SWOMCD
SPC MCD 192146
ALZ000-FLZ000-MSZ000-192315-
MESOSCALE DISCUSSION 0528
NWS STORM PREDICTION CENTER NORMAN OK
0446 PM CDT SUN APR 19 2009
AREAS AFFECTED...PORTIONS SERN MS...WRN-CENTRAL AL.
CONCERNING...TORNADO WATCH 173...
VALID 192146Z - 192315Z
THE SEVERE WEATHER THREAT FOR TORNADO WATCH 173 CONTINUES.
CONTINUE WW ALONG/AHEAD OF PREFRONTAL BOUNDARY DESCRIBED BELOW.
OCCASIONAL TIGHTENING OF CYCLONIC SHEAR HAS BEEN NOTED IN A FEW
CELLS WITHIN WW AREA DURING PAST 2-3 HOURS...AND REMAINS POSSIBLE.
SEVERAL MIXED/OFFSETTING FACTORS ARE EVIDENT...BUT WILL MAINTAIN AT
LEAST MRGL TORNADO POTENTIAL FOR TIME BEING.
SFC MESOANALYSIS SHOWS COLD FRONT MOVING EWD INTO NWRN MS...AND
ACROSS S-CENTRAL LA. PREFRONTAL SFC TROUGH AND COLLOCATED
CONFLUENCE LINE STILL IS WELL-DEFINED ACROSS EXTREME ERN MS FROM
NEAR CBM SSWWD TO JUST E OF PIB TO NEAR SIL. BOTH BOUNDARIES WILL
CONTINUE MOVING EWD...WITH AREA OF PRONOUNCED SFC VEERING BETWEEN
THEM THAT WILL LIMIT FRONTAL CONVERGENCE. MEANWHILE...PREFRONTAL
BOUNDARY WILL CONTINUE TO FORM EFFECTIVE WRN LIMIT FOR MOST
CONVECTIVE DEVELOPMENT. LOW LEVEL SHEAR WILL REMAIN STRONGEST E OF
THIS BOUNDARY ACROSS AL...WHERE RELATIVELY BACKED SFC WINDS VEER
SHARPLY WITH HEIGHT INTO LLJ THAT HAS WEAKENED TO ABOUT 35 KT.
EXPECT LLJ TO STRENGTHEN AGAIN AND ELONGATE HODOGRAPHS AFTER DARK E
OF CONFLUENCE LINE. UNTIL THEN...HOWEVER...PROFILES SHOULD REMAIN
FAVORABLE FOR SUPERCELLS WITH 0-1 KM SRH GENERALLY 300-500 J/KG.
SRH MAX SHOULD SHIFT EWD OR ENEWD ACROSS CENTRAL AL. ONE LIMITING
EFFECT WILL BE SLOWLY DECREASING BUOYANCY WITH TIME -- RELATED TO
LOSS OF STRONGEST DIURNAL HEATING. ALSO...DRIER AIR MASS OVER
E-CENTRAL/NERN AL REDUCES CAPE CONSIDERABLY WITH EWD EXTENT...AND
NARROWS OPTIMALLY MOIST BOUNDARY LAYER PLUME ACROSS WRN/CENTRAL AL.
MOIST ADVECTION MAY OFFSET THIS FACTOR SOMEWHAT THROUGH EARLY
EVENING...ESPECIALLY AS VERTICAL MIXING DIMINISHES.
..EDWARDS.. 04/19/2009
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...BMX...HUN...MOB...JAN...LIX...
LAT...LON 30648770 30448845 30728901 31308893 33308820 34188808
34238706 33908711 33778660 33398641 33078655 33058684
31978687 31958646 31528652 31508668 30978673 31028756
30648770
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