Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 211159 AAA AFDJKL AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE JACKSON KY 759 AM EDT SUN SEP 21 2014 .UPDATE... ISSUED AT 745 AM EDT SUN SEP 21 2014 HOURLY GRIDS HAVE BEEN UPDATED BASED ON RECENT OBSERVATIONS. THERE IS NOT MUCH ACTIVITY IN ADVANCE OF THE APPROACHING COLD FRONT AT THIS POINT. HOWEVER...THERE IS NOT MUCH CLOUD COVER OVER THE CWA OTHER THAN RIVER VALLEY FOG AND SOME STRAY MID AND HIGH CLOUDS. THIS SHOULD ALLOW FOR SOME HEATING DURING THE AM AND AS THE HEIGHTS ARE PROJECTED TO FALL OVER THE OH VALLEY AS THE SHORTWAVE DROPS THROUGH THE GREAT LAKES...ADDITIONAL BANDS OF SHOWERS AND SOME THUNDERSTORMS SHOULD DEVELOP. THE 9Z HRRR AS WELL AS THE 0Z AND 6Z GFS AND TO SOME DEGREE THE NAM GUIDANCE IS IN LINE WITH THIS THINKING. OVERALL...NO MAJOR CHANGES WERE MADE TO THE GRIDS ATTM. && .SHORT TERM...(TODAY THROUGH MONDAY) ISSUED AT 410 AM EDT SUN SEP 21 2014 EARLY THIS MORNING....AN UPPER LEVEL RIDGE WAS CENTERED OVER THE SOUTHERN ROCKIES AND WEST TX REGION WITH RIDGING NORTHWEST INTO THE ROCKIES AND EAST INTO THE SOUTHERN APPALACHIAN REGION. TO OUR SOUTHEAST A TROUGH OF LOW PRESSURE EXTENDED FROM THE CAROLINA COASTLINE SOUTH INTO FL AND THE EASTERN GULF OF MEXICO. AN INITIAL SHORTWAVE IS MOVING INTO THE EASTERN GREAT LAKES REGION WITH THE MAIN SHORTWAVE OF INTEREST LOCALLY WORKING THROUGH THE UPPER MIDWEST AND WESTERN GREAT LAKES REGION ATTM. AT THE SFC...HIGH PRESSURE WAS CENTERED ACROSS THE SOUTHEASTERN CONUS WITH A SFC LOW PRESSURE WORKING ACROSS THE GREAT LAKES REGION. A COLD FRONT EXTENDED SOUTH AND SOUTHWEST FROM THE LOW INTO THE MID MS VALLEY REGION WITH THE BOUNDARY BEGINNING TO APPROACH THE LOWER OH VALLEY REGION. THROUGH THE PERIOD...THE RIDGING INTO THE SOUTHEASTERN CONUS WILL BE SHUNTED TO THE SOUTH WITH THE SOUTHEASTERN TROUGH...THE INITIAL TROUGH AND THE TROUGH APPROACHING FROM THE NORTHWEST CARVING OUT A TROUGH FROM ONTARIO AND QUEBEC INTO NORTHEASTERN US REGION DOWN INTO THE OH VALLEY REGION BY THIS EVENING. THIS TROUGH AXIS IS EXPECTED TO SHIFT EAST AND NORTHEAST PUSHING EAST AND SOUTHEAST OF EAST KY BY MID MORNING ON MONDAY AND EXTEND FROM QUEBEC INTO THE MID ATLANTIC STATES AND INTO THE SOUTHEASTERN STATES AT THE END OF THE PERIOD. THIS TROUGH WILL PUSH THE COLD FRONT SOUTH AND EAST OF THE OH RIVER THIS MORNING INTO EARLY AFTERNOON AND ACROSS CENTRAL AND EASTERN KY THIS AFTERNOON INTO THE EARLY EVENING HOURS. SFC HIGH PRESSURE CURRENTLY OVER THE PLAINS STATES WILL BUILD INTO THE OH VALLEY REGION BEHIND THE BOUNDARY AND IS EXPECTED TO BE CENTERED FROM THE MID OH VALLEY REGION WEST TO THE MID MS VALLEY REGION BY THE END OF THE PERIOD. SOME VALLEY FOG IS PRESENT THIS MORNING ALONG WITH SOME PASSING CLOUDS IN THE 6 TO 8KFT RANGE. 