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000
FXUS63 KJKL 230021 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
821 PM EDT Mon Apr 22 2024

.KEY MESSAGES...

- Frost is expected in many sheltered valley locations late
  tonight into early Tuesday morning.

- Dry and breezy conditions are possible on Tuesday and could
  approach critical fire weather thresholds.

- Below normal temperatures return from Wednesday into Thursday
  morning, bringing the risk for at least patchy frost in valleys.

&&

.UPDATE...
Issued at 821 PM EDT MON APR 22 2024

Some minor adjustments were made to hourly temperatures,
dewpoints, and winds early in the period based on recent
observation trends. High pressure centered across the
Appalachians will gradually shift east overnight. This combined
with afternoon mixed dewpoints in the mid 20s to low 30s will set
the stage for frost in valley locations once again. These valley
locations are already starting to decouple per observations. Much
of the area will average lows in the 30 to 35 degree range with a
few of the normally colder rural valley locations likely dropping
to 28 or 29. Coalfield ridgetops will likely experience light
southerly flow overnight and not fall much below 40 in most
instances, if that, and should not be affected by frost. The Frost
Advisory still looks on track.

&&

.SHORT TERM...(This evening through Tuesday night)
Issued at 308 PM EDT MON APR 22 2024

The afternoon surface analysis shows high pressure has settled
into the Lower Mississippi River Valley this afternoon, and in the
mid-levels, we see a shortwave ridge nosing into the Ohio Valley.
This surface high will transition to the southeast states
tonight, leading to some return flow at the surface, and an upper-
level low will begin pushing toward the Great Lakes, leading to
some mid- to high-level clouds pushing into the Ohio Valley. This
could limit the temperatures from dropping off tonight,
particularly on the ridges, where we will remain more mixed
through the night. However, in the valleys, there is some ability
to get lower temperature wise if the clouds are thinner and mixing
is less of a factor. Given the uncertainty, we opted to keep
mostly lower to mid-30s for lows in the valleys tonight, but we
could see some upper 20s if the clouds are thinner. Meanwhile, the
ridges will most likely decrease into the upper 30s to lower 40s.
Even in the fifth percentile, the NBM appears to be struggling
with that idea, so it leaned more toward COOP MOS guidance to
obtain a better sense of the possibility tonight. Therefore, we
will keep the Frost Advisory going late tonight into Tuesday
morning.

The previously mentioned cold front will slowly push toward
eastern Kentucky, and mid-level ridging will push east on Tuesday.
This will mainly lead to increased cloud cover throughout the day,
from northwest to southeast. However, ample mixing will be
possible through the day before thicker clouds arrive, and this
could lead to wind gusts of 20 to perhaps 25 mph through the late
morning and afternoon. The mixing being deeper and the dry air
noted just above could lead to a dry day and did undercut
dewpoints some from the sometimes too high NBM. This cold front
will finally push across the area Tuesday night, bringing in a 60
to 80 percent chance of showers. The ensembles and even the
usually overdone NAM couldn`t muster up enough instability to
support any thunderstorms with this round of convection,
particularly since this front becomes more anemic with time. Also,
overall amounts will be on the lighter side, with the probability
of PWAT values above 1 inch only around 40 percent less for most
locations from the HREF CAMs. Also, LPMM rainfall totals from the
HREF are generally less than a tenth of an inch for most locations
as well.

.LONG TERM...(Wednesday through Monday)
Issued at 429 PM EDT MON APR 22 2024

The 22/12z model suite analysis beginning Wednesday morning shows a
shortwave trough, over the Lower Great Lakes/Ohio Valley, riding
around a much deeper upper level trough/low over Quebec. Relatively
higher heights are in place off to the west across the High
Plains. Further upstream, a closed ~535 dam low is coming ashore
British Columbia near the 54th parallel while a southern stream
~564 dam low is approaching the California coast. At the surface,
a cold front extends from Labrador down to a loosely organized
low pressure over the the St. Lawrence Valley/Northern New
England and then further southwest in the Lower Ohio Valley and
from there more west southwestward into the Southern Plains. A
chilly Canadian high pressure is found behind the front and
centered north of Lake Superior.

