Area Forecast Discussion
Issued by NWS Jackson, KY-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS63 KJKL 270320 AAA
Area Forecast Discussion...UPDATED
National Weather Service Jackson KY
1120 PM EDT FRI AUG 26 2016
-- Changed Discussion --Issued at 1120 PM EDT FRI AUG 26 2016
The forecast is on track, just did a quick touch up to the T/TD
and sky grids per the latest Obs and trends. These have been sent
to the NDFD and web servers.
UPDATE Issued at 740 PM EDT FRI AUG 26 2016
23z sfc analysis shows high pressure off to the northeast of
Kentucky helping to keep the eastern part of the state dry while
scattered thunderstorms are found on the fringes of this high.
Warm and humid conditions continue with dry bulb temperatures in
the upper 70s to mid 80s currently with dewpoints running in the
low to mid 70s most places, yielding heat indices in the low to
mid 90s. Winds are not much help with the heat this evening with
the majority of observations light and variable. Meanwhile, skies
are mostly clear through the region aside from storm clouds to the
south and west of the area. Look for a similar night as last with
mostly clear skies and muggy conditions. Patchy valley fog will be
locally dense during the late night hours, but likely not quite as
pervasive as last night/early this morning. Have updated the
forecast to reflect this and also to tweak the near term T/Td
grids per the latest ShortBlend guidance, obs, and trends. These
updated grids have been sent to the NDFD and web servers.
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.SHORT TERM...(This evening through Saturday night)
Issued at 331 PM EDT FRI AUG 26 2016
Upper level high pressure center continues to churn from the
Appalachians into the Mid-Atlantic, with disturbances and associated
storms riding around its western periphery from the Mid-Mississippi
Valley into the Ohio Valley and Great Lakes. Weak surface ridging
across the Ohio Valley and Great Lakes will keep light downslope flow
in place, thus maintaining a relatively drier airmass across eastern
Kentucky. Still seeing dewpoints in the mid 60s to low 70s, but this
is lower than those in the low to mid 70s experienced yesterday.
This afternoon`s cumulus field has therefore been more shallow and
less vast in coverage, allowing temperatures to continue climbing
through the upper 80s and into the lower 90s within the next hour
Clearing skies will then take place this evening. Expecting fog
development to be less robust than what occurred last night given
lower crossover temperatures with this afternoon`s lower dewpoints.
Light downslope flow should preclude much in the way if any fog from
occurring in the higher terrain of eastern Kentucky. Will likely
still see patchy development, perhaps becoming dense at times, in a
few of the typically fog-prone river valleys.
Saturday should be largely a repeat of today, but will leave
isolated storm mention in place across southeastern Kentucky into
the Lake Cumberland region as a slight uptick in deep layer moisture
occurs as aforementioned surface ridging to the north shifts east.
Will continue to see shortwave perturbations move around the
western periphery of the upper high, with a stronger wave expected
to move through the northern Plains into the western Great Lakes.
While forcing from this latter feature will be displaced well
northwest of the Bluegrass, strong diabatic heating once again,
evidenced by temperatures climbing into the low-mid 90s, combined
with veering winds ushering in this slightly greater moisture
could be enough to spark a shower or storm across the higher
terrain. Most likely scenario is for convection to occur along the
Cumberland Plateau and move north/northwest into the Lake
Cumberland region during the mid-late afternoon. Without any real
semblance of forcing aloft, any storm should remain shallow and of
the pulse variety. Warm and humid conditions will then bring
another night of patchy valley fog Saturday night into Sunday.
.LONG TERM...(Sunday through Friday)
Issued at 331 PM EDT FRI AUG 26 2016
The period will begin with a large ridge of high pressure parked off
the southeastern CONUS. The flow around the western edge of the high
will continue to bring warm and moist air off the western Gulf of
Mexico into the Ohio and Tennessee valley regions. The warm and
humid air mass that will be in place should provide enough energy to
spark showers and storms across the area, particularly in our more
rugged terrain, as it appears there will still be no well defined
trigger available. The best chances for rain will be during the
afternoon and evening hours during the period, with disorganized
scattered convection expected at best.
Temperatures will be hot and muggy to start things off, with daily
highs in the lower 90s Sunday and Monday, and around 90 on Tuesday.
Wednesday should be slightly cooler, as clouds and precipitation
cool things off a bit. Highs on this day are forecast to be in the
upper 80s for most locations. By Thursday we may even see a weak
cold front move through from the north. This change in air mass
would allow for even cooler readings, with highs on Thursday in the
mid 80s on tap, with the warmest readings in our far south along
the Tennessee border.
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
ISSUED AT 800 PM EDT FRI AUG 26 2016
VFR conditions with light winds will persist through the rest of
the evening at all sites. Then we will once again see some fog
development, potentially becoming dense in some river valleys.
Current thinking remains that terminals will see less of a threat
for dense development given strong heating and lack of rain
today, but persistence and nearby presence of weak surface ridging
centered near the Great Lakes warrants maintaining at least some
MVFR/IFR visibilities for now at LOZ/SME/SYM from approximately
8-13Z. Very light downslope flow should provide just enough
subsidence to keep fog from reaching SJS/JKL. Dewpoints also mixed
a tad lower early this afternoon, so crossover temperatures will
have a little tougher time being reached, likely inhibiting
widespread fog development.