Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 131056 AAC
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
656 AM EDT Fri Oct 13 2017

.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 12Z TAFS through 12Z Friday night)
ISSUED AT 700 AM EDT FRI OCT 13 2017

Areas of dense valley fog have developed overnight and has
affected the TAF sites per obs and GOES 16 Nighttime Microphysics
RGB. Initial IFR conditions, possibly below airport min, will
improve through around 14Z to 15Z. A brief period of stratocu in
the MVFR range is possible as the fog lifts before all locations
improve to VFR. Valley fog could again form tonight, with MVFR
status or stratocu possibly being more favored in the west as
southerly flow lead to increasing low level moisture.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 10 AM EDT this morning for KYZ044-
050>052-058>060-068-069-079-080-083>088-104-106>120.

&&

$$

UPDATE...JP
SHORT TERM...JP
LONG TERM...KAS
AVIATION...JP



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