Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 080307 AAB AFDJKL AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE JACKSON KY 1107 PM EDT MON JUL 7 2014 .UPDATE... ISSUED AT 1055 PM EDT MON JUL 7 2014 THE CONVECTION WORKING INTO THE REGION HAS WEAKENED DUE TO THE DRIER AIRMASS IN PLACE. LOW LEVEL MOISTURE WILL INCREASE OVERNIGHT AS THE LOW LEVEL JET WILL PICK UP AHEAD OF THE APPROACHING FRONT AND SHORTWAVE... AND CONVECTION MAY REDEVELOP OR PICK BACK UP AT THAT POINT. THE PREVIOUS FORECAST ALREADY HAD THIS HANDLED...SO GRIDS WERE MAINLY UPDATED FOR RECENT OBSERVATIONS AND RADAR TRENDS. UPDATE ISSUED AT 755 PM EDT MON JUL 7 2014 THE FIRST FEW HOURS OF THE FORECAST HAVE BEEN ADJUSTED FOR TRENDS IN CONVECTION TO OUR NORTHWEST AND WEST. THE LINE OF STORMS OVER SOUTH CENTRAL KY CONTINUES TO MOVE EAST SOUTHEAST...BUT WHAT IS LEFT OF THIS LINE SHOULD NEAR THE PULASKI AND WAYNE COUNTY AREA OF THE LAKE CUMBERLAND REGION ABOUT DARK. ALSO...THE HEAVY RAIN PRODUCING CLUSTER OF STORMS OR REMNANTS OF WHAT IS OVER NORTHERN KY COULD ALSO NEAR FLEMING COUNTY ABOUT 10 PM. HOWEVER...WITH THE AIRMASS CONSIDERABLY DRIER OVER EASTERN KY...THIS ACTIVITY SHOULD WEAKEN OR POSSIBLY DISSIPATE AS IT GETS INTO THE JKL CWA. ADDITIONAL CONVECTION LATER ON TONIGHT CANNOT BE RULED OUT AS A COLD FRONT AND LEAD UPPER LEVEL WORK ACROSS THE REGION. THE CHANCES FOR THUNDERSTORMS...SOME POSSIBLY SEVERE...WILL BE GREATER ON TUESDAY AND TUESDAY EVENING AS THE BOUNDARY AND STRONGER SHORTWAVE APPROACH THE OH VALLEY REGION. && .SHORT TERM...(THIS EVENING THROUGH WEDNESDAY NIGHT) ISSUED AT 317 PM EDT MON JUL 7 2014 THE QUIET WEATHER WE HAVE EXPERIENCED RECENTLY IS ABOUT TO COME TO AN ABRUPT END AS A COLD FRONT PASSES THROUGH THE REGION BRINGING THE POTENTIAL FOR A SEVERE WEATHER OUTBREAK TUESDAY INTO TUESDAY NIGHT. OUR ATMOSPHERE REMAINS CAPPED THIS AFTERNOON KEEPING CONVECTION TO OUR NORTH. THIS CAP WILL ERODE OVERNIGHT AND THUNDERSTORM ACTIVITY NOW FIRING ALONG A WARM FRONT OVER INDIANA AND OHIO WILL WANT TO SAG SOUTHWARD TOWARD OUR REGION. 12Z MODEL GUIDANCE AND HI RES NEAR TERM MODELS HAVE CONTINUED THE SLOWER TREND WITH ANY SHOWERS/STORMS TONIGHT SO DELAYED THE INCREASE IN POPS A FEW MORE HOURS. LOCATIONS NORTH OF THE MOUNTAIN PARKWAY STAND THE BEST CHANCE OF SEEING A SHOWER OR THUNDERSTORM TONIGHT. OVERNIGHT TEMPS SHOULD BOTTOM OUT BETWEEN 65 AND 70 WITH A LIGHT SOUTHERLY BREEZE ENGAGED FOR MOST AREAS. ON TUESDAY...LOW PRESSURE WILL TRACK ACROSS THE GREAT LAKES AND THE TRAILING COLD FRONT WILL SWEEP ACROSS EAST KENTUCKY TUESDAY NIGHT. THE EVOLUTION OF TOMORROW/S SEVERE THREAT IS STILL A LITTLE UNCERTAIN AS THERE MAY BE MORE THAN ONE ROUND OF SHOWERS/STORMS AND ANY MORNING CONVECTION COULD HINDER THE DEVELOPMENT OF THE SECOND ROUND. HOWEVER...SHOULD MORNING CONVECTION STAY SCATTERED IN NATURE THE SEVERE THREAT WILL HAVE A LOT GOING FOR IT...INCLUDING THE POTENTIAL FOR STRONG ATMOSPHERIC INSTABILITY...DECENT WIND SHEAR...AND FAVORABLE UPPER LEVEL JET DYNAMICS. THE SEVERE THREAT PEAKS IN THE LATE AFTERNOON AND EVENING HOURS...AND THEN DIMINISHES THROUGH THE NIGHT. THE FRONT WILL SLOW AS IT DROPS THROUGH THE AREA AND THE THREAT FOR SHOWERS/STORMS WILL LINGER THROUGH THE DAY ON WEDNESDAY...AND INTO THE EVENING OVER SOUTHEAST KENTUCKY. .LONG TERM...(THURSDAY THROUGH MONDAY) ISSUED AT 335 PM EDT MON JUL 7 2014 MODEL AGREEMENT IS BEST THURSDAY THROUGH FRIDAY...THEN SIGNIFICANT DIFFERENCES EMERGE HEADING INTO NEXT WEEKEND INTO EARLY NEXT WEEK. THUS...CONFIDENCE IS HIGHEST THROUGH ABOUT FRIDAY NIGHT...BUT BELOW AVERAGE FROM SATURDAY INTO MONDAY. TO START THE PERIOD...THE MAIN SHORTWAVE TROUGH WILL HAVE MOVED WELL EAST OF THE AREA BEFORE THE START OF THE PERIOD. HOWEVER...ANOTHER SHORTWAVE MOVING THROUGH THE ANTICIPATED EASTERN NORTH AMERICAN TROUGH SHOULD CROSS THE AREA ON THURSDAY. THIS SHORTWAVE MAY NOT BRING MORE THAN SOME DIURNALLY DRIVEN CU...BUT LOW LEVEL MOISTURE MAY BE SUFFICIENT FOR ISOLATED SHOWERS ACROSS THE SOUTH...CLOSER TO THE FRONTAL ZONE ACROSS THE SOUTHEAST. THEN...A PERIOD OF HEIGHT RISES IS ANTICIPATED ACROSS THE SOUTHEAST AND OH VALLEY REGIONS AS THE EASTERN NOAM TROUGH LIFTS ON OUT AND WEAKENS...AND HIGH PRESSURE CENTERED OVER THE FOUR CORNERS REGION AND SOUTHERN ROCKIES AND ENCOMPASSING MUCH OF THE WESTERN CONUS BUILDS TOWARD THE CENTRAL AND SOUTHERN PLAINS AND LOWER MS VALLEY. AT THE SFC...HIGH PRESSURE SHOULD BUILD INTO THE REGION FROM THE GREAT LAKES BY LATE THURSDAY INTO THURSDAY NIGHT AND GENERALLY REMAIN DOMINANT INTO FRIDAY NIGHT AS IT SHIFTS INTO THE NORTHEASTERN STATES AND MID ATLANTIC. THIS HIGH SHOULD BRING A SOMEWHAT DRIER AIRMASS INTO THE REGION AND COLDER OVERNIGHT LOWS ON THU NIGHT AS COMPARED TO THE NEXT COUPLE OF NIGHTS. QUESTIONS REMAIN WITH TIMING AND TRACK OF SHORTWAVES MOVING AROUND THE RIDGE AND THEN MOVING EAST SOUTHEAST TOWARD THE NORTHERN PLAINS AND GREAT LAKES BY FRIDAY AND INTO THE WEEKEND. THE GFS MAY HAVE CONVECTIVE FEEDBACK ISSUES WITH THE SHORTWAVE TO MOVE FROM THE NORTHERN PLAINS INTO THE UPPER MS VALLEY REGION LATE FRI INTO EARLY ON SATURDAY AND PERHAPS INTO SATURDAY NIGHT AND A FURTHER NORTH DEVELOPMENT OF CONVECTION NEARER TO THE GREAT LAKES DURING THE PERIOD. THERE ARE ALSO DIFFERENCES IN THE STRENGTH OF THE RIDGE OVER THE ROCKIES INTO THE SOUTHERN PLAINS AND RIDGING OVER THE ATLANTIC. THE ECMWF CONTINUES WITH A WETTER...CLOUDIER AND SLIGHTLY COLDER SCENARIO OVER THE WEEKEND INTO EARLY NEXT WEEK...WHILE THE GFS IS DRIER AND WARMER. THE MODELS ALSO DIFFER IN THE POSITION OF THE UPPER LOW OVER CENTRAL CANADA WITH THE ECMWF MUCH FURTHER SOUTH AND LOWER WITH HEIGHTS ACROSS THE GREAT LAKES AND OH VALLEY REGION BY THE START OF NEXT WEEK WITH THE GFS ALSO SLOWER TO DO THIS. THE MODELS THOUGH ALSO APPEAR RATHER CONSISTENT OVER THE PAST COUPLE OF RUNS WITH THESE DIFFERENCES. LOW LEVEL MOISTURE THROUGH SHOULD INCREASE ONCE THE SFC HIGH MOVES EAST BY THE START OF THE WEEKEND. THE REMNANTS OF THE NEAR TERM BOUNDARY MAY RETURN NORTH AS A WARM FRONT OVER THE WEEKEND IN ADVANCE OF THE NEXT SHORTWAVE TROUGH AND ASSOCIATED SFC COLD. OVERALL BOTH THE GFS AND ECMWF HAVE A COLD FRONT APPROACHING THE AREA AT THE END OF THE PERIOD...AND PRECIPITATION CHANCES APPEAR BEST ON MONDAY...IF NOT LATER PER GFS. CONSIDERING ALL THE UNCERTAINTY IN TIMING AND TRACKS OF SHORTWAVES BY SATURDAY THROUGH THE END OF THE PERIOD...OPTED TO GO WITH THE EXTENDED GRID LOAD MODEL BLEND GIVING WEIGHT TO PERSISTENCE AND THE MODEL CONSENSUS. THIS GENERALLY REFLECTED LOWER POPS AND WARMER TEMPS THAN THE ECMWF MIGHT SUGGEST BY THE WEEKEND INTO EARLY NEXT WEEK...BUT IF THE GFS WERE TO VERIFY TEMPS WOULD BE WARMER AND THE THREAT OF PRECIPITATION LESS AND LATER. ATTM...POPS OVER THE WEEKEND INTO EARLY NEXT WEEK OF SLIGHT CHANCE TO CHANCE WERE USED. SINCE THE UPPER RIDGE AT THIS POINT IS NOT EXPECTED TO BE CENTERED CLOSE ENOUGH TO EASTERN KY FOR TEMPS TO BE MORE THAN A COUPLE OF DEGREES ABOVE NORMAL ON AVERAGE. && .AVIATION...(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING) ISSUED AT 800 PM EDT MON JUL 7 2014 VFR CONDITIONS SHOULD PREVAIL THROUGH AT LEAST 18Z IN MOST LOCATIONS... EXCEPT FOR LOCALIZED REDUCTIONS IN AND NEAR THUNDERSTORMS TO MVFR OR POSSIBLY MOMENTARILY IFR. A LINE OF STORMS MIGHT AFFECT SME BETWEEN 1Z AND 4Z IF IT HOLDS TOGETHER. OTHERWISE...MOST TSRA SHOULD BE NORTH OF A JKL TO SJS LINE THROUGH 16Z...BEFORE CHANCES INCREASE FROM NORTH TO SOUTH. CONFIDENCE IN TIMING IS LOW...BUT ANTICIPATE THE MOST WIDESPREAD SHOWERS AND STORMS TO OCCUR AT THE TAF SITES AFTER 18Z...WHEN SEVERE THUNDERSTORMS WITH DAMAGING WINDS AND LARGE HAIL WILL BE POSSIBLE. LOW LEVEL WIND SHEAR WILL ALSO BE A CONCERN AFTER ABOUT 09Z AND BEFORE HIGHER WINDS ALOFT SURFACE AFTER 14Z TO 15Z. WIND GUSTS UP TO 20 KT OR SO SHOULD RESUME THEREAFTER WITH DAYTIME MIXING. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...JP SHORT TERM...ABE LONG TERM...JP AVIATION...JP

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