JKL issues Area Forecast Discussion (AFD) at Dec 11, 1:00 AM EST393
FXUS63 KJKL 110600 AAA
AFDJKL
AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
100 AM EST Wed Dec 11 2024
.KEY MESSAGES...
- Rain redevelops overnight from west to east and transitions to a
period of snow early this morning before ending from west to
east.
- Some snow accumulations are expected this morning, most notably
at elevations above 2,000 feet with up to 3 inches possible but
an inch or less expected in the valleys. The snow could be
heavy for a time in the southeast parts of the area around mid
morning
- Snow showers, a few briefly heavy and gusty, could bring
additional minor, but highly variable, snow accumulations this
evening into tonight.
&&
.UPDATE...
Issued at 1135 PM EST TUE DEC 10 2024
Looking at the 00Z data and more recent runs from the CAMs have
decided to upgrade our southeast counties from the SPS to a Winter
Weather Advisory from 6 am through 12 pm (noon). The primary
concern is the morning rush hours into mid morning as the snow
looks to come down at a high rate for a couple of hours due to a
baroclinic leaf formation from a passing sfc low. This snow will
likely accumulate as some slush on warm roads in the lower
elevations with a bigger threat stick and accumulate more above
2000 feet. Anticipate as much as 3 inches will occur on the top of
Black Mountain. Overall, the impacts will be limited, but for a
few hours at its peak it could be consequential and worthy of an
Advisory.
The rest of the area will see a briefer period of snow as the
cold air comes in on the backside of the developing baroclinic
leaf that primarily targets the far east Wednesday morning. Warm
roads will keep any slick spots very limited outside of the higher
snowfall rates expected in the advisory area. Otherwise, have
also added in the latest obs and trends for the T/Td/Sky grids
with this update as well as matching up the PoPs with the near
term radar tendencies and CAMs guidance. These adjustments have
been sent to the NDFD and web servers along with a freshening of
the zones, HWO, and SAFs. In addition to the WWA issuance, an SPS
was put out for the rest of the area concerning both shots of
snow expected on Wednesday.
UPDATE Issued at 803 PM EST TUE DEC 10 2024
Early evening update is out with minor modifications to PoPs,
mainly to keep shower activity the remainder of this evening more
confined to the Virginia border counties with a sharper gradient
downward to the northwest. Other updates were minimal and
insignificant to the forecast.
Models are in good agreement on a baroclinic leaf developing
toward morning and moving north-northeast across eastern Kentucky.
These features can sometimes over-perform with regards to
precipitation intensity, so this bears watching. However, with
record high temperatures today in the mid-60s and very marginal
temperatures, would expect snow accumulations to be confined to
grassy areas and elevated surfaces. The exception would be the
higher elevations along the Virginia border.
&&
.SHORT TERM...(This evening through Wednesday night)
Issued at 529 PM EST TUE DEC 10 2024
Regional radar mosaic shows a line of showers extending from
Inez to Hazard to Middlesboro at 22z. A MSLP/observations
analysis reveals that this line of convection is along a cold
front that is slowly sliding eastward through Coalfields. Ahead of
the boundary, temperatures range in the mid to upper 60s at lower
elevations while temperatures have dropped into the 50s behind
the boundary. A notable wind shift from southwest to northwest is
also noted with the boundary. This cold front extends southward
from an ~1008 mb low centered over far southeastern Ohio all the
way to the Mississippi River Delta. The front precedes a longwave
trough extending from the Central Canadian Arctic to northeast
Mexico. A potent vorticity lobe is found just east of the trough
axis from Illinois down the Central Texas. Further poleward within
the trough, an ~506 dam low is diving southward through Manitoba.
A secondary surface cold front is found ahead of this upper low
from near International Falls, MN to to over Nebraska and then
northwestward along the eastern slopes of the Northern Rockies.
The cold front presently crossing the area will shift off to the
east over the next couple of hours before becoming nearly
stationary. The associated showers will follows suit until
reaching the immediate vicinity of the Virginia border where they
are likely to train southwest to northeast through the evening.
Rainfall rates should be low enough to preclude any hydro issues.
