Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 221842 AAC AFDJKL AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE JACKSON KY 242 PM EDT TUE JUL 22 2014 .UPDATE... ISSUED AT PM EDT TUE JUL 22 2014 HOURLY GRIDS HAVE BEEN FRESHENED UP BASED ON RECENT SATELLITE IMAGERY AND OBSERVATIONS. THE ONLY RADAR RETURNS SO FAR HAVE BEEN ACROSS CENTRAL KY AND THESE ARE JUST SHOWERS AND SPRINKLES OF FAR WITH TOPS LESS THAN 20KFT. WITH MID LEVEL WARM AIR EXPECTED TO REMAIN...MAINLY JUST ISOLATED TO SCATTERED SHOWERS ARE ANTICIPATED THROUGH EVENING. HOWEVER...IN A FEW LOCATIONS INSTABILITY MAY BE SUFFICIENT FOR PARCELS TO REACH HIGH ENOUGH FOR A COUPLE OF THUNDERSTORMS. DESPITE THE WARM TEMPS AND MID 60S TO AROUND 70 DEWPOINTS LEADING TO SBCAPE 1500 TO 2500 J/KG AND MLCAPE 1000 TO 1500 J/KG OVER THE WESTERN PART OF THE AREA...TRIGGERS ARE WEAK AND WITH THE WARM MID LEVEL AIR...COVERAGE SHOULD AGAIN BE LIMITED. FOR NOW...WE HAVE OPTED TO KEEP ISOLATED TO SCATTERED COVERAGE...BUT PENDING DEVELOPMENT BY AFTERNOON ISSUANCE WE MAY DROP TO ISOLATED IN ALL AREAS. UPDATE ISSUED AT 1107 AM EDT TUE JUL 22 2014 THE GRIDS...ZFP...AND HWO WERE UPDATED MAINLY TO REMOVE MORNING FOG FROM THE FORECAST. THE REGION WILL REMAIN IN BETWEEN AN UPPER LOW MEANDERING ACROSS THE SOUTHEAST AND A SHORTWAVE AND DEVELOPING TROUGH OVER SOUTHERN CANADA AND THE GREAT LAKES REGION. THIS PUT THE AREA JUST TO THE SOUTH AND EAST OF A RIDGE AXIS EXTENDING FROM THE ROCKIES EAST INTO THE OH VALLEY REGION. THIS LEAVES THE AREA UNDER WEAK STEERING FLOW AND SHEAR AND LITTLE OR NO UPPER LEVEL SUPPORT FOR FORCING THROUGH THIS EVENING. THE LATEST GFS AND NAM FORECAST SOUNDINGS HAVE MID LEVEL WARM AIR AND KEEPS THE ATMOSPHERE CAPPED AT JKL THROUGH THIS EVENING. NEAR LOZ...THERE IS A BIT WEAKER CAPPING IN BOTH MODELS...BUT AT BOTH LOCATIONS THE 6Z AND 12Z NAM HAVE THE STRONGER CAP. SOME SHALLOW SHOWERS OR SPRINKLES MAY STILL OCCUR ACROSS THE NORTHWEST TWO THIRDS OF THE AREA...BUT THUNDER CHANCES APPEAR VERY LOW. THE 12Z NAM FORECAST SOUNDINGS INDICATE A WEAKER CAP IN THE TIER OR TWO OF COUNTIES ALONG THE TN AND VA BORDER FROM MCCREARY NORTH AND EAST TO PIKE COUNTY. CONVECTION APPEARS MORE PROBABLE IN THIS AREA...BUT COVERAGE IN ALL AREAS MAY AGAIN BE LIMITED IN COVERAGE SIMILAR TO YESTERDAY. WE WILL CONTINUE TO EVALUATE TRENDS AND CU FOR POSSIBLE LOWERING OF POPS INTO THIS EVENING. UPDATE ISSUED AT 745 AM EDT TUE JUL 22 2014 SOME OF THE DEEPER VALLEYS HAVE SOME DENSE FOG THAT HAS DEVELOPED OVERNIGHT AND IS NOW STARTING TO LIFT A BIT. LOW TEMPERATURES HAVE DROPPED INTO THE UPPER 60S TO AROUND 70 IN MOST PLACES. HAVE UPDATED TO INPUT THE LATEST OBS INTO THE GRIDS. THE REST OF THE FORECAST IS GOOD TO GO. HAVE SENT THE GRIDS TO NDFD AND THE WEB SERVERS. && .SHORT TERM...