Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 291511 AAB AFDJKL AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE JACKSON KY 1111 AM EDT WED JUL 29 2015 .UPDATE... ISSUED AT 1111 PM EDT WED JUL 29 2015 THE REGION IS IN THE WARM SECTOR AS AN AREA OF LOW PRESSURE TRACKS ACROSS NORTHERN ONTARIO. A WARM AND RATHER MOIST AIRMASS REMAINS IN PLACE ACROSS THE AREA. DEWPOINTS REMAIN IN THE UPPER 60S TO MID 70S. HOWEVER...THE AIRMASS IS NOT QUITE AS MOIST THROUGH THE ENTIRE COLUMN ACROSS THE CENTRAL AND EASTERN PART OF THE AREA WITH PW THERE AROUND 1.6 INCHES. PW ACROSS THE WEST IS AROUND 1.8 TO 1.9 INCHES. WITH DAYTIME HEATING...LOW CLOUDS SHOULD EVENTUALLY LIFT INTO CU ACROSS THE SOUTHWEST PART OF THE AREA. THE AIRMASS SHOULD ALSO DESTABILIZE WITH ML CAPES EXPECTED TO REACH THE 1000 TO 1500 J/KG RANGE ACROSS THE WEST BY MID AFTERNOON. THE MOISTURE GRADIENT ACROSS CENTRAL KY INTO THE WESTERN PART OF THE CWA MAY BE A FOCUS FOR CONVECTIVE DEVELOPMENT LATER TODAY. ALSO...THE HIGHER TERRAIN ALONG THE VA BORDER THAT IS GETTING PLENTY OF SUNSHINE ATTM AND DIFFERENTIAL HEATING NEAR WHERE HEAVIER RAIN FELL ON TUESDAY MAY ALSO BE POSSIBLE LOCATIONS FOR THE FIRST CELL DEVELOPMENT. SHEAR IS RATHER WEAK TODAY...AND CELLS SHOULD MORE OR LESS PROPAGATE VIA OUTFLOW BOUNDARIES. MORE ORGANIZED CONVECTION...AND POSSIBLE A BROKEN LINE OF LINE SEGMENTS OF STORMS SHOULD NEAR THE REGION AROUND SUNSET. ISOLATED TO SCATTERED POPS. UPDATE ISSUED AT 805 AM EDT WED JUL 29 2015 MADE ONLY MINOR UPDATES FOR EARLY MORNING OBS. && .SHORT TERM...(TODAY THROUGH THURSDAY) ISSUED AT 411 AM EDT WED JUL 29 2015 ISOLATED SLOW MOVING SHOWERS HAVE PERSISTED DURING THE NIGHT IN THE SOUTHEAST PART OF THE FORECAST AREA. FORECAST SOUNDINGS SHOW THAT SOME ADDITIONAL DEVELOPMENT CAN NOT BE RULED OUT THIS MORNING...BUT THE PROBABILITY AT ANY GIVEN LOCATION IS LOW. ADDITIONAL DEVELOPMENT OF SHOWERS/THUNDERSTORMS IS MORE PROBABLE BY THIS AFTERNOON AS HEATING OCCURS. MOST OF THEM SHOULD DIE OUT AGAIN IN THE EVENING WITH LOSS OF HEATING. A COLD FRONT WILL PASS LATE TONIGHT AND THURSDAY MORNING. A FEW SHOWERS MAY LINGER ALONG AND AHEAD OF THE FRONT IN THE SOUTHEAST PART OF THE AREA ON THURSDAY MORNING. HOWEVER...DRIER AIR ALOFT AND A POST FRONTAL INVERSION WILL PUT AN END TO ANY LINGERING SHOWERS...WITH MOST OF THURSDAY BEING DRY. .LONG TERM...(THURSDAY NIGHT THROUGH TUESDAY) ISSUED AT 354 AM EDT WED JUL 29 2015 WE WILL BE IN A POST FRONTAL REGIME TO START OFF THE EXTENDED FORECAST AT 0Z FRIDAY. SURFACE HIGH PRESSURE WILL CONTINUE TO TAKE HOLD THROUGH THE DAY FRIDAY WITH SLIGHTLY COOLER NRLY WINDS AT THE SURFACE. MEANWHILE...A STRONG UPPER LEVEL LOW WILL BECOME NEARLY STATIONARY ACROSS HUDSON BAY...ROTATING AROUND THE BAY FROM FRIDAY THROUGH AT LEAST MONDAY. THIS WILL KEEP A LONGWAVE TROUGHING PATTERN ACROSS MUCH OF THE MIDWEST AND EASTERN CONUS...CONTINUING THE NW FLOW REGIME ACROSS THE OHIO RIVER VALLEY. THIS NW FLOW WILL PROVIDE THE PERFECT SCENARIO FOR SHORTWAVES TO TRACK SE ALONG THE TROUGH AND INTO THE OHIO VALLEY AS IT ROUNDS THE BASE OF THE TROUGH. HOWEVER...HIGH PRESSURE WILL HAVE HOLD AT THE SURFACE. THE QUESTION THROUGHOUT THE EXTENDED IS WHETHER OR NOT THIS HIGH PRESSURE WILL BE STRONG ENOUGH TO SWAY THE IMPACT OF THESE SHORTWAVES AS THEY MOVE THROUGH EASTERN KY. THE FIRST OF THESE SHORTWAVES WILL MOVE THROUGH SATURDAY INTO SUNDAY. AS OF 0Z FRIDAY...THE ACCOMPANYING SURFACE COLD FRONT IS POSED TO BE LOCATED ACROSS THE NORTHERN PLAINS AND UPPER GREAT LAKES REGION...AND WILL SHIFT SOUTHWARD THROUGHOUT THE DAY FRIDAY AS THE SHORTWAVE NEARS. HOWEVER...THIS BOUNDARY WILL BE MOISTURE DEPRIVED AND FAIRLY WEAK. LATEST MODELS ARE STILL SHOWING SOME DISAGREEMENT ON IF THIS BOUNDARY WILL BE ABLE TO SUSTAIN PRECIPITAL MOISTURE AS IT MOVES INTO THE OHIO RIVER VALLEY. JUST LIKE YESTERDAY...THE GFS IS POINTING TOWARDS A FEW SCATTERED SHOWERS MAKING IT INTO THE CWA...WHILE THE ECMWF IS KEEPING US DRY. MEANWHILE...DESPITE THE PLAN VIEW GFS OUTPUT...THE GFS FORECAST SOUNDINGS ARE ONLY POINTING AT A NARROW WINDOW OF MID LEVEL MOISTURE WITH ABUNDANT DRY AIR NEAR THE SURFACE. THIS IS MORE CHARACTERISTIC OF SOME SCT TO BKN CLOUD COVER RATHER THAN RAINFALL. AS SUCH...WILL CONTINUE TO TREND TOWARD THE DRIER ECMWF. THE NEXT SHORTWAVE AND SURFACE BOUNDARY WILL MOVE THROUGH TUESDAY INTO WEDNESDAY AS WE FINISH OUT THE 7 DAY FORECAST. GRANTED...THIS IS FAR OUT IN THE FORECAST...BUT MODELS ARE IN SURPRISINGLY GOOD AGREEMENT IN THE UPPER LEVELS...SO CONFIDENCE IS A BIT HIGHER. THIS PARTICULAR UPPER LEVEL SHORTWAVE WILL SHOW SIGNIFICANT DIGGING AS IT NEARS THE OHIO VALLEY REGION...LENDING TO A STRONGER SURFACE BOUNDARY. IF THIS PROVES TO BE TRUE...WE MAY SEE OUR NEXT BETTER CHANCE FOR SHOWERS AND THUNDERSTORMS DURING THIS TIME. AS FOR TEMPERATURES... THE POST FRONTAL CONDITIONS AND DRIER NW FLOW WILL BRING IN SLIGHTLY COOLER TEMPERATURES TO START OFF FRIDAY. HOWEVER...STRONG SURFACE HIGH PRESSURE IN PLACE AND CLEAR SKIES WILL PROMOTE MAXIMUM DAYTIME RADIATION...SO THE TEMP DROP WILL NOT BE THAT GREAT...STILL MAINTAINING LOW TO MID 80S. PERHAPS MORE NOTICEABLE THAN THE SLIGHT CHANGE IN TEMPERATURES WILL BE THE DECREASE IN HUMIDITY...AS LIGHT WINDS AT THE SURFACE AND NW FLOW ALOFT WILL PROMOTE LOWER RH VALUES. AS HIGH PRESSURE REMAINS IN PLACE THROUGH MUCH OF THE EXTENDED...EXPECT TEMPS TO GRADUALLY WARM A DEGREE OR TWO EACH DAY...STAYING IN THE MID 80S THROUGH THE WEEKEND AND INTO NEXT WEEK. MEANWHILE...MAXIMUM RADIATIONAL COOLING DURING THE OVERNIGHT WILL KEEP OVERNIGHT LOWS IN THE LOW TO MID 60S THROUGH THE BEGINNING OF NEXT WEEK. && .AVIATION...(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING) ISSUED AT 805 AM EDT WED JUL 29 2015 CONDITIONS WERE MOSTLY IFR OR WORSE AT THE START OF THE PERIOD. IMPROVEMENT WILL OCCUR DURING THE MORNING...WITH GENERALLY VFR ARRIVING EARLY IN THE AFTERNOON. HOWEVER... THE DAYTIME WARMING SHOULD ALSO LEAD TO ADDITIONAL SCATTERED SHOWERS AND THUNDERSTORM DEVELOPMENT THIS AFTERNOON. THEY WILL BRING LOCALIZED IFR. THE SHOWERS AND THUNDERSTORMS SHOULD THEN LARGELY DIMINISH IN THE EVENING WITH LOSS OF HEATING. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...JP SHORT TERM...HAL LONG TERM...JMW AVIATION...HAL

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