Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 290800 AFDJKL AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE JACKSON KY 400 AM EDT SUN MAR 29 2015 .SHORT TERM...
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(TODAY THROUGH MONDAY) ISSUED AT 400 AM EDT SUN MAR 29 2015 TWO ISSUES TO DEAL WITH...FIRST BEING VERY LOW RELATIVE HUMIDITIES THIS AFTERNOON. SECOND CONCERNS THE PASSAGE OF A SFC COLD FRONTAL SYSTEM TONIGHT. SHORT WAVE RIDGING ALOFT AND SFC HIGH PRESSURE MOVING OFF TO THE EAST THROUGH THE DAY WILL KEEP SKIES MOSTLY CLEAR THROUGH MUCH OF THE DAY AS SOUTHERLY RETURN FLOW INCREASES. COMBINED THIS WILL ALLOW VERY DRY AIR TO MIX DOWN INTO THE BOUNDARY LAYER AND EVENTUALLY TO THE SFC...ALL WHILE TEMPERATURES MAKE A STRONG REBOUND. AS A RESULT RELATIVE HUMIDITIES WILL DROP INTO THE TEENS BY THIS AFTERNOON...WELL BELOW CRITICAL FIRE WEATHER THRESHOLDS. SHORT WAVE TROUGH MOVING THROUGH THE GREAT LAKES LATE TODAY AND TONIGHT WILL SEND A SFC COLD FRONTAL BOUNDARY THROUGH THE REGION. CLOUDS WILL INCREASE AHEAD OF THIS SYSTEM LATE THIS AFTERNOON. MODELS ALSO DEVELOP A BAND OF SHOWERS ALONG AND AHEAD OF THIS SYSTEM. HOWEVER...VERY DRY BOUNDARY LAYER WILL EAT AWAY AT SOME OF THE MODEL/S ADVERTISED QPF VALUES. CONSEQUENTLY WE ARE EXPECTING ONE OF THOSE RELATIVELY HIGH POP...LOW QPF EVENTS. THE FRONTAL BOUNDARY WILL BE THROUGH EASTERN KENTUCKY BY MONDAY MORNING. FORTUNATELY...CONSIDERING THAT THE ORIGIN OF THE AIR MASS BEHIND THIS FRONT IS PACIFIC IN NATURE...TEMPERATURES WILL TURN OUT TO BE WARMER BEHIND THE SYSTEM THAN AHEAD. STAYED FAIRLY CLOSE TO THE BLEND OF MODEL SOLUTIONS AND GUIDANCE FOR POPS AND TEMPS. .LONG TERM...(MONDAY THROUGH SATURDAY) ISSUED AT 245 PM EDT SAT MAR 28 2015 THE FORECAST PERIOD WILL BE ACTIVE WITH SEVERAL SHORT WAVES MOVING FAIRLY QUICKLY THROUGH ZONAL FLOW...WITH RAIN CHANCES INCREASING DURING THE LATTER HALF OF THE WEEK. THE ZONAL FLOW WILL RESULT IN MILD TEMPERATURES...AND AS INSTABILITY INCREASES LATER IN THE WEEK THUNDERSTORMS WILL ALSO BECOME POSSIBLE. THERE IS GOOD MODEL AGREEMENT TO START THE PERIOD...BUT SIGNIFICANT DIFFERENCES DEVELOP BY LATE IN THE WEEK. AT THE START OF THE PERIOD SURFACE HIGH PRESSURE WILL BE NOSING EAST FROM THE MID MS VALLEY...WHILE A SHORT WAVE AND ASSOCIATED SURFACE LOW MOVE INTO THE NORTHERN PLAINS. THIS LOW WILL TRACK INTO THE GREAT LAKES ON TUESDAY...BRINGING A WARM FRONT ACROSS THE AREA THAT WILL THEN BE QUICKLY FOLLOWED BY A COLD FRONT. HOWEVER...MOISTURE LOOKS TO BE LIMITED AND THE MODEL BLEND KEEPS THE FORECAST DRY FOR TUESDAY...WITH ONLY A SLIGHT CHANCE OF RAIN TUESDAY NIGHT. WILL FOLLOW NEIGHBORING WFOS TO N...E AND W...AND LOWER PROBABILTIES SLIGHTLY FOR TUESDAY NIGHT...THUS RESULTING IN NO MENTION OF RAIN FOR TUESDAY NIGHT. ANOTHER SHORT WAVE AND SURFACE LOW LOOK TO TRACK ACROSS ONTARIO ON THURSDAY...WITH ASSOCIATED FRONTS MOVING ACROSS OUR AREA AND BRINGING BETTER RAIN CHANCES. THE TRAILING COLD FRONT WITH THIS SYSTEM LOOKS TO STALL SOMEWHERE FROM THE GREAT LAKES OR OH VALLEY INTO THE SOUTHERN PLAINS...WITH LOW PRESSURE DEVELOPING OVER THE SOUTHERN PLAINS THURSDAY NIGHT. IT IS AT THIS POINT THAT THE MODELS BEGIN TO SHOW SIGNIFICANT DIFFERENCES. THE ECMWF IS VERY AGGRESSIVE WITH PHASING THE NORTHERN AND SOUTHERN STREAMS AS WE MOVE TOWARDS THE WEEKEND...WITH THE SOUTHERN PLAINS SURFACE LOW DEEPENING RAPIDLY AS IT MOVES TOWARDS THE GREAT LAKES ON FRIDAY. THE GFS IS MUCH WEAKER ALOFT AND AT THE SURFACE...WITH THE SURFACE LOW TRACKING MORE EASTWARD IN FLATTER FLOW. BOTH SCENARIOS RESULT IN SHOWER AND THUNDERSTORM CHANCES FOR OUR REGION...BUT THE ECMWF SOLUTION WOULD RESULT IN A SEVERE WEATHER THREAT AS WELL. THIS WILL NEED TO BE WATCHED AS WPC NOTES THE CANADIAN AND GFS ARE BEGINNING TO TREND TOWARDS MORE AMPLIFIED SOLUTIONS...BUT WPC AND WE ARE NOT YET COMMITTED TO THE FULLY PHASED ECMWF SOLUTION.
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&& .AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT) ISSUED AT 200 AM EDT SUN MAR 29 2015 SURFACE HIGH PRESSURE CENTERED OVER PORTSMOUTH OHIO WILL KEEP OUR SKIES CLEAR AND WINDS LIGHT THROUGH TOMORROW MORNING. AS THIS HIGH PRESSURE MOVE EASTWARD SOUTHERLY GRADIENT FLOW WILL INCREASE THROUGH THE DAY SUNDAY AHEAD OF APPROACHING COLD FRONTAL SYSTEM. WINDS SHOULD INCREASE TO AROUND 10KTS AND BECOME GUSTY LATER IN THE DAY. CLOUDS WILL INCREASE AND SCATTERED SHOWERS WILL BEGIN TO DEVELOP SUNDAY EVENING...GENERALLY FROM AROUND 03Z AND AFTER. && .JKL WATCHES/WARNINGS/ADVISORIES...NONE. && $$ SHORT TERM...RAY LONG TERM...SBH AVIATION...RAY

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