AREA FORECAST DISCUSSION
NWS LOUISVILLE KY
AFDSDF 330 AM EST FRI APR 4 2003
FIRST OF TWO DISTINCT 500MB WAVES BARRELING EWD OUT OF MEAN
TROFINESS OVER WRN NOAM TO IMPACT THE LMK FA TODAY/TONIGHT. ASSOC
SFC CYCLONE TRANSLATING NEWD ALONG SHARP SFC BAROCLINIC ZONE
ORIENTED FROM KS THRU SRN GREAT LAKES. FA FIRMLY WITHIN WARM SECTOR,
AS SFC LOW TRACKS ACROSS IL/IN TODAY, WITH A COLD FRONT SWEEPING
SEWD THRU FA TONIGHT.
SCT-BKN PCPN BREAKING OUT ATTM OVER IL/IN ASSOC WITH LOW-LEVEL WARM
FRONTOGENESIS AND ZONE OF MID-LEVEL INSTABILITY, WHILE A SWATH OF
MID/HIGH LEVEL CLOUDINESS SPREADS ACROSS THE MS/OH RIVER VALLEYS,
WITH SOME EMBEDDED -SHRA OVER WRN KY/TN AHEAD OF A SMALL 500MB WAVE.
RECENT ACARS RAOBS OUT OF KSDF AND UPSTREAM AT KMEM SHOW A
SUBSTANTIAL CAP JUST ABV 800MB, SO QUESTION IS WHETHER THIS FEATURE
WILL BE ERODED THRU THE DAY BY CONVECTION/SYNOPTIC ASCENT. PER FCST
700MB OMEGA FIELDS OVER THE FA, LARGE SCALE FORCING AT A RELATIVE
MINIMUM TODAY, SO THE AREAL EXTENT OF PRE-FRONTAL CONVECTIVE PCPN
GFS/ETA ARE PRODUCING OVER FA MAY BE OVERDONE. BUT WITH THAT SAID, I
CAN'T COMPLETELY RULE OUT SOME SCT PCPN TODAY, GIVEN POTENTIAL
UNRESOLVED FEATURES WITHIN NWP DATA, 6HR MOS POPS ON THE ORDER OF
30-40%, AND ACTIVITY SW OF FA ATTM. OVERALL THINKING IS THAT CAP
OVER WARM SECTOR MAY REMAIN STRONGER THAN MODELS FCST.
WITH SOME HINTS OF SUNSHINE THIS AFTERNOON BASED ON SATELLITE TRENDS
UPSTREAM, INSTABILITY OVER LOWER OH VALLEY WILL GROW, POOLING AHEAD
OF INCOMING FRONT. STG FORCING ALONG FRONT SIGNALS A LINEAR
CONVECTIVE MODE WITH EMBEDDED BOWS BY THE TIME IT GETS TO OUR
LONGITUDE. IMPRESSIVE LOW-LEVEL WIND FIELDS/HODOGRAPHS AND DRY AIR
ABV 800MB INDICATING THAT DAMAGING WINDS ARE A VERY REAL
POSSIBILITY. GFS/ETA 0-1KM SR-HELICITIES SUGGEST SOME EMBEDDED
TORNADOES MAY NOT BE OUT OF THE QUESTION AS WELL, ESPECIALLY IF SFC
WINDS BECOME AS BACKED AS THE ETA FCSTS. CERTAINLY AGREE WITH 6Z SPC
DAY ONE OUTLOOK THAT DISPLAYS HATCHED 25% WIND DAMAGE AREA OVER MUCH
OF LMK FA.
ONCE THAT BUSINESS MOVES OUT, A GOOD PART OF THE UPCOMING WEEKEND
LOOKS QUIET WX WISE, AS SHORTWAVE 500MB RIDGING MOVES THRU ERN
CONUS. SFC CIRCULATION ASSOC WITH SECOND MID-LEVEL WAVE COMING OUT
OF THE WEST ALLOWS FOR A WARM FRONT TO MOVE NWD INTO FA SUN EVENING.
PLUME OF ELEVATED INSTABILITY AND MOISTURE ABOVE WARM-FRONTAL
INTERFACE MAY BE ENOUGH TO KICK OFF SOME SCT SHRA OVER FA AFTER
18Z/SUN, DEVELOPING FROM S TO N. HWVR, LIFT FOR THIS PCPN APPEARS TO
BE ASSOC WITH AN MCV THAT THE GFS DEVELOPS FROM SIG CONVECTION OVER
SRN PLAINS EARLY SUN, SO WITH UNCERTAINTY WILL KEEP POPS IN LOW CHC
CATEGORIES. PCPN CHCS CONTINUE INTO MON, ASSOC WITH WARM FROPA AND
ATTENDANT SFC LOW PASSAGE. PER 0Z GFS BUFKIT RAOBS, ATMOSPHERE ABV
900MB DRIES OUT QUICKLY LATE MON ENDING PCPN CHCS, BUT HINTS THAT
LOW BKN/OVC CLOUDS COULD HANG AROUND THRU EARLY TUE.
EXTENDED NOTES: 0Z GFS OUT TO 180HRS SHOWS LARGE, COOL, SLOW-MOVING
SURFACE HIGH SETTLING OVER MUCH OF THE CONUS TUE, WITH LITTLE OR NO
PCPN EXPECTED TUE-THU OVER LMK FA. NEW MEX MOS GUIDANCE MINIMA ARE
SIGNIFICANT COOLER TUE, SO WILL TREND TOWARDS THESE NEW DATA IN
EXTENDED GRIDS.
