Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 300656 AFDJKL AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE JACKSON KY 256 AM EDT TUE SEP 30 2014 .SHORT TERM...(TODAY THROUGH WEDNESDAY) ISSUED AT 256 AM EDT TUE SEP 30 2014 CLEAR SKIES...COMBINED WITH MID LEVEL SUBSIDENCE...AND LIGHT WINDS...HAS LED TO THE DEVELOPMENT OF DENSE FOG ACROSS EASTERN KENTUCKY THIS MORNING. THIS FOG WILL CONTINUE THROUGH DAYBREAK...BEFORE BURNING OFF BY 9 OR 10 AM. A FAIRLY PLEASANT DAY IS ON TAP. A SHORTWAVE TROUGH WILL WORK SOUTH ACROSS OHIO AND INTO WEST VIRGINIA TODAY...PUSHING A WEAK COLD FRONT SOUTHWARD INTO NORTHERN KENTUCKY. THE BEST FORCING IS EXPECTED TO STAY TO OUR NORTH AND EAST AS THE FRONT JUST GRAZES OUR NORTHERN AREAS. WHILE A FEW SPRINKLES MAY BE POSSIBLE...MODELS GENERALLY KEEP THE AREA DRY. THUS...PLAN TO STICK WITH A DRY FORECAST...ALTHOUGH A STRAY SHOWER COULD GET FAIRLY CLOSE TO OUR NORTHERN AREAS BY LATE IN THE DAY. TONIGHT...THE SHORTWAVE WILL DEPART AS THE BOUNDARY STALLS ACROSS EASTERN KENTUCKY. NO FORCING OR INSTABILITY TO SPEAK OF...SO WILL STICK WITH THE DRY FORECAST THROUGH TONIGHT. MOISTURE POOLING ALONG THE BOUNDARY COULD YIELD ANOTHER NIGHT OF DENSE FOG...ESPECIALLY IN THE RIVER VALLEYS YET AGAIN. PLAN TO INCLUDE THIS IN THE HWO THIS MORNING. ANOTHER PLEASANT DAY IS ANTICIPATED ON WEDNESDAY AS HIGH PRESSURE BUILDS OVER THE AREA. TEMPERATURES TODAY AND WEDNESDAY WILL BE FAIRLY SIMILAR WITH READINGS GENERALLY AROUND 80 AND LOWS TONIGHT WILL FALL BACK INTO THE 50S. .LONG TERM...(WEDNESDAY THROUGH MONDAY) ISSUED AT 352 PM EDT MON SEP 29 2014 SHORTWAVE UPPER LEVEL RIDGING IS EXPECTED TO BE THE DOMINANT WEATHER FEATURE AT THE START OF THE PERIOD AS IT GRADUALLY SHIFTS FROM AN AXIS OF THE MID SOUTH TO GREAT LAKES REGION TO THE EASTERN SEABOARD FROM WEDNESDAY INTO THURSDAY NIGHT. AT THE SAME TIME...AN UPPER LEVEL LOW/TROUGH WILL GRADUALLY DEPART THE NORTHEASTERN U.S. AND MOVE ON OFF INTO THE ATLANTIC. AT THE SAME TIME...ANOTHER UPPER LEVEL RIDGE IS EXPECTED TO SHIFT EAST FROM THE EASTERN PACIFIC INTO THE WESTERN CONUS. IN BETWEEN...AN UPPER LEVEL TROUGH WILL GRADUALLY MOVE FROM THE ROCKIES AND PLAINS STATES EAST AND APPROACH THE MS VALLEY REGION AND UPPER MIDWEST REGION BY THU EVENING. THE RIDGE ACROSS THE EASTERN SEABOARD SHOULD DEPART INTO THE ATLANTIC TO END THE WEEK AND OVER THE WEEKEND...WITH UPPER LEVEL RIDGING REMAINING IN PLACE ACROSS THE WESTERN CONUS. THIS WILL LEAD TO A RATHER DEEP EARLY FALL TROUGH EXTENDING FROM EASTERN CANADA SOUTH INTO MUCH OF THE CENTRAL AND EASTERN CONUS. AS THE UPPER TROUGH BEGINS TO MOVE INTO THE EASTERN CONUS...THE ASSOCIATED SFC COLD FRONT WILL APPROACH EASTERN KY ON THU NIGHT AND CROSS THE AREA ON FRIDAY. A SECONDARY SFC TROUGH/COLD FRONT SHOULD MOVE ACROSS THE REGION ON SATURDAY INTO SATURDAY EVENING AND USHER IN POSSIBLY THE COLDEST AIR MASS SO FAR THIS FALL. MODELS ALSO BRING ANOTHER SHORTWAVE THROUGH THE TROUGH IN NW FLOW LATE IN THE PERIOD. THE DEPARTING UPPER LEVEL AND ASSOCIATED SFC HIGH WILL BRING MILD... ABOVE NORMAL TEMPERATURES FOR WED INTO THU. TEMPERATURES SHOULD REACH THE LOW...TO PERHAPS MID 80S IN SEVERAL LOCATIONS BOTH DAYS. ACROSS THE SOUTHEAST PART OF THE CWA...A NON IDEAL DOWNSLOPING COMPONENT TO THE WIND SHOULD LEAD TO SOME OF THE HIGHER READINGS IN VALLEYS IMMEDIATELY DOWNWIND OF THE VA BORDER AT LOCATIONS SUCH AS HARLAN...CUMBERLAND...WHITESBURG...JENKINS...AND ELKHORN CITY. THE PATTERN FAVORS A MEDIUM TO LARGE