594  
FXUS63 KJKL 121434  
AFDJKL  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE JACKSON KY  
934 AM EST TUE DEC 12 2017  
   
UPDATE
 
 
ISSUED AT 934 AM EST TUE DEC 12 2017  
 
HAVE UPDATED TEMPERATURES AND PRECIP TYPE FOR TODAY AND TONIGHT  
BASED ON LATEST OBS AND MODEL DATA. ONCE CLOUD ICE PRODUCTION  
BEGINS, THE STEEP LOW LEVEL LAPSE RATES HEADED IN WILL RESULT IN  
RAIN VS. SNOW TEMPS BEING FAIRLY WARM IN THE UPPER 30S TODAY.  
 
UPDATE ISSUED AT 710 AM EST TUE DEC 12 2017  
 
THE SNOW IS STARTING TO DEVELOP OVER THE AREA. HAVE UPDATED THE  
FORECAST MAINLY TO ADD IN THE LATEST T AND TD OBS/TRENDS. DID FINE  
TUNE THE POPS AND WILL LIKELY WIPE OUT THE FREEZING PCPN WITH AN  
UPDATE BEFORE 8 AM. LOOK FOR A NEW SET OF ZONES, UPDATED SPS, AND  
HWO WITH THAT ISSUANCE. THE UPDATED GRIDS HAVE BEEN SENT TO THE  
NDFD AND WEB SERVERS.  
 

 
   
SHORT TERM
 
(TODAY THROUGH WEDNESDAY)  
ISSUED AT 305 AM EST TUE DEC 12 2017  
 
07Z SFC ANALYSIS SHOWS A FAIRLY STRONG AREA OF LOW PRESSURE MOVING  
EAST THROUGH NORTHWEST PENNSYLVANIA. A COLD FRONT FROM THIS SYSTEM  
IS POISED TO ENTER KENTUCKY FROM THE NORTHWEST. MUCH COLDER AIR  
TRAILS THE FRONT ALONG WITH BRISK NORTHWEST WINDS. OUT AHEAD OF  
IT, GOOD MIXING THROUGH THE NIGHT THANKS TO A MODERATELY STRONG  
LOW LEVEL JET IS KEEPING THE TEMPERATURES UP EVEN IN THE SHELTERED  
VALLEYS WHERE READINGS ARE DOWN TO THE LOW AND MID 40S. HOWEVER,  
A HOLE IN THE CLOUD COVER IS PUSHING EAST INTO EASTERN KENTUCKY  
AND WOULD EXPECT TO SEE BETTER COOLING BENEATH THIS FOR THE NEXT  
FEW HOURS - BUT THE WINDS MIXING WARMER AIR FROM ALOFT AND  
LOCATIONS SURROUNDING THE VALLEYS WILL LIKELY KEEP THEM WELL  
ABOVE FREEZING THROUGH DAWN. OTHERWISE, TEMPERATURES ARE MILD  
AHEAD OF THE FRONT RANGE FROM THE LOW 50S IN THE FAR SOUTHEAST TO  
THE LOWER 40S IN THE NORTHWEST WITH MOST PLACES IN THE MID TO  
UPPER 40S. DEWPOINTS, MEANWHILE ARE RUNNING IN THE UPPER 20S TO  
LOWER 30S ACROSS THE AREA. SFC WINDS ARE GUSTING MOST PLACES, FROM  
THE SOUTHWEST IN THE FAR EAST TO MORE WESTERLY IN THE WEST, AT  
BETWEEN 20 AND 25 MPH.  
 
NOT MUCH PCPN IS SHOWING UP ON RADAR ATTM EVEN BEHIND THE FRONT -  
THOUGH SOME DRIZZLE IS SHOWING UP IN THE OBS UPSTREAM. DO EXPECT  
IT TO START POPPING UP IN OUR NORTHWEST OVER THE NEXT COUPLE OF  
HOURS BUT FALLING INTO A RELATIVELY WARM BOUNDARY LAYER WITH  
LIMITED OPPORTUNITY TO WETBULB COOLER. AS SUCH, AM NOW LOOKING AT  
MORE IN THE WAY OF LIQUID DRIZZLE/SPRINKLES THROUGH DAWN - OWING  
TO A LACK OF ICE CRYSTALS IN THE COLUMN INITIALLY. SNOW ARRIVES  
SHORTLY AFTER DAWN MOST PLACES ONCE THE COLUMN HAS HAD A CHANCE  
TO COOL. THERE ALSO IS A SMALL POTENTIAL FOR FREEZING  
RAIN/SPRINKLES IN THE COUPLE TO FEW HOURS FOLLOWING SUNRISE AS  
THE COLDER AIR MOVES IN, HOWEVER WARM SFC TEMPERATURES - ROAD  
PAVEMENT READINGS ARE IN THE UPPER 30S TO LOW 40S ATTM - WILL  
LIMIT THIS CONCERN TO ELEVATED SFCS LIKE RAILINGS, DECKS, AND  
PERHAPS UNTREATED BRIDGES/OVERPASSES WILL TAILOR THE ONGOING SPS  
TO ADDRESS THESE CONCERNS INITIALLY. THE SNOW EXPECTATIONS  
ARE ELABORATED ON FURTHER DOWN THIS DISCUSSION.  
 
