Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS01 KWNS 222001
SWODY1
SPC AC 221959

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0159 PM CST MON DEC 22 2014

VALID 222000Z - 231200Z

...THERE IS A MRGL RISK OF SVR TSTMS OVER PARTS OF THE LOWER MS
VALLEY AND CENTRAL GULF COAST REGION...

...SUMMARY...
ISOLATED SEVERE STORMS MAY OCCUR THIS AFTERNOON THROUGH EARLY
TUESDAY OVER PARTS OF THE LOWER MISSISSIPPI VALLEY AND CENTRAL GULF
COAST REGION.

...20Z UPDATE...
FORECAST SCENARIO REMAINS ESSENTIALLY UNCHANGED /SEE PRIOR
DISCUSSION BELOW/...INCLUDING ASSOCIATED CAVEATS/LIMITATIONS
ASSOCIATED WITH WHAT IS STILL EXPECTED TO BE A SPORADIC/ISOLATED
SEVERE RISK AT MOST. BASED ON LATEST OBSERVATIONS/ GUIDANCE...THE
MARGINAL RISK WAS SPATIALLY ADJUSTED ACROSS A SMALL PART OF LA/MS
WHERE STORM COVERAGE SHOULD REMAIN LIMITED WITHIN THE MARGINALLY
MOIST WARM SECTOR GIVEN RESIDUAL MID-LEVEL CAPPING /REFERENCE 12Z
SOUNDINGS FROM LAKE CHARLES AND JACKSON MS/ AMID THE ABSENCE OF
GREATER FORCING FOR ASCENT.

..GUYER.. 12/22/2014

.PREV DISCUSSION... /ISSUED 1029 AM CST MON DEC 22 2014/

...SYNOPTIC SETUP...
PATTERN WILL FURTHER AMPLIFY OVER THE LWR 48 THROUGH TUE AS RIDGE
REMAINS STNRY OFF THE CA CST WHILE BROAD TROUGH STRENGTHENS OVER THE
CNTRL U.S. INTENSIFICATION OF THE TROUGH WILL BE ACCOMPLISHED BY THE
CONTINUED SSE ADVANCE OF 175 KT JET STREAK NOW CROSSING THE NRN
RCKYS...AND BY A SERIES OF WEAKER IMPULSES OVER THE NRN AND CNTRL
PLNS EXPECTED TO CONSOLIDATE INTO A CLOSED LOW OVER THE LWR MO VLY.
THIS SETUP WILL STRENGTHEN AND SLIGHTLY BACK EXISTING SWLY FLOW OVER
THE LWR MS VLY/GULF CST.

AT LWR LVLS...WRN PART OF WEAK FRONT THAT HAS BEEN STALLED OVER THE
NRN GULF OF MEXICO AND THE WRN ATLANTIC IN RECENT DAYS SHOULD BEGIN
DRIFTING N LATER TODAY AND TNGT AS SFC PRESSURES FALL OVER THE LWR
MS AND TN VLYS. NWD MOVEMENT OF THE FRONT WILL ALLOW FAIRLY
SUBSTANTIAL MOISTURE /PW AROUND 1.50 INCHES/ NOW OVER THE CNTRL AND
ERN GULF TO SPREAD INLAND ACROSS THE CNTRL/ERN GULF CST
REGION...WITH SFC DEWPOINTS IN THE UPR 50S F EXPECTED AS FAR N AS
THE AL-MS-TN BORDER AREA BY 12Z TUE. SFC CYCLOGENESIS
WILL...HOWEVER...LIKELY REMAIN WELL REMOVED FROM THE RETURNING
MOISTURE...WITH THE MAIN SFC LOW EXPECTED TO FORM OVER SRN IA/NRN
MO...BENEATH INTENSIFYING UPR VORT.

...LWR MS VLY/CNTRL GULF CST LATER TODAY THROUGH EARLY TUE...
COMBINATION OF GRADUALLY STRENGTHENING SWLY FLOW AND INCREASING
MOISTURE WILL YIELD AN ENVIRONMENT THAT WILL BECOME AT LEAST
CONDITIONALLY FAVORABLE FOR STRONG TO SVR TSTMS...MAINLY LATER TODAY
THROUGH EARLY TUE OVER THE CNTRL GULF CST REGION. MODEST LARGE-SCALE
FORCING FOR ASCENT AND ABSENCE OF STRONG LOW-LVL SOURCES OF ASCENT
SUGGEST...HOWEVER...THAT THE SVR THREAT SHOULD REMAIN SPORADIC...AND
COVERAGE ISOLD.

STRENGTHENING SWLY DEEP SHEAR WILL RESULT IN SIZABLE...LOOPED
LOW-LVL HODOGRAPHS BY THIS EVE AND THROUGH EARLY TUE IN ZONE OF WEAK
TO MODEST SFC-BASED INSTABILITY /SBCAPE 250-1000 J PER KG/ NEAR
NWD-MOVING FRONT OVER SRN PARTS OF LA-MS-AL AND THE WRN FL
PANHANDLE. SATELLITE/MODEL DATA SUGGEST...HOWEVER...THAT LARGE-SCALE
FORCING FOR ASCENT WILL BE LIMITED UNTIL PERHAPS LATE IN THE PERIOD
WHEN A JET-ENTRANCE REGION CIRCULATION EVOLVES OVER THE CNTRL GULF
CST. MEANWHILE...MID-LVL LAPSE RATES WILL BE WEAK.

NEVERTHELESS...WITH SFC DEWPOINTS INCREASING TO THE MID-UPR 60S F
ALONG THE CNTRL GULF CST...WEAKLY CONFLUENT LOW-LVL FLOW MAY BE
SUFFICIENT TO SUPPORT A COUPLE SHORT LINES/SMALL CLUSTERS OF SFC OR
NEAR-SFC-BASED STORMS LATE TNGT AND EARLY TUE FROM SRN LA-SRN MS EWD
INTO THE WRN FL PANHANDLE. THIS ACTIVITY...AND ANY MORE WDLY
SCTD...SMALL STORMS THAT MAY FORM S OF THE FRONT...COULD CONTAIN A
SPORADIC TORNADO/ISOLD DMGG WIND THREAT...ESPECIALLY GIVEN ENHANCED
LOW-LVL VEERING PROFILES NEAR THE BOUNDARY.

FARTHER N...STRENGTHENING 925-850 MB WAA/MOISTURE TRANSPORT SHOULD
FOSTER INCREASING COVERAGE OF ELEVATED CONVECTION/STORMS NNEWD INTO
THE LWR OH VLY BY MORNING.




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