604
FXUS63 KJKL 181055 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
655 AM EDT Sun Aug 18 2024

.KEY MESSAGES...

- Below normal temperatures are expected today through Wednesday
  behind a cold front passage today.

- Showers and thunderstorms will remain possible today and
  Monday, especially in the afternoon and early evening, with a
  drying trend for Tuesday into Wednesday.

&&

.UPDATE...
Issued at 655 AM EDT SUN AUG 18 2024

Early morning update to the forecast to incorporate developing
showers across our northern zones. Showers in northwest flow are
beginning to kick off a little earlier than expected. In general,
the probability of showers and thunderstorms will be increasing
through the morning. Brought hourly temps in line with current
surface observations as well. No other significant changes to the
forecast package at this time. Updated zones and grids have been
issued.


&&

.SHORT TERM...(Today through Monday)
Issued at 432 AM EDT SUN AUG 18 2024

Aloft, eastern Kentucky will be under a northwest flow regime
through the period. Great Lakes mid/upper level low begins to fill
and opens up into a trough as it begins to lift northeast out of the
region. Short wave energy will be dropping into the base of the mean
trough centered over the Midwest today. At the surface, a cold front
is current poised to move through eastern Kentucky and is expected
to be southeast of our forecast area by around mid-day. There is
good model agreement with respect to this timing, both among
operational models and CAMs.

Sensible weather features the beginning of a cool spell with
afternoon high temperatures some 5-10 degrees below our normal mid
80s. However, initially our area will have to deal with the threat
of rain through the period, mainly in the afternoon and early
evening during peak heating. If forecast soundings and profiles are
correct, lapse rates are not great above the first ~4-5 kft of the
boundary layer, but the column aloft is cold enough that any
convection that does fire will have the opportunity to develop into
thunderstorms, especially today. MLCAPES climb to between 750-1250
J/kg during peak heating this afternoon. Bulk shear is weak across
the area today and Monday, on average less than 20kts. Also, by
Monday afternoon, there is a mid level cap that begins to form as
ridging begins to spread over the region. In general instability
showers and thunderstorms can be expected during the afternoon hours
over much of the forecast area today and mainly over our central and
southeastern zones Monday. Convection is expected to unorganized and
discrete.

.LONG TERM...(Monday night through Saturday)
Issued at 432 AM EDT SUN AUG 18 2024

This particular long term forecast package is defined by clearer
skies and cooler temperatures than what we have witnessed here in
Eastern Kentucky as of late. This drier and cooler air will advect
into the region via northwesterly/northerly flow throughout the
atmospheric column on the backside of the now-ejected upper level
low pressure system that caused this weekend`s active weather. At
the surface, a high pressure system will drop into the Great Lakes
Region from Canada. Together, these features will work to instill
a modified continental polar airmass over the forecast area. This
notion is confirmed by modeled NOAA HYSPLIT back trajectories for
next week, which suggest that this airmass originated in
Northwestern Ontario/Saskatchewan. This particular piece of
forecast guidance also suggests that the air will be subsiding
(sinking) as it approaches the Ohio River Valley, which reaffirms
the notion that this airmass will be dry. As such, skies should be
mostly clear next week, although the potential for some Canadian
wildfire smoke to advect into the air aloft will need to be
monitored closely in the coming days.

In short, fall-like sensible weather should settle into Eastern
Kentucky on Monday night and stick around until Thursday, when the
surface high shifts east and southerly return flow begins to
slowly reintroduce warm, moist air into the column. Under clear
skies, expect well-defined ridge-valley temperature splits and
perhaps the formation of patchy valley fog on Monday, Tuesday, and
Wednesday evenings. In low-lying areas, overnight lows could drop
down into the upper 40s on Tuesday and Wednesday, whereas
ridgetops will see MinTs in the lower 50s. Afternoon highs will be
climatologically cooler than normal for this same time period,
with temperatures staying in the 70s across the entire area on
these dates. By Thursday, a warming trend will emerge, and
afternoon highs will incrementally increase into the 80s and then
perhaps the lower 90s in the Bluegrass by Saturday afternoon. Both
low temperatures and dewpoints will recover into the 60s in this
same time frame, and cloud coverage should subtly increase in
response to these warmer temperatures. Precipitation chances,
however, remain suppressed below 10 percent for the entirety of
this week`s forecast. Thus, no hazardous weather is expected at
this point for the Monday night to Saturday timeframe.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
ISSUED AT 228 AM EDT SUN AUG 18 2024

Showers and thunderstorms continue to wane across the area.
Main forecast challenge will be residual moisture and the
development of low stratus and at times fog. MOS guidance is
generally optimistic, especially with VSBYS. However, LIFR to MVFR
CIGS can not be ruled out at times. Regional satellite does show
some patchy, transient low stratus going through cycles of
developing and dissipation across the area. In addition, ensemble
solutions show a fairly high probability (60-80%) of at least
LIFR CIGS at times through 13-14Z. Ensemble mean VSBYS also drop
to between 2-5 miles at times, especially across the north where
there is a bit more clearing and thus a better chance for the
development of patchy fog. Thus the potential for lower stratus,
and at times some light fog will exist through the remainder of
the overnight, or until the surface front clears the area.
Currently the surface boundary is positioned roughly from KFGX to
KFFT, to just south of KSDF. It will take from now until around
15Z for the surface front to move completely southeast of the
forecast area. Winds will be light, around 5 kts from the west,
but will veer out of the west-northwest through the day at 5-10
kts.

&&

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

$$

UPDATE...RAY
SHORT TERM...RAY
LONG TERM...MARCUS
AVIATION...RAY