THE MODELS ARE IN EXCELLENT AGREEMENT ALOFT AS THIS ZERO HOUR AS  
THE NEXT SYSTEM MOVES IN. TWIN POL TROUGHING WILL SWING INTO THE  
OHIO VALLEY TODAY WITH A LEAD IMPULSE PASSING TO OUR NORTHEAST BY  
12Z. THE CORE OF THE TROUGH WILL THEN PRESS INTO THE OHIO VALLEY  
THROUGH THE AFTERNOON WITH PLENTY OF ENERGY AND HEIGHT FALLS  
WORKING OVER EASTERN KENTUCKY. JUST AS QUICK AS IT ARRIVES TODAY  
THIS TROUGH WILL LIFT OUT TO THE NORTHEAST TONIGHT WITH HEIGHTS  
REBOUNDING IN NORTHWEST FLOW. THE FLOW WILL SWIFTLY BECOME MORE  
ZONAL BY THE END OF THE DAY WEDNESDAY WITH THE NEXT IMPULSE MOVING  
IN FROM THE WEST. THIS LATTER FEATURE IS SIMILARLY HANDLED IN THE  
GFS AND ECMWF, BUT LEAD THE LAGGING CMC. WILL FAVOR THE BLEND  
HERE STICKING CLOSE TO THE MAJORITY CONSENSUS. OTHERWISE, HAVE  
USED THE HIGHER RESOLUTION MODELS MOST HEAVILY THROUGH TODAY FOR  
SPECIFIC FORECAST DETAILS WITH BETTER THAN AVERAGE CONFIDENCE.  
 
SENSIBLE WEATHER TODAY WILL SEE THE FRONT AND ITS DYNAMICS BRING  
SHOWERS TO THE AREA GOING OVER TO - FROM WEST TO EAST SNOW DURING  
THE MORNING. SOME INSTABILITY WILL BE AVAILABLE TO HELP DRIVE  
THIS CONVECTION INTO THE AFTERNOON FOR OUR EASTERN ZONES AS THE  
SNOW PATCHES/BANDS SCATTER OUT. A BETTER GREAT LAKE MOISTURE  
FETCH LOOKS TO SET UP JUST NORTHEAST OF THE AREA LATER THIS  
AFTERNOON AND EVENING LIKELY SPARING THE JKL CWA FROM AN EXTENDED  
SNOW THREAT. HAVE GONE ABOVE THE BLENDED POPS THIS MORNING AND  
INTO THE AFTERNOON IN FAVOR OF THE SCENARIO DEPICTED BY THE HRRR  
AND CAMS. LOOK FOR TEMPERATURES TO FALL THROUGH THE DAY WITH SOME  
INSOLATION LIMITING ACCUMULATIONS COMPARED TO THE LAST EVENT.  
ADDITIONALLY, THE ROAD SFC TEMPERATURES WILL BE MUCH HIGHER THAN  
THEY WERE SATURDAY AGAIN MINIMIZING ICING IMPACTS. ACCORDINGLY,  
WILL CONTINUE TO HANDLE THIS EVENT WITH AN SPS FOCUSING ON  
VARIABLE VISIBILITY CONCERNS WITH ANY SQUALLS GIVEN THE STRENGTH  
OF THE LOW LEVEL WIND FIELD. THESE NORTHWEST WINDS BRING IN  
COLDER AIR TONIGHT AND HAVE GONE A BIT LOWER THAN THE BLEND IN  
OUR MORE OPEN AREAS AND THE RIDGES FOR LOWS TONIGHT. SIMILARLY, 45  
ON WEDNESDAY, KEPT THOSE LOCATIONS AS TOUCH COOLER WITH VARIABLE  
CLOUD COVER BETWEEN QUICK HITTING SYSTEMS/CLIPPERS KEEPING THE  
SUNSHINE FROM CONTRIBUTING MUCH. WINDS WERE RAISED TODAY AND ON  
WEDNESDAY AS THE BLEND SEEMS TO BE TOO INFLUENCED BY THE LOW  
BIASED URMA FOR SITUATIONS SUCH AS THESE.  
 
LOOK FOR THE SPS TO CONTINUE THROUGH THE EARLY EVENING FOR THE CWA  
WITH LESS FOCUS ON THE FREEZING PCPN POTENTIAL IN FAVOR OF  
HIGHLIGHTING THE MORE CONVECTIVE SNOW SHOWERS LATER THIS MORNING  
AND THIS AFTERNOON WITH EVEN SOME SQUALLS POSSIBLE.  
   
