SWODY1
SPC AC 240057
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0757 PM CDT TUE SEP 23 2008
VALID 240100Z - 241200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF SW IA...FAR SE
NEB...NE KS...
...UPPER MIDWEST/MID-MO VALLEY AND CNTRL PLAINS...
WATER VAPOR CURRENTLY SHOWS A WELL-DEVELOPED PROGRESSIVE UPPER-LEVEL
TROUGH OVER THE WRN DAKOTAS WITH A NARROW DRY SLOT ADVANCING EWD
INTO WRN MN ATTM. THE RUC ANALYZES A 30 TO 40 KT LOW-LEVEL JET
ACROSS THE WARM SECTOR FROM SE NEB NNEWD ACROSS IA INTO ERN MN WHERE
NUMEROUS THUNDERSTORMS ARE ONGOING. THIS CONVECTION SHOULD PERSIST
THROUGH THIS EVENING INTO THE OVERNIGHT PERIOD AS THE LOW-LEVEL JET
STRENGTHENS. IN SPITE OF THE WEAKER LARGE-SCALE ASCENT IN THE CNTRL
PLAINS...THE AMOUNT OF INSTABILITY SHOULD ALLOW THE THUNDERSTORMS IN
NCNTRL KS TO PERSIST THROUGH MUCH OF THE EVENING. AN ISOLATED
THUNDERSTORM MAY ALSO INITIATE FURTHER SOUTHWEST ACROSS SW KS OR THE
TX PANHANDLE.
CONCERNING THE SHEAR ENVIRONMENT...WSR-88D VWPS ALONG THE AXIS OF
THE LOW-LEVEL JET SHOW 0-6 KM SHEAR VALUES OF 30 TO 40 KT. THIS
AMOUNT OF SHEAR SHOULD BE SUFFICIENT FOR ORGANIZED MULTICELLS AND
BOWING LINE-SEGMENTS MAINLY ACROSS WRN IA...SE NEB AND NCNTRL KS
WHERE INSTABILITY AND LOW-LEVEL MOISTURE IS LOCALLY MAXIMIZED. THE
00Z TOPEKA SOUNDING HAS A SFC-3 KM LAPSE RATE AROUND 8.0 C/KM
SUGGESTING LOW-LEVEL THERMODYNAMICS MAY BE SUFFICIENT FOR A FEW
DAMAGING WIND GUSTS EARLY THIS EVENING. IN ADDITION...THE RUC SHOWS
AN AXIS OF STEEP MID-LEVEL LAPSE RATES FROM SW KS EXTENDING NEWD
INTO WRN IA WHICH ALONG WITH THE INSTABILITY MAY ALLOW THE THREAT
FOR LARGE HAIL TO PERSIST FOR A FEW MORE HOURS.
...ERN DAKOTAS...
A WELL-DEFINED PROGRESSIVE UPPER-LEVEL TROUGH OVER THE CNTRL DAKOTAS
WILL CONTINUE EWD THIS EVENING INTO THE ERN DAKOTAS. SCATTERED
THUNDERSTORMS ARE ONGOING EAST OF THE UPPER-LEVEL TROUGH ALONG THE
LEADING EDGE OF LARGE-SCALE ASCENT. THIS ACTIVITY SHOULD PERSIST FOR
A FEW MORE HOURS BEFORE SFC TEMPS BEGIN TO RAPIDLY COOL. THE 00Z
SOUNDING IN ABERDEEN SD IS SAMPLING THE COLD AIR ALOFT ASSOCIATED
WITH THE UPPER-LEVEL TROUGH WITH A 500 MB TEMP AROUND -20 C. THIS
COMBINED WITH ABOUT 60 KT OF VERTICAL SHEAR SHOULD SUPPORT A
MARGINAL THREAT FOR HAIL WITH THE MORE INTENSE CELLS.
..BROYLES.. 09/24/2008
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