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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS63 KJKL 212026 CCA
AFDJKL

AREA FORECAST DISCUSSION...CORRECTED
National Weather Service Jackson KY
426 PM EDT Sun Apr 21 2024

.KEY MESSAGES...

-- Changed Discussion --
- Fair weather lasts at least into Tuesday afternoon.

- Frost is expected in most places by dawn on Monday, and
  possibly again by dawn on Tuesday in many valley locations.

- A moisture-starved cold front is forecast to pass Tuesday night
  into Wednesday morning, bringing a round of light rain mainly
  for northern locations.

- Below normal temperatures return from Wednesday into Thursday
  morning before a warm front arrives on Friday and ushers in
  well above normal temperatures for the weekend.
-- End Changed Discussion --

&&

.SHORT TERM...(This evening through Monday night)
Issued at 416 PM EDT SUN APR 21 2024

A very quiet short term period is in store, with temperatures
being the only concern. Surface high pressure centered near OK
late today is ridging northeast over the Ohio Valley, while a
progressive upper level trough approaches us from the northwest.
The surface high is supplying a cool and dry air mass, and
mid/high clouds have largely departed to the east in association
with a smaller wave caught in the flow ahead of the main upper
level trough. That will leave us with clearing skies this
evening, with diurnal cu drying up. Good radiating conditions
should result in a bigger drop in temperatures tonight, with frost
for most locations. Steep low level lapse rates may initially
inhibit decoupling, but think that surface cooling will eventually
win out.

Sunshine, ridging aloft passing over, and a lack of cold air
advection on Monday will allow for a bit warmer readings than on
Sunday, but will still be cool enough to allow for another frost
potential with diurnal cooling on Monday night. A return of warm
air advection will keep ridges milder on Monday night, but valleys
should readily decouple from the flow and chill. The GFS is
suggesting high clouds will show up during the night ahead of the
next system approaching from the Midwest. This could impact
radiating to some extent. All that said, frost shouldn`t be quite
as widespread, but the eventual need for an advisory can`t be
ruled out.

.LONG TERM...(Tuesday through Sunday)
Issued at 416 PM EDT SUN APR 21 2024

The 21/12z model suite analysis beginning Tuesday morning shows an
upper level ridge axis along the southern foothills of the
Appalachians northeastward off the New Jersey Coast. Meanwhile, a
shortwave trough is passing into the Upper Great Lakes as it rides
along the southern periphery of an ~505 dam low rotating just north
of James Bay. Looking further west, ridging is in place over much of
western Canada and the western CONUS. Off the West Coast, there are
two closed lows, one well of the coast of California and the other
off of the Alaska Panhandle. At the surface, a ridge of high
pressure is weakening as it departs off the Atlantic Seaboard on
Tuesday. Meanwhile, a weak low pressure is passing from the Great
Lakes into the St. Lawrence Valley, with a trailing cold front in
tow.

As that cold front approaches on Tuesday, the southwesterly return
flow ramp up through the day across eastern Kentucky while strong
heating will support deep mixing. GFS BUFKIT momentum transfer
output supports gusts reaching 20 to 25 mph during the afternoon.
The front moves in from the northwest Tuesday night but will be
moisture starved. At this point, model soundings show very little to
no instability. In models that are generous enough to show meager
instability, the equilibrium levels are likely to low to support
charge generation for thunder. Thus there is no mention of
thunderstorms in the afternoon forecast package. Once that front
clears the area early Wednesday morning, along with any of its
associated showers, the models have come into better agreement
depicting a seasonably chilly air mass moving in the from the north
on Wednesday as high pressure builds across the Great Lakes. The
drier and cooler air should move more quickly into place across the
northern half of the forecast area, whereas over southern locales,
that air mass will be slower to infiltrate as the cold front itself
will begin to stall to our south. With dew points falling to near or
below freezing in the north, would not be shocked to see some patchy
frost showing up in northern valleys. This possibility is supported
by the GFS COOP MOS at Sandy Hook which on the latest run predicted
a low of 30F for Thursday morning. As the surface high moves to our
east on Thursday, southerly flow will return bringing back warmer
temperatures. Even so, there could still be  an ~8 to 10 degree
north-south daily maximum temperature spread as the cooler air mass
is slower to retreat from northern locales.

The southern stream Pacific low will by this time be passing over
the Desert Southwest, having opened into a trough and will initiate
cyclogenesis in the lee of the Central Rockies on Friday. In
response, the cold front that dropped south earlier in the week will
lift back northward as a warm front on Friday and Friday night.
Models are coming into somewhat better agreement on the potential
for a light QPF as the front passes through eastern Kentucky.
Thereafter, our corner of the Commonwealth will remain solidly
with in the warm sector through the weekend. The upper level
shortwave and its attendant surface low quickly scoot
northeastward toward Ontario on Saturday. In the wake of this
trough, remnant energy from the former northern Pacific upper low
will open and deepen into trough over the Western CONUS and then
initiate another low passing on along a similar track early next
week, staying well to our northwest. It does appear that the
second low pressure will finally send a cold front our way, but
likely not before Monday night or Tuesday at the earliest. In the
meantime, any rain chances in the warm sector will likely depend
upon subtle perturbations passing aloft and right now quiescent
conditions look to prevail for most of the weekend. However it
should be noted that the southwesterly 850mb jet of 15 to 30 knots
could easily be tapped into on both weekend days when strong
solar insolation deepens the mixing layer to near that level.

In sensible terms, look for high pressure to bring one more dry day
on Tuesday with mild temperatures in the 67-74 range.
Southwesterly breezes could gust to between 20 and 25 mph at
times in the afternoon. Rain chances rise from the northwest
Tuesday evening as the cold front approaches and peak overnight
before falling off on Wednesday. Overall QPF with this system is
light (less than 0.15 inch in northern counties ranging to little
or nothing along the Kentucky/Tennessee border). Thunder was
removed from the forecast due to the lack of deep instability.
Behind the cold front, mostly clear skies return for Wednesday
along with initially cooler temperatures. Forecast highs range
from the mid 60s to around 70 on Wednesday while lows dip into the
lower 30s northern hollows to mid 40s southern ridges on
Wednesday night. Light southerly winds return on Thursday,
boosting temperatures a few degrees in southern locales, such that
highs are forecast to range from the mid 60s north of I-64 to the
mid 70s in deeper valleys along the Tennessee border. Increasing
clouds follow for Thursday night along with at least chance PoPs
on Friday with the arrival of a warm front. Once that warm front
passes, temperatures are forecast to surge to around 80 on
Saturday and into the middle 80s on Sunday while nighttime lows
range mainly in the 60s. A shower or thunderstorm cannot be ruled
out on either weekend day, but most of the time should be dry. It
will also be breezy each day with gusts in the 15 to 30 mph
expected both afternoons.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
ISSUED AT 400 PM EDT SUN APR 21 2024

VFR conditions and winds mostly less than 10 kts will prevail
through the period.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
Frost Advisory from 1 AM to 9 AM EDT Monday for KYZ044-050>052-
058>060-068-069-079-080-083>088-104-106>120.

&&

$$

SHORT TERM...HAL
LONG TERM...GEERTSON
AVIATION...HAL