423
FXUS63 KJKL 011653 AAB
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
1253 PM EDT Wed May 1 2024

.KEY MESSAGES...

- Very warm this afternoon, followed by near-record highs on
  Thursday.

- Shower and thunderstorm chances return to the forecast Friday
  through Tuesday.

&&

.UPDATE...
Issued at 1220 PM EDT WED MAY 1 2024

Hourly grids were freshened up based on recent observations and
trends. Sfc and upper level high pressure will lead to warmer and
drier weather compared to Tuesday with a few passing cirrus and
fair weather diurnally driven cumulus.

&&

.SHORT TERM...(Today through Thursday)
Issued at 308 AM EDT WED MAY 1 2024

A very foggy start this morning for most of the forecast area; areas
along the escarpment are the exception as of this writing. However,
satellite trends show some subtle westward expansion of fog.
Therefore, there is still time for the likes of Somerset and
Morehead to experience fog. Conditions were ripe for fog given
rainfall that occurred during the day followed by clearing skies
and calm wind. While we will mix out nicely this afternoon
(temperatures soaring well into the 80s with dew points in the
50s), ensemble forecast soundings indicate the low-level
inversion will come roaring back overnight. Due to the anticipated
daytime mixing, we think the fog will be less widespread.
Therefore, we`ve introduced fog to the river valleys tonight to
start. This can be finessed further by day shift.

An upper-level ridge in place over the Southeast US amplifies on
Thursday, resulting in a hot afternoon. High temperatures will be
close to records. Jackson`s record is 87 set in 2012 while London`s
is 88 set in 1959. Relative humidities will plummet in the
afternoon which raises a non-zero fire weather concern (similar
conditions today, though RH value will be slightly higher). Of
course, recent rain will squelch the concern overall, as will
light wind.

One last item to consider on Thursday is a non-zero chance of an
isolated pop-up thunderstorm. The forecast remains dry at this time,
but this possibility was noted in the CAMs. Dew points in the 50s
will result in significant dew point depressions which will be
challenging to overcome. Ensemble soundings indicate marginal
instability of about 500j/kg and virtually no shear. However,
convective temperatures will likely be met which could afford at
least some cumulus clouds attempting to bubble up. Forcing may come
in the form of a weak perturbation rippling atop the ridge, ahead of
an incoming trough digging in over the lower Mississippi River
Valley.

.LONG TERM...(Thursday night through Tuesday)
Issued at 400 AM EDT WED MAY 1 2024

The 01/00z model suite analysis beginning Thursday evening shows a
stout upper level ridge axis extending from the Southeast US
northward in the eastern Ontario province. Broad troughing is
situated across the northwestern third of the CONUS around a
parent ~543 dam low spinning over southern Saskatchewan.
Translating down the surface, eastern Kentucky is sandwiched
between high pressure centered near Bermuda and a weak low
pressure over/near southeast Minnesota. A cold front extends
southward from that low across the Plains into Central Texas.

The upper level ridging will be shunted southeastward through the
upcoming weekend while the upper low tracks eastward into
Ontario. This will lead to a nearly zonal flow aloft over the
Ohio Valley by Sunday and Monday. Meanwhile at the surface, the
low pressure will lift toward the Hudson Bay and occlude on Friday
and Saturday. The system`s trailing cold front slows as it
approaches the Ohio Valley on Friday and eventually hangs up out
in the vicinity of the Ohio River on Saturday. By Saturday night
and Sunday a disturbance passing aloft, perhaps briefly initiating
a wave of low pressure that could push the boundary more firmly
south of the Ohio River by Sunday night. These system`s likely
lead to a couple of round of rainfall, primarily late Friday into
Saturday and again on Sunday. Looking ahead to early next week,
models are latching onto a deeply digging trough transiting the
Western CONUS late Sunday/Sunday night before quickly becoming
negatively-tilted and closing off into a low somewhere near/over
the Northern Plains. A strong low pressure system developing ahead
of this trough in the lee of the rockies would force the
aforementioned frontal boundary back northward as a warm front
early next week amidst an intensifying southerly return flow.
Multiple PWAT surges interacting with this frontal boundary may
lead to additional rainfall opportunities for us on Monday and
Tuesday.

In more sensible terms, shower and thunder chances return on Friday
as the cold front initially approaches. The latest guidance would
suggest that the activity reaches locations west of I-75 in the
morning and later in the day further east, perhaps not before Friday
night east of US-23. The arrival timing of that boundary`s
associated cloud cover will dictate high temperatures which are
presently forecast to range from the upper 70s in the west to well
into the mid 80s in the Big Sandy basin. Episodic hit-and-miss
shower and thunderstorm chances will then follow for each day
through the remainder of the period. While a shower or
thunderstorm appears possible at just about any time, the highest
chances are generally during the afternoon and evening when
instability will be greatest. Daily maximum temperatures are
forecast to drop back into the mid 70s to lower 80s for the
Saturday to Monday timeframe before rebounding into the lower to
middle 80s on Tuesday. Meanwhile, nighttime lows are forecast to
range from the mid 50s to mid 60s through the period.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
ISSUED AT 1245 PM EDT WED MAY 1 2024

VFR will largely prevail through the period with sfc and upper
level ridging dominating. The exception will be fog potential
between about 05Z and 14Z again tonight though as noted by the
previous forecaster, this should be more confined to the river
valleys and along some of the larger creeks and lakes. Some MVFR
fog could still develop at some of the TAF sites, with LAMP
suggesting IFR or lower potential at KSJS and KSYM. Any fog should
lift and dissipate by 14Z, with VFR returning to all areas at
that time.

&&

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

$$

UPDATE...JP
SHORT TERM...BROWN
LONG TERM...GEERTSON
AVIATION...JP