SPC DAY-1 CONVECTIVE OUTLOOK
SPC DAY-1 CONVECTIVE OUTLOOK
21 Jan 1999 - 10:55:48 UTC disclaimer "for information regarding the availability and timeliness of forecasts and products.
ZCZC MKCSWODY1 000 ACUS1 KMKC 211055 MKC AC 211055 CONVECTIVE OUTLOOK...REF AFOS NMCGPH94O. VALID 211200Z - 221200Z THERE IS A HIGH RISK OF SVR TSTMS THIS AFTERNOON AND EARLY EVENING OVER MUCH OF CENTRAL AND EASTERN ARKANSAS...SOUTHWEST TENNESSEE... NORTHEAST LOUISIANA...AND NORTHERN AND WESTERN MISSISSIPPI. THE HIGH RISK IS TO THE RIGHT OF A LINE FROM 20 E JAN 45 NNW MCB 15 W HEZ 30 SW MLU 15 WNW ELD 15 W HOT 50 S HRO 45 ESE HRO 10 SSW ARG 15 WSW DYR 25 SE MKL 30 W MSL CBM 20 E JAN. THERE IS A SLGT RISK OF SVR TSTMS TO THE RIGHT OF A LINE FROM 25 ESE BPT 30 NW LCH 45 SSE SHV 25 NNE SHV 45 SE PGO 35 NW FSM 25 SSW JLN 30 NW SGF 30 ESE VIH 10 ENE OWB 40 WNW CSV 15 E BHM 30 S MOB. GEN TSTMS ARE FCST TO THE RIGHT OF A LINE FROM 25 ESE BPT 25 WSW POE 25 SE SHV 25 E GGG TYR 35 SSW DAL 30 W SEP 25 WSW ABI 40 NW BGS 45 E ROW 20 SW 4CR 20 W GNT 80 SSE U17 30 ENE BCE 35 SE U24 50 ENE U24 25 NE PUC 40 NE CNY 15 E MTJ 30 WNW TAD 25 E CAO 45 NE AMA 10 NE FSI 50 NW MLC 20 ENE BVO 20 E CNU 20 N UIN 20 NNW MMO 30 WSW GRR ARB 15 S CAK 45 ESE PKB PSK SPA ATL PNS. ...SYNOPSIS... A STRONG UPPER JET DIGGING INTO THE GREAT BASIN EARLY THIS MORNING WILL CAUSE STRONG AMPLIFICATION OF FLOW OVER THE SOUTH CENTRAL STATES AND EVENTUALLY FORM A DEEP CLOSED LOW OVER EASTERN OKLAHOMA/KANSAS BY 22/12Z. CYCLOGENESIS OVER OKLAHOMA IS LIKELY DURING THE DAY...WITH THE LOW EVENTUALLY ACCELERATING ACROSS NORTHWEST ARKANSAS INTO MISSOURI LATE TONIGHT. EAST-WEST WARM FRONT EXTENDING INTO THE OHIO VALLEY WILL LIFT NORTH INTO THE SOUTHERN GREAT LAKES TONIGHT. MEANWHILE...A PACIFIC COLD FRONT/DRY LINE SHOULD PUSH ACROSS CENTRAL AND EAST TEXAS. ...SEVERE THUNDERSTORM FORECAST DISCUSSION... ...LOWER MISSISSIPPI RIVER VALLEY... ---THE POTENTIAL EXISTS FOR A SIGNIFICANT SEVERE THUNDERSTORM OUTBREAK INCLUDING ISOLATED INTENSE TORNADOES THIS AFTERNOON AND EVENING--- MOIST/UNSTABLE WARM SECTOR IS ALREADY IN PLACE OVER SOUTHERN PORTION OF THE OUTLOOK AREA...WITH DEWPOINTS IN THE LOWER TO MIDDLE 60S AS FAR NORTHEAST AS SOUTHWEST TENNESSEE AND SOUTHERN ARKANSAS AT THIS TIME. AS SOUTHWESTERLY 850 MB JET INCREASES TO 60 KNOTS BY THE MIDDAY HOURS OVER THE LOWER MISSISSIPPI RIVER VALLEY...LOW LEVEL MOISTURE WILL ADVECT EVEN FURTHER NORTH BY THE AFTERNOON HOURS. STEEP 850-500 MB LAPSE RATES OF 6.5 TO 7.5 C/KM WERE ALREADY PRESENT...SUGGESTING THAT ETA FORECAST MUCAPE OF 1000-2000 J/KG IS REASONABLE FOR THE AFTERNOON AND EVENING HOURS. SOUTHWESTERLY 500 MB FLOW OF 60-70 KNOTS WILL PROVIDE FAVORABLE DEEP LAYER SHEAR FOR SEVERE THUNDERSTORMS INCLUDING SUPERCELLS... WITH FORECAST BRN