Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 210552 AAC AFDJKL AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE JACKSON KY 152 AM EDT TUE APR 21 2015 .UPDATE...
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ISSUED AT 140 AM EDT TUE APR 21 2015 ONLY SOME VERY SUBTLE CHANGES WERE MADE TO THE HOURLY SKY...TEMPERATURE...WIND AND DEWPOINT GRIDS FOR THE NEXT SEVERAL HOURS. THESE ACCOUNTED FOR RECENT TRENDS IN SFC OBSERVATIONS AND ACCOUNTED FOR THE BAND OF GENERALLY MID LEVEL CLOUDS THAT EXTENDED BACK INTO PARTS OF NORTHERN MIDDLE TN AND CENTRAL KY THAT SHOULD ADVECT OVER THE REGION DURING THE NEXT 3 TO 5 HOURS OR SO. UPDATE ISSUED AT 1045 PM EDT MON APR 20 2015 THE SHOWERS ARE MOSTLY OUT OF EASTERN KENTUCKY WITH JUST A BRIEF PERIOD OF TRAILING SPRINKLES. HAVE UPDATED THE GRIDS TO REFLECT THIS AND ALSO ADJUSTED THE T AND TD GRIDS PER THE LATEST OBS AND TRENDS. THESE UPDATES HAVE BEEN SENT TO THE NDFD AND WEB SERVERS. A FRESHENED SET OF ZONES WERE ALSO ISSUED. UPDATE ISSUED AT 815 PM EDT MON APR 20 2015 23Z SFC ANALYSIS SHOWS THE COLD FRONT NOW EAST OF KENTUCKY WITH JUST SOME LINGERING SHOWERS TRAILING BEHIND...AS SEEN ON RADAR. ACCORDINGLY...HAVE UPDATED THE GRIDS AND ZONES TO REMOVE THE THUNDER AND TAPER OFF THE SHOWER CHANCES THROUGH THE EVENING. IN THE WAKE OF THE FRONT...TEMPERATURES ARE FALLING THROUGH THE CWA WITH LOW 50S IN THE WEST AND NEAR 60 DEGREE READINGS IN THE FAR EAST. DEWPOINTS ARE LIKEWISE DROPPING...CURRENTLY FROM THE MID 40S NORTHWEST TO LOWER 50S IN THE SOUTHEAST. WEST WINDS TO 10 TO 20 MPH WILL CONTRIBUTE TO THE COOLER AND DRIER ADVECTION THROUGH THE REST OF THE EVENING BEFORE THEY TAPER OFF...AS WELL. EXPECT THE CLOUDS TO GRADUALLY BREAK UP THROUGH THE NIGHT WITH THE DRIER AIR AND LIGHT WINDS HELPING TO KEEP ANY FOG CONFINED TO JUST THE DEEPER VALLEYS. FOR THIS UPDATE...HAVE ALSO FINE TUNED THE TEMPS AND DEWPOINTS THROUGH THE REST OF THE NIGHT PER THE LATEST SHORTBLEND GUIDANCE...OBS...AND TRENDS. THESE UPDATES HAVE BEEN SENT TO THE NDFD AND WEB SERVERS ALONG WITH A FRESHENED SET OF ZONES AND HWO.
