Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 211506 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE JACKSON KY
1106 AM EDT SUN SEP 21 2014

.UPDATE...
ISSUED AT 1106 AM EDT SUN SEP 21 2014

THE SURFACE COLD FRONT IS CURRENTLY NEAR A KCVG TO KSDF TO KPAH
LINE. A PRE-FRONTAL SURFACE TROUGH OUT AHEAD OF THE MAIN BOUNDARY IS
STARTING TO INITIATE TO SOME SCATTERED SHOWER ACTIVITY GENERALLY
SOUTH OF THE MOUNTAIN PARKWAY ACROSS EASTERN KENTUCKY. CLOUD COVER
HAS EXPANDED RAPIDLY ACROSS THE AREA THIS MORNING...AND THE LATEST
LOW-LEVEL AND MID-LEVEL LAPSE RATES ARE LOOKING WEAK ACCORDING TO THE
SPC MESO-ANALYSIS. GIVEN THESE TRENDS...HAVE REDUCED THE THUNDER
CHANCES AS WELL AS THE SMALL HAIL MENTION IN THE HWO. WILL LEAVE THE
MENTION OF SOME BRIEF HEAVY RAINFALL AND GUSTY WINDS FOR NOW. ALSO
TRIMMED A FEW DEGREES OFF OF THE HIGHS GIVEN THE THICKER CLOUDS
ALREADY ON TOP OF US. UPDATES HAVE BEEN SENT.

UPDATE ISSUED AT 745 AM EDT SUN SEP 21 2014

HOURLY GRIDS HAVE BEEN UPDATED BASED ON RECENT OBSERVATIONS. THERE IS
NOT MUCH ACTIVITY IN ADVANCE OF THE APPROACHING COLD FRONT AT THIS
POINT. HOWEVER...THERE IS NOT MUCH CLOUD COVER OVER THE CWA OTHER
THAN RIVER VALLEY FOG AND SOME STRAY MID AND HIGH CLOUDS. THIS SHOULD
ALLOW FOR SOME HEATING DURING THE AM AND AS THE HEIGHTS ARE PROJECTED
TO FALL OVER THE OH VALLEY AS THE SHORTWAVE DROPS THROUGH THE GREAT
LAKES...ADDITIONAL BANDS OF SHOWERS AND SOME THUNDERSTORMS SHOULD
DEVELOP. THE 9Z HRRR AS WELL AS THE 0Z AND 6Z GFS AND TO SOME DEGREE
THE NAM GUIDANCE IS IN LINE WITH THIS THINKING. OVERALL...NO MAJOR
CHANGES WERE MADE TO THE GRIDS ATTM.

&&

.SHORT TERM...(TODAY THROUGH MONDAY)
ISSUED AT 410 AM EDT SUN SEP 21 2014

EARLY THIS MORNING....AN UPPER LEVEL RIDGE WAS CENTERED OVER THE
SOUTHERN ROCKIES AND WEST TX REGION WITH RIDGING NORTHWEST INTO THE
ROCKIES AND EAST INTO THE SOUTHERN APPALACHIAN REGION. TO OUR
SOUTHEAST A TROUGH OF LOW PRESSURE EXTENDED FROM THE CAROLINA
COASTLINE SOUTH INTO FL AND THE EASTERN GULF OF MEXICO. AN INITIAL
SHORTWAVE IS MOVING INTO THE EASTERN GREAT LAKES REGION WITH THE MAIN
SHORTWAVE OF INTEREST LOCALLY WORKING THROUGH THE UPPER MIDWEST AND
WESTERN GREAT LAKES REGION ATTM. AT THE SFC...HIGH PRESSURE WAS
CENTERED ACROSS THE SOUTHEASTERN CONUS WITH A SFC LOW PRESSURE
WORKING ACROSS THE GREAT LAKES REGION. A COLD FRONT EXTENDED SOUTH
AND SOUTHWEST FROM THE LOW INTO THE MID MS VALLEY REGION WITH THE
BOUNDARY BEGINNING TO APPROACH THE LOWER OH VALLEY REGION.