(TODAY THROUGH WEDNESDAY) ISSUED AT 348 AM EDT TUE JUL 22 2014 CURRENT CONDITIONS ACROSS EASTERN KENTUCKY FEATURES SOME DISSIPATING CLOUD COVER AS SOME UPPER LEVEL RIDGING IS NUDGING INTO THE AREA FROM THE HEIGHT CENTER OVER THE SOUTH CENTRAL PLAINS. WITH THIS DISSIPATION...SOME FOG WILL DEVELOP IN THE VALLEYS TOWARDS DAWN. WILL ADJUST TEMPERATURES A BIT AS WELL TO ADDRESS THE LOW TEMPS IN THE MORE SHELTERED VALLEYS. HEADING INTO THE DAY...THE MENTIONED RIDGE AND WARMER MID LEVEL TEMPS INTO THE MID LEVELS WILL IMPACT THE AIR MASS OVER EASTERN KENTUCKY. THIS WILL IMPEDE CONVECTION AGAIN TODAY BUT MAINLY IN THE NORTHWESTERN COUNTIES. MODELS HAVE UNDERESTIMATED THE STRENGTH OF THE RIDGE AXIS NUDGING INTO THE AREA ON MONDAY BUT RECENT RUNS LOOK TO HAVE HANDLED THIS SCENARIO BETTER. WILL GO WITH AERIAL COVERAGE AGAIN BUT WITH MAINLY ISOLATED COVERAGE NORTHWEST TO SCATTERED IN THE SOUTHEAST ALONG THE MOUNTAINOUS COUNTIES. HEADING INTO WEDNESDAY...THE STRONG SHORTWAVE MOVING INTO THE GREAT LAKES REGION AND LOWER OH VALLEY WILL PUSH THROUGH. THIS MAY BE SCENARIO MAY BE ANOTHER EXAMPLE OF THE ENERGY GOING THROUGH THE BASE OF THE TROUGH AND BECOMES CUT OFF FROM THE MID LEVEL RIDGES OVER THE SOUTHERN CONUS. NONETHELESS...WILL GO WITH NUMEROUS COVERAGE INTO WEDNESDAY AS THE FRONT APPROACHES AND SOUTHWEST FLOW INCREASES. PLENTY OF INSTABILITY LOOKS TO BE PRESENT WITH THIS SET UP WITH CAPE VALUES GETTING INTO THE 2500 J/KG RANGE AND WHILE THE CAP STILL LOOKS TO BE PRESENT...THE FORCING AVAILABLE SHOULD BE ENOUGH TO OVERCOME IT. THIS AND SPC HAS ASSIGNED A 5% SEVERE THREAT FOR THE NORTHWESTERN COUNTIES. THOUGH WITH THE SLIGHT INCREASE STEERING FLOW...MAY NEED TO TAKE THE DURATION OVER AN AREA CONCERN. SHEAR LOOKS TO BE WEAK AS WELL FOR THIS SET UP SO ANY SEVERE CONCERN WOULD BE ISOLATED FOR COLLAPSING CELLS WITH NO ORGANIZATION. WILL GO WITH HIGH POPS THROUGH WEDNESDAY WITH NO SEVERE MENTION BUT WITH SOME LOCALLY HEAVY RAINFALL POSSIBLE. SLIGHTLY ABOVE NORMAL TEMPS AND DEW POINTS CLIMBING INTO THE LOW 70S LOOK TOP BE THE CASE THROUGH THE SHORT TERM. .LONG TERM...(WEDNESDAY NIGHT THROUGH MONDAY) ISSUED AT 348 AM EDT TUE JUL 22 2014 THE MODELS ARE IN ONLY FAIR AGREEMENT ALOFT THROUGH THE EXTENDED PORTION OF THE FORECAST. WHILE THEY ALL DEPICT THE ABNORMAL PATTERN OF A STRONG FOUR CORNERS REGION RIDGE AND DEEP TROUGHING IN THE EAST CONTINUING THROUGH THE END OF THE WEEK AND INTO THE START OF THE NEXT WEEK...THEY DIFFER ON THE MAGNITUDE AND TIMING OF THE EVOLVING EASTERN TROUGH...PARTICULARLY OVER THE WEEKEND AND INTO MONDAY. SPECIFICALLY...FALLING HEIGHTS OVER KENTUCKY WILL BE THE RULE INTO THURSDAY NIGHT AS THE RETROGRADING LOW TO THE SOUTH PULLS AWAY AND THE NORTHERN STREAM SENDS A SERIES OF SHORTWAVES THROUGH THE AREA IN NORTHWEST FLOW. THIS EASTERN TROUGH PULLS AWAY TO START THE WEEKEND WITH HEIGHTS CLIMBING TEMPORARILY BEFORE THEY FALL AGAIN IN THE FACE OF A NODE OF THE LARGE NORTHEAST TROUGH GEARING UP FOR A DIVE INTO THE UPPER MIDWEST AND OHIO VALLEY. THE 00Z GFS IS MOST AGGRESSIVE WITH THIS EVOLUTION WHILE THE 12 ECMWF KEEPS ITS CORE WAVE FURTHER TO THE NORTHWEST AND LAGS THE GFS DEVELOPMENT. HOWEVER...THE LATEST CMC AND ECMWF ARE TRENDING MORE TOWARD THE GFS. REGARDLESS... NORTHWEST FLOW WILL DOMINATE THE LOCAL PATTERN AS HEIGHTS FALL INTO MONDAY MORNING. EVENTUALLY...THE ECMWF CATCHES UP...WITH THE DEEPER AND MORE WESTERN TROUGH IDEA OF THE GFS BUT SOME SIGNIFICANT DIFFERENCES REMAIN WITH THE PATTERN OVER THE OHIO VALLEY TO CLOSE OUT THE WEEK. THE BETTER AGREEMENT EARLIER IN THE EXTENDED SUPPORTS A BLENDED SOLUTION WHILE THE LARGER SPREAD LATER ON LOWERS CONFIDENCE SO THAT THE ENSEMBLES AND A SLIGHT LEAN TOWARD THE GFS ARE PREFERRED SOLUTIONS. SENSIBLE WEATHER WILL FEATURE AN APPROACHING COLD FRONT SERVING AS A FOCUSING MECHANISM FOR SHOWERS AND THUNDERSTORMS WEDNESDAY NIGHT INTO THURSDAY. COOLER AND DRIER AIR WILL FILTER INTO THIS PART OF THE STATE LATER IN THE DAY THURSDAY PUTTING AN END TO THE CONVECTIVE CHANCES FROM NORTHWEST TO SOUTHEAST. DRY AND RELATIVELY COOL WEATHER FOLLOWS INTO THE START OF THE WEEKEND THANKS TO A BRIEF VISIT OF HIGH PRESSURE. HOWEVER...THE COLD FRONT THAT BROUGHT THE DRIER WEATHER WILL START TO SURGE NORTH OVER THE WESTERN PARTS OF THE REGION AND BRING WARMTH...MOISTURE...AND BETTER CONVECTIVE CHANCES BACK INTO THE AREA ON SATURDAY. A SERIES OF SHORT WAVES AT MID LEVELS...THE DEVELOPING TROUGH...AND THE SFC FRONTAL STRUCTURE OVER THE OHIO VALLEY KEEP SHOWER AND THUNDERSTORM CHANCES GOING INTO SUNDAY AND MONDAY. THE CR GRID LOAD PROVIDED A DECENT START TO THE FORECAST FOR THE EXTENDED...THOUGH DID ADJUST THE POPS TO ADD A TINGE OF DIURNAL TO THE TIMING OF THE CONVECTION. ALSO...TWEAKED THE LOW TEMPERATURE GRIDS A TAD TO REFLECT RIDGE AND VALLEY DIFFERENCES WEDNESDAY AND THURSDAY NIGHT. && .AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON) ISSUED AT 215 PM EDT TUE JUL 22 2014 CU WILL CONTINUE TO DEVELOP AND THEN GRADUALLY MIX OUT BY EVENING. ISOLATED TO POSSIBLY SCATTERED SHRA AND SOME TSRA WILL CONTINUE TO DEVELOP THROUGH THE EVENING. THERE MAY BE MORE FOG DEVELOPMENT TONIGHT WITH SOUTHWEST FLOW AHEAD OF AN APPROACHING COLD FRONT...BUT CONFIDENCE IN THIS IS NOT ALL THAT HIGH SINCE FOG AT THE TAF SITES WAS NOT PROLIFIC EARLIER TODAY. MOST CONVECTION ASSOCIATED WITH THE FRONT SHOULD HOLD OFF UNTIL 16Z AND AFTER. WINDS WILL BE LIGHT THROUGH THE PERIOD. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...JP SHORT TERM...SHALLENBERGER LONG TERM...GREIF AVIATION...JP

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