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&& .SHORT TERM...(THIS EVENING THROUGH TUESDAY NIGHT) ISSUED AT 355 PM EDT MON APR 20 2015 A DEEP UPPER LEVEL LOW IS CURRENTLY SPIRALING NEAR THE MANITOBA/ONTARIO BORDER...WITH THE REFLECTIVE SURFACE LOW JUST ABOUT NORTH OF THE GREAT LAKES AND ITS ATTENDANT COLD FRONT STRUNG OUT SOUTH ACROSS CENTRAL OHIO AND THEN DOWN THROUGH EASTERN KENTUCKY AND TENNESSEE. CONVECTION HAS POPPED UP ACROSS THE AREA THIS AFTERNOON...WITH THE BEST COVERAGE OCCURRING ALONG AND WEST OF A LINE FROM MOREHEAD TO STANTON TO MONTICELLO. A FEW THUNDERSTORMS HAVE DEVELOPED AS WELL...HOWEVER THESE HAVE BEEN ISOLATED AT BEST. ADDITIONALLY... SOUTHWEST TO WEST SURFACE WINDS OF 10 TO 20 MPH...WITH GUSTS AROUND 30 MPH CONTINUE IN CYCLONIC FLOW AROUND THE NORTHERN LOW. SCATTERED TO NUMEROUS SHOWERS...ALONG WITH A STRAY THUNDERSTORM WILL GRADUALLY WORK EAST ACROSS THE AREA THROUGH THIS EVENING... AS THE SHEARED OUT COLD FRONT EVENTUALLY MAKES IT THROUGH THE ENTIRE COMMONWEALTH. CONVECTION WILL THEN WIND DOWN FROM WEST TO EAST...WITH HIGH PRESSURE BUILDING IN ACROSS THE LOWER MISSISSIPPI VALLEY. SOME LATE CLEARING WILL ALLOW FOR SOME LOWER 40 DEGREE READINGS IN PLACES OUT WEST...WITH MAINLY MID 40S EXPECTED ELSEWHERE. TUESDAY WILL FEATURE ANOTHER BREEZY DAY...AS WE MIX DEEP IN THE CONTINUED CYCLONIC FLOW...WITH FAIRLY STOUT WIND FIELDS STILL IN PLACE. GUSTS WILL RANGE FROM 25 TO 35 MPH. HIGHS WILL RECOVER TO THE MID 60S FOR MOST LOCATIONS. ANOTHER COLD FRONT WILL APPROACH THE AREA FROM THE NORTHWEST LATE IN THE DAY...AS ANOTHER SPOKE OF ENERGY ROTATES AROUND THE NORTHERN UPPER LEVEL LOW. THIS WILL BRING AT LEAST A SLIGHT CHANCE OF A FEW SHOWERS TO THE NORTH LATE IN THE DAY. BETTER CHANCES WILL OCCUR TUESDAY NIGHT AS THE FRONT DRAWS CLOSER TO THE AREA. LOWS TUESDAY NIGHT SHOULD BE A LITTLE MILDER GIVEN THE CLOUD COVER AND MIXED BOUNDARY LAYER...WITH MID TO UPPER 40S EXPECTED. .LONG TERM...(WEDNESDAY THROUGH MONDAY) ISSUED AT 355 PM EDT MON APR 20 2015 THE GFS AND ECMWF MODELS WERE IN DECENT AGREEMENT WITH THE OVERALL LARGE SCALE WEATHER PATTERN IN THE EXTENDED THIS GO ROUND. THE CONSENSUS WAS FOR A LARGE SCALE TROUGH TO MOVE ACROSS THE UPPER GREAT LAKES REGION INTO NORTHERN NEW ENGLAND WEDNESDAY AND WEDNESDAY NIGHT. A COLD FRONT EXTENDING SOUTHWARD FROM THIS TROUGH IS EXPECTED TO MOVE ACROSS THE OHIO AND TENNESSEE VALLEY REGIONS...BRING SCATTERED RAIN SHOWERS TO THE AREA TO BEGIN THE PERIOD. THE PRECIPITATION IS THEN FORECAST TO EXIT THE AREA BY AROUND DAWN ON THURSDAY...AS A RIDGE OF HIGH PRESSURE SETTLES OVER THE AREA BEHIND THE DEPARTED FRONT. MUCH COOLER AND DRIER AIR IS THEN ON TAP TO SPILL INTO THE AREA THURSDAY NIGHT...MAKING FOR A DRY FORECAST DURING THAT TIME FRAME. ANOTHER SHOT OF RAIN IS FORECAST FROM FRIDAY THROUGH SUNDAY...AS AN AREA OF LOW PRESSURE MOVES OUT OF THE CENTRAL PLAINS AND YET AGAIN CROSSES THE OHIO AND TENNESSEE VALLEYS. THIS WEATHER SYSTEM LOOKS LIKE IT WILL BE SLOWER AND HAVE QUITE A BIT MORE MOISTURE TO WORK WITH THEN AT THE