533
FXUS63 KLMK 170556
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
1256 AM EST Fri Jan 17 2025

...Updated Aviation Discussion...

.KEY MESSAGES...

*  Patchy fog possible tonight, with the greatest chance for fog
   along and west of I-65. A few slick spots will be possible due to
   re-freezing of melted snow/ice as well as possible freezing fog.

*  Light to moderate rain expected Friday night and Saturday
   morning, with precipitation possibly ending as flurries or light
   snow late Saturday into Sunday.

*  Frigid arctic air to invade the region late in the weekend
   through early next week. Wind chills in the single digits likely
   Monday and Tuesday, with a period below zero Monday morning.
   Single digits are also likely Wednesday morning.

&&

.UPDATE...
Issued at 957 PM EST Thu Jan 16 2025

Evening satellite imagery shows partly cloudy skies across the
region.  High cirrus was building into the region from the
northwest, but is generally patchy in nature.  Temps were in the
lower 30s in most locations, but a few pockets of upper 20s were
noted out west of I-65.  For the overnight period, main forecast
concern is that winds will slacken off and then pick up out of the
south/southeast and lead to some warm advection fog to develop.
Think overall that fog will be more patchy in nature and focused
mainly west of I-65 and out over far SW IN.  Will continue the
Special Weather Statement highlighting the potential for water re-
freeze on roads (bridges/overpasses) and for the patchy freezing
fog.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 325 PM EST Thu Jan 16 2025

This afternoon, most of the region is experiencing sunny skies,
which has helped temperatures to warm into the upper 30s and lower
40s across southern IN/north central KY and into the mid-40s to
around 50 across south central KY. The sfc pressure trough which
brought increased clouds and a few snow flurries to the region this
morning has quickly passed to the east of the Appalachians, with NW
flow aloft now in place over the region. Westerly winds have been
breezy so far today thanks to a fairly strong pressure gradient in
between the departing trough and an approaching area of high
pressure over the Plains.

Areas of H85 cold advection continue to swing from the Great Lakes
toward the middle Appalachians, with areas of low stratus clipping
northern and eastern portions of the forecast area in association
with this low-level cold advection. So far, these clouds have
scattered as they have moved into northern portions of the area,
although another cold advection lobe and area of clouds will
approach the region from northern IL/IN later this evening.

This evening into tonight, as the trough near the Appalachians moves
farther to the east, temperatures will begin to warm from the
southwest as ridging moves toward the area. There is some
uncertainty as to the extent of low clouds this evening, with clouds
expected to be the most persistent along and east of US 127. Where
more clearing occurs, there is a signal in hi-res guidance for fog,
as sfc high pressure moving just south of the area will allow winds
to become light overnight. While low-level moisture has had more
potential to mix out today with the greater sunshine, dewpoints in
the upper 20s and lower 30s are near/above expected lows tonight,
which supports fog potential. The 12Z HREF has 50-60% chances of
visibility less than 1 mile, especially across portions of southern
and southwest IN and KY west of I-65. With temperatures falling
below freezing overnight, some freezing fog potential also exists,
which could cause slick roads in addition to areas where snow/ice
has melted today. However, since the existence of fog is still
somewhat uncertain, will hold off on any headlines at this time and
monitor obs/guidance trends this evening.

For the day on Friday, the low-level temperature ridge will move
over the Ohio Valley as southerly flow increases on the western side
of sfc high pressure. Once any lingering fog burns off tomorrow
morning, mostly sunny skies are expected the rest of the day until
high clouds begin to move in from the west in the late afternoon
hours. Recent guidance has been too cold on full sun days,
especially across snow-free areas of southern KY, so have gone
considerably above NBM guidance for highs tomorrow. Will advertise
highs ranging from the mid 40s across southern IN and the KY
Bluegrass to the mid 50s across southern KY.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Issued at 325 PM EST Thu Jan 16 2025

Friday Night - Sunday...

Widespread rain overspreads the area Friday night ahead of a
shortwave trough embedded within the larger zonal flow pattern. Rain
lingers into Saturday, before cold air builds in behind the passing
frontal boundary Saturday night into Sunday. The recent trend with
this rainfall has gone downward with amounts expected to mostly
between .25" to .5". Areas across southern KY should expect the
higher amounts, with locations across the north more likely to see
the lower end of the range. Still have to factor in the amount of
liquid sitting on top of the snowpack, which will reduce a little
between now and rainfall onset. Today`s 18z snow core yielded .8" of
liquid, that still needs to melt off. Shouldn`t be enough to cause
any flooding concerns, especially with the downward trend in QPF for
Friday night/Saturday.

Much colder air does set back into the area on Saturday night and
Sunday with lows in the teens to low 20s by sunrise. Highs on Sunday
likely do not make it out of the 20s. There is some concern for
black ice Saturday night given melting snow/ice, possibly wet roads
from earlier rainfall, and a lack of wind to dry things out.
Something to watch for going forward.

Also going to carry some lingering light snowfall through
Sunday/Sunday night as low level moisture is trapped, and we may end
up with a window for a decent fetch off of Lake Michigan for
moisture enhanced snow showers across our NE. Not expecting a lot
accumulation with this, but given the cold air and potential for
high snow ratios we could end up with some minor accums that could
cause some impacts. Stay tuned.

Sunday night - Thursday...

Arctic high pressure at the surface and nearly full CONUS troughing
envelop the area heading into early week. Expect bitter cold
temperatures, and mainly dry conditions. Do have to watch for
activity to the south of our CWA, that at the moment, looks to stay
suppressed to the south. Any northward trends would bring our area
(especially southern KY) more into play for some wintry impacts, but
right now this portion of the forecast remains cold and dry.

Lows mostly in the single digits are expected each morning Monday
through Wednesday, with a slight trend toward milder lows in the low
20s by Thursday AM. Meanwhile, highs are expected in the teens and
low 20s Mon/Tue, with a slight trend toward milder temps near
freezing by Wed. Wind chills may dip down around our -5F threshold
at times either of the coldest morning, so a Cold Weather Advisory
is a possibility for some of the CWA (mainly the north CWA). Another
thing to keep an eye on going forward.

&&

.AVIATION /06Z TAFS THROUGH 12Z SATURDAY/...
Issued at 1255 AM EST Fri Jan 17 2025

VFR conditions are expected through the next 24 hours or so before
the next wave of rain moves into the region. Currently, keeping an
eye on possible LLWS beginning around 00z Saturday. This will be
added to future TAFs if the signal remains. The current low level
cloud cover at SDF and LEX is expected to continue lifting and
will move east of the airfields over the never few hours.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...None.
IN...None.

&&

$$

UPDATE...MJ
SHORT TERM...CSG
LONG TERM...BJS
AVIATION...KDW