Additional energy riding up the eastern side of the trough will
initiate a new surface low riding along the stalled front after
midnight, causing the precipitation shield to expand
northwestward over the Coalfields again through the wee hours of
Wednesday morning. Meanwhile, ongoing low-level CAA will push
temperatures downward through the night and into the mid 30s to
mid 40s, west-to-east, by around 5 AM EDT. Meanwhile, high
resolution models are showing a northeast-to-southwest oriented
band of snow developing over Indiana/Western Kentucky after
midnight due to zone of enhanced lifting/frontogenesis ahead of
the aforementioned vorticity lobe. That band is depicted as
generally broadening and intensifying as it moves eastward across
the Commonwealth and gains access to better moisture, eventually
merging with the precipitation shield over eastern Kentucky. As
the surface low passes to our east of the Appalachian Mountain
spine early Wednesday morning, cold air will rush in from the
west, drop temperatures into the lower to mid 30s, and flip rain
over to all snow between 5 AM and 9 AM EST. A brief period of
sleet is possible as the transition occurs, primarily east of the
Pottsville Escarpment. The snow continues light to moderate at
times before tapering off in the Lake Cumberland area as early as
7 AM EST, lingering as late as 12 PM EST over Pike County. The
warm antecedent ground and air temperatures should limit
accumulations to less than one half inch primarily on grassy and
elevated surfaces across a majority of the area. The area with the
best chances for impactful accumulation is from Martin down to
Bell County and eastward where the snow will persist the longest
and snowfall rates will be highest. In this area, up to around one
half inch of snow accumulation is forecast in valleys and up to 2
inches is possible at elevations above 2,000 feet (the higher
amounts may be enough for some instances of sloppy snow sticking
to highways). Once the snow ends, clouds are expected to break
partially and allow temperatures to warm back into the mid to
upper 30s at lower elevations during the afternoon.
As temperatures warm at the surface, cold air advection in the low-
levels ahead of the secondary cold front will lead to steepening
lapse rates Wednesday evening. Model soundings suggest that these
showers will have excellent access to the dendritic growth zone
which combined with moderately strong background flow could lead
to squall-like conditions in the heaviest activity. The equilibrium
level could flirt with -20C, perhaps even supporting enough
charge generation for a rumble of thunder in the most robust
updrafts. The snow showers wane to just a few flurries during the
late evening and early overnight as cold, dry air rushes in
behind the secondary front. Due to the showery nature of the
snowfall, accumulations could vary over short distances. The snow
showers could briefly coat pavement at some lower elevation
locales, but warm surface temperatures should tend to melt off
most of the snow that tries to accumulate. Grassy and elevated
surfaces should fare better, picking up to one half inch of new
accumulation in most cases. An isolated amount nearing an inch
cannot be ruled out. Temperatures are expected to fall into the
upper teens to mid 20s, northeast to southeast, by late Wednesday
night.
.LONG TERM...(Thursday through Tuesday)
Issued at 555 PM EST TUE DEC 10 2024
The 500H trough axis departs to our east Thursday morning with
subsequent ridging building eastward through Thursday night. An
associated surface high crests over eastern Kentucky Thursday
evening. Chilly 850 mb temperatures down to around -5 to -10C
yield to moderating temperatures on the backside of the surface
high on Thursday night and Friday. Thereafter, a rather active
pattern ensues with the first of two Pacific 500H troughs passing
over the Ohio Valley this weekend, supporting an area of low
pressure passing to our north. The system's associated cold front
drops south of the Ohio River and stalls overhead or nearby
Sunday night. This boundary does little to cool our air
temperatures. The second storm system of Pacific origin then
approaches toward the end of period, though model agreement is not
great with respect to the details at this time.
In sensible terms, expect partly cloudy to most clear skies Thursday
and Thursday night. Temperatures will be chilly with highs only in
the mid 30s north to around 40 near the Tennessee border while lows
dip back into the mid 10s to mid 20s Thursday night. Clouds
increase on Friday while winds pick up from the southeast,
boosting temperatures into the mid 40s to lower 50s. Temperatures
dip back into the 20s and 30s Friday night, holding steady or
rising late. Rain chances return Saturday and peak Saturday night
(80-90 PoP) before tapering off on Sunday. After a lull in the
rain chances Sunday night and Monday, the threat for rain
increases again Monday night into Tuesday. Forecast day high
temperatures from Saturday through Tuesday range in the 50s while
night temperatures bottom out in the mid 30s to mid 40s.
&&
.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
ISSUED AT 100 AM EST WED DEC 11 2024
Low CIGs in the IFR to LIFR range will continue to hold over the
forecast area into the morning hours. An uptick in precipitation
follows through 08Z as temperatures drop to near freezing,
transitioning the precipitation over to snow toward and shortly
after sunrise. VIS restrictions to IFR will be possible (even
lower for a brief time at KSJS) with the snow. Conditions improve
late in the morning from west to east into the afternoon. Later,
towards sunset, scattered snow showers develop and move into the
area from the west, mostly after 22Z. Though extremely low
confidence, a few lightning strikes are possible, along with brief
squall conditions with the snow showers toward the end of the TAF
period. Winds will be generally from the northwest at 5 to 10 kts
through the day, but look for an uptick in the evening to 10 to
15 kts with gusts up to 25 kts from the west accompanying any of
the more robust snow showers.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 6 AM this morning to noon EST today
for KYZ087-088-110-113-115-117>120.
&&
$$
UPDATE...GREIF
SHORT TERM...GEERTSON
LONG TERM...GEERTSON
AVIATION...CMC/GREIF
Source:
JKL issues Area Forecast Discussion (AFD) at Dec 11, 1:00 AM EST---------------
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