JKL issues Area Forecast Discussion (AFD) at Jul 28, 12:07 PM EDT781
FXUS63 KJKL 281607
AFDJKL
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1207 PM EDT Sun Jul 28 2024
.KEY MESSAGES...
- There is a threat for excessive rainfall from multiple rounds of
showers and thunderstorms Sunday through Wednesday, which may
lead to localized flooding at times. A lesser probability of
showers and thunderstorms will extend through late week.
&&
.UPDATE...
Issued at 1207 PM EDT SUN JUL 28 2024
Midday update covering the rest of the afternoon increases the
PoPs as showers and thunderstorms move toward the area. Additional
development seems probable across eastern Kentucky with any
amount appreciable amount of clearing that can increase
instability.
UPDATE Issued at 1023 AM EDT SUN JUL 28 2024
Expanding PoP and Sky grids north and east quicker than the
previous forecast. A broken line of showers has developed along
the leading moisture and instability gradient, moving northeast.
Widespread showers and thunderstorms are also a bit farther east
across central Kentucky than previous hourly forecasts indicated,
so updated extend into the afternoon and evening to account for
this.
UPDATE Issued at 906 AM EDT SUN JUL 28 2024
Any mention of fog for this morning has been removed from
forecasts and the forecast grids. The fog diminished quickly over
the last hour.
UPDATE Issued at 806 AM EDT SUN JUL 28 2024
Early morning obs were blended into the forecast without any
substantive changes.
&&
.SHORT TERM...(Today through Monday)
Issued at 513 AM EDT SUN JUL 28 2024
Early this morning, upper level ridging extends from MI south to
the gulf coast, while surface high pressure is just the east,
running along the Appalachians. An weak upper level low is
centered over northern MO. The high/ridging is continuing to bring
us dry weather early this morning. The air mass emanating from
the surface high is still resulting in temperatures and dew
points relatively low for mid summer, especially in northeast
Kentucky.
The high/ridging will cede control today to the upper level
regime advancing from the west. The upper low will move north
northeast and get absorbed into the prevailing westerlies aloft
tonight. However, troughing will continue to extend southward and
advance to eastern KY by late Monday. During this time,
southwesterly low level flow along with the advancing upper
trough will bring deep moisture over our area, supporting showers
and thunderstorms. Precipitable water will climb to 1.75-2" and
atmospheric flow will be relatively light and unidirectional. CAPE
profiles will be tall and relatively thin. The combination will
support a potential for locally heavy rainfall, especially on
Monday.
.LONG TERM...(Monday night through Saturday)
Issued at 354 AM EDT SUN JUL 28 2024
Upper level troughing will be the name of the game throughout the
extended period for eastern KY. A strong upper level low will be
present across the Atlantic Seaboard today. A second incoming trough
will begin to impact the Ohio Valley from the west by this evening,
eventually merging with the stronger system to the east through the
day Monday, setting the stage for the start of the extended period
Monday night into Tuesday morning. This upper level low is expected
to shift northward into New England through Tuesday, but will leave much
of the eastern Conus in a deep troughing pattern as a result, wedged
between two large high pressure ridges - one across the far southern
Conus and one out in the Atlantic. This pattern also leaves much of
the region vulnerable to additional shortwaves passing through
during this time.
Models do try to show some of the upper level ridge to our SW trying
to spread its way towards the Commonwealth, including rising heights
across Kentucky, for Wednesday night and Thursday, but JKL's
location on the northern fringes of these height rises likely won't
be enough to stop waves of energy from moving through much of the
Ohio Valley during this time. Models then show a stronger shortwave
moving back into the region from the NW by Friday, re-establishing
the troughing's hold across the eastern Conus once more, resulting
in lowering heights and the return of a more active pattern for
Friday and heading into the weekend. Model solutions really start to
diverge by the weekend, which could play an impact in the sensible
weather.
Given the troughing pattern through the majority of the period, and
JKL's general location on the SW flow side, it's not a surprise that
SW flow will descend all the way to the surface and persists through
much of the extended period. This will result in two things -
moisture and heat. Not expecting any large-scale airmass changes or
frontal boundaries while in this pattern, so hot and humid
conditions with increased moisture and instability will be the name
of the game. Highs will top out around the mid and upper 80s on
Tuesday, but will warm into the upper 80s and low 90s for much of
the rest of the forecast period. Humidity will make it feel
somewhere between the mid 90s and 100 degrees during this time.
Shower and thunderstorm chances are on tap nearly every day.
In addition, as mentioned before, there will be daily chances for
showers and thunderstorms. Even Thursday, as heights rise some
across the region, we will still not be immune to some instability
and generally diurnally driven convection during the afternoon, with
chance pops across much of the CWA. Did not have enough confidence
to deviate away from the NBM pops at this point, but did try to peak
them during the afternoon when instability and lift will be their
highest, without the presence of a passing boundary.
WPC has placed much of the JKL CWA in a slight risk for excessive
rainfall from 12Z Monday through 12Z Wednesday. Their main
concern is the increased precipitable water (again, thank you
strong SW flow) which could lead to heavy downpours. That being
said, much of eastern KY has received very little rainfall over
the past month, with a few exceptions, so most locations should be
able to handle decent rainfall amounts. There isn't a very
defined boundary setting up for which these storms will likely
train (perpendicular to the flow), though can't rule out that if
storms do develop and move over the same location with heavy rain
rates/amounts multiple times, this could lead to some isolated
concerns. Will continue to monitor this as we get closer to time,
but right now confidence isn't very high in a widespread flash
flood concern. Meanwhile, SPC has eastern KY in a marginal
thunderstorm risk for Tuesday, followed by general thunderstorms
after that. Again, without lack of forcing/lift outside of
afternoon heat/mixing, generally expect diurnally driven pulsy
showers and storms with this pattern, limiting their lifespan and
strength.
When doing the forecast yesterday, decided not to include any
ridge/valley temperature differences during the extended period,
given the clouds and moisture in place, and without the presence of
a high pressure system moving overhead (subsidence). The latest
model runs are trending a bit clearer overnight for the second half
of the week and into the weekend, though confidence is still quite
low as precip chances will also continue into the overnight. Went
ahead and dropped valleys down just a few degrees and lowered their
winds by a few kts. However, still expect that there could be
moments of clearing in the clouds overnight which may result in
temperature drops outside of valleys. The same goes for fog as well.
It is likely with so much moisture that we could see some fog
overnight in places, but exactly when and where this will set up is
unknown, and may not be confined to just the valley locations.
&&
.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
ISSUED AT 806 AM EDT SUN JUL 28 2024
Valley fog is affecting a few places early this morning.
Otherwise, conditions are VFR .
Mainly VFR conditions were present to start the period. Although,
valley fog was present in a few valleys, and isolated showers had
developed from around McKee to Monticello. The fog will dissipate
this morning, but the showers will increase in coverage and
develop eastward. While most places can expect rain at some
point today or this evening, specific timing at TAF sites is
problematic and only VCSH and VCTS was used in TAFs for the time
being. The showers and thunderstorms will bring localized sub-VFR
conditions. Forecast uncertainty increase tonight, but a modest
decrease in precipitation is forecast for this evening. However,
fog could develop in the lingering moist air.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...CMC
SHORT TERM...HAL
LONG TERM...JMW
AVIATION...HAL
Source:
JKL issues Area Forecast Discussion (AFD) at Jul 28, 12:07 PM EDT---------------
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