Area Forecast Discussion
Issued by NWS Jackson, KY

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000
FXUS63 KJKL 131801
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
201 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...(Saturday night through Thursday)
Issued at 325 AM EDT FRI OCT 13 2017

Clouds will be on the increase Saturday night ahead of an
approaching cold front. The clouds and increasing gradient ahead
of the front will keep fog from forming overnight. The cold front
will slide southeast across eastern Kentucky during the day
Sunday. Models continue to trend towards a faster frontal passage,
and it now looks like the front will be through the area by early
Sunday evening. With increasing confidence on rain chances with
good GFS ensemble support, will go categorical with the rain
chances on Sunday. Plan to maintain the slight chance of thunder
as we can`t rule out some isolated storms. Should be a rather
gusty day for eastern Kentucky with some wind gusts up to 15 or 20
mph. A few high gusts would be possible on ridgetops and in the
Bluegrass region. Rain chances will diminish from northwest to
southeast Sunday evening with drier and much cooler weather
settling into the area to start the new work week. Highs on Monday
will only reach into the low 60s.

Strong upper level ridging will develop and maintain itself over
the region through the remainder of the week. As the ridge axis
slowly shifts east, heights will rebound allowing for a nice
recovery in temperatures as we head through the week. The airmass
will also feature very dry conditions. This will support
undercutting guidance dewpoints by a good 5 to 10 degrees each
afternoon, putting relative humidities down between 20 and 30
percent each afternoon. While the extended stretch of dry
afternoons is expected, winds should be fairly light through the
week, so wildfire concerns should remain somewhat low. We will see
areas of dense valley fog each morning through the week. Some
widely isolated instances of frost may be possible Tuesday and
Wednesday morning, although conditions continue to favor more of a
fog threat as cross over temperatures will remain somewhat
elevated.

&&

.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...KAS
AVIATION...JMW



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