148
FXUS63 KLMK 050355
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
1055 PM EST Wed Dec 4 2024

.KEY MESSAGES...

*  Windy conditions expected through tonight with gusts of 35-40 mph
   possible.

*  Light precipitation tonight and a quick temperature drop may
   result in scattered slick spots on roads Thursday morning.

*  Cold wind chills in the single digits Thursday morning and teens
   in the afternoon.

*  Warming temperatures are expected through the weekend, with the
   next chance for widespread precipitation coming as rain Sunday
   night into Monday.

&&

.UPDATE...
Issued at 1055 PM EST Wed Dec 4 2024

Well...that escalated quickly. After an afternoon and evening of
overachieving winds, the post-frontal surge across central Illinois
and central Indiana is putting out 50-60 mph winds as cold advection
gives us a deeply mixed boundary layer. Expect that surge to get
into southern Indiana and near the Ohio River by 05-06Z, and push
across the rest of the CWA within a few hrs after that. Look for
gusts around 50 mph, with a 1-2 hour window in any given location.
As a result we have gone with a Wind Advisory valid til 09Z for
southern Indiana and the northern half of central Kentucky.

Issued at 950 PM EST Wed Dec 4 2024

Mild and breezy SW flow in place across the Ohio Valley with a pre-
frontal trof draped across southern Indiana, currently generating
scattered light rain showers from Seymour eastward across the
Cincinnati area.  We are seeing more isolated coverage back to the
west toward Jasper, but the emphasis there is on isolated. Expect
this feature to push through in the next couple hours, followed
fairly closely by the main cold front, which extends roughly from
Fort Wayne to Terre Haute to St Louis. Best chance for seeing rain
will be east of I-65 and north of I-64, while areas south of the
Parkways will almost certainly remain dry.

Winds continue to overachieve compared to model guidance, but our
currently advertised window for gusts around 30 mph covers it pretty
well. Could see another brief 35 mph surge just behind the front,
but it will not last and it remains below advisory thresholds.

For the most part the cold air will be chasing the moisture out of
the area, but there is some brief overlap where we could squeeze out
a few snow showers as temps drop sharply with fropa. Forecast
heading into Thu morning is pretty well on track, with min temps
either side of 20 and wind chills in the single digits.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 314 PM EST Wed Dec 4 2024

Southerly warm air advection continues through the rest of today
into tonight before a cold front arrives overnight tonight. Synoptic
scale ascent and moisture depth associated with the frontal system
increase this evening into tonight. The potent mid-level vorticity
maximum rotates over the Lower Great Lakes and Upper Ohio Valley as
the strong cold front sweeps southeast through the area. Scattered
showers most likely late this evening into the overnight and ending
by sunrise Thursday. During this timeframe, the best chance (greater
than 40% chance) will be northeast of a Salem IN to Campbellsville
KY line. P-type looks mainly liquid through about Midnight, with a
changeover to scattered snow showers for the 12-4 AM time frame.
This is a very light QPF event, but any scattered snow showers
tonight could produce a quick dusting. Little to no snow
accumulations are expected.

Temperatures plummet early Thursday morning with very strong CAA in
the wake of the cold front. Temperatures are expected to drop into
the teens to 20s by daybreak. Precipitation will likely diminish by
sunrise. But given the light QPF overnight and quick temperature
crash, some scattered slick spots will certainly be possible for the
Thursday morning commute. This concern is highest from southern IN
southeast through north-central KY and the Bluegrass Region. In
addition, NW winds will remain fairly breezy in the strong CAA
regime. In short, expect a very chilly Thursday morning with wind
chills in the single digits to teens and possible slick spots on
roads. Plan ahead and give yourself some extra travel time Thursday
morning.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
Issued at 314 PM EST Wed Dec 4 2024

Thursday Night - Saturday Night...

The heart of the continental polar air mass will be over the region
Thursday evening as sfc high pressure spreads from the lower
Missouri Valley into the Mississippi Valley. With the pressure
gradient weakening over the area, winds should be light, which will
help in keeping wind chills "only" in the upper single digits and
low teens Thursday night into Friday morning. With mostly clear
skies expected into Friday morning, radiational cooling should be
uninhibited, and low temperatures are expected to fall into the low-
to-mid teens across most of the area. In the coldest locations,
temperatures may fall as low as the upper single digits.

After another chilly day on Friday with high temperatures in the
30s, a gradual warming trend is expected through the weekend. Mid-
and upper-level troughing will eject eastward into the North
Atlantic as sfc high pressure moves into the southeastern US. The
Rex Block upper pattern over the western CONUS will begin to
untangle itself as another polar stream disturbance moves in from
the Gulf of Alaska. Until the southern stream upper low over the
southwest US begins to eject into the southern Plains on Sunday,
moisture return is expected to be limited, and dry weather is
expected through Sunday morning.

Sunday into Early Next Week...

Once the closed low over the southwest US opens up and ejects
eastward on Sunday, rich moisture from the Gulf of Mexico will be
drawn northward into the Tennessee and Ohio Valleys. ECMWF and NAEFS
ensemble mean integrated vapor transport and precipitable water
exceeds the 90th percentile of model climatology Sunday night into
Monday, with mean PW values ranging between 1 and 1.25". Anomalous
moisture content combined with support from the upper shortwave will
allow for the development of widespread precipitation across the
region Sunday afternoon through the day on Monday. With the region
being squarely in the warm sector of this system, temperatures will
be above normal for the end of the weekend into early next week and
any precipitation should fall as rain. For the Sunday night-Monday
period raw ensemble probabilities of QPF over 1" are 20-30%, while
the NBM has 1" QPF exceedance probabilities between 50-70%.

Once this wave of precipitation lifts through the region Monday
night, the sfc front will still be lagging to the west of the area.
Indeed, ensemble guidance diverges considerably after next Monday,
with large spreads in temperature and moisture guidance as we head
into the middle of next week. With the main upper level trough still
lagging behind, it is possible that additional waves of
precipitation will continue into the middle of next week.
Temperatures should trend downward from Monday night into Wednesday,
and if enough cold air seeps into the region, p-type may become
questionable later into next week. However, forecast confidence in
specifics beyond Monday is quite low at this time.

&&

.AVIATION /00Z TAFS THROUGH 06Z SATURDAY/...
Issued at 639 PM EST Wed Dec 4 2024

Impacts:

* Gusty winds from the SW this evening, peaking with a period of 30
  kt gusts after shift to WNW around midnight.

* Brief and light precip with the wind shift, with transient MVFR
  vis possible.

Discussion: Prevailing VFR expected through the valid TAF period.
Will initialize with gusts around 25 kt from the SW this evening,
and bump those gusts up near 30 kt with the wind shift to WNW around
midnight. Medium confidence in these gusts as the winds have been
overachieving, and this forecast is a bump upward from model
guidance. Low-level jetting is respectable with 40-45 kt just 2000
feet off the deck, but with the stronger than advertised sfc winds,
it`s too marginal to justify LLWS.

Low clouds scatter out before daybreak at SDF and BWG, and more
toward mid-morning at LEX with diminishing NW winds. Will hang on to
gusts just shy of 20 kt for much of the day, after which the
gradient further relaxes Thu evening.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...Wind Advisory until 4 AM EST /3 AM CST/ Thursday for
     KYZ023>025-028>043-045>049-053>057.
IN...Wind Advisory until 4 AM EST /3 AM CST/ Thursday for
     INZ076>079-083-084-089>092.

&&

$$

UPDATE...RAS
SHORT TERM...MCK
LONG TERM...CSG
AVIATION...RAS