SWODY1
SPC AC 091956
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0256 PM CDT THU SEP 09 2010
VALID 092000Z - 101200Z
...THERE IS A SLGT RISK OF SVR TSTMS INTO EARLY TONIGHT FOR THE NRN
HIGH PLAINS...
...NRN HIGH PLAINS...
NO CHANGES NEEDED AS OBJECTIVE ANALYSES SHOWED AIR MASS
DESTABILIZING ACROSS WRN NEB/SD INTO SERN MT...ALONG AND E OF LEE
TROUGH AND INVOF DEEPENING SURFACE LOW OVER SERN MT. EFFECTIVE BULK
SHEAR IS STRENGTHENING /35-50 KT/ ACROSS THE CENTRAL/NRN HIGH PLAINS
THIS AFTERNOON AS STRONGER JET CORE ATTENDANT TO ID SHORTWAVE TROUGH
SPREADS NEWD.
...CENTRAL ND...
ONGOING ELEVATED TSTMS /LOCATED N-E OF BIS/ MAY PRODUCE AN ISOLATED
HAIL THREAT THIS AFTERNOON GIVEN EFFECTIVE BULK SHEAR /30-35 KT/...
MARGINAL INSTABILITY AND MIDLEVEL LAPSE RATES NEAR 7 C/KM. THIS
AREA CONTINUES TO WARRANT LOW SEVERE PROBABILITIES.
...CENTRAL/NRN AR...
NO CHANGES NEEDED WITH THIS OUTLOOK MAINTAINING A LOW TORNADO
PROBABILITY /2 PERCENT/ ACROSS NRN HALF OF AR...WITH GREATEST
POTENTIAL...THOUGH STILL A LOW THREAT...ACROSS NWRN AR WHERE THE LOW
LEVEL SW-NE ORIENTED CONFLUENCE ZONE INTERSECTS THE WARM FRONT.
SUFFICIENT DEEP LAYER SHEAR SUPPORTING ORGANIZED STORMS RESIDES N/NE
OF THE WARM FRONT WHICH EARLY THIS AFTERNOON EXTENDED FROM SWRN TN
WNWWD THROUGH NRN AR TO A WEAKENING SURFACE LOW /ATTENDANT TO TC
HERMINE/ OVER FAR SERN KS. HOWEVER...CURRENT LOW LEVEL EFFECTIVE
SRH /200-300 M2 PER S2/ EXTENDING INTO NWRN AR INVOF THE WARM FRONT
SUGGESTS A NON-ZERO TORNADO THREAT THROUGH THE AFTERNOON. FURTHER
WEAKENING AND VEERING OF THE SWLY LLJ INTO WRN/NRN AR SHOULD REDUCE
THIS LOW SEVERE WEATHER THREAT BY THIS EVENING.
...DOWNEAST MAINE...
COLD MIDLEVEL TEMPERATURES...ATTENDANT TO CLOSED LOW MOVING ACROSS
MAINE...COMBINED WITH SURFACE HEATING AND DEWPOINTS IN THE UPPER 50S
HAS RESULTED IN MARGINAL INSTABILITY IN ADVANCE OF A WIND SHIFT. A
FEW LIGHTNING STRIKES REMAIN POSSIBLE YET THIS AFTERNOON...PRIOR TO
SURFACE BOUNDARY...WHICH CURRENTLY EXTENDED FROM NRN WASHINGTON TO
LINCOLN COUNTIES...MOVES OFFSHORE. LIMITED POTENTIAL FOR STRIKES
AND EXPECTED SHORT DURATION PRECLUDES THE INCLUSION OF A GENERAL
TSTM AREA FOR THIS REGION.
..PETERS.. 09/09/2010
.PREV DISCUSSION... /ISSUED 1128 AM CDT THU SEP 09 2010/
...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.
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