SWODY1
SPC AC 220558
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1158 PM CST SAT JAN 21 2012
VALID 221200Z - 231200Z
...THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF ERN AR...WRN TN
AND NRN MS...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE LOWER TO
MID MS VALLEY...OH AND TN VALLEYS...
...REGIONAL SEVERE WEATHER EVENT LIKELY TO OCCUR ACROSS PARTS OF THE
LOWER TO MID MS VALLEY INTO THE TN VALLEY SUNDAY EVENING...
...LOWER TO MID MS VALLEY/TN VALLEY...
A POWERFUL UPPER-LEVEL TROUGH OVER THE ROCKIES WILL MOVE EWD INTO
THE GREAT PLAINS TODAY AND INTO THE MS VALLEY THIS EVENING. THE
TROUGH WILL BECOME NEGATIVELY-TILTED AS AN UPPER-LEVEL LOW CLOSES
OFF OVER THE UPPER MIDWEST. AHEAD OF THE SYSTEM...A 50 TO 70 KT
LOW-LEVEL JET WILL EXPAND NWD ACROSS THE MID-MS VALLEY TODAY WITH
STRONG MOISTURE ADVECTION TAKING PLACE IN THE LOWER MS VALLEY. SFC
DEWPOINTS IN THE LOWER TO MID 60S F ARE FORECAST TO REACH AS FAR
NORTH AS MEMPHIS TN BY LATE AFTERNOON WHERE THE NAM AND GFS DEVELOP
A POCKET OF MODERATE INSTABILITY SSWWD ACROSS ERN AR. MODEL
FORECASTS RAPIDLY INITIATE STORMS ALONG THE INSTABILITY AXIS AROUND
23/00Z. THESE STORMS SHOULD QUICKLY EXPAND IN COVERAGE AS A LINEAR
MCS ORGANIZES AND MOVES EWD ACROSS THE TN VALLEY SUNDAY EVENING.
AS THE UPPER-LEVEL TROUGH APPROACHES THE MID MS VALLEY LATE SUNDAY
AFTERNOON...A CYCLONICALLY CURVED 70 TO 90 KT MID-LEVEL JET WILL
CREATE A STRONG WIND FIELD FAVORABLE FOR SEVERE STORMS. INTERACTION
BETWEEN THE MID-LEVEL AND LOW-LEVEL JETS WILL ENHANCE LOW-LEVEL
SHEAR WITH TORNADIC SUPERCELLS POSSIBLE. THIS THREAT SHOULD BE
GREATEST AS DISCRETE STORMS INITIATE IN ERN AR AND MOVE EWD INTO NW
MS AND INTO THE MEMPHIS AREA EARLY THIS EVENING. FORECAST SOUNDINGS
FOR MEMPHIS AT 03Z SHOW 0-3 KM STORM RELATIVE HELICITIES OF 400 TO
450 M2/S2 SUGGESTING A FEW STRONG TORNADOES MAY OCCUR WITH A
LONG-TRACK TORNADO POSSIBLE. THE MORE DOMINANT SUPERCELLS MAY ALSO
HAVE A THREAT FOR ISOLATED VERY LARGE HAIL BUT THIS THREAT APPEARS
CONDITIONAL UPON THE DEVELOPMENT OF INTENSE DISCRETE SUPERCELLS. THE
GREATER THREAT SHOULD BE FOR DAMAGING WIND GUSTS AS A LINE FORMS
THIS EVENING AND MOVES EWD ACROSS WRN TO MIDDLE TN...NRN MS AND NRN
AL. SOME WIND GUSTS OF GREATER THAN 70 KT APPEAR POSSIBLE DUE TO THE
STRONG WIND FIELDS AND VERY FOCUSED LARGE-SCALE ASCENT.
...MID MS AND OH VALLEY...
A POWERFUL UPPER-LEVEL TROUGH WILL MOVE ACROSS THE OZARK PLATEAU
EARLY THIS EVENING AS NUMEROUS THUNDERSTORMS INITIATE IN THE MID-MS
VALLEY. VERY STRONG LARGE-SCALE ASCENT ASSOCIATED WITH THE
UPPER-LEVEL TROUGH AND UNIDIRECTIONAL WIND PROFILES EVIDENT ON
FORECAST SOUNDINGS SHOULD RESULT IN RAPID LINEAR DEVELOPMENT THIS
EVENING FROM ERN IL SWD INTO WRN KY. A WIND DAMAGE THREAT SHOULD
DEVELOP AS THE LINE SURGES QUICKLY EWD ACROSS THE OH VALLEY DURING
THE MID TO LATE EVENING. FORECAST SOUNDINGS ACROSS MUCH OF THE OH
VALLEY DURING THE 03Z TO 06Z TIMEFRAME SUGGEST THAT A COOL SFC
INVERSION WILL EXIST IN SPITE OF STRONG MOISTURE ADVECTION. FOR THIS
REASON...THE TORNADO THREAT IS EXPECTED TO REMAIN MARGINAL EXCEPT IN
SRN KY WHERE SFC DEWPOINTS COULD APPROACH 60 F.
..BROYLES/GARNER.. 01/22/2012
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