Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 292025 CCA AFDJKL AREA FORECAST DISCUSSION...CORRECTED NATIONAL WEATHER SERVICE JACKSON KY 352 PM EDT MON SEP 29 2014 .SHORT TERM...(THIS EVENING THROUGH TUESDAY NIGHT) ISSUED AT 352 PM EDT MON SEP 29 2014 THE MODELS WERE IN GOOD AGREEMENT REGARDING THE LARGE SCALE WEATHER PATTERN AND SENSIBLE WEATHER FOR THE FIRST 36 HOURS OF THE FORECAST. THE CONSENSUS VIEW IS FOR A WEAK MID LEVEL LOW PRESSURE SYSTEM TO MOVE OUT OF THE CENTRAL GREAT LAKES REGION TONIGHT AND MOVE ACROSS THE EASTERN OHIO VALLEY. THE MOST EASTERN KENTUCKY SHOULD SEE FROM THIS SYSTEM IS SCATTERED LOW AND MIDDLE LEVEL CLOUDS NORTH OF THE MOUNTAIN PARKWAY THIS EVENING THROUGH THE EARLY OVERNIGHT HOURS. ONCE THIS INITIAL DISTURBANCE PASSES BY...IT APPEARS LIKELY THAT A FAIRLY WELL DEVELOPED RIDGE OF HIGH PRESSURE ALOFT WILL SETTLE OVER THE AREA FOR A FEW DAYS. THIS RIDGE WILL BRING SLIGHTLY ABOVE NORMAL TEMPERATURES TO THE AREA THROUGH TOMORROW NIGHT...WITH HIGHS TOPPING OUT IN THE UPPER 70S AND LOWER 80S ON TUESDAY...AND LOWS IN THE 50S TONIGHT AND TOMORROW NIGHT. WIDESPREAD VALLEY FOG WILL BE ON TAP AGAIN THE NEXT COUPLE OF NIGHTS AS WELL...PARTICULARLY NEAR RIVERS AND LAKES. ALL IN ALL THE FOLKS OF EASTERN KENTUCKY CAN EXPECT PARTLY CLOUDY TO MOSTLY CLEAR SKIES THROUGH TOMORROW NIGHT ALONG WITH LIGHT WINDS...ABOVE NORMAL TEMPERATURES...AND LATE NIGHT AND EARLY MORNING FOG. .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 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON) ISSUED AT 136 PM EDT MON SEP 29 2014 PARTLY TO MOSTLY CLOUDY SKIES WILL PREVAIL AT THE TAF SITES THIS AFTERNOON...AS A MID LEVEL DISTURBANCE MOVE ACROSS THE OHIO AND TENNESSEE VALLEY REGIONS. A BROAD FIELD OF SCATTERED TO BROKEN CUMULUS CLOUDS HAS FORMED THIS AFTERNOON AS A RESULT OF THE PREVIOUSLY MENTIONED WEAK WEATHER SYSTEM. CURRENT RADAR IMAGERY ALSO REVEALS THAT A FEW VERY LIGHT RAIN SHOWERS AND SPRINKLES HAVE ALSO POPPED UP. THIS TREND SHOULD CONTINUE THROUGH THE REMAINING AFTERNOON HOURS AS THE SUN HEATS THINGS UP. THE SHOWERS SHOULD DISSIPATE QUICKLY AND BE GONE JUST AFTER SUN SET. AREAS OF MOSTLY VALLEY FOG CAN ALSO BE EXPECTED ACROSS THE AREA TONIGHT...WITH IFR TO LIFR CONDITIONS EXPECTED IN THE DENSEST FOG. WITH CLEAR SKIES...LIGHT WINDS...AND LOW LEVEL MOISTURE IN PLACE OVERNIGHT...IT IS LIKELY THAT ALL THE TAF SITES EXCEPT SYM WILL SEE DENSE FOG BETWEEN 9 AND 12Z TOMORROW. THE FOG SHOULD BE GONE BY BETWEEN 10 AND 1030 AM ON TUESDAY. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...AR LONG TERM...JP AVIATION...AR

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