Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 210554 AAA

National Weather Service Jackson KY
154 AM EDT Wed Mar 21 2018

Issued at 154 AM EDT WED MAR 21 2018

As the main low pressure system moves to our east, the
precipitation is pivoting around the low as seen by current radar
returns. For the next hour or so, the western portion of the CWA
will be in a precip lull according to latest radar trends.
Current obs show very little precip accumulation in the southwest
as well. Because of this, and the warmer temps to the southwest,
have lowered SnowAmt and QPF in the west/southwestern valleys a
touch to account for lower accumulation. Have also populated PoPs
with CONSShort to reflect the lull in precip in the west. Rain is
continuing to change over to snow for the far eastern portion of
the CWA, but should be all snow after 2 AM or so. Updates have
been sent to NDFD and the web.

UPDATE Issued at 1150 PM EDT TUE MAR 20 2018

The column continues to cool across the region as the upper level
low nears East KY and a surface low work into WV. Black Mountain
Mesonet temperatures have dropped to 27 from the mid 30s over a
couple of hours ago while the Pike County Mesonet has dropped to
32. Rain continues to change to snow from west to east and models
generally have precipitation mainly as snow overnight filling in
due to steepening lapse rates and upslope flow. The previous
forecast and amounts still appear on track so no major
adjustments were made at this time. Hourly temperatures and
dewpoints were freshened up with weather also refreshed

UPDATE Issued at 810 PM EDT TUE MAR 20 2018

Rain or drizzle continues across East KY although some
observations in the Bluegrass region such as LEX and DVK are now
reporting snow. Colder air continues to gradually advect in on
northwest winds with much of the western border of the CWA now at
34 to 35 degrees. The Koomer Ridge RAWS site at the top of Slade
is now down to 34 as well. Temperatures are also slowly dropping
in the higher terrain above 2500 feet with Black Mountain now down
to 38.

Temperatures will continue to slowly cool as the west to northwest
flow continues and the upper low center nears from Central KY. As
the column cools rain should change to wet snow over the western
counties over the next couple of hours and as temperatures cool
above 2500 feet a changeover to snow should occur there. The
remainder of the area should gradually change over to snow
overnight as temperatures cool toward the freezing mark. The
latest changeover should be in some of the deeper valleys in the
Big Sandy region and upper reaches of the Kentucky River and
Cumberland River basins. Temperatures were updated based on these
trends which generally cooled northern and western locations and
the high terrain a degree or two over the next few hours with
some adjustments also made to snow to liquid ratios to account for
marginal air temperatures and warm ground temperatures overnight
and into Wednesday.

These changes generally led to little substantial changes over
most of the area. However, a little quicker drop in higher
elevation temperatures resulted in higher amounts above 2500 feet.
In general, event total snowfall and location of the highest
amounts are generally in good agreement with the the High
Resolution Ensemble/SPC HREF peak amounts.

With temperatures near freezing and falling snow, the morning
commute should be impacted in several locations.


.SHORT TERM...(This evening through Wednesday night)
Issued at 351 PM EDT TUE MAR 20 2018

An upper level low will slowly drift across the area through
Wednesday. The milder temperatures presently over the area will
turn much cooler tonight as the system begins to move eastward.
The cooler temperatures over the western half of the state will
advect into the area with rain changing over to snow. The better
deformation zone for snowfall will reside to our north and
northwest overnight, but we should see enough wrap around moisture
to yield some light snow for most of the area through most of the
night. Areas in the east may not see a changeover until 5 or 6 am
as the warm air may hold on in the deeper valleys. The snow will
continue through the day Wednesday with the deformation band of
snow sinking southward into our area during the day. This will
lead to more snow. Surface temperatures will play a key role in
potential impacts as they may only fall to around freezing
tonight, then reach the mid 30s Wednesday afternoon. With the
already warm ground and solar insolation being late March, it may
be hard to accumulate much snow during the daylight hours on
Wednesday. Thus, our best potential for impactful snowfall will be
towards dawn tonight with temperatures a touch below freezing.
However, unless rates are sufficient enough, we may not see much
accumulation on roads. Thus, expecting most of accumulations to
occur on elevated surfaces or grassy areas. Elevations above 3000
feet may see more impact on the roads as temperatures stay below
freezing late tonight through Wednesday. going with snow ratios
generally around 10:1, brought snowfall amounts down a bit across
the board, but still generally in the 1 to 3 inch range for most

Snow will wind down to flurries Wednesday night before the
flurries end by dawn as much drier air works into the area. Skies
may actually clear out by Thursday morning as well. With skies
clearing late, we may see some cold temperatures down into the
lower to mid 20s, especially with any snow that may be on the

.LONG TERM...(Thursday through Tuesday)
Issued at 445 PM EDT TUE MAR 20 2018

The models are in fairly good agreement aloft through the start of
the weekend before the spread becomes rather large into early next
week. They all depict deep troughing spinning off the Northeast
Coast while ridging dominates the Rockies through the end of the
work week. The western ridge will break down later Friday and
allow for more energy to spread into Kentucky in nearly zonal
flow. By Sunday, larger differences are noted between the ECMWF
with its deeper and further west upper low to the northeast and
the GFS`s more aggressive ridging though the Plains and into
Central Canada. Meanwhile, the energy from the West Coast will be
slipping through the state in northwest flow. Despite the rising
heights that follow, more energy - though dampening - passes by
into Monday. The model differences become rather large into
Tuesday with the ECMWF having two deep upper lows - one just off
the East Coast with another over the northern Baja with ridging
between for Kentucky. In the GFS the Kentucky ridging is similar -
if further east - while its troughs are weaker and shifted east of
the ECMWF`s. Again, without regard to the ridging additional
energy moves into Kentucky on Tuesday. Given the good model
agreement early on and larger discrepancies later a general model
blend made for a reasonable starting point to the forecast.

Sensible weather will feature the area drying out on Thursday but
not long as another front will set up through the JKL CWA to end
the work week bringing in more pcpn. With this, enough cold air
looks to remain in the northern parts of eastern Kentucky for a
mixture of rain and snow to occur Friday night. Again a sfc low
coming out of the Plains will pass almost due east through
Kentucky maintaining the cold air north and warmer conditions in
the southern part of the JKL CWA. This system passes through by
Saturday night, but not before potentially yielding up to an inch
of snow accumulation for our northern counties and a soaking rain
in the south. Again any drying looks to be brief with the nearby
boundary and energy aloft contributing to more rain moving in to
start the next work week - but generally warmer than we have seen
for these past several events.

Made some minor adjustments for terrain Thursday night and again
Monday night. As for PoPs, went above guidance for the
Friday night/Saturday system given the storm track right across
the area.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)

IFR/LIFR ceilings with light precipitation, mainly in the form of
snow, will continue across the area through 12z, as low pressure
continues to rotate near the region. Light snow will continue
during the day on Wednesday, with a gradual diminishment from
west to east towards 00z. VFR conditions will eventually return
towards the end of the period, as the system departs to our east.
West to northwest winds are expected at around 10 kts, with gusts
of around 20 kts at times during the day on Wednesday.


Winter Weather Advisory until 8 PM EDT this evening for KYZ044-

Winter Weather Advisory until 8 PM EDT this evening for KYZ079-



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