Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 200813 AFDJKL AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE JACKSON KY 413 AM EDT SAT SEP 20 2014 .SHORT TERM...
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(TODAY THROUGH SUNDAY) ISSUED AT 355 AM EDT SAT SEP 20 2014 EARLY THIS MORNING...AN UPPER LEVEL RIDGE OF HIGH PRESSURE CENTERED OVER THE SOUTHERN ROCKIES TO SOUTHERN PLAINS REGION WITH RIDGING EAST INTO THE LOWER OH VALLEY WAS IN PLACE. ACROSS THE SOUTHEASTERN US... A BROAD UPPER LEVEL LOW WAS PRESENT. MEANWHILE A SERIES OF SHORTWAVES WERE IN THE NORTHERN STREAM WITH A WEAK LEAD SHORTWAVE NEAR THE MID MS VALLEY REGION WITH ANOTHER SHORTWAVE NEARING THE NORTHERN GREAT LAKES EXTENDING FROM WESTERN ONTARIO INTO THE UPPER MIDWEST AND DOWN INTO THE CENTRAL PLAINS REGION. FURTHER NORTHWEST ANOTHER SHORTWAVE IS MOVING ACROSS THE CANADIAN PLAINS. THROUGH THE SHORT TERM PERIOD...THE LEAD WEAK SHORTWAVE WILL WORK ACROSS THE AREA THROUGH EARLY TO MID AFTERNOON AS HEIGHTS BEGIN TO FALL IN THE OH VALLEY REGION WHILE THE UPPER LEVEL RIDGE BUILDING NORTH ACROSS THE ROCKIES AND INTO THE INTERIOR NORTHWESTERN US. DOWNSTREAM ACROSS THE GREAT LAKES AND EASTERN US...A TROUGH OF LOW PRESSURE WILL BEGIN TO BE CARVED OUT BY THE TWO MAIN SHORTWAVES AND SOUTHEASTERN CONUS TROUGH BEGINNING TO MERGE INTO IT. THE ASSOCIATED SFC LOW WILL TRACK WELL NORTH OF KY...BUT THE TRAILING COLD FRONT WILL WORK INTO THE LOWER OH VALLEY REGION TONIGHT AND THEN MOVE ACROSS THE COMMONWEALTH THROUGH THE END OF THE PERIOD...WHEN IT SHOULD BE CLOSE TO EXITING INTO VA. SCATTERED TO BROKEN CLOUDS IN THE 4 TO 7KFT RANGE HAVE DEVELOPED OVERNIGHT IN THE WARM SECTOR. OUTSIDE OF THESE CLOUDS VALLEY FOG IS LIKELY STILL PRESENT AND MAY BE DENSE AT LEAST IN SOME SPOTS ALONG THE RIVERS AND LARGER STREAMS AND LAKES. DEWPOINT DEPRESSIONS ARE LARGER NEARER TO THE VA BORDER WHERE A DOWNSLOPE FLOW HAS BEEN PRESENT WITH SPEEDS OF 10 MPH OR MORE ACROSS THE HIGH TERRAIN AND OBSERVATIONS SUPPORT ANY FOG BEING MUCH MORE LOCALIZED THERE. THIS FOG SHOULD GRADUALLY BEGIN TO LIFT THROUGH SUNRISE AND THEN DISSIPATE BY A COUPLE OF HOURS AFTER SUNRISE. IN ADDITION...WHERE CLOUDS FORM THIS FOG WILL TEND TO DISSIPATE AS WELL. THE MODEL GUIDANCE BRINGS THE WEAK MID LEVEL DISTURBANCE TOWARD THE AREA FOR THE REMAINDER OF THE NIGHT AND INTO THE EARLY AFTERNOON. THE 0Z NAM AND SOME OF THE NEAR TERM GUIDANCE SUCH AS THE HRRR ALSO DEVELOP SOME CONVECTION THIS MORNING THROUGH EARLY AFTERNOON MAINLY ACROSS THE WESTERN HALF OF THE CWA. MOS GUIDANCE ACROSS THESE LOCATIONS DOES NOT HAVE A SLIGHT CHANCE POPS AND MODEL CONSENSUS BLENDS GENERALLY STAYED BELOW SLIGHT AS WELL. HOWEVER...WE OPTED TO GO WITH SLIGHT CHANCE IN THESE WESTERN LOCATIONS FOR TODAY...WHICH WAS IN BETTER AGREEMENT WITH SURROUNDING WFOS. THE MAIN PRECIPITATION CHANCE DURING THE SHORT TERM PERIOD AND THE ENTIRE FORECAST PERIOD FOR THAT MATTER WILL COME AS THE TROUGH BEGINS TO TAKE SHAPE LATE TONIGHT INTO THE DAY ON SUNDAY AND THE COLD FRONT ENTERS EASTERN KY. THIS COLD FRONT AND THE APPROACHING TROUGH IS EXPECTED TO BRING A BAND OF SCATTERED OR BETTER COVERAGE OF CONVECTION AS IT WILL BE MOVING ACROSS EASTERN KY DURING THE DAYTIME. ISOLATED TO SCATTERED CONVECTION MAY REACH THE NORTHERN PART OF THE CWA TOWARD DAWN...BUT THE BEST CHANCE FOR CONVECTION WILL BE CLOSER TO THE COLD FRONT GENERALLY DURING THE AFTERNOON HOURS. THUNDERSTORMS WILL BE CAPABLE OF BRIEF HEAVY RAIN AND POSSIBLY SOME GUSTY WINDS...PENDING THE DEGREE OF INSTABILITY. .LONG TERM...