Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 201217 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE JACKSON KY
817 AM EDT MON APR 20 2015

.UPDATE...
ISSUED AT 800 AM EDT MON APR 20 2015

HOURLY GRIDS HAVE BEEN FRESHENED UP BASED ON RECENT OBSERVATIONS
AND RADAR TRENDS. THE EARLIER BAND OF CONVECTION HAS WEAKENED AND
IS NOW MOVING INTO VA AND WV. ADDITIONAL CONVECTION SHOULD DEVELOP
LATER THIS MORNING OR EARLY IN THE AFTERNOON.

&&

.SHORT TERM...(TODAY THROUGH TUESDAY)
ISSUED AT 355 AM EDT MON APR 20 2015

THERE ARE TWO MAIN CONCERNS THIS FORECAST CYCLE. THE FIRST CONCERN
IN THE CONVECTIVE LINE APPROACHING THE SOUTHWEST PART OF THE CWA
THAT IS RUNNING OUT AHEAD OF AN APPROACHING COLD FRONT. SOME
STRONG WIND GUSTS HAVE BEEN OBSERVED CLOSER TO THE I 65 CORRIDOR
IN TN AND KY WITH THIS LINE. SPC MESOANALYSIS STILL INDICATED
DECENT SHEAR AND SOME MARGINAL TO MODEST CAPE AHEAD OF THE LINE
INTO THE LAKE CUMBERLAND REGION. THIS REGION WILL CONTINUE TO BE
MONITORED FOR STRONG THUNDERSTORMS OVER THE NEXT COUPLE OF HOURS.
THE REGION REMAINS IN A MARGINAL SEVERE THUNDERSTORM RISK FOR THE
REST OF THE OVERNIGHT HOURS.

OTHERWISE...THE REMNANTS OF THIS CONVECTION SHOULD MOVE ACROSS THE
AREA WITHIN A COUPLE OF HOURS OF DAWN. THERE MAY BE A RELATIVE
LULL IN ACTIVITY FOR A COUPLE OF HOURS AFTER THIS AREA PASSES...BEFORE
ADDITIONAL SHOWER AND THUNDERSTORM DEVELOPMENT ALONG AND IN
ADVANCE OF THE ACTUAL COLD FRONT ITSELF AND APPROACHING 500 MB
TROUGH AXIS. THE STRENGTH OF THIS ACTIVITY WILL BE DETERMINED BY
HOW MUCH THE EARLY DAY CONVECTION SUPPRESSES INSTABILITY AHEAD OF
THE FRONT AND ANY HEATING THAT MAY BE ABLE TO OCCUR ACROSS THE
CENTRAL AND EASTERN CWA. THE NAM HAS A BIT MORE WARMING AND THUS
IS CONSIDERABLY MORE UNSTABLE WITH CAPE INTO THE 1000 TO 1500 J/KG
RANGE DURING THE AFTERNOON WHILE THE GFS HAS MUCH LESS
INSTABILITY. SPC HAS A MARGINAL RISK FOR SEVERE THUNDERSTORMS
ACROSS THE EASTERN TWO THIRDS OF THE AREA FOR THE UPCOMING DAY ON
MONDAY. STRONG WIND GUSTS WOULD BE THE PRIMARY THREAT FROM ANY
AFTERNOON TO EARLY EVENING ACTIVITY AND HAIL WOULD ALSO BE
POSSIBLE.

THE THREAT FOR SHOWERS WILL WANE BEHIND THE FRONT THIS EVENING
WITH SFC HIGH PRESSURE ACROSS THE SOUTHERN STATES NOSING INTO THE
COMMONWEALTH OVERNIGHT AND INTO THE DAY ON TUESDAY. HOWEVER...A
WEAK COLD FRONT OR SFC TROUGH IS EXPECTED TO APPROACH THE REGION
LATE IN THE PERIOD...ALONG WITH A MID LEVEL SHORTWAVE. MOISTURE
WITH THIS SYSTEM WILL BE RATHER LIMITED AND NOT MUCH MORE THAN AN
INCREASE IN MID LEVEL CLOUDS IS EXPECTED BEFORE THE END OF THE
PERIOD. A STRAY SHOWER OR SOME SPRINKLES CANNOT BE RULED OUT AT
THE VERY END OF THE PERIOD NEAR THE I 64 CORRIDOR AND NORTH.

