JKL issues Area Forecast Discussion (AFD) at Dec 2, 11:50 PM EST050
FXUS63 KJKL 030450 AAA
AFDJKL
AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
1150 PM EST Mon Dec 2 2024
.KEY MESSAGES...
- The snow from another quick hitting clipper type system is
winding down across the area with some light accumulations still
possible through the early morning hours in the highest terrain.
- Look out for slippery spots on area roads overnight.
- Temperatures will remain below normal for the week, with only a
small potential for light precipitation, from time to time.
&&
.UPDATE...
Issued at 1150 PM EST MON DEC 2 2024
The accumulating snow is coming to an end across far southeast
Kentucky, but still affecting the higher terrain. Will keep the
SPS going for the CWA due to the falling temperatures and reports
of slick spots through the area from previous wet roads freezing
up in places. Have updated the forecast grids mainly to fine tune
the PoPs and snow through the rest of the night. Did also include
the latest obs and trends for the T/Td/Sky grids. These
adjustments have been sent to the NDFD and web servers along with
a freshening of the zones, HWO, SPSs, and SAFs.
UPDATE Issued at 725 PM EST MON DEC 2 2024
00Z sfc analysis shows that clipper system we have been tracking
is now moving into eastern Kentucky ahead of a chilly area of high
pressure. This system is bringing the best potential for
accumulations for the Cumberland Valley as its main focus slips
through southeast Kentucky. Currently, temperatures are running
in the upper 20s to lower 30s, most places across the area but
dewpoints vary from the mid teens north to the upper 20s in the
south. This will mean the north will see a slower moistening and
less of the snow able to reach the ground whereas a solid dusting
to inch will be possible in Cumberland Valley locations.
Meanwhile, winds are northwest at 5 to 10 mph with occasional
higher gusts adding to the chill and swirling the falling snow -
reducing visibilities, at times. Have updated the forecast to
enhance the southern PoPs a bit in accordance with the latest
radar and CAMs trends. Did also add in the current obs and
tendencies for the T/Td grids. These adjustments have been sent to
the NDFD and web servers along with a freshening of the HWO and
an expanded SPS covering the near term snow impacts and also
refreeze concerns into the later hours tonight.
&&
.SHORT TERM...(This evening through Tuesday night)
Issued at 428 PM EST MON DEC 2 2024
Clouds are rolling in from the west as a chilly December afternoon
comes to a close. Temperatures range from the lower 20s atop Big
Black Mountain to the upper 30s at the Middlesboro Airport. Regional
radar shows light to moderate echoes following closely behind a
cloud shield advancing eastward across the Coalfields. However,
dry air at the surface, evident from widespread dew points in the
teens, is precluding the precipitation from reaching the ground so
far. In fact, surface observations suggest that snow is not yet
reaching the ground for most locations east of I-65. Looking
aloft, a deep trough remains entrenched over the eastern CONUS. An
embedded reinforcing 500H vort max/shortwave trough is diving
southeast toward the Lower Ohio Valley while an attendant ~1027 mb
clipper low races southeastward through Missouri.
The aforementioned weak clipper low becomes diffuse this evening as
it crosses the Tennessee Valley before redeveloping late tonight
off the South Carolina coast. Northwesterly flow brings a period
of low-level cold air advection behind the clipper late tonight
into Tuesday morning. Ridging aloft and high pressure at the
surface then build east during the day on Tuesday with the high
cresting over eastern Kentucky Tuesday evening/early overnight.
The high-resolution models are in good agreement showing a period of
light snow as the clipper low passes this evening. The clouds will
need to precipitate for at least a couple of hours before the low-
levels of the atmosphere are sufficiently moist for snow to reach
the surface at the lower elevations. That process should occur
quicker at the higher elevations where the thinner layer of near-
surface dry air will moisten more quickly. Expect light snow to
reach the ground in the Cumberland basin by around 6 PM EST (cannot
rule out a flurry earlier) and then rapidly spread eastward to the
West Virginia border in just a couple of hours. The snow diminishes
to lingering upslope flurries and snow showers between 8 PM EST in
western counties to around midnight along the Virginia border as CAA
ensues. The leftover flurries and snow showers become confined to
the highest elevations through the remainder of the night and then
end altogether on Tuesday morning as CAA advection wanes and the
low-level air mass dries out. During this event, the better
forcing will remain near and southwest of US-460 where a general
dusting to one half inch of snowfall can be expected at the lower
elevations (though an isolated amount approaching 1 inch cannot be
ruled out). For the higher mountain counties (Bell, Harlan, and
Letcher), the forecast snowfall amounts increase to between 1 and
2 inches above 2,500 feet. Forcing will be weak and the snow
production will occur mainly in the DGZ, supporting a fluffy, dry
natured snow. Slippery spots will be possible overnight where
snow occurs, primarily due to melting snow leading to wet roadways
which then freeze due to dropping air temperatures.
