Mesoscale Discussion 69

Issued

Feb 1, 2011, 12:00 PM CST (18:00 UTC)

Expired

Feb 1, 2011, 1:00 PM CST

In force

60 min

Issued by

the Storm Prediction Center

• Tornado Watch 10Feb 1, 1:05 PM CST

299 
ACUS11 KWNS 011801
SWOMCD
SPC MCD 011800
ALZ000-FLZ000-MSZ000-LAZ000-011900-

MESOSCALE DISCUSSION 0069
NWS STORM PREDICTION CENTER NORMAN OK
1200 PM CST TUE FEB 01 2011

AREAS AFFECTED...SRN-ERN LA/SWRN...WEST CENTRAL TO CENTRAL MS

CONCERNING...TORNADO WATCH 9...

VALID 011800Z - 011900Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 9 CONTINUES.

AREAS E OF WW 9 OVER SERN MS  AND SWRN AL WILL NEED TO BE MONITORED
FOR A NEW WATCH AS THE AIR MASS CONTINUES TO SLOWLY DESTABILIZE.

THREAT FOR DAMAGING WINDS AND A FEW TORNADOES CONTINUES ACROSS
ERN...SRN AND SERN LA INTO SWRN MS.  CURRENT TRENDS IN RADAR IMAGERY
SHOWED THE NRN EXTENT OF THE STORMS...NOW ENTERING SWRN MS...WILL
EXIT THE NERN PART OF WW 9 BY 20Z...WHILE THE SRN EXTENT SHOULD
REACH THE SERN PART OF THIS WATCH AROUND 21Z.  MEANWHILE...SEVERE
WEATHER THREAT WILL CONTINUE TO END WITH THE PASSAGE OF THE SQUALL
LINE...SUCH THAT PARISHES AND COUNTIES CAN BE REMOVED FROM WW 9 WEST
OF THIS LINE.

AT 17Z...PRIMARY CYCLONE WAS LOCATED OVER E CENTRAL AR...WITH TRENDS
IN MID-LATE MORNING SURFACE ANALYSES SHOWED PRESSURE FALLS FROM AR
INTO SERN MO AND MID SOUTH SUPPORTING A CONTINUED ENE TRACK OF THIS
FEATURE.  MEANWHILE...TWO CORRIDORS OF SURFACE PRESSURE RISES
EXTENDED SWD AND SWWD FROM THE LOW WITH THE LEADING ONE LOCATED
IMMEDIATELY IN THE WAKE OF THE SQUALL LINE...WHILE THE SECOND
PRESSURE RISE AREA ACROSS E TX MARKS THE LEADING EDGE OF THE COLDER
AIR WITH THE ARCTIC FRONT.  AT 1730Z...REGIONAL RADAR IMAGERY SHOWED
THE SQUALL LINE/LEAD WIND SHIFT EXTENDING SSWWD FROM VICINITY OF HEZ
TO SOUTH CENTRAL LA...WITH THIS LINE TRACKING EWD AT 35 KT AND
EMBEDDED CELLS MOVING ENE UP TO 50 KT.  A WARM FRONT EXTENDED FROM
VICINITY OF BTR ESEWD TO OFF THE MS GULF COAST AND 50-60 MILES S OF
THE FL PANHANDLE.  LOW LEVEL WAA ALONG THE WARM FRONT WILL CONTINUE
TO SUPPORT TSTM DEVELOPMENT AHEAD OF THE PRIMARY SQUALL LINE...WITH
STRONG LOW LEVEL SHEAR /EFFECTIVE SRH 300-700 M2 PER S2/ INVOF OF
THE WARM FRONT SUGGESTING A THREAT FOR ENHANCED LOW LEVEL ROTATION.
MODIFIED 15Z SLIDELL SPECIAL SOUNDING FOR CURRENT SURFACE CONDITIONS
INDICATED AN UNCAPPED ENVIRONMENT WITH MLCAPE CLOSE TO 400 J/KG AND
AN INCREASE IN LOW LEVEL HODOGRAPH CURVATURE SINCE 12Z.

50+ KT SLY LLJ EXTENDING INTO THE LOWER MS VALLEY/ADJACENT GULF
COAST STATES WILL MAINTAIN AN INFLUX OF MOISTURE...WITH SURFACE
DEWPOINTS IN THE LOWER-MID 60S ACROSS SERN LA AND FAR SRN MS
SPREADING INTO SWRN AL THIS AFTERNOON.  DESPITE LIMITED DIABATIC
HEATING...THIS MOISTURE AND MIDLEVEL LAPSE RATES /6.5-7.0 C PER KM/
WILL CONTINUE TO SUPPORT MARGINAL INSTABILITY /MLCAPE AOB 500 J PER
KG/.  THESE FACTORS COMBINED WITH BULK SHEAR IN EXCESS OF 50+ KT
WILL MAINTAIN SUPPORT FOR ORGANIZED STORMS/A FEW SUPERCELLS AS
ACTIVITY ADVANCES EWD THIS AFTERNOON.

..PETERS.. 02/01/2011

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...MOB...JAN...LIX...LCH...

LAT...LON   29139268 31019180 32579119 32838973 32178907 31668798
            31458700 30028702 29608814 28898865 28618914 28769127
            29149195 29139268

Mesoscale Discussions in Mississippi, 2011Mesoscale Discussions in Louisiana, 2011Mesoscale Discussions in Alabama, 2011Every mesoscale discussion in 2011

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive.