Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 131156 AAA AFDJKL AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE JACKSON KY 756 AM EDT SUN JUL 13 2014 .UPDATE...
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ISSUED AT 750 AM EDT SUN JUL 13 2014 HOURLY GRIDS HAVE BEEN FRESHENED UP BASED ON THE RECENT OBSERVATIONS. OTHERWISE...NO AWOS OR ASOS SITES WERE REPORTING FOG...AS THE MID CLOUD DECK HAS GENERALLY HINDERED IT FROM DEVELOPING. WITH THAT IN MIND... FOG WAS REMOVED FROM THE GRIDS TO START THE DAY. OTHERWISE...THE PREVIOUS FORECAST REMAINS ON TARGET WITH ISOLATED TO SCATTERED CONVECTION ANTICIPATED TO BEGIN TO DEVELOP AROUND OR SHORTLY AFTER NOON.
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&& .SHORT TERM...(TODAY THROUGH MONDAY) ISSUED AT 420 AM EDT SUN JUL 13 2014 AN UPPER LEVEL RIDGE WAS CENTERED ACROSS PARTS OF THE SOUTHERN PLAINS AND EXTENDING EAST INTO THE SOUTHEASTERN STATES...WITH THE RIDGE EXTENDING INTO THE INTER MOUNTAIN WEST. MEANWHILE TO ITS EAST A TROUGH EXTENDED SOUTH INTO THE UPPER MS VALLEY REGION AND NORTHERN GREAT LAKES FROM A RATHER STRONG MID SUMMER UPPER LEVEL LOW CENTERED OVER NORTHWEST ONTARIO. ONE MID LEVEL SHORTWAVE IS WORKING ACROSS THE OH VALLEY REGION AT THIS TIME...WITH ANOTHER WORKING ACROSS THE GREAT LAKES REGION. THIS COMBINATION IS PUSHING A RATHER SHEARED OUT EAST TO WEST COLD FRONT INTO THE SOUTHERN GREAT LAKES TO MID MS VALLEY REGION...WITH THE FRONT ALSO APPROACHING THE LOWER OH VALLEY REGION. MID AND HIGH CLOUDS CONTINUE TO WORK GRADUALLY EAST SOUTHEAST ACROSS MUCH OF THE AREA. PARTS OF THE SOUTHERN CWA NEAR THE KY/VA/TN TRI STATE AREA HAVE EXPERIENCED THE LEAST AMOUNT OF CLOUDS AND TEMPERATURES...ESPECIALLY IN VALLEYS HAVE BEEN SLIGHTLY COLDER IN THESE LOCATIONS. SO FAR THIS MORNING...NO ASOS OR AWOS SITES HAVE REPORTED ANY FOG. HOWEVER...NEAR ZERO DEWPOINT DEPRESSIONS IN SOME VALLEY LOCATIONS SUGGEST THAT AT LEAST SOME LIGHT RIVER VALLEY FOG IS PROBABLY OCCURRING. THE SHORTWAVE GENERALLY PASSING BY TO THE NORTH OVER THE NEXT FEW HOURS WILL SERVE TO FURTHER SHEAR OUT THE COLD FRONT FROM EAST TO WEST WITH IT STALLING OUT AND WASHING OUT OR MERGING WITH A MORE SUBSTANTIAL COLD FRONT THAT SHOULD APPROACH THE OH VALLEY LATE IN THE PERIOD. THIS SECOND COLD FRONT WILL BE PUSHED SOUTHEAST AS THE UPPER LEVEL FLOW DROPS SOUTH INTO THE GREAT LAKES REGION ON MONDAY...WITH THE OVERALL PATTERN AMPLIFYING. THIS UPPER LOW AND THE ASSOCIATED SHORTWAVES TO ROTATE THROUGH THE DEVELOPING TROUGH SHOULD LEAD TO AN INCREASE IN FORCING LATE TONIGHT AND ON MONDAY. RETURN LOW AND MOISTURE FLUX AHEAD