JKL issues Area Forecast Discussion (AFD) at Aug 12, 4:40 AM EDT967
FXUS63 KJKL 120840 CCA
AFDJKL
AREA FORECAST DISCUSSION...CORRECTED
National Weather Service Jackson KY
440 AM EDT Tue Aug 12 2025
.KEY MESSAGES...
-An unsettled weather pattern is forecast from Tuesday through
Thursday, bringing multiple rounds of showers and thunderstorms.
-Some storms from Tuesday to Thursday may produce torrential
downpours, leading to a threat of localized flash flooding.
-For the upcoming weekend, the rain threat decreases and a more
typical summer pattern of isolated popup showers and storms,
along with hotter temperatures climbing back to near 90F.
&&
.SHORT TERM...(Today through Wednesday)
Issued at 425 AM EDT TUE AUG 12 2025
Conditions are quiet across Eastern Kentucky again early this
morning with patchy fog in the sheltered mainstem river valleys
and thermometers primarily in the upper 60s and lower 70s. Mid-
level clouds are on the increase from the south as the low-level
flow has veered southerly enough for less shadowing from the
Southern Appalachians. The latest surface analysis shows the high
responsible for quiet weather of recent days now well off the Mid-
Atlantic Coast. A ~998mb low pressure is noted over northwest
Ontario with an associated cold front extending southward into
Minnesota and then more southwest into Nebraska. Multiple weak
surface features are noted out ahead of the front, including a
subtle trough extending from the Missouri Bootheel to near
Cincinnati and then eastward into the foothills of the Central
Appalachians. A glimpse aloft shows that the 500 hPa ridge over
the Eastern CONUS in recent days is steadily breaking down ahead
of a pronounced but gradually flattening trough extending from
the Hudson Bay southward into the Southern Plains. Multiple weak
perturbations are riding through and ejecting out of the trough.
Moisture levels, which did not increase nearly as much as
expected yesterday, should finally surge higher today as deep
layer flow becomes more consistently south to southwest ahead of
the approaching trough. This should cause PWATs to surge upwards,
with the RAP13 and HREF mean suggesting widespread 1.8 to 2.0 inch
values across the CWA by this evening. Falling heights will also
aid in a modest steepening of mid-level lapse rates, allowing for
deep but relatively thin CAPE profiles supportive of
thunderstorms. The modeled MUCAPE by this afternoon is not
particularly high (generally 1,000 to 2,000 J/kg) and shear is
minimal (less than 15 kts), keeping any real severe threat in
check. Even so, the increasingly tropical PWAT levels and a deep
warm cloud layer are supportive of torrential downpours. Outside
of a few isolated pockets in Letcher, Bell, and McCreary counties,
soil moistures have dried out substantially in recent days. This
combined with mean wind in the cloud layer of 10 to 15 kts should
be enough to keep individual cells progressive and limit hydro
concerns unless activity impacts sensitive locations such as those
mentioned above. Training, while briefly possible, is not that
favored without a focused forcing mechanism, at least for today.
As for the arrival of rain chances, isolated to widely scattered
activity could develop over the next few hours in far southern
counties as moisture transport ramps up on a modest low-level jet.
However, more substantive convection is favored to hold off until
the afternoon for most locations north of the Cumberland River
Basin. Convection should diminish in coverage this evening and
tonight with the loss of diurnal heating, but at least isolated
activity is probable overnight as the upper level trough and its
attending cold front approach. The most vigorous energy associated
with the trough will cross the Commonwealth on Wednesday and
should support numerous to widespread deep convection. The
ingredients will be there for localized excessive rainfall --
skinny CAPE profiles, PWATs close to daily maximums (near 2.0
inches), high relative humidity levels up to around the
Equilibrium level and a deep warm cloud layer all support
efficient rainfall processes while unidirectional flow near
parallel to the approaching boundary could promote cell training.
Accordingly, WPC is maintaining a Marginal Risk (1/4) for
excessive rainfall across the entire area. Where the convection is
most persistent, instances of flooding or even flash flooding
cannot be ruled out.