BEGINNING OF THE PERIOD. THEREFORE...PRECIPITATION CHANCES FOR THE FRIDAY THROUGH SUNDAY TIME FRAME ARE FORECAST TO BE SUBSTANTIALLY HIGHER THAN WEDNESDAY/S SYSTEM. THE PEAK TIME FOR RAIN WITH THIS SECOND SYSTEM LOOKS TO BE SATURDAY MORNING...BASED ON THE LATEST MODEL DATA AT LEAST. BOTH THE MODELS ALSO HAVE A THIRD SLUG OF PRECIPITATION MOVING ACROSS THE AREA AT THE VERY END OF THE PERIOD. WITH BOTH MODELS SUGGESTING SOMETHING FOR THE END OF THE PERIOD...DECIDED TO INCLUDE A SLIGHT CHANCE OF RAIN FOR LATE SUNDAY NIGHT...BUT THIS WAS DONE WITH GREAT UNCERTAINTY FIGURED IN. BASED ON THE LACK OF INSTABILITY AVAILABLE...AND THE COOLER THAN NORMAL AIR MASS EXPECTED...DECIDED NOT TO INCLUDE THUNDER IN THE FORECAST IN THE EXTENDED. THE MODELS SOUNDINGS SIMPLY DID NOT SEEM TO SUPPORT IT AT THIS TIME. TEMPERATURES BEYOND WEDNESDAY WILL LIKELY BE WELL BELOW NORMAL...WITH A COOLER THAN NORMAL AIR MASS MOVING SOUTHWARD OUT OF CANADA TO START THE PERIOD OFF. HIGHS EACH DAY FROM THURSDAY ONWARD ARE FORECAST TO TOP OUT IN THE UPPER 50S AND LOWER 60S...WITH OVERNIGHT LOWS MOSTLY IN THE LOW TO MID 40S. THE ONE EXCEPTION LOOKS LIKE IT WILL BE LATE THURSDAY NIGHT INTO EARLY FRIDAY MORNING...AT WHICH TIME TEMPERATURES MAY BOTTOM OUT IN THE MID TO UPPER 30S ACROSS AREA. BASED ON SOME MOS DATA...SOME OF OUR DEEPER...MORE SHELTERED...AND NORMALLY COLDER VALLEYS COULD SEE LOWS DROPPING TO 34 OR 35 DEGREES IF WE GET ENOUGH CLEARING AND WINDS GO CALM THURSDAY NIGHT. THIS WILL BEAR WATCHING FOR SURE...AND BASED ON ALL THAT...FROST WILL BE MENTIONED YET AGAIN IN THE HAZARDOUS WEATHER OUTLOOK FOR THE THURSDAY NIGHT INTO FRIDAY MORNING PERIOD. && .AVIATION...
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(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT) ISSUED AT 145 AM EDT TUE APR 21 2015 VFR STRATOCU OR MID LEVEL CLOUDS WILL CONTINUE TO WORK ACROSS THE REGION DURING THE FIRST 3 TO 5 HOURS OF THE PERIOD. THEREAFTER...ENOUGH DRYING OF THE COLUMN WILL OCCUR AND WHEN COMBINED WITH SFC HIGH PRESSURE BRIEFLY NOSING INTO THE AREA...SKIES SHOULD BECOME MOSTLY CLEAR DURING THE 9Z TO 16Z TIMFRAME. HOWEVER...ANOTHER MID LEVEL DISTURBANCE AND ASSOCIATED COLD FRONT WILL APPROACH THE REGION DURING THE LAST 12 HOURS OF THE PERIOD. WINDS WILL REMAIN 5 TO 10KT OR LESS DURING THE OVERNIGHT HOURS. VFR IS EXPECTED TO PERSIST ON AVERAGE THROUGH THE END OF THE PERIOD...ALTHOUGH ISOLATED TO SCATTERED SHRA OR SPRINKLES ARE POSSIBLE BETWEEN 21Z AND 6Z AT THE TAF SITES AS THE FRONT NEARS. IN ADVANCE OF THE FRONT ON TUESDAY...GUSTY WEST WINDS WITH SUSTAINED SPEEDS IN MOST LOCATIONS OVER 12 KT WITH GUSTS TO AROUND 25KT ARE EXPECTED TO DEVELOP BY THE 14Z TO 15Z TIMEFRAME IN MOST LOCATIONS AND CONTINUE THROUGH AROUND 22Z SO. WINDS SHOULD THEN SLACKEN TO 10KT OR LESS THROUGH THE END OF THE PERIOD.
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&& .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...JP SHORT TERM...GEOGERIAN LONG TERM...AR AVIATION...JP

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