236
FXUS63 KLMK 070117
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
817 PM EST Mon Jan 6 2025

...Forecast Update...

.KEY MESSAGES...

* Snow ending and winds diminishing by early evening, but impacts to
  travel will linger behind departing winter storm.

* High confidence in bitterly cold temperatures this week as an
  Arctic airmass overspreads the region. Still a chance of sub-zero
  temperatures in southern Indiana Thursday morning.

* Minor snow accumulations expected Friday into Saturday as another
  winter system moves across the Southeast US. South-central
  Kentucky has the highest chance of one inch or more of snowfall.

&&

.UPDATE...
Issued at 816 PM EST Mon Jan 6 2025

Went ahead and added patchy flurries to the forecast. Several obs
across the CWA are reporting them from time to time, and seeing some
blips on mosaic radar. Given the expansive stratus deck and colder
air moving in, think these could persist through a good chunk of the
night. Only change at this time.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 333 PM EST Mon Jan 6 2025

Upper low continues to open up as the trof axis pushes into West
Virginia, and deformation snows are now exiting the Bluegrass
region. Will end the winter headlines a few hrs early for most of
the area, as the only areas that still have measurable snow falling
are along and east of the I-75 corridor. By the original 00Z
expiration time, any lingering snow should be far enough east to let
the Warning drop for the remaining counties, but will highlight
continued travel impacts.

Dry and cold northerly flow will dominate tonight and Tuesday, with
very cold temperatures incoming. Forecast min temps tonight will be
mainly in the teens, with the main bust potential attached to how
much clearing takes place. If skies clear over the deep snowpack,
readings could drop well into the single digits, but overall expect
partly to mostly cloudy skies courtesy of the Lake Michigan plume.
For Tuesday a 1040mb sfc high settles over the northern Plains, with
ridging oriented west to east into the Ohio Valley, so winds go
light/variable. However there`s enough of a northerly component to
keep clouds coming southward from Lake Michigan. Look for highs in
the mid/upper 20s with limited sunshine.

&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
Issued at 354 PM EST Mon Jan 6 2025

Synopsis...Active large-scale pattern in the medium-range as several
shortwaves drop from Canada into the CONUS supported by several
blocking features. First one is a Rex Block promoted by upper high
over Greenland and a low located in Newfoundland. Second synoptic
player is a anomalous high extending across the Caribbean while the
final one is a ridge amplifying from a high over the Northeast
Pacific into the West Coast. Meanwhile, Arctic surface high pressure
digging across the Plains and eventually crossing the Ohio Valley
will drive well below-normal temperatures the rest of the week. The
bitterly cold airmass in place will also promote snow as the main
precipitation type during the Friday-Saturday timeframe when another
winter system tracking along the Southeast US is expected to bring
minor accumulations to the Lower Ohio Valley.

Model Evaluation/Confidence...High confidence in gelid temperatures
Wednesday evening through Friday morning as surface high pressure
ushers in a slightly modified Arctic airmass, besides there will be
sufficient snow covering the ground to enhance the cooling effect.
There is also high confidence in coldest temperatures occurring
Thursday morning with probabilities of near-zero lows higher than
60% for areas along and especially north of the Ohio River. As for
the snow chances this weekend, there is better confidence (medium to
high) in minor snow accumulations Friday into Saturday. The
increasing confidence is a result of main deterministic models
coming into agreement with the wave phasing over the West and the
attendant surface low track. For that matter, CMC has now trended
towards the GFS/ECMWF/ICON solution while the UKMET is farther
north. Perhaps there is still uncertainty in exact snow amounts, but
most likely expecting minor snow accumulations with the highest
storm totals over south-central Kentucky.

Tuesday - Thursday...Mostly to cloudy conditions will continue
Tuesday and most of Wednesday as wrap-around moisture translate
through the region under light westerly surface winds. Still
mentioning a conditional probability for non-impactful, isolated
flurries if a seeder-feeder mechanism realizes as mid-level clouds,
accompanying a shortwave digging from the Great Lakes, stream over
the ongoing low-level clouds. No additional snowfall accumulations
are anticipated from that activity if it materializes. Biggest
headline for this week will be the bitterly cold temperatures with
below-freezing highs every day and single-digit lows Wednesday and
Thursday mornings. Given ongoing snowpack, continuous below-freezing
temperatures, and clearing skies accompanying the surface high
pressure, near-zero to slightly negative lows are expected Thursday
morning. Greatest probability for such gelid values are focused
along the Ohio River and southern Indiana.

Friday - Monday...Surface low tracking across the Southeast US along
with unidirectional southwest flow aloft will provide sufficient
lift and moisture to allow a shield of snow to overspread the region
Friday into Saturday. GFS forecast soundings support light to
moderate wet snowfall Friday evening with perhaps a chance of
stronger rates Saturday as DGZ lapse rates slightly improve.
Overall, best chances of heavy snowfall appear to fall well south of
the Ohio Valley closer to the surface low center. Anticipated
amounts for the period might range from 1 to 2 inches along south-
central Kentucky and decreasing northward.

&&

.AVIATION /00Z TAFS THROUGH 06Z THURSDAY/...
Issued at 630 PM EST Mon Jan 6 2025

Satellite imagery shows an expansive stratus deck over much of the
eastern CONUS, and more specifically over the Ohio River Valley.
Guidance tries to be optimistic in clear this deck out later tonight
into late morning tomorrow, however decided to be a bit more
pessimistic given its prominence. As a result, will keep MVFR
ceilings in for much of this forecast cycle, but do expect it will
waver above and below 2k feet. Otherwise, look for a light NW and
then N wind. KLEX/KHNB are currently not reporting, so be mindful of
that.

&&

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

&&

$$

UPDATE...BJS
SHORT TERM...RAS
LONG TERM...ALL
AVIATION...BJS