Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 171747 AFDJKL AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE JACKSON KY 147 PM EDT SUN AUG 17 2014 .UPDATE... ISSUED AT 146 PM EDT SUN AUG 17 2014 LINE OF SHOWERS AND A FEW THUNDERSTORMS NOW OVER THE WESTERN PART OF THE FORECAST AREA CONTINUES TO MOVE EAST AND WEAKEN WITH TIME. THIS LINE WILL CONTINUE TO WEAKEN AS IT MOVES EAST THROUGH THE REMAINDER OF THE AFTERNOON. MAIN HEAVY RAIN THREAT STILL APPEARS TO BE LATER TONIGHT INTO EARLY MONDAY MORNING AS THE UPPER LEVEL LOW AND TROUGH PROGRESS EAST AND 8H LOW LEVEL JET RAMPS UP AND LIFT INCREASES. BASED ON 12Z SOUNDINGS AND SOME GOES SOUNDER DATA AVAILABLE BEFORE THE WIDESPREAD CLOUDS MOVED IN...PWS AROUND 2 INCHES SEEM REASONABLE AS FORECAST BY THE MAJORITY OF THE MODEL DATA FOR LATER TONIGHT. UPDATE ISSUED AT 939 AM EDT SUN AUG 17 2014 ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS CONTINUE ACROSS THE AREA THIS MORNING...BUT ARE DIMINISHING. TOTAL LIGHTNING DATA IS SHOWING SOME IN CLOUD LIGHTNING WITH STORM OVER MENIFEE COUNTY. THIS HAS BEEN THE ONLY LIGHTNING NOTED IN OUR AREA THIS MORNING. FOCUS IS ON LARGE CONVECTIVE COMPLEX OVER WESTERN KY ASSOCIATED WITH THE MCV CENTERED OVER S IL/W KY. SATELLITE AND RADAR TRENDS HAVE SHOWN SOME OVERALL WEAKENING...HOWEVER NEW CONVECTION IS NOW DEVELOPING ON THE LEADING EDGE OF THIS SYSTEM...AND IT MAY SUSTAIN ITSELF INTO THE EARLY AFTERNOON. CURRENT MOVEMENT AND PROJECTED DEVELOPMENT ON THE LEADING EDGE WOULD BRING SHOWERS AND THUNDERSTORMS INTO THE WESTERN PART OF THE FORECAST AREA BETWEEN 11 AM AND NOON. ENVIRONMENT LOOKS LESS FAVORABLE FOR THIS CONVECTION TO MAINTAIN STRENGTH AS IT WILL MOVE EAST QUICKER THAN THE SUPPORTING UPPER TROUGH. THE LATEST HRRR DOES SHOW THE REMNANTS OF THE WESTERN KY CONVECTION MOVING ACROSS OUR AREA THIS AFTERNOON...BUT WEAKENING AS IT DOES SO. A QUICK LOOK AT THE 12Z SOUNDINGS SHOWS PW OF 1.32 AT ILN AND 1.83 AT OHX. BASED ON GOES SOUNDER DATA IT APPEARS THE OHX SOUNDING IS MORE REPRESENTATIVE OF THE AIR MASS OVER THE MAJORITY OF OUR AREA. AS THE TROUGH AXIS NOW OVER IL INTO SE MO MOVES EAST 8H WINDS OVER EASTERN KY WILL INCREASE THIS EVENING AND INTO THE NIGHT. THIS...COMBINED WITH HIGH PWS POINT TOWARDS THE BEST CHANCE FOR HEAVY RAIN FROM THIS EVENING INTO THE OVERNIGHT PERIOD. WILL UPDATE NDFD AND ASSOCIATED PRODUCTS SHORTLY AFTER 10 AM EDT TO ACCOUNT FOR LATEST OBSERVATIONAL TRENDS. UPDATE ISSUED AT 705 AM EDT SUN AUG 17 2014 CONDITIONS THIS MORNING ACROSS THE AREA FEATURE SOME SHOWERS NOW MOVING THROUGH THE AREA WITH A WEAKENED MCV UPSTREAM IN WESTERN KENTUCKY MAKING ITS WAY INTO CENTRAL KENTUCKY. THIS FEATURE WILL POSE A CONCERN FOR THE AREA TODAY AS IT SLOWLY TRACKS INTO EASTERN KENTUCKY BY THE AFTERNOON. THE ONE FORECAST CHALLENGE TODAY IS HOW FAVORABLE THE ENVIRONMENT WILL BE TO THIS FEATURE. MODEL SOUNDINGS...AS WELL AS THE HRRR DO NOT FAVOR INTENSIFYING THIS SYSTEM. SURFACE INSTABILITY WITH THE GFS IS RATHER LACKING AND THE HRRR SHOWS NO REAL INCREASE IN THE ECHOS. NONETHELESS...THE HEAVY RAIN THREAT MAY BEGIN SLIGHTLY EARLIER TODAY AS THE CURRENT SITUATION SEEMS TO JIVE WITH THE EXCESSIVE RAINFALL FORECAST. AS WELL...THE POSSIBILITY OF A STRONG STORM POSSESSING GUSTY WIND CAPABILITY INTO THIS AFTERNOON. && .SHORT TERM...(TODAY THROUGH MONDAY) ISSUED AT 330 AM EDT SUN AUG 17 2014 CURRENT CONDITIONS ACROSS THE AREA AS OF 07Z FEATURE SOME SHOWERS MOVING THROUGH EASTERN KENTUCKY FORMED BY SOME OVERRUNNING MOISTURE OVER A WEAK SURFACE WARM FRONT DEVELOPING AS A LOW PRESSURE CENTER OUT WEST CONTINUES TO DEVELOP AND SLOWLY MOVE EAST. A DRY LAYER AT THE SURFACE OVER MUCH OF THE AREA HAS HINDERED MEASURABLE PRECIP. HOWEVER...THIS BOUNDARY LAYER HAS AND WILL CONTINUE TO MOISTENED UP QUITE A BIT THROUGH THE PERIOD OF THE MORNING HOURS AS SOUTHERLY FLOW INCREASES AND RAINFALL FALLS OVER THESE AREAS. THIS RAINFALL ALONG WITH THE SURFACE BOUNDARY WILL WEAKEN AND LIFT OFF TO THE NORTHEAST AS THE LOW OUT WEST MOVES EAST. THIS WILL RESULT IN A BETTER CHANCE FOR SHOWERS AND THUNDERSTORMS AS THE BETTER FORCING AND MOISTURE MOVES EAST THIS AFTERNOON AND INTO THE EVENING. HEADING INTO THIS EVENING AND TONIGHT...THE SURFACE LOW BEGINS TO ENTER CENTRAL KY AND EVENTUALLY EASTERN KENTUCKY INTO MONDAY. MENTIONING THE FACT THAT THE MODELS HAVE NOT HANDLED THIS FEATURE WELL...ESPECIALLY THE NAM. MODEL SOUNDINGS FOR THE GFS AND NAM HAVE HAD SOLUTION PRETTY FAR APART WITH CONCERN WITH AVAILABLE MOISTURE WITH PWATS FOR THE NAM BEING WELL OVER 2.10 INCHES AND THE GFS BEING AROUND 1.70 INCHES. A SLIGHT RISK OF EXCESSIVE RAIN WAS ISSUED FOR THE AREA MAINLY ALONG THE I-75 CORRIDOR AND WEST FOR TONIGHT THROUGH MONDAY. THE FACT THAT THERE IS SO MUCH INCONSISTENCY IN THE MODELS...STORM MOTION IS ABOVE 10 KNOTS...AND FINALLY THE ADVERTISED WAVE LOOKS MUCH LESS POTENT THAN ADVERTISED...IT APPEARS THE RISK OF FLASH FLOODING WILL BE QUITE LOCALIZED AND ONLY CENTERED AROUND AREAS THAT ARE STILL DRYING OUT FROM LAST WEEK RAINS. ALSO AREAS WHERE STORMS MOVE REPEATEDLY OVER THE SAME AREA. AS SUCH...WILL ONLY CONTINUE MENTIONING THIS RISK IN THE HWO BASED UPON REASONING AS WELL AS COLLABORATION WITH SURROUNDING OFFICES. HOWEVER...THE WAVE AS WELL AS THE SURFACE FEATURE IS MOVING THROUGH QUITE SLOW SO THE CHANCE FOR STORMS TO MOVE OVER REPEATEDLY IS CERTAINLY A GOOD POSSIBILITY. THE CHALLENGING PORTION OF THE FORECAST WILL BE TONIGHT AND INTO MONDAY AND IDENTIFYING WHICH AREAS WILL RECEIVE HEAVY RAIN AND ALSO MONDAY AFTERNOON AS BASED UPON MODEL SOUNDINGS...A DRY LAYER DOES SHOW UP IN THE GFS IN CONJUNCTION WITH SOME GOOD INSTABILITY AND SHEAR. A MARGINAL SEVERE THREAT MAY ARISE. A CHALLENGING AND MURKY SHORT TERM FORECAST LOOKS TO BE THE CASE WITH A FEW CONCERNS. .LONG TERM...