Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 212234

National Weather Service Jackson KY
634 PM EDT Wed Oct 21 2020

Issued at 634 PM EDT WED OCT 21 2020

Did a quick update to refresh the temps based on the current
observations. As the sun begins to set, some of our locations,
specifically the deeper NE valleys, are already starting to drop
off quickly significantly. We are still early enough in the
evening shift that it may be too early to decide if the low
temperatures for these locations will hold...but the forecast
seems to trend pretty well. Will update as necessary as new
observations come in. Otherwise, clouds are quickly dissipating
with the loss of daytimd heating/mixing, and winds are fairly
light. All updates have been published and sent to NDFD/web.


.SHORT TERM...(This evening through Thursday night)
Issued at 525 PM EDT WED OCT 21 2020

A modestly amplified long wave pattern is currently in place
across the CONUS. Ridging remains positioned along the eastern
Pacific as well as the western Atlantic. Ridging extends southwest
from this center into the central and southern Appalachians.
Broad cyclonic flow extends south into the northern CONUS from a
low center near northeast Nunavut. At the surface, seasonably
strong high pressure is sprawled from Alaska into western Canada,
with another area of high pressure centered across northwestern
Atlantic, with ridging extending southwest through the Mid-
Atlantic region and through the lower Mississippi Valley. Eastern
Kentucky has enjoyed the high pressure influence, with scattered
cumulus on the gradual demise. Highs today were in the upper 70s
to lower 80s.

The models are in good agreement through the short term, with
troughing deepening across the Rockies/Plains, as short wave
energy arcs from the Northern Great Basin through the Northern
Plains/Upper Midwest by early Friday morning. This will gradually
buckle the western Atlantic ridge through the period. At the
surface, low pressure will emerge from the Central Plains. This
low will move northeast, centering itself across the Great Lakes
by late Thursday night, which will result in the advancement of a
cold front towards the Mississippi Valley.

Dry weather will continue to be the rule across eastern Kentucky
through the short term, as we remain under the influence of high
pressure and modest return flow. Mostly clear skies and valley fog
will be seen tonight, with valleys dipping into the lower 50s,
while ridges remain in the upper 50s. Thursday should see
temperatures similar to perhaps a degree warmer compared to today,
around 80 degrees, under mostly sunny skies. By Thursday night,
eastern valleys will likely dip into the lower 50s once again,
while broader valleys remain in the mid to upper 50s. Ridges will
be warmer still, generally lower 60s, given the slightly better
southerly flow in place.

.LONG TERM...(Friday through Wednesday)
Issued at 525 PM EDT WED OCT 21 2020

At the beginning of the forecast period, the ridging that was over
our area aloft starts to get eroded by an approaching trough. We
then enter the beginning of a stretch of more active weather as a
wave moving through the trough supports a surface low moving into
eastern Canada. This low will drag a cold front east across the
Mississippi Valley towards our area. With the support of a moist
airmass and this approaching front, our area sees an increase in
rain chances through the afternoon and continues through the
night and into the day Saturday. There is still some instability
shown in forecast soundings, so have continued to keep mention of
thunder. There is starting to be more agreement over how the
progression of this front is handled Saturday onward. It`s set to
push further through the area than previously shown, before
eventually stalling Saturday night and then lifting northward on
Sunday. Temps stay warm Friday with highs in the upper 70s, helped
by the southerly to southwesterly flow ahead of the front. With
the front`s arrival Saturday, highs cool to the low 60s to low 70s.
Nighttime lows go from the mid to upper 50s Friday to the low to mid
50s Saturday night. High temperatures rebound some on Sunday and
Monday, back into the mid 70s, while lows continue in the mid to
upper 50s.

After a breif period of decreased PoPs on Sunday, rain returns to
the forecast Monday as a developing surface low pushes a second cold
front towards the area. This is supported aloft by a second, more
potent wave riding through the upper levels and amplifying the
trough. There is still a decent amount of uncertainty over timing,
with a fairly large spread in guidance for Tuesday. So, have kept
closer to the NBM solution during that time period for now. In
general though, slight chance to chance PoPs continue through
Tuesday before gradually fading through Wednesday and temps start to
cool down.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)

Scattered 4k feet agl cumulus will dissipate by early this
evening. MVFR or worse fog will develop once again tonight,
particularly in the deeper river valleys. Have followed the
persistence idea at KLOZ, KSME, and KSYM, patterning after what
had occurred last night. Did allow for a slightly later start for
the visibility restrictions, given the relatively drier
conditions compared to yesterday. The fog will burn off through
14z, with VFR conditions returning. Southwest winds of 5 to 8 kts
will become light by early this evening.




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