SWODY2
SPC AC 151727
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1227 PM CDT FRI JUN 15 2007
VALID 161200Z - 171200Z
..THERE IS A SLGT RISK OF SVR TSTMS FROM THE NRN ROCKIES INTO NRN
PLAINS...
..THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF VA...NC...SC...
..SYNOPSIS...
LOWER LATITUDE BLOCKING PATTERN FROM THE WRN ATLANTIC TO SWRN STATES
WILL BEGIN TO BREAK DOWN DURING THE TWO PERIOD AS POLAR BRANCH OF
WESTERLIES AMPLIFIES OVER SRN CANADA AND THE NRN INTERMOUNTAIN
REGION. THE PRIMARY FEATURE OF INTEREST WITHIN THIS LARGER-SCALE
AIRFLOW REGIME WILL BE AMPLIFYING SHORT WAVE TROUGH TRANSLATING EWD
THROUGH THE NRN ROCKIES.
IN THE LOW-LEVELS...LEE CYCLONE ATTENDANT TO THIS STRENGTHENING
UPPER SYSTEM WILL DEEPEN OVER WY PRIOR TO DEVELOPING NEWD INTO SWRN
ND BY 17/12Z. PORTION OF BAROCLINIC ZONE IMMEDIATELY E OF THIS LOW
WILL LIFT NWD AS A WARM FRONT THROUGH THE NRN PLAINS...WHILE FARTHER
TO THE E...BOUNDARY WILL PUSH MORE SLOWLY SEWD THROUGH PARTS OF THE
UPPER GREAT LAKES INTO OH VALLEY. ELSEWHERE...LEE TROUGH OR WEAK
COLD FRONT WILL BECOME BETTER DEFINED SATURDAY OVER THE PIEDMONT OF
VA/NC/SC.
..NRN ROCKIES INTO NRN HIGH PLAINS...
STRENGTHENING ELY/SELY LOW-LEVEL FLOW TO THE E AND N OF DEEPENING
SURFACE LOW OVER WY WILL ALLOW FOR THE WWD ADVECTION OF RICHER
BOUNDARY LAYER MOISTURE INTO PARTS OF CNTRL/ERN MT WITH DEWPOINTS
INCREASING THROUGH THE LOW/MID 50S. THIS LOW-LEVEL MOISTURE
INCREASE WILL OCCUR BENEATH A PLUME OF STEEP MID-LEVEL LAPSE
RATES...EFFECTIVELY CONTRIBUTING TO A MODERATELY UNSTABLE AIR MASS
WITH MLCAPES INCREASING TO AROUND 500 J/KG OVER WRN MT...TO AS HIGH
AS 1500-2500 J/KG OVER SERN MT INTO SD.
INITIAL TSTM DEVELOPMENT IS ANTICIPATED BY MID AFTERNOON ALONG
PACIFIC COLD FRONT AND/OR COMPLEX TERRAIN OVER THE ID PNHDL INTO WRN
MT WITH ADDITIONAL STORMS ALSO BECOMING INCREASINGLY LIKELY THROUGH
THE LATE AFTERNOON AND EARLY EVENING HOURS SEWD ALONG LEE TROUGH
INTO PARTS OF CNTRL/ERN WY...AS WELL AS ALONG PRIMARY BAROCLINIC
ZONE OVER S-CNTRL/SERN MT INTO CNTRL SD. THE MOST INTENSE
CONVECTIVE DEVELOPMENT IS EXPECTED TO OCCUR SATURDAY EVENING FROM
CNTRL MT ESEWD INTO PARTS OF NWRN SD WHERE THE MODERATE INSTABILITY
WILL BE COLOCATED WITH 50-60 KT OF EFFECTIVE BULK SHEAR AND 0-3 KM
SRH OF 250-350 M2/S2.
GIVEN THIS ENVIRONMENT...THERE APPEARS TO BE A HIGH LIKELIHOOD OF
SUPERCELLS WITH THE INITIAL STORM DEVELOPMENT WITH THE POTENTIAL FOR
A FEW TORNADOES...LARGE HAIL AND DAMAGING WINDS. STORMS ARE
EXPECTED TO GROW UPSCALE INTO MULTIPLE CLUSTERS WITH MAINLY A WIND
AND HAIL THREAT CONTINUING OVERNIGHT ACROSS ERN MT AND MUCH OF
ND...PERHAPS AS FAR E AS NWRN MN.