(MONDAY NIGHT THROUGH SATURDAY) ISSUED AT 500 AM EDT SUN AUG 17 2014 MODELS CONTINUE TO DISPLAY GOOD AGREEMENT THROUGH THE EXTENDED... INTERESTINGLY WITH THE GFS SHOWING A BIT MORE CONTINUITY THAN THE ECMWF THIS CYCLE. MID AND UPPER PATTERN WILL BE QUASI ZONAL AS A PROGRESSIVE BUT SLOW LOW AMPLITUDE WAVE MOVES ACROSS THE GREAT LAKES REGION. PATTERN AMPLIFIES A BIT TOWARDS THE END OF THE EXTENDED WINDOW WITH OUR FORECAST AREA ON THE EASTERN PERIPHERY OF RIDGE THAT EXTENDS FROM THE SOUTHERN PLAINS/MISSISSIPPI RIVER DELTA TO THE UPPER MIDWEST. AT THE SURFACE...LOW PRESSURE WILL BE EXITING TO OUR EAST JUST AS A SECOND LOW PRESSURE SYSTEM ROLLS THROUGH THE GREAT LAKES REGION BY MID WEEK. THE GREAT LAKES LOW WILL PULL A SURFACE COLD FRONTAL BOUNDARY ACROSS THE OHIO VALLEY. THIS FRONTAL BOUNDARY WILL BECOME ORIENTED IN A NORTHWEST TO SOUTHEAST DIRECTION...PARALLEL TO THE UPPER FLOW PATTERN ON THE EASTERN SIDE OF THE AFOREMENTIONED RIDGE. THUS WITH LITTLE TO NO FORCING AT THE MID AND UPPER LEVELS... THIS BOUNDARY WILL ESTABLISH A STATIONARY BAROCLINIC ZONE ACROSS THE REGION WHICH APPEARS TO SET UP JUST TO OUR NORTH AND EAST. IT APPEARS THIS ZONE WILL BECOME THE FOCUS OF ADDITIONAL SHOWER AND THUNDERSTORM ACTIVITY...AND SHOULD BE CLOSE ENOUGH THAT THE THREAT OF RAIN WILL CONTINUE TO EXIST FOR OUR AREA THROUGH THE REMAINDER OF THE FORECAST. MODELS EVEN HINT AT THE POSSIBILITY OF A SERIES OF MCS TYPE SYSTEMS DEVELOPING AND MOVING ALONG THIS ZONE...POSSIBLY AFFECTING PORTIONS OF OUR AREA. FOR SENSIBLE WEATHER...THE MOST SIGNIFICANT AND NOTABLE DIFFERENCE IN OUR WEATHER WILL BE THE RETURN OF TRUE SUMMER LIKE CONDITIONS WITH SEASONABLY WARM AND HUMID AFTERNOONS AND MUGGY NIGHTS. TWEAKED TEMPS TOWARDS LATEST MODEL BLENDS WHICH RESULTED IN ONLY MINOR CHANGES TO PREVIOUS FORECASTS. THE DAILY THREAT OF SOME TYPE OF SHOWER AND THUNDERSTORM ACTIVITY WILL ENSURE AN OVERALL UNSETTLED WEATHER PATTERN...ESPECIALLY IF CONDITIONS BECOME FAVORABLE FOR THE OCCASIONAL MCS SYSTEM TO MATERIALIZE AND MOVE THROUGH THE REGION. && .AVIATION...(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING) ISSUED AT 146 PM EDT SUN AUG 17 2014 A BAND OF SHOWERS AND A FEW THUNDERSTORMS WILL WEAKEN AS IT MOVES EAST ACROSS THE FORECAST AREA THROUGH THE REMAINDER OF THE AFTERNOON. IN THE PRECIPITATION AREA MVFR TO IFR CONDITIONS CAN BE EXPECTED...WITH VFR PREVAILING OUTSIDE OF THE RAIN AREA. LOW PRESSURE OVER SOUTHERN INDIANA AND WESTERN KY WILL MOVE EAST TONIGHT BRINGING WIDESPREAD RAIN ALONG WITH SOME THUNDERSTORMS TO THE AREA. CONDITIONS WILL DETERIORATE AFTER 03Z WITH WIDESPREAD MVFR TO IFR CONDITIONS EXPECTED FOR LATE TONIGHT INTO MONDAY MORNING. CONDITIONS WILL BE SLOW TO IMPROVE ON MONDAY. THE RAIN AND THUNDERSTORMS WILL END FROM WEST TO EAST DURING THE MORNING BUT LOW CLOUD AND FOG WILL LINGER AFTER THE RAIN ENDS. VFR CONDITIONS ARE EXPECTED TO RETURN MONDAY AFTERNOON. WINDS WILL REMAIN LIGHT THROUGH THE FORECAST PERIOD. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...SBH SHORT TERM...SHALLENBERGER LONG TERM...RAY AVIATION...RAY

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