SPC 1200Z Day 1 Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1256 AM CDT WED AUG 07 2013 VALID 071200Z - 081200Z ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE SOUTH-CENTRAL PLAINS... ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE MIDWEST/LOWER GREAT LAKES... ...SYNOPSIS... A CLOSED UPPER TROUGH WILL CONTINUE TO SLOWLY PIVOT OVER NORTHERN PORTIONS OF MANITOBA/ONTARIO...WITH A CYCLONIC BELT OF RELATIVELY STRONG MID-UPPER LEVEL WESTERLIES EXTENDING FROM THE NORTHERN HIGH PLAINS TO THE GREAT LAKES REGION. MEANWHILE...A SPLIT FLOW REGIME WILL PERSIST OVER THE WESTERN CONUS...WITH A SOUTHERN STREAM UPPER LOW CROSSING NM AS ANOTHER UPPER LOW SLOWLY APPROACHES COASTAL PORTIONS OF ORE/NORTHERN CA. ...SOUTH-CENTRAL PLAINS TO OZARKS... INITIALLY...A WEAKENING MCS IS LIKELY TO BE ONGOING ACROSS THE OZARKS THIS MORNING...WHILE OUTFLOW/DIFFERENTIAL HEATING HELPS TO REESTABLISH AN EFFECTIVE ROUGHLY WSW-ENE FRONTAL ZONE AND AN ASSOCIATED CORRIDOR OF MODERATE-STRONG INSTABILITY INTO THIS AFTERNOON. A SLOW-MOVING UPPER LOW WILL APPROACH THE REGION FROM THE SOUTHWEST /NM/ AND INFLUENCE WHAT WILL LIKELY BE ANOTHER ROUND OF MCS DEVELOPMENT INTO TONIGHT. INITIALLY...STORMS ARE EXPECTED TO DEVELOP/INCREASE WITHIN A SOUTH-CENTRAL HIGH PLAINS CORRIDOR INCLUDING SOUTHEAST CO/NORTHEAST NM INTO SOUTHWEST KS AND THE TX/OK PANHANDLES AND FAR WESTERN OK. WITH THE BOUNDARY LAYER HAVING BECOME MODERATELY TO STRONGLY UNSTABLE ALONG/SOUTH OF THE EFFECTIVE FRONTAL ZONE...VEERING WIND PROFILES WILL SUPPORT SOME INITIAL MODE SUPERCELLS/INTENSE MULTICELLS CAPABLE OF LARGE HAIL/DAMAGING WINDS AND PERHAPS A TORNADO. AN MCS SEEMS LIKELY TO EVOLVE BY EVENING WITHIN A CORRIDOR ACROSS NORTH-CENTRAL OK/SOUTHERN KS VIA A NOCTURNALLY STRENGTHENING LOW LEVEL JET AND ASSOCIATED WARM ADVECTION/MOISTURE TRANSPORT REGIME. HEAVY RAIN ASIDE...DAMAGING WINDS WILL BE A CONCERN AS THE COMPLEX GRADUALLY SPREADS EASTWARD TONIGHT. ...MIDWEST/OH VALLEY/LOWER GREAT LAKES... INITIAL FACTOR WILL BE THE POSSIBILITY OF AN ONGOING MCS ACROSS THE LOWER GREAT LAKES...ALTHOUGH THE MCS SHOULD ENCOUNTER A RELATIVELY MORE STABLE AIRMASS THIS MORNING AS IT PROGRESSES SOUTHEASTWARD. THE BOUNDARY LAYER WILL OTHERWISE CONTINUE TO MOISTEN ACROSS THE REGION AHEAD OF AN UPSTREAM EAST-SOUTHEASTWARD MOVING COLD FRONT...ESPECIALLY IN AREAS SOUTH-SOUTHWEST OF THE EARLY DAY MCS AND ASSOCIATED CONVECTIVE OUTFLOW. A CORRIDOR OF MODERATE/POTENTIALLY STRONG INSTABILITY SHOULD MATERIALIZE THIS AFTERNOON