Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 250722 AAD
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
222 AM EST Sat Feb 25 2017

.UPDATE...
Issued at 210 AM EST SAT FEB 25 2017

Grids were updated based on recent radar, observation and short
term model trends. This led to only minor adjustments to pops, but
did fine tune the wetbulb cooling as the showers and thunderstorms
arrive. Many of the thunderstorms have been containing pea sized
hail and this trend should continue for the next hour or two
across the far southeast part of the area before storms exit the
area.

UPDATE Issued at 949 PM EST FRI FEB 24 2017

Current conditions feature the area of showers and storms at the
CWA doorstep along the I-75 corridor. It seems that no dominant
cold pool or organization of the cells in central Kentucky, or
Tennessee for that matter has occurred. Thus, with the cap still
in place over eastern Kentucky, will be hard pressed to see any
severe convection tonight. So have updated to pull the severe
wording from the forecast but have left in the mention of strong
storms with the potential to produce gusty winds and small hail.
Have updated the HWO as well to take out the severe wording and
input the mention of strong storms.

UPDATE Issued at 713 PM EST FRI FEB 24 2017

Current conditions feature a line of showers and segments of
strong to severe thunderstorms in central Kentucky to the west
tracking northeast. Fine tuned the pops to account for a more
timely arrival into eastern Kentucky. Decided to keep the severe
mention in the forecast though, with heating lost and instability
becoming more elevated, the cap in place more and more hints at
any severe weather in eastern Kentucky will be dependent on what
develops in central Kentucky and advects in. Mainly in the form of
a squall line or bowing segments. As well, the main threat
continues to be damaging winds. Onset into Kentucky may be as soon
as 9pm. A new ZFP was sent out to account for these changes.

&&

.SHORT TERM...(This evening through Saturday night)
Issued at 517 PM EST FRI FEB 24 2017

South-southwest flow aloft will become more westerly through the
short term as a potent storm system plows through the Great
Lakes, pulling a trough through the Commonwealth over the next 24
hours. Surface low pressure over Lake Michigan will continue to
move off to the northeast, pulling a cold front eastward through
the region, and into eastern Kentucky during the overnight.

A line of thunderstorms currently developing across the Midwest
will move into our forecast area through the overnight period.
HRRR timing of the main line of convection has been fairly
consistent and generally agrees with what has been advertised.
Some thunderstorms could produce severe weather with the main
threat being damaging winds. Hail will be a secondary threat and a
brief, isolated tornado can not be ruled out.

Moisture, or the lack thereof will be the primary limiting factor
to severe weather as dew points will top out in the mid 50s ahead
of the front. Timing of the cold front through eastern Kentucky
will also be a limiting factor. Regardless bulk shear is very
impressive with this system, 40-70 kts, with the majority of the
shear realized in the lowest 3 km. Thus the potential for bowing
cells and line segments will be favored. Surface based
instability to support this storm mode is not ideal but does
appear to be sufficient. Consequently damaging winds are the
primary severe weather threat. This has a distinctive QLCS flavor
to it and considering the environment as a whole feel an isolated
tornado can not be ruled out, though features of this type tend to
be weaker than most and short lived. Low wet bulb temperatures
and freezing levels suggest hail will be a possibility as well.

Colder air invades the coal fields on Saturday and will set
things up for a rather chilly weekend in general. Gusty winds will
combine with strong cold air advection to make for a less than
optimal day for outdoor activities.

.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 06Z TAFS through 06Z Saturday night)
ISSUED AT 139 AM EST SAT FEB 25 2017

The first few hours of the TAFs were adjusted to account for
timing of the broken line of convection moving across the area.
A period of MVFR to possible brief IFR visibility is anticipated
due to moderate to briefly heavy rainfall with CIGS possibly
also falling briefly into the MVFR range as showers and
thunderstorms pass. Winds will initially be southwesterly ahead
of the front with some gusts of 20 to 30 KT with initial shower
and thunderstorm activity. As the cold front moves across the
area during the first 3 hours of the period, winds will become
more west to northwesterly averaging around 10KT with some gusts
up to 20KT possible. Low end MVFR to VFR conditions are then
anticipated for a couple hours behind the front before CIGS return
to VFR on average. Winds should increase again on o then increase
again tomorrow afternoon with westerly winds gusting up to 25
knots as well.

&&

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

$$

UPDATE...JP
SHORT TERM...RAY
LONG TERM...AR
AVIATION...JP


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