(SUNDAY NIGHT THROUGH FRIDAY) ISSUED AT 324 AM EDT SAT SEP 20 2014 A QUICK MOVING COLD FRONT WILL BE EXITING THE REGION AS OF 0Z MONDAY. MODELS CONTINUE TO COME INTO A BETTER AGREEMENT FOR THE ENDING TIME OF PRECIP ASSOCIATED WITH THE FRONT...WITH THE NW EXPECTED TO CLEAR OUT BY 0Z...AND FINALLY THE SE JUST AFTER 6Z MONDAY. LATEST FORECAST SOUNDINGS ARE STILL ONLY SUPPORTING MARGINAL INSTABILITY FOR THE PRECIP ACCOMPANYING THIS FRONT...QUICKLY DISSIPATING AS WE LOSE DAYTIME HEATING...AND ONCE THE FRONTAL BOUNDARY HAS PASSED. AS SUCH...THUNDER WAS MENTIONED IN PREVIOUS FORECAST PAST 0Z...AND HAS ALSO BEEN INCLUDED BY SURROUNDING OFFICES THROUGH THE FIRST PART OF THE EVENING. DID NOT FEEL CONFIDENT ENOUGH TO YANK MENTION OF THUNDER COMPLETELY AT 0Z...SO KEPT MENTION OF SLIGHT CHANCE THUNDER WITH CHANCE POPS THROUGH 3Z...WHICH CONSEQUENTLY IS ABOUT THE SAME TIME CHANCE POPS EXIT THE REGION ANYWAYS. THERE IS SOME CONCERN THAT THE COMBINATION OF STRONG SUBSIDENCE BEHIND THE FRONT...IN ADDITION TO THE LINGERING MOISTURE ACROSS THE REGION...WILL LEAD TO A WIDESPREAD FOG EVENT BY LATE SUNDAY NIGHT...OR PERHAPS A LOW STRATUS EVENT. THE EXTENT OF EITHER OF THESE IS STILL SOMEWHAT UNCERTAIN. DECIDED TO INCREASE CLOUDS SLIGHTLY OVERNIGHT SUNDAY NIGHT/MONDAY MORNING...BUT DID NOT MENTION FOG AT THIS TIME. AS THE FRONT QUICKLY DEPARTS SUNDAY EVENING/NIGHT...KY WILL FIND ITSELF ON THE BACKSIDE OF THE UPPER LEVEL TROUGHING PATTERN...WITH STRONG NW FLOW BRINGING MUCH COOLER CANADIAN AIR INTO THE REGION. AS HIGH PRESSURE TAKES HOLD...DRY AND SUNNY SKIES WILL PREVAIL DURING THE DAY MONDAY...BUT HIGH TEMPERATURES WILL STRUGGLE TO MAKE IT TO THE 70 DEGREE MARK. AIRMASS MODIFICATION...NAMELY THE LESSENING OF STRONG PRESSURE GRADIENT/NW FLOW AS THE UPPER LEVEL RIDGE TAKES FULL CONTROL...WILL SLOWLY ALLOW TEMPS TO RISE THROUGHOUT THE REMAINDER OF THE EXTENDED FORECAST PERIOD. HOWEVER WE LIKELY WON/T SEE TEMPS HIT ABOVE THE 80 DEGREE MARK AGAIN UNTIL AT LEAST NEXT WEEKEND. MEANWHILE...WITH SUCH STRONG SUBSIDENCE IN CONTROL...THERE WILL BE LITTLE CONCERN FOR CLOUDS...LET ALONE PRECIP CHANCES. ALL IN ALL IT LOOKS TO BE A GORGEOUS AUTUMN-LIKE WEEK AHEAD.
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&& .AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT) ISSUED AT 150 AM EDT SAT SEP 20 2014 ASIDE FROM VALLEY FOG DEVELOPING...AND THEN LIFTING AND DISSIPATING THROUGH 13Z TO 14Z...VFR CONDITIONS WITH LIGHT WINDS WILL PREVAIL DURING THE PERIOD. A COLD FRONT AND ASSOCIATED INCREASE IN CLOUDS IS EXPECTED LATE IN THE PERIOD. THE FOG IS AGAIN EXPECTED TO FOLLOW ITS TYPICAL LATE SUMMER/EARLY AUTUMN PATTERN OF DEVELOPING FIRST IN DEEP VALLEYS AND THEN GROWING IN BREADTH AND DEPTH...WITH THE POTENTIAL TO BEGIN TO REACH SOME RIDGES AND OPEN TERRAIN BY DAWN...SUCH AS MVFR AT SJS IF WINDS SLACKEN AND POSSIBLY MVFR AT SME WHERE THE CURRENT DEWPOINT DEPRESSION IS LOW BUT THERE ARE SCT CLOUDS AS WELL. THE LARGER RECENT OBSERVED DEWPOINT DEPRESSION OF 7 AT LOZ POINTS TOWARD ANY FOG THAT DEVELOPS BEING IN THE VFR RANGE. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...JP LONG TERM...JMW AVIATION...JP

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