SWOMCD
SPC MCD 190410 COR
MNZ000-IAZ000-NEZ000-SDZ000-190600-
MESOSCALE DISCUSSION 1797
NWS STORM PREDICTION CENTER NORMAN OK
1110 PM CDT SAT AUG 18 2007
AREAS AFFECTED...PORTIONS SERN SD...NERN NEB...NWRN/N-CENTRAL IA.
CONCERNING...TORNADO WATCH 615...
VALID 190410Z - 190600Z
CORRECTED FOR WW TYPE
THE SEVERE WEATHER THREAT FOR TORNADO WATCH 615 CONTINUES.
CONVECTION IS SLOW TO DEVELOP ACROSS SERN SD...LIKELY RELATED TO
LACK OF LIFT RESULTING FROM COMBINATION OF SHALLOW SLOPE OF FRONTAL
ZONE IN THIS AREA AND LOSS OF SFC DIABATIC HEATING. SHOWERS AND
WEAK TSTMS ARE MOVING ENEWD APPROXIMATELY 20 KT OVER PORTIONS BOH
HOMME/HUTCHINSON COUNTIES -- AS OF 445Z -- WITH SOME POTENTIAL FOR
INTENSIFICATION DURING NEXT 2-3 HOURS AS ACTIVITY MOVES TOWARD FSD
AREA...NWRN CORNER IA AND SWRN CORNER MN. MESOANALYSIS SHOWS
FRONTAL-WAVE LOW BETWEEN MHE-YKN...WITH QUASISTATIONARY FRONTAL ZONE
EWD OVER NWRN IA THEN SEWD ACROSS CENTRAL IA. LOW LEVEL VERTICAL
SHEAR WILL REMAIN MAXIMIZED AND MOST FAVORABLE FOR SUPERCELLS ALONG
AND JUST N OF FRONT...WITH 0-3 KM SRH AOA 300 J/KG ESTIMATED FROM
FSD AREA EWD. MODIFIED RUC SOUNDINGS SUGGEST THAT EFFECTIVE PARCELS
WILL REMAIN ROOTED AT OR VERY NEAR SFC ALONG FRONT FOR ANOTHER 2-3
HOURS...PARTICULARLY NEAR AND ESE OF SFC WAVE WHERE STRONGEST SFC
THETAE PERSISTS. RICH LOW LEVEL MOISTURE WILL CONTINUE OVER
REGION...ESPECIALLY E AND SE OF SFC LOW WHERE NARROW CORRIDOR OF
1500-2500 J/KG MLCAPE WILL CONTINUE THROUGH ABOUT 05Z. SBCINH IS
FCST TO INCREASE GRADUALLY...HOWEVER...AS MOIST SFC AIR MASS
SLOWLY/DIABATICALLY COOLS.
OTHERWISE...ALTHOUGH AIR MASS REMAINS FAVORABLY MOIST AND SHEARED
ALONG/S OF FRONT...OTHER FACTORS -- INCLUDING WEAK FORCING AND LACK
OF SIGNIFICANT SHALLOW CONVECTION EVIDENT IN IR IMAGERY -- INDICATE
SEVERE PROBABILITIES ARE DIMINISHING. LOOSELY ORGANIZED BAND OF
STG-SVR TSTMS -- MOVING EWD 20-25 KT INTO WRN-MOST CHERRY COUNTY NEB
-- SHOULD NOT REACH WW BEFORE SCHEDULED EXPIRATION. THEREFORE...PER
COORDINATION W/LBF/OAX...SOME COUNTIES S OF SD/NEB BORDER MAY BE
CLEARED BEFORE 5Z.
.EDWARDS.. 08/19/2007
..PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...ARX...MPX...DMX...FSD...OAX...ABR...LBF...UNR...
42090014 42980020 42999949 43519956 43559931 43959934
43929895 44249885 44179641 43849645 43839482 43519487
43509304 42189298 42219640 42429744 42429832 42069828
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