Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 251538 AAA

National Weather Service Jackson KY
1038 AM EST Sat Feb 25 2017

Issued at 1038 AM EST SAT FEB 25 2017

A few changes were made to the forecast this morning. Updated the
zone forecast text product to reflect falling temperatures for the
rest of today, as opposed to mentioning maximum temperatures,
which have already occurred across the area. Also modified the
weather types for today to reflect only sprinkles or snow
flurries, with the flurries being confined to the high terrain
along the VA border. Any outdated wording that was in the zone
forecast text product was also removed. The new forecast has been
already been issued.

UPDATE Issued at 705 AM EST SAT FEB 25 2017

The deeper moisture has just about exited far southeastern KY and
pops have been adjusted early in the period to account for this.
A dry slot will work across the area early in the period, though
shallow low level moisture will return by late morning to early
afternoon as the shortwave trough approaches and a return or
continuation of stratocu and cumulus is expected. The low level
flow will have an upslope component and the shallow moisture is
expected to be near the -10C level. This may be sufficient for a
few sprinkles or perhaps an isolated light shower by midday to
the afternoon as lapse rates steepen. A few flurries cannot be
completely ruled out by evening. However, drier air moving in as
high pressure builds into the TN Valley should put an end to the
threat for sprinkles or flurries during the evening. Temperatures
are expected to be nearly steady or slowly falling in the morning
with a more substantial fall in the afternoon as the core of the
cold airmass nears.


.SHORT TERM...(Today through Sunday)
Issued at 425 AM EST SAT FEB 25 2017

A cold front associated with a deep low pressure system moving
from the Great Lakes and into Ontario is currently moving across
East KY. The boundary is currently located from between KHTS and
KCRW south southwest to just west of KSJS and KPBX to near K1A6
and then to near KTYS and KCHA. An area of showers associated with
the front and associated mid and upper level trough and forcing along
with some embedded thunderstorms are moving across the area.
However, these are slowly tapering off from west to east with the
thunder generally confined to areas near or east of the front from
portions of the Big Sandy region southwest near the VA border.
Temperatures have initially web bulbed with the precipitation
into the 50s while colder and drier air is filtering into the area
behind the front and temperatures and dewpoints in the west have
dropped into the 40S.

As the front moves into VA over the next hour or so, the threat
for any lingering thunder will end although some showers will
persist for a couple of hours or so behind the front until the
deeper moisture departs and forcing decreases. Cold air advection
will continue today as the mid and upper level trough axis
approaches with the coldest of the airmass arriving this afternoon
and evening. 850mb temperatures should fall below 0C by midday and
bottom out near -10C late this evening into very early on Sunday.
At the surface, high pressure will build east from the Plains and
this combination should bring steady to slowly falling
temperatures through the morning and gradually falling
temperatures in the afternoon. The highest elevations above 2500
feet should drop to around freezing or below by sunset while the
remainder of the area should fall below 40 by dark. There should
be a period of relatively less cloud cover in the morning as a dry
slot between the front and upper level trough moves across the
area. Limited low level moisture will linger with cu and or
stratocu developing or increasing from midday into the afternoon
as the cold advection steepens lapse rates. This moisture may be
sufficient with some ice present in the clouds for a few sprinkles
by this afternoon and perhaps a few flurries in some areas toward
sunset, particularly the highest elevations.

As the high builds east this evening and tonight and is centered
over the TN Valley, the pressure gradient will decrease as will low
level moisture. This should occur first across the southwest part
of the area and a bit later in the northeast. This pattern will
favor a bit colder low temperatures in the lower 20s for some
normally colder southern valley locations though all locations
should fall into the 20s.

The high will begin to move east of the area on Sunday and with
a considerable amount of sunshine, high temperatures should rise
to near normal levels for the end of February as the airmass
moderates rather quickly. The airmass will also be dry and rh
should bottom out briefly below 30 percent in some locations.

.LONG TERM...(Sunday through Friday)
Issued at 315 PM EST FRI FEB 24 2017

The extended portion of the forecast will be fairly active, with
alternating periods of wet and dry weather and warm and cooler
conditions. The period will likely start off dry, with slightly
above normal temperatures Sunday and Sunday night. The pattern is
then expected to shift on Monday, as a weak warm front moves through
the area, bringing persistent southerly flow and warmer air into the
region. Rain showers should begin to move into the area from the
southwest and west late Sunday night into early Monday morning. The
rain will overspread the entire area by late Monday afternoon and
early Monday evening, as an area of low pressure moves along what
will become a nearly stalled out frontal boundary. This pattern is
tentatively expected to persist through late in the day on Tuesday.
A wave of low pressure is then forecast to form along the western
end of the stalled front Tuesday night. This second area of low
pressure is then expected to push eastward on Wednesday, and will
drag another cold front across the lower Ohio valley and Tennessee
valley regions. This boundary may be just strong enough, and just
enough moisture an instability available, for a few thunderstorms to
form along and just ahead of the front, as it moves across the
region. Once the front moves past us Wednesday night, any
thunderstorms should give way to all rain showers. We may even see
enough cold air filter in behind the system to allow some snow to
mix in with whatever rain is left. The last of this precipitation
should be out of the area by late Thursday morning. Thursday and
Thursday night should be mostly dry. There is an outside chance that
a few rain and snow showers will move across the area along and
north of I64 to end the period, with due to uncertainty, this should
be taken with a grain of salt.

Temperatures in the extended on average will be above average each
day, with the warmest days being Monday, Tuesday, and Wednesday,
when the highs will be in the 50s and 60s. Closer to normal values
should be experienced on  Thursday, when the mercury is forecast to
max out lower 50s. Nightly lows should be in 30s, 40s, and 50s.


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

Initial lower end of VFR and MVFR Cigs are expected to start the
period though as drier air moves into the area combined with
mixing by the 14Z to 18Z period, all locations are expected to
become VFR. A few sprinkles and perhaps a flurry cannot be ruled
out through 23Z. Winds should increase by 16Z with daytime
heating with generally west winds 10 to 15KT with some gusts as
high as 20 to 25 mph. The pressure gradient will slacken by 0Z to
6Z with winds becoming light at the end of the period.




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