SWODY1
SPC AC 241957
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0257 PM CDT SUN OCT 24 2010
VALID 242000Z - 251200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM PARTS OF THE LOWER OH/MID
MS VALLEYS SWD INTO CENTRAL/ERN TX...TO THE CENTRAL GULF COAST
STATES...
...E TX INTO LOWER MS VALLEY...
FORECAST IS GENERALLY ON TRACK WITH RESPECT TO INCREASING SEVERE
WEATHER THREAT ACROSS PARTS OF NERN TX/ARKLATEX INTO SRN AR/NRN LA
WITH RECENT ISSUANCE OF TORNADO WATCH 707. THE SLIGHT RISK AND
SEVERE PROBABILITIES HAVE BEEN EXTENDED SWD AND SWWD 1-2 ROWS OF
COUNTIES ACROSS SERN TX INTO SOUTH CENTRAL TX WHERE OBJECTIVE
ANALYSES ARE CURRENTLY SHOWING MLCAPE 1500-2000 J/KG. IN
ADDITION...EFFECTIVE BULK SHEAR IS INCREASING AS STRONGER MIDLEVEL
FLOW MOVES THROUGH THE BASE OF A FAIRLY SUBSTANTIAL SHORTWAVE TROUGH
TRACKING EWD ALONG THE RED RIVER TO CENTRAL TX. FORCING FOR ASCENT
ATTENDANT TO A LEAD SHORTWAVE TROUGH...NOW LIFTING NEWD ACROSS THE
OZARKS REGION...AND ADDITIONAL FORCING WITH EWD MOVING SRN OK/TX
TROUGH WILL SUPPORT CONTINUED TSTM DEVELOPMENT INTO THE EVENING
ACROSS THIS PORTION OF THE SLIGHT RISK AREA.
...SERN LA/CENTRAL GULF COAST STATES...
NO CHANGES TO THE FORECAST ARE NEEDED ACROSS THIS REGION. GREATEST
STORM COVERAGE SHOULD BE FOCUSED ALONG LOW LEVEL CONVERGENCE
ZONES...SIMILAR TO THE CORRIDOR CURRENTLY EXTENDING FROM SERN LA
NNEWD THROUGH SRN TO ERN MS. ANOTHER LOW LEVEL CONVERGENCE ZONE
THAT SHOULD BE MONITORED...AT LEAST IN THE SHORT TERM...HAS BEEN
DEVELOPING OFFSHORE SERN LA IN A N-S ORIENTATION. AS LOW LEVELS
CONTINUE TO MOISTEN ACROSS THIS REGION THROUGH TONIGHT SUPPORTING
LOW LCLS...MODELS SUGGEST INCREASING LOW LEVEL SHEAR BENEATH
STRENGTHENING SWLY MIDLEVEL FLOW WITH APPROACHING TROUGH. THIS WILL
FAVOR A RISK FOR A FEW TORNADOES AND STRONG WIND GUSTS WITH ANY
SUSTAINED STORMS THAT REMAIN ROOTED IN THE BOUNDARY LAYER.
...MID MS/LOWER OH VALLEYS...
SLIGHT RISK REMAINS ACROSS THIS AREA. AN APPARENT LOW LEVEL
CONVERGENCE ZONE MAY BE DEVELOPING OVER SERN-EAST CENTRAL MO /INVOF
UNO-FAM/...WITH THE ENVIRONMENT BECOMING MODERATELY UNSTABLE WITH
EFFECTIVE BULK SHEAR RANGING FROM 30-40 KT. FORCING FOR ASCENT
ATTENDANT TO A LEAD SHORTWAVE TROUGH MOVING NEWD THROUGH THE OZARKS
REGION AT THIS TIME MAY PROVE SUFFICIENT IN SUPPORTING TSTM
DEVELOPMENT YET THIS AFTERNOON INTO THE EVENING FROM SERN MO TO
PARTS OF IL.
..PETERS.. 10/24/2010
.PREV DISCUSSION... /ISSUED 1108 AM CDT SUN OCT 24 2010/
...ERN TX INTO LOWER MS VALLEY...
WELL-DEFINED VORTICITY MAXIMUM OVER WRN TX THIS MORNING WILL
INTENSIFY THROUGH THE DAY ONE PERIOD WHILE PROGRESSING EWD THROUGH
THE LOWER MS VALLEY INTO CNTRL GULF STATES. THIS SYSTEM WILL BE
ATTENDED BY A CORRIDOR OF MODEST HEIGHT FALLS AND A 50+ KT MIDLEVEL
JET STREAK WITH A COUPLED UPPER-LEVEL JET STRUCTURE ENHANCING
DEEP-LAYER ASCENT OVER THE REGION LATER TODAY INTO TONIGHT. LATEST
MESOANALYSIS INDICATES A PRE-FRONTAL TROUGH SITUATED ALONG THE I-35
CORRIDOR WHICH WILL LIKEWISE MOVE EWD...LIKELY SERVING AS THE FOCUS
FOR STRONG TO SEVERE TSTM DEVELOPMENT OVER PORTIONS OF ERN TX THIS
AFTERNOON. ADDITIONAL DIURNALLY-ENHANCED STORMS WILL BE POSSIBLE
ALONG WARM FRONT LIFTING NWD FROM THE CNTRL GULF COAST...AS WELL AS
ALONG BANDS OF ENHANCED LOW-LEVEL CONFLUENCE IN THE OPEN WARM SECTOR
OVER PARTS OF LA/MS/AR.
