875
FXUS63 KLMK 212359
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
659 PM EST Thu Nov 21 2024

...Updated Aviation Discussion...

.KEY MESSAGES...

*  The best chance for any local minor impact will be from southeast
   Indiana to the Bluegrass region of Kentucky.

*  Gusty winds tonight and Friday, with some gusts around 35 to 40
   mph. The strongest gusts likely today.

*  Gusty winds during snow showers will likely result in brief
   periods of reduced visibility.

*  Much colder weather tonight and Friday with wind chill values in
   the 20s and 30s.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 346 PM EST Thu Nov 21 2024

This evening, an upper low will be centered near southwest
Pennsylvania. The circulation has two surface lows rotating around
it, one over northwest Indiana and the other just off the New Jersey
coast. Throughout the night, the surface low over Indiana will
continue to weaken as it gets pushed southeast towards Lexington,
opening into a positively tilted surface trough. The other surface
low, in the Atlantic, will become stacked under the upper low near
New York Friday morning.

The surface low dropping across Indiana and heading towards the CWA
is part of a larger shortwave rotating around the aforementioned
upper low. It`s this shortwave that is driving the forcing of the
snow showers, currently over central Indiana and areas to the north
and northwest, that are headed towards southern Indiana and central
Kentucky. Besides pushing the precipitation, the deep layer low
pressure circulation is driving northwest flow into the region at
all levels, resulting in deep cold air advection. Model soundings
continue to show the warmest air in the column is at the surface
with the rest of the column well below freezing with no hint of a
warm nose. P-type isn`t really an issue. If the near surface
temperature gets too warm to support snow, a few areas could see
rain, but in most places snow will remain until reaching the
surface.

As the snow moves into the region, model sounds shower deep
saturation, including saturation of the DGZ, but on the back side of
the precipitation around 2-3z in southern Indiana, soundings show
the DGZ drying with saturation remaining below the DGZ. When this
occurs, snow will end and a short window of drizzle could be
possible.

Surface temperatures are expected to remain above freezing for most
of the night, but areas east of Interstate 65 near Madison, Indiana
and in the Bluegrass region of Kentucky are expected to see
temperatures at least touch freezing before temperatures start to
warm again on Friday. Warm surface temperatures and borderline air
temperatures will limit impacts on road surfaces. Accumulation will
be driven more by rates than freezing temperatures. Most roadways
are expected to remain wet with snow melting on contact. Grassy and
elevated surfaces will see better accumulations. The forecast has
the northeast half of the CWA seeing between 0.1" to 2.8" with most
seeing 1" to 1.5" of snow. The highest amounts will be in the cooler
areas between Madison, IN and Lexington, KY. These totals are what
is expected to fall from the sky and doesn`t take into account
melting which is again expect to be substantial. The Winter Weather
Advisory will remain in place to cover conditions tonight.

During the day on Friday, the shortwave bringing the heavier
snowfall will be well out of the area. Skies are expected to remain
mostly cloudy, and with cold air advection remaining in place, kept
high temperatures on the cooler side of guidance in the low to mid
40s. Remaining deep layer moisture streaming south over Indiana is
expected to cause rain over southeast Indiana and the Bluegrass
region during the afternoon.

&&

.LONG TERM /FRIDAY THROUGH THURSDAY/...
Issued at 346 PM EST Thu Nov 21 2024

The upper low bringing the cold and blustery conditions over the
next few days will begin to lift into the Canadian Maritimes over
the first half of the weekend. As is common in a pattern with an
exiting upper low, low-level moisture is expected to remain trapped
below a mid-level subsidence inversion, keeping grey skies and cool
temperatures in the region Friday night into Saturday morning. With
surface pressure ridging moving into the area by Saturday evening,
cold advection should ease on Saturday, with temperatures warming
into the upper 40s and low-to-mid 50s Saturday afternoon, and
temperatures may warm more if clouds are faster to clear. For the
second half of the weekend, the overall pattern will become more
zonal, with subtle upper ridging moving over the area on Sunday. As
the sfc/low-level high moves into the southeast U.S., return flow
should set up over the Ohio Valley, continuing the upward trend in
temperatures into Sunday.

The next chance for precipitation across the region is expected on
Monday as a low-amplitude upper wave moves across the Great Lakes.
Sfc low pressure will develop over the upper Midwest Sunday night,
with a cold front extending south into the mid-Mississippi Valley.
While the ECMWF and GEFS ensemble mean depict an 850 mb jet strength
exceeding the 90th percentile Monday morning, this jet will be
fairly zonally oriented, and will thus be unable to fully tap into
Gulf moisture. As a result, moisture should be limited and total
precipitation amounts should be modest. Current 25th-75th percentile
QPF range is between 0.10 and 0.30" for the Monday-Monday night
system. Ahead of the cold front on Monday, temperatures will remain
above normal, with highs expected in the low-to-mid 60s.

High pressure moving across the area on Tuesday should bring a
reprieve in rain chances, though this should be fairly brief as the
overall pattern remains progressive. As we approach Thanksgiving,
run-to-run model consistency and forecast confidence decreases,
though there is a fairly consistent signal for a return to active
weather across the region. A large-scale wave ejecting out of the
western CONUS with baroclinity/zonal flow downstream will create a
setup where multiple disturbances ride along a boundary, bringing
multiple chances for precipitation during the mid-late week period.
At this time, the precipitation is expected to be predominantly
liquid, though a cooling trend is likely as we head through the last
week of November.

&&

.AVIATION /00Z TAFS THROUGH 06Z SUNDAY/...
Issued at 659 PM EST Thu Nov 21 2024

Light to briefly moderate snow is ongoing across the region as a
strong mid level disturbance rotates through. Seeing a mix of MVFR
and IFR conditions where the snow is the heaviest. These conditions
will be most likely at SDF, LEX, RGA, although HNB will likely get
in on low MVFR ceilings as well into the overnight. Most of the
gusts have subsided with low level lapse rates becoming less steep
with the loss of heating, however few gusts up around 20-25 mph may
still be possible overnight. Expecting snow to end around midnight
at SDF, and in the early morning hours at LEX/RGA.

Surface winds will quickly veer around from a W component this
evening to a NW component later tonight as the surface low quickly
moves through. Then, a steady WNW to NW continues through tomorrow
with continued mostly MVFR ceilings. The best chance for a brief
break in lower ceilings will be from around sunrise through mid to
late morning.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...Winter Weather Advisory until 7 AM EST Friday for KYZ031>037-
     039>043-047>049-055>057-066-067.
IN...Winter Weather Advisory until 7 AM EST Friday for INZ079.

&&

$$

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