JKL issues Area Forecast Discussion (AFD) at Dec 31, 8:52 AM EST220
FXUS63 KJKL 311352
AFDJKL
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
852 AM EST Tue Dec 31 2024
.KEY MESSAGES...
- Well above normal temperatures today will be followed by a
return to winter cold to start the new year.
- Quick-moving low pressure will bring another light round of
rainfall on today along with strong south to southwest winds
gusting to between 30 and 40 mph at most locations.
- Any thunderstorms this morning/early afternoon could become
strong to severe with damaging winds and large hail possible; an
isolated brief tornado cannot be ruled out.
- A fast-moving clipper system may bring light snow accumulations
to the forecast area on Friday.
- A dynamic storm system may bring a mix of wintery precipitation
types to Eastern Kentucky next Sunday and Monday.
&&
.UPDATE...
Issued at 851 AM EST TUE DEC 31 2024
SPC has issued a Marginal risk for severe weather across most of
eastern Kentucky today. All modes of severe weather (hail, wind,
and tornadoes) are possible. The latest observations have been
blended in the hourly forecast.
&&
.SHORT TERM...(Today through Wednesday)
Issued at 531 AM EST TUE DEC 31 2024
Temperatures are holding steady or rising early this morning as
clouds and winds increase ahead of an incoming storm system.
Temperatures as of 10z, ranged from the mid 30s in the coldest
northeastern hollows to the mid/upper 50s near and west of I-75 and
I-64 north. Regional radar shows an area of showers, with a few
embedded thunderstorms, lifting through the Lower Ohio Valley ahead
of a warm front that extends from an ~994 mb surface low over
Illinois southeastward to the vicinity of Lake Cumberland and then
southward into Tennessee. A cold front is evident behind the warm
front, extending from the low toward the Gulf of Mexico, just east
of the Mississippi River.
Model guidance is in good agreement showing this area of low
pressure skimming just north of the Ohio River today and approaching
the southern shore of Lake Erie by mid-evening. As the low passes,
the associated warm conveyor belt jet (50+ knots @850mb) will help
propel the warm front through eastern Kentucky this morning. Our CWA
will be briefly in the warm sector until the trailing cold front
sweeps through during the early to mid afternoon. Various model
solutions show a narrow tongue of of modest surface-based shallow
instability within the warm sector. Meanwhile, the presence of the
strong wind field around the low should yield sufficient EBWD (up to
~35-40 kts) to maintain supercellular structures. While the latest
NAM12 remains quite modest with just a couple hundred J/kg of skinny
instability, the RAP13 has suggested up 500 J/kg of surface-based
instability, a significant portion of which is in the hail growth
zone. If any shallow supercells develop within the warm sector,
there will almost certainly be a risk of small hail. Additionally,
low MLLCLs, up to ~180 J/kg 0 to 3km CAPE, and modest turning in the
low-level hodograph (at least in the RAP13) would suggest that
tornadogenesis cannot be ruled out should a sustained supercell
develop. Also, multiple model soundings now show the equilibrium
levels rising above -20C, warranting the addition of thunder to
today's forecast.
Aside from the possibility of thunderstorms, gusty winds are likely
to develop as low-level lapse rates steepen in the warm sector under
diurnal heating later this morning and then remain steep this
afternoon due to cold air advection behind the cold front. BUFKIT
momentum transfer suggests that south to southwesterly gusts will be
strongest between roughly 10 AM and 3 PM EST before subsiding later
in the afternoon. Forecast wind gusts were marginally strong enough
to warrant the issuance of a Wind Advisory for most of eastern
Kentucky from 8 AM through 7 PM EST. Another brief uptick in the
wind gusts is possible this evening, but speeds should generally
remain below advisory criteria. The surface low pressure responsible
for this inclement weather will continue lifting away into western
New York tonight but moisture will continue to wrap in around the
backside of the low. This low-level moisture combined with upslope
flow will keep light showery precipitation across the area
overnight. As 850mb temperatures fall to between ~-5 to -8C by late
tonight, anticipate that showers will mix with and change over to
snow for most locations, first over the mountaintops near the
Virginia border and also north of I-64. By late Wednesday morning,
expect all precipitation to be falling in the form of snow. Snow
showers and flurries can be expected to continue through the
afternoon on Wednesday amidst northwest upslope flow lingers behind
the departing low pressure. Given warm ground temperatures, snow
accumulation will likely be minimal to nil outside of the highest
mountains.
In sensible terms, look for showers to pass through eastern Kentucky
this morning, possibly with a embedded rumble of thunder.
Temperatures will warm well into the 50s for a time once the warm
front passes and skies may clear partially, especially late morning.
South to southwesterly winds will become gusty, peaking between 30
and 40 miles per hour at most locations. If a thunderstorm develops
during this time, it could become strong. Any sunshine will be short-
lived as clouds thicken and showers redevelop during the early to
mid-afternoon and temperatures will drop back into the 40s. Showers
continue through tonight and gradually mix with and change over to
light snow showers/flurries at most locations as temperatures dip
into the middle 30s at lower elevations and into the lower 30s to
upper 20s above ~1,500 feet. Any remaining rain showers in the
deepest valleys of the Big Sandy basin will switch to snow on
Wednesday morning. Snow showers and flurries are then expected to
continue for the remainder of Wednesday while temperatures hold in
the mid to upper 30s at lower elevations and in the upper 20s to
lower 30s above 2,500 feet. Little or no snow accumulation is
expected, except perhaps an inch or two over the highest portions of
Big Black and Pine mountains.
