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May 4, 2014 1300 UTC Day 1 Convective Outlook

May 4, 2014

May 4, 2014 1300 UTC Day 1 Convective Outlook

day1otlk

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0741 AM CDT SUN MAY 04 2014

VALID 041300Z – 051200Z

…NO SVR TSTM AREAS FORECAST…

…SUMMARY…
ISOLATED THUNDER MAY OCCUR OVER PARTS OF MAINE…AND FROM EASTERN KENTUCKY INTO THE WESTERN VIRGINIAS TODAY. WIDELY SCATTERED THUNDERSTORMS WITH SMALL HAIL ARE POSSIBLE LATE TONIGHT INTO EARLY MONDAY MORNING OVER PARTS OF INDIANA AND OHIO. ELSEWHERE…A FEW THUNDERSTORMS MAY RESULT IN LOCALLY GUSTY WINDS FROM SOUTHERN MONTANA TO SOUTHWESTERN SOUTH DAKOTA.

…SYNOPSIS…
IN MIDDLE-UPPER LEVELS…BROADLY CYCLONIC FLOW/ISOHYPSE CURVATURE WILL PERSIST OVER MIDDLE 2/3 OF CONUS FOR MUCH OF PERIOD…EXPANDING EWD ACROSS UPPER GREAT LAKES REGION WITH TIME. THIS WILL OCCUR AS
1. NEGATIVELY TILTED SHORTWAVE TROUGH CURRENTLY OVER ERN NY/WRN NEW ENGLAND MOVES EWD AND EVOLVES INTO CLOSED 500-MB CYCLONE OVER NOVA SCOTIA BY 12Z…AND
2. TRAILING SHORTWAVE TROUGH NOW OVER UPPER MI CROSSES MID-ATLC REGION AROUND 00Z THEN MOVES OFFSHORE TO MERGE CYCLONE OVER CANADIAN MARITIMES.

MEANWHILE…STG SHORTWAVE TROUGH WITH EMBEDDED/NEARLY CLOSED 500-MB LOW IS EXPECTED TO MOVE SLOWLY SEWD ACROSS COASTAL PAC NW AND ADJACENT WATERS THROUGH PERIOD.

11Z SFC CHART SHOWED LOW OVER EXTREME ERN ONT/SRN QUE BORDER REGION…WITH WEAK COLD FRONT SWWD OVER INDIANA. ELONGATED AREA OF FRONTAL LOW PRESSURE WAS ANALYZED FROM NERN CO TO N-CENTRAL KS…WITH QUASISTATIONARY FRONT EXTENDING EWD OVER NRN MO TO COLD-FRONTAL SEGMENT IN INDIANA. BY 00Z…FEATURES OVER CENTRAL PLAINS TO LOWER OH VALLEY SHOULD MOVE LITTLE…WITH NWWD EXTENSION OF FRONT AND LEE TROUGH COLLOCATED OVER NERN WY/NWRN NEB/SWRN SD AREA. MEANWHILE CYCLONE CENTER SHOULD CROSS MAINE…NEARLY VERTICALLY STACKED WITH 500-MB LOW…WHILE COLD FRONT MOVES TO DELMARVA AREA…SWRN VA AND CENTRAL/NRN KY. BY 12Z THIS FRONT SHOULD REACH SC BUT BECOME QUASISTATIONARY NWWD TOWARD SRN INDIANA. WARM FRONT WILL EXTEND WWD ACROSS S-CENTRAL IL AND NRN MO INTO WEAK FRONTAL-WAVE LOW OVER CENTRAL/ERN KS.

…CENTRAL APPALACHIANS THIS AFTN…
GRADUAL WIND SHIFT WITH WEAK CONFLUENCE IS EXPECTED THIS AFTN INVOF FRONTAL ZONE…WHERE COMBINATION OF DIURNAL/DIABATIC HEATING AND WEAK FRONTAL ASCENT MAY LEAD TO SCATTERED SHALLOW/ISOLATED DEEP CONVECTION. HOWEVER…CONFIDENCE IN MORE THAN ISOLATED TSTMS IS LOWER THAN PREVIOUS OUTLOOK GIVEN DRY UPSTREAM AIR MASS IN WARM SECTOR…AND VEERED PREFRONTAL FLOW CONTRIBUTING TO LACK OF STRONGER CONVERGENCE. FCST SOUNDINGS SUGGEST STG BOUNDARY-LAYER MIXING AND INVERTED-V THERMODYNAMIC PROFILES…BUT GIVEN WEAK LAPSE RATES ALOFT…INSUFFICIENT MOISTURE FOR MORE THAN VERY BRIEF/WEAK TSTMS WITH GUSTY BUT SUB-SVR WINDS.

…INDIANA/OH OVERNIGHT…
WIDELY SCATTERED TSTMS MAY DEVELOP IN BAND OF ELEVATED FRONTAL FORCING AND LOW-LEVEL WAA OVERNIGHT…MAINLY FROM ABOUT 06Z ONWARD…STREAKING ESEWD ACROSS THIS REGION. MOST MODELS APPEAR TOO AGGRESSIVE WITH LOW-LEVEL MOISTENING GIVEN DRY AIR UPSTREAM — E.G. NEAREST 8-10 DEG C 850-MB DEW POINTS BEING OVER SRN GULF AND S FL WITH ANTICYCLONE IN BETWEEN. AS SUCH…PROGGED NOCTURNAL MUCAPES OVER 1000 J/KG APPEAR OVERDONE…WITH BAND OF MOISTENING IN LAYER NEAR 850 MB MORE LIKELY RELATED TO PRECIP GENERATION THAT DEPLETES REAL CAPE. DEEP SHEAR WILL BE FAVORABLE…HOWEVER CLOUD-WATER CONTENT AND BUOYANCY EACH SHOULD BE TOO LOW TO SUPPORT MORE THAN BRIEF/SUB-SVR HAIL.

…NRN ROCKIES TO WRN DAKOTAS…
WIDELY SCATTERED…SHALLOW…HIGH-BASED TSTMS ARE POSSIBLE MAINLY FROM MID-AFTN INTO EARLY EVENING OVER THIS CORRIDOR…AS SFC HEATING CONTRIBUTES TO MRGL CAPE AND HEIGHTS BEGIN TO FALL IN WAKE OF SHORTWAVE RIDGING. MODIFIED FCST SOUNDINGS SUGGEST RELATIVELY UNINHIBITED BELT OF ENHANCED MID-UPPER-LEVEL WSWLYS IS FCST — E.G. 50-60 KT AT 500 MB. HOWEVER…WLY LOW-LEVEL FLOW WILL OFFSET THAT IN TERMS OF FAVORABLE DEEP SHEAR…EXCEPT NEAR FRONT/LEE TROUGH IN NERN WY AND SWRN SD WHERE STRONGER CORES MAY OFFER HAIL APCHG SVR LIMITS. SOME OF THAT FLOW ALOFT MAY BE TRANSFERRED TO SFC THROUGH WELL-MIXED BOUNDARY LAYER…BUT BUOYANCY WILL BE LIMITED BY LACK OF GREATER MOISTURE. OVERALL…SVR POTENTIAL APPEARS TOO MEAGER FOR UNCONDITIONAL PROBABILITIES.

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