Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 231803
AFDJKL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON KY
103 PM EST TUE DEC 23 2014

.UPDATE...
ISSUED AT 1020 AM EST TUE DEC 23 2014

SATELLITE THIS MORNING SHOWING A FEW BREAKS IN THE CLOUDS
PARTICULARLY ACROSS SE PORTIONS OF THE CWA. ALSO SEEING A FEW SHOWERS
MOVING ALONG THE WESTERN CWA BORDER. CLOUDS AND SHOWERS EXPECTED TO
INCREASE THROUGH THE DAY TODAY. EVEN SLIGHT CHANCE OF A THUNDERSTORM
ONCE WE MOVE INTO THE AFTERNOON HOURS FROM SW TO NE. NO MAJOR CHANGES
MADE THIS UPDATE. DID FRESHEN UP THE GRID WITH LATEST OBS AND TRENDS.

UPDATE ISSUED AT 638 AM EST TUE DEC 23 2014

NO UPDATE PLANNED THIS MORNING. SCATTERED SHOWERS CONTINUE TO SLIDE
NORTH ACROSS THE WESTERN HALF OF THE AREA. LATEST HRRR IS FLUCTUATING
A BIT NOW ON THE EXPECTED ARRIVAL OF MORE WIDESPREAD RAIN LATER THIS
AFTERNOON...BUT STILL BRINGS MOST OF IT INTO THE AREA BY EARLY
EVENING. WON`T MAKE ANY CHANGES AT THIS TIME AND SEE IF THE NEXT FEW
RUNS LOCK ONTO BETTER TIMING.

&&

.SHORT TERM...(TODAY THROUGH WEDNESDAY)
ISSUED AT 315 AM EST TUE DEC 23 2014

A CUT OFF LOW CONTINUES TO SPIN ACROSS THE CENTRAL PLAINS THIS
MORNING WITH BROAD SOUTHWEST FLOW ACROSS THE OHIO RIVER VALLEY. LOW
LEVEL FLOW REMAINS SOUTHEAST ACROSS EASTERN KENTUCKY. A LULL IN
PRECIPITATION IS OCCURRING PRESENTLY ACROSS THE AREA AS THE LATEST
WAVE RESPONSIBLE FOR SOME RAIN EARLIER TONIGHT HAS EXITED TO THE
NORTH. HOWEVER...MORE SHOWERS ARE SPREADING NORTH OUT OF CENTRAL
TENNESSEE AND WILL PROVIDE SOME RAIN INTO SOUTHERN KENTUCKY OVER THE
NEXT FEW HOURS. THE BEST CHANCES FOR RAIN THROUGH MIDDAY WILL REMAIN
ACROSS THE WESTERN HALF OF THE AREA.

ANOTHER WILL EMERGE FROM THE UPPER LEVEL TROUGH AND PUSH NORTH ACROSS
THE TENNESSEE VALLEY THIS AFTERNOON AND EVENING...BRINGING WIDESPREAD
SHOWERS BACK TO THE AREA. THE SHOWALTER INDEX REMAINS NEGATIVE
THROUGH THE NEXT 24 TO 36 HOURS ACROSS MOST OF THE AREA. THUS...ANY
ENHANCED AREAS OF LIFT WILL PROVIDE THE POSSIBILITY OF SOME THUNDER.
THE THUNDER THREAT SHOULD REMAIN ALL ELEVATED LATER TODAY AND
TONIGHT. GIVEN THE TREMENDOUS LIFT ARRIVING LATE IN THE DAY AND THE
WIDESPREAD COVERAGE DEPICTED IN THE HRRR...HAVE OPTED FOR
CATEGORICAL POPS LATE IN THE DAY INTO TONIGHT. AS THIS INITIAL WAVE
EXITS TO THE NORTH...WE MAY SEE ANOTHER LULL THROUGH A PORTION OF
TONIGHT. HOWEVER...ANOTHER STRONG WAVE WILL PUSH NORTH LATE TONIGHT
WITH AN AREA OF LOW PRESSURE TRACKING NORTHWARD ACROSS CENTRAL
KENTUCKY. THIS WILL BRING ANOTHER ROUND OF WIDESPREAD SHOWERS AND
EMBEDDED THUNDERSTORMS TO THE AREA.

