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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS63 KJKL 050447
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1147 PM EST Thu Mar 4 2021

.UPDATE...
Issued at 1147 PM EST THU MAR 4 2021

A few lower clouds are working into far eastern Kentucky, but this
has mostly been few to scattered in nature. This likely brought on
by a weaker wave. Outside of this cold air continues to work
southward tonight under the northerly flow around a surface high
pushing into the Great Lakes. Updated the forecast to align
mainly hourly temperatures closer to the latest obs and trends.
Also added a little more cloud coverage in far eastern Kentucky.

UPDATE Issued at 933 PM EST THU MAR 4 2021

Surface high pressure is pushing southward into the Ohio Valley
this evening. This is providing cold air advection under northerly
flow. Adjusted the temperatures to handle the latest obs and
trends, but otherwise there are no other changes planned at this
time.

&&

.SHORT TERM...(This evening through Friday night)
Issued at 640 PM EST THU MAR 4 2021

An amplified upper level pattern is currently in place, with a
deeper upper level low across eastern Quebec, allowing for
troughing along the Eastern Seaboard. Sharper ridging is aligned
from western Canada down through the northern Rockies, with an
upper level low undercutting the ridge axis rotating towards the
southern Plains. At the surface, high pressure is sprawled from
north central Canada down through the Tennessee Valley. Delayed
cool air advection, combined with sunny skies and plenty of low
level dry air, allowed for another overachieving high temperature
forecast. Readings topped out in the upper 50s and lower 60s
across the southern half of the forecast area, with mainly mid to
upper 50s seen north.

The upper level pattern will continue to amplify through the short
term, with broad troughing expanding further west from the Eastern
Seaboard with time. By early Saturday, the trough will reside over
most locations east of the Mississippi River. This will result in
cooler temperatures across the Ohio and Tennessee valleys, but
also continued tranquil weather, thanks to dry air being
maintained in the low and mid levels.

Cooler nights and days are ahead for eastern Kentucky, as low
level flow becomes more north to northwest through the period, as
high pressure gradually builds in across the Ohio Valley. Lows
will average in the low to mid 20s in the valleys, with mid to
upper 20s on the ridges. Highs on Friday will range from the mid
to upper 40s for most locations, with a few lower 50s across the
far southwest. Skies will be mostly clear, besides some passing
high clouds Friday afternoon and evening.

.LONG TERM...(Saturday through Thursday)
Issued at 450 PM EST THU MAR 4 2021

Quiet weather, courtesy high pressure, will persist through most
of the long-term period as the models remain in excellent to good
agreement into the middle of next week. A storm system could bring
rain chances by next Thursday or Friday but significant model
spread remains. Beginning Saturday morning, the latest models
show ~1035 mb surface high pressure dropping southward from
western Ontario/eastern Manitoba while a ridge of high pressure
extends southeastward to over the Carolinas. This will keep a dry
northwesterly flow over eastern Kentucky for Saturday and Sunday.
The high pressure center will gradually move southeastward and
crest over the Ohio Valley and Great Lakes late Sunday and over
the Carolinas on Monday. Southwesterly flow will develop along the
back side of the high, ushering in moderating temperatures and
slowly rising humidity levels. Dry weather will continue into
mid-week before a cold front and its supporting upper level
trough approach from the northwest on Wednesday with increasing
mid-to-upper level moisture and a tightening pressure gradient.
Some rain chances are possible by Thursday or Friday.

In sensible terms, look for clear to partly cloudy skies through
Tuesday. Initially, a chilly northwesterly breeze on Saturday will
keep high temperatures in the 40s to possibly 50s near the
Tennessee border. That breeze should slacken on Sunday allowing
the bright sunshine to boost highs to within a few degrees of 50.
The moderating trend will continue on Monday with temperatures
nearing 60 and reaching well into the 60s for Tuesday. The
combination of light winds, clear skies, and very dry air will
result in sharp ridge-valley temperature splits each night. The
coldest nights will be Saturday and Sunday nights when some of the
more sheltered valleys could drop well into the mid-to-upper
teens; but the thermal belt ridges should bottom out in the mid
to upper 20s. Relative humidity levels will drop sharply each
morning, bottoming out between 20 and 35 percent on each
afternoon through Tuesday. Fortunately, winds should remain fairly
light. Southwesterly flow will strengthen and become gustier on
Wednesday and Thursday. While much of the guidance suggests that
humidity levels will recover to above critical fire levels by
Wednesday, warmer than than currently forecast temperatures could
result in lower humidity levels. Given this potential, those with
fire weather concerns may want to monitor forecast trends as we
approach the middle of next week. By Thursday or Friday, increased
cloud cover and rising rain chances return.

The NBM guidance has generally been too diurnally limited and
moist in recent days relative to observed values. This might be
due, at least in part, to the various models struggling to resolve
strong sensible daytime heating and also the NBM time-lagged bias
corrections. Therefore, high temperatures were adjusted 2 degrees
higher than NBM guidance for each afternoon through Tuesday. Low
temperatures were also lowered sharply towards COOP MOS in valley
locations to account for rapid radiational cooling each night. Dew
points were lowered toward the raw model guidance and the GFS MOS
through the entire period.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
ISSUED AT 708 PM EST THU MAR 4 2021

There is the potential for some high clouds by late in the period,
but outside of this no issues with CIGs or Vis. The front has
passed bringing mostly lighter northerly flow to the region at
around 5 to 10 knots.

&&

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

$$

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