SPC 1730Z Day 2 Outlook
DAY 2 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1224 PM CDT WED AUG 21 2013 VALID 221200Z - 231200Z ...NO SVR TSTM AREAS FORECAST... ...SYNOPSIS... IN MID-UPPER LEVELS...NRN STREAM IS FCST TO BECOME SOMEWHAT MORE AMPLIFIED THROUGH DAY-2. SHORTWAVE TROUGH -- NOW EVIDENT IN MOISTURE CHANNEL IMAGERY OVER SK -- IS FCST TO MOVE ESEWD AND STRENGTHEN. PERTURBATION SHOULD REACH LS BY 22/12Z...SERN ONT/SWRN QUE BY 23/00Z...AND MAINE BY END OF PERIOD. IN ADVANCE OF THAT SYSTEM...WEAK TROUGH NOW OVER INDIANA SHOULD MOVE OFFSHORE MID-ATLC AND NC AROUND 23/00Z. FARTHER W...WEAK PERTURBATION NOW OVER SRN ID BORDER REGION IS EXPECTED TO MIGRATE SLOWLY THROUGH MEAN RIDGE POSITION OVER NRN ROCKIES...REACHING SRN MT AND NRN WY AROUND 23/00Z...AND WRN SD OVERNIGHT. PERSISTENT/WELL-DEFINED MID-UPPER CYCLONE...INITIALLY LOCATED OFFSHORE CENTRAL CA -- IS EXPECTED TO DEVOLVE TO OPEN-WAVE TROUGH EARLY IN PERIOD WHILE MOVING ASHORE BETWEEN SFO AND CAPE MENDOCINO. RESULTING SHORTWAVE TROUGH SHOULD MOVE NNEWD ACROSS NRN CA AND SRN/CENTRAL ORE THROUGH REMAINDER PERIOD...WHILE CONTINUING TO DEAMPLIFY. AT SFC...COLD FRONT WAS EVIDENT FROM NERN MN SWWD ACROSS E-CENTRAL/S-CENTRAL SD TO NERN WY. BY 22/12Z...FRONT SHOULD BE LOCATED FROM LH TO SRN WI TO CENTRAL IA...SRN NEB AND NERN CO. NEB/CO SEGMENT OF FRONT SHOULD MOVE LITTLE THROUGH DAYLIGHT HOURS...WHILE ERN PORTION OF FRONT PROCEEDS TO ST LAWRENCE VALLEY AREA OF SRN QUE...LE...NRN INDIANA...CENTRAL IL...AND NRN MO BY 23/00Z. AT THAT TIME...SFC TROUGH SHOULD EXTEND FROM FRONTAL INTERSECTION OVER NERN CO/SWRN NEB REGION SWD ACROSS ERN CO...PERHAPS WITH WEAK/ACCOMPANYING LOW. BY END OF PERIOD...FRONT SHOULD EXTEND FROM NEAR NEW ENGLAND COAST SWWD ACROSS CENTRAL APPALACHIANS...THEN WWD OVER SRN IL...WHILE MOVING NWD AS WARM FRONT OVER PORTIONS ERN NEB AND WRN SD. ...NERN CONUS... WIDELY SCATTERED TO SCATTERED TSTMS SHOULD DEVELOP INVOF SFC COLD FRONT DURING AFTN...OVER LOWER GREAT LAKES REGION...WITH ADDITIONAL TSTMS POSSIBLE ENEWD ACROSS SRN QUE AND NRN MAINE. ISOLATED DAMAGING GUSTS APCHG SVR LIMITS ARE POSSIBLE. ALTHOUGH STRONGEST FLOW ALOFT SHOULD REMAIN BEHIND SFC COLD FRONT...LARGE-SCALE ASCENT WILL INCREASE THROUGH AFTN ABOVE FRONT WITH APCH OF SHORTWAVE TROUGH. SFC DEW POINTS GENERALLY 60S F...ALONG WITH PREFRONTAL BOUNDARY-LAYER HEATING...WILL OFFSET WEAK LAPSE RATES ALOFT ENOUGH TO SUPPORT 500-1000 J/KG MLCAPE OVER MAINE AND NY...AND 1000-1500 J/KG SWWD OVER PORTIONS PA/OH. LACK OF STRONGER PRESENCE OF AT LEAST THESE THREE FACTORS...DEEP-LAYER LAPSE RATES...LOW-LEVEL FLOW...AND VERTICAL SHEAR...APPEARS TO PRECLUDE MORE SUBSTANTIAL/ORGANIZED SVR THREAT. ...CENTRAL HIGH PLAINS... BY MID-LATE AFTN...LIGHT ELY/NELY FLOW NEAR FRONT AND NW OF LEE TROUGH/LOW SHOULD ADVECT FAVORABLE LOW-LEVEL MOISTURE ONTO HIGHER TERRAIN OF SERN WY AND NERN CO...WITH DEW POINTS RANGING FROM 50S F THERE TO 60S ACROSS PORTIONS SWRN/CENTRAL NEB. WIDELY SCATTERED TSTMS SHOULD DEVELOP DURING AFTERNOON IN THOSE AREAS. ADDITIONAL CONVECTION IS POSSIBLE ALONG NRN EDGE OF STRONGLY HEATED/MIXED AIR OVER SWRN NEB/NWRN KS. ISOLATED SVR HAIL AND/OR DAMAGING GUSTS MAY OCCUR. THOUGH STG DIRECTIONAL SHEAR IS EXPECTED IN THIS REGIME...WEAK LOW-LEVEL SPEEDS WILL LIMIT HODOGRAPH SIZE...AND LACK OF STRONGER MID-UPPER WINDS WILL RESTRICT DEEP SHEAR. AS SUCH...ANY SUPERCELL POTENTIAL APPEARS MRGL/TRANSIENT...AND OVERALL SVR THREAT APPEARS RATHER DISORGANIZED. ...NRN CA...NWRN NV...SRN ORE... APCHG SHORTWAVE TROUGH WILL LEAD TO STRENGTHENING MID-UPPER FLOW THROUGH AFTN ACROSS PARTS OF THIS AREA -- E.G. 60-70 KT AT 250 MB AND 30-40 KT AT 500 MB -- AS WELL AS INCREASING DCVA/UVV ALOFT. LATTER WILL COMBINE WITH DIABATIC SFC HEATING TO YIELD FAVORABLY STEEP LOW-MIDDLE LEVEL LAPSE RATES...ACCOMPANIED BY ENOUGH PW TO SUPPORT 40S-50S F SFC DEW POINTS IN LOWER ELEVATIONS. WIDELY SCATTERED TO SCATTERED TSTMS SHOULD DEVELOP DURING AFTN AND MOVE PRIMARILY NWD TO NNEWD. MODIFIED FCST SOUNDINGS SUGGEST 500-1000 J/KG MLCAPE AND 30-45 KT EFFECTIVE SHEAR MAGNITUDES...IN SUPPORT OF ISOLATED SVR GUST/HAIL POTENTIAL WITH THIS CONVECTION. ..EDWARDS.. 08/21/2013
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day2otlk_1730.html
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