Issued by NWS Louisville, KY
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000 FXUS63 KLMK 202013 AFDLMK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LOUISVILLE KY 310 PM EST TUE JAN 20 2009 .SHORT TERM (TONIGHT AND WED)... WILL MAKE ONLY SUBTLE CHANGES TO THE ONGOING FCST FOR THIS PERIOD. CLOUDS/FLURRIES ACRS THE ERN 1/2 OF OUR FA ARE DIURNALLY ENHANCED AND BEGINNING TO SHOW A BIT MORE EWD MOVEMENT AS WINDS AT CLOUD LEVEL BACK FROM NLY TO NNW. AT THE SAME TIME...SATELLITE IMAGERY IS INDICATING LO LEVEL LAKE MICHIGAN MOISTURE FETCH PRODUCING CLOUDS/FLURRIES ACRS WRN INDIANA/WCNTRL KY WHICH SHUD TRANSLATE INTO OUR FA TNGT WHILE LIKELY DISSIPATING A BIT AFTER SUNSET. NAM IS MORE LIBERAL WITH KEEPING LOW CIGS ACRS MUCH OF OUR FA TNGT INTO WED MRNG...GFS LESS SO. END RESULT WILL BE A PARTLY TO MOSTLY CLDY FCST FOR TNGT WITH SCT FLURRIES CONTINUING INTO THIS EVE...AT LEAST FOR THE ERN 2/3RDS OF OUR FA. THE FEWEST CLOUDS SHUD BE OVER THE WRN THIRD OF OUR FA TNGT WITH A DECREASING CLOUD TREND FROM SW TO NE WED AS WINDS BACK TO W AND THEN SW DURG THE DAY. A WARMING TREND WILL COMMENCE WED WITH INCREASING SUNSHINE AND A WIND SHIFT TO SW. BEFORE THAT...WINDS WILL BECOME LIGHT TNGT AS RIDGE AXIS MOVES ACROSS AND TEMPS FALL INTO THE LOWER/MID TEENS. ONCE THE LOW CLOUDS MOVE OUT WED...SOME HIGH/MID CLOUDS WILL DEVELOP IN MID LEVEL WARM ADVECTION PATTERN. OVERALL...A PARTLY SUNNY DAY WITH AFTN TEMPS ABOUT 10 DEGS WARMER THAN TDA. .LONG TERM (WEDNESDAY NIGHT THROUGH TUESDAY)... WEDNESDAY NIGHT THROUGH SATURDAY NIGHT... FAIRLY QUIET WEATHER PATTERN SETTING UP FOR THIS PORTION OF THE FCST PD. PERHAPS THIS IS THE CALM BEFORE THE STORM (SEE NEXT SECTION). EARLY IN THE PD...UPPER LEVEL WILL BE FLATTENING OUT A BIT AS UPPER LEVEL TROUGH OVER THE EAST MOVES OUT AND THE WESTERN RIDGE BREAKS DOWN AS THE PATTERN TRANSITIONS TO MORE OF A SPLIT FLOW REGIME. WITH SFC RIDGING BUILDING IN AND RISING HEIGHTS ALOFT DRY WEATHER ALONG WITH SUNNY DAYS AND CLEAR NIGHTS LOOK LIKE A GOOD BET FOR WEDNESDAY NIGHT THROUGH THURSDAY NIGHT. TEMPERATURES LOOK TO MODERATE THROUGH THE PD WITH HIGHS THU WARMING INTO THE LOWER TO MID 40S IN THE NORTH WITH MID TO UPPER 40S IN THE SOUTH. LOWS THU MORNING WILL BE IN THE LOW TO MID 20S. FRI MORNING LOWS SHOULD BE SOME 8-10 DEG WARMER WITH READINGS IN THE LOWER TO MID 30S. FRIDAY IS A LITTLE TOUGH TO PIN DOWN ATTM. THE LATEST MODEL DATA SUGGESTS THAT A WEAK H5 WAVE WILL SWING THROUGH AND BRING CLOUDS AND SHOWERS TO THE REGION. THIS HAS BEEN IN THE MODELS OVER THE PAST FEW DAYS...SO WILL CONTINUE TO RUN SMALL PRECIPITATION CHANCE FOR FRIDAY. WITH CLOUDS AND PRECIP...HAVE UNDERCUT GUIDANCE A BIT AND GONE WITH MID AND UPPER 40S FOR HIGHS. IF PRECIPITATION DOES NOT MATERIALIZE...THEN A SHOT AT 50 IS POSSIBLE. PRECIPITATION LOOKS TO LINGER INTO FRIDAY