Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 291750 AFDJKL AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE JACKSON KY 150 PM EDT SUN MAR 29 2015 .UPDATE... ISSUED AT 1117 AM EDT SUN MAR 29 2015 FORECAST SEEMS TO BE IN PRETTY GOOD SHAPE THROUGH THIS MORNING WITH HIGH PRESSURE IN CHARGE. LOADED IN THE LATEST OBSERVATIONAL DATA FOR TEMPS...DEW POINTS...AND WINDS TO MAKE SURE THE NEAR TERM FORECAST WAS WELL REPRESENTATIVE OF ONGOING CONDITIONS. WILL CONTINUE TO CLOSELY MONITOR TEMPS AND DEW POINTS AS WE HEAD INTO THE AFTERNOON AND RH VALUES ARE IN A DECLINING STATE. UPDATE ISSUED AT 700 AM EDT SUN MAR 29 2015 FORECAST IS ON TRACK THIS MORNING. KENTUCKY MESONET INDICATING MANY LOCATIONS HAVE DROPPED INTO THE MID AND UPPER TEENS THIS MORNING. WE HAVE SEEN A RECORD LOW TEMP HERE AT JKL AS WELL. TEMPS WILL WARM QUICKLY AFTER SUNRISE. FORECAST PACKAGE ONLY REQUIRED A FEW TWEAKS TO BRING GRIDS IN LINE WITH HOURLY OBS. && .SHORT TERM...(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 NIGHT THROUGH SATURDAY) ISSUED AT 440 AM EDT SUN MAR 29 2015 THE RECENT GFS AND ECMWF RUNS ARE GENERALLY GOOD AGREEMENT TROUGH THE PERIOD. THE PERIOD IS EXPECTED TO BEGIN WITH A WESTERN US RIDGE EXTENDING NORTH INTO THE CANADIAN ROCKIES AND EASTERN AK...WITH A TROUGH FROM THE PLAINS INTO EASTERN CANADA AND THE EASTERN US. THE AXIS OF THIS TROUGH IS EXPECTED TO EXTEND FROM NORTHERN CANADA SOUTH INTO THE NORTHEASTERN STATES AND THEN SOUTH TO THE EAST OF FL. AN UPPER LEVEL LOW IS PROJECTED TO BE TO THE WEST OF THE BAJA OF CALIFORNIA AT THAT TIME AS WILL A TROUGH EXTENDING FROM THE GULF OF AK SOUTH ACROSS PORTIONS OF THE EASTERN PACIFIC TO THE WEST OF THE US AND CANADIAN COAST. AS THE WEEK PROGRESSES THE PATTERN WILL HAVE A ZONAL FLAVOR WITH THE TROUGH OVER EASTERN CANADA AND NORTHEASTERN STATES BECOMING MORE BROAD AND THE RIDGE INITIALLY OVER THE WEST COAST SHIFTING TO THE PLAINS BY MIDWEEK. MEANWHILE...THE TROUGH INITIALLY WEST OF THE BAJA OF CALIFORNIA IS EXPECTED TO GET KICKED INTO THE SOUTHERN PLAINS BY THE TROUGH WORKING INTO THE WESTERN US. THIS BY WED EVENING...THE 0Z GFS AND 0Z CONSENSUS IS FOR RIDGE AXIS TO HAVE MOVED TO THE LOWER OH VALLEY TO GREAT LAKES WITH SOME MODEL VARIABILITY WITH THE SHORTWAVE MOVING FROM THE SOUTHERN PLAINS INTO THE MS VALLEY REGION. AT THAT POINT...HEIGHTS ARE EXPECTED TO BE FALLING OVER THE PLAINS REGION. WED NIGHT INTO THU...THE SHORTWAVE RIDGE AXIS IS PROJECTED TO HAVE SHIFTED FURTHER EAST AND NORTHEAST FROM THE MID ATLANTIC STATES NORTH INTO ONTARIO AND QUEBEC WITH UNCERTAINTY INCREASING IN THE STRENGTH OF THE TROUGH MOVING AT THAT POINT FROM THE PLAINS TOWARD THE MS VALLEY REGION AND WESTERN GREAT LAKES. THE MODEL CONSENSUS FROM THE 0Z GFS AND 0Z ECMWF IS FOR THE SHORTWAVE TROUGH TO GENERALLY PASS SOUTH OF EASTERN KY ACROSS THE SOUTHEASTERN STATES...BUT UPPER LEVEL FLOW BECOMING MORE WESTERLY TO SOUTHWESTERLY BY LATE THU INTO THU NIGHT AS THE 500 MB TROUGH APPROACHES LEADING TO A WARMER AND MORE MOIST AIR MASS MOVING IN. THE CONSENSUS IS ALSO FOR THE TROUGH TO MOVE FURTHER EAST INTO ONTARIO AND QUEBEC AS WELL AS THE GREAT LAKES AND NEAR THE OH VALLEY REGION BY THE END OF THE PERIOD. JUST BEYOND THE PERIOD...A RIDGE IS EXPECTED ACROSS THE ROCKIES WITH EASTERN CANADIAN TO EASTERN CONUS TROUGHING. THIS PATTERN WILL BRING AT LEAST SOMEWHAT CHANGEABLE WEATHER DUE TO THE QUASI ZONAL PATTERN. EARLY IN THE PERIOD...WEAK SFC HIGH