LMK issues Area Forecast Discussion (AFD) at Jan 2, 6:20 AM EST ...Updated Aviation Discussion...751
FXUS63 KLMK 021120
AFDLMK
Area Forecast Discussion
National Weather Service Louisville KY
620 AM EST Thu Jan 2 2025
...Updated Aviation Discussion...
.KEY MESSAGES...
* A quick-moving clipper will bring a chance for light snow late
tonight night into early Friday morning. Minor travel impacts at
rush hour Friday morning are possible from southern Indiana to the
Kentucky Blue Grass.
* A Significant winter storm, will move across the Ohio Valley
Sunday and into Monday (with high confidence). Forecast confidence
on precipitation types and amounts remains low.
* Much colder air will move into the region behind this system for
the remainder of the week. Very high confidence on this scenario.
&&
.SHORT TERM /THROUGH FRIDAY/...
Issued at 242 AM EST Thu Jan 2 2025
Sfc high pressure will slowly work eastward across the TN Valley
during the day today. Aloft, we will be under a quasi-zonal flow out
of the west-northwest. As the sfc high passing by to the south, sfc
winds will be generally out of the southwest with cloud coverage
ranging from partly to mostly sunny skies through most of the day.
This will help to warm temperatures to near seasonal normals in the
low/mid 40s for afternoon highs.
Clipper system coming out of the Dakotas/Upper Midwest today will
push into the Ohio Valley tonight and spread a brief period of light
snow across mainly southern IN and north central KY into the Blue
Grass early tomorrow morning between 08z-14z. Model soundings show
fair amount of dry air as we go into the evening but as the system
approaches, the column will saturate into the DGZ but be fairly
shallow below 700mb. This will be enough to produce a brief period
of light snow or flurries in the pre dawn hours. Given that these
snow showers could be occurring just before or during the morning
commute, especially around the Lexington Metro tomorrow morning
there, is a low end impact potential. Snow amounts will be generally
around a coating on grassy and elevated surfaces as temperatures
will be above freezing for most of the overnight and during the main
snow event. This clipper works quickly through and should be out of
the area by mid morning. Colder air will advect in behind keeping
temperatures in the mid 30s for most of KY and low 30s for southern
IN. Skies will also clear behind the system with a brisk northwest
wind in the afternoon with gusts of 20-25 mph. Wind chill values
will make it feel like it is in the low/mid 20s.
&&
.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Issued at 242 AM EST Thu Jan 2 2025
Well...we have a significant winter storm Sunday-Monday and then it
turns cold (maybe even gelid)! The storm will bring a potpourri of
winter weather and a cold rain along the TN state line, a mixed bag
in the middle (with an gradient of fzra and icing), and opportunity
for heavy snow in S IN and Nrn Bluegrass. The Euro EFI and Shift of
Tails is pegging the Ohio Valley!
Fri Night - Sat Night...
This is the lull before the storm with ridging and dry benign
weather. This is the pick day of the weekend. The Massie Rose 1000-
850 mb thickness temperature technique yields highs Saturday will be
in the 30-35 F degree range. Clouds will be sparse Sat
evening...allowing the entire CWA to drop quickly blo freezing and
eventually bottom out into the upper teens and lower 20s. This is
critical to the onset of the precip for Sunday daybreak.
Sunday through Wednesday...
Overview...
Well...forecast confidence continues to increase for a significant
winter storm across the Ohio Valley on Sunday and Monday. First of
all the storm culprit is not even on the US mainland and will not be
until Friday in the WA Cascades down to Crater Lake NP OR. There is
lots of RAOB sampling to occur to help with this challenging
forecast.
2nd...there is still ALOT of uncertainty w.r.t. eventual evolution
and track of this system. This will largely affect precipitation
types and amounts for the area!! There are so many factors to this
forecast such as the very dry airmass initially in place Sunday. It
will be challenging for locations north of the surface low path to
climb above freezing. At Noon Sunday the freezing line will be near
the BG/Wrn KY Parkway but dewpoints remain in the low to middle 20s
with widespread light to mdt pcpn.
With a persistent East to Northeasterly wind, there will be a
several hour window of wet-bulbing, which may keep CWA blo freezing
for quite a spell.
There is global model consensus on the storm with some minor timing
issues. Overall the ECM is colder and less aggressive with ice than
the GFS. The GFS warm nose is stronger Sunday afternoon and evening
and would set up a much more dire ice potential somewhere near the
parkways. If we were to have a slightly cooler model solution could
produce more sleet and alleviate the heavy icing threat. Still lots
of details to ascertain 4 days out.
