JKL issues Area Forecast Discussion (AFD) at Jul 23, 2:40 AM EDT162
FXUS63 KJKL 230640 AAC
AFDJKL
AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
240 AM EDT Tue Jul 23 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
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.
&&
.UPDATE...
Issued at 215 AM EDT TUE JUL 23 2024
Pops were inserted a bit further north over the next couple of
hours based on recent radar trends, with some scattered pops for
the activity in the Mountain Parkway vicinity and near JKL that
is moving generally northeast. Minor adjustments were also made
to hourly temperatures based on recent trends.
UPDATE Issued at 708 PM EDT MON JUL 22 2024
Showers and thunderstorms have redeveloped near and along much of
the Tennessee/Kentucky border early this evening while sparse
light shower activity has been noted further north. Expect the
activity near the Tennessee border to slowly lift northward and
largely dissipate by 2 to 3z. Most of the impacts should remain
south of US-421. An instance or two of flooding cannot be ruled
out if cells train over locations that received heavy rainfall
amounts earlier today.
&&
.SHORT TERM...(This evening through Tuesday night)
Issued at 452 PM EDT MON JUL 22 2024
Regional radar imagery shows convection over far southeastern
Kentucky generally waning, though additional pin-prick convection
has started bubbling up further northwest closer to Lake
Cumberland and also over the northern Kentucky River basin.
Temperatures at 2045z are mild, ranging from the mid 70s in
locations recently impacted by rainfall up to the lower/middle 80s
in the Lake Cumberland area where sunshine has been most
persistent. The regional surface analysis shows a wavering cold
front draped from southern West Virginia westward (bisecting the
WFO Jackson CWA roughly in half) to a subtle wave of low pressure
near Bowling Green. Aloft, a positively tilted trough axis lingers
from Eastern Canada down through the Mid-Mississippi Valley and
from thence into the Southern Plains. Upper level ridging remains
in place over the Great Antilles and far Southeastern US. Deep
southwesterly flow between the features continues to channel
moisture into eastern Kentucky, as evidenced by PWATs of ~1.5 to
1.6 inches.
The upper level pattern will remain largely unchanged during the
short-term period. Impulses embedded within the flow aloft, weak
convergence along the wavering frontal boundary, and differential
diurnal surface heating will, at different times and in unique
combinations, act as mechanisms for initiating and/or sustaining
convection. Convection late this afternoon and evening appears to
be due to a combination of all three. The subtle upper level
perturbation is fostering a very weak wave to ride along the front
this evening. Expect a brief uptick in convection this evening,
though mostly over the southern half of the CWA, before
diminishing with the loss of daytime heating. Most locations
should be dry after sunset, though an isolated rogue shower or
thunderstorm cannot be ruled out overnight. The combination of
recent rainfall, suppressed daytime highs and some partial
clearing overnight will set the stage for areas of fog in many
valley locations, and likely at least patchy fog elsewhere.
Temperatures will be mild only bottoming out in the middle to
upper 60s.
Looking ahead to Tuesday, any substantial breaks in the cloud cover
will fade as the next impulse arrives. Model agreement is fairly
good that convection will be likely south of the Mountain Parkway
(chance north), especially during the afternoon and early evening.
Though there could be a lull in the activity Tuesday evening, the
next disturbance follows quickly on Tuesday night with convection
again increasing overnight. Southeast Kentucky (roughly south of
the Mountain Parkway and the lingering frontal boundary) will
remain the focus area for most of this convection. Locations that
have received multiple inches of rain in recent days (most of Clay
and Owsley counties as well as smaller portions of Lee, Breathitt,
Perry, Leslie, Laurel, Knox, Bell, Harlan, Letcher, and Pike
counties) will be more vulnerable to future rounds of rainfall
causing excessive runoff and flooding. However, forecaster
confidence in any particular one or group of these counties seeing
the brunt of the additional rainfall is low due to the obscurity
of the weak forcing mechanisms. WPC has maintained a marginal risk
for excessive rainfall for portions of southeast Kentucky through
the short-term. The diurnal temperature cycle will also remain
subdued on Tuesday and Tuesday night with highs in the lower to
middle 80s and lows in the mid to upper 60s.
