LMK issues Area Forecast Discussion (AFD) at Jan 7, 9:55 PM EST889
FXUS63 KLMK 080255
AFDLMK
Area Forecast Discussion
National Weather Service Louisville KY
955 PM EST Tue Jan 7 2025
.KEY MESSAGES...
* High confidence in bitterly cold temperatures this week as an
Arctic airmass overspreads the region. Coldest temperatures are
expected Wednesday through Thursday night with sub-zero values
possible Thursday morning.
* Medium to high confidence in measurable snow Friday into Friday
night. The highest potential for heavier (>4") snow accumulations
lies across southern KY where minor impacts cannot be ruled out.
&&
.UPDATE...
Issued at 955 PM EST Tue Jan 7 2025
Tonight's temperatures had to be bumped warmer as the stratus layer
is blocking any radiative cooling, and with winds being light out of
the northwest to west-northwest, CAA is limited. Some will continue
to see a few flurries tonight, but besides the scattered flurries,
it will be a fairly quiet night.
&&
.SHORT TERM /THROUGH TONIGHT/...
Issued at 339 PM EST Tue Jan 7 2025
Cold and overall quiet weather will persist for the next 24 hrs as a
1040mb sfc high builds down the Plains, with E-W oriented ridging
into the Ohio Valley. Mid-level NW flow is cyclonically curved with
a couple of weak ripples swinging through, helping to maintain a
fairly extensive stratus shield. Not expecting much change, with
scattered flurries possible especially from southeast Indiana into
the Bluegrass region. Can't rule out a few snow showers with some
localized enhancement downwind from strong sources of particulate
emissions.
Overnight min temps expected to be generally in the teens as the
cloud cover will mostly keep readings from bottoming out. Bust
potential does exist in any areas that see a lot of clearing, as
temps there will easily drop into the single digits. However,
confidence is low that we will see sufficient clearing.
High pressure continues to build eastward on Wednesday, and the
chances for snow showers/flurries will end as low-level flow backs
almost to due west. Temp recovery will be limited by cloud cover,
with most locations struggling into the mid 20s.
&&
.LONG TERM /WEDNESDAY THROUGH TUESDAY/...
Issued at 339 PM EST Tue Jan 7 2025
Synopsis...Continuous shortwave progression over the CONUS under a
larger blocking pattern and amid cold temperatures will increase
chances of periodic snowfalls over the Ohio Valley during the next 7
days. At the beginning of the period, Arctic surface high pressure
will transition west to east across the region while northern-stream
shortwave and closed low phase over the Rockies. Then, resultant
amplified upper-level energy moves eastward favoring cyclogenesis
over the Gulf Coast and pushing a cold front across the Mid
Mississippi Valley. As stated in previous discussions, snow is still
expected during the Friday-Saturday period with accumulations
trending upward with this update. Another shortwave trough will
approach the Ohio Valley late this weekend and although the system
will be weaker and moisture starve, there is a low chance of some
flurries or light snow. Next week remains cold with potential for at
least light snow chances based on further shortwave intrusion Canada.
Model Confidence/Evaluation...Models maintain high probabilities of
near-zero temperatures Thursday morning along and north of the Ohio
River. The new challenge now is if apparent temperatures will be low
enough (at least -5 degF) to host a Cold Weather Advisory Wed night
into Thu morning. Although confidence in near or slightly below zero-
zero temperatures are high, probabilities of apparent temperatures
below -5 are about 50% or so. As a result, will hold on issuing
headlines with this update pending better agreement on lingering low-
level cloud cover ahead of the approaching surface high pressure.
Switching to snowfall totals by the end of the week, most of the
deterministic and ensemble guidance is trending towards higher
values. Notably, the GFS and CMC are promoting the highest totals
while the ECMWF and ICON are a bit lower, especially to the northern
half of the forecast area. On the other hand, NAM and UKMET propose
a solution of the lower end of the spectrum with low values confined
to southern Kentucky.
Wed Night - Thu Night...Well-advertised, bitterly cold temperatures
during the morning hours supported by cooling effect from snowpack,
light winds, and clearing trend ahead of the Arctic surface high. As
explained above, will not issue a Cold Weather Advisory for this
period with the current forecast, but there is ongoing collaboration
with neighboring offices to consider headlines tonight or tomorrow.
Stay tuned! Otherwise, temperatures will recover during the day on
Thursday given mostly clear skies and unblocked solar heating.
Expect a few inches of the snowpack to melt helping to raise
temperatures (although they will stay below the freezing point).
Thursday night lows will drop to the teens and low 20s but overall
expect a gradual warm up as winds shift to the southeast and clouds
turn overcast ahead of the storm system tracking across the
Southeast US.
Friday - Sunday...Biggest change for this period is the increase of
snowfall totals with the Friday-Saturday winter system. As mentioned
above, the totals have gone up by 1 to 1.5 inches with southern
Kentucky now around 4 inches and southern IN/north-central KY
between 1-2 inches. The reasoning behind augmenting the totals could
be found in the better dynamical lift and stronger moisture
advection from the Gulf in the latest model runs. Also, expect
further refinements of those totals as we head closer to Friday. GFS
soundings show slightly steepened lapse rates in the DGZ during the
day on Friday along with a below freezing vertical profile with
perhaps the heaviest rates Friday evening into the first overnight
hours. Saturday should be a quiet day with fairly stable
temperatures. A weaker shortwave trough moving north of the region
could induce some flurries or light snow on Sunday, but heavy snow
is not anticipated at the moment as moisture remains well south of
Kentucky.
&&
.AVIATION /00Z TAFS THROUGH 06Z FRIDAY/...
Issued at 649 PM EST Tue Jan 7 2025
The forecast period is expected to remain fairly quiet. Winds will
remain out of the northwest to west. Moisture around and below 850
mb will keep clouds mostly in MVFR levels. A few flurries could fall
out of this deck at times, but it should be limited.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
KY...None.
IN...None.
&&
$$
UPDATE...KDW
SHORT TERM...RAS
LONG TERM...ALL
AVIATION...KDW
Source:
LMK issues Area Forecast Discussion (AFD) at Jan 7, 9:55 PM EST---------------
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