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000
FXUS63 KJKL 202000
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
400 PM EDT Sat Apr 20 2024

.KEY MESSAGES...

- Fair weather lasts through early in the new workweek.

- Frost will be possible in some sheltered valley locations Sunday
  morning, but is expected to be most widespread Sunday
  night/Monday morning and again Monday night/Tuesday morning,
  especially through the valleys.

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

- Confidence in weather forecast late next week is lower than
  normal at this range due to significant weather model differences.

&&

.UPDATE...
Issued at 1042 AM EDT SAT APR 20 2024

Morning observations have been blended into the hourly forecast,
without any substantive changes.

UPDATE Issued at 645 AM EDT SAT APR 20 2024

One more update has been sent out to raise PoPs for the next
couple of hours along the Tennessee border as a fast-moving
disturbance grazes the area with shower activity.

UPDATE Issued at 633 AM EDT SAT APR 20 2024

Early morning update is out, with the main change lowering the
hourly dew points in the grids quicker than before. Otherwise,
there are no changes to the forecast.

&&

.SHORT TERM...(Today through Sunday)
Issued at 300 AM EDT SAT APR 20 2024

Lower-level cloud cover and some patchy fog diminishes through
this morning generally from northwest to southeast as a large
expansive surface high over the central US expands across the Ohio
River Valley, with fair conditions prevailing through Sunday. A
slight chance of rain is introduced clipping the far southern
portion of the CWA, mainly around the Middlesboro area, for a few
hours Sunday morning as a system slides by to the south, but even
here measurable rain chances are less than 20 percent.

The cooler and drier air mass and cloud cover from a passing
southern stream system will play a role in how low temperatures fall
tonight, and additionally whether the area sees any frost. COOP MOS
values continue to trend slightly warmer for lows tonight, likely
due to more extensive cloud cover, with most forecasts trending
toward the mid to upper 30s compared to lower to mid 30s. This will
likely favor frost formation tonight at least an on isolated to
widely scattered basis, but perhaps not on a widespread basis. Given
the low confidence, will allow day shift to assess the need for a
Frost Advisory for tonight.

.LONG TERM...(Monday through Saturday)
Issued at 400 PM EDT SAT APR 20 2024

The 20/12z model suite analysis beginning Monday morning shows a
shortwave trough over the Tennessee Valley as it rides through
cyclonic flow around a deep ~498 dam low over the northern Hudson
Bay. Upper level shortwave ridging is found upstream across the
mid-Mississippi Valley and also from the Upper Midwest into
Manitoba. An ~534 dam low is passing over Saskatchewan. A much
more substantial high amplitude longwave trough/low are found off
well off the West Coast. At the surface, high pressure ridging,
centered over the Ozarks, extends from eastern Texas through the
Ohio Valley/Great Lakes and up toward James Bay. Meanwhile low
pressure is situated over southern Saskatchewan.

Quiet weather will persist on Monday and Monday night as the
aforementioned surface high translates east across our region.
Another night of frost concern in valleys is probable on Monday
night given the dry air mass with light winds and mostly clear
skies. Heading into the Tuesday and Tuesday night, the upper low,
over Saskatchewan initially, will translate eastward to over the
St. Lawrence Valley, bringing its attending surface low with it
while also dropping a cold front toward the Ohio Valley. There is
substantial disagreement as to how much this weaker upper low will
interact with the deep upper low over eastern Canada. The
deterministic 12z GFS as well as the GEFS generally insist on the
two lows phasing and dropping down toward New England, which would
lead to a significant surge of cold air spilling southward in the
Ohio Valley behind the cold frontal passage early Wednesday. This
however, is not supported by the deterministic 12z ECWMF/GDPS nor
those model`s most recent associated ensemble systems. After high
pressure makes a brief return on Thursday, the next upper level
trough (or troughs) will approach the Ohio Valley. The significant
model differences emerging from the mid-week system continue into
the weekend, leading to lower than normal forecaster confidence
in the details. Rain chances could return as early as Friday
morning, though many ensemble members favor any notable rain
chances holding off until later in the weekend or even some point
in the following week. This could mean the difference between a
several day stretch of mainly dry and very mild weather or just
cool, damp and rainy conditions. The NBM offered a compromise
solution for the forecast during these uncertain portions of the
forecast. Significant refinements are likely once models present
a more cohesive solution.

In sensible terms, high pressure will bring fair weather and a
warming trend through Tuesday. Monday will be milder than Sunday
with widespread maximum temperatures in the lower to middle 60s
under a cool northerly breeze. Winds won`t shift to the southwest
until Monday night when the high pressure ridge axis passes. With
the high pressure still in place, another chilly night can be
expected Monday night with minimum temperatures deep in the 30s
for many deeper valley locales. Ridges will largely see minimum
temperatures in the lower to middle 40s. Milder temperatures can
be expected on Tuesday as return flow increases ahead of the next
cold front -- southwesterly breezes gusting up to around 20-25 mph
will help raise afternoon temperatures into the 68-74 range for
most locations. Rain chances rise from the northwest Tuesday
evening as that cold front approaches and peak overnight before
falling off on Wednesday. Overall QPF with this system is light
(less than 0.20 inch in northern counties ranging to little or
nothing along the Kentucky/Tennessee border). Thunder was removed
from the forecast due to lack of instability. The weather pattern
from Wednesday onward is less certain due to significant model
disagreement. For right now though,temperatures behind the front
are expected to cool off into the 60s to near 70 on Wednesday and
Thursday, under partly cloudy to mostly clear skies. Frost cannot
be ruled out again in the sheltered valley locales on late
Wednesday night and Thursday morning as low temperatures are
forecast to most likely range in the lower to mid 30s in those
areas. Temperatures up to the lower 40s on are forecast on ridges.
There are scenarios in which these values could run several
degrees warmer or cooler. Southerly return flow returns by Friday
as the next storm system approaches, but the return of substantial
rain chances in our area remains uncertain. If the drier
scenarios materialize, a warm weekend will be on tap with
temperatures climbing back to above normal. If the wetter
solutions play out, then conditions would take on a more soggy
character with near to below normal temperatures.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
ISSUED AT 134 PM EDT SAT APR 20 2024

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

&&

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

$$

UPDATE...HAL/CMC
SHORT TERM...CMC
LONG TERM...GEERTSON
AVIATION...HAL