SWODY1
SPC AC 182000
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0300 PM CDT TUE SEP 18 2007
VALID 182000Z - 191200Z
..THERE IS A SLGT RISK OF SVR TSTMS PORTIONS CENTRAL PLAINS...
..SYNOPSIS...
UPPER AIR PATTERN REMAINS DOMINATED BY MEAN WRN TROUGH AND
POSITIVELY TILTED RIDGING FROM VICINITY TX COAST NEWD ACROSS NRN NEW
ENGLAND. CUT-OFF MID/UPPER LEVEL LOW OVER FL WILL CONTRIBUTE TO GEN
THUNDER POTENTIAL OVER THAT REGION THIS AFTERNOON AND TONIGHT.
FARTHER NW...SEVERAL SMALL VORTICITY MAXIMA ARE PHASED AS SHORTWAVE
TROUGH -- NOW EVIDENT IN MOISTURE CHANNEL IMAGERY OVER BLACK HILLS
AND CENTRAL/SRN HIGH PLAINS. THIS TROUGH SHOULD LIFT NEWD AND
DEAMPLIFY SLIGHTLY THROUGH TONIGHT... REACHING PORTIONS MID/UPPER MS
VALLEY BY 19/12Z. SERIES OF INITIALLY LOW-AMPLITUDE SHORTWAVE
PERTURBATIONS AND SPEED MAXIMA OVER WRN BC AND ADJACENT PACIFIC ARE
FCST TO CONTINUE PHASING AND DIGGING SSEWD THROUGH REMAINDER
PERIOD...LEADING TO CLOSED LOW OVER SWRN WA/NWRN ORE BY 19/12Z.
AT SFC...WAVY COLD FRONT IS ANALYZED FROM NRN MN SWWD ACROSS SERN
SD...S-CENTRAL/SWRN NEB...NWRN KS...E-CENTRAL CO. WEAK LOW HAS BEEN
ANALYZED JUST S FRONT FOR A COUPLE HOURS...NEAR HLC...AND SHOULD BE
OVERTAKEN/APPENDED WITH FRONTAL ZONE SHORTLY. CO PORTION OF FRONT
SHOULD STALL THIS EVENING. FRONT SHOULD MOVE EWD ACROSS MN AND
INTO WRN IA...WHILE MOVING SLOWLY SWD INTO MORE OF NRN KS. DRYLINE
-- INITIALLY INTERSECTING FRONT OVER NWRN KS -- IS EXPECTED TO
REMAIN OVER OK/TX PANHANDLE AND WRN KS...WITH MINOR OSCILLATIONS
POSSIBLE BEFORE SLGT NOCTURNAL RETREAT.
..CENTRAL PLAINS...
INITIAL CLOUD/PRECIP BAND FROM SW OK TO WRN LS IS OCCURRING IN BELT
OF LOW LEVEL WAA...SUBTLE MID/UPPER LEVEL ASCENT...AND FAVORABLE
MOISTURE WITH GPS INDICATED PW 1.5-2 INCH IN NARROW PLUME. THIS
ACTIVITY IS EXPECTED TO SHIFT NEWD ACROSS SRN/CENTRAL LOW
PLAINS...MID MS VALLEY AND WI...WITH WIDELY SCATTERED TSTMS IN
CLUSTERS AND SMALL BANDS. SVR POTENTIAL WILL BE LIMITED BY WEAKNESS
OF LAPSE RATES AND BY LACK OF STRONGER LOW LEVEL FORCING.
BEHIND INITIAL BAND...PRIND LAPSE RATES WILL CONTINUE TO STEEPEN IN
BOTH LOW AND MIDDLE LEVELS...RELATED TO REMAINDER OF AFTERNOON
INSOLATION AND MIDLEVEL DESTABILIZATION FROM DPVA.
MEANWHILE...FAVORABLE MOISTURE WILL PERSIST WITH SFC DEW POINTS
MID-UPPER 60S OVER KS/NEB...WITH NARROW BAND OF 70S FROM CENTRAL KS
TO OK. THESE FACTORS ARE CONTRIBUTING TO INCREASING BUOYANCY --
E.G. MLCAPES 1500-2000 J/KG -- AND WEAKENING SBCINH FROM
CENTRAL/NERN NEB SSWWD ACROSS WRN KS. THIS WILL SUPPORT SCATTERED
TSTMS INVOF SFC FRONTAL ZONE AND ALONG/AHEAD OF DRYLINE...WITH
SUPERCELL EVOLUTION POSSIBLE IN ANY RELATIVELY DISCRETE/SUSTAINED
ACTIVITY. DAMAGING GUSTS AND LARGE HAIL EACH ARE POSSIBLE.
GREATEST JUXTAPOSITION OF BUOYANCY AND SHEAR DURING REST OF
AFTERNOON SHOULD REMAIN OVER S-CENTRAL NEB INTO NRN KS...WHERE 45-55
KT EFFECTIVE SHEAR MAGNITUDES ARE EVIDENT IN RUC FCST SOUNDINGS.
HOWEVER...LOW LEVEL HODOGRAPHS MAY REMAIN RATHER SMALL GIVE SWLY SFC
WINDS AND RELATED LACK OF MORE ROBUST DIRECTIONAL SHEAR. CONVECTION
SHOULD CONTINUE AFTER 03Z AND MOVE EWD ACROSS CENTRAL PLAINS TOWARD
IA/NWRN MO...SVR PROBABILITIES DIMINISHING WITH TIME DUE TO
WEAKENING INSTABILITY.
.EDWARDS.. 09/18/2007
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
To unsubscribe from WX-STORM send e-mail to LISTSERV@PO.UIUC.EDU with
"unsub wx-storm" in the body of your message. For more information write chris@lib.siu.edu.
No comments:
Post a Comment