Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 181419
AFDJKL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON KY
1019 AM EDT SAT APR 18 2015

.UPDATE...
ISSUED AT 1018 AM EDT SAT APR 18 2015

JUST UPDATED THE FORECAST GRIDS...ZONE FORECAST TEXT PRODUCT...AND
HAZARDOUS WEATHER OUTLOOK TO REMOVE MENTION OF FOG. ALSO REMOVED
ANY OUTDATED WORDING FROM THE ZONES. THE FORECAST IS OTHERWISE ON
TRACK WITH NO OTHER CHANGES NEEDED.

UPDATE ISSUED AT 800 AM EDT SAT APR 18 2015

HOURLY GRIDS HAVE BEEN UPDATED BASED ON RECENT OBSERVATIONS. NO
MAJOR CHANGES WERE NEEDED AT THIS TIME. THE FOG IS STILL EXPECTED
TO LIFT AND DISSIPATE AROUND 9 AM EDT.

&&

.SHORT TERM...(TODAY THROUGH SUNDAY)
ISSUED AT 345 AM EDT SAT APR 18 2015

SHORTWAVE UPPER LEVEL RIDGING AND RIDGING EXTENDING DOWN TO NEAR
THE SFC WAS THE DOMINANT FEATURE ACROSS THE LOWER OH VALLEY AND
INTO THE CENTRAL APPALACHIAN REGION. WITH MAINLY JUST CIRRUS
OVERHEAD...TEMPERATURES IN THE VALLEY LOCATIONS HAVE DROPPED OFF
WELL INTO THE 50S. VALLEY FOG HAS BEGUN TO DEVELOP...ACROSS THE
CUMBERLAND VALLEY PER SME AND EKQ OBS. IN OTHER LOCATIONS...RH
FROM KY MESONET SITES AND THE SLOWING RATE OF TEMPERATURE DROP AS
WELL AS IOB OBSERVATION POINT TOWARD VALLEY FOG ELSEWHERE AS WELL.
THIS VALLEY FOG SHOULD CONTINUE TO DEVELOP OVER THE NEXT COUPLE OF
HOURS. UPSTREAM OF THE REGION A CLOSED LOW CONTINUED TO SPIN OVER
THE SOUTHERN CO/NORTHER NW REGION WITH MOISTURE STREAMING NORTH
ACROSS MUCH OF THE SOUTHERN PLAINS INTO THE CENTRAL  PLAINS
REGION...ESPECIALLY FROM EAST TX NORTH INTO KS AND MO.

THROUGH THE SHORT TERM PERIOD...THE CLOSED LOW IS EXPECTED TO MOVE
EAST INTO THE CENTRAL PLAINS AND APPROACH THE MID MS VALLEY
REGION. AS IT DOES SO...IT WILL BEGIN TO MERGE WITH A NORTHERN
STREAM SYSTEM DROPPING SOUTHEAST. THIS NORTHERN STREAM SYSTEM WILL
BE NEARING NW ONTARIO BY THE END OF THE PERIOD. WEAK SHORTWAVES IN
THE SOUTH TO SOUTHWEST FLOW ALOFT SHOULD MOVE ACROSS THE TN AND OH
VALLEY REGION FROM TONIGHT THROUGH THE END OF THE PERIOD. THE MOST
SIGNIFICANT ONE HOWEVER...WILL ROTATE INTO THE REGION LATER
TONIGHT AND INTO THE DAY ON SUNDAY. AT THE SAME TIME...SOMEWHAT
COMPLEX AND BAGGY SFC LOW PRESSURE IS EXPECTED TO DEVELOP OVER THE
LOWER MS VALLEY REGION BY THIS EVENING  AND THEN TRACK NEARLY DUE
NORTH TO NEAR THE CONFLUENCE OF THE OH AND MS RIVERS BY DAWN ON
SUNDAY. THE SFC LOW SHOULD THEN TRACK NORTHER NORTH TO JUST SOUTH
OR SOUTHEAST OF LAKE MICHIGAN BY THE END OF THE PERIOD. AS THE
LOW TRACKS NORTH IT WILL SEND A WARM FRONT NORTH INTO EASTERN KY
ON SUNDAY. LATE IN THE PERIOD...THE SW CORNER OF THE CWA MAY BE IN
THE WARM SECTOR BETWEEN THE WARM FRONT AND A COLD FRONT NEARING
THE MS VALLEY. THIS SYSTEM WILL TRANSPORT DECENT MOISTURE NORTH
INTO THE REGION AND WITH SOME MID LEVEL SUPPORT AS WELL AS
ISENTROPIC LIFT...MEASURABLE RAIN IS ANTICIPATED AREA WIDE...
ESPECIALLY ON SUNDAY. THUNDERSTORMS AREA ALSO POSSIBLE...
ESPECIALLY FROM LATE TONIGHT AND INTO THE DAY ON SUNDAY. IF
DESTABILIZATION CAN OCCUR...ESPECIALLY ACROSS THE SOUTH OR
SOUTHWEST...A STRONGER STORM OR TWO CANNOT BE RULED OUT.

