Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 151547
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1147 AM EDT Sun Oct 15 2017

.UPDATE...
Issued at 1146 AM EDT SUN OCT 15 2017

A few isolated showers have developed ahead of the original
leading line of showers, while the original line has diminished on
the northern end. Main area of showers remains back across IN and
western KY closer to the cold front. Currently no lightning is
being detected with the convection, but a few lightning strikes
remain possible. Have updated NDFD and associated products mainly
to refine timing of showers and isolated thunderstorms.

UPDATE Issued at 947 AM EDT SUN OCT 15 2017

Low clouds are moving quickly into the eastern part of the
forecast area, and have updated NDFD to increase sky cover at a
faster pace. Timing the line of showers currently moving across IN
brings the first chance of rain to the northwest part of the
forecast area around 1PM. This is a about an hour faster than the
latest runs of the HRRR, but overall there is good agreement in
timing based on short range guidance, extrapolation and current
hourly NDFD. The leading edge of the showers have shown a
decreasing intensity trend, and with more extensive low level
cloud cover ahead of the convection limiting the chance for
increasing low level stability it may be hard to generate
convection that would produce thunder this afternoon.

UPDATE Issued at 745 AM EDT SUN OCT 15 2017

Low clouds continue to expand to the west and south of the area
early this morning as low level moisture increases in advance of
an approaching cold front. Meanwhile, fog lingers in some valley
locations, mainly in the Big Sandy Valley, but this should
continue to dissipate over the next hour or two. Hourly sky,
temperature and dewpoint grids have been updated accordingly.

&&

.SHORT TERM...(Today through Monday)
Issued at 358 AM EDT SUN OCT 15 2017

Early this morning, an upper level ridge was in place across the
southeast Conus with a trough moving through the Central Conus
and another ridge in place across the southwest Conus. At the
surface, an area of low pressure was moving into the Great Lakes
region with a cold front trailing south into the southern Plains.
High pressure was centered to the east and northeast of the area
and extended into the Southeastern Conus. Despite the increasing
pressure gradient between the approaching front and high, several
valley locations south of the Mountain Parkway corridor remain
decoupled per observations with GOES 16 satellite imagery
indicating generally less extensive valley fog compared to 24
hours ago.

Models remain in good agreement with the timing of the cold front
into the region today arriving during the afternoon as the
surface low tracks by well to the north of the region in advance
of the eastward moving upper trough. Low level moisture will
increase this morning as the front approaches and winds should
also increase in the morning as the pressure gradient tightens.
Mixing prior to the arrival of the front during the morning could
yield some wind gusts in the 20 to 30 mph range. A relatively
narrow band of showers and perhaps some thunderstorms should
accompany the front as it moves east. Instability is expected to
be limited as the front passes, but have continued with a slight
chance of thunderstorms. Some heating of the airmass should occur
ahead of the front so thunderstorms cannot be ruled out,
especially in the southeast half of the area per recent HRRR runs.
High temperatures should be reached around the arrival time of
the precipitation with a mixture of cold air advection and
wetbulbing leading to falling temperatures by mid afternoon into
the evening.

As the front pushes southeast, the threat for showers will
end from northwest to southeast during the evening. Models
continue to have the highest qpf in the southeastern counties or
in the area where convection could be a bit stronger due to
potentially greater instability. High temperatures should be
reached around the arrival time of the precipitation with a
mixture of cold air advection and wetbulbing leading to falling
temperatures by mid afternoon into the evening. Cold advection
will continue on Sunday night with temperatures dropping into the
40s or noticeably colder than recent days.

Behind the front on Monday, sfc high pressure will begin to build
into the area from the west. Lingering low clouds should lift and
decrease in coverage during the morning, eventually lifting into
a cumulus field and mixing out through late afternoon. High
temperatures will be considerably lower than recent days reaching
near the 60 degree mark, or about 8 to 10 degrees below normal for
mid October.

.LONG TERM...(Monday night through Saturday)
Issued at 235 AM EDT SUN OCT 15 2017

Models in good agreement on persistent upper level ridging to hold
over the region through the remaining portion of the week and
through next weekend. As the surface ridge slides east through the
week, the boundary layer will warm allowing for a nice recovery in
temperatures as we head through the middle to latter half of the
week. We could be approaching some record highs by late in the week
or next weekend. Continued to the trend of going on the high end
of guidance with temperatures for highs and colder at night. This
is in line with the very dry airmass over the region this week. We
will also contend with some valley fog each morning through the
week. Also, given the dry airmass, models are way too aggressive
in moisture recovery through the week, and continued to go well
under guidance for dewpoints through next Saturday. This puts
afternoon RH`s between 20 and 30 percent. Fortunately for wildfire
concerns, there should be almost no wind through the week.

Cross over temperatures heading into Monday night look to be
around 40, which is a tad high to support frost formation. Thus,
looking more like we should see primarily fog. However, better
mixing on Tuesday will bring the cross over temperatures down into
the low to mid 30s, setting the stage for slightly better frost
potential for Tuesday night, but confined to the coldest sheltered
eastern valleys. For the most part, this does not look like a
robust frost event for the area.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
ISSUED AT 947 AM EDT SUN OCT 15 2017

A quick update on aviation weather.Low clouds with MVFR ceilings
are spreading across the forecast area. The expectation is that
MVFR ceilings will prevail into the early afternoon in most areas.
Winds will gust in excess of 20 knots at times today, and have
already noted a 29 knot gust at SYM.

Previous discussion follows.

Low clouds in the MVFR or VFR range will increase this morning in
advance of a cold front per recent satellite trends as low level
moisture increases. A line of showers is expected to overspread
the area from northwest to southeast generally after 16Z, with a
few thunderstorms also possible. MVFR and some IFR reductions are
expected with these. Winds will increase into the 10 to 15KT range
through 16Z, with some gusts topping 20 kts. Some higher gusts
will be possible as the showers arrive and in any thunderstorms. A
shift in winds to the west northwest and eventually northwest
along with a decrease in speed is expected starting around 20Z
first in the northwest as the front passes. Low clouds in the MVFR
range will linger well into the second 12 hours of the period
behind the front.

&&

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

$$

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



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