Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 111130

National Weather Service Jackson KY
630 AM EST Mon Dec 11 2017

Issued at 630 AM EST MON DEC 11 2017

The forecast is looking good so far this morning, so no major
update is planned at this time. Used the latest obs to freshen
things up and establish new trends in the hourly forecast grids.


.SHORT TERM...(Today through Tuesday)
Issued at 427 AM EST MON DEC 11 2017

A complicated forecast is in store for the short term across
eastern Kentucky. Light precipitation is expected to begin moving
into the area late tonight ahead of an approaching and fast moving
area of low pressure aloft. Precipitation should begin as drizzle
and then transition to a mix of freezing drizzle, drizzle, and
light snow showers during the early morning hours just before
sunrise on Tuesday. Once we get more ice aloft early Tuesday
morning, the precipitation should then transition over to a mix of
rain and snow showers, and then all snow showers as temperatures
fall to around freezing by late morning and early afternoon. There
could be enough ice accumulation to create some slick spots on
area roadways early Tuesday morning, so caution should be used if
out driving during that time. Any snow accumulations on Tuesday
should be light and confined mainly to ridgetops, grassy areas,
and elevated surfaces. Temperatures will be fairly mild today,
with highs forecast to reach the mid to upper 40s for most
locations. A few spots along the Tennessee border may see the
lower 50s, and a few north locales may only reach the lower 40s.
We will see dry conditions today through early tonight along with
generally partly cloudy skies. Overnight lows should fall to
around freezing. Tuesdays highs are expected to max out in the low
to mid 30s, most likely early in the morning before the bulk of
the expected snow begins to fall. Temperatures will then likely
begin falling during the day, as our upper level weather system
begins to pull east of the area.

.LONG TERM...(Tuesday night through Sunday)
Issued at 445 AM EST MON DEC 11 2017

The models are in general agreement aloft through the extended
portion of the forecast, though they still differ significantly
on some of the key smaller scale features that will affect the
area during this time frame. For the bulk of the long term,
troughing will dominate the northeast quarter of the nation. The
core of this trough will move from the central Great Lakes east to
northern New England from Tuesday night into Wednesday. As it
does so the heights will rebound over eastern Kentucky from very
low values Tuesday evening. The flattening northwest flow in the
wake of the larger trough`s departure will support a minor wave
rolling east into Kentucky Wednesday night - strongest in the
ECMWF as it has been for the past few runs. This wave now has some
support from the CMC but the GFS is weaker and further southwest
with its version of the impulse. Accordingly, confidence is lower
than normal for the mid portion of the extended. The models do
line up better by the end of the work week as a full latitude
trough takes shape with plenty of energy spreading into the Deep
South. Again the ECMWF is the strongest with this portion of the
trough than the other models but that has been the case for the
past several runs. Leaning towards the Euro solution will limit
the impacts for eastern Kentucky, though. The models all carry
this trough through the area by Friday evening with heights on the
rebound for the weekend in northwest, to increasingly zonal, 5H
flow. Upstream another smaller trough will take shape and head
toward the area for Sunday, but the pattern buckles enough that
eastern parts of the nation will see southwest flow ahead of this
trough along with some decent height rises. The meat of this
trough reached the JKL CWA Sunday afternoon in the ECMWF but not
until that night in the GFS. This uncertainty and the amount
earlier in the period makes a general model blend the best
starting point option but some adjustments will be needed at
times to lean more strongly toward the ECMWF - in general.

Sensible weather will feature a very cold start to Wednesday in
the wake of a fast moving clipper system with readings in the
teens most places and brisk winds driving wind chills down into
the single digits around dawn. After a chilly day Wednesday the
night will be milder than Tuesday`s as a WAA pattern takes hold
at least briefly ahead of the next clipper system inbound for
Thursday. This one looks to bring another quick shot of colder
air into eastern Kentucky along with the threat for additional
light pcpn. This will take the form of rain showers during the
day possibly mixing with snow showers by evening before continuing
as scattered light snow showers through the night into Friday
morning for most of the area - departing late in the far east.
Warmer conditions truly move in on Saturday and continue into
Sunday with low 50s anticipated for highs to close out the weekend
though a southern sfc wave looks to bring rain chances to the area
from the southwest, as well.

Made only minor adjustments to temperatures through the period
mainly for terrain effects Wednesday and Friday/Saturday nights.
Again more substantial adjustments were made to PoPs and snow
chances through the week beefing up the potential lingering in our
higher terrain Tuesday night and again for Thursday evening into
the day Friday.


.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)

A ridge of high pressure will bring mostly clear to partly cloudy
skies to the TAF sites through the end of the period. Winds
should remain out of the southwest or southwest through out the
period, peaking at around 5KTs Monday afternoon. We can expect
drizzle, freezing drizzle, and isolated to scattered light snow
showers to begin moving across eastern Kentucky after 6Z tonight.
The freezing drizzle could lead to some icing issues toward the
end of the TAF period. In spite of that, VFR conditions are still
expected to prevail through the end of the period.




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