RIDGE/VALLEY SPLIT ON WED NIGHT AS WELL. SOME GUSTY WINDS ARE POSSIBLE ACROSS THE MOUNTAINS AS A RATHER SHARP COLD FRONT APPROACHES ON THU NIGHT. RETURN FLOW AHEAD OF THE BOUNDARY AND THE APPROACHING TROUGH SHOULD BRING A BRIEF PERIOD OF RATHER DEEP MOISTURE TO THE REGION FROM LATE THURSDAY NIGHT INTO EARLY ON FRIDAY. IN ADDITION...A SHORTWAVE MOVING ACROSS THE ROCKIES AND PLAINS STATES EARLY IN THE PERIOD WILL MOVE INTO THE TN AND OH VALLEY REGION ON TUE NIGHT AND BEGIN TO TAKE ON A NEGATIVE TILT...LEADING TO BETTER FORCING AND CONFIDENCE IN MEASURABLE PRECIP ACROSS THE REGION WITH THIS EVENT. THE ECMWF REMAINS A BIT FASTER BRINGING THE SHORTWAVE TROUGH AND FRONT ACROSS THE REGION LATE THU NIGHT AND FRIDAY. ELEVATED INSTABILITY SHOULD BE SUFFICIENT FOR SOME ISOLATED THUNDER LATE THU NIGHT...DESPITE THE RATHER UNFAVORABLE TIMING OF THIS TIME OF YEAR...WITH SUFFICIENT INSTABILITY LINGER INTO FRI MORNING FOR A CONTINUED CHANCE OF ISOLATED TO SCATTERED THUNDER. BEHIND THE BOUNDARY FROM MIDDAY FRI TO FRI EVENING...WINDS COULD ALSO BE GUSTY...BUT THE GFS RUNS ARE A BIT STRONGER WITH WINDS ALOFT AND MOMENTUM MIX DOWN POTENTIAL COMPARED TO THE ECMWF RUNS. LIKELY POPS RESULTED FROM THE MODEL BLEND...WITH THIS LIKELY BECOMING A CATEGORICAL EVENT AT SOME POINT AS THE EVENT APPROACHES. THERE ARE MODEL DIFFERENCES WITH THE MAIN TROUGH AS IT APPROACHES MOVES ACROSS THE GREAT LAKES AND OHIO VALLEY FROM FRIDAY INTO SATURDAY NIGHT...WITH RECENT ECMWF RUNS SLOWER AND DEEPER/LOWER WITH HEIGHTS ACROSS THE GREAT LAKES AND OH VALLEY FROM FRI NIGHT INTO SATURDAY NIGHT AND COLDER WITH THE AIR MASS BY AT LEAST 3 TO 5 DEGREES C FROM LATE FRI NIGHT INTO EARLY ON SUNDAY. THIS LEADS TO THE DISPARITY IN GUIDANCE MAX T FOR SAT INTO SUNDAY OF AT LEAST 8 TO 13 DEGREES FROM COLDEST TO WARMEST AND MIN T DIFFERENCES ON THE ORDER OF 5 DEGREES OR MORE. OVERNIGHT MINS...ESPECIALLY SAT NIGHT MAY LARGELY DEPEND ON THE DEGREES OF CLEARING OR THE PRESENCE OF ANY LOW AND MID CLOUDS AS SEVERAL WEAKER SHORTWAVES MOVE THROUGH THE TROUGH. A STRONGER WAVE ON SUN NIGHT INTO MONDAY SHOULD BRING AT LEAST MORE CLOUD COVER IF NOT THE CHANCE FOR SOME RAIN SHOWERS. THE COLDER ECMWF SOLUTIONS WOULD SUPPORT MORE CLOUD COVER SAT NIGHT...WHILE THE WARMER GFS IS ALSO MORE MOIST...SO CONFIDENCE IN MIN T IS NOT HIGH. WITH CLOUD COVER ANTICIPATED...MIN T MAY BE MORE ELEVATION/COLD AIR ADVECTION DEPENDENT...BARRING ANY SIGNIFICANT CLEARING...THUS RIDGETOPS AND THE HIGHEST TERRAIN COULD END UP BEING THE COLDEST ON SAT NIGHT AND SUN NIGHT. GIVEN THAT THE MODELS CONTINUE TO HAVE A THEME OF THE GFS WARMER AND THE ECMWF MUCH COLDER FROM SAT THROUGH THE END OF THE PERIOD...THE MODEL BLEND SEEMED TO BE THE BEST COURSE OF ACTION AT THIS TIME. THE BOTTOM LINE IS THE PERIOD BEGINS MILD AND THEN ENDS WITH BELOW NORMAL TEMPERATURES. && .AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT) ISSUED AT 123 AM EDT TUE SEP 30 2014 CLEARING SKIES AND NEARLY CALM WINDS WILL LIKELY RESULT IN AREAS OF DENSE FOG ACROSS EASTERN KENTUCKY. HAVE ALLOWED FOR LIFR OR WORSE CONDITIONS BUILDING IN AT ALL TAF SITES THROUGH 12Z. ONCE THE FOG BURNS OFF BETWEEN 13 AND 14Z...VFR CONDITIONS WILL RETURN. WINDS WILL REMAIN LIGHT THROUGH THE PERIOD AS WELL. && .JKL WATCHES/WARNINGS/ADVISORIES... DENSE FOG ADVISORY UNTIL 10 AM EDT THIS MORNING FOR KYZ058>060- 068-069-079-080-083>088-106>120. && $$ SHORT TERM...KAS LONG TERM...JP AVIATION...KAS

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