SWODY1
SPC AC 210551
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1251 AM CDT THU JUL 21 2011
VALID 211200Z - 221200Z
...THERE IS A SLGT RISK OF SVR TSTMS NRN-CNTRL NEW ENGLAND...
...THERE IS A SLGT RISK OF SVR TSTMS CNTRL PLAINS/MIDDLE MO
VALLEY...
UPPER RIDGE ACROSS MUCH OF THE CNTRL AND ERN U.S. WILL DEAMPLIFY
TODAY AS A STRONG BELT OF WLY/S PERMEATE MUCH OF THE NRN TIER OF
STATES IN RESPONSE TO A SERIES OF UPPER TROUGHS PROGRESSING EWD N OF
THE U.S./CANADIAN BORDER. MOST NOTABLE UPPER FEATURE WILL BE A
DISTURBANCE--CONVECTIVELY MODIFIED--AND EMBEDDED ON THE SRN FRINGE
OF THE MANITOBA/WRN ONTARIO UPPER TROUGH...THAT WILL MOVE QUICKLY
EWD FROM ERN ONTARIO TO THE ST. LAWRENCE SEAWAY BY MIDDAY AND THEN
TO THE CANADIAN MARITIMES BY FRIDAY MORNING. ANOTHER MID-LEVEL
PERTURBATION WILL DRIFT EWD FROM THE CNTRL HIGH PLAINS TO THE
CORNBELT AHEAD OF ANOTHER DIGGING SPEED MAX IN THE PACIFIC NW.
IN THE LOW LEVELS...A COLD FRONT IN ASSOCIATION WITH THE SHORTWAVE
TROUGH AFFECTING NRN NEW ENGLAND WILL PUSH EWD THROUGH THIS REGION
DURING THE AFTERNOON/EVENING HOURS. THIS BOUNDARY WILL PROBABLY BE
MODULATED TO A CERTAIN EXTENT BY ONGOING CLUSTER/MCS ACROSS
ONTARIO/QUEBEC THAT MAY PERSIST AND POSSIBLY SERVE AS AN EFFECTIVE
IMPETUS FOR SEVERE STORM DEVELOPMENT FOR NEW ENGLAND. TRAILING
PORTION OF THIS BOUNDARY WILL EXTEND WWD THROUGH THE SRN GREAT LAKES
INTO THE CNTRL HIGH PLAINS WHERE THE FRONT WILL RETREAT NWD ACROSS
PARTS OF THE CORNBELT LATE. HERE TOO...ISOLD STRONG-SEVERE STORMS
ARE FORECAST TO DEVELOP INVOF THE BOUNDARY ON THE SRN FRINGE OF THE
STRONGER WLY/S.
...NRN-CNTRL NEW ENGLAND...
DETERMINISTIC MODELS INDICATE THAT STRONG SURFACE HEATING...ALONG
WITH INCREASING LOW LEVEL MOISTURE...FED BY A PLUME OF UPPER 60S TO
LOWER 70S DEWPOINTS...AND A PIECE OF THE CNTRL U.S. EML WILL
PROBABLY YIELD 1000-2500 J/KG MLCAPE BY EARLY-MID AFTERNOON. SOME
UNCERTAINTY EXISTS REGARDING THE DEGREE OF DESTABILIZATION WITH
FARTHER N EXTENT DUE PRIMARILY TO THE EVOLUTION OF ANY MCS THAT
MOVES INTO THE REGION FROM CANADA BY LATE MORNING-EARLY AFTERNOON.
REGARDLESS...IT APPEARS MORE THAN ADEQUATE INSTABILITY SHOULD
DEVELOP DUE TO INCREASING LOW LEVEL MOISTURE FROM THE SW-W GIVEN
APPRECIABLE LOWER TO MID-LEVEL FLOW ASSOCIATED WITH THE APPROACHING
SHORTWAVE TROUGH. INCREASING SHEAR PROFILES ACROSS THE REGION WILL
STRONGLY FAVOR ORGANIZED STORMS --INCLUDING SUPERCELLS/FORWARD
PROPAGATING SYSTEM WITH BOWING SEGMENTS-- AND MAY BE CONDUCIVE FOR A
CORRIDOR OF DMGG WINDS...ESPECIALLY IN CLOSER PROXIMITY TO THE
SURFACE LOW /I.E. NRN 2/3RDS MAINE/. MODEL GUIDANCE INDICATES THAT
THE SURFACE LOW WILL UNDERGO SUBSTANTIAL DEEPENING THROUGH THE
AFTERNOON HOURS--WITH ISALLOBARIC FORCING/RELATIVE BACKING OF LOW
LEVEL WINDS AND A 50 KT LLJ ENLARGING LOW LEVEL HODOGRAPHS /300+
M2/S2 EFFECTIVE SRH/. THE SUPERCELL THREAT AND ASSOCIATED HAZARDS
/INCLUDING ISOLD TORNADO POTENTIAL/ APPEAR GREATEST ACROSS MAINE
WHERE DEEP TROPOSPHERIC WIND PROFILES WILL BE STRONGEST. FARTHER
S...STORM COVERAGE SHOULD BE LESS BUT POSE AN ISOLD DMGG WIND/LARGE
HAIL RISK.
...CENTRAL PLAINS/MIDDLE MO VALLEY...
WITH THE AID OF A MODERATE/VEERING LOW LEVEL JET IN VICINITY OF A
SURFACE FRONT ZONE...ONE OR MORE TSTMS CLUSTERS ARE FORECAST TO BE
ONGOING EARLY THURSDAY MORNING ACROSS PORTIONS OF THE CNTRL PLAINS.
DEBRIS CLOUD COVER MAY HINDER DESTABILIZATION WHILE OTHERWISE
EFFECTIVELY SHIFTING THE FRONT SOUTHWARD...BUT IT SEEMS PROBABLE
THAT MODERATE DESTABILIZATION WILL OCCUR NEAR THE FRONT WHERE LOW
LEVEL MOISTURE WILL BE GREATEST. ALTHOUGH DEEP LAYER FLOW WILL BE
MODEST...VEERING WINDS MAY SUPPORT SOME STORM ORGANIZATION IN THE
FORM OF MULTICELLULAR CLUSTERS/TRANSIENT SUPERCELL STRUCTURES
CAPABLE OF WIND DMGG/SOME HAIL AND PERHAPS A BRIEF TORNADO. THIS
ACTIVITY MAY GROW UPSCALE INTO A MCS ACROSS ERN NEB/NERN KS INTO WRN
IA AS THE LLJ REINVIGORATES BY THE LATE EVENING.
FARTHER WEST...OTHER ISOLATED SEVERE TSTMS WILL BE POSSIBLE ACROSS
THE CENTRAL HIGH PLAINS THURSDAY AFTERNOON/EVENING VIA A
POST-FRONTAL UPSLOPE REGIME.
...SOUTHEAST STATES/CAROLINAS...
VERTICAL SHEAR/LAPSE RATES ALOFT WILL BE VERY WEAK/POOR...BUT A
SEASONABLY MOIST/UNSTABLE AIRMASS MAY SUPPORT A SPORADIC THREAT FOR
POCKETS OF ISOLD WIND DMGG FROM WET MICROBURSTS DURING THE AFTERNOON
HOURS.
..SMITH/KERR/COHEN.. 07/21/2011
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