Timing/Details...
Precip looks to break out within a warm advective scheme Sunday
morning as the surface low moves into Mo Ozarks. The pre-existing
cold air mass is not overly deep, but will be deep enough to support
snow and some sleet at precipitation onset.
Increasing swly flow ahead of the system will transport copious
moisture northward. PWATS of 1 to 1.20 along the TN state line to
0.75-0.85 in Srn IN. The surge of warmer air that will move into the
region aloft first, and then eventually down to the surface. This
would result in a precipitation change from snow over to a mix of
snow/sleet/freezing rain and plain cold rain (along the TN border).
At this time range, forecast confidence on how far north the warmer
air will get or what the overall thermal profile will look like
across much of Kentucky remains rather low.
At this time, looks like 3 primary areas of precip...
Area 1 Srn IN... Starts off with snow around daybreak, with mix of
sleet/fzra Sun PM and then back to all snow through 15z Mon. The
further north you go the cold air is likely to be of sufficient
depth to keep the precip mostly snow. Some of the probabilistic data
shows >50% of several inches of snow across out most nrn CWA.
Area 2 North Cumberland Parkway to Ohio River...Starts off with
light snow and some sleet and then changes abruptly to mix of
freezing rain, sleet, and some snow. The GFS is simply nasty for
fzra. Looks to be 21z-06z to be worst of it, and then turns back to
snow by 12z Mon.
There is an increasing probability of a corridor of significant
icing that may occur somewhere in KY with classic deep warm layer
above shallow sub freezing layer. With 45 kt 850 mb swly jet, along
with an intensifying surface thermal gradient may lead to a stronger
area of frontogenesis across the region where banded heavy
precipitation may occur. The 1000-850 mb frontogenesis parameter is
pegging around the BG/Wrn KY Parkway for an area most concerning for
significant accretion.
Area 3 Bottom 2 tiers of KY Counties...Starts of with freezing rain
Sunday morning and then turns over to a cold rain and
eventually turns over the snow before ending by 15-18z Mon.
High Confidence for significant amounts of wintry precipitation
Sunday and Monday time frame. Negative impacts to travel and
infrastructure will be possible. It remains too early to even
remotely speculate on snow and ice amounts. We are focused on
science and service and not hype or speculation.
Coordinated with ILN/JKL/OHX/IND/PAH and all agreed to not issue a
winter storm watch this forecast for the 5th period which would
extend into the 7th period. Should future forecasts continue to
trend in their current directions, Winter Storm Watches will be
needed by Friday.
Mon Night - Wednesday
A very deep cold airmass pushes in and becomes entrenched over at
least half of the US. Looking at temp anomalies, there is a
distinct 2-3 SD blo normal throughout the troposphere! One caveat
to the vexing question... "How cold will it be next week...which is
its dependent on our ice and snow depth from the Sun-Mon storm.
For now going well blo NBM and deterministic guidance, which is
highs 18-23 F. and lows in the teens Mon nights, but single digits
Tue night. Cloud cover is the key to how cold we can get. If we
lose clouds, temps will be much colder, especially north of the
Parkways.
Weather Tidbit...
Jan 3 2002...An ice storm struck Atlanta, canceling thousands of
flights at ATL!
Jan 3 2000...A F3 ripped through Owensboro, KY heavily damaging
Kentucky Wesleyan College.
&&
.AVIATION /12Z TAFS THROUGH 18Z FRIDAY/...
Issued at 615 AM EST Thu Jan 2 2025
There remains a few mid clouds over LEX/RGA this morning, these
clouds are expected to clear later this morning as sfc high pressure
continues to build over the OH and TN Valleys during the day. VFR
will remain the flight rules today into this evening. Winds will be
out of the southwest around 5Kts. Weak clipper system will increase
clouds and bring a chance of snow to the area between 08-12z. These
snow showers will be quick and generally light. CIGs will also drop
to MVFR to potentially a brief period of IFR. Behind the system,
winds will increase out of the northwest and could get gusts of
20Kts. Flight categories will also improve to VFR through the day on
Friday.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
KY...None.
IN...None.
&&
$$
SHORT TERM...BTN
LONG TERM...JDG
AVIATION...BTN
Source:
LMK issues Area Forecast Discussion (AFD) at Jan 2, 6:20 AM EST ...Updated Aviation Discussion...---------------
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