LMK issues Area Forecast Discussion (AFD) at Nov 26, 6:29 AM EST
497
FXUS63 KLMK 261129
AFDLMK
Area Forecast Discussion
National Weather Service Louisville KY
629 AM EST Tue Nov 26 2024
.KEY MESSAGES...
* Dry and sharply cooler today as a cold pattern takes hold for the
upcoming week.
* Next round of rain arrives late Wednesday. Rain chances peak
Wednesday night into early Thursday morning, with a dreary and
chilly Thanksgiving Day expected.
* Much colder temperatures are likely this weekend into the first
few days of December. There is a low confidence chance for light
snow Saturday night into Sunday morning.
&&
.SHORT TERM /THROUGH TONIGHT/...
Issued at 326 AM EST Tue Nov 26 2024
Cold advection is well established behind the departing front, with
NW winds staying up through the night in a mixy boundary layer. High
pressure will build in quickly from the west today, allowing winds
to slack off as the center of the high settles near Louisville by
early evening.
The CAA pattern is one where temps usually struggle, but with
advection going nearly neutral by midday, we'll go for a bit more
recovery than we would otherwise expect in NW flow. It'll still be a
chilly day, with temps struggling into the mid/upper 40s, perhaps
just touching 50 in southern Kentucky and urban Louisville.
Sfc high retreats into West Virginia overnight, and high clouds
increase from the NW as the next system emerges onto the Plains.
Look for a quick drop in temps this evening, then leveling off after
midnight.
&&
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 326 AM EST Tue Nov 26 2024
===== Wednesday - Thursday =====
Sfc high pressure will be departing off to our east Wednesday
morning as upper zonal flow breaks down in response to a
strengthening upper shortwave swinging across the Central US. The
associated sfc low will be pushing east-northeast from Oklahoma
through the morning hours, ramping up low-level southwest flow out
ahead of it. Soundings continue to show rather dry air below 700 mb
into the afternoon, so any initial WAA radar echoes will likely be
virga. Increasing SW flow within the 850mb layer will continue to
strengthen our moisture transport, and we'll likely see our column
become saturated by the late afternoon or early evening hours.
Most of the accumulating rainfall will come after 00z Thursday
(Wednesday night) as the sfc low tracks across the Tennessee Valley.
The previous discussion mentioned the 12z suite was coming into
better agreement, and we see a similar trend with the 00z guidance
as well, with the GFS, ECMWF, and GDPS all within reasonable
agreement on the placement and timing of the sfc low for Wednesday
night. The sfc low is expected to move from central Arkansas to
south-central Kentucky between 00-06z, which will be when our
highest rain chances of the period will be. Thermal profiles will be
supportive of liquid with this system, with temps remaining above
freezing up to 8k ft. Little to no instability is expected. Temps
overnight are expected to remain above freezing, with most in the
upper 30s and lower 40s.
Rain chances will linger into Thursday morning as the sfc low pushes
east, though trends have been shifting towards a drier Thanksgiving
afternoon and evening. Total QPF with this wave is expected to be
between 0.25-0.50 inches of rain. Drier conditions will filter in
from west to east during the late morning, and just about all
locations should be rain free by 18-21z. Stronger CAA will be taking
over in the wake of the sfc low, with NW winds limiting sfc temps to
the low to mid 40s. Despite the drier trends for Thursday, thick
cloud cover will still blanket the entire area as we remain under
large scale upper level troughing.
===== Friday - Weekend =====
CAA and NW flow will continue to influence our region for Friday.
Sfc pressure gradient will enhance our sfc winds, with wind gusts
potentially reaching 20 mph. With temps only progged to hit the mid
to upper 30s, the NW winds will support wind chills in the 20s
during the day. As we head into Friday night and Saturday morning,
the pressure gradient will weaken, resulting in our winds becoming
more relaxed. We'll finally clear out from the clouds, which will
favor radiational cooling. We'll have temps drop into the upper
teens north of the KY Parkways, and lower 20s to the south for
Saturday morning.
The upper flow briefly flattens out for Saturday, but another weak
shortwave will be riding through the flow and making its way toward
the lower Ohio Valley. Temps for Saturday will be similar to Friday.
There is good model agreement on seeing the shortwave approach our
area by Saturday night. While moisture associated with this wave
will not be great, model soundings show enough saturation up to the
DGZ to produce some light precip. Our thermal profile will be well
below freezing, so no p-type issues are expected. At least flurries
will be possible, but some pockets of light snowfall can't be ruled
out at this time either. Accumulations are expected to remain under
an inch, but wouldn't be surprised if we some areas get a light
dusting of snow by Sunday morning. LREF 100-member ensemble shows a
15-25% prob of at least 1 inch of snow, though the caveat here is
that it is using 10:1 snow ratios. Given the cold airmass expected,
we could end up with ratios closer to 15:1.
There is much higher confidence in a renewed shot of cold air for
the second half of the weekend into early next week. Temperatures
next Sunday and Monday may struggle to surpass the freezing mark
during the day with lows at night primarily in the teens. In line
with the CPC 6-10 day outlook, there is very high confidence in
below normal temperatures for the start of December.
&&
.AVIATION /12Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 621 AM EST Tue Nov 26 2024
Boundary-layer mixing in cold advection is winning the battle and
has lifted cigs above 2000 feet, but we'll stay MVFR through mid-
morning when the stratus clears out. HNB is the lone exception as
the deck is already scattering out there.
NW winds continue to diminish and will be light WNW through the day
as high pressure settles overhead. Look for light SE return flow to
set up quickly this evening as the high retreats eastward into West
Virginia. Warm advection aloft will result in cirrus ceilings
shortly after sunset, lowering into a mid-level deck for HNB after
midnight.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
KY...None.
IN...None.
&&
$$
SHORT TERM...RAS
LONG TERM...CJP
AVIATION...RAS
Source: LMK issues Area Forecast Discussion (AFD) at Nov 26, 6:29 AM EST (https://mesonet.agron.iastate.edu/p.php?pid=202411261129-KLMK-FXUS63-AFDLMK)
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