ACROSS PORTIONS OF IL/INDIANA INTO LOWER MI/OH AHEAD OF THE FRONT...WITH THE STRONGEST VERTICAL SHEAR FOCUSED OVER NORTHERN PORTIONS OF THAT CORRIDOR IN VICINITY OF THE GREAT LAKES. THE PRIMARY UNCERTAINTY IS WHAT MAY BE RELATIVELY MODEST OVERALL FORCING FOR ASCENT/MASS CONVERGENCE NEAR THE ADVANCING COLD FRONT. EVEN SO...SUFFICIENT DESTABILIZATION/FRONTAL UPLIFT SHOULD ALLOW FOR AT LEAST SOME NEAR-FRONTAL FOCUSED SURFACE BASED CONVECTION...WITH THE POTENTIAL FOR ISOLATED BOUTS OF SEVERE WIND/HAIL. ...TN VALLEY... IN THE PRESENCE OF LOW-LEVEL CONFLUENCE...DAYTIME HEATING WITHIN A MOISTURE RICH/WEAKLY CAPPED BOUNDARY LAYER WILL LIKELY PROMOTE SCATTERED TSTM DEVELOPMENT BY EARLY AFTERNOON ACROSS THE TN VALLEY. PRECIPITABLE WATER VALUES IN EXCESS OF 2 INCHES AND GENERALLY WEAK VEERING FLOW WILL SUPPORT MULTICELLS CAPABLE OF ISOLATED WET MICROBURSTS AND THE POSSIBILITY OF LOCALIZED WIND DAMAGE. ...NORTH-CENTRAL HIGH PLAINS... A POST-FRONTAL LOW-LEVEL UPSLOPE REGIME AND SUFFICIENT MOISTURE SHOULD ALLOW FOR ISOLATED/WIDELY SCATTERED TSTMS THIS AFTERNOON/EARLY EVENING ACROSS AREAS SUCH AS EASTERN WY INTO WESTERN SD/NEB PANHANDLE. WHILE BUOYANCY WILL BE RELATIVELY MODEST...30-35 KT MID-LEVEL WESTERLIES COMBINED WITH VEERING LOWER TROPOSPHERIC WINDS MAY ALLOW FOR A FEW SUPERCELLS/SUSTAINED MULTICELLS CAPABLE OF SEVERE HAIL/WIND. ...NORTHERN/EAST-CENTRAL MT... POSSIBLY AIDED BY A GLANCING SOUTHEASTWARD-MOVING MID-LEVEL IMPULSE/SPEED MAX...ISOLATED TSTMS SHOULD DEVELOP ACROSS FAR SOUTHERN ALBERTA AND NORTH-CENTRAL/EAST-CENTRAL MT THIS AFTERNOON/EARLY EVENING. THE BOUNDARY LAYER WILL NOT BE PARTICULARLY MOIST...BUT A STEEP LAPSE RATE ENVIRONMENT AND RELATIVELY STRONG WIND PROFILES /ACCENTUATED BY 40+ KT MID-LEVEL WEST-NORTHWESTERLY WINDS/ MAY ALLOW FOR SOME STRONGER/POSSIBLY SEVERE TSTMS CAPABLE OF HAIL/WIND. ...SOUTHERN ORE/FAR NORTHERN CA... A SLOW-MOVING UPPER LOW WILL GRADUALLY SPREAD NORTHEASTWARD AND APPROACH COASTAL PORTIONS OF ORE/NORTHERN CA...WITH DOWNSTREAM HEIGHT FALLS ACROSS ORE/WESTERN GREAT BASIN. ALTHOUGH THE RELATIVE EARLINESS OF THE PRIMARY PIVOTING IMPULSE PROVIDES A BIT OF UNCERTAINTY...FORCING FOR ASCENT/MODEST MOISTURE SHOULD ALLOW FOR THE SUSTENANCE/DEVELOPMENT OF HIGH-BASED TSTMS DURING THE AFTERNOON. GIVEN A WELL-MIXED ENVIRONMENT...LOCALIZED DOWNBURSTS WILL BE POSSIBLE. ..GUYER/ROGERS.. 08/07/2013
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day1otlk_1200.html
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