AS FOR THE NEAR TERM...THE VALLEY FOG SHOULD LIFT AND DISSIPATE
BY ABOUT 14Z...OR 10 AM. THEN SUNSHINE THROUGH SOME HIGH CLOUDS IS
ANTICIPATED. TEMPERATURES SHOULD WARM WELL INTO THE 70S AND REACH
OR EXCEED 80 IN SEVERAL LOCATIONS. MOISTURE MAY INCREASE JUST
ENOUGH NEAR THE TN BORDER EAST TO RIGHT ALONG THE VA BORDER WHERE
MODELS INDICATE A SUBTLE CONVERGENCE ZONE FOR A STRAY SHOWER OR
TWO LATE THIS AFTERNOON OR EVENING. THE CONSENSUS OF THE SHORT
TERM AND HIGHER RESOLUTION MODELS SUCH AS THE NAM...HRRR AND THE
RAP POINT TOWARD THIS POTENTIAL. HOWEVER...THE BULK OF THE SHOWERS
SHOULD HOLD OFF UNTIL AFTER DARK...AND IN FACT AFTER MIDNIGHT OR
LATER IN MOST LOCATIONS. INSTABILITY MAY INCREASE ENOUGH FOR A
FEW EMBEDDED RUMBLES OF THUNDER ACROSS THE SOUTHWEST OVERNIGHT.
THE PRESSURE GRADIENT WILL ALSO BE INCREASING AS THE NIGHT
PROGRESSES AND INTO THE DAY ON SUNDAY. THIS SHOULD LEAD TO THE
HIGHER ELEVATION EXPOSED LOCATIONS SUCH AS THE TOP OF BLACK MTN
AND THE VALIDATES AREA OF PIKE COUNTY PICKING UP SUSTAINED WINDS
OF 15 TO 20 MPH AFTER MIDNIGHT ON SUNDAY TOWARD DAWN. SOME GUSTS
THERE IN THE 30 TO 40 MPH RANGE ARE CERTAINLY POSSIBLE. THE
SOUTHEAST FLOW PATTERN WILL NEED TO BE WATCHED FOR POSSIBLE MTN
WAVE GUSTS INTO HARLAN AND LETCHER COUNTIES JUST DOWNWIND OF BLACK
AND PINE MOUNTAINS. THE FORECAST SOUNDINGS FROM THE NAM SEEM TO
SHOW MIXING FOR SEVERAL THOUSAND FEET ABOVE THE TOP OF THE BLACK
MTN AND HIGH KNOB REGION WHILE THE GFS SOUNDINGS HAVE THE TOP OF
THE INVERSION NEAR 850 MB...SO THIS LEADS TO UNCERTAINTY IN ANY
POSSIBLE MTN WAVE DEVELOPMENT LATE ON SAT NIGHT NEAR THE VA
BORDER.

OTHERWISE...A BAND OF SHOWERS IN ADVANCE OF THE WARM FRONT SHOULD
LIFT NORTHEAST...WITH THE BULK OF THE SOUTHWEST PART OF THE CWA
STANDING THE BEST CHANCE FOR MEASURABLE RAIN BEFORE DAWN ON
SUNDAY. THE REMAINDER OF THE AREA SHOULD RECEIVE SHOWERS AND SOME
EMBEDDED THUNDER FROM SUNDAY MORNING THROUGH MID AFTERNOON ON
SUNDAY. AS ALREADY MENTIONED...SOME REDEVELOPMENT WOULD BE
POSSIBLE MAINLY ACROSS THE SOUTHWEST LATE IN THE DAY. A STRONG
STORM OR TWO CANNOT BE RULED OUT IN THAT AREA WITH STRONG WIND
GUSTS AND POSSIBLY MARGINALLY SEVERE HAIL. SPC HAS HIGHLIGHTED
THIS REGION FOR A MARGINAL RISK OF SEVERE THUNDERSTORMS WITH
PROBABILITIES MUCH HIGHER FROM THE MID MS VALLEY SOUTH TO THE GULF
COAST REGION.

