Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 250705

National Weather Service Jackson KY
305 AM EDT Sat May 25 2019

Issued at 105 AM EDT SAT MAY 25 2019

Models are generating precip toward dawn and into the day
Saturday. This occurs as moisture is advected northeastward into
the area around 800-850 mb overnight. Clouds with this are evident
over western KY and middle TN currently. Have further fined tuned
POPs based on the NAM and HRRR, with values currently capped at
low chance, and the highest probability in our northern counties.
However, pending development, this may need to be raised at a
later time for some locations. Have also updated overnight lows
based on latest trends.

UPDATE Issued at 1059 PM EDT FRI MAY 24 2019

Issued an update to the forecast to input the latest observations
into the grids and trend them through the overnight hours. Some
fog is likely buy confined to the river valleys. This certainly
won`t be dense. A weak disturbance crossing the along northern KY
will pose the small chance of a few showers and thunderstorms late
tonight and into the day tomorrow. Due to the amount of
instability tomorrow, will leave the chance for precip in.

UPDATE Issued at 747 PM EDT FRI MAY 24 2019

Issued an update to input the latest observations and trend them
through the evening and into the overnight hours. The cap in place
is too strong this evening so have cut out the pops this evening
into much of the overnight. Showers and storms will still be
possible late tonight as another weak disturbance will move into
the area.


.SHORT TERM...(This evening through Saturday night)
Issued at 334 PM EDT FRI MAY 24 2019

The afternoon surface analysis shows a boundary remains nearby,
with high pressure off to our south. The low level convergence for
forcing has been east into West Virginia and therefore have kept
PoPs in the slight range in the far east this afternoon. Any
convection that does fire today will diminish this evening, as we
loose the day time heating and better instability. Given the lack
of better moisture from storms did reduce fog to patchy given the
persistence of lesser fog over the past few days.

The NAM and some of the CAMs have supported the idea of greater PoPs
early in the day Saturday and lesser in the afternoon. This seems
to be driven by an upper level wave at the 500mb level riding
along in the quasi-zonal flow setting up across the Ohio Valley.
Did Place better PoP around 17z to 18z timeframe, but this might
need to be adjusted back closer to the morning hours given the
wave timing. The short and longer range model blends supported
more in the afternoon hours, but leaned in the middle to best
capture a compromise in the timing of better convection.

Fog for Saturday night will be dependent on if and where rain
falls during the day on Saturday, but kept the idea of river
valley fog going from previous forecast package. Given the
clearing skies and nearby ridging will keep the slight
ridge/valleys splits again for Saturday night, but a few more
clouds should arrive toward dawn Sunday influenced by approaching
upper level wave.

.LONG TERM...(Sunday through Friday)
Issued at 334 PM EDT FRI MAY 24 2019

Upper level ridging over the southeastern United States will be the
dominant weather feature for us during the first part of the coming
week. This will result in much above normal temperatures during the
first half of the week, and will tend to limit shower and
thunderstorm chances. Mean upper level troughing will continue
across the western U.S.

On Sunday a short wave trough moving through the Great Lakes and
Ohio Valley along the northern periphery of the ridge will result in
a weak cold front dropping south across OH and IN, possibly reaching
northern KY before stalling. This will bring a chance of showers and
thunderstorms to the northern part of the area. While the wind
fields will not be impressive, there should be considerable
instability. As a result a few storms in the northern part of the
forecast area could be strong on Sunday. The SPC Day 3 Thunderstorm
Outlook has the marginal risk area just clipping the northern part
of our forecast area.

On Monday the front should lift back northeast as a warm front, and
this will keep a small chance for showers and storms in the
northeast part of the forecast area. The dominant upper level ridge
will then reassert itself with dry hot weather on Tuesday. On
Wednesday significant short wave energy ejecting out the mean
western trough will move northeast and interact with upper level low
pressure over central and eastern Canada. As result the mean
southeast U.S. ridge will be suppressed during the latter part of
the week, with a surface cold front likely pushing south across our
area on Thursday. This will bring the best overall chances of
showers and thunderstorms to the area during the coming week, with
temperatures closer to normal by Friday.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)

Mainly VFR conditions with clear skies prevailed at the start of
the period. However, valley fog was beginning to develop over
south central and southeast KY, and will continue to become more
prevalent overnight. It will bring localized VLIFR conditions
until a little past sunrise, but should not affect TAF sites.

An area of clouds with bases around 5K ft was over south central
KY at the start of the period, with a few showers as well. This
area of clouds is expected to develop northeastward overnight and
on Saturday, and the showers will expand in coverage, with
thunderstorms also possible. This will affect much of the JKL
forecast area, especially our northwestern counties. Sub-VFR
conditions will be possible in the heavier showers or
thunderstorms. However, timing uncertainty and expected coverage
don`t support using anything more than vcsh or vcts in TAFs. The
precip is expected to exit to our east and northeast by late in
the day, leaving VFR conditions with mostly clear skies from
Saturday evening through the end of the period.




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