SWODY2
SPC AC 181729
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1229 PM CDT SUN MAR 18 2012
VALID 191200Z - 201200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM IA...WRN MO...ERN KS SSWWD
TO THE LOWER RIO GRANDE VALLEY...
...SYNOPSIS...
GOOD MODEL AGREEMENT EXISTS WITH THE EVOLUTION OF THE UPPER FLOW
PATTERN ACROSS MUCH OF NORTH AMERICA THROUGH AT LEAST DAY 2. A
LARGE SCALE TROUGH IN THE WEST WILL CONTINUE TO SHIFT SLOWLY EWD
ACROSS THE ROCKIES INTO THE GREAT PLAINS...WHILE THE DOWNSTREAM
RIDGE OVER THE ERN STATES UNDERGOES FURTHER STRENGTHENING WITH
HEIGHTS RISING OVER JAMES/HUDSON BAYS AND QUEBEC. A SERIES OF
SHORTWAVE TROUGHS WILL CONTINUE TO TRANSLATE THROUGH THE PARENT
TROUGH. BY LATE DAY 2...MODELS SUGGEST A TRANSITION IN THE UPPER
FLOW PATTERN IS EXPECTED AS A STRENGTHENING WLY PACIFIC JET IS
EXPECTED TO MOVE INTO WA/ORE...RESULTING IN A SPLIT FLOW REGIME
BEGINNING TO DEVELOP BY 12Z TUESDAY OVER THE ROCKIES/GREAT PLAINS.
AT THE SURFACE...HIGH PRESSURE WILL PREVAIL OVER THE ERN AND WRN
PORTIONS OF COUNTRY...WHILE A N-S COLD FRONT ASSOCIATED WITH THE
ADVANCING TROUGH CROSSES THE PLAINS STATES THROUGH THE PERIOD. ONE
SURFACE LOW WILL TRACK FROM ND INTO CANADA...AND A SECOND LOW IS
EXPECTED TO FORM AT THE SRN EXTENT OF THE FRONT OVER THE LOWER RIO
GRANDE VALLEY AS THE SRN EXTENT OF THE WRN TROUGH EDGES EWD. THE
COLD FRONT WILL BE THE FOCUS FOR A N-S ZONE OF STORMS EXTENDING FROM
THE CANADIAN TO THE MEXICAN BORDERS.
...MID MO VALLEY SSWWD TO THE LOWER RIO GRANDE VALLEY...
SHOWERS AND STORMS...POSSIBLY WITH AN ONGOING SEVERE THREAT /REF
CONVECTIVE DAY 1 OUTLOOK/...SHOULD EXTEND ACROSS PARTS OF KS/OK/TX
AT THE START OF THE PERIOD ALONG THE PACIFIC COLD FRONT. WEAKER
CONVECTION SHOULD EXTEND N/NEWD INTO THE MID-LOWER MO VALLEY REGION.
THE ONGOING PRECIPITATION AND CLOUD COVER...BEING CARRIED
CONTINUALLY NNEWD BY THE STRONG MERIDIONAL FLOW ALOFT...SHOULD
HINDER DESTABILIZATION POTENTIAL. THIS WILL LIKEWISE LIMIT THE
ASSOCIATED SEVERE WEATHER POTENTIAL N OF THE SRN PLAINS WHERE A
LOWER PROBABILITY THREAT FOR HAIL/WIND IS EXPECTED.
THE FOCUS FOR GREATER SEVERE POTENTIAL REMAINS FROM ERN KS/WRN MO
SWD INTO SERN OK AND SWD ACROSS E TX ON THE SERN FRINGE OF ONGOING
STORMS. AFTERNOON DESTABILIZATION WILL SUPPORT MLCAPE OF 1000-2000
J/KG IN THIS FOCUS AREA...WITH STORMS INTENSIFYING/REDEVELOPING
THROUGH PEAK HEATING.
AS STRONG /60 TO 70 KT/ SWLY FLOW AT MID LEVELS OVERSPREADS THE
MOIST/UNSTABLE BOUNDARY LAYER FEATURING SSELY PRE-FRONTAL WINDS...
