SPC AC 010535
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1235 AM CDT SUN JUL 01 2007
VALID 011200Z - 021200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS ERN MT...ND...AND NWRN
MN...
...SYNOPSIS...
BROAD UPPER RIDGE WILL PERSIST ACROSS THE NCNTRL U.S. AND CNTRL
CANADA THIS PERIOD AS LOWER AMPLITUDE WAVES EMANATE FROM CYCLONIC
FLOW ACROSS THE PACIFIC NORTHWEST AND TRANSLATE THROUGH THE RIDGE
FROM THE CANADIAN PRAIRIES/NRN PLAINS TO THE UPPER MS VALLEY.
DEEP-LAYER NWLY FLOW WILL PERSIST FROM THE GREAT LAKES ACROSS THE OH
VALLEY AND MID ATLANTIC REGIONS WITHIN SRN PORTIONS OF LARGE SCALE
TROUGH LOCATED ACROSS ERN CANADA AND THE NORTHEAST. SEVERAL DAYS OF
WIDESPREAD DIURNAL CONVECTION HAVE AIDED IN PUSHING A WEAK/SEGMENTED
FRONTAL ZONE SWD/SWWD INTO THE SOUTHEAST...TN AND MID/LOWER MS
VALLEYS. ABUNDANT TROPICAL MOISTURE PERSISTS WITHIN THIS FRONTAL
ZONE. MEANWHILE...LONG-LIVED MID LEVEL WEAKNESS COINCIDENT WITH
DEEP-LAYER MOISTURE ACROSS THE SCNTRL U.S. WILL CONTINUE TO AID
DIURNAL TSTM DEVELOPMENT FROM TX/ERN OK ACROSS AR/LA.
HOT CONDITIONS AND HIGH TERRAIN AFTERNOON STORMS WILL OCCUR WITHIN
BLOCKING RIDGE ACROSS THE SOUTHWEST AND ROCKIES.
...MT/ND/NRN MN...
LOW LEVEL MOISTURE CONTINUES TO GRADUALLY INCREASE ACROSS THE NRN
PLAINS BENEATH STRONG CAP EVIDENT ON ABR AND BIS SOUNDINGS LAST
EVENING. LATEST GUIDANCE INDICATES 60-65F DEWPOINTS AND STEEP LAPSE
RATES ASSOCIATED WITH EML WILL CONTRIBUTE TO THE DEVELOPMENT OF
STRONG DESTABILIZATION FROM CNTRL/ERN MT EWD ACROSS ND THIS
AFTERNOON WITH MLCAPES OF 1500-2500 J/KG.
NAM-WRF/GFS AND SREF REMAIN IN GOOD AGREEMENT IN THE EVOLUTION OF A
LOW AMPLITUDE SHORT WAVE TROUGH TRANSLATING EWD FROM CNTRL MT
TODAY...AND CRESTING BROAD RIDGE SITUATED ACROSS ND THROUGH TONIGHT.
SYNOPTIC FORCING FOR ASCENT WITH THIS FEATURE IS EXPECTED TO ENHANCE
LOW-LEVEL CONVERGENCE INVOF SFC LEE/THERMAL LOW AND ACT TO OVERCOME
WARM SECTOR CAPPING. TSTM DEVELOPMENT SHOULD ENSUE... INITIALLY
ACROSS MT...AND THEN EWD ACROSS ND THROUGH THE EVENING.
FORECAST SOUNDINGS SUGGEST THAT VERTICAL SHEAR WILL BE MORE THAN
SUFFICIENT /40-50KT/ FOR ORGANIZED/ROTATING STORMS CAPABLE OF
POTENTIALLY VERY LARGE HAIL AND DAMAGING WINDS. A TORNADO THREAT MAY
EVOLVE FOR A FEW HOURS NEAR AND NORTHEAST OF THE SURFACE LOW/TROUGH
WHERE FORECAST LOW LEVEL SHEAR PROFILES APPEAR SUPPORTIVE OF
MESOCYCLONES. OVERALL PATTERN ALSO SUGGESTS THAT
SCATTERED...INITIALLY DISCRETE...CONVECTION MAY GROW UPSCALE INTO A
SEVERE MCS. NOCTURNAL LLJ INCREASES TO 40KT AND SHOULD MAINTAIN MASS
AND MOISTURE FLUX INTO THE CONVECTIVE GENERATION REGION THROUGH THE
LATE EVENING. MCS SCENARIO IS FURTHER SUPPORTED BY BOTH GFS AND
NAM-WRF WITH DAMAGING WIND THREAT POSSIBLY INCREASING AND SPREADING
EWD FROM ERN ND INTO WRN MN DURING THE NIGHT.
...SOUTHEAST TO LOWER MS VALLEY...
WEAKENING/FRACTURED LOW-LEVEL FRONTAL BOUNDARIES...RESIDUAL OUTFLOW
BOUNDARIES...AND SEA BREEZES WILL EXIST AMIDST VERY MOIST AND
INCREASINGLY UNSTABLE AIR MASS ACROSS THESE REGIONS. DIURNAL HEATING
WILL CONTRIBUTE TO THE DEVELOPMENT OF MODERATE TO LOCALLY STRONG
AFTERNOON INSTABILITY WITH MLCAPES OF 2000-3000 J/KG. VERTICAL SHEAR
WILL REMAIN QUITE WEAK BENEATH MID/UPPER LEVEL FLOW AOB 15KT.
THUS...DEGREE OF INSTABILITY SUGGESTS THE POTENTIAL WILL EXIST FOR A
FEW ORGANIZED MULTICELL CLUSTERS AND PULSE STORMS CAPABLE OF
ISOLATED TO WIDELY SCATTERED HAIL AND LOCALLY STRONG WIND EVENTS.
GIVEN THE DIFFICULTY IN DEFINING A MORE CONCENTRATED AREA FOR ROBUST
AND LONGER-LIVED SEVERE STORMS...A BROAD REGION OF LOW SEVERE
PROBABILITIES WILL BE MAINTAINED ACROSS THESE AREAS FOR THIS
OUTLOOK.
...ROCKIES...
WIDELY SCATTERED STRONG TO ISOLATED SEVERE STORMS ARE AGAIN POSSIBLE
OVER THE HIGHER TERRAIN OF CO/NM DURING THE AFTERNOON AND EARLY
EVENING. WEAK LARGE SCALE FORCING SHOULD KEEP SEVERE POTENTIAL QUITE
CONFINED IN SPACE/TIME.
..CARBIN/JEWELL.. 07/01/2007
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