Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 210140 AFDJKL AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE JACKSON KY 940 PM EDT SUN JUL 20 2014 .UPDATE...
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ISSUED AT 940 PM EDT SUN JUL 20 2014 SHOWERS LINGERING ACROSS THE AREA THIS EVENING. THERE IS A VERY GRADUAL DECREASE IN ACTIVITY. BUT WITH THE PERSISTENT NATURE OF THE THUNDERSTORMS...ASSOCIATED WITH THE MAIN CLUSTERS OF SHOWERS DECIDED TO INTRODUCE ISOLD THUNDER FOR THE FIRST COUPLE HOURS OF THE UPDATE. OTHERWISE BROUGHT GRIDS INTO LINE WITH HOURLY TRENDS. UPDATE ISSUED AT 709 PM EDT SUN JUL 20 2014 QUICK UPDATE FOR THE UPTICK IN SHOWER ACTIVITY ACROSS THE AREA LATE THIS AFTERNOON/EARLY THIS EVENING. SHORT WAVE CURRENTLY DROPPING SOUTHEASTWARD INTO THE MID OHIO VALLEY REGION IN COMBINATION WITH FAVORABLE DIURNAL HEATING IS RESPONSIBLE FOR THE LATE DAY INCREASE. ONE PARTICULAR CLUSTER OF SHOWERS OVER THE BLUEGRASS HAS MANAGED TO STRENGTHEN INTO THUNDERSTORMS. IN ADDITION...CLUSTERS HAVE MANAGED TO PRODUCE A FEW OUTFLOW BOUNDARIES ACROSS THE AREA THAT ARE KICKING OFF ADDITIONAL SHOWERS. INCREASED POPS LATE THIS AFTERNOON AND EARLY THIS EVENING TO LINE UP WITH CURRENT RADAR TRENDS. TWEAKED GRIDS FOR HOURLY OBS AS WELL. WITH EXTREMELY ISOLD NATURE OF THUNDER LEFT MENTION OF OUT OF THE ZONE PACKAGE...PREFERRING TO MENTION IN OUR GRAPHICAL-NOWCAST PRODUCTS.
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&& .SHORT TERM...(THIS EVENING THROUGH MONDAY NIGHT) ISSUED AT 319 PM EDT SUN JUL 20 2014 A WEAK LOW PRESSURE CENTER JUST OFF TO OUR SOUTH HAS CONTROLLED TODAY/S WEATHER...BRINGING MOIST CONDITIONS WITH LOW CLOUDS AND DRIZZLE/LIGHT RAIN SHOWERS THROUGH THE FIRST PART OF THE DAY. DURING THE AFTERNOON...SHOWERS FINALLY BEGAN PUSHING TO THE NE...WHILE SMALL ISOLATED/SCATTERED SHOWERS STARTED POPPING UP ACROSS PORTIONS OF EASTERN KY. THE LOW...CURRENTLY OVER MIDDLE TN...WILL QUICKLY DROP SOUTHWARD LATE THIS AFTERNOON...PULLING THE BEST INSTABILITY AND MOISTURE WITH IT. EXPECT ISOLATED TO SCATTERED SHOWERS TO CONTINUE INTO THE LATE AFTERNOON...BEFORE TAPERING OFF BY EVENING. BASED ON THE CURRENT LACK OF INSTABILITY AND THUNDERSTORM DEVELOPMENT...WENT AHEAD AND REMOVED ANY MENTION OF THUNDER FROM THE FORECAST FOR THE REMAINDER OF TODAY AND THIS EVENING. THOUGH CLOUD COVER COULD LINGER IN SOME LOCATIONS OVERNIGHT...OTHERS CAN EXPECT SOME DECENT CLEARING. LOWS WILL REGULATE AROUND NORMAL...IN THE LOW TO MID 60S ACROSS THE REGION. GIVEN THE AMOUNT OF LOW LEVEL MOISTURE ACROSS THE AREA...AND THE EXPECTATION OF ANOTHER STRONG SUBSIDENCE INVERSION SETTING UP OVERNIGHT...FOG SHOULD ONCE AGAIN BE THE MAIN CONCERN