Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 180541 AAC

National Weather Service Jackson KY
141 AM EDT Wed Oct 18 2017

Issued at 137 AM EDT WED OCT 18 2017

High pressure remains in control of the weather across the OH
Valley early this morning. A few high clouds are passing across
the region at this time. GOES 16 data indicate that river valley
fog has begun to form and given low or 0 dewpoint depressions in
these locations and light winds it should become dense in some
locations and persist until after sunrise. The current SPS and
social media messaging have this well covered at this point. Hourly
grids of wx, T, and Td have been updated based on recent
observations and trends. However, this led to no substantial
changes at this time.

UPDATE Issued at 1050 PM EDT TUE OCT 17 2017

Temperatures are running a couple degrees above last night`s
values at this time so the current forecast and just spotty frost
looks to be on track. Have updated and sent out the SPS for this
and dense river valley fog. Also updated the T and Td grids per
the latest obs and trends. These have been sent to the NDFD and
web servers.

UPDATE Issued at 8:00 PM EDT TUE OCT 17 2017

23z sfc analysis shows high pressure firmly in control of the
weather through eastern Kentucky. However, a batch of generally
thin and high clouds will cross into the region through at least
the first part of the night likely affecting the otherwise perfect
conditions for radiational cooling. We should still see
temperatures fall into the mid and upper 30s in the more sheltered
locations with low 40s found on the ridges by dawn. Again expect
the fog to dominate over frost with dense areas anticipated along
the rivers and lakes. Given the widely scattered frost and dense
fog issues late tonight into Wednesday morning will continue the
highlights in the ongoing SPS and HWO. Currently readings are in
the mid 50s on the ridges with upper 40s seen already in the
sheltered valleys while dewpoints are generally in the upper 30s
to lower 40s and the winds remain light. have updated the
forecast mainly to fine tune spot min temperatures and frost/fog
configuration later tonight. Did also incorporate the latest T/Td
obs and trends into those grids along with an update to sky cover
through the near term. These grids have been sent to the NDFD and
web servers.


.SHORT TERM...(This evening through Wednesday night)
Issued at 305 PM EDT TUE OCT 17 2017

The afternoon surface analysis shows a fairly broad area of high
pressure extending from the Mid-Atlantic to northeast Arkansas.
The highest surface pressure seems to point to West VA being
closest to the center of this high. The latest GOES-16 Sat data
shows a few high clouds now moving into western Kentucky in
advance of a weak upper level trough. These clouds will advance
eastward tonight and this could play a tricky role on fog and
frost overnight. Overall keep the coldest temperatures in the far
eastern deeper valley locations where you are getting better
mixing of drier air than yesterday. Given the potential for fog
and at least patchy frost will lean toward a SPS for now, as
factors mentioned before lead to some potential complications in
formation of weather elements. The frost and fog will generally
dissipate between 13 the 14Z Wednesday morning and we will be left
with mostly sunny skies. There could be a few afternoon high
clouds as the upper level wave axis moves slowly eastward across
the Ohio Valley. The area of surface high pressure will however
remain near by and lead to clear and calm conditions again
Wednesday night. That said, the temperatures will remain coolest
in the far eastern valleys based on the surface high location and
slight height rises in the Lake Cumberland region. Given the
temperatures are not as low will keep the patchy valley fog
mention only.

.LONG TERM...(Thursday through Tuesday)
Issued at 305 PM EDT TUE OCT 17 2017

Dry and pleasant weather is in store for the majority of the
extended period, as a strong ridge of high pressure is forecast to
remain in place across the region. Daytime highs are expected to be
above normal during the period, with daily max values in the 70s
expected across the area. Nightly lows should also be above normal,
with nightly minimums ranging from the mid to upper 40s Thursday
night and Friday night and the upper 40s to mid 50s Saturday night
and Sunday night. A pattern change is in store to close out the
weekend, and based on the latest model data, it appears that next
batch of rain will arrive in the area Sunday night, as a large
trough of low pressure, and its attendant surface cold front, makes
it way across the central and eastern CONUS. The highest probability
for rain will likely be from around dawn on Monday through Monday
night, as the cold front moves slowly across the region. Light to at
times moderate rain showers will affect eastern Kentucky during the
passage of the front. Another shot of colder air is expected to
filter into the area once the front passes by to begin the upcoming
work week.


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

High pressure will remain in control of the weather through the
TAF period. Mostly VFR conditions are expected to persist through
the period, with the exception being in the river valleys and near
larger creeks and lakes, where fog that has already developed or
will be developing over the next few hours could become dense in
some locations, especially between 8Z and 13Z. Some of the fog
could advect into SME overnight with this less probable at the
other TAF sites. The fog will lift and should dissipate between 13
and 14Z. Winds through the TAF period will remain light averaging
out of the southeast to south.




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