Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 191514

National Weather Service Jackson KY
1014 AM EST Fri Jan 19 2018

Issued at 1013 AM EST FRI JAN 19 2018

Updated the grids to input the latest observations and trend them
into the noontime hours. Clears skies will be in place through
the day.

UPDATE Issued at 705 EST FRI JAN 19 2018

Hourly grids have been freshened up based on recent observations.
After a chilly start in the valleys in the 5 to 10 above zero
range, with high pressure in control and mostly sunny to sunny
skies expected along with continued warm advection, temperatures
will moderate to near normal levels.


.SHORT TERM...(Today through Saturday)
Issued at 359 AM EST FRI JAN 19 2018

Early this morning, a trough extended from the Canadian Maritimes
into the Mid Atlantic States. A shortwave ridge was off the mid
Atlantic states while a shortwave trough with little moisture
extended from the OH Valley to TX. At the surface, high pressure
was centered over the Gulf Coast States with ridging north into
the Appalachian region. A considerable ridge to valley
temperature split was in place this morning, with some of the
normally colder valley locations in East KY around 10 above at
this time and ridges and more open terrain areas in the low to mid
20s. 850 mb temperatures have warmed considerably over the past 24
hours and were around 1C at this time. Snow cover remains in many
locations with about 2 inches at JKL with 2-4 inches likely in
many locations, with lesser amounts on south and west slopes and
in some deeper valleys.

The snow cover and cold valley start should again limit how far
temperatures can climb today despite continued warm advection as
the center of the surface high moves to the south and east with
return flow between this high and lower pressure over the High
Plains continues. 850 mb temperatures should moderate to around 4C
by this evening and or roughly 3 or 4C higher than Thursday
evening. This and less of a snow pack and mostly sunny skies with
just some high clouds should yield high temperatures around 10F
higher than Thursday. The MET MOS seems to again be a high
outlier with the MAV MOS and Superblend in the low to mid 40s or
very close to normal for this time in January. Did not stray far
from the Superblend guidance though with the snow cover opted to
undercut it by about a degree or two.

High pressure will remain across the Southeast Conus tonight and
into the day on Saturday. However, models have a west to west
southwest low level jet developing tonight and into Saturday which
combined with an upper low moving into the Southeast bring
increasing low level and moisture and clouds late tonight and into
the day on Saturday. After another night with rather steep
nocturnal inversion and ridge/valley temperature split and
normally colder eastern and southeastern valleys in the upper
teens to around 20 and ridges in the upper 20s to around 30, the
increasing low clouds should suppress highs on Saturday below
previously forecast values in the mid 50s to closer to Superblend
numbers nearer to the 50 degree mark.

The low level moisture will increase in depth on Saturday and
some sprinkles or light drizzle cannot be ruled out completely
late on Saturday or Saturday evening. Confidence in timing of the
moisture increase and depth was not high enough just yet to
introduce any sprinkles or slight pops late in the period. At this
time any measurable precipitation should hold off until the start
of the long term period when low level moisture will deepen

.LONG TERM...(Saturday night through Thursday)
Issued at 350 AM EST FRI JAN 19 2018

The models are in reasonable agreement with the long wave pattern
for most of the extended period. The period will begin with the
closed near the Gulf Coast region and pseudo zonal pattern across
the Ohio Valley. The system of interest for the period will be
centered near the four corners region. This upper level closed low
will eject into the Central Plains by Sunday and eventually move
into the Upper Midwest by the Monday. This upper low will track
across the Great Lakes Monday night into Tuesday and then the
pattern flattens again in wake of the upper level trough.

The period will begin will solid return flow in place across the
Ohio and Tennessee Valleys. The issue for Saturday night into
Sunday will be the isentropic lift ahead of the approaching cold
front. We will see enough low level moisture in place to produce
some light rain and maybe even drizzle at times Saturday night
into Sunday. This shallow moisture will begin to lift by late
Sunday afternoon into Sunday and provide a brief period of dry
weather. As the closed low ejects into the Central Plains it will
bring a PV anomaly east and lead to deepening of a surface low as
it moves northeast into the Upper Plains.

This previously mentioned system will eventually send a cold front
across the Ohio and Tennessee Valleys and lead to widespread rain
showers across the region Monday into Monday evening. The timing
on the front has been a bit slower in the ECMWF compared to the
GFS, but given the front and low level jet felt the categorical
POPs were warranted. In the wake of the front the models disagree
on the amount of left over moisture Monday night into Tuesday.
Given this will stick with the lower blended guidance for now. The
soundings do suggest you get into the ice eventually so at least
some spots could see a mix of rain and snow before the better
moisture exits. It should be mentioned, ahead and on the backside
of this system will be the potential for gusty winds given the
tightening pressure gradient and strengthening low level jet. We
will be cooler and drier in the wake of the cold front Tuesday
into Wednesday night, but these numbers will be close to normal
values for this time of year, with highs in the low to mid 40s and
lows in the upper 20s.


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

High pressure across the southeast Conus will lead to mostly
clear skies and VFR conditions with winds of 10KT or less through
the TAF period. Moisture will begin to increase late in the
period and some low or mid level clouds will be possible. However,
VFR should prevail through the period.




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