SHEAR OF 50-100 M2/S2 OVER THE HIGH RISK AREA. FORECAST HODOGRAPHS HAVE FAVORABLE CURVED CHARACTERISTICS IN THE LOWER LEVELS...RESULTING IN 0-3 KM STORM RELATIVE HELICITIES OF 300-500 M2/S2. THUS...ENVIRONMENT IS CERTAINLY FAVORABLE FOR DEVELOPMENT OF SUPERCELLS/TORNADOES. WATER VAPOR IMAGERY CURRENTLY INDICATES A VORTICITY MAXIMUM MOVING EAST NORTHEASTWARD INTO SOUTHERN OKLAHOMA...AND THIS FEATURE IS FORECAST TO LIFT INTO MISSOURI BY THE AFTERNOON HOURS. ETA INDICATES RAPID DEVELOPMENT OF THUNDERSTORMS DURING THE MORNING HOURS AHEAD OF THIS FEATURE AND NEAR THE SURFACE WARM FRONT ACROSS NORTHERN PORTIONS OF THE SLIGHT RISK AREA. HOWEVER...MOST SIGNIFICANT SEVERE THREAT APPEARS TO BE RELATED TO TRAILING VORTICITY MAXIMUM THAT IS EXPECTED TO MOVE ACROSS NORTH TEXAS AND INTO EASTERN OKLAHOMA BY THE EARLY EVENING HOURS. THIS FEATURE IS NOT EASILY SEEN IN CURRENT WATER VAPOR IMAGERY...BUT WILL LIKELY EMERGE NEAR DEVELOPING WAVE CLOUD OVER EAST CENTRAL NEW MEXICO IN THE NEXT FEW HOURS. 12 HOUR 500 MB HEIGHT FALLS OF 60 TO 120 METERS WILL SPREAD ACROSS MUCH OF THE SOUTH CENTRAL STATES AS THE TROUGH SHARPENS LATE THIS AFTERNOON AND TONIGHT. VERY LARGE VALUES OF UPPER DIVERGENCE/UVVS ARE FORECAST TO DEVELOP FROM NORTHEAST LOUISIANA INTO TENNESSEE/KENTUCKY BY THE EVENING HOURS IN DIFFLUENT AREA BETWEEN NORTHERN AND SOUTHERN BRANCHES OF THE UPPER JET. THUS...SCATTERED SUPERCELLS/TORNADOES DURING THE LATE AFTERNOON AND EARLY EVENING HOURS WILL LIKELY EVOLVE INTO A SQUALL LINE LATER TONIGHT AS THE ACTIVITY SPREADS EAST OF THE MISSISSIPPI RIVER. HOWEVER...EMBEDDED BOW ECHOES/HP SUPERCELLS WITHIN THE SQUALL LINE COULD CONTINUE TO PRODUCE ISOLATED TORNADOES THROUGHOUT THE NIGHT. IN ADDITION TO THREAT FOR TORNADOES...SINCE LAPSE RATES ARE STEEP AND WET BULB ZERO HEIGHTS SHOULD RANGE FROM 7500-9500 FEET AGL...THE THREAT FOR LARGE HAIL APPEARS RATHER HIGH AS WELL. DURING THE NIGHTTIME HOURS...LIKELY DEVELOPMENT OF A SQUALL LINE WILL CONSEQUENTLY INCREASE THE THREAT FOR DAMAGING WINDS. ...GENERAL THUNDERSTORM FORECAST DISCUSSION... ...FOUR CORNERS AREA INTO THE RED RIVER AREA... SWATH OF CONVECTION AND ISOLATED THUNDERSTORMS WILL LIKELY SPREAD EAST-SOUTHEASTWARD OVER THE NEXT 24 HOURS ON THE CYCLONIC SIDE OF DIGGING UPPER JET. 850-500 MB LAPSE RATES WILL BE QUITE STEEP...RANGING FROM 7.5 TO 8.5 C/KM. ...SOUTHERN APPALACHIANS TO THE SOUTHERN GREAT LAKES... STRONG WARM ADVECTION PATTERN ON NOSE OF 60 KNOT 850 MB JET WILL PROVIDE FAVORABLE ENVIRONMENT FOR WIDESPREAD PRECIPITATION OVER THE NEXT 24 HOURS. DEGREE OF DESTABILIZATION DUE TO LOW LEVEL POSITIVE THETA-E ADVECTION SUGGESTS CLUSTERS OF EMBEDDED ELEVATED THUNDERSTORMS ARE POSSIBLE. ..CRAVEN/VESCIO.. 01/21/99 NNNN
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