.LONG TERM...(Wednesday night through Monday)
Issued at 551 AM EST Tue Dec 31 2024
After any lingering snow flurries on the backside of the first
storm system of 2025 taper off early on Wednesday night,
temperatures are expected to cool off into the mid 20s. Quasi-
zonal flow aloft and a building surface high pressure system will
yield drier and relatively clearer conditions on Thursday, but a
fast-moving clipper system is expected to approach the area on
Thursday night. Overnight lows below freezing across the entire
area and sufficiently cold temperatures aloft support some snow
falling as this system passes through, but daytime highs in the
mid/upper 30s will limit accumulation totals. Guidance continues
to resolve the best atmospheric moisture closer to the Ohio River
on Friday. As flow shifts to a more NW orientation on the system's
backside, orographic lift may locally enhance snow totals in the
higher elevation locations. Given these two caveats, our
northernmost and easternmost counties are the most likely to see
measurable snow with this clipper system. However, accumulation
totals are unlikely to surpass one inch since the system looks to
quickly eject off to the east overnight.
Cold air advection intensifies in the wake of Friday's system, and
the first weekend of 2025 looks accordingly chilly. Overnight lows
on Friday will dip down into the teens across the entire forecast
area, and temperatures will struggle to rise above freezing on
Saturday afternoon. Probabilistic ensemble guidance continues to
suggest that there is a greater than 70 percent chance for high
temperatures to remain below 32 degrees on Saturday. Likewise, there
is a greater than 50 percent chance that Saturday night's lows will
dip down into the teens once again. This colder airmass will set the
stage for potentially impactful winter weather on Sunday and Monday,
although forecast uncertainty remains relatively high beyond
Saturday night.
A stronger and more dynamic storm system is expected to approach the
Ohio River Valley early next week. Confidence is high that the
temperatures out ahead of this system will be cold enough to support
some form of frozen precipitation. On the other hand, confidence is
low in the exact positioning of the system's surface low and frontal
boundaries. These details will prove crucial in diagnosing
precipitation types via atmospheric temperature profiles as the
event approaches, and the greater than usual model spread in the
forecast temperatures for next Sunday and Monday precludes the
mention of anything more than a wintery mix of rain and snow in the
forecast grids for now. Interests are encouraged not to read too
much into a singular model run's precipitation/accumulation output
at this moment in time, as great variability from run to run has
been observed.
Instead, it is important to look towards the overall trends,
available ensemble data, and meteorological theory to explore the
possible outcomes to this event. At the onset of precipitation, the
antecedent coldness throughout the column will lend itself towards
snow. However, it remains uncertain how much warm air will advect
into the atmospheric column ahead of a surface warm front pushing
north out of the Tennessee Valley. If this boundary makes it to
Cumberland River Basin, isentropic upglide will introduce a warm
nose to the thermal profile over much of the forecast area. If the
parent low takes a more northwesterly path and said boundary moves
closer to the I-64 corridor, the area may transition fully into the
warm sector of this system. If the surface low takes a more
southeasterly track and the boundary remains closer to the Tennessee
River, less warm air would make it into the atmosphere over our
forecast area. The first solution would yield in a messier
precipitation type forecast, with a transition from snow to ice to
rain and then back to snow possible. The second solution would
lend itself to rain during the warmer afternoon hours, although
probabilistic ensemble data suggests that the likelihood of this
is decreasing. The third solution could result in enhanced snow
accumulations, but the 10 to 15 degrees of model spread in the
temperature forecast for both Sunday and Monday afternoons means
that it is far too early to forecast specific accumulation totals
for any precipitation type. Interests are encouraged to stay tuned
to future forecast packages as the guidance suite ingests higher
quality upstream observations and comes towards a consensus in the
coming days.
An even colder airmass looks to move into Eastern Kentucky in the
wake of this system. The latest Climate Prediction 8-14 Day
Temperature Outlook highlights a greater than 90 percent chance of
below normal temperatures next week across our forecast area, and an
ensemble signal for a period of sub-freezing temperatures during
both the daytime and nighttime hours has emerged next week. As we
monitor the potential for impacts from this wintery weather pattern,
readers are encouraged to review the winter weather preparedness
information available at weather.gov/safety/winter in the coming
days, as it could come in handy once the cold air arrives this
weekend.
&&
.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
ISSUED AT 728 AM EST TUE DEC 31 2024
VFR conditions were observed at TAF issuance. Showers and low
VFR/high MVFR ceilings will continue to spread from west-to-east
this morning with the passage of a warm front. An isolated
thunderstorm is possible with the warm frontal passage and then
in the warm sector late this morning and early afternoon. The
greatest risk for a thunderstorm will be at JKL and SJS. The risk
for any thunderstorms will come to and end with the passage of a
cold front during the early to mid afternoon. Behind the cold front,
light showery precipitation is expected to linger while ceilings
drop to low MVFR/IFR for the remainder of the TAF period
Any low-level wind shear early in the TAF period due to the strong
wind field aloft will be replaced by strong southerly to
southwesterly winds gusting to between 30 and 36 kts by late
morning as low-level mixing commences. Those winds will veer more
westerly behind the cold front this afternoon and slowly subside
this evening and tonight.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 7 PM EST this evening for KYZ044-050>052-
058>060-068-069-079-080-083>088-104-106-108>118-120.
&&
$$
UPDATE...GEERTSON
SHORT TERM...GEERTSON
LONG TERM...MARCUS
AVIATION...GEERTSON
Source:
JKL issues Area Forecast Discussion (AFD) at Dec 31, 8:52 AM EST---------------
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