.LONG TERM...(TUESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 332 AM EDT MON APR 20 2015

PERIOD WILL BEGIN WITH HIGH MOVING SOUTH OF THE REGION AND WEAK
FRONTAL BOUNDARY DROPPING SOUTH ACROSS THE OHIO VALLEY. THIS WILL
BRING SOME RAIN SHOWERS ACROSS PORTIONS OF THE REGION. GIVEN
GUIDANCE CONTINUES TO HAVE SOME DISCREPANCIES ON EXACT
TIMING...WILL STAY IN THE CHANCE TO SLIGHT AT THIS POINT. GIVEN
THAT THIS FRONT IS WEAKER AND PWATS IN THE 0.50 TO 0.80 RANGE
WOULD THINK QPF WILL BE GENERALLY LIGHT WITH THIS SYSTEM. DO KEEP
RAIN SHOWERS AS WE MOVE INTO WEDNESDAY AND DO INTRODUCE AFTERNOON
THUNDERSTORMS IN THE SOUTH NEAR THE TN/VA BORDE45R. THIS SEEMED
WARRANTED GIVEN A BIT MORE INSTABILITY IN THE AFTERNOON HOURS AND
FOR NOW CAPPED THIS AT SLIGHT CHANCE. CHANCES MAY NEED TO BE
INCREASED IN SUBSEQUENT FORECAST RUNS DEPENDING ON HOW THIS FRONT
PROGRESSES. DOES LOOK LIKE WE GET ANOTHER BREAK AS HIGH PRESSURE
TRIES TO BUILD SOUTHEAST ACROSS THE REGION WEDNESDAY NIGHT INTO
THURSDAY.

THE FORECAST BECOMES LESS CLEAR AS WE MOVE FARTHER INTO THE LONG
TERM...AS ALL EYES TURN TOWARD UPPER LEVEL SHORTWAVE EJECTING OUT
OF THE DESERT SOUTHWEST. LATEST GFS MODEL RUN IS MUCH MORE
PROGRESSIVE WITH THIS SYSTEM THAN THE ECMWF AND GEM. THE GFS IS
ALSO STRONGER WITH THE SURFACE LOW AS IT BRINGS A LESS FLATTENED
SHORTWAVE ACROSS THE TN AND OH VALLEYS. THE 00Z GFS AND 00Z GFS
ENSEMBLE MEAN ARE IN DECENT AGREEMENT WITH PLACEMENT OF SURFACE
LOW AND UPPER LEVEL PATTERN. HOWEVER GIVEN UNCERTAINTY WILL STICK
CLOSE TO MODEL BLEND AT THIS POINT BEING THAT THIS IS DAY 5 AND 6.
THIS WOULD YIELD THE BEST POPS FRIDAY NIGHT INTO SATURDAY. NOW THE
FASTER GFS ALSO BRINGS TO QUESTION IF WE WILL SEE THE COLDER TEMPS
FRIDAY MORNING THAT WERE PREVIOUSLY EXPECTED...SO HAVE BACKED OFF
ON THIS NOTION GIVEN THAT BOTH MODELS HAVE TRENDED WARMER AT 850MB
FROM PREVIOUS RUNS. HIGH TEMPS THROUGH THE PERIOD WILL GENERALLY
BE AROUND 10 DEGREES BELOW NORMAL.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 800 AM EDT MON APR 20 2015

ONE ROUND OF CONVECTION IS DEPARTING THE AREA ATTM...WITH SOME
MVFR OR MVFR IN ITS WAKE. LATER THIS MORNING INTO THE
AFTERNOON...GENERALLY 15Z OR LATER ADDITIONAL CONVECTION SHOULD
DEVELOP AND WORK ACROSS THE REGION THROUGH 0Z. THIS WILL BRING
MVFR OR EVEN IFR IN ANY OF THE STRONGER SHOWERS OR THUNDERSTORMS
FOR BRIEF PERIOD A TIME. BETWEEN 0Z AND 6Z...AS THE ASSOCIATED
COLD FRONT DEPARTS...VFR CONDITIONS WILL RETURN. WINDS WILL PICK
UP OUT OF THE SOUTHWEST TO WEST THROUGH 16Z...WITH SOME GUSTS
TOPPING 20 KTS. THE PRESSURE GRADIENT WILL SLACKEN BETWEEN 0Z AND
6Z AND WINDS SHOULD BECOME LIGHT AND VARIABLE LATE.

&&

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

$$

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



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