The cold front will be departing southeast Kentucky first thing
Wednesday morning, quickly bringing associated precipitation to an
end. Behind that front, drying northwest flow will knock 850 mb
temperatures back into the 2-6C range during the afternoon and
evening, coolest in the north. High pressure will then crest
directly over the Great Lakes on Wednesday night as troughing
begins to pull away to the northeast. The driest and coolest air
mass will be in place over locations north of the Mountain
Parkway and this is where there will be the greatest concern for
frost in valleys. Further south, moisture will linger for longer
as the cold front`s southward progress slows, and that will tend
to keep overnight temperatures warmer. As the surface high departs
off to our east northeast on Thursday, southerly flow returns
bringing back warmer temperatures, most notably in more southern
locations.

Meanwhile, the southern stream Pacific low will be passing
through the Desert Southwest, having opened into a trough and will
initiate lee cyclogenesis east 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, spreading moisture back across eastern Kentucky along with
slight chance to chance PoPs. Overall QPF as the front passes
through eastern Kentucky appears to be on the order of a few
tenths or less. Thereafter, eastern Kentucky will remain solidly
within a warm sector air mass through Monday. The southern stream
upper level shortwave trough and it surface reflection quickly
lift northeastward toward Ontario on Saturday, stay well to our
northwest. Behind this trough, remnant energy from the former
northern stream 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, again tracking well to our
northwest. It does appear that the second low pressure will
finally pull a cold front our way with area-wide rain chances,
but likely not before Monday night at the earliest. Any rain
chances between Saturday and Monday will be dependent upon
subtle disturbances aloft and/or mesoscale effects. As of now,
most of the weekend and first day of the new work week looks to
be largely rain-free. Even so, it should be noted that a moderate
southwesterly 850 mb flow at ~15 to 30 knots could be mixed down
each each afternoon leading to gusty breezes.

In sensible terms, look for cloud cover and any lingering showers
over far southeast Kentucky to give way to clearing skies from the
northwest on Wednesday. Forecast maximum temperatures range from
the lower 60s north of I-64 to the lower 70s in the southeastern
Kentucky Coalfields valleys. Look for mostly clear skies and chilly
lows on Wednesday night, ranging from the mid 30s in northern
valleys to the mid 40s on southern ridgetops. Patchy to areas of
frost are forecast, most prevalent in valleys north of the
Mountain Parkway. A significant warmup is then in store heading
into the weekend and early next week. Forecast highs range from
the upper 60s to mid 70s on Thursday. A warm front does bring
clouds and some chance for showers or even a thunderstorm on
Friday/Friday night. Once that front passes, there could be a few
showers or storms around at times, but most of the time should be
dry until Monday afternoon or evening. Forecast maximum
temperatures warm into the mid 70s on Saturday, near 80 on
Saturday, and mainly lower to middle 80s on Sunday and Monday.
Meanwhile, nighttime lows from Friday night onward will be very
mild, mostly ranging in the 55 to 65 range.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
ISSUED AT 815 PM EDT MON APR 22 2024

Surface high pressure will gradually shift east and southeast
through the period while a cold front will approach the OH Valley
region on Tuesday. With a dry airmass in place initially and only
an increase in high clouds followed by mid level clouds during
the second half of the period, VFR will prevail. Winds will
generally be light and variable in valleys and south at less than
10KT on ridges through 14Z to 16Z, before mixing leads to
southwest winds of 5 to 15KT to end the period, with some gusts up
to 20KT or higher.

&&

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

&&

$$

UPDATE...JP
SHORT TERM...DJ
LONG TERM...GEERTSON
AVIATION...JP