OVERNIGHT TONIGHT. INCLUDED PATCHY FOG ACROSS THE ENTIRE CWA...WITH AREAS OF FOG IN THE RIVER VALLEYS. THERE IS THE POTENTIAL THAT SOME OF THESE LOCATIONS COULD SEE DENSE FOG...ESPECIALLY AREAS THAT RECEIVED RAINFALL DURING THE DAY TODAY. THEN FOR TOMORROW...EXPECT A MORE TYPICAL SUMMER TIME DIURNAL PATTERN TO TAKE OVER. AIR MASS MODIFICATION /ALONG WITH SOME CLEARING DURING THE DAY/ WILL ALLOW FOR TEMPS TO RISE INTO THE UPPER 80S. CONVECTION WILL THEN BE POSSIBLE DURING THE AFTERNOON HOURS...ESPECIALLY IN THE SE. WINDS WILL BE VERY LIGHT...WITH LITTLE FORCING. CHOSE TO KEEP ONLY ISOLATED THUNDER WORDING IN THE FORECAST FOR THE AFTERNOON...GIVEN THE LACK OF A GOOD WIND PROFILE...INSTABILITY...AND A DECENT MID LEVEL INVERSION ON THE LATEST FORECAST SOUNDING. EXPECT CONVECTION TO DIE OUT IN THE EVENING WITH THE LOSS OF DIURNAL HEATING. WITH MORE CLEARING EXPECTED OVERNIGHT MONDAY NIGHT...TEMPS SHOULD DROP BACK DOWN INTO THE MID AND UPPER 60S...WHICH IS STILL A FEW DEGREES WARMER THAN WHAT IS EXPECTED FOR TONIGHT. .LONG TERM...(TUESDAY THROUGH SUNDAY) ISSUED AT 420 PM EDT SUN JUL 20 2014 THE LONG TERM PERIOD WILL BEGIN WITH RIDGING CENTERED OVER THE SOUTHERN ROCKIES WITH ANOTHER RIDGE CENTERED OFF THE SOUTHEAST US COAST. IN BETWEEN AN UPPER LEVEL LOW IS EXPECTED TO BE OVER THE SOUTHEAST US. A SHORTWAVE OR SERIES OF SHORTWAVES IS EXPECTED TO BE WORKING FROM THE US CANADIAN BORDER/UPPER MS VALLEY TOWARD THE GREAT LAKES AT THAT TIME. THROUGH TUE NIGHT...INTO WED...THE PATTERN IS STILL EXPECTED TO AMPLIFY A BIT AROUND MIDWEEK WITH THE RIDGE STRENGTHENING A BIT OVER THE WESTERN CONUS AND THE INITIAL SHORTWAVE TREKKING ACROSS THE GREAT LAKES AND INTO THE NORTHEAST. ANOTHER SHORTWAVE SHOULD ROTATE AROUND A CLOSED LOW OVER CANADA ACROSS SOUTHERN CANADA AND THE GREAT LAKES REGION. DURING THIS PERIOD...THE SOUTHEAST UPPER LEVEL LOW SHOULD MEANDER SLOWLY WEST. THIS SCENARIO SHOULD LEAD TO A PERIOD OF WEST NORTHWEST TO NORTHWEST FLOW ALOFT ACROSS PARTS OF THE EASTERN CONUS FROM WED NIGHT INTO FRI. THIS SHOULD COMBINATION SHOULD SEND A COLD FRONT TOWARD THE REGION ON WED INTO AND THEN ACROSS THE AREA WED NIGHT INTO THU. THE GFS RUNS CONTINUE TO PUSH THE BOUNDARY FURTHER SOUTHEAST AND FASTER THAN THE ECMWF RUNS. THIS LEADS TO A BIT OF UNCERTAINTY IN AMOUNT OF MOIST AND PRECIP CHANCES FROM THU NIGHT INTO FRI. ALSO FROM THU INTO THE WEEKEND...THE PATTERN SHOULD BEGIN TO FLATTEN OUT AGAIN AS A RATHER ROBUST UPPER LOW IS EXPECTED TO WORK FROM THE PACIFIC NORTHWEST GRADUALLY EAST NEAR THE US/CANADIAN BORDER THROUGH THE START OF THE WEEKEND. THEN LATE IN THE PERIOD... THIS UPPER LOW IS PROGGED TO APPROACH THE GREAT LAKES REGION WITH THE PATTERN AGAIN