Area Forecast Discussion
Issued by NWS Jackson, KY

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159
FXUS63 KJKL 241052
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
652 AM EDT Fri Mar 24 2017

.UPDATE...
Issued at 645 AM EDT FRI MAR 24 2017

IR SAT this morning showing an area of lower clouds likely due to
isentropic lift continuing to expend north out of Middle
Tennessee. While initial expansion into the greater Tennessee
Valley was blocked by the Cumberland Plateau the next surge will
not be blocked as much. Therefore, did opt to increase cloud
cover particularly across the western portion of the CWA.
Temperatures have been a bit of a challenge, and continue to be
with cooler spots being the deeper valleys that have been able to
decouple. Updates sent to NDFD and Web.

&&

.SHORT TERM...(Today through Saturday)
Issued at 357 AM EDT FRI MAR 24 2017

Morning surface analysis indicates surface high pressure centered
off the coast of VA/NC. A weak warm front is progressing NE and
while there is a slight kink in isobars the front is tough to
define. Winds have already switched to a more southeast to south
direction around the surface high this morning. Therefore
temperatures are mild at the more mixed sites. The exception to
the rule are the deeper valley locales where decoupling is leading
to lower 40s. First forecast challenge of the day will be cloud
cover. We have seen clouds streaming out of the TN Valley and
southward likely associated with isentropic ascent ahead of the
approaching system in the Front Range. Most of the model soundings
indicate some lower clouds are not out of the question as we move
through the day. Right now keeping the better coverage across the
western and northern portions of the CWA and seems reasonable
right now based on the SAT trends. The next challenge will be how
much moisture recovery do we get particularly in the far east
toward the Big Sandy. There will be decent afternoon mixing and
given the strengthening LLJ would lead to 15 to 20 mph gusts
particularly in the Lake Cumberland and Bluegrass. Overall think
recovery should be enough to lead to higher RH than yesterday, but
even so far east could be looking at lower 30 RH values. All of
this will play a crucial role in temperatures and did lean up a
bit given SUPERBLEND was higher than previous forecast.

Tonight the cloud challenge will continue as the lower deck is
expected to dissipate. However, we will keep a higher deck at
minimum, but the deeper valleys could see a decent split once
again. Think this will be more confined to the far eastern valleys
given the better LLJ to the west. Moving into Saturday the clouds
will continue to be on the increase through the day and more a
top down saturation seen in the model sounding data. The one
caveat to the increased cloud cover will be the backed flow by
Saturday afternoon which could promote downslope flow in the far
east. That said, did opt to keep lesser coverage as you move east.
Also think most will remain dry on Saturday given upper level
trough will negatively tilt across the Midwest and slow surface
features down. However, did opt to bring slight POPs in the Lake
Cumberland region by late Saturday given some CAMs support the
possibility.

.LONG TERM...(Saturday night through Thursday)
Issued at 357 AM EDT FRI MAR 24 2017

A stacked low pressure system over MO at the start of the period
will be weakening as it slowly moves northeast, reaching the Great
Lakes Sunday night. A stream of moisture off the Gulf of Mexico
coupled with the approaching upper level system will bring showers
to most places Saturday night and Sunday. Weak instability should
also be present, and justifies including a mention of thunderstorms.
As the disintegrating system passes to our north, its cold front is
expected to dissolve and leave us without a change in air mass.
Models show another weakening low pressure system coming out of the
southern plains early in the work week and moving up the Ohio
Valley. This time around, cold frontal passage is expected to occur,
accompanied by an increase in the POP for Monday night into Tuesday.
The GFS and ECMWF are in a little bit better agreement now, as
compared to 24 hours ago, and are both showing the front settling
far enough to our south to allow a period of mainly dry weather from
Tuesday night into Thursday. Yet another in a parade of systems is
expected to track from the southern plains to the Ohio Valley at the
end of the week. While precip from this system can`t be ruled out on
Thursday, it`s more likely to hold off just a bit longer.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
ISSUED AT 652 AM EDT FRI MAR 24 2017

IR SAT coupled with obs are showing an area of lower clouds moving
northeast out of Middle Tennessee. However, this deck is expected
to remain VFR at or around 5 KFT through the day. Then by this
evening expect this lower deck to dissipate and we will be left
with high clouds. Low level jet will continue to increase leading
to gustier winds in the Lake Cumberland and Bluegrass around 15
to 20 knots at times. Overall winds will be out of the southwest
through the day, but are expected to back some out of the south
and southeast tonight as they decrease.

&&

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

$$

UPDATE...DJ
SHORT TERM...DJ
LONG TERM...HAL
AVIATION...DJ



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