SWODY1
SPC AC 232236
DAY 1 CONVECTIVE OUTLOOK AMEND 1
NWS STORM PREDICTION CENTER NORMAN OK
0536 PM CDT SAT JUL 23 2011
VALID 232230Z - 241200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE CNTRL PLAINS ACROSS
THE UPPER MIDWEST INTO THE GREAT LAKES...
AMENDED FOR SLIGHT MODIFICATIONS IN MID-MO VALLEY AND MAINE
...AMENDMENT...
HAVE ADDED PARTS OF THE MID-MO VALLEY AND OH VALLEY INTO THE SLIGHT
RISK AREA. HAVE REMOVED THE SLIGHT RISK FROM NRN MAINE.
NO CHANGES MADE TO OVERALL PROBABILITY OF SEVERE WEATHER ACROSS THE
CNTRL PLAINS AND UPPER MIDWEST. ROBUST TSTM DEVELOPMENT STILL
APPEARS LIKELY INVOF SFC LOW AND ALONG FRONT AND OUTFLOW BOUNDARIES
FROM SERN SD INTO MN/NRN IA AND EVENTUALLY WRN WI OVER THE NEXT
SEVERAL HOURS. THIS SHOULD OCCUR AS LARGER SCALE FORCING ASSOCIATED
WITH ND SHORT WAVE TROUGH BRUSHES THE REGION COINCIDENT WITH MAX
HEATING.
IN NRN MAINE...ADDED GREATER PROBABILITY OF SEVERE HAIL GIVEN
THERMODYNAMIC REGIME AND SOME POTENTIAL FOR AN ISOLATED
SUPERCELL...IN ADDITION TO WIND THREAT WITH PRE-FRONTAL QLCS.
ELSEWHERE POORLY ORGANIZED PULSE STORMS FROM THE SRN ROCKIES ACROSS
THE CNTRL PLAINS...AND ACROSS THE CAROLINAS/MID ATLANTIC REGIONS
WILL OCCASIONALLY PRODUCE LOCALIZED HIGH/DAMAGING GUSTS THROUGH
EARLY EVENING.
..BROYLES.. 07/23/2011
.PREV DISCUSSION... /ISSUED 1127 AM CDT SAT JUL 23 2011/
...UPPER MS VALLEY REGION...
QLCS CURRENTLY ARCS FROM EXTREME WRN UPPER MI AND NWRN WI INTO
EXTREME SERN MN...WITH STRONGEST STORMS LOCATED ON THE SRN END OF
THE SYSTEM. VISIBLE IMAGERY SHOWS A CORRIDOR OF CLEAR SKIES FROM
EXTREME SERN MN INTO SWRN AND CENTRAL WI /NORTH OF A DOWNSTREAM BAND
OF CONVECTION FROM IA INTO NRN IL/ WHERE STRONGER DIABATIC HEATING
AND DESTABILIZATION ARE EXPECTED TO OCCUR. THIS AREA IS ALSO WITHIN
THE SRN EXTENT OF MODERATE WESTERLY FLOW ALOFT CONTRIBUTING TO
SUFFICIENT DEEP LAYER SHEAR TO MAINTAIN ORGANIZED CONVECTIVE
STRUCTURES INCLUDING BOW ECHOES AND BRIEF SUPERCELLS. CURRENT
STORMS MAY CONTINUE INTO THE AFTERNOON HOURS WITH THE PRIMARY THREAT
FOR DAMAGING WIND GUSTS AND LARGE HAIL.
REDEVELOPMENT OF STORMS IS EXPECTED THIS AFTERNOON OVER PARTS OF THE
ERN DAKS...WRN MN...AND POSSIBLY NWRN IA AS A STRONG UPSTREAM SHORT
WAVE TROUGH ROTATES ENEWD ACROSS ND TOWARD THE CANADIAN BORDER.
SURFACE PATTERN IN ADVANCE OF THE UPPER TROUGH IS COMPLICATED BY
MULTIPLE SYNOPTIC-SCALE AND CONVECTIVELY GENERATED BOUNDARIES. THE
PRIMARY COLD FRONT IS LIKELY TO SPREAD EWD MOVING INTO WRN MN AND
SERN SD BY LATE AFTERNOON/EVENING...WHILE THE OUTFLOW BOUNDARY FROM
THE QLCS SLOWS ITS SWD PROGRESS WITH THE WRN PART OF THE OUTFLOW
POSSIBLY LIFTING NWD OVER NWRN IA. THESE BOUNDARIES WILL PROVIDE A
FOCUS FOR NEW STORM DEVELOPMENT AS CLEARING AND SUBSEQUENT
DESTABILIZATION OCCUR IN THE WAKE OF THE INITIAL QLCS.
A STRONG WESTERLY MID/UPPER JET WILL PROGRESS ACROSS ND AND NRN MN
THIS AFTERNOON...PROVIDING STRONG DEEP LAYER SHEAR OVER THE REGION.
BACKED LOW LEVEL WINDS NORTH OF THE OUTFLOW AND/OR EFFECTIVE
SYNOPTIC WARM FRONT WILL ALSO ENHANCE LOW LEVEL SHEAR/SRH. SEVERE
STORMS /INCLUDING A FEW SUPERCELLS/ ARE EXPECTED TO DEVELOP WITH
LARGE HAIL...DAMAGING WINDS...AND A FEW TORNADOES POSSIBLE DURING
THE INITIAL STAGES. ACTIVITY IS EXPECTED TO EVENTUALLY GROW UPSCALE
INTO ONE OR TWO BOWING SYSTEMS THIS EVENING AS COLD POOLS
CONGEAL...WITH THE PRIMARY THREAT TRANSITIONING TO WIND DAMAGE
TONIGHT.
...SRN GREAT LAKES/MID ATLANTIC STATES...
MOIST AND UNSTABLE AIR MASS PERSISTS /ESPECIALLY FROM IL INTO OH AND
WRN PA/...WHERE SURFACE DEW POINTS ARE IN THE 70S AND VISIBLE
IMAGERY SHOWS AREAS WITH FEW CLOUDS...WHICH IS PROMOTING STRONG
HEATING AND DESTABILIZATION. STRONGER WINDS ALOFT AND VERTICAL
SHEAR ARE GENERALLY NORTH OF THE MORE FAVORABLE THERMODYNAMIC
ENVIRONMENT...HOWEVER WESTERLY MID LEVEL FLOW OF 2O-30 KT SHOULD BE
SUFFICIENT TO SUPPORT ORGANIZED MULTICELL CONVECTIVE STRUCTURES.
STRONGER STORMS WILL BE CAPABLE OF WET MICROBURSTS INTO THE EVENING
HOURS.
...NRN ME...
A STRONG SHORT WAVE TROUGH CURRENTLY OVER SRN QUEBEC IS EXPECTED TO
CONTINUE EWD TODAY...AS A VERY STRONG MID/UPPER LEVEL JET STREAK
SPREADS EWD ACROSS ME. AIR MASS IS EXPECTED TO WARM/DESTABILIZE IN
ADVANCE OF AN APPROACHING COLD FRONT...WITH STORMS
DEVELOPING/SPREADING INTO THE AREA THIS AFTERNOON AND EVENING.
STRONG VERTICAL SHEAR /40-50 KT IN THE LOWEST 6 KM/ SUGGESTS
POTENTIAL FOR SEVERE STORMS WITH WIND DAMAGE BEING THE PRIMARY
THREAT.
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