Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 181840 AAA

National Weather Service Jackson KY
240 PM EDT Mon Sep 18 2017

Issued at 200 PM EDT MON SEP 18 2017

Did a quick update mainly to fine tune sky cover and adjust the
near term T/Td grids per the latest obs and trends. These have
been sent to the NDFD and web servers.

UPDATE Issued at 1050 AM EDT MON SEP 18 2017

14z sfc analysis shows a relatively weak area of high pressure in
place over eastern Kentucky. Once again, this did lead to a good
night of radiational cooling which allowed areas of fog to form
during the night becoming locally dense in the river valleys. The
fog has just about dissipated now with mostly sunny skies in
place. Some mid and lower level clouds are found to the west and
drifting this way. The high res models are still indicating that
a few showers or a storm could develop this afternoon in the
western parts of the CWA so that part of the forecast appears to
be on track. Currently, temperatures are running in the mid to
upper 60s most places while dewpoints remain elevated in the low
60s and winds are light/variable. Updated the grids mainly to
remove the fog, incorporate the latest obs and trends into the T
and Td grids, and also to adjust the sky cover toward current
conditions post fog lift out. The grids have been sent to the NDFD
and web servers. An updated HWO and set of zones have been issued,
as well.

UPDATE Issued at 629 AM EDT MON SEP 18 2017

No update needed at this time with fog still ongoing in the
valleys. Just made a few minor tweaks to temperatures to account
for latest trends.


.SHORT TERM...(Today through Tuesday)
Issued at 341 AM EDT MON SEP 18 2017

Areas of dense valley fog have developed this morning and much
like the past few mornings, will continue past daybreak before
burning off by 10 am. As for the rest of the day, mid/upper level
ridging will remain in place today, keeping a rather stout cap in
place. However, 00z models are showing a bit of a weakening in
the cap in our southwest zones (near the I-75 corridor and west)
this afternoon. This weakening could coincide with a few isolated
showers this afternoon. Confidence is not high on this activity
developing as overall forcing will be weak, but could be enough
moisture pooling to allow for a few cells to pop up. Any activity
will quickly fade away this evening. As skies clear out once more,
another night of dense valley fog is anticipated with little
change from the current night.

Better rain chances will spread in on Tuesday as a mid level vort
max crosses the Ohio river valley bringing some height falls.
This should help to weaken the cap and provide some weak forcing
allow for isolated to scattered showers and storms. No threat for
any strong storms as wind shear will remain non-existent under the
upper level ridge.

.LONG TERM...(Tuesday night through Sunday)
Issued at 341 AM EDT MON SEP 18 2017

There is decent model agreement with an amplifying long wave
pattern. Deeper troughing establishes itself across the West,
with renewed ridging across the Great Lakes and Ohio Valley
regions, while the tropics remain active across the western
Atlantic and into the Eastern Seaboard.

Initially, the ridging in the East will be weaker, allowing for
some passing short wave energy to allow for the small threat of
mainly diurnally driven showers and a few thunderstorms. For
eastern Kentucky, the highest overall POPs for the middle and
end of the week look to occur on Wednesday. For Thursday and
Friday, some slight chances will be possible along the far south
and near the terrain, where enough moisture may pool to allow for
a few afternoon and evening pop ups.

This weekend, both the GFS and ECMWF show a building ridge across
the Great Lakes and Ohio Valley regions. The ECMWF is a little
stronger with the ridge, suppressing convection across the area,
while the GFS is a bit weaker, allowing for a few storms along
the terrain and west of I-75. Given the overall strength of the
ridge and predominantly east and northeast flow in the lower
atmosphere, will go with a dry forecast. Consequently, went a
touch higher than the blended guidance for the highs.

Temperatures throughout the period will average above normal, with
highs in the low to mid 80s, and lows around 60.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)

After a day and evening of VFR conditions, fog is expected again
tonight, with developing commencing after 03z, but not likely
impacting TAFS until after 06z. Fog should be similar to the
past several nights and be confined mainly to the valleys, but
still creep up into a couple of the airport sites for a time. Have
used a tempo in a few of the TAFs for this concern. Light winds
are expected through the period.




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