AS THE LOW PRESSURE SYSTEM STRENGTHENS AND HEADS INTO MICHIGAN ON
WEDNESDAY...IT WILL SEND A STRONG COLD FRONT TO THE EAST ACROSS
KENTUCKY. AGAIN...GOOD CONVERGENCE AND LIFT ALONG THE FRONT SHOULD
PROVIDE ANOTHER PERIOD OF WIDESPREAD SHOWERS. THIS FRONT WILL ALSO
PRODUCE THE BEST CHANCE OF THUNDER THROUGH THE FORECAST PERIOD AS IT
CROSSES THE AREA IN THE AFTERNOON AND EVENING HOURS. THIS TIME
AROUND...WE MAY BE ABLE TO GENERATE ENOUGH SURFACE BASED INSTABILITY
TO POSSIBLY MIX DOWN SOME OF THE STRONGER WINDS AS THE SHOWERS ALONG
THE FRONT PUSH EAST. THIS COULD YIELD WINDS 45+ KNOTS. EVEN WITHOUT
THE INSTABILITY...SYNOPTIC WINDS WILL TURN QUITE GUSTY JUST BEHIND
THE FRONT WITH WIND GUSTS REACHING AS HIGH AS 40 MPH AT TIMES. AS THE
FRONT PUSHES EAST...WE SHOULD FINALLY SEE PRECIPITATION COME TO AN
END FROM WEST TO EAST THROUGH THE EVENING HOURS WEDNESDAY AS A DRY
SLOT OVERSPREADS THE AREA.

TEMPERATURES WILL REMAIN ON THE MILD SIDE THROUGH WEDNESDAY WITH
HIGHS WELL INTO THE 60S BOTH DAYS AND LOWS TONIGHT ONLY IN THE 50S.

.LONG TERM...(WEDNESDAY NIGHT THROUGH MONDAY)
ISSUED AT 425 AM EST TUE DEC 23 2014

THE PERIOD WILL BEGIN WITH A DEEP CLOSED LOW AND ASSOCIATED SFC
SYSTEM CENTERED OVER THE GREAT LAKES REGION WITH A TROUGH EXTENDING
SOUTH INTO THE MS VALLEY. RIDGING IS EXPECTED TO BE OFF THE SOUTHEAST
US COAST WITH RIDGING ALSO OVER NORTHERN MEXICO AND INTO THE SOUTHERN
AND CENTRAL ROCKIES. A TROUGH IS EXPECTED TO BE WORKING ACROSS THE
NORTHWESTERN CONUS AT THAT POINT AS WELL. FROM THU INTO THE START OF
THE WEEKEND...THE DEEP LOW INITIALLY OVER THE GREAT LAKES WILL TRACK
NORTH ACROSS ONTARIO AND QUEBEC AND INTO THE MARITIMES WITH THE
TRAILING TROUGH AXIS MOVING ACROSS THE AREA EARLY IN THE PERIOD ON
WED NIGHT INTO EARLY ON THU. RIDGING SHOULD THEN WORK ACROSS THE
EASTERN CONUS FROM LATER ON CHRISTMAS DAY INTO FRIDAY. MEANWHILE THE
COLD FRONT TRAILING FROM THE SYSTEM MOVING THROUGH THE GREAT LAKES
INITIALLY SHOULD HAVE EXITED INTO WV OR SHOULD EXIT INTO WV VERY
EARLY IN THE PERIOD. A DRY SLOT SHOULD WORK ACROSS THE AREA EARLY IN
THE PERIOD PER RECENT MODEL CONSENSUS FOLLOWED BY SOMEWHAT DEEPER
WRAPAROUND MOISTURE LATER ON WED NIGHT. SFC HIGH PRESSURE WILL BUILD
IN BEHIND THE DEPARTING LOW PRESSURE SYSTEM FOR THU NIGHT INTO FRI
NIGHT.

FROM WED INTO FRIDAY...A TROUGH WILL HAVE DEVELOPED AND WORKED ACROSS
THE WESTERN CONUS AND SHOULD BE MOVING INTO THE PLAINS BY THE START
OF THE WEEKEND. AT THAT POINT...THE MOST RECENT GFS AND ECMWF RUNS
BEGIN TO DIFFER IN TIMING OF INDIVIDUAL WAVES BUT THERE IS A GENERAL
THEME OF LOWERING HEIGHTS ACROSS THE EASTERN SEABOARD AND SOUTHEAST
FROM THE WEEKEND INTO EARLY NEXT WEEK WITH A TROUGH OVER THE WESTERN
INTO THE CENTRAL CONUS BECOMING INCREASINGLY BROAD WITH TIME. THE
GENERAL CONSENSUS IS FOR A COLD FRONT TO ENTER THE LOWER OH AND
APPALACHIAN REGION FROM FRI NIGHT INTO SATURDAY AND THEN SHIFT SOUTH
OF THE REGION AS EARLY AS SAT AFTERNOON OR EVENING PER THE GFS AND
AS LATE SAT NIGHT INTO SUN PER THE ECMWF.