In sensible terms, look for fog in valleys to lift and dissipate
mid-morning with clouds increasing from south to north. There is a
chance for a few showers or perhaps a rumble of thunder this
morning over the Cumberland Basin, but the better rain chances
(40% north to 70% south) come this afternoon. It will be
seasonably hot and humid with high temperatures in the mid to
upper 80s for most, though the warmer spots north of the Mountain
Parkway where sunshine lingers longer could flirt with the 90F.
Shower and thunderstorm coverage diminishes this evening but some
sporadic activity is likely to persist overnight. Fog is possible
in sheltered locales where skies try to clear. It will be warm and
muggy with low temperatures in the mid 60s to around 70. Looking
ahead to Wednesday, scattered to widespread showers and
thunderstorms, some with torrential downpours, are expected.
Isolated high water or flash flooding is possible where activity
persists longest. Temperatures will be cooler due to the rain and
rather extensive cloud cover, likely only reaching the mid 80s at
best.
.LONG TERM...(Wednesday through Monday)
Issued at 255 PM EDT MON AUG 11 2025
At the beginning of the period, a 500-mb trough - centered over
Ontario - will begin pivoting on its axis and lifting to the
northeast. As such, the associated surface cold front that has been
moving southeastward from the Upper Midwest will stall just
northwest of our forecast area and become stationary. Through
Friday, light, quasi-zonal flow aloft will cause this stationary
front to remain draped east-west just north of our area. As
shortwave features meander through this flow, an active weather
pattern will exist for the first half of the period. By Saturday and
Sunday, a weak ridge moves into the area, bringing with it quiet,
warm conditions that will prevail through the remainder of the
period.
The main show will be Wednesday afternoon through Thursday morning
with forcing associated with the east-west oriented stationary
front, near unidirectional flow, and deep moisture profiles. The
stationary front will serve as a moisture convergence zone. A weak
surface high over Florida will bring anomalous moisture northward
from the Gulf. The 850-300 mb mean wind is also forecasted to be
slow and westerly, further causing concern for training storms
parallel to the boundary. Additionally, all of the precip efficiency
parameters are in place for heavy rainfallhigh PWs (~1.8 inches), a
long, skinny CAPE profile, a deep warm cloud layer, and decent RH
values at low- and mid levels (>75-80%). With all of these factors
in place, WPC maintains a Marginal (level 1/4) risk for flash
flooding Wednesday through Thursday morning. Dry ground conditions
will keep higher-impact flooding concerns at a minimum, but multiple
rounds of heavy rain (or simply slow-moving, high-efficiency storms)
could lead to localized hydrologic concerns. Due to the broader
precip potential and cloud cover, high temperatures should also be
lower (mid to upper 80s) during this time.
By Friday, a weak ridge approaches from the west, leading to mid-
level northwesterly flow that cuts off the main moisture driving the
prior flooding concern. Thus, convection will become more isolated
and diurnally driven. By Saturday, the ridge will be over the area,
bringing with it quiet, warm conditions. Sunny days will lead to
highs of 90-95F that will prevail through the rest of the period.
Clear conditions will also lead to the potential for nighttime fog
in the river valleys, especially with increased ground moisture
after the Wed/Thurs event.
&&
.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
ISSUED AT 157 AM EDT TUE AUG 12 2025
Terminals were VFR at issuance time. Valley fog is developing and
should persist through 13Z. It is not out of the question some
could sneak into KLOZ or KSME; however, as these sites were rain-
free yesterday, confidence in including any reductions was not
high enough to include at this time. Scattered convection should
develop and affect portions of the region after ~16Z Tuesday. Some
MVFR or lower reductions are possible within convection along
with gusty and erratic winds. Outside of convection, winds will be
light and variable.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM...GEERTSON
LONG TERM...HARDY
AVIATION...GEERTSON/JP
Source:
JKL issues Area Forecast Discussion (AFD) at Aug 12, 4:40 AM EDT---------------
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