JKL issues Area Forecast Discussion (AFD) at Aug 28, 4:43 PM EDT003
FXUS63 KJKL 282043
AFDJKL
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
443 PM EDT Wed Aug 28 2024
.KEY MESSAGES...
- Record or near record high temperatures are forecast through
Friday.
- A modest cool-down is expected for the weekend and beyond.
- While showers and thunderstorms are possible Friday through
Sunday, the greatest potential for rain will occur on Saturday.
&&
.SHORT TERM...(This evening through Thursday night)
Issued at 435 PM EDT WED AUG 28 2024
Late this afternoon, an upper level ridge was centered across the
southeastern U.S and extended into the Appalachians. Further west
and northwest, an upper level low was centered near the
MT/Alberta/Saskatchewan border area. At the surface, a frontal
zone extended from portions of the Northeast across the southern
Great Lakes region to lower pressure in the Northern Plains. Sfc
high pressure was centered in the Southern Appalachians. A minimum
in PW extended from western TN into SW VA and portions of
southern WV. Nearer to the OH River and north PW is in the 1.6 to
1.8 inch range. Temperatures so far today have peaked in the 90s
for locations below 2500 feet elevation. Daytime heating and
mixing of the relatively drier air across southeastern KY in an
area of PW analyzed at 1.4 to 1.5 inches has allowed dewpoints to
drop into or remain largely in the low to mid 60s for most
locations. MLCAPE across the area is not much more than 500 J/kg.
Mid level lapse rates across the area are largely 6C/km or less,
while low level lapse rates are around 6C/km. Convection has
recently developed in portions of Northern KY and OH where
moisture and instability is a bit more notable. Locally over
eastern KY, cumulus has developed across the region this
afternoon.
Tonight and Thursday, an upper level ridge is expected to remain
centered across the Southeast Conus while the upper level low
moves gradually east across Canada to Manitoba by Thursday evening
with an associated trough south into the northern to central
Plains at that point. The upper level ridge should remain centered
in the vicinity of the southern Appalachians through Thursday
night as the upper low tracks northeast toward Hudson Bay and the
trailing shortwave trough axis extends into the Upper MS Valley to
end the period. Meanwhile, the sfc front north of the area should
sag a bit toward the OH River tonight and Thursday, but stay
north of the eastern KY. This boundary should lift back north late
Thursday and Thursday night as low pressure evolves well to the
northwest of the OH Valley.
This evening, as convection evolves over northern KY and southern
nearer to the OH River an outflow or additional development into
northern sections of the area cannot be completely ruled out,
generally north of Interstate 64. Some convective allowing model
runs have suggested this possibility so a slight pop was continued
for that area during the evening hours. Otherwise, with upper
level ridging remaining centered across the Southeast Conus and
sfc high pressure in place across the Southern Appalachians, the
cumulus should diminish by around sunset once again. With light
winds in place and limited cloud cover anticipated and factoring
in the afternoon min dewpoints from today, deeper valleys should
again experience temperatures dropping into the mid 60s while
ridgetops should settle into the lower 70s. Following highs today
about 3 degrees warmer than Tuesday, lows tonight should
generally be a couple of degrees warmer than what was experienced
this morning.
For Thursday, 12Z HREF mean 850 mb temperatures are similar to
what occurred today. Highs were forecast similar to what has been
observed so far today. NBM deterministic dewpoints were again
undercut and trended toward the NBM 10th percentile factoring in
the rather dry airmass and recent dry weather. Some convective
allowing model runs have a bit more convective development
compared to today and further south into the CWA. Confidence in
this is not overly high, but at a minimum, more cumulus should
develop. Slight pops were carried for areas generally near and to
the east and northeast of US 421. Any convection should wane on
Thursday evening, with at least a small ridge valley split should
follow as well. Lows are expected to average another degree warmer
compared to what occurs tonight.
.LONG TERM...(Thursday night through Tuesday)
Issued at 540 AM EDT WED AUG 28 2024
The upper level ridge over the southeast CONUS bringing us our
hot weather will be weakening by the time the long term period
begins. This should allow a cold front to sink south to near the
Ohio River by Thursday evening before it stalls. The presence of
the front along with the weakening upper high and a
modifying/moistening air mass could be enough to allow a few
thunderstorms to develop or carry over into the evening, mainly
for our northern counties closest to the front and in our
southeast counties with elevated terrain. Any convection should
die out in the night.
With the same air mass in place, sunshine and heating on Friday
will again bring an unseasonably hot day for late August. Another
cold front will approach from the northwest on Friday, supported
by an upper trough dropping east southeast over the upper Midwest
and Great Lakes. Southwest low level flow ahead of the front will
continue to carry moisture into the area and will probably fuel
isolated to scattered thunderstorm development in the afternoon
after sufficient heating/destabilization occurs. Unlike Thursday
night, there's a better possibility for some activity to carry
into the night as the cold front approaches and geopotential
height falls continue with the advancing upper trough. What's
left of the weakening cold front is expected to move through KY on
Saturday and Saturday evening. With the diurnal heating cycle on
Saturday, we should see our highest POP, and likely category has
been used. The clouds and precip will also hold temperatures down
on Saturday.
An impulse moving through the developing eastern CONUS upper
trough will send another cold front southeast into KY late Sunday
and exiting southeast Sunday night. Precip is more questionable
with this front due to the previous one taking out much of the low
level moisture. The best chance at rain will be in southeast KY on
Sunday, where the low level moisture will linger the longest.
Both the ECMWF and GFS look like they have a strong enough surge
of cooler and drier air behind Sunday's front so that we see a
return of dry weather at least for Monday and possibly Tuesday,
along with more comfortable temperatures and humidity. The models
generate a few diurnal showers over the high terrain near the KY
and TN borders on Tuesday afternoon. Have allowed for a 20% POP
there, but that may be questionable.
&&
.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
ISSUED AT 228 PM EDT WED AUG 28 2024
VFR conditions were prevailing across all of eastern KY and the
TAF sites at issuance time. Some cumulus have developed in the 5
to 6kft range and some of these will likely linger into the
evening, before dissipating toward sunset. Some convection may
develop near or north of the area as the afternoon progresses, and
this could potentially affect KSYM and have maintained VCTS for
KSYM between 21Z and 03Z. Outside of any isolated convection in
the north, light and variable winds are expected.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...JP
LONG TERM...HAL
AVIATION...JP
Source:
JKL issues Area Forecast Discussion (AFD) at Aug 28, 4:43 PM EDT---------------
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