Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 220824 AFDJKL AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE JACKSON KY 424 AM EDT MON SEP 22 2014 .SHORT TERM...(TODAY THROUGH TUESDAY) ISSUED AT 402 AM EDT MON SEP 22 2014 SUBSTANTIAL DRY AIR HAS MOVED IN ACROSS MUCH OF EASTERN KY AFTER A DEPARTING COLD FRONT FROM EARLIER IN THE DAY. HOWEVER...A DISTURBANCE CURRENTLY MOVING ACROSS THE UPPER GREAT LAKES REGION HAS CAUSED A BROAD DECK OF 2 TO 3 KFT CLOUDS. ACCORDING TO THE LATEST IMAGERY...THESE CLOUDS ARE CONTINUING TO PUSH SSE-WARD AND ARE EXPECTED TO ENTER INTO EASTERN KY OVER THE NEXT SEVERAL HOURS. THE LEADING EDGE OF THIS CLOUD DECK IS ALREADY PUSHING INTO SJS OBSERVATION SITE IN THE FAR EASTERN PORTION OF THE CWA. THE LATEST OBSERVATIONS UPSTREAM...ALONG WITH THE LATEST MODEL SOUNDINGS AND LAMP GUIDANCE...ALL POINT AT THIS CLOUD DECK REMAINING MVFR. DURING THE DAY TODAY...STRONG SUBSIDENCE WILL TAKE HOLD ACROSS THE REGION UNDER SURFACE HIGH PRESSURE AND RISING UPPER LEVEL HEIGHTS AS A LONGWAVE TROUGH DEPARTS EAST FROM THE AREA. THIS WILL LEAD TO A THINNING OF CLOUDS THROUGHOUT THE MORNING AND AN INFLUX OF COLD DRY CANADIAN AIR. WINDS WILL REMAIN OUT OF THE NORTH BOTH AT THE SURFACE AND UPPER LEVELS AS THE STRONGLY DISPLACED NORTHERN JET CONTINUES MOVE EASTWARD ACROSS THE REGION FOLLOWING THE LONGWAVE PATTERN. EXPECT HIGHS TODAY TO BE MUCH LOWER THAN THAT OF YESTERDAY...ONLY REACHING THE UPPER 60S IN MOST LOCATIONS. SIMILARLY...WITH THE LOSS OF DAYTIME HEATING...RADIATIONAL COOLING WILL BE AT A MAXIMUM UNDER MOSTLY CLEAR SKIES. THIS WILL ALLOW FOR TEMPS TO DROP WELL BELOW NORMAL...INTO THE LOW TO MID 40S ACROSS THE REGION FOR LOWS. SOME OF THE DEEPEST RIVER VALLEYS WILL LIKELY SEE FOG DEVELOPMENT AS THE DEW POINTS REMAIN HIGHER IN THESE LOCATIONS. THE NORTHERN JET WILL PUSH OFF EAST OF THE AREA BY TUESDAY/TOMORROW. WHILE WINDS WILL REMAIN NORTHERLY...THEY WILL NOT BE QUITE AS STRONG IN THE MID AND UPPER LEVELS. CONTINUED SUNSHINE ACROSS THE AREA WILL ALSO WORK TO MODIFY TEMPS SLIGHTLY HIGHER AS STRONG HIGH PRESSURE REMAINS OVERHEAD. DAYTIME HIGHS ARE EXPECTED TO REACH THE LOW 70S IN SOME LOCATIONS...WHILE SOME OF THE HIGHER ELEVATIONS MAY CONTINUE TO SEE UPPER 60S. .LONG TERM...(TUESDAY NIGHT THROUGH SUNDAY) ISSUED AT 410 AM EDT MON SEP 22 2014 THE MODEL CONSENSUS IS FOR AN UPPER LEVEL RIDGE TO EXTEND FROM THE DESERT SOUTHWEST EAST INTO THE LOWER MS VALLEY AND THEN NORTH INTO THE LOWER OH VALLEY AND CENTRAL GREAT LAKES REGION TO START THE PERIOD. AN UPPER LEVEL LOW/TROUGH IS EXPECTED TO LINGER ALONG THE EASTERN SEABOARD WITH ANOTHER UPPER LOW OVER THE NORTHERN PLAINS REGION...AS THE MAIN BAND OF WESTERLIES WILL BE DISPLACED WELL NORTH OF THE US/CANADIAN BORDER AT THE START OF THE PERIOD. AT THAT POINT...CORRESPONDING SFC HIGH PRESSURE IS EXPECTED TO BE CENTERED OVER QUEBEC WITH RIDGING SOUTH INTO THE OH VALLEY AND MS VALLEY REGIONS. FROM TUESDAY NIGHT INTO THE WEEKEND...A TROUGH IS EXPECTED TO WORK INTO THE WESTERN CONUS...BUT THERE ARE SOME MODEL DIFFERENCES IN TIMING AND DETAILS. THE UPPER LEVEL RIDGE INITIALLY CENTERED OVER THE SOUTHWESTERN CONUS IS EXPECTED TO BUILD NORTH INTO HE NORTHERN PLAINS/UPPER MIDWEST REGION AND