THROUGH THE PERIOD...THE RIDGING INTO THE SOUTHEASTERN CONUS WILL BE
SHUNTED TO THE SOUTH WITH THE SOUTHEASTERN TROUGH...THE INITIAL
TROUGH AND THE TROUGH APPROACHING FROM THE NORTHWEST CARVING OUT A
TROUGH FROM ONTARIO AND QUEBEC INTO NORTHEASTERN US REGION DOWN INTO
THE OH VALLEY REGION BY THIS EVENING. THIS TROUGH AXIS IS EXPECTED TO
SHIFT EAST AND NORTHEAST PUSHING EAST AND SOUTHEAST OF EAST KY BY MID
MORNING ON MONDAY AND EXTEND FROM QUEBEC INTO THE MID ATLANTIC
STATES AND INTO THE SOUTHEASTERN STATES AT THE END OF THE PERIOD.
THIS TROUGH WILL PUSH THE COLD FRONT SOUTH AND EAST OF THE OH RIVER
THIS MORNING INTO EARLY AFTERNOON AND ACROSS CENTRAL AND EASTERN KY
THIS AFTERNOON INTO THE EARLY EVENING HOURS. SFC HIGH PRESSURE
CURRENTLY OVER THE PLAINS STATES WILL BUILD INTO THE OH VALLEY REGION
BEHIND THE BOUNDARY AND IS EXPECTED TO BE CENTERED FROM THE MID OH
VALLEY REGION WEST TO THE MID MS VALLEY REGION BY THE END OF THE
PERIOD.

SOME VALLEY FOG IS PRESENT THIS MORNING ALONG WITH SOME PASSING
CLOUDS IN THE 6 TO 8KFT RANGE. 1A6 AND I35 RECENTLY REPORTED VIS DOWN
BELOW 1 MILE WITH DENSE FOG AT I35. PATCHY FOG HAS BEEN INCLUDED IN
THE GRIDS FOR THE REMAINDER OF THE OVERNIGHT WITH A COUPLE MORE HOURS
OF PATCHY DENSE FOG IN THE GRIDS FOR THE DEEPER EASTERN AND SOUTHEASTERN
VALLEY LOCATIONS IN PORTIONS OF THE BIG SANDY...KENTUCKY...LIKING AND
UPPER CUMBERLAND RIVER BASINS. IN MORE OPEN TERRAIN LOCATIONS...THE
PRESSURE GRADIENT HAS BEEN SUFFICIENT TO DISSIPATE THE FOG OVER THE
PAST COUPLE OF HOURS OR PREVENT IT FROM FORMING ALL TOGETHER.

A COUPLE BANDS SHOWERS AND SOME THUNDERSTORMS ARE EXPECTED TO MOVE
INTO OR DEVELOP ACROSS EASTERN KY BY LATE MORNING INTO THE EARLY
AFTERNOON HOURS AND DEPART MOST OF THE AREA BY SUNSET...AS THE COLD
FRONT APPROACHES AND WORKS ACROSS THE REGION. THE MODEL CONSENSUS AND
RECENT SHORT TERM MODEL RUNS OF THE HRRR SUGGEST THAT THE BEST
CHANCES FOR MEASURABLE PRECIPITATION AND THUNDER WILL BE ACROSS THE
SOUTHERN HALF OF THE CWA. POPS IN THE 50 TO 60 DEGREE RANGE WERE USED
IN THIS AREA. PENDING THE DEGREE OF INSTABILITY FROM HEATING AND LOW
LEVEL MOISTURE INCREASE AHEAD OF THE FRONT...MODEL FORECAST MID LEVEL
DRYING...AND DECENT SPEED SHEAR COULD COMBINE FOR THE STRONGEST
STORMS TO PRODUCE SOME HAIL OR STRONG WINDS GUSTS DURING THE
AFTERNOON TO EARLY EVENING. THE SPC DAY 1 OUTLOOK IS ALSO CONSISTENT
WITH THIS THINKING. THIS POTENTIAL WILL BE ADDED TO THE HWO. WITH A
MODERATE PRESSURE GRADIENT ACROSS THE REGION AND SOME STRONGER WINDS
ALOFT THAT COULD MIX DOWN...SUSTAINED WINDS OF 10 MPH OR SO WILL BE
POSSIBLE LATE THIS MORNING INTO EARLY THIS AFTERNOON...ESPECIALLY
ACROSS THE MORE OPEN TERRAIN LOCATIONS ACROSS THE WESTERN AND
NORTHWESTERN PARTS OF THE CWA AND THE HIGHER TERRAIN. SOME GUSTS
OUTSIDE OF ANY CONVECTION INTO THE 20 TO 25 MPH ALSO APPEAR POSSIBLE.