LONG TERM
 
(WEDNESDAY NIGHT THROUGH MONDAY)  
ISSUED AT 245 AM EST TUE DEC 12 2017  
 
THE EXTENDED WILL BE FAIRLY ACTIVE AND WILL FEATURE SEVERAL PERIODS  
OF PRECIPITATION, AS MULTIPLE WEATHER SYSTEMS MOVE ACROSS THE  
EASTERN PORTION OF THE CONUS. THE FIRST EPISODE OF PRECIPITATION IS  
SLATED TO OCCUR WEDNESDAY NIGHT THROUGH LATE THURSDAY MORNING, AS A  
WEAK AREA OF LOW PRESSURE ALOFT MOVES ACROSS THE OHIO VALLEY. RAIN  
AND SHOWERS WILL BE ON TAP FOR THAT PERIOD, WITH LITTLE IF ANY SNOW  
ACCUMULATIONS EXPECTED. THE SECOND PERIOD OF PRECIPITATION IS  
EXPECTED THURSDAY NIGHT THROUGH LATE FRIDAY NIGHT. TEMPERATURES  
DURING THIS PERIOD SHOULD BE A BIT COOLER, SO MORE SNOW IS EXPECTED  
ACROSS THE AREA. VERY LIGHT SNOW ACCUMULATIONS MAY OCCUR EARLY  
FRIDAY NIGHT, AS A CLIPPER TYPE SYSTEM MOVES QUICKLY THROUGH THE  
REGION. A THIRD PERIOD OF PRECIPITATION IS FORECAST FOR SUNDAY  
THROUGH MONDAY. THIS PRECIP WILL BE ASSOCIATED WITH A LARGER SCALE  
AND MORE POTENT AREA OF LOW PRESSURE THAT IS PROGGED TO MOVE OUT OF  
THE SOUTHERN PLAINS AND EVENTUALLY ACROSS THE TENNESSEE AND OHIO  
VALLEY REGIONS. TEMPERATURES SHOULD BE WARM ENOUGH DURING THE  
PASSAGE OF THIS SYSTEM FOR MOSTLY RAIN TO OCCUR ACROSS THE AREA.  
SOME SNOW SHOWERS MAY MIX WITH RAIN SUNDAY NIGHT INTO EARLY MONDAY  
MORNING, AS SOME COLDER AIR FILTERS INTO THE REGION. IF ANY SNOW  
ACCUMULATIONS DO OCCUR SUNDAY NIGHT, THEY WILL BE VERY LIGHT AND  
LIKELY CONFINED TO GRASSY AREAS AND ELEVATED SURFACES.  
 
TEMPERATURES DURING THE EXTENDED WILL VARY QUITE A BIT, WITH SOME  
DAYS FEATURING HIGHS IN THE 30S AND 40S, AND OTHER DAYS WITH HIGHS  
IN THE 40S AND 50S. NIGHTLY LOWS WILL NOT BE QUITE AS VARIED, WITH  
MIN VALUES IN THE 20S AND 30S EXPECTED.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)  
ISSUED AT 725 AM EST TUE DEC 12 2017  
 
A CLIPPER SYSTEM IS WORKING THROUGH THE AREA THIS MORNING WITH A  
MIX OF LIGHT RAIN AND SNOW MOVING THROUGH THE AREA. A CHANGEOVER  
TO ALL SNOW WILL OCCUR FROM NORTHWEST TO SOUTHEAST LATE THIS  
MORNING AS THE COLUMN COOLS. TEMPERATURES WILL DROP THROUGHOUT  
THE DAY WITH STRONG CAA. SOME OF THE MORE ROBUST SNOW SHOWERS  
COUPLED WITH GUSTY WINDS WILL LEAD TO IFR OR LOWER VIS AT TIMES.  
WINDS WILL BE GUSTY THROUGH THE DAY WITH SOME LOCATIONS SEEING  
GUSTS OF 20 TO 25 KNOTS AT TIMES. WINDS WILL BE WEST TO NORTHWEST  
THROUGH THE PERIOD. CONDITIONS WILL IMPROVE LATER IN THE  
AFTERNOON FROM SOUTHWEST TO NORTHEAST WITH VFR CIGS RETURNING AND  
THE SNOW SHOWERS SCATTERING OUT - THOUGH ANY PLACE HIT BY ONE OF  
THE STRONGER SHOWER COULD SEE VIS AND CIGS BRIEFLY DROP INTO THE  
IFR OR LOWER RANGE. WINDS WILL SETTLE DOWN AFTER SUNSET FROM THE  
NORTHWEST AT GENERALLY AROUND 10 KTS.  
 

 
   
JKL WATCHES/WARNINGS/ADVISORIES
 
 
NONE.  

 
 

 
 
UPDATE...HAL  
SHORT TERM...GREIF  
LONG TERM...AR  
AVIATION...GREIF  
 
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