SWODY2
SPC AC 251741
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1241 PM CDT FRI JUN 25 2010
VALID 261200Z - 271200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE CENTRAL/NRN PLAINS TO
THE OH VALLEY/SRN GREAT LAKES REGION...
...NRN/CENTRAL PLAINS TO UPPER MS VALLEY...
MODELS ARE IN GENERAL AGREEMENT SHOWING A PAIR OF SHORTWAVE TROUGHS
WILL PROGRESS EWD FROM MT AND NEWD FROM THE CENTRAL ROCKIES/HIGH
PLAINS REGION ON SATURDAY RESULTING IN DOWNSTREAM HEIGHT FALLS AS
THESE FEATURES PHASE OVER NEB/DAKOTAS BY 27/00Z.
IN THE LOW LEVELS...MODELS DIFFER IN THE PLACEMENT OF AN OUTFLOW
BOUNDARY ATTENDANT TO AN ONGOING MCS AT 12Z SATURDAY OVER THE SWRN
GREAT LAKES. DESPITE THE EARLY PERIOD PLACEMENT OF THIS
BOUNDARY...THERE IS GENERAL MODEL AGREEMENT THAT AN E-W BOUNDARY
WILL BECOME ESTABLISHED FROM SRN WI/NRN IL WNWWD INTO SRN SD BY
SATURDAY AFTERNOON. MEANWHILE...A COLD FRONT ATTENDANT TO THE
PHASING PROGRESSIVE SHORTWAVE TROUGHS SHOULD ADVANCE EWD ACROSS THE
NRN PLAINS...REACHING THE UPPER MS VALLEY TO CENTRAL PLAINS BY 12Z
SUNDAY.
CURRENT THINKING SUGGESTS...HEIGHT FALLS AHEAD OF THE UPSTREAM
SHORTWAVE TROUGHS AND AN EVENTUAL WEAKENING CAP WITHIN A
MOIST/MODERATELY TO STRONGLY UNSTABLE AIR MASS PRECEDING THE COLD
FRONT WILL SUPPORT TSTM DEVELOPMENT ALONG THE AFOREMENTIONED
BOUNDARIES AND WITHIN UPSLOPE REGIME INTO WY. MLCAPE 2000-3000 J/KG
AND EFFECTIVE BULK SHEAR WILL BE SUFFICIENT FOR SUPERCELLS/BOWING
STRUCTURES. SOME UNCERTAINTY EXISTS WITH THE AMOUNT OF STORM
COVERAGE ALONG THE ERN EXTENT OF THE E-W BOUNDARY OVER SRN MN/NRN
IA. HOWEVER...POTENTIAL DOES EXIST FOR ONE OR MORE MCS/S TO DEVELOP
SATURDAY EVENING/NIGHT FROM THE DAKOTAS/NEB AND ALSO THROUGH PARTS
OF THE UPPER MS VALLEY. THUS...LARGE SLIGHT RISK AREA WILL BE
MAINTAINED WITH THIS OUTLOOK.
...LOWER MI/OH VALLEY EWD TO SRN NEW ENGLAND...
MODELS REMAIN FAIRLY CONSISTENT SHOWING A FORWARD PROPAGATING MCS
WILL BE ONGOING AT 12Z SATURDAY ACROSS PARTS OF SRN WI/NRN IL/LAKE
MI. GIVEN MODERATE INSTABILITY AND WLY 40+ KT LLJ EXTENDING INTO
THIS REGION...POTENTIAL EXISTS FOR AT LEAST SOME SEVERE WEATHER
/DAMAGING WINDS AND HAIL/ ACCOMPANYING THIS MCS AT THE START OF DAY
2.
SWLY/WLY LOW LEVEL WINDS EXTENDING INTO LOWER MI...NRN IND/OH SHOULD
ALLOW MOISTURE /SURFACE DEWPOINTS IN THE 60S/ TO ADVECT ENEWD IN
ADVANCE OF THE ONGOING MCS AND BENEATH PLUME OF STEEP MIDLEVEL LAPSE
RATES. THIS WILL SUPPORT MODERATE INSTABILITY AND SUBSEQUENT
POTENTIAL FOR THE MCS TO BE MAINTAINED OR INCREASE IN
INTENSITY...DESPITE A DECREASE IN THE LLJ. GIVEN QPF TRENDS IN
MODEL DATA...THE SLIGHT RISK AREA HAS BEEN EXPANDED NWD ACROSS MORE
OF CENTRAL LOWER MI. DAMAGING WINDS AND HAIL WILL BE POSSIBLE AS
THE MCS PROGRESSES EWD ACROSS LOWER MI AND NRN IND/ NRN OH.
WEAKENING LLJ SUGGESTS TORNADO THREAT SHOULD BE LOW... BUT THIS
THREAT CANNOT BE RULED OUT. THE SEVERE WEATHER THREAT COULD REACH
ERN LAKE ERIE AND PARTS OF THE UPPER OH VALLEY BY LATE
AFTERNOON/EARLY EVENING. HOWEVER...INSTABILITY IS EXPECTED TO
DECREASE WITH EWD EXTENT...RESULTING IN LOWER SEVERE PROBABILITIES
ACROSS SRN NY/CENTRAL PA.
...MID ATLANTIC STATES...
ALTHOUGH A RESIDUAL MOIST AIR MASS EXTENDING NWD FROM THE CAROLINA'S
INTO SRN NJ SHOULD BECOME MODERATELY UNSTABLE ON
SATURDAY...UNCERTAINTY REMAINS REGARDING SUFFICIENT DEEP LAYER
FORCING TO SUPPORT A GREATER COVERAGE OF STORMS/SEVERE THREAT. DEEP
LAYER SHEAR IS EXPECTED TO BE STRONG ENOUGH FOR ORGANIZED STORMS
FROM AT LEAST NC NWD INTO NJ. HOWEVER...THIS OUTLOOK WILL MAINTAIN
LOW SEVERE PROBABILITIES...GIVEN THE UNCERTAINTY IN STRENGTH AND
TIMING OF WEAK IMPULSES ALOFT TRACKING ESEWD ACROSS THIS REGION.
...SRN NEW ENGLAND AND MAINE...
MODELS SUGGEST A COUPLE OF WEAK IMPULSES AND A WEAK SURFACE BOUNDARY
WILL TRACK ESEWD ACROSS NRN NEW ENGLAND DURING DAY 2 WITHIN CYCLONIC
FLOW REGIME ALONG SRN PERIPHERY OF LARGE VORTEX CENTERED OVER ERN
CANADA. WEAK INSTABILITY IS EXPECTED TO LIMIT THE OVERALL SEVERE
WEATHER THREAT...THOUGH DESTABILIZATION INTO DOWNEAST MAINE DURING
PEAK HEATING COMBINED WITH SUFFICIENT DEEP LAYER SHEAR SUGGESTS A
FEW SEVERE STORMS ARE POSSIBLE. FARTHER S...TIMING OF FRONT INTO
SRN NEW ENGLAND DURING THE EVENING AND WEAK INSTABILITY SHOULD TEND
TO LIMIT THE SEVERE WEATHER THREAT ACROSS THIS PART OF NEW ENGLAND.
..PETERS.. 06/25/2010
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