.LMK...NONE.
XXV
AREA FORECAST DISCUSSION
NWS LOUISVILLE KY
AFDSDF 211 AM EST FRI APR 4 2003
FIRST OF TWO DISTINCT 500MB WAVES BARRELING EWD OUT OF MEAN
TROFINESS OVER WRN NOAM TO IMPACT THE LMK FA TODAY/TONIGHT. ASSOC
SFC CYCLONE TRANSLATING NEWD ALONG SHARP SFC BAROCLINIC ZONE
ORIENTED FROM KS THRU SRN GREAT LAKES. FA FIRMLY WITHIN WARM SECTOR,
AS SFC LOW TRACKS ACROSS IL/IN TODAY, WITH A COLD FRONT SWEEPING
SEWD THRU FA TONIGHT.
SCT-BKN PCPN BREAKING OUT ATTM OVER IL/IN ASSOC WITH LOW-LEVEL WARM
FRONTOGENESIS AND ZONE OF MID-LEVEL INSTABILITY, WHILE A SWATH OF
MID/HIGH LEVEL CLOUDINESS SPREADS ACROSS THE MS/OH RIVER VALLEYS.
4-5Z ACARS RAOBS OUT OF KSDF SHOW A SUBSTANTIAL CAP JUST ABV 800MB,
SO QUESTION IS WHETHER THIS FEATURE WILL BE ERODED THRU THE DAY BY
CONVECTION/SYNOPTIC ASCENT. PER FCST 700MB OMEGA FIELDS OVER THE FA,
LARGE SCALE FORCING AT A RELATIVE MINIMUM TODAY, THEREFORE THINK
MUCH OF THE PRE-FRONTAL CONVECTIVE PCPN GFS/ETA ARE PRODUCING OVER
FA IS INCORRECT. 0Z LMK-MM5 ACTUALLY KEEPS MOST OF THE FA DRY THRU
TODAY. THINKING IS THAT CAP MAY REMAIN STRONGER THAN MODELS FCST.
BUT WITH THAT SAID, I CAN'T COMPLETELY RULE OUT SOME SCT TSRA TODAY,
GIVEN POTENTIAL UNRESOLVED FEATURES WITHIN NWP DATA AND 6HR MOS POPS
ON THE ORDER OF 30-40%.
WITH SOME HINTS OF SUNSHINE THIS AFTERNOON BASED ON SATELLITE TRENDS
UPSTREAM, INSTABILITY OVER LOWER OH VALLEY WILL GROW, POOLING AHEAD
OF INCOMING FRONT. STG FORCING ALONG FRONT SIGNALS A LINEAR
CONVECTIVE MODE WITH EMBEDDED BOWS BY THE TIME IT GETS TO OUR
LONGITUDE. IMPRESSIVE LOW-LEVEL WIND FIELDS/HODOGRAPHS AND DRY AIR
ABV 800MB INDICATING THAT DAMAGING WINDS ARE A VERY REAL
POSSIBILITY. GFS/ETA 0-1KM SR-HELICITIES SUGGEST SOME EMBEDDED
TORNADOES MAY NOT BE OUT OF THE QUESTION AS WELL, ESPECIALLY IF SFC
WINDS BECOME AS BACKED AS THE ETA FCSTS. CERTAINLY AGREE WITH 6Z SPC
DAY ONE OUTLOOK THAT DISPLAYS HATCHED 25% WIND DAMAGE AREA OVER MUCH
OF LMK FA.
ONCE THAT BUSINESS MOVES OUT, A GOOD PART OF THE UPCOMING WEEKEND
LOOKS QUIET WX WISE, AS SHORTWAVE 500MB RIDGING MOVES THRU ERN
CONUS. SFC CIRCULATION ASSOC WITH SECOND MID-LEVEL WAVE COMING OUT
OF THE WEST ALLOWS FOR A WARM FRONT TO MOVE NWD INTO FA SUN EVENING.
PLUME OF ELEVATED INSTABILITY AND MOISTURE ABOVE WARM-FRONTAL
INTERFACE MAY BE ENOUGH TO KICK OFF SOME SCT SHRA OVER FA AFTER
18Z/SUN, DEVELOPING FROM S TO N. HWVR, LIFT FOR THIS PCPN APPEARS TO
BE ASSOC WITH AN MCV THAT THE GFS DEVELOPS FROM SIG CONVECTION OVER
SRN PLAINS EARLY SUN, SO WITH UNCERTAINTY WILL KEEP POPS IN LOW CHC
CATEGORIES. PCPN CHCS CONTINUE INTO MON, ASSOC WITH WARM FROPA AND
ATTENDANT SFC LOW PASSAGE. PER 0Z GFS BUFKIT RAOBS, ATMOSPHERE ABV
900MB DRIES OUT QUICKLY LATE MON ENDING PCPN CHCS, BUT HINTS THAT
LOW BKN/OVC CLOUDS COULD HANG AROUND THRU EARLY TUE.
EXTENDED NOTES: 0Z GFS OUT TO 180HRS SHOWS LARGE SLOW-MOVING SURFACE
HIGH SETTLING OVER MUCH OF THE CONUS TUE, WITH LITTLE OR NO PCPN
EXPECTED TUE-THU OVER LMK FA.
.LMK...NONE.
XXV