THE WRAPAROUND MOISTURE LATE TONIGHT INTO EARLY ON MONDAY MAY BE DEEP
ENOUGH AS THE 500 MB TROUGH AXIS WORKS ACROSS THE REGION WITH THE LOW
LEVEL FLOW BEING DEEP ENOUGH FOR TOUCH OF DRIZZLE OR SPRINKLES
GENERALLY ACROSS THE EASTERN PART OF THE CWA AND THE VA BORDER
COUNTIES. THE 0Z GFS GENERATES SOME LIGHT QPF IN SOME OF THIS AREA
LATE TONIGHT INTO EARLY ON MONDAY. THE OTHER OPERATIONAL MODELS HAVE
ANY MEASURABLE PRECIP FURTHER NORTHEAST INTO WV. EITHER WAY THERE
SHOULD BE A PERIOD OF LOW STRATUS OR STRATOCU OVERNIGHT INTO EARLY ON
MONDAY ACROSS THE EASTERN HALF OR SO OF THE CWA. OVERNIGHT LOWS
TONIGHT WILL BE MORE COLD AIR ADVECTION DRIVEN WITH SOME OF THE FAR
EASTERN VALLEY LOCATIONS THAT WARMEST ON AVERAGE.

THE LINGERING CLOUDS AND COLD AIR ADVECTION WILL BRING TEMPERATURES
AT LEAST 10 DEGREES BELOW NORMAL FOR MOST LOCATIONS ON MONDAY. THE
MORNING STRATOCU SHOULD GRADUALLY LIFT INTO SOME FLAT CU JUST BELOW
THE SUBSIDENCE INVERSION WITH THESE GRADUALLY MIXING OUT OR LARGELY
MIXING OUT BY THE END OF THE PERIOD...EXCEPT POSSIBLY THE FAR
SOUTHEAST PART OF THE CWA.

.LONG TERM...(MONDAY NIGHT THROUGH SATURDAY)
ISSUED AT 348 AM EDT SUN SEP 21 2014

A STRONG UPPER LEVEL RIDGE WILL MOVE FROM THE CENTRAL CONUS AT 0Z
TUESDAY...TO THE MISSISSIPPI RIVER VALLEY BY 12Z.
MEANWHILE...SURFACE HIGH PRESSURE WILL ALSO REMAIN STRONG OVER THE
REGION...WITH WINDS BOTH AT THE SURFACE AND ALOFT PULLING DRY AND
COLDER AIR IN FROM CANADA. SOME OF THE STRONGEST WINDS ALOFT WILL BE
MOVING OFF TO OUR EAST WITH THE DEPARTING UPPER LEVEL TROUGH...BUT
COLD AIR WILL LINGER THROUGH THE DAY TUESDAY. MORNING LOWS WILL ONLY
BE IN THE LOW TO MID 40S...WITH AFTERNOON HIGHS TOPPING OUT AROUND
OR JUST ABOVE THE 70 DEGREE MARK. OVER THE COURSE OF THE EXTENDED
PERIOD...THE SURFACE HIGH WILL SHIFT SLIGHTLY TO OUR NE...BUT THE
UPPER LEVEL RIDGE WILL REMAIN BLOCKED OVER THE REGION. AS SUCH...DRY
AIR WILL PERSIST ACROSS MUCH OF THE OHIO RIVER VALLEY...THOUGH THE
LOSS OF STRONGEST NRLY WIND FLOW AT BOTH THE SURFACE AND ALOFT WILL
LEAD TO AIR MASS MODIFICATION AND RISING TEMPERATURES THROUGHOUT THE
EXTENDED. TEMPS WILL REACH THE 80 DEGREE MARK IN SOME LOCATIONS ONCE
MORE BY SATURDAY.

