982
FXUS63 KJKL 171204 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
804 AM EDT Sat Aug 17 2024

.KEY MESSAGES...

- Strong to severe storms are expected to impact the area today.
  Damaging wind gusts appears to be the greatest hazardous
  weather threat and would most likely be associated with more
  organized storms...i.e. line segments and storm clusters.

- Below normal temperatures are expected Sunday through Wednesday
  behind a cold front passage late Saturday night.

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

&&

.UPDATE...
Issued at 659 AM EDT SAT AUG 17 2024

Area webcams and a couple incoming COOP reports indicate that
visibilities are improving at the surface, and much of the fog
appears to be lifting across the area. Consequently allowed the
special weather statement to expire and this early morning update
is mainly to bring forecast products in agreement with current
trends. Otherwise, grids were in good shape. No other changes to
the forecast package at this time.

&&

.SHORT TERM...(Today through Sunday)
Issued at 448 AM EDT SAT AUG 17 2024

Aloft, low over the Great Lakes Region will spin its way from
Lake Superior to Lake Erie/Ontario during the short term. Two
short wave disturbances will be rotating around the southern
periphery of the trough early in the period as the low slides
southeastward. The first is expected to pass through the
Commonwealth very early in the period, while the second of the two
short waves drops southeast into the Ohio Valley later this
evening. Recent model guidance has been somewhat inconsistent with
the evolution of sensible weather, putting into question the
exact amount and timing of convection each wave will generate
across the area.

Overall, the bulk of guidance suggests at least two general
rounds of precipitation today. Earlier solutions had convection
firing across eastern Kentucky during the morning, but trends
delay the start of convection until mid-day or just after. The
second round has been more consistent and transits our forecast
area this evening. Thinking is today`s rainfall may be broken up
in several rounds, similar to Friday, where segments of organized
convection transit different portions of the area at various times
through the afternoon and evening.

Based on some of the latest CAM solutions, the best bulk shear is
found across our southern zones Saturday, but is marginal at
30-35 kts. Better environmental shear (35-45 kts) develops by late
afternoon into this evening. The best instability is realized
during the daylight hours with heating, with MLCAPE climbing to
1500-2500 J/kg...with greater CAPE centered more across our
southwestern zones. Wind fields aloft could be more favorable with
H500 and H850 winds averaging less than 35 kts over eastern
Kentucky. In addition, the best diffluent flow aloft is earlier in
the day. Low level lapse rates appear strong (7-8C/km+), but mid
level lapse rates are relatively weak (~ 5C/kg). Overall have
definitely seen more impressive storm environments. But SPC does
have the area within a marginal to slight risk today.
Consequently, strong storms could be possible, and a few storms
producing severe weather can not be ruled out. If analysis of the
storm environment is accurate, damaging wind gusts would be the
greatest hazardous weather threat and would most likely be
associated with more organized storms...i.e. line segments and
storm clusters. Without steeper lapse rates aloft and other more
favorable storm environmental parameters, feel the hail threat
will be minimal.

A third short wave rounds the bottom of the trough by Sunday.
Forecast soundings show ample instability across the area with
MLCAPES climbing to between 1000-1500 J/kg during peak heating of
the afternoon. However, bulk shear is around 15 kts or less, which
is not favorable for organized convection. Interestingly, the NBM
blend continues to advertise a consistently high 80-90% PoP for
Sunday; quite high considering the nature of convection will be
strongly driven by diurnal heating...instability showers and
thunderstorms. Thus while activity will be scattered, effectively
there is high probability most of the forecast area will measure.

.LONG TERM...(Sunday night through Friday)
Issued at 448 AM EDT SAT AUG 17 2024

After one last day of active weather on Monday, the upper level
low responsible for this weekend`s convection will open up into
broader troughing and eject up into New England next week. In its
wake, forecast guidance places Eastern Kentucky in a regime of
generally weak meridional flow aloft. At the surface, the model
suite collectively suggests that a high pressure will push into
the Great Lakes region. Together, these features reinforce the
idea that next week`s weather will be both cooler and drier than
what we have witnessed here as of late.

As hinted at above, rain chances remain in the forecast for
Monday, albeit at slightly lower values than the previous days.
With the passage of Sunday`s frontal boundary, the best surface-
level support for organized convection will be removed far from
the forecast area. Thermodynamic support will also be fairly
meager, with afternoon highs only in the mid to upper 70s.
However, favorable PVA on the backside of the troughing aloft will
support scattered shower activity into the afternoon hours. The
greatest PoPs will be in our eastern tier counties, where
northwesterly flow throughout the column may locally enhance
chances on the windward side of higher terrain via orographic
lifting processes. Rain chances dwindle down during the evening
and overnight hours on Monday as dry air advection begins to
dominate and skies correspondingly clear. Overnight lows on Monday
will be in the low to mid 50s, and these cooler temperatures
foreshadow the fall-like conditions in the forecast for the much
of the work week.

Under mostly clear skies and a modified continental polar
airmass, temperatures will be below average values on Tuesday and
Wednesday. Afternoon highs will be in the mid to upper 70s, with
efficient diurnal mixing processes reducing the dewpoint and thus
the relative humidity. Overnight, expect pretty potent
ridge/valley thermal splits, with some of the deepest valleys
potentially dropping into the upper 40s on Tuesday and Wednesday
nights. Elsewhere, expect MinTs in the 50-55 range. While it will
feel great outside for much of next week, this little taste of
fall will not last forever. The surface high responsible for this
will shift east on Thursday, bringing about a shift to southerly
winds by Friday. Temperatures respond by increasing a little each
day, and highs will return to near climatological norms (mid to
upper 80s) on Friday. As the high shifts east, ridge/valley splits
will be favored in the more eastern locations for Thursday night
and perhaps additional nights. PoPs will remain below 10 percent
through the rest of the period though. Thus, with the exception of
Monday, the weather in this particular long term forecast package
will be pleasant.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
ISSUED AT 803 AM EDT SAT AUG 17 2024

At issuance time, conditions ranged from LIFR to VFR as fog and
low stratus are gradually lifting and in the process of mixing out.
In addition to any low clouds or fog, some high clouds were
passing by from time to time as well. The fog and stratus should
continue to lift and dissipate through 13Z or no later than 14Z
and give way to VFR areawide. KSME and KSJS are not affected by
reductions initially, however, KJKL, KLOZ, and KSYM are. Rounds of
convection are expected to affect the area at times after 15Z as
a series of disturbances cross the area and interact with daytime
heating. Disturbances continuing to cross the area will lead to
lingering chances for convection even after 00Z. Reductions to
MVFR and IFR will be possible briefly as these pass a location.
Winds initially light and variable, will average from the
southwest at around 10KT or less during the 14Z to 00Z timeframe.
Light and variable winds are expected thereafter. Stronger gusts
are anticipated in thunderstorms, especially during the afternoon
and evening. Late in the period, guidance suggests some reductions
down into the MVFR range or lower are possible

&&

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

$$

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