DEVELOPING STORMS WITHIN THE FAVORABLY SHEARED ENVIRONMENT WILL
QUICKLY BECOME SEVERE/SUPERCELLULAR...WITH VERY LARGE HAIL AND
LOCALLY DAMAGING WINDS POSSIBLE. A TORNADO THREAT WILL ALSO
EXIST...GIVEN AMPLE LOW-LEVEL SHEAR WITHIN A MOIST BOUNDARY LAYER.
MONDAY NIGHT...INCREASINGLY LINEAR ORGANIZATION OF THE CONVECTION IS
EXPECTED ALONG THE SLOWLY ADVANCING FRONT. WHILE THE SEVERE THREAT
IS EXPECTED TO PERSIST INTO THE OVERNIGHT PERIOD...THE THREAT FOR
HEAVY RAIN SHOULD ALSO INCREASE GIVEN OVERALL SLOW MOVEMENT OF THE
CONVECTIVE BAND AND POTENTIAL FOR TRAINING CONVECTION.
FARTHER N ACROSS THE ERN DAKOTAS/MN...STRENGTHENING DEEP LAYER SHEAR
AND MARGINAL INSTABILITY WILL MAINTAIN A LOWER PROBABILITY FOR
SEVERE STORMS. HOWEVER...IF GREATER INSTABILITY IS FORECAST BY
LATER MODELS...THEN PARTS OF THIS REGION COULD REQUIRE AN UPGRADE TO
HIGHER PROBABILITIES/CATEGORICAL SEVERE RISK IN UPCOMING OUTLOOKS.
...PARTS OF THE CENTRAL APPALACHIANS INTO VA/NC...
A PLUME OF MIDLEVEL LAPSE RATES /7-7.5 C PER KM/...CURRENTLY
RESIDING OVER THE TN AND LOWER OH VALLEYS WILL SPREAD ESEWD WITHIN
NWLY FLOW REGIME ALOFT INTO VA/NC. THIS COMBINED WITH SOME SURFACE
HEATING AND ESELY SURFACE WINDS MAINTAINING SURFACE DEWPOINTS IN THE
MID-UPPER 50S F SHOULD RESULT IN MLCAPE INCREASING TO AT LEAST 1000
J/KG PER FORECAST SOUNDINGS. FORCING FOR ASCENT ATTENDANT TO THE OH
VALLEY SHORTWAVE TROUGH MOVING SEWD ACROSS THIS REGION ON MONDAY...
WHERE THE AIR MASS SHOULD BE MODERATELY UNSTABLE...SUGGESTS TSTMS
WILL BE POSSIBLE OVER THE HIGHER TERRAIN AND DOWNSTREAM INTO VA/NC.
ALTHOUGH LOWER TROPOSPHERIC WINDS WILL BE QUITE WEAK...NWLY
MID-UPPER LEVEL WINDS WITH THE STRONGEST SPEEDS /50-60 KT/ LOCATED
ABOVE 500 MB WILL CONTRIBUTE TO EFFECTIVE BULK SHEAR OF 25-30 KT.
THIS SHEAR COMBINED WITH THE MODERATE INSTABILITY WILL BE SUFFICIENT
FOR MULTICELLS WITH ISOLATED HAIL AND LOCALLY STRONGER WIND GUSTS
POSSIBLE. GIVEN THE PRESENCE OF A SHORTWAVE TROUGH MOVING ACROSS
THIS REGION AND MIDLEVEL LAPSE RATES EXPECTED TO BE STEEPER THAN
TODAY...LOW SEVERE PROBABILITIES WILL BE INTRODUCED WITH THIS
OUTLOOK. IF GREATER INSTABILITY AND/OR STRONGER SHEAR IS FORECAST
IN LATER GUIDANCE...THEN PARTS OF THIS REGION MAY REQUIRE AN UPGRADE
TO A CATEGORICAL SEVERE RISK.
..PETERS.. 03/18/2012
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