NIGHT WITH COLDER AIR LEADING TO A CHANGEOVER TO A BIT OF SNOW. WE LOOK TO BE IN BETWEEN SYSTEMS ON SATURDAY...BUT MID AND HIGH LEVEL CLOUDS MAY LEAD TO A PARTLY TO MOSTLY CLOUDY DAY WITH HIGHS IN THE UPPER 20S IN THE NORTH AND LOWER 30S IN THE SOUTH. OVERNIGHT LOWS WILL DROP TO AROUND 20 IN THE NORTH FOR SUNDAY MORNING WITH LOWER TO MID 20S IN THE SOUTH. SUNDAY THROUGH TUESDAY... LONG RANGE MODEL SOLUTIONS CONTINUE TO SHOW A VERY ACTIVE WEATHER PERIOD SHAPING UP FOR MUCH OF THE OHIO VALLEY IN THIS PORTION OF THE FORECAST PERIOD. LATEST MODEL TRENDS CONTINUE TO INDICATE THE STRONG POSSIBILITY OF A LARGE OVERRUNNING PRECIPITATION EVENT WHICH COULD BRING SIGNIFICANT AMOUNTS OF WINTRY PRECIPITATION TO MUCH OF THE LOWER OHIO AND TENNESSEE VALLEYS. QUIET WEATHER LOOKS ON TAP FOR SUNDAY AS SFC HIGH SLIDES EAST ACROSS THE REGION AND THE UPPER LEVEL FLOW BEGINS TO TRANSITION TO MORE OF A WSW OR SW FLOW. SHALLOW COLD AIR MASS WILL REMAIN IN PLACE THROUGHOUT THE DAY WITH HIGHS ONLY WARMING INTO THE UPPER 20S IN THE NORTH WITH LOWER 30S IN THE SOUTH. BY LATE SUNDAY...ALL EYES WILL BE WATCHING HOW THE MODELS DEVELOP THE STRONG TROUGH THAT IS FORECAST TO IMPACT THE WESTERN U.S. THE CRUX OF THE POSSIBLE WINTER STORM FOR THE OHIO VALLEY DEPENDS ON HOW DEEP THIS TROUGH DIGS. SHOULD THE TROUGH DIG FURTHER SOUTH INTO SOUTHERN CA/NV/AZ...THIS WILL PUMP UP THE SOUTHEAST RIDGE AND ALLOW WARMER AIR TO COME IN ALOFT WHICH WOULD RESULT IN A MAJOR ICING EVENT FOR THE OHIO VALLEY. IT SHOULD BE NOTED THAT IN PROGRESSIVE FLOW PATTERNS LIKE THIS...THE GFS TENDS TO OVER DEVELOP AND DIG TROUGHS TOO MUCH (WELL DOCUMENTED GFS BIAS). SO THIS IS SOMETHING TO WATCH. ON THE OTHER HAND...IF THE WESTERN TROUGH DOES NOT DIG AND HEADS MORE TOWARD THE EAST...THEN THE SOUTHEAST RIDGE WOULD BE MORE SUPPRESSED AND WE WOULD BE LOOKING AT MUCH MORE OF A SNOW SITUATION RATHER THAN ICE. AT THIS TIME...HAVE GONE MORE WITH A 50/50 BLEND OF THE 12Z EURO AND GFS SOLUTIONS. FORECAST CONFIDENCE ON HAVING A MAJOR PRECIPITATION EVENT IS ABOVE AVERAGE. HOWEVER...THERE ARE MAJOR QUESTIONS REGARDING THE OVERALL THERMAL STRUCTURE WHICH WOULD RESULT IN DIFFERENT P-TYPES. WE WILL BE RAISING POPS SIGNIFICANTLY FOR MON-TUE AND FOR NOW WILL SIMPLY MENTION A MIX OF RAIN/SNOW AND ADDRESS THE ONGOING P-TYPE ISSUES IN LATER FORECASTS. STAY TUNED! && .AVIATION (18Z TAFS)... COLD NLY FLOW WILL PERSIST THROUGH TONIGHT...HOWEVER WINDS WILL SHIFT TO SW WED. OCCASIONAL FLURRIES WILL CONTINUE MUCH OF THE AFTN INTO THE EARLY EVE...LOWERING VSBY TO MVFR FOR BRIEF PERIODS OF TIME...MAINLY FOR THE LEX AND SDF TAF. BKN TO OVC MVFR LOW CIGS SHUD BECOME SCTD TNGT AS HIGH PRES BUILDS IN FROM THE SW. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...NONE. IN...NONE. && $$ WEATHER.GOV/LOUISVILLE SHORT TERM...DK LONG TERM....MRJ AVIATION.....11
