Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 301417
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1017 AM EDT Thu Mar 30 2017

.UPDATE...
Issued at 1017 AM EDT THU MAR 30 2017

No significant changes were made at this point. Early morning
showers have moved out of the area. Did make a minor change to
raise the POP above zero area wide for the rest of today, with a
peak 10% category in the eastern part of the area. Can`t rule out
some showers popping up, but the potential is still too low to
make a mention of it in the worded forecasts.

UPDATE Issued at 657 AM EDT THU MAR 30 2017

The narrow band of showers that had formed over central Kentucky
earlier is now crossing our northern counties and actually
producing some pretty decent thunderstorms at the moment. Did a
quick update to toss thunder in with this morning activity. All of
it will be exiting east in the next few hours, leaving behind dry
conditions for the remainder of the daylight hours today. Latest
HRRR/RAP show convection this evening starting to roll into
eastern Kentucky between 8 and 11 PM. This is in line with the
current forecast. Thus, no other changes needed right now. Grids
have been saved an sent to reflect the thunder over the next hour
or two.

&&

.SHORT TERM...(Today through Friday)
Issued at 309 AM EDT THU MAR 30 2017

An area of low pressure resides over eastern Kansas this morning
with a warm front extending east across central Missouri and into
western Kentucky. A cold front is advancing eastward across the
Ozarks region. Isentropic ascent associated with the warm front
advancing towards eastern Kentucky has led to a increase in
mid/high clouds this morning. Still some support in the hi-res
short term models to support some light showers/sprinkles early
this morning as the isentropic ascent in the mid levels continues
to increase. In fact, a few showers are already trying to get
going out across central Kentucky and this should continue to
expand in coverage as it moves northeastward. The threat for
showers will be short lived as downsloping south-southeast flow
takes hold through the day. This leads us to our first threat of
the day, an enhanced fire danger. Temperatures will soar to around
80 this afternoon. Dewpoints should mix out into the mid to upper
40s, putting relative humidities between 25 and 35 percent
areawide. While this is not in the critical range, it is close. In
addition, winds will crank up this afternoon with deep mixing
taking place. Sustained winds of 10 to 20 mph are likely along
with wind gusts up to 35 mph. The dry air combined with these
strong winds could will create an enhanced fire danger today,
especially for areas that have managed to dry out over the past 24
to 36 hours. Will highlight the fire danger in the HWO and fire
weather forecast this morning.

As we head into the evening hours, the low over Kansas this
morning will push east across central Illinois and Indiana. The
trailing cold front will lead to shower and thunderstorm
developing across southern Illinois/Indiana, southward into
western Kentucky and western Tennessee. This activity will push
east/northeast through the evening hours. This activity will be
aided by a potent shortwave it it tracks into eastern Kentucky
tonight. This leads to our second threat, severe storm potential
tonight. Shear will be tremendous with this system, but
instability may be a bit more of a question. With dewpoints slow
to come up through the day, the question is, can we generate
enough instability to allow for a more robust severe threat.
Certainty a questionable setup for eastern Kentucky given the lack
of surface instability. However, in this case, we have lots of
forcing spreading east across the area and this could compensate
for the lack of instability. The storm prediction center has
expanded the slight risk of severe storms over all of eastern
Kentucky and this seems very reasonable considering the trends.
The enhanced risk is sitting just to our west, and would not be
surprised to see it expanded west today depending on how things
unfold upstream. Best threat would be in our western counties as
these areas are less likely be be downsloped and thus dewpoints
more likely to come up in these areas. Things become more
questionable to the east. Main threats appear to be damaging winds
and large hail, although a brief tornado spin up cannot be ruled
out. Heavy rainfall will be possible with strong lift associated
with the shortwave and PW`s near 1.25 inches. This could produce
some rainfall totals in excess of 1 inch tonight.

Forcing will depart to the east early Friday morning, but the
upper level trough will become anchored over the region keeping
some moisture and cloud cover over the region. This may lead to
scattered to numerous rain showers Friday afternoon. Mid level
lapse rates not quite steep enough to support thunder, but are
very close.  Should be a much cooler day with highs in the 60s.

.LONG TERM...(Friday night through Wednesday)
Issued at 450 AM EDT THU MAR 30 2017

The models are only in broad agreement on the pattern aloft and
just through the first part of the extended portion of the
forecast before diverging by start of next week. The split nature
of the flow through North America continues to give the models
trouble with respected to timing and placement of the key features
through next week. The first of these is a trough departing to
the northeast late Friday into Saturday morning. While the models
are different, even at this early stage, these discrepancies will
have little effect on eastern Kentucky`s weather in an environment
of rising heights and a building ridge throughout the region.
Ridging peaks over Kentucky early Sunday before a broad and rather
open trough moves east through the Southern Plains. The GFS is a
tad stronger, faster, and off to the northeast of the ECMWF
version with this trough while the CMC is more similar to the
latter model. Southwest flow over the region will carry energy
into our area through the end of the weekend. The core of the
trough itself will slowly move to the lower Mississippi Valley
while a significant wave lifts northeast through Kentucky out
ahead of the main trough. At this point, the GFS remains more
open with its trough than the ECMWF and also exhibits more of a
connection with the faster northern stream. The net result is that
the GFS takes the core of its mid level low through the Tennessee
Valley ahead of the ECMWF by as much as 12 hours with the CMC in
between. These significant differences carry through the day
Monday and into early Tuesday before all models take the lower
heights off to the east and allow for a return of mid level
ridging over Kentucky. These differences lower the confidence in
any specific solution from the models, but do indicate that we
will see a wx maker moving through during this time frame -
and likely a tad quicker or slower than suggested by the
consensus solution depending on how reality breaks with the progs.
For now, will favor a blend with a preferred lean toward the CMC
and ECMWF - slowing the arrival and departure of the sensible wx
effects. Ridging will dominate the rest of the extended but
another strong trough does approach from the west late Wednesday -
again faster in the GFS than the ECMWF.

Sensible weather will feature a cool and cloudy start to the
weekend before high pressure moderates and warms for Sunday.
Showers and thunderstorms will then be possible by Monday morning
as a deep southern surface low plods east toward the area. This
looks to pass right over Kentucky keeping high PoPs in the
forecast along with a chance for thunderstorms. The damp weather
will dry out later Tuesday with little cool air to be found in its
wake continuing the mild temperatures through the rest of the
extended, particularly on Wednesday where low to mid 70s are
anticipated for the afternoon.

Did make some minor adjustments to the lows early and late in the
period to account for the terrain distinctions outside of the
rainier ones to start the new week. As for PoPs - have tempered
them a bit from early Monday through Tuesday owing to the model
differences and lower confidence in their individual solutions -
though showers will be in the likely range for much of this time
frame.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
ISSUED AT 657 AM EDT THU MAR 30 2017

VFR conditions will prevail through this evening. Some mid/high
level clouds will be drifting across the area through this evening.
Showers and storm chances will increase after 00z this evening.
With the onset of convection, we may see a period of MVFR cigs and
visbys with the storms with cigs lowering to low end MVFR by
daybreak Friday. We may even be able to squeeze out some patchy
IFR cigs late tonight.

&&

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

$$

UPDATE...HAL
SHORT TERM...KAS
LONG TERM...GREIF
AVIATION...KAS


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