Temperatures fall into the mid 10s north of I-64 ranging to the
lower 20s in southeastern locales, except back into the 10s above
2,000 feet. With the air mass drying out, sunshine will gradually
break out on Tuesday, warming temperatures back into the lower
30s a the lower elevations ranging down to around 20 atop Big
Black Mountain. More widespread lows in the mid to upper 10s are
anticipated in the valleys on Tuesday night, though weak WAA
developing on the back side of the surface high should help hold
minimum temperatures in the lower to middle 20s at most other
locations.
.LONG TERM...(Wednesday through Monday)
Issued at 336 PM EST MON DEC 2 2024
Winter is officially upon us it seems, and this will continue well
into the extended.
On Wednesday, strong northerly flow will be in place, as a closed
upper level low begins to sink southwards towards the Upper Great
Lakes during the afternoon hours. As troughing continues to take
hold across the Ohio Valley in response to this upper level low, a
surface system will also be present, along with a cold front. This
cold front will traverse the state, bringing increased moisture and
energy Wednesday night and Thursday morning. Models are in fairly
good agreement that the best moisture will be wrapped around the
low pressure systems to our north, with only light QPF amounts
expected in the JKL CWA, generally under a tenth of an inch. With
a strong push of cold Canadian air already in place, only
increasing behind the front, it's no surprise that temperatures
will be well below freezing. This will keep all precip in the form
of snow. However, unless QPF trends increase, the snow amounts
don't look to be that impactful - just a dusting to a few tenths
of an inch. This will be a system to continue to monitor for any
fluctuations in precip and snowfall, but the second push of cold
air is something to be certain about.
High temperatures on Thursday will struggle to make it above
freezing in some locations, especially north of the Mountain
Parkway. The upper level system will continue to shift eastward and
into New England by Thursday evening/night. Meanwhile, a large area
of surface high pressure will begin to nose into KY from the west,
while NW flow continues aloft promoting CAA. This combination of
increasing subsidence and CAA aloft will lead to one of the coldest
nights of the season so far - with lows in the low to mid teens by
Thursday night.
This surface high pressure should remain in place through at least
Friday night, with temperatures slowly modifying warmer. The warmest
will be on Saturday and Sunday as we see more return flow across the
region, and highs bounce back to the 40s (and even some 50s on
Sunday). Also by Saturday, the models really start to diverge in
solutions. Both the GFS and ECMWF show a quick-moving system moving
through the Great Lakes on Saturday, but the timing and movement are
in question after that. The GFS shows an additional system to our
south at this time, while the ECWMF does not. If the GFS is true,
this could lead to some pops moving through the CWA Saturday
evening/night. Given the uncertainty, just stuck with the NBM
solution, which does hint at slight chance pops and the potential
for light rain or snow during this time. The GFS continues to pull
this southern system northward into southeast Kentucky through
Sunday. Meanwhile, the ECMWF does not realize this same system until
an entire day later, and keeps the CWA dry until Monday morning.
Again, the NBM is continuing to favor the GFS, or perhaps bridging
the gap between the two, keeping at least slight to chance pops in
place from Sunday through Monday. Obviously expect this forecast
to change as we get closer to time and models come into better
solutions. However for now, with this being a southern system, and
increasing temperatures, this should imply that the main precip
type will be rain and not snow.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
ISSUED AT 700 PM EST MON DEC 2 2024
Predominantly VFR conditions will still prevail into this
evening. However, mainly light snow from a weak clipper system
is now moving into western TAF sites affecting them for a time
this evening before diminishing later in the night. This should
result in a period of MVFR at TAF sites south of the Mountain
Parkway before gradual improvement back to VFR late tonight/Tuesday
morning. A brief period of reduced visibility or MVFR ceilings is
possible further north under any heavier flurry activity; but
confidence in occurrence was too low to mention in the SJS/SYM
TAFs at this time. Winds will be northwest at 5 to 10 kts for the
evening then diminishing to light and variable overnight into
Tuesday at 5 kts or less.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...GREIF
SHORT TERM...GEERTSON
LONG TERM...JMW
AVIATION...GEERTSON/GREIF
Source:
JKL issues Area Forecast Discussion (AFD) at Dec 2, 11:50 PM EST---------------
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