1A6 AND I35 RECENTLY REPORTED VIS DOWN BELOW 1 MILE WITH DENSE FOG AT I35. PATCHY FOG HAS BEEN INCLUDED IN THE GRIDS FOR THE REMAINDER OF THE OVERNIGHT WITH A COUPLE MORE HOURS OF PATCHY DENSE FOG IN THE GRIDS FOR THE DEEPER EASTERN AND SOUTHEASTERN VALLEY LOCATIONS IN PORTIONS OF THE BIG SANDY...KENTUCKY...LIKING AND UPPER CUMBERLAND RIVER BASINS. IN MORE OPEN TERRAIN LOCATIONS...THE PRESSURE GRADIENT HAS BEEN SUFFICIENT TO DISSIPATE THE FOG OVER THE PAST COUPLE OF HOURS OR PREVENT IT FROM FORMING ALL TOGETHER. A COUPLE BANDS SHOWERS AND SOME THUNDERSTORMS ARE EXPECTED TO MOVE INTO OR DEVELOP ACROSS EASTERN KY BY LATE MORNING INTO THE EARLY AFTERNOON HOURS AND DEPART MOST OF THE AREA BY SUNSET...AS THE COLD FRONT APPROACHES AND WORKS ACROSS THE REGION. THE MODEL CONSENSUS AND RECENT SHORT TERM MODEL RUNS OF THE HRRR SUGGEST THAT THE BEST CHANCES FOR MEASURABLE PRECIPITATION AND THUNDER WILL BE ACROSS THE SOUTHERN HALF OF THE CWA. POPS IN THE 50 TO 60 DEGREE RANGE WERE USED IN THIS AREA. PENDING THE DEGREE OF INSTABILITY FROM HEATING AND LOW LEVEL MOISTURE INCREASE AHEAD OF THE FRONT...MODEL FORECAST MID LEVEL DRYING...AND DECENT SPEED SHEAR COULD COMBINE FOR THE STRONGEST STORMS TO PRODUCE SOME HAIL OR STRONG WINDS GUSTS DURING THE AFTERNOON TO EARLY EVENING. THE SPC DAY 1 OUTLOOK IS ALSO CONSISTENT WITH THIS THINKING. THIS POTENTIAL WILL BE ADDED TO THE HWO. WITH A MODERATE PRESSURE GRADIENT ACROSS THE REGION AND SOME STRONGER WINDS ALOFT THAT COULD MIX DOWN...SUSTAINED WINDS OF 10 MPH OR SO WILL BE POSSIBLE LATE THIS MORNING INTO EARLY THIS AFTERNOON...ESPECIALLY ACROSS THE MORE OPEN TERRAIN LOCATIONS ACROSS THE WESTERN AND NORTHWESTERN PARTS OF THE CWA AND THE HIGHER TERRAIN. SOME GUSTS OUTSIDE OF ANY CONVECTION INTO THE 20 TO 25 MPH ALSO APPEAR POSSIBLE. THE WRAPAROUND MOISTURE LATE TONIGHT INTO EARLY ON MONDAY MAY BE DEEP ENOUGH AS THE 500 MB TROUGH AXIS WORKS ACROSS THE REGION WITH THE LOW LEVEL FLOW BEING DEEP ENOUGH FOR TOUCH OF DRIZZLE OR SPRINKLES GENERALLY ACROSS THE EASTERN PART OF THE CWA AND THE VA BORDER COUNTIES. THE 0Z GFS GENERATES SOME LIGHT QPF IN SOME OF THIS AREA LATE TONIGHT INTO EARLY ON MONDAY. THE OTHER OPERATIONAL MODELS HAVE ANY MEASURABLE PRECIP FURTHER NORTHEAST INTO WV. EITHER WAY THERE SHOULD BE A PERIOD OF LOW STRATUS OR STRATOCU OVERNIGHT INTO EARLY ON MONDAY ACROSS THE EASTERN HALF OR SO OF THE CWA. OVERNIGHT LOWS TONIGHT WILL BE MORE COLD AIR ADVECTION DRIVEN WITH SOME OF THE FAR EASTERN VALLEY LOCATIONS THAT WARMEST ON AVERAGE. THE LINGERING CLOUDS AND COLD AIR ADVECTION WILL BRING TEMPERATURES AT LEAST 10 DEGREES BELOW NORMAL FOR MOST LOCATIONS ON MONDAY. THE MORNING STRATOCU SHOULD GRADUALLY LIFT INTO SOME FLAT CU JUST BELOW THE SUBSIDENCE INVERSION WITH THESE GRADUALLY MIXING OUT OR LARGELY MIXING OUT BY THE END OF THE PERIOD...EXCEPT POSSIBLY THE FAR SOUTHEAST PART OF THE CWA. .LONG TERM...