PRESSURE IS EXPECTED TO BE CENTERED OVER THE MIDDLE TN TO CENTRAL KY REGION...WHICH MOVES INTO THE SOUTHEASTERN STATES ON MON NIGHT INTO TUE. MEANWHILE A NORTHERN STREAM COLD FRONT SHOULD DROP SOUTH OF THE GREAT LAKES AND INTO THE OH VALLEY REGION.ON TUE INTO TUE NIGHT...BUT BE RATHER MOISTURE STARVED AT THAT POINT WITH HIGH PRESSURE OVER THE GREAT LAKES AND NORTHEAST NOSING INTO THE AREA FOR A TIME. MEANWHILE...AS A LOW PRESSURE SYSTEM DEVELOPS AND TRACKS RATHER QUICKLY NEAR THE US CANADIAN BORDER TO JUST NORTH OF LAKE SUPERIOR FROM WED INTO WED NIGHT...A WARM FRONT SHOULD LIFT NORTH ACROSS EASTERN KY. THIS WILL PUT THE REGION IN THE WARM SECTOR FOR THU INTO FRI...WITH ANTHER WAVE DEVELOPING ALONG THE FRONT AND TRACKING FROM THE PLAINS TO MID MS VALLEY REGION THU INTO EARLY FRIDAY AND THEN FURTHER NORTHEAST WHICH MAY SLOW DOWN THE EASTWARD PROGRESS OF THE COLD FRONT ASSOCIATED AS THE TROUGH GRADUALLY MOVES INTO THE EASTERN CONUS AROUND THE END OF THE PERIOD. DURING THIS PERIOD...FROM LATE WED NIGHT INTO SATURDAY THERE WILL BE A CHANCE FOR SHOWERS. THE CHANCES WILL BE HIGHEST FROM THURSDAY NIGHT INTO FRIDAY NIGHT. MODEL GUIDANCE SUGGESTS THERE COULD BE TWO PERIODS WHERE PRECIPITATION CHANCES POSSIBLY MAX OUT...FROM THU NIGHT INTO EARLY ON FRIDAY AND THEN LATE FRIDAY INTO FRIDAY EVENING. THE FIRST ROUND WOULD BE WITH SOME INSENTROPIC LIFT AND POSSIBLY SOME JET INTERACTION AND THE SECOND ROUND NEAR AND AFTER THE COLD FRONTAL PASSAGE AND POSSIBLE INTERACTION WITH SOME UPPER JET DYNAMICS. MOISTURE INCREASES SUCH THAT THUNDER HAS BEEN INCLUDED FROM THURSDAY INTO FRIDAY...BUT CHANCES ARE PROBABLY BEST THU NIGHT AS WINDS THROUGH THE COLUMN INCREASE AND WITH PW INCREASING SOME GOOD RAINERS AND POSSIBLY A STRONG STORM OR TWO. CHANCES MAY ALSO PEAK AT SOME POINT ON FRIDAY...PENDING THE TIMING OF THE FRONTAL PASSAGE. THERE SHOULD BE A GRADUAL MODERATING TREND FROM TUE INTO THU OR FRI AS 850 MB TEMPS CLIMB FROM NOT FAR FROM 0C AT PRESENT TO 10 TO 12C BY THU INTO FRIDAY. A DROP IN 850 MB TEMPS SHOULD DROP AS THE TROUGH MOVES IN LATE NEXT WEEK WITH THE CURRENT MODEL CONSENSUS ONLY DOWN TO AROUND -5C...BUT THERE IS UNCERTAINTY AND TIME WILL TELL. && .AVIATION...
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(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON) ISSUED AT 149 PM EDT SUN MAR 29 2015 HIGH PRESSURE IS CURRENTLY EXITING TO THE SE OF THE REGION...WITH RETURN FLOW HAVING SHIFTED WINDS TO A MORE SRLY DIRECTION GENERALLY LESS THAN 10 KNOTS. DEW POINTS WILL REMAIN QUITE LOW THROUGH THE DAY...WITH MOSTLY CLEAR SKIES EXPECTED...AND THE POTENTIAL FOR A FEW GUSTS IN THE 15KT RANGE. BY LATE THIS AFTERNOON/EVENING...A COLD FRONT WILL APPROACH KY FROM THE WEST...BRINGING AN INCREASE IN CLOUD COVER ACROSS EASTERN KY FROM NW TO SE. LATEST FORECAST SOUNDINGS ARE SHOWING A QUICK DECREASE IN CIGS FROM VFR TO MVFR BETWEEN 0 AND 2Z THIS EVENING...AND POTENTIALLY DOWN TO IFR AS THE RAIN SETS IN OVERNIGHT. RAIN SHOULD BE QUITE LIGHT IN NATURE...WITH LITTLE EXPECTED IN THE WAY OF VIS RESTRICTIONS /GENERALLY MVFR OR HIGHER/...THOUGH SOME FOG MAY DEVELOP AND LINGER INTO THE MORNING HOURS. EXPECT CIGS TO SLOWLY MIX BACK OUT TO VFR AFTER 12Z TOMORROW.
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&& .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...JMW SHORT TERM...RAY LONG TERM...JP AVIATION...JMW

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