.LONG TERM...(Wednesday through Monday)
Issued at 504 PM EDT MON JUL 22 2024
Operational models are in good agreement through Dy4, Fri before
diverging from Dys 5-7, Sat-Mon. Ensemble solutions mirror their
respective parent models but show a little better agreement
through Dy5, Saturday. GFS/GEFS is a bit faster/stronger with
ridging over the eastern CONUS by Dy5, Saturday. Ensemble cluster
analysis confirms more uncertainty (lower confidence) in the
forecast for the Dys 5-7 time frame. Looking just at numbers,
majority of members appears to favor ever so slightly the idea of
some lingering troughiness over the upper portions of the Ohio
Valley by Dy5 and weaker ridging over the Upper midwest and
Midwest/Great Lakes proper. These upper level patterns will have a
significant influence on how strong surface high pressure (the
Bermuda High) eventually builds back into the southeastern CONUS,
if at all. This also has a direct impact on temperatures beyond
day 4-5 and whether we return back to the very hot muggy weather
that has defined much of the summer thus far, or whether we remain
closer to normal as experienced over the past week.
Sensible weather features a continuation of unsettled weather
through the first part of the extended, then a more likely return
to some semblance of more typical, summer like weather. A
noticeable trend will be for lower PoPs, less convection through
the period with time. Daily temperatures will also trend upwards,
from around or just below normal to just above normal. The surface
frontal zone in place across the area that is providing a focus
for mainly daytime convection will gradually dissipate by the end
of the week, only to be replaced by another surface cold front
that will drop southward into the Commonwealth by Thursday. At
this time it is uncertain how far this front will make it through
eastern Kentucky or if it will stall out across the area before
dissipating.
Main hazards through the period will remain hydro related, and
generally within the first half of the extended. PWATs generally
remain below 2 inches through that time frame and storm motions
remain relatively high at around 15kts. A surface front does drop
into the area by Thu/Fri, which would help enhance the threat of
more organized convection, and possibly some training along the
remnants of our current frontal zone, although it will be
dissipating as well. Ensemble probabilities continue to advertise
a low probability of widespread, significant rainfall. Thus at
this time, the overall threat for significant, widespread, high
impact flooding is low. Rainfall could be heavy at times, but
localized. Thus any flooding threats and corresponding impacts are
expected will be isolated and related to rounds of convection
passing over the same areas. A clearer picture will develop as
models have time to congeal on a solution that better captures the
evolution of the forecast with future runs.
&&
.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
ISSUED AT 230 AM EDT TUE JUL 23 2024
Mostly VFR ceilings prevailed at issuance time. While fog was
affecting valleys and some areas outside of the deeper valleys with
reductions in visibility into the MVFR or even the IFR ranges.
IFR fog was reported at issuance time at KSJS with MVFR fog at
KSME. Some convection was occurring at issuance time as well near
the Mtn Pkwy vicinity and near KJKL and KSJS. Guidance is
persistent with at least some further fog formation before 12Z and
the potential for some low stratus, though the areal extent of
fog or any low stratus is uncertain due to passing clouds and
anticipated isolated convection. With guidance and or persistence
most favored for reductions due to fog at KSME, KLOZ, and KSJS,
it was included for theses sites for a few hours, before
improvements around or just after 13Z. Given sufficient clearing,
valley fog at non TAF sites down to LIFR or lower is possible for
few hours before 13Z when improvements should occur due to
lifting and mixing out. Chances for showers and storms will
increase during the day on Tuesday, peaking between about 16Z and
23Z. Reductions to MVFR or IFR and gusty and erratic winds will
accompany any heavier showers and storms. Outside of convection,
winds will largely remain light and variable through the TAF
period.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...JP
SHORT TERM...GEERTSON
LONG TERM...RAY
AVIATION...JP
Source:
JKL issues Area Forecast Discussion (AFD) at Jul 23, 2:40 AM EDT---------------
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