(MONDAY NIGHT THROUGH SATURDAY) ISSUED AT 348 AM EDT SUN SEP 21 2014 A STRONG UPPER LEVEL RIDGE WILL MOVE FROM THE CENTRAL CONUS AT 0Z TUESDAY...TO THE MISSISSIPPI RIVER VALLEY BY 12Z. MEANWHILE...SURFACE HIGH PRESSURE WILL ALSO REMAIN STRONG OVER THE REGION...WITH WINDS BOTH AT THE SURFACE AND ALOFT PULLING DRY AND COLDER AIR IN FROM CANADA. SOME OF THE STRONGEST WINDS ALOFT WILL BE MOVING OFF TO OUR EAST WITH THE DEPARTING UPPER LEVEL TROUGH...BUT COLD AIR WILL LINGER THROUGH THE DAY TUESDAY. MORNING LOWS WILL ONLY BE IN THE LOW TO MID 40S...WITH AFTERNOON HIGHS TOPPING OUT AROUND OR JUST ABOVE THE 70 DEGREE MARK. OVER THE COURSE OF THE EXTENDED PERIOD...THE SURFACE HIGH WILL SHIFT SLIGHTLY TO OUR NE...BUT THE UPPER LEVEL RIDGE WILL REMAIN BLOCKED OVER THE REGION. AS SUCH...DRY AIR WILL PERSIST ACROSS MUCH OF THE OHIO RIVER VALLEY...THOUGH THE LOSS OF STRONGEST NRLY WIND FLOW AT BOTH THE SURFACE AND ALOFT WILL LEAD TO AIRMASS MODIFICATION AND RISING TEMPERATURES THROUGHOUT THE EXTENDED. TEMPS WILL REACH THE 80 DEGREE MARK IN SOME LOCATIONS ONCE MORE BY SATURDAY. THE LATEST ECMWF MODEL IS POINTING AT A WEAK LOW DEVELOPING NEAR THE REGION LATE IN THE PERIOD...NAMELY SATURDAY AND SUNDAY...ALLOWING MOISTURE FLOW AND PRECIP CHANCES TO MOVE INTO PORTIONS OF THE CWA. WHILE A COUPLE OF OUR NEIGHBORING OFFICES WERE ON BOARD WITH INCLUDING SLIGHT CHANCE POPS...THE UNCERTAINTY FAVORED LEAVING THEM OUT AT THE JKL CWA AT THIS TIME. SO FAR...THE MODEL AGREEMENT PAST THE MID TERM IS QUITE LOW. THE ECMWF SEEMS TO BE THE OUTLIER WITH THIS PRECIP...AND VERY LOW QPF AT THAT. MORE THAN LIKELY...THE SUPER BLEND IS BEING INFLUENCED BY THIS LATEST ECMWF RUN...WHICH LED TO THE MENTION OF A FEW 15 POPS IN THE SATURDAY NIGHT FORECAST. MEANWHILE...THE GFS SHOWS NO SIGN OF THIS LOW NEAR THE REGION /IT HAS IT DEVELOPING MUCH FARTHER S AND MUCH WEAKER/ OR ANY PRECIP MOVING INTO KENTUCKY. GIVEN THE UNCERTAINTY AT THIS POINT...LOWERED ANY 15 POPS FOR SATURDAY NIGHT BACK DOWN TO 14. WILL WAIT UNTIL MODELS COME INTO BETTER AGREEMENT OR SHOW MORE CONSISTENCY BETWEEN RUNS BEFORE DECIDING TO INCLUDE POPS IN THE FORECAST PACKAGE. && .AVIATION...(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING) ISSUED AT 745 AM EDT SUN SEP 21 2014 OUTSIDE OF SOME LINGERING FOG...AFFECTING SME WITH MVFR...VFR SHOULD PREVAIL AT THE TAF SITES THROUGH AT LEAST THE FIRST 6 HOURS OF THE PERIOD. SOME LINGERING IFR OR LOWER FOG WILL LIFT OUT OF SOME OF THE DEEPER VALLEY LOCATIONS THROUGH 14Z. A COLD FRONT WILL DROP SOUTH ACROSS THE COMMONWEALTH TODAY WITH CLOUDS AND SOME SHOWERS AND SOME THUNDERSTORMS...MAINLY FROM 16Z THROUGH 0Z. AT THIS TIME...IT APPEARS CIGS AND VIS WITH SHRA AND SOME TSRA SHOULD GENERALLY REMAIN IN THE VFR RANGE...THOUGH SOME BRIEF MVFR IS POSSIBLE IN SOME OF THE STRONGER SHOWERS OR STORMS. AS THE NOCTURNAL INVERSION MIXES OUT THROUGH 16Z...LIGHT WINDS SHOULD BECOME SOUTHWEST TO WEST AND INCREASE TO AROUND 10KT FOR THE TAF SITES BY AROUND 16Z...WITH SOME GUSTS UP TO 20KT POSSIBLE...ESPECIALLY BETWEEN 16Z TO 22Z. WINDS WILL BECOME MORE NORTHWESTERLY BEHIND THE FRONT GENERALLY 21Z THROUGH 0Z AND AS THE PRESSURE GRADIENT RELAXES WINDS SHOULD DECREASE TO BELOW 10KT LATE IN THE PERIOD. SOME STRATOCU WITH WRAP AROUND MOISTURE AND UPPER DISTURBANCE MAY BRING MVFR CIGS LATE IN THE PERIOD. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...JP SHORT TERM...JP LONG TERM...JMW AVIATION...JP

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