..VA/NC/SC...
AS MENTIONED ABOVE...LEE TROUGH OR WEAK COLD FRONT WILL BECOME
BETTER DEFINED THROUGH THE DAY OVER THE PIEDMONT REGION. SLY
LOW-LEVEL FLOW AHEAD OF THIS FRONT WILL SUPPORT DEWPOINTS INCREASING
THROUGH THE 60S. THIS LOW-LEVEL MOISTURE COUPLED WITH MODEST LAPSE
RATES WILL RESULT IN THE DEVELOPMENT OF MODERATE AFTERNOON
INSTABILITY WITH MLCAPES OF 1000-1500 J/KG. FORCING ATTENDANT TO
SHORT WAVE TROUGH TRANSLATING SEWD THROUGH THE CNTRL APPALACHIANS IN
CONJUNCTION WITH TERRAIN AND BOUNDARY FORCING IN THE LOW-LEVELS
SHOULD RESULT IN AN INCREASE IN TSTM DEVELOPMENT BY AFTERNOON ACROSS
SLIGHT RISK AREA. MODEST DEEP LAYER VERTICAL SHEAR OF AROUND 30 KT
WILL BE SUPPORTIVE OF A FEW ORGANIZED...SEVERE STORMS WITH THE MAIN
THREATS BEING LARGE HAIL AND DAMAGING WINDS.
..TX...
WEAKENING MID/UPPER-LEVEL LOW WILL REMAIN QUASI-STATIONARY OVER THE
RED RIVER VALLEY THROUGH THE PERIOD. ASSOCIATED REGION OF
WEAK...LARGE-SCALE FORCING FOR ASCENT WILL ACT ON MODERATELY
UNSTABLE AIR MASS /MLCAPES OF 1500-2500 J PER KG/...RESULTING IN
CONSIDERABLE TSTM DEVELOPMENT THROUGH THE AFTERNOON AND EVENING
HOURS. WEAK VERTICAL SHEAR WILL LIMIT MORE ORGANIZED...SEVERE STORM
DEVELOPMENT. LOCALIZED...MARGINALLY SEVERE STORM CLUSTERS WILL BE
POSSIBLE...LIKELY BEING DRIVEN MESOSCALE BOUNDARIES AND/OR MCV/S
REMNANT FROM FRIDAY/S TSTM DEVELOPMENT. GIVEN THE UNCERTAINTY IN
THE DEVELOPMENT/LOCATION OF THESE FEATURES...
CATEGORICAL/PROBABILISTIC FORECASTS HAVE BEEN DOWNGRADED.
..UPPER MIDWEST...
A FEW STRONG TO MARGINALLY SEVERE STORMS WILL BE POSSIBLE SATURDAY
AFTERNOON INTO EVENING ALONG FRONT OVER SRN MN/NRN IA INTO WI WHERE
AIR MASS WILL BECOME MODERATELY UNSTABLE. GENERALLY WEAK VERTICAL
SHEAR SHOULD LIMIT A MORE SUBSTANTIAL SEVERE THREAT...THEREFORE ONLY
LOW SEVERE PROBABILITIES HAVE BEEN MAINTAINED.
..SRN FL PENINSULA...
RICH...BOUNDARY LAYER MOISTURE /DEWPOINTS OF 70-75F/ WILL LARGELY
CONTRIBUTE TO A MODERATELY UNSTABLE AIR MASS /MLCAPES OF 2000-2500 J
PER KG/ BY AFTERNOON. TSTMS WILL LIKELY BE FOCUSED PRIMARILY ALONG
SEA BREEZE BOUNDARIES WITH SOME THREAT OF MARGINALLY SEVERE HAIL
AND/OR LOCALLY STRONG WIND GUSTS WITH THE MOST INTENSE STORMS.
RELATIVELY WEAK VERTICAL SHEAR SHOULD LIMIT A MORE ORGANIZED STORM
THREAT.
.MEAD.. 06/15/2007
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