DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 071942
SWODY1
SPC AC 071940

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0240 PM CDT FRI SEP 07 2012

VALID 072000Z - 081200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM NERN OK TO WRN PA/NY...

A FEW MINOR ADJUSTMENTS HAVE BEEN MADE TO THE 1630Z OUTLOOK. THE
FIRST IS TO EXPAND THE SLIGHT RISK EWD ACROSS WRN PA TO ACCOUNT FOR
THE EXPANSION OF ROBUST UPDRAFTS WITHIN THE MODESTLY STRONG WLY FLOW
REGIME. LATEST RADAR DATA EXHIBITS A CONSIDERABLE AMOUNT OF
CONVECTION HAS DEVELOPED ALONG AN E-W CORRIDOR JUST SOUTH OF LAKE
ERIE. TRAILING THIS NEW DEVELOPMENT...A FAIRLY SUBSTANTIAL BAND OF
CONVECTION ASSOCIATED WITH AN MCS IS PROGRESSING ACROSS NWRN OH. A
WEAK MCV APPEARS TO BE EMBEDDED ALONG THE NRN PORTIONS OF THE MCS
NEAR SENECA COUNTY OH AND THIS FEATURE MAY ENHANCE THE
AFOREMENTIONED E-W BAND OF TSTMS SOUTH OF LAKE ERIE.

ANOTHER ADJUSTMENT TO THE EARLIER OUTLOOK IS TO ACCOUNT FOR THE
RECENT INTENSIFICATION OF TSTMS ACROSS ERN KS. THIS ACTIVITY IS
ASSOCIATED WITH SURGING COLD FRONT AND IS EVOLVING ALONG NERN PLUME
OF FAIRLY STEEP LAPSE RATES JUST NORTH OF DEEPLY MIXED AIRMASS OVER
THE SRN PLAINS. GIVEN THE DEVELOPING LINE SEGMENTS APPROACHING THE
SERN KS/SWRN MO BORDER HAVE INCREASED SEVERE PROBS JUST DOWNSTREAM
TO ACCOUNT FOR AN ENHANCED WIND/HAIL THREAT ACROSS THIS REGION.

..DARROW.. 09/07/2012

.PREV DISCUSSION... /ISSUED 1128 AM CDT FRI SEP 07 2012/

...ERN OK NEWD ACROSS THE MID MS/OH VALLEYS THROUGH EARLY TONIGHT...

A STRONG EARLY-SEASON COLD FRONT IS MOVING SWD INTO THE SRN
PLAINS...AND SEWD ACROSS THE MID MS VALLEY AND UPPER GREAT LAKES.
THIS FRONT IS ASSOCIATED WITH AN AMPLIFYING MIDLEVEL TROUGH THAT IS
PROGRESSING SEWD FROM THE CENTRAL/NRN PLAINS AND THE UPPER MS
VALLEY. ON THE MESOSCALE...A SEPARATE REMNANT FRONTAL SEGMENT
EXTENDS FROM THE SAINT LAWRENCE VALLEY TO NRN INDIANA...WHERE IT IS
INTERSECTED BY AN OUTFLOW BOUNDARY WITH ONGOING CONVECTION ACROSS
CENTRAL IL AND NRN INDIANA. REGIONAL 12Z SOUNDINGS SUGGEST THAT
SURFACE TEMPERATURES IN THE LOW-MID 80S WITH BOUNDARY LAYER
DEWPOINTS NEAR 70 F WILL REDUCE CONVECTIVE INHIBITION AND RESULT IN
MLCAPE NEAR 2500 J/KG IN ADVANCE OF THE ONGOING STORMS.
THUS...SURFACE-BASED CONVECTION IS LIKELY ACROSS IL/INDIANA/OH THIS
AFTERNOON...WITH AN ACCOMPANYING RISK FOR DAMAGING WINDS/LARGE HAIL
GIVEN THE MODERATE INSTABILITY AND THE SRN FRINGE OF THE MODERATE
MIDLEVEL FLOW/SHEAR. THE AFTERNOON CONVECTION COULD SPREAD AS FAR E
AS WRN PA BEFORE WEAKENING THIS EVENING.

FARTHER W AND LATER THIS AFTERNOON...ADDITIONAL THUNDERSTORM
DEVELOPMENT IS EXPECTED ALONG THE COLD FRONT FROM E/NE OK NEWD
ACROSS MO/NW AR/SRN IL. STRONG SURFACE HEATING AND STEEP
LOW-MIDLEVEL LAPSE RATES WILL PROMOTE STRONG DOWNDRAFTS WITH THE
POTENTIAL FOR DAMAGING SURFACE WINDS. CONVECTION WILL LIKELY GROW
UPSCALE INTO A LINE ALONG THE FRONT...WITH THE SEVERE RISK EXPECTED
TO PERSIST INTO EARLY TONIGHT AS STORMS SPREAD SEWD ACROSS AR/WRN
TN/KY.

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