THE LATEST ECMWF MODEL IS POINTING AT A WEAK LOW DEVELOPING NEAR THE
REGION LATE IN THE PERIOD...NAMELY SATURDAY AND SUNDAY...ALLOWING
MOISTURE FLOW AND PRECIP CHANCES TO MOVE INTO PORTIONS OF THE CWA.
WHILE A COUPLE OF OUR NEIGHBORING OFFICES WERE ON BOARD WITH
INCLUDING SLIGHT CHANCE POPS...THE UNCERTAINTY FAVORED LEAVING THEM
OUT AT THE JKL CWA AT THIS TIME. SO FAR...THE MODEL AGREEMENT PAST
THE MID TERM IS QUITE LOW. THE ECMWF SEEMS TO BE THE OUTLIER WITH
THIS PRECIP...AND VERY LOW QPF AT THAT. MORE THAN LIKELY...THE SUPER
BLEND IS BEING INFLUENCED BY THIS LATEST ECMWF RUN...WHICH LED TO
THE MENTION OF A FEW 15 POPS IN THE SATURDAY NIGHT FORECAST.
MEANWHILE...THE GFS SHOWS NO SIGN OF THIS LOW NEAR THE REGION /IT
HAS IT DEVELOPING MUCH FARTHER S AND MUCH WEAKER/ OR ANY PRECIP
MOVING INTO KENTUCKY. GIVEN THE UNCERTAINTY AT THIS POINT...LOWERED
ANY 15 POPS FOR SATURDAY NIGHT BACK DOWN TO 14. WILL WAIT UNTIL
MODELS COME INTO BETTER AGREEMENT OR SHOW MORE CONSISTENCY BETWEEN
RUNS BEFORE DECIDING TO INCLUDE POPS IN THE FORECAST PACKAGE.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)
ISSUED AT 745 AM EDT SUN SEP 21 2014

OUTSIDE OF SOME LINGERING FOG...AFFECTING SME WITH MVFR...VFR SHOULD
PREVAIL AT THE TAF SITES THROUGH AT LEAST THE FIRST 6 HOURS OF THE
PERIOD. SOME LINGERING IFR OR LOWER FOG WILL LIFT OUT OF SOME OF THE
DEEPER VALLEY LOCATIONS THROUGH 14Z. A COLD FRONT WILL DROP SOUTH
ACROSS THE COMMONWEALTH TODAY WITH CLOUDS AND SOME SHOWERS AND SOME
THUNDERSTORMS...MAINLY FROM 16Z THROUGH 0Z. AT THIS TIME...IT APPEARS
CIGS AND VIS WITH SHRA AND SOME TSRA SHOULD GENERALLY REMAIN IN THE
VFR RANGE...THOUGH SOME BRIEF MVFR IS POSSIBLE IN SOME OF THE
STRONGER SHOWERS OR STORMS. AS THE NOCTURNAL INVERSION MIXES OUT
THROUGH 16Z...LIGHT WINDS SHOULD BECOME SOUTHWEST TO WEST AND
INCREASE TO AROUND 10KT FOR THE TAF SITES BY AROUND 16Z...WITH SOME
GUSTS UP TO 20KT POSSIBLE...ESPECIALLY BETWEEN 16Z TO 22Z. WINDS WILL
BECOME MORE NORTHWESTERLY BEHIND THE FRONT GENERALLY 21Z THROUGH 0Z
AND AS THE PRESSURE GRADIENT RELAXES WINDS SHOULD DECREASE TO BELOW
10KT LATE IN THE PERIOD. SOME STRATOCU WITH WRAP AROUND MOISTURE AND
UPPER DISTURBANCE MAY BRING MVFR CIGS LATE IN THE PERIOD.


&&

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

$$

UPDATE...GEOGERIAN
SHORT TERM...JP
LONG TERM...JMW
AVIATION...JP





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