Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 131849
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
249 PM EDT Fri Oct 13 2017

.UPDATE...
Issued at 1236 PM EDT FRI OCT 13 2017

Did an update to remove fog wording from the forecast package.
Also made sure the near term forecasts were on track with current
observations, especially the temperatures and winds. Otherwise
forecast is in good shape thus far. All updates have been sent to
NDFD/web.

UPDATE Issued at 1015 AM EDT FRI OCT 13 2017

Loaded in the latest observations to make sure the near term grids
were on track with current conditions, especially the temperatures
as they continue to warm this morning. Fog is still prevalent
across eastern Kentucky, but with abundant sunshine and heating it
is in the act of dissipating. As such, the Dense Fog Advisory was
allowed to expire at 10am despite some locations still reporting
dense fog. All forecast products were also updated to remove the
headline. All changes have been published and sent to NDFD/web.

UPDATE Issued at 645 AM EDT FRI OCT 13 2017

Expanded the fog advisory to include the remainder of the area.
Valleys across the remainder of the area experiencing dense fog in
many locations per reports and what can be inferred from GOES
imagery.

UPDATE Issued at 503 AM EDT FRI OCT 13 2017

GOES nighttime cloud microphysics RGB and observations continue to
to indicate that the dense fog is widespread in portions of the
Cumberland Valley. A dense fog advisory has been issued for that
area until 10 AM EDT.

&&

.SHORT TERM...(Today through Saturday)
Issued at 410 AM EDT FRI OCT 13 2017

Early this morning, surface high pressure was centered to the
northeast of the area though the ridge extended back into the Ohio
Valley region. Meanwhile an upper level ridge was centered over
the Lower MS Valley region and extended across the eastern Conus.
Low level moisture remains below about 5000 feet despite the
clearing that occurred on Thursday afternoon and evening. This
has given way to what appears to be extensive valley fog on GOES
16 imagery such as the nighttime cloud microphysics RGB and GOES
as it is likely rather16 10.3-3.9 fog product. Patchy stratus
and stratocu is also present.

The upper level ridge is expected to flatten a bit through the
period and become aligned from GA/Carolinas across the southeast
through the end of the short term period. At the same time, the
surface high will shift to the east and lead to increasingly
southerly flow today and on Saturday as a low pressure system
begins to approach.

The main forecast concern early this morning is the extent of
mainly valley fog through mid morning as well as stratus. For now
have continued with the SPS and highlighted the threat on social
media though the threat will continue to be monitored for a dense
fog advisory for portions of the area.

The fog should gradually lift through the morning into at least
some brief cumulus. With more sunshine compared to Thursday and
the model consensus of temperatures reaching the 70s to around 80,
a mild day is in store.

Low level moisture should increase starting today with dewpoints
climbing through the 50s. The depth of the low level moisture
should increase tonight per both the NAM and GFS and more in the
way of stratus and or stratocu formation is possible along with
some valley fog as well. If the moisture were to deepen
sufficiently, some drizzle could even fall from any potential
stratus particularly in the southwest part of the area. At this
point, drizzle was not included, but it is likely sky cover may
need to be increased for Saturday night and drizzle potential will
be monitored. The low clouds and status should gradually lift
into a cumulus deck on Saturday. Saturday will again be mild with
rather moist dewpoints for mid October.

.LONG TERM...(Sunday through Friday)
Issued at 250 PM EDT FRI OCT 13 2017

The focus of the Sunday through Friday period will be the passage of
a cold front on Sunday and a period of more autumn like weather next
week. Model trends point towards a quicker passage of the cold front
on Sunday, with the front clearing the area by early Sunday evening.
Instability on Sunday still appears limited, but there should be
enough instability in a narrow ribbon in advance of the front to
support at least the mention of a slight chance of thunder. We will
continue with the forecast of a slight chance of thunder on Sunday
which is in agreement with previous NDFD forecasts, and the latest
SPC Day 3 Outlook which places our entire area in the general
thunder outlook. Even if there end up being no thunderstorms on
Sunday, which certainly is possible, it will still be rather breezy
with some gusts to near 30 mph especially in the Bluegrass counties
and other more open areas.

A surface high will build into the area early next week in the wake
of the cold front, and bring drier and cooler conditions. The
superblend and model guidance support widespread mid to upper 30
degree minimum temperatures Tuesday morning and scattered mid and
upper 30 degree temperatures on Wednesday morning. Use of the
forecast builder generates areas of frost, especially on Tuesday
morning. However, as is often the case, fog formation in river and
stream valleys will inhibit frost formation. Despite that, some
areas should see their first frost of the season. We will continue
to highlight the frost possibility in the HWO. As the week
progresses the surface high will drift east and upper level ridging
with rising heights will bring a warming trend to the area.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
ISSUED AT 201 PM EDT FRI OCT 13 2017

Fog was slow to dissipate this morning, especially near the
Cumberland River, including KSME and KLOZ. Now sunny skies are in
place across all of eastern Kentucky with surface high pressure in
control. Winds will remain light and variable throughout the
afternoon and through the rest of the TAF period as well. The next
concern will be overnight when temperatures fall and another llvl
inversion sets up, trapping moisture near the surface. Given the
extensive fog last night, and a similar set up tonight with high
pressure in the area, expect another night of fog, especially in
the valleys. Went low end IFR conditions at all TAF sites (except
JKL which was not heavily impacted this morning), but it is
possible that all TAF sites could fall below that between 6 and
13Z. A small caveat will be the western sites (KSME/KLOZ) which
could see some southerly flow pick up late in the night,
increasing the moisture and favoring more llvl stratus rather than
fog. If winds don`t pick up until after daybreak however, as is
currently forecast, fog will still be favored. Fog will be slow to
dissipate once again during the morning tomorrow, but will
eventually give way to mostly clear skies and then some scattered
diurnal CU around 2500-3000ft in the afternoon.

&&

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

$$

UPDATE...JMW
SHORT TERM...JP
LONG TERM...SBH
AVIATION...JMW



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