THE UPPER LEVEL TROUGH AND WRAPAROUND MOISTURE SHOULD LEAD TO SHOWER
AND DRIZZLE CHANCES FROM WED NIGHT INTO MIDDAY ON THURSDAY. SOME SNOW
COULD MIX IN AS WELL. LOCATIONS BELOW 2000 OR 2500 FEET ELEVATION
SHOULD REMAIN ABOVE FREEZING ON WED NIGHT. BEHIND THE DEPARTING
SYSTEM AND IN ADVANCE OF A SFC HIGH...THE LOW LEVEL FLOW WILL BECOME
TOO SOUTHWEST FOR IDEAL UPSLOPE FLOW BUT LOW LEVEL LAPSE RATES WILL
SUPPORT THE CHANCES FOR SHOWERS AND OR DRIZZLE. IN ADDITION...MODEL
FORECAST SOUNDINGS INDICATE THAT ICE CRYSTALS COULD BE LOST AT TIMES
LEADING TO LIGHT PRECIP POSSIBLY FALLING FROM CLOUDS WHERE ICE IS NOT
PRESENT...LEADING TO JUST RAIN OR DRIZZLE AT TIMES. THERE MAY BE
TIMES WHERE ICE IS PRESENT SO SOME FLURRIES OR LIGHT SNOW WOULD ALSO
BE POSSIBLE...BUT CHANCES FOR THIS ARE BEST ON THE RIDGES. A BIT OF
FREEZING DRIZZLE ALSO CANNOT BE RULED OUT LATE WED NIGHT INTO EARLY
ON THURSDAY FOR ELEVATIONS ABOVE 2000 OR 2500 FEET ELEVATION. THE
PRESSURE GRADIENT WILL REMAIN RATHER STEEP WELL INTO WED NIGHT...SO
WIND GUSTS AS HIGH AS 35 TO 40 MPH WILL BE POSSIBLE. A SLIGHTLY
STRONGER GUST CANNOT BE RULED OUT ABOVE 2500 FEET. AS THE MOISTURE
BECOMES INCREASINGLY SHALLOW AS CHRISTMAS DAY PROGRESSES ANY LINGERING
DRIZZLE SHOULD DISSIPATE WITH SOME PARTIAL CLEARING...ESPECIALLY IN
WESTERN SECTIONS. HIGH PRESSURE SHOULD LEAD TO DRY WEATHER FOR THU
EVENING INTO MOST OF FRIDAY NIGHT.

BOTH OF SCENARIOS FROM THE 0Z GFS AND 0Z ECMWF RUNS POINT TOWARD
MAINLY RAIN...POSSIBLY MIXING WITH OR CHANGING TO SNOW ON SAT INTO
SAT NIGHT. CURRENT MODEL RUNS HAVE A WAVE DEVELOPING ON SAT INTO SAT
NIGHT ALONG THE BOUNDARY THAT WILL HAVE PASSED TO OUR SOUTH WITH AN
INVERTED TROUGH EXTENDING TO ITS NORTH IN RESPONSE TO A SHORTWAVE
WORKING FROM HE SOUTHERN ROCKIES ACROSS THE SOUTHERN PLAINS AND INTO
THE SOUTHEASTERN CONUS FROM SAT NIGHT INTO SUN NIGHT. THE MODELS
TRACK THE SFC WAVE ACROSS THE SOUTHEASTERN STATES DURING THAT TIME. IF
DEEP ENOUGH MOISTURE LINGERS AS THIS SYSTEM DEPARTS ON SUN NIGHT INTO
EARLY ON MONDAY...SOME SNOW MIGHT MIX IN.

OVERALL..TEMPERATURES THROUGH THE PERIOD WILL REMAIN NEAR NORMAL TO
ABOVE NORMAL AS THE CORE OF THE COLDER AIRMASSES REMAINS MAINLY
BOTTLED UP OVER CANADA AND NEARER TO THE US/CANADIAN BORDER. THE
BIGGEST DEPARTURES SHOULD OCCUR FROM FRI INTO SATURDAY. SOME MODEL
GUIDANCE SUGGESTS THAT AT LEAST A GLANCING BLOW OF COLDER AIR MAY
AFFECT THE AREA AROUND THE MIDDLE OF NEXT WEEK...BUT THERE HAS BEEN
PLENTY OF MODEL DIFFERENCES FROM RUN TO RUN AND MODEL TO MODEL DURING
THAT TIME PERIOD.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 100 PM EST TUE DEC 23 2014

THIS AFTERNOON MOST SPOTS ARE DRY...HOWEVER SHOWERS AND EVEN A FEW
THUNDERSTORMS ARE MOVING NE OUT OF MIDDLE TN. THESE SHOWERS AND
THUNDERSTORMS ARE EXPECTED TO SLOWLY PROGRESS NE OVER THE NEXT FEW
HOURS AND AFFECT SME AND LOZ FIRST. THESE SHOWERS AND THUNDERSTORMS
WILL CONTINUE TO SPREAD ACROSS THE REGION THROUGH THE DAY INTO THE
OVERNIGHT. MOST AREAS THIS AFTERNOON HAVE BEEN BETWEEN VFR/MVFR CIGS
AND THIS WILL TREND TOWARD MVFR AND EVEN CLOSER TO IFR OVER MUCH OF
THE TAF PERIOD AS WE SEE MULTIPLE ROUNDS OF SHOWERS AND SLIGHT CHANCE
OF THUNDERSTORMS. HEAVIER SHOWERS COULD ALSO BRIEFLY REDUCE VIS TO
NEAR IFR CONDITIONS.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...DJ
SHORT TERM...KAS
LONG TERM...JP
AVIATION...DJ





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