DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 020545
SWODY1
SPC AC 020543

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1243 AM CDT SUN SEP 02 2012

VALID 021200Z - 031200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE UPPER MS
VALLEY AND NRN PLAINS...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE TN
VALLEY...

...UPPER MS VALLEY/NRN PLAINS...
A BROAD UPPER-LEVEL TROUGH WILL MOVE EWD ACROSS THE NCNTRL STATES
TODAY AS A COLD FRONT ADVANCES SEWD ACROSS THE DAKOTAS. A NARROW
CORRIDOR OF MODERATE INSTABILITY SHOULD DEVELOP THIS AFTERNOON JUST
AHEAD OF THE COLD FRONT FROM NW MN SSWWD INTO ERN SD. ALTHOUGH A
CAPPING INVERSION SHOULD EXIST ACROSS THE UPPER MS VALLEY THIS
MORNING...THE CAP IS FORECAST TO WEAKEN ENOUGH THIS AFTERNOON TO
ALLOW FOR STORM INITIATION ALONG PORTIONS OF THE FRONT. THE GFS
MODEL SUGGESTS STORMS WILL FIRST DEVELOP IN NW MN AND EXPAND SWD
WITH TIME EVENTUALLY REACHING FAR ERN SD DURING THE EARLY EVENING.
THE MODELS SUGGEST THE CONVECTION WILL PERSIST THROUGH MUCH OF THE
EVENING AS LOW-LEVEL FLOW INCREASES WITH A CONVECTIVE CLUSTER
POTENTIALLY REACHING THE MN-WI STATE-LINE SOMETIME AFTER MIDNIGHT.

NAM FORECAST SOUNDINGS ACROSS THE UPPER MS VALLEY AT 00Z/MON JUST
AHEAD OF THE FRONT SHOW SFC DEWPOINTS IN THE UPPER 50S TO AROUND 60
F WITH MLCAPE VALUES OF 1500 TO 2000 J/KG. THIS COMBINED WITH 30 TO
40 KT OF DEEP LAYER SHEAR SHOULD BE ENOUGH FOR SEVERE STORM
DEVELOPMENT. LAPSE RATES ALONG AND JUST AHEAD OF THE FRONT ARE
FORECAST TO BE VERY STEEP FROM THE SFC TO 700 MB. THIS ALONG WITH
LARGE TEMP-DEWPOINT SPREADS SHOULD BE FAVORABLE FOR DAMAGING OUTFLOW
GUSTS AS DOWNDRAFTS ACCELERATE IN THE HOT AND RELATIVELY DRY
AIRMASS. THE STEEP LAPSE RATES AT MID-LEVELS MAY ALSO BE SUFFICIENT
FOR HAIL ESPECIALLY IF STORMS CAN DEVELOP ROTATION. THE SEVERE
THREAT COULD BE DELAYED UNTIL EVENING IF THE CAP TAKES LONGER TO
DIMINISH THAN IS CURRENTLY FORECAST.

...TN AND OH VALLEYS...
AN UPPER-LEVEL LOW WILL MOVE SLOWLY EWD TODAY ACROSS THE MID MS
VALLEY. AHEAD OF THE LOW...MODERATE TO STRONG INSTABILITY IS
FORECAST TO DEVELOP FROM THE TN VALLEY NWD INTO THE OH VALLEY BY
AFTERNOON. THE MODELS DEVELOP NUMEROUS THUNDERSTORMS ON THE WRN EDGE
OF MODERATE INSTABILITY WITH SEVERAL CLUSTERS PERSISTING INTO THE
EVENING. THE NAM AND GFS SUGGEST THE GREATEST CONVECTIVE COVERAGE
WILL EXIST FROM MIDDLE TO ERN TN EXTENDING SWWD INTO NRN AL AND NRN
MS WHERE LOW-LEVEL FLOW WILL BE ENHANCED AND AN MCS COULD ORGANIZE
BY THE EVENING.

NAM FORECAST SOUNDINGS ACROSS THE TN VALLEY LATE THIS AFTERNOON SHOW
A VERY MOIST AND UNSTABLE AIRMASS WITH MLCAPE VALUES REACHING THE
2500 TO 3000 J/KG RANGE. THIS COMBINED WITH 25 TO 35 KT OF DEEP
LAYER SHEAR SHOULD BE SUPPORTIVE OF SEVERE STORMS AND SUPERCELL
DEVELOPMENT WILL BE POSSIBLE. SFC DEWPOINTS IN THE LOWER 70S F...0-1
KM SHEAR OF 30 TO 35 KT WITH SOME DIRECTIONAL SHEAR BELOW 850 MB MAY
ENOUGH FOR AN ISOLATED TORNADO THREAT WITH THE MORE DOMINANT
SUPERCELLS. WIND DAMAGE ALSO WILL BE POSSIBLE ESPECIALLY WITH THE
MORE INTENSE LINE SEGMENTS. THE HAIL THREAT SHOULD REMAIN ISOLATED
MAINLY DUE TO WARM MID-LEVEL TEMPS.

...MID-ATLANTIC/CAROLINAS...
AN UPPER-LEVEL RIDGE SHOULD BE IN PLACE TODAY ACROSS THE
MID-ATLANTIC WITH MODERATE INSTABILITY DEVELOPING BENEATH THE RIDGE
FROM MD SWWD INTO THE CAROLINAS. FORECAST SOUNDINGS AT 21Z ALONG
THIS CORRIDOR GENERALLY SHOW MLCAPE IN THE 2000 TO 3000 J/KG RANGE.
IN SPITE OF THE STRONG INSTABILITY...DEEP LAYER SHEAR IS FORECAST TO
REMAIN QUITE WEAK SUGGESTING ANY STORMS THAT INITIATE WILL BE PULSE
IN NATURE. AS LOW-LEVEL LAPSE RATES BECOME VERY STEEP IN THE MID TO
LATE AFTERNOON...A FEW DAMAGING WIND GUSTS WILL BE POSSIBLE WITH
CELLS THAT HAVE ACCESS TO THE STRONGEST INSTABILITY.

..BROYLES/MOSIER.. 09/02/2012

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