MESO: Mesoscale Discussion 1878

ACUS11 KWNS 040229
SWOMCD
SPC MCD 040228
ALZ000-MSZ000-040330-

MESOSCALE DISCUSSION 1878
NWS STORM PREDICTION CENTER NORMAN OK
0928 PM CDT MON SEP 03 2012

AREAS AFFECTED...ERN MS...WRN AL

CONCERNING...TORNADO WATCH 612...

VALID 040228Z - 040330Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 612 CONTINUES.

SUMMARY...THE THREAT FOR DAMAGING WINDS AND A BRIEF TORNADO OR TWO
CONTINUES ACROSS THE WATCH AREA FOR THE NEXT HOUR OR TWO.
HOWEVER...WANING INSTABILITY RESULTANT FROM BOUNDARY LAYER COOLING
AND DECOUPLING SHOULD PROMOTE A DOWNWARD TREND IN CONVECTIVE
ACTIVITY AND AN INCREASINGLY MARGINAL SEVERE THREAT. THIS DOWNWARD
TREND IS EXPECTED TO PRECLUDE ANY DOWNSTREAM WW ISSUANCE.

DISCUSSION...ACTIVITY ACROSS THE SRN PART OF THE WATCH AREA HAS
EXITED THE WATCH AREA AND REMAINS SUB-SEVERE. A FEW STRONG WIND
GUSTS ARE POSSIBLE BUT MOST OF THIS ACTIVITY HAS WEAKENED.

ACTIVITY ACROSS CNTRL PORTIONS OF THE WATCH /W-CNTRL AL/ EXHIBITED
SOME SLOW FORWARD-PROPAGATION TO THE SW BUT DID NOT BECOME ORGANIZED
INTO A LINEAR MCS. INSTEAD...NUMEROUS CELL MERGERS PROMOTED BRIEF
UPDRAFT INTENSIFICATION/ROTATION WITH VERY HEAVY RAINFALL AND SOME
STRONG WINDS. EXPECT A SIMILAR TREND TO CONTINUE...ESPECIALLY ACROSS
PICKENS...TUSCALOOSA...AND GREENE COUNTIES WHERE A WEAK CONVECTIVE
LINE IS MOVING SWD AND WILL LIKELY INTERSECT THE ONGOING ACTIVITY
ACROSS THE AREA. BOUNDARY LAYER COOLING SHOULD PROMOTE A GRADUAL
WEAKENING TREND WITH THE PRIMARY THREATS OF DAMAGING WINDS AND VERY
HEAVY RAINFALL. ENVIRONMENTAL CONDITIONS RESULTING FLASH FLOOD
POTENTIAL MENTIONED IN SPC MCD 1875 REMAIN LARGELY UNCHANGED WITH A
DISPLACEMENT SWWD INTO THE COUNTIES MENTIONED ABOVE. CONVECTIVE
TRENDS WILL BE MONITORED BUT A DOWNSTREAM WATCH IS NOT CURRENTLY
ANTICIPATED.

..MOSIER.. 09/04/2012

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

ATTN...WFO...TAE...BMX...MOB...MEG...JAN...

LAT...LON 32928933 33108931 33118920 33228919 33198910 33568906
33578901 33748902 33818891 33818873 33688871 33678842
33738832 33738826 33708750 33608738 33568728 33448726
33358725 33228726 33158722 33158684 33078678 33068660
33028652 32898650 32808644 32768641 32768596 32488586
32418603 32288594 32198601 32058600 32028588 31938582
31908566 31698569 31618572 31558582 31618597 31618622
31548644 31548671 31408667 31188674 31278686 31248758
31278780 31178801 31128841 31898847 32938835 32928933

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