OF THIS BOUNDARY IS LEADING TO A SUBSTANTIAL INCREASE IN MOISTURE AT THE LOW LEVELS AND ALOFT. THIS INCREASE IN MOISTURE WILL CONTINUE WITH PW EXPECTED TO GRADUALLY CLIMB TO CLIMB TO ABOUT 1.75 INCHES BY LATE AFTERNOON OR EARLY EVENING...WITH SLIGHTLY HIGHER VALUES ANTICIPATED ACROSS THE FAR NORTHWEST. MODEL FORECAST SHOW SOME FLUCTUATIONS IN PW VALUES DUE TO DIFFERENT TIMING OF CONVECTION AND SHORTWAVES. THE GFS SHOWS THE MOST VARIABILITY OF PW FROM TONIGHT INTO MONDAY. MEANWHILE THE NAM HAS THE HIGHEST VALUES ON AVERAGE. CONVECTION WILL BE POSSIBLE AT ANY TIME FROM MIDDAY TODAY THROUGH THE END OF THE PERIOD. MODEL GUIDANCE CONTINUES TO SHOW THE POTENTIAL FOR CONVECTION TO DEVELOP ACROSS THE HIGHER TERRAIN NEAR THE VA/TN/KY TRI STATE AREA FIRST AND THEN ACROSS THE NORTHERN PART OF THE CWA CLOSER TO THE BOUNDARY AND PASSING SHORTWAVES. GREATER INSTABILITY AND A BIT STRONGER SHEAR LATER THIS AFTERNOON AND EVENING SHOULD BE REALIZED ACROSS THE NORTHWEST COUNTIES. MODELS DEVELOP SOME MODERATE INSTABILITY ACROSS THAT AREA...A FEW STRONG TO POSSIBLY A SEVERE THUNDERSTORM OR TWO MAY OCCUR. CONVECTION BY THIS EVENING OR TONIGHT ALSO MIGHT TRAIN WEST TO EAST ACROSS PARTS OF THE AREA...ESPECIALLY NORTHWEST WITH THE STEERING FLOW BECOMING NEARLY PARALLEL TO THE STALLING BOUNDARY. WITH THE PW NEAR OR ABOVE THE 75TH PERCENTILE LOCALLY HEAVY RAIN MAY BE PRIMARY THREAT ACROSS THE NORTH FROM LATE THIS AFTERNOON INTO TONIGHT. RECENT DAYS HAVE BEEN DRY AND MANY LOCATIONS HAVE BELOW NORMAL RAINFALL OVER THE PAST 4 TO 6 WEEKS...SO IT WOULD TAKE AN INITIAL SHOT OR TWO OF HEAVY RAIN FOLLOWED BY ADDITIONAL HEAVY RAIN SHORTLY THEREAFTER TO PRIME ANY LOCATION. ON MONDAY...THE GREATER INSTABILITY SHOULD RESIDE FURTHER SOUTHEAST OF THE STALLED BOUNDARY AND THE APPROACHING FRONT. THIS COMBINED WITH FORCING FROM HEIGHT FALLS...SHOULD AGAIN LEAD TO ROUNDS OF SHOWERS AND THUNDERSTORMS. IF PARTS OF THE REGION CLEAR OUT FOR A FEW HOURS... A PREFRONTAL MULTICELL CLUSTER OR LINE OR TWO OF STORMS COULD BECOME STRONG TO SEVERE AS MODERATE INSTABILITY IS FORECAST BY THE MODELS ACROSS THE SOUTH. STRONG WIND GUSTS AND LOCALLY HEAVY RAIN WOULD AGAIN APPEAR TO BE THE MAIN THREATS FROM THE STORMS. AGAIN...DEPENDING ON THE EVENTUAL MAGNITUDE AND EXTENT OF INSTABILITY SOME LOCALLY HEAVY RAIN MIGHT BE A GREATER CONCERN THAN THE SEVERE THREAT. .LONG TERM...