AMPLIFYING OR RETURNING TO A WESTERN CONUS RIDGE AND EASTERN CONUS TROUGH. PRECIPITATION CHANCES INITIALLY SHOULD BE GENERALLY DIURNALLY DRIVEN WITH WEAK DISTURBANCES WORKING AROUND THE SOUTHEASTERN CONUS UPPER LOW POSSIBLY ENHANCING CHANCES ACROSS PARTS OF THE SOUTH OR SOUTHEAST. THEN AS THE SHORTWAVES APPROACH AND SEND THE COLD FRONT TOWARD AND THEN ACROSS THE REGION...UNSETTLED WEATHER IS ANTICIPATED FORM WED AFTERNOON INTO THU EVENING. HIGH CHANCE TO LIKELY POPS WERE USED DURING THIS PERIOD AS THE PREFRONTAL AIR MASS AND THE UPPER SUPPORT SHOULD COMBINE WITH THE BOUNDARY FOR GOOD CONVERGE OF CONVECTION. THE MODEL CONSENSUS BLEND WAS USED FOR POPS ON THU NIGHT INTO FRI. THE GFS MODEL RUNS IN GENERAL ARE DRIER THROUGH THIS PERIOD... WHILE THE ECMWF IS WETTER AS IT HAS THE BOUNDARY CLOSER TO THE AREA THAT PERIOD. DIURNALLY DRIVEN ISOLATED CONVECTION APPEARS POSSIBLE TO START THE WEEKEND ON SATURDAY AS THE FLOW BECOMES MORE WESTERLY...BUT ANY PASSING DISTURBANCE COULD INTERACT WITH DAYTIME HEATING. THEN AS THE TROUGH BEGINS TO DEVELOP LATE IN THE PERIOD...COVERAGE OF CONVECTION SHOULD INCREASE ALONG WITH THE CHANCES FOR CONVECTION AT NIGHT. TEMPERATURES WILL AVERAGE A BIT ABOVE NORMAL FOR TUE INTO WED...BUT BEHIND THE BOUNDARY DROP A FEW DEGREES BELOW NORMAL FOR THU INTO SAT. THE BIGGEST DEPARTURES OF ABOUT 5 TO 8 DEGREES WILL OCCUR WITH DAYTIME HIGHS ON THU...AND IN HIGHS IN GENERAL. && .AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING) ISSUED AT 824 PM EDT SUN JUL 20 2014 UPPER LEVEL DISTURBANCE AND DAYTIME HEATING HAS KICKED OFF SHOWER ACTIVITY ACROSS THE AREA. MOST OF THE ACTIVITY HAS BEEN GENERALLY EITHER SIDE OF A LINE FROM KEKQ TO KSYM. LONDON AND JACKSON HAD SHOWERS PASS OVER THE TERMINALS. CONSIDERING TIME OF OCCURRENCE AND THE FACT THAT WE ARE WELL INTO THE EARLY EVENING NOW...EXPECT FOG MAY FORM A BIT EARLIER THAN MODEL GUIDANCE MIGHT SUGGEST AT LONDON AND JACKSON. MODEL GUIDANCE TAKES ALL AIRPORTS DOWN INTO LIFR TERRITORY THROUGH THE EARLY MORNING HOURS MONDAY DUE TO FOG. WITH RECENT RAINFALL ACROSS PORTIONS OF THE AREA AND SIGNIFICANT INCREASE IN BOUNDARY LAYER MOISTURE...SEE NO REASON TO DOUBT MODEL GUIDANCE THROUGH THE FIRST 8 TO 12 HOURS OF THE FORECAST. ONCE FOG BURNS OFF THROUGH THE MID TO LATE MORNING TIMEFRAME MONDAY...VFR CONDITIONS SHOULD RETURN THROUGH THE REMAINDER OF THE TAF PERIOD. A FEW DIURNAL SHOWERS AND THUNDERSTORMS COULD BE POSSIBLE AFTER 18Z TOMORROW... MAINLY OVER THE HIGHER TERRAIN TO OUR SOUTHEAST. WINDS WILL BE LIGHT. && .JKL WATCHES/WARNINGS/ADVISORIES...NONE. && $$ UPDATE...RAY SHORT TERM...JMW LONG TERM...JP AVIATION...RAY

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