Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 040850

National Weather Service Jackson KY
450 AM EDT Tue Oct 4 2022

.SHORT TERM...(Today through Wednesday)
Issued at 450 AM EDT TUE OCT 4 2022

08Z sfc analysis shows high pressure in place to the north of
the state with weaker low pressure to the east. This is keeping
light northeast flow of air over eastern Kentucky under clear
skies. These conditions have meant a good night for radiational
cooling resulting in dense river valley fog in the central and
southeast parts of the area, patchy frost in the northwest parts,
and an overall ridge to valley temperature split. Specifically,
the fog was thick enough, per observations and on satellite, that
an SPS is out highlighting the low visibility concerns this
morning. Also, temperatures are varying from the upper 30s in
sheltered valleys in the west while mid 40s are reported on the
ridges and for much of the south. Dewpoints, meanwhile, are
generally in the upper 30s north to mid 40s south.

The models remain in good agreement aloft through the short term
portion of the forecast. They all depict the closed troughing to
the east weakening and starting to move offshore. As it pulls
away some weak ridging slips over Kentucky tonight and Wednesday
in advance of another trough moving toward the area from the
northwest. The small model spread again supported using the NBM as
the starting point for the forecast grids along with some
adjustments within its own PDF to address drier conditions each
afternoon - due to deep mixing.

Sensible weather will feature a warmer and drier day, today, as
less clouds will mean better and deeper mixing - reaching the
drier air aloft to be brought to the sfc. This happens both this
afternoon and Wednesday afternoon so have used the NBM`s 10
percentile values for dewpoints during these key times. For
tonight, similar to this current night we anticipate a decent
ridge to valley temperature split owing to good radiational
cooling under clear skies and light winds. Additionally, look for
river valley fog to again form - though likely not quite as thick
as this morning - along with patchy frost in the most sheltered

Did make the usual terrain based adjustments tonight as well as
the above described dewpoint/humidity changes. The PoPs remain
near zero in the models and saw no reason to adjust them.

.LONG TERM...(Wednesday night through Monday)
Issued at 343 AM EDT TUE OCT 4 2022

1. Clear skies and colder temperatures will allow for damaging frost
development from Friday night through Sunday morning.

2. Widespread damaging frost or killing freeze possible Saturday
night into Sunday morning.

Analysis and Discussion: Weak ridging develops behind the departing
closed circulation situation off the Eastern Seaboard for the start
of the period. As the forecast area sits under and eventually on the
southwestern flank of the ridge, temperatures are forecast to warm
in the mid-70s. However, models continue to dig a trough out of the
Upper Midwest for late Thursday into Friday. The associated surface
low is progged to move through northern Ohio and southern Michigan
with the weak cold front progged to move through the region on
Friday. The weak front won`t produce much in measurable
precipitation as moisture is lacking. Therefore, the only way to
know a front went through is the temperature drop behind the front.
Temperatures from Friday to Saturday are still expected to be around
10 to 15 degrees cooler. Overnight lows are still expected to be 15
to 20 degrees colder. As a result of the colder temperatures;
widespread frost and freeze potential exists through the weekend.
Nonetheless, models are still hinting at a rather active period with
another trough digging out of the southern Canada but this one
staying further to the north but once again, moisture is lacking;
therefore, little impacts are to be expected. Otherwise with the
lack of moisture, the period looks to remain mostly dry with
temperatures climbing back into the mid-70s through the end of the


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)

VFR conditions will mostly prevail through the period, as high
pressure remains over the Great Lakes into Tuesday. River valley
fog is thickening per satellite and has already impacted the KSJS
terminal. Perhaps KSME also sees some reductions into dawn but
the rest of the TAF sites should be unaffected. Winds will be
light and variable into the morning before picking up out of the
north, but still less than 10 kts, through the afternoon.




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