Thursday, September 9, 2010

DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 091629
SWODY1
SPC AC 091628

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1128 AM CDT THU SEP 09 2010

VALID 091630Z - 101200Z

...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON INTO EARLY
TONIGHT FOR THE NRN HIGH PLAINS...

...NRN HIGH PLAINS THIS AFTERNOON INTO EARLY TONIGHT...
NO SUBSTANTIAL CHANGES TO THE PRIOR OUTLOOK AREA AND REASONING. A
HIGH-AMPLITUDE TROUGH WILL MOVE EWD FROM THE NRN ROCKIES/GREAT BASIN
TO THE NRN HIGH PLAINS BY EARLY FRIDAY. THE MIDLEVEL TROUGH WILL BE
PRECEDED BY A LEE CYCLONE THAT WILL DEVELOP NEWD FROM SE MT TO WRN
ND...WHILE S OF THE CYCLONE A LEE TROUGH WILL MOVE SLOWLY EWD THIS
EVENING ACROSS THE NRN AND CENTRAL HIGH PLAINS. BOUNDARY LAYER
DEWPOINTS IN THE LOW-MID 60S ARE RETURNING NNWWD IN A CORRIDOR FROM
NEB TOWARD WRN ND TO THE E OF THE LEE TROUGH AND S OF A WARM
FRONT...AND BENEATH A PLUME OF 7-7.5 C/KM MIDLEVEL LAPSE RATES.
WITH ADDITIONAL SURFACE HEATING THROUGH THE AFTERNOON... MLCAPE
VALUES WILL LIKELY INCREASE TO THE 1000-2000 J/KG RANGE... WITH
MINIMAL CONVECTIVE INHIBITION BY LATE AFTERNOON ALONG THE LEE
TROUGH.

THUNDERSTORM DEVELOPMENT IS EXPECTED BY 21-23Z NEAR THE SURFACE LOW
CLOSE TO THE MT/ND BORDER...AND SWD ALONG THE LEE TROUGH NEAR THE
WY/SD BORDER. DEEP-LAYER VERTICAL SHEAR AND INSTABILITY WILL BE
FAVORABLE FOR SUPERCELLS AND ORGANIZED LINE SEGMENTS...WITH AN
ACCOMPANYING RISK FOR LARGE HAIL AND DAMAGING WINDS. A COUPLE OF
TORNADOES WILL ALSO BE POSSIBLE THIS EVENING...PRIMARILY ACROSS NW
SD/SW ND IN PROXIMITY TO THE WARM FRONT WHERE THE INITIAL STORMS
WILL BE SUPERCELLULAR AND SOMEWHAT STRONGER LOW-LEVEL SHEAR WILL
CORRESPOND WITH THE LOW-LEVEL MOISTURE/INSTABILITY AXIS. THE SEVERE
STORM THREAT WILL BEGIN TO DIMINISH TONIGHT TOWARD THE CENTRAL
DAKOTAS.

...CENTRAL/NRN AR THIS AFTERNOON...
THE REMNANTS OF TROPICAL DEPRESSION HERMINE ARE MOVING ENEWD FROM NE
OK/SE KS TO NW AR AND SW MO...ALONG AND N OF SURFACE WARM FRONT NEAR
I-40 ACROSS AR. SURFACE-BASED STORMS CAN BE EXPECTED NEAR THE
INTERSECTION OF THE WARM FRONT AND THE PRIMARY CONFLUENCE BAND WHICH
EXTENDS FROM SE OK INTO NW AR...WHICH ALSO COINCIDES WITH THE BELT
OF STRONGER LOW-LEVEL SLY/SWLY FLOW AND EFFECTIVE SRH IN EXCESS OF
200 M2/S2. THERE WILL BE A WINDOW OF OPPORTUNITY FOR A FEW ROTATING
STORMS THIS AFTERNOON...AND PERHAPS A BRIEF TORNADO ...ALONG THE
WARM FRONT WITH THE REMNANTS OF HERMINE...BEFORE THE SYSTEM WEAKENS
AND THE BOUNDARY LAYER STABILIZES BY LATE EVENING. AT THIS
TIME...THE TORNADO THREAT APPEARS TO BE REDUCED A LITTLE FROM PRIOR
DAYS...SO WILL MAINTAIN 2% TORNADO PROBABILITY AREA.

..THOMPSON/ROGERS.. 09/09/2010

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