JKL issues Area Forecast Discussion (AFD) at Jul 21, 4:25 PM EDT423
FXUS63 KJKL 212025
AFDJKL
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
425 PM 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...(This evening through Monday night)
Issued at 425 PM EDT SUN JUL 21 2024
19Z sfc analysis shows a wavy frontal boundary over southeast
Kentucky this afternoon with ample moisture in place as PWATs peak
near 1.8 inches for our area. This is enough to keep showers and a
few thunderstorms - especially south where CAPE is maximized -
going into the evening. This trend seems to be a repeat of 24
hours ago as the morning showers became more robust through the
day but also trended further southeast chasing the better
instability with a tendency for training and local high water
concerns. As such, sunshine has again returned to the northwest
half of the area allowing temperatures there to spike after
spending much of the day under the clouds. This dichotomy shows up
well in the current readings - varying from the mid 80s northwest
to the low and mid 70s with the rain in the southeast. Meanwhile,
amid light winds away from any storms, dewpoints are elevated
in the upper 60s to lower 70s.
The models, and their individual ensemble suites, continue to be
in terrific agreement aloft through the the short term portion of
the forecast. They all depict broad troughing through the mid
section of the nation anchored with a center northeast of Canada
and downstream of the southern Nevada ridge out west. Locally, a
5h height minima will collect some mid level energy over the
Midwest into tonight while heights remain fairly high for a
trough and broad southwest flow aloft holds in place. This flow
will encourage moisture to keep streaming into eastern Kentucky
with some energy around to help activate it - but still mainly
diurnally driven. Given the still small model spread have gone
with the NBM as the starting point for the forecast grids with
little adjustment needed aside from some incorporation of the
latest CAMs guidance for PoPs.
Sensible weather features a steady state bout of humid weather
with mainly diurnally driven showers and thunderstorms through
Monday night. High PWs will keep a threat of excessive rainfall in
the forecast where ever training of convection occurs. However,
widespread incidents of local flooding or more impactful events
are not expected owing to a lack of stronger support or a better
wind field aloft. Each night will be mild with limited radiational
cooling keeping temperatures fairly uniform and the fog more
patchy depending on the rain pattern of the previous day.
The main changes to the NBM starting point consisted of adding in
some PoPs details from the CAMs through Monday morning. Did not
make much change to temperatures or dewpoints from the NBM through
the period.
.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.
&&
.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
ISSUED AT 230 PM EDT SUN JUL 21 2024
Similar to yesterday, convection was occurring near and southeast
of a a KSME to KLOZ to KJKL to KSYM line at issuance time
associated with a nearby stalled frontal boundary. Within the
convection, especially further south, reductions to MVFR and IFR
were occurring. After this latest round of convection fades late
this afternoon A lull should occur during evening into the
overnight and again allow for fog to develop in areas that
received more substantial rainfall amounts this past day.
Reductions to MVFR or lower could affect these areas from 06Z
onward. Meanwhile, another approaching impulse aloft could lead
to an increase in convection into Monday morning. Outside of
stronger convection, winds will be light and variable.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...GREIF
LONG TERM...MARCUS
AVIATION...JP/GREIF
Source:
JKL issues Area Forecast Discussion (AFD) at Jul 21, 4:25 PM EDT---------------
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