JKL issues Area Forecast Discussion (AFD) at Dec 4, 5:48 AM EST482
FXUS63 KJKL 041048
AFDJKL
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
548 AM EST Wed Dec 4 2024
.KEY MESSAGES...
- After temperatures climb mostly into the 40s today, another
arctic cold front will push through tonight and send
temperatures plummeting.
- The front will bring snow showers to many locations late tonight
and early Thursday morning, with light accumulations possible
(generally a half inch or less).
- Temperatures will warm over the weekend, with above normal
readings expected early next week, along with wet weather.
&&
.SHORT TERM...(Today through Thursday)
Issued at 548 AM EST WED DEC 4 2024
A very strong and large surface low pressure system is moving
southeast over southern Ontario this morning, followed closely
behind by a supporting deep upper low. The system will turn east
and should reach New Brunswick by late Thursday. Meanwhile surface
high pressure is over the southeast CONUS this morning. As the
large cyclone sends an arctic cold front through most of the
eastern CONUS over the next couple of days, the high will be
suppressed southward and high pressure associated with the arctic
air mass will settle southeast over the Midwest.
A tight pressure gradient around the storm system will bring us
warm air advection on brisk southwest winds today into tonight.
Our strongest low level winds, potentially 60+ kts at 850mb, will
occur this afternoon and early evening. However, this will be
above a temperature inversion which will prevent mixing to the
ground. The greatest we'll probably see at ground level ahead of
the front is not much above 30 mph, and most likely in the open
terrain of our western counties and on ridgetops.
A few light showers may try to form in the elevated warm/moist
layer this afternoon or early evening, but it's questionable if
any rain would even make it through the drier air below. Precip
will be more likely behind the front later tonight as low level
lapse rates steepen in the cold air advection. While some rain
can't be ruled out early on in this activity, due to much colder
air aloft it would go quickly over to snow as temperatures fall
below about 37 deg F. With the moist, shallow convective layer
expected to extend well into the dendritic growth zone, there
could be some pretty good but brief bursts of snow in the showers,
especially in our northern and eastern counties. This would
especially be the case in southeast Kentucky where upslope
flow/convergence would be maximized. Our strongest surface winds
are most likely to come just after frontal passage tonight. Even
though the wind maxima at 850 will have passed, the steep surface
based lapse rates will allow what's left of the wind to mix down,
with 30-40 mph gusts likely to occur some places.
Snow showers will linger longest into Thursday morning in
southeast KY. Even when it's all done, most accumulations should
be light at less than an inch (probably not much more than a half
inch). However, some localized higher amounts won't be ruled out
if banded snow showers were to develop and persist over the same
locations. The arrival of much drier arctic air and mixing away of
the lingering moisture will put an end to snow showers and
flurries and allow clouds to decrease in the afternoon. Even with
some limited sun, temperatures will have trouble climbing and
should remain below freezing.
.LONG TERM...(Thursday night through Tuesday)
Issued at 515 AM EST Wed Dec 4 2024
This weekend's forecast features a welcome return to relatively
warmer and drier weather here in Eastern Kentucky, although a strong
signal for wet weather has emerged in the forecast guidance for
early next week. Temperatures (both high and low) are expected to
gradually rise each day during the long term forecast period before
this warming trend culminates in the passage of a cold front at some
point next Tuesday. Compared to this time yesterday, deterministic
models are more aligned in how they resolve the parent upper
atmospheric synoptic features responsible for this trend, which has
increased confidence in the wet start to the next work week. The
forecast guidance suite remains in generally good agreement with the
weather pattern through the end of this week, with a surface high
pressure system building into the area on Thursday night and weak
ridging building in aloft by Sunday. Therefore, confidence in the
entire long term forecast is above average.
The period open on Thursday evening with its coldest temperatures.
The aforementioned surface high will be nudging into the
commonwealth from the NW by this time, allowing skies to clear
across most of the area. At the same time, the winds responsible for
Thursday's chilly daytime temperatures will begin to subside,
priming the atmosphere for efficient radiational cooling.
Confidence is high that most of the area will see overnight lows in
the teens, but it is uncertain at this moment in time whether or not
the boundary layer will fully decouple, especially across the
eastern valleys. Further away from the high's influence, cloud
coverage will be the slowest to erode there, so mesoscale satellite
trends will need to be monitored as Thursday's wintery weather
clears the area. While readers are encouraged to dress warm on
Friday morning regardless of the exact low temperature forecast
(minimum apparent temperatures with be within a few degrees of 10
area wide), if this decoupling can happen, our coldest valleys may
reach the single digits on the thermometer.
During the day on Friday, temperatures will steadily rise into the
lower 30s under relatively sunnier skies. A quick-moving shortwave
upper level disturbance passing through to our northeast may produce
some high clouds, but dry air advection should limit coverage. Sky
grids were increased from the NBM in accordance with this, but the
drier and warmer trend prevails into Saturday as the surface high
increases its influence. Low temperatures on Saturday morning will
be centered around 20 degrees, hovering just above this value on the
ridgetops and dropping into the teens one more time in the valleys.
Saturday's highs will then cross into the 40s for the first time
this month, with overnight lows in the 30s.
On Sunday, the flow aloft backs towards the southwest, and the
resultant moisture advection will bring an end to the clearer and
drier sensible weather conditions. Throughout the day and into
Monday, the cutoff upper level low that has been spinning over Baja
California is expected to eject up the Southern Rockies and into the
central Plains. As it does so, it will phase with a Pacific trough
to its northwest. This will place Kentucky in a regime of divergent
southwesterly flow aloft for a prolonged period of time early next
week. The previously-discussed surface high will be shunted to the
southeastern CONUS, and surface winds here will adopt
southerly/southwesterly components accordingly. Thus, the moisture
return into early next week is expected to be quite effective and
deep. Saturated model soundings and ensemble-modeled PWATS >200%
above climatological norms give credence to the >80% NBM PoPs across
the entire forecast area on Monday and Monday night. Expect cloud
coverage and some lighter precipitation to spread from West to East
on Sunday night, before repeated rounds of rain on Monday. On
Tuesday, the conglomerate upper level features will propagate
eastwards in the form of an elongated, positively-tilted trough. This
will be represented at the surface by an occluding wave cyclone
and a trailing cold front. The exact forward progression speed and
timing of these surface features' approach to the Ohio River
Valley remains somewhat unclear, but most models resolve them
still to the northwest of the area on Tuesday. This will allow
warm/moist air advection and precipitation chances to continue for
at least one more day, before FROPA eventually yields in a NW to
SE clearing/cooling trend. Monday and Tuesday's sensible weather
forecasts look quite similar to one another at this moment in time
- rainy and seasonably warm, with highs in the upper 50s and lows
in the 40s.
&&
.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
ISSUED AT 1257 AM EST WED DEC 4 2024
VFR conditions have returned to the area under clear skies.
Ceilings mainly in the 4-6K ft range are forecast to return
during the day Wednesday and persist through the end of the
period. Winds will pick up out of the southwest during the day
Wednesday, with gusts of 20-30 kts by late the day which will last
into the night.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...HAL
LONG TERM...MARCUS
AVIATION...HAL
Source:
JKL issues Area Forecast Discussion (AFD) at Dec 4, 5:48 AM EST---------------
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