JKL issues Area Forecast Discussion (AFD) at Dec 13, 4:19 PM EST402
FXUS63 KJKL 132119
AFDJKL
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
419 PM EST Fri Dec 13 2024
.KEY MESSAGES...
- Temperatures warm to above normal this weekend into early next
week.
- Periods of rain are forecast to impact the area at times from
late Saturday evening into Tuesday.
&&
.SHORT TERM...(This evening through Saturday night)
Issued at 418 PM EST FRI DEC 13 2024
A quiet mid-December afternoon is coming to a close as high clouds
stream across the Eastern Kentucky Coalfields. A pronounced
temperature gradient is in place over the state with temperatures
ranging from the upper 40s/lower 50s in the broad river valleys of
the Kentucky and Cumberland River basins down the mid 30s toward the
northern tip of Fleming County. The surface analysis shows not only
the stark temperature contrasts but a southerly winds up to around
the Mountain Parkway while winds are generally more northerly to the
north of the Mountain Parkway. This quasi-stationary boundary
extends westward to an area of low pressure developing in the lee of
the Rockies over northeast Mexico. Looking aloft, an area of loosely
organized 500H vorticity energy is crossing the Lower and Middle
Mississippi Valley while high-level moisture streams out ahead over
the Ohio Valley. Behind this energy, subtle shortwave ridging is
found from the Ozarks up into the Red River Valley of the North.
Further upstream, a trough of Pacific origin is crossing the
Continental Divide and is the parent feature fostering the
cyclogenesis in the lee of the Rockies.
The previously mentioned 500H vort energy will cross the
Commonwealth this evening and depart overnight, taking the high-
level moisture with it. This will set the stage for skies to clear
out for several hours as the subsequent shortwave ridging crosses
the Ohio Valley late in the night. The high-levels will moisten
again and gradually saturate downward through the day on
Saturday/Saturday evening as integrated vapor transport increases
ahead of the approaching Pacific trough. At the surface, this upper
level pattern will translate to the low pressure wave in the lee of
the Rockies riding the stationary boundary out onto the Plains
tonight and Saturday. As that surface low moves in the Lower
Missouri Valley Saturday evening, the system's warm conveyor belt
jet will begin pushing the lingering quasi-stationary boundary back
north as a warm front. The combination of increasing moisture and
isentropic upglide will lead to rain breaking out from from west to
east mid-evening Saturday and persisting through the overnight.
MUCAPE in the some of the model soundings is marginally sufficient
to support an isolated rumble of thunder, but confidence in
occurrence was too low to include at any particular geographic area
of the forecast at this time (the 13/12z HREF thunder probabilities
remain under 10%).
In sensible terms, high clouds will thin this evening while winds
remain light, setting the stage for another chilly night of lows
ranging from the lower 20s in northern sheltered valleys to the
lower 30s on thermal belted ridges and in broad southern valleys.
Clouds increase again on Saturday while light downslope
southeasterly breezes help boost high temperatures into the 50s for
most of the lower elevations. The only exception will be a few of
the warmest spots near the Tennessee border that could flirt with 60
while the coolest spots north of I-64 near the lingering boundary
might struggle to reach 50. Rain, perhaps showery at times, is
forecast to develop from west to east between 9 PM and 2 AM EST
Saturday Evening/Night. A stray rumble of thunder cannot be ruled
out as well. Saturday night's low temperatures are forecast to range
in the 40s.
.LONG TERM...(Saturday night through Thursday)
Issued at 323 AM EST FRI DEC 13 2024
The forecast period begins with the approach of a surface low. The
upper-level support for the feature moved onshore this morning and
will quickly move across the CONUS through the weekend. Leeside
Rockies cyclogenesis is expected overnight Friday into Saturday with
the trough forecast to traverse the Plains and be on the doorstep of
the Commonwealth by the start of the forecast period. Starting late
Saturday night into Sunday morning, increasing PoP is expected to
spread across the CWA with 70-90% PoP forecast by Sunday morning.
Showers will persist through the day Sunday into the overnight.
However, a second, stronger system is forecast to follow on the
heels of the Sunday system and bring another round of showers for
Monday into Tuesday. Forecast rainfall totals, ranging from Saturday
night through Tuesday afternoon, are around 2.00" in the Bluegrass/
I-64 corridor with decreasing amounts to around an inch for the
southeastern high terrain. Temperatures through the first part of
the period are forecast to be above average with highs climbing
upper-40s for Sunday, mid-50s for Monday and upper-40s to low-50s on
Tuesday before the cold front, associated with the second system,
crosses through the CWA. Overnight lows will remain above average as
well but will quickly fall into the mid-20s to mid-30s behind the
cold front.
Weak high pressure will build back into the area late Tuesday
afternoon and will linger into early Wednesday but will quickly exit
as another system approaches the area. This third system of the
period is forecast to develop over the southern Mississippi Valley
and eject northeast into the Tennessee Valley early Wednesday
morning. As this system moves northeast, increasing PoP chances are
expected through the day and persist through the end of the period.
As colder air filters into the region, rain will change over to snow
and with warming expected through the day, a change back to rain
will follow. While this is what's in the grids, long-term
deterministic models are in disagreement on this potential for the
end of the period. The ECMWF is the most aligned with the scenario
above with the GFS being the outlier bringing high pressure and dry
weather for the end of the period. As for temperatures, a brief
warmup is expected on Wednesday before the system is forecast to
bring another round of colder air which will remain in place for the
end of the forecast period.
&&
.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
ISSUED AT 1237 PM EST FRI DEC 13 2024
VFR conditions will prevail through the TAF period. High clouds
and occasionally some mid level clouds are expected throughout the
period. Winds be light and variable.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...GEERTSON
LONG TERM...VORST
AVIATION...GEERTSON/CMC
Source:
JKL issues Area Forecast Discussion (AFD) at Dec 13, 4:19 PM EST---------------
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