SWODY2
SPC AC 021738
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1238 PM CDT FRI JUL 02 2010
VALID 031200Z - 041200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE UPPER MIDWEST SSWWD TO
NRN/WRN NEB AND SERN WY...
...SYNOPSIS...
A SPLIT FLOW REGIME IS EXPECTED TO DEVELOP OVER THE NWRN U.S. ON
SATURDAY AS STRONGER BAND OF WLY MID-UPPER LEVEL WINDS REACH SWRN
CANADA THIS FORECAST PERIOD. A SHORTWAVE TROUGH...CURRENTLY LOCATED
OFF THE COASTS OF SERN AK/NWRN BC...WILL DIG SEWD WITHIN THE SRN
BRANCH OF THE SPLIT FLOW THROUGH THE PAC NW TOWARD NV. THIS WILL
SUPPORT THE SRN EXTENT OF THE WRN LONGWAVE TROUGH TO LAG OVER THE
GREAT BASIN THROUGH DAY 2. A STRONG RIDGE EXTENDING OVER THE SOUTH
CENTRAL STATES TO GREAT LAKES AND ACROSS MUCH OF THE ERN U.S. WILL
LIMIT EWD SHIFT OF A TROUGH FROM THE NRN ROCKIES TO ND/CENTRAL
CANADA THIS PERIOD. MODELS MAINTAIN ONLY WEAK HEIGHT FALLS ACROSS
NEB TO THE UPPER MIDWEST. THE EVOLUTION OF THE UPPER FLOW PATTERN
SUGGESTS A COLD FRONT WILL MOVE SLOWLY E/SEWD ACROSS THE
DAKOTAS/NEB...AND SHOULD REACH NRN MN TO NWRN KS AND ERN CO BY 12Z
SUNDAY.
MEANWHILE...WEAK IMPULSES WILL TRACK NNEWD ALONG THE WRN PERIPHERY
OF THE UPPER RIDGE FROM THE SRN HIGH PLAINS TO UPPER MS VALLEY...
WHILE ADDITIONAL IMPULSES MOVE THROUGH THE GREAT BASIN TO THE UPPER
MIDWEST. MODELS ARE IN GENERAL AGREEMENT SUGGESTING IMPULSES FROM
THESE TWO VORTICITY STREAMS SHOULD PHASE OVER THE MID MO TO UPPER MS
VALLEYS DURING THE LATTER HALF OF DAY 2.
...ERN DAKOTAS/WRN AND NRN MN/NRN AND WRN NEB/SERN WY...
GIVEN SLOW E/SEWD MOVEMENT OF THE COLD FRONT...A MINOR WWD
ADJUSTMENT OF THE SLIGHT RISK IN ERN ND/SD HAS BEEN MADE IN THIS DAY
2 OUTLOOK. THE SLIGHT RISK AREA HAS ALSO BEEN EXPANDED WNWWD INTO
SERN WY TO ACCOUNT FOR TSTM DEVELOPMENT/SEVERE WEATHER POTENTIAL AS
THE COLD FRONT REACHES THIS AREA LATE SATURDAY AFTERNOON/EARLY
EVENING.
AT 12Z SATURDAY...TSTMS...POTENTIAL SRN EXTENT OF AN MCS MAINLY OVER
CANADA...MAY BE AFFECTING FAR NRN/NERN MN. THIS ACTIVITY SHOULD
WEAKEN AND/OR MOVE AWAY FROM NRN MN. MEANWHILE...SLY LOW LEVEL FLOW
ACROSS THE PLAINS WILL MAINTAIN RICH MOISTURE ADVECTION INTO THE NRN
PLAINS/UPPER MIDWEST WITH SURFACE DEWPOINTS IN THE UPPER 60S TO
AROUND 70 REACHING THE ERN DAKOTAS/WRN MN BY SATURDAY AFTERNOON.
THIS COMBINED WITH SURFACE HEATING AHEAD OF THE COLD FRONT AND
BENEATH A PLUME OF STEEP MIDLEVEL LAPSE RATES WILL RESULT IN
MODERATE TO VERY STRONG INSTABILITY IN THE WARM SECTOR. MLCAPE
VALUES TO AROUND 3000 J/KG SHOULD DEVELOP ACROSS NERN SD/ERN ND AND
NWRN MN. WEAK HEIGHT FALLS ACROSS THE SLIGHT RISK AREA SUGGEST THE
NEWD TRACKING IMPULSES AND CONVERGENCE ALONG THE FRONT WILL BE
REQUIRED TO OVERCOME A CAPPING INVERSION EXPECTED OVER THIS REGION
SATURDAY. ALTHOUGH STRONGER MID-UPPER LEVEL SWLY FLOW/ DEEP LAYER
SHEAR IS EXPECTED TO LAG THE COLD FRONT...SUFFICIENT SHEAR /AROUND
30 KT/ WILL SUPPORT MULTICELLS AND POSSIBLE SUPERCELL STRUCTURES
WITH INITIAL ACTIVITY NOT EXPECTED TO MAKE MUCH MOVEMENT OFF THE
COLD FRONT. GIVEN DEGREE OF INSTABILITY OVER THE ERN DAKOTAS/NWRN
MN...VERY LARGE HAIL WILL BE POSSIBLE WITH VALUES EXCEEDING 2 INCHES
IN DIAMETER. DAMAGING WINDS WILL ALSO BE A THREAT WITH THE ACTIVITY
ALONG THE FRONT AND WITH ANY COLD POOL GENERATION.
A STRENGTHENING/VEERING LLJ FROM THE CENTRAL PLAINS TO THE UPPER
MIDWEST SATURDAY NIGHT WILL LIKELY RESULT IN UPSCALE GROWTH OF ONE
OR MORE MCS/S FROM NEB INTO THE UPPER MS VALLEY WITH PRIMARY THREAT
BECOMING DAMAGING WINDS...THOUGH HAIL WILL BE POSSIBLE.
...CENTRAL/SRN HIGH PLAINS...
LOW SEVERE WEATHER PROBABILITY /5 PERCENT/ HAS BEEN SHIFTED WWD IN
THIS OUTLOOK TO ACCOUNT FOR GREATER POTENTIAL OF ISOLATED STRONG TO
SEVERE STORM SATURDAY AFTERNOON. STRONG SURFACE HEATING OVER THE
HIGH PLAINS OF ERN CO/ERN NM JUXTAPOSED ALONG WRN EXTENT OF MOISTURE
RETURN WILL RESULT IN MODERATE INSTABILITY ESPECIALLY FROM THE
CENTRAL HIGH PLAINS INTO NERN NM WHERE MIDLEVEL LAPSE RATES WILL BE
THE STEEPEST. THE SRN EXTENT OF STRONGER SWLY FLOW ALOFT WILL
PROMOTE EFFECTIVE BULK SHEAR /25-30 KT/ FAVORABLE FOR MULTICELLS
WITH HAIL AND DAMAGING WIND.
..PETERS.. 07/02/2010
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