321
FXUS63 KJKL 210924
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
524 AM EDT Sun Jul 21 2024

.KEY MESSAGES...

- Showers and thunderstorms will impact the region at times this
  week. Probabilities will generally peak each afternoon and
  evening.

- Any areas that receive successive rounds of heavy rainfall over
  could experience instances of localized flooding.

- Highs will be near normal (mid 80s) to about 5 degrees below
  normal throughout the period, with humidity running high.

&&

.SHORT TERM...(Today through Monday)
Issued at 520 AM EDT SUN JUL 21 2024

Early this morning, southwest flow aloft was in places across the
Lower OH Valley into the Appalachian region between an upper level
ridge that was centered over the western Atlantic in the vicinity
of Bermuda and extended into the eastern Gulf of Mexico and an
upper level trough that extended from eastern Canada across the
Great Lakes into the mid MS Valley to Arklatex vicinity. Meanwhile
over the western Conus, another upper level ridge was in place.
Multiple shortwaves were moving between these systems in
southwest flow and one of these is leading to convection in
central portions of KY to the west of Interstate 75. At the
surface, a frontal zone that extended from NC across the
Appalachians to the TN Valley to portions of the Southern Plains
was gradually lifting north from middle and eastern TN and toward
eastern KY. Fog was also present in valleys despite passing low
and mid level clouds with this fog generally more prevalent where
heavier rain fell on Saturday. At this point, temperatures were in
the mid 60s to low 70s range.

Today through Monday, the upper level pattern is expected to
generally change little with upper level ridging remaining in
place from the western Atlantic into the Gulf of Mexico and
across the western Conus with a trough axis/upper low to the west
and northwest of the Commonwealth in between these systems. Weak
shortwaves in southwest flow should cross the Lower OH Valley from
time to time, with the consensus of the guidance that the first
of these crossing eastern KY this morning and another works across
the Lower OH Valley later tonight into Monday. At the sfc the
quasi stationary frontal zone may in general meander into the
norther portion of the CWA through Monday. Sfc dewpoints are
expected to be in the mid 60s to low 70s range through the period,
while PW early this morning is expected in the 1.3 to 1.7 inch
range from north of southwest, should climb to the 1.5 to 1.7
inch range this afternoon and remain in that general range through
Monday.

Through this morning, an initial peak in chances for convection is
anticipated for western and southern locations, while diurnal
heating will lead to a peak areawide this afternoon. Coverage
during the afternoon to early evening should be greatest to the
south of the Mountain Parkway. Convection cannot be ruled through
the evening and into the night, though a relative lull is
anticipated from late evening into the start of the overnight
hours with the loss of daytime heating, before chances increase
toward morning ahead of the next shortwave. Chances for convection
continue into the day on Monday as the next shortwave crosses the
Lower OH Valley with a likely peak in the afternoon with daytime
heating. Locations that experience multiple rounds of convection
would receive some heavy rain and localized flooding cannot be
completely ruled as Monday progresses. With some areas generally
in the south and southeast having received heavy rain on Saturday,
those areas might be most susceptible to this potential. WPC has
placed the southern portions of the area in a marginal risk for
excessive rainfall on Monday.

Highs today and Monday will be in the low to mid 80s with rounds
of clouds and convection affecting the area, lower than what was
experienced much of last week. Normal highs for this time of year
are in the mid 80s. Lows tonight are also expected to be right at
normal.

.LONG TERM...(Monday night through Saturday)
Issued at 410 AM EDT SUN JUL 21 2024

Guidance continues to place eastern Kentucky in a corridor between
upper level troughing over the Midwest and upper level ridging over
the southeastern states for the beginning of the long term forecast
period. During this period, both of these features attempt to
dig/build into the area, and as this happens, a series of shortwave
disturbances will eject into the Ohio River Valley amidst the
southwesterly flow aloft that is associated with these upper level
patterns. These upper level winds will advect sufficient moisture
throughout the atmospheric column, which suggests that clouds will
linger around in the sky through the first half of the work week.

In this weather pattern, rain chances will thus be driven by two
factors: the exact timing of the aforementioned shortwave features
and the diurnal temperature cycle. Models continue to disagree on
the exact timing of these features, but rain chances should peak in
the afternoon and evening hours in accordance with maximum daytime
heating and its associated convective lift on Tuesday, Wednesday,
and Thursday.

Due to the potential for multiple rounds of rainfall that exists in
this pattern, a marginal risk for flash flooding exists,
particularly across southeastern portions of the forecast area that
have seen antecedent rains this weekend. Ensemble mean PWAT values
do not necessarily support any widespread flooding concerns, but it
is worth noting that the past few runs of the GFS have been a bit
more aggressive, with a localized PWAT maxima of greater than 2
inches across the far southern portions of our forecast area on
Tuesday into Wednesday. This trend, coupled with the vorticity
maxima of a passing upper level disturbance in this time frame,
suggests that the greatest rain chances and accumulations will exist
in the afternoon and evening hours on these two days. Exact rainfall
amounts will vary given forecast uncertainties, but any locality
that sees enhanced amounts of precipitation multiple days in a row
will need to be monitored closely for flooding potential.

The other chief impact of this disturbed weather pattern will be
seasonally mild temperatures. Given the proximity of upper level
troughing, enhanced cloud coverage will work to relegate
temperatures to around or below seasonal norms (highs in the mid
80s, lows in the upper to mid 60s) on Tuesday, Wednesday, and
Thursday. However, a subtle warming trend is expected by the end of
the long term forecast period, as ridging begins to build into the
area and winds correspondingly shift. As such, drier air will seep
into portions of the column, suppressing cloud coverage and slightly
reducing PoPs compared to the previous days. By next weekend,
temperatures will likely approach the upper 80s once again, with
lows sticking around their seasonably appropriate values in the mid
60s.

&&

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

$$

SHORT TERM...JP
LONG TERM...MARCUS
AVIATION...JP