SUSTAINED SLY LOW-LEVEL FLOW IN ADVANCE OF MIDLEVEL IMPULSE WILL
CONTINUE TO DRAW AN INCREASINGLY MOIST BOUNDARY LAYER NWD THROUGH
THE REGION WITH DEW POINTS IN THE 60S TO AROUND 70 F. WHEN COUPLED
WITH ABUNDANT SUNSHINE AND STEEPENING MIDLEVEL LAPSE
RATES...AFTERNOON ENVIRONMENT IS FORECAST TO BECOME MODERATELY
UNSTABLE WITH MLCAPE VALUES APPROACHING 1500-2500 J/KG FROM THE
ARKLATEX SWWD INTO THE TX HILL COUNTRY...AND 1000-2000 J/KG ACROSS
REMAINDER OF EXPANDING WARM SECTOR.
12Z MODEL GUIDANCE SUGGESTS THAT BULK OF WARM SECTOR WILL RESIDE
ALONG SRN FRINGE OF STRONGER LOW-LEVEL FLOW ASSOCIATED WITH A LLJ
CORE THAT WILL GENERALLY EXTEND FROM AR NEWD INTO THE GREAT LAKES.
HOWEVER...STRENGTHENING MID AND HIGH-LEVEL WIND FIELD ACCOMPANYING
ABOVE-MENTIONED VORTICITY MAXIMUM WILL YIELD 40-50 KT OF DEEP WSWLY
SHEAR...SUFFICIENT FOR ORGANIZED STORM MODES INCLUDING SUPERCELLS
AND BOWING STRUCTURES. THE STRONGEST STORMS WILL BE CAPABLE OF
DAMAGING WINDS AND A FEW TORNADOES WITH THE GREATEST HAIL THREAT
LIKELY DEVELOPING OVER ERN TX WHERE THE GREATEST AIR MASS
DESTABILIZATION IS EXPECTED.
REFORMATION OF A 30-40 KT LLJ IS FORECAST OVER THE LOWER MS VALLEY
INTO CNTRL GULF STATES OVERNIGHT WHICH WILL SUPPORT THE CONTINUED
MOISTENING OF THE BOUNDARY LAYER. GIVEN THE ASSOCIATED
STRENGTHENING OF THE LOW-LEVEL SHEAR...A RISK FOR A FEW TORNADOES
AND STRONG WIND GUSTS WILL EXIST WITH ANY SUSTAINED STORMS THAT CAN
REMAIN ROOTED IN THE BOUNDARY LAYER.
...MID MS/OH VALLEY...
IN THE WAKE OF SHORT WAVE TROUGH CURRENTLY LIFTING NEWD THROUGH
IL/IND...UPSTREAM VORTICITY MAXIMUM OVER THE MID MO VALLEY WILL
PROGRESS EWD TODAY IN TANDEM WITH AN ASSOCIATED WEAK COLD FRONT. AS
MENTIONED IN PREVIOUS SECTION...THE BELT OF STRONGER LOW-LEVEL FLOW
WILL REMAIN FOCUSED AHEAD OF THIS FRONT...HASTENING THE NWD/NEWD
FLUX OF AN INCREASINGLY WARM AND MOIST AIR MASS. WHILE GENERALLY
WEAK MIDLEVEL LAPSE RATES WILL TEND TO LIMIT THE DEGREE OF AIR MASS
DESTABILIZATION...DAYTIME HEATING TO THE W OF ELEVATED TSTM CLUSTER
OVER IND...AND E OF MORE WIDESPREAD STRATUS OVER IA/MO WILL YIELD A
CORRIDOR OF MODERATE INSTABILITY WITH AFTERNOON MLCAPE APPROACHING
1000 J/KG.
FORCING FOR ASCENT IN ADVANCE OF UPSTREAM IMPULSE IS EXPECTED TO
SUPPORT THE DEVELOPMENT OF TSTMS THIS AFTERNOON WITHIN INSTABILITY
AXIS FROM PARTS OF SERN MO INTO CNTRL/SRN IL. GIVEN THE MODERATELY
STRONG SWLY WIND FIELD...THE POTENTIAL WILL EXIST FOR A FEW
ORGANIZED STORMS CAPABLE OF DAMAGING WIND GUSTS AND PERHAPS A BRIEF
TORNADO OR TWO.
...PACIFIC NW...
A POWERFUL 100+ KT MIDLEVEL JET STREAK NOW MOVING ONTO THE COAST
WILL DEVELOP SEWD INTO THE GREAT BASIN THROUGH THE PERIOD. THE
LARGE-SCALE PATTERN EVOLUTION WILL SUPPORT SIGNIFICANT HEIGHT
FALLS/DYNAMIC FORCING FOR ASCENT SPREADING INLAND THROUGH THE NRN
INTERMOUNTAIN REGION AND GREAT BASIN. 12Z MODEL GUIDANCE CONTINUES
TO INDICATE THAT AN AXIS OF WEAK INSTABILITY WILL DEVELOP TODAY
ALONG THE COAST WITHIN MOIST...ONSHORE FLOW REGIME. GIVEN THE
EXTREMELY STRONG AMBIENT WIND FIELD AND RESULTING POTENTIAL FOR
DOWNWARD MOMENTUM TRANSFER...A RISK FOR LOCALLY DAMAGING WIND GUSTS
WILL EXIST WITH ANY MORE ROBUST CONVECTIVE ELEMENTS THAT CAN DEVELOP
AND BECOME SUSTAINED.
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