOR THE DEVELOPMENT OF A FEW STRONG TO
MARGINALLY SEVERE STORMS ALONG/AHEAD OF PACIFIC FRONT WITH A RISK
FOR LOCALLY DAMAGING WIND GUSTS AND PERHAPS SOME HAIL.

..MEAD/GRAMS.. 09/22/2010

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