BECOME CENTERED OVER THAT REGION BY FRI...BEFORE SHIFTING EAST INTO THE GREAT LAKES REGION. MUCH OF THE CENTRAL AND EASTERN CONUS WILL BE TO SOME DEGREE INFLUENCED BY UPPER LEVEL RIDGING FROM MID TO LATE THIS WEEK...BUT THERE WILL ALSO BE SOME WEAKNESS IN THE RIDGE AS WELL...THAT THE GFS AND ECMWF HAVE HAD SOME DIFFERENCES IN PLACEMENT AND DETAILS WITH FROM RUN TO RUN AND MODEL TO MODEL FOR THE PAST FEW DAYS. OVERALL...THE PATTERN SHOULD BE RATHER BENIGN. THE MODEL CONSENSUS IS THAT RATHER DRY AIR WILL PERSIST ACROSS MUCH OF THE OHIO RIVER VALLEY...THROUGH AT LEAST WED NIGHT OR THU. THE 0Z ECMWF IS MORE MOIST IN THE LOW LEVELS FROM THU THROUGH THE END OF THE PERIOD AS COMPARED TO THE 0Z GFS AND EVEN THE 12Z ECMWF FOR THAT MATTER AS IT KEEPS A WEAKNESS IN THE RIDGE OVER THE REGION OR CLOSE TO THE REGION. AS NOTED BY THE PREVIOUS FORECASTER...THE LOSS OF NORTHERLY FLOW AT BOTH THE SURFACE AND ALOFT...ESPECIALLY THE LOWEST LEVELS AND MORE OF A WEAK EASTERLY FLOW WILL LEAD TO GRADUAL AIR MASS MODIFICATION...WITH INCREASES IN MAX AND MIN TEMPERATURES FROM DAY TO DAY AND A GRADUAL INCREASE IN DEWPOINTS FROM MID TO LATE WEEK. MODELS REMAIN IN NOT VERY GOOD AGREEMENT OVER THE WEEKEND AT THE END OF THE PERIOD AND THUS CONFIDENCE IS LOWER THAN AVERAGE. RATHER SHALLOW WEAK SOUTHEAST FLOW AS IS IN THE 0Z ECMWF WOULD LIMIT PRECIPITATION THREAT TO POSSIBLY DIURNALLY DRIVEN ON SUNDAY OR POSSIBLY EARLIER UNTIL THE WEAKNESS THAT THE 0Z MODELS AGREE ON OVER THE CENTRAL AND SOUTHERN PLAINS AT THE START OF THE WEEKEND LIFTS ON OUT TO THE NORTH AND NORTHEAST. THE 0Z GFS IS QUICKER TO BRING THIS FEATURE NORTH AND NORTHEAST AT THE END OF THE PERIOD THAN THE 0Z ECMWF BUT DOES NOT BRING DEEPER MOISTURE TO THE AREA UNTIL AFTER THE PERIOD. THE MODEL CONSENSUS BLEND GRID LOAD HAD SLIGHT CHANCES IN THE SOUTHWEST CWA BEFORE THE END OF THE PERIOD WHICH WAS IN LINE WITH THE PREVIOUS FORECAST AND DID NOT CHANGE THIS ATTM. PRECIPITATION CHANCES MAY BE A BIT HIGHER EARLY NEXT WEEK JUST PAST THE END OF THE PERIOD IF A PATTERN CLOSER TO THE 0Z GFS ENSEMBLE MEAN OR 0Z ECMWF WERE TO VERIFY. && .AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT) ISSUED AT 204 AM EDT MON SEP 22 2014 SUBSTANTIAL DRY AIR HAS MOVED IN ACROSS MUCH OF EASTERN KY AFTER A DEPARTING COLD FRONT FROM EARLIER IN THE DAY. HOWEVER...A DISTURBANCE CURRENTLY MOVING ACROSS THE UPPER GREAT LAKES REGION HAS CAUSED A BROAD DECK OF MVFR CLOUDS. ACCORDING TO THE LATEST IMAGERY...THESE CLOUDS ARE CONTINUING TO PUSH SSE-WARD AND ARE EXPECTED TO ENTER INTO EASTERN KY WITHIN THE NEXT SEVERAL HOURS. GIVEN THE LATEST OBSERVATIONS UPSTREAM...AND WITH SUPPORT FROM THE LATEST MODEL SOUNDINGS AND LAMP GUIDANCE...DECIDED TO INCREASE CLOUD DECK HEIGHTS BACK TO MVFR AS THEY MOVE ACROSS THE REGION. OTHERWISE...PATCHY FOG SHOULD ONLY BE CONFINED TO THE DEEPEST VALLEYS AND IN SOME LOCATIONS THAT RECEIVED RAINFALL TODAY...BUT SHOULD GENERALLY STAY OUT OF THE TAF SITES. BY LATE TOMORROW MORNING...STRONG SUBSIDENCE WILL TAKE HOLD...WITH CLOUDS LIFTING TO VFR AND THINNING OUT THROUGH THE AFTERNOON. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...JMW LONG TERM...JP AVIATION...JMW

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