(MONDAY NIGHT THROUGH SATURDAY) ISSUED AT 315 AM EDT SUN JUL 13 2014 THE MODELS BEGIN THE EXTENDED PERIOD IN PRETTY GOOD AGREEMENT. THE LARGE SCALE WEATHER PATTERN FEATURES A DEEP TROUGH OF LOW PRESSURE IN THE UPPER ATMOSPHERE MOVING EAST OUT OF THE GREAT LAKES REGION AND INTO NEW ENGLAND MONDAY NIGHT THROUGH TUESDAY NIGHT. THE WEATHER MAKE WITH THIS SYSTEM FOR EASTERN KENTUCKY WILL BE A POTENT SURFACE COLD FRONT. THIS FRONT LOOKS TO BE ORIENTED FROM WEST TO EAST AND...IF THE MODELS BE TRUE...WILL MOVE SLOWLY ACROSS CENTRAL AND EASTERN KENTUCKY MONDAY NIGHT AND TUESDAY. NUMEROUS SHOWERS AND STORMS ARE EXPECTED TO BREAK OUT ALONG THE BOUNDARY IN THE WARM AND HUMID AIR MASS THAT WILL BE IN PLACE. SOME OF THE STORMS MONDAY EVENING COULD BE STRONG TO SEVERE WITH DAMAGING WINDS AND LOCALLY HEAVY RAINFALL BEING THE PRIMARY THREATS. ONCE THE COLD FRONT MOVES OUT OF THE AREA TUESDAY NIGHT...A LARGE RIDGE OF CANADIAN HIGH PRESSURE WILL USHER COOLER AND DRIER AIR INTO THE AREA THROUGH THE END OF THE WEEK. THE MODELS DIVERGE A BIT WITH THEIR SOLUTIONS FROM FRIDAY NIGHT ONWARD...SO THAT PORTION OF THE FORECAST WILL BE LOWER CONFIDENCE. THAT BEING SAID...INCORPORATED THE POSSIBILITY OF ISOLATED SHOWERS AND STORMS FOR FRIDAY ONWARD DUE TO MODEL UNCERTAINTY. TEMPERATURES TO BEGIN THE PERIOD WILL BE QUITE UNSEASONABLE...WITH HIGHS ONLY MAKING IT INTO THE MID TO UPPER 70S FROM TUESDAY THROUGH THURSDAY. THE AIR MASS WILL MODIFY SLIGHTLY TO END THE WEEK AND INTO THE WEEKEND...AS HIGHS ARE EXPECTED TO WARM TO AROUND 80 FROM FRIDAY ONWARD. OVERNIGHT LOWS WILL BE MOSTLY IN THE LOW TO MID 60S...WITH COOLER LOWS OF THE MID TO UPPER 50S TUESDAY NIGHT AND WEDNESDAY NIGHT AS THE NEW AIR MASS SETTLES OVER THE REGION. && .AVIATION...
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(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING) ISSUED AT 750 AM EDT SUN JUL 13 2014 PREDOMINANTLY VFR IS EXPECTED TO CONTINUE FOR MUCH OF THE PERIOD. WINDS WILL GENERALLY BE LIGHT AS WELL ALTHOUGH DURING PEAK HEATING... ALTHOUGH DURING PEAK HEATING WINDS MAY BECOME A BIT GUSTY AND SUSTAINED AS HIGH AS 10KT OUT OF THE SOUTHWEST AS A COLD FRONT DROPS INTO THE OH VALLEY INCREASES THE PRESS GRADIENT. THE EXCEPTION DURING THE FIRST 12 HOURS TO VFR WILL BE IN ANY SHOWERS AND THUNDERSTORMS POPPING UP AROUND 16Z AND AFTER...WHERE LOCALIZED RESTRICTIONS TO MVFR OR IFR CIGS/VSBY ARE POSSIBLE. MORE ORGANIZED SHRA AND TSRA SOUTHEAST ACROSS THE AREA FROM 22Z THROUGH THE END OF THE PERIOD. AGAIN LOCALIZED RESTRICTIONS ARE POSSIBLE WITH THIS. AS FOR NOW... WE HAVE CONTINUED TO GO WITH VCTS AT ALL FOUR TAF SITES.
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&& .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...JP SHORT TERM...JP LONG TERM...AR AVIATION...JP

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