.LONG TERM...(SUNDAY NIGHT THROUGH FRIDAY)
ISSUED AT 315 AM EDT SAT APR 18 2015

FIRST ROUND OF SHOWERS AND THUNDERSTORMS WILL BE MOVING EAST OF
THE REGION TO START THE PERIOD. A LULL IN THE PRECIP WILL BE
POSSIBLE OVERNIGHT SUNDAY AS ANOTHER LOW PRESSURE DEVELOPS ACROSS
THE MIDWEST. THIS WILL BE PRIMARILY DUE TO ANOTHER SPOKE OF
ENERGY ROUNDING THE BASE OF A NORTHERN STREAM UPPER LEVEL CLOSED
LOW. THIS WILL SWING A COLD FRONT ACROSS THE REGION MONDAY WITH
INCREASED CHANCES OF SHOWERS AND THUNDERSTORMS ESPECIALLY IN THE
AFTERNOON. THE MODEL SOUNDINGS ARE MEAGER WITH THE QPF AND
MOISTURE IS SHALLOW WITH PWATS AROUND AOA 0.80 DURING THE DAY ON
MONDAY. THEREFORE KEEP QPF AROUND A QUARTER OF A INCH IN THE
AFTERNOON. MODELS ARE IN GOOD AGREEMENT WITH THE SETUP AND
PROGRESSION OF THIS SYSTEM THIS FRONT WILL USHER IN COOLER AND
DRIER AIR AS WE MOVE INTO THE EARLY PART OF NEXT WEEK. HIGH
TEMPERATURES WILL TOP OUT IN THE LOWER 60S BY TUESDAY AND LOWS IN
THE LOWER 40S AT TIMES. MODELS ARE A BIT MORE DIVERGENT AS WE MOVE
INTO THE LONGER RANGE PORTION OF THE FORECAST. THE GFS WANTS TO
BRING A WEAK WAVE ACROSS THE REGION AS WE MOVE INTO EARLY
WEDNESDAY...WHILE THE ECMWF AND GEM ARE A BIT DRIER. THERE SEEMS
TO ALSO BE A WEAKER FRONT DURING THIS PERIOD AS WELL...HOWEVER
GIVEN THAT THE QPF IS QUITE LOW WILL LEAN TOWARD THE SLIGHT POPS
GIVEN IN THE BLEND. THESE POPS PERSIST INTO THURSDAY AT THIS POINT
AND THIS SEEMS REASONABLE GIVEN THE UNCERTAINTY ASSOCIATED WITH
THE GUIDANCE IN THIS PERIOD.

THEN WE TURN OUR EYES TO A MORE SUBSTANTIAL SYSTEM AS WE MOVE INTO
FRIDAY TIME FRAME. THIS IS ASSOCIATED WITH A SHORTWAVE EJECTING
OUT OF THE DESERT SOUTHWEST FRIDAY. DIFFLUENCE ALOFT WILL AID IN
SPREADING OVERRUNNING PRECIP EAST INTO THE REGION LATE FRIDAY.
THE GFS IS THE MOST PROGRESSIVE...BUT BOTH MODELS THE GFS AND
ECMWF AT LEAST HAVE THE GENERAL SETUP AS WE MOVE INTO LATE NEXT
WEEK. THIS DEVELOPING SYSTEM IS ALSO CORROBORATED BY THE 00Z GFS
ENSEMBLE MEAN...WITH DECENT CONTINUITY BETWEEN THE OPERATIONAL
RUN. RIGHT NOW WILL KEEP POPS IN THE SLIGHT TO CHANCE RANGE ON
FRIDAY AS MOST THE BETTER DYNAMICS COME INTO PLAY AS WE MOVE INTO
FRIDAY NIGHT AND SATURDAY WHICH ARE BEYOND THE SCOPE OF THIS
FORECAST PERIOD.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 750 AM EDT SAT APR 18 2015

ONCE LINGERING FOG IN THE VALLEYS AND SOME LOCATIONS WHERE THE FOG
HAS LIFTED TO THE RIDGETOPS DISSIPATES THROUGH AROUND 13Z...12 TO
15 HOURS OF VFR IS EXPECTED AS HIGH PRESSURE DOMINATES. HOWEVER...
AS THE NEXT LOW PRESSURE SYSTEM APPROACHES...IT WILL SEND A WARM
FRONT TOWARD THE LOWER OH VALLEY REGION. IN ADVANCE OF THIS WARM
FRONT...THE ATMOSPHERE WILL SATURATE AND RAIN SHOWERS AND POSSIBLY
A STRAY THUNDERSTORM OF TWO ARE EXPECTED...MAINLY BETWEEN 5Z AND
12Z. VIS AND OR CIGS AT LOZ AND SME SHOULD FALL INTO THE MVFR
RANGE BEFORE THE END OF THE PERIOD...AND IFR IS POSSIBLE IF
RAIN FALLS HARD ENOUGH.


&&

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

$$

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


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