LMK issues Area Forecast Discussion (AFD) at Dec 16, 9:51 AM EST
428
FXUS63 KLMK 161451
AFDLMK
Area Forecast Discussion
National Weather Service Louisville KY
951 AM EST Mon Dec 16 2024
.KEY MESSAGES...
* Multiple waves of rain are expected Today and Tuesday
Night/Wednesday with isolated thunder chances. Possible ponding
and nuisance flooding.
* Cold temperatures return Thursday and continue into the weekend.
Flurries possible on Friday.
&&
.UPDATE...
Issued at 950 AM EST Mon Dec 16 2024
Current surface and upper-level mesoanalysis reveal low-level jet
oriented SW to NE across the Mid Mississippi Valley this morning
with a cold front draped right behind it. Ongoing precipitation
activity is driven by isentropic lifting associated with the LLJ
with coverage expanding towards late morning and early afternoon as
the jet tracks across the forecast area. Highest QPF focuses along
the Ohio River with ponding or minor flooding issues, at best. Aside
from moderate to locally heavy showers, enhanced forcing and decent
mid-level lapse rates will support elevated thunderstorms the rest
of the morning into the early afternoon. Although there are
differences between HREF members, CAM models continue hinting at a
possibility of a broken line of convection immediately ahead of
front later this afternoon and evening. Biggest question is
instability distribution at that time given cloudy skies and lapse
rates, but enhanced gusty winds and lightning could occur as
convection appears to be more surface based.
&&
.SHORT TERM /THROUGH TONIGHT/...
Issued at 342 AM EST Mon Dec 16 2024
Currently, a large stacked low pressure system is sliding east
across the North Dakota/Minnesota/Canada border while its trailing
cold front is entering the Ozarks. Ahead of the front, a southwest
to northeast oriented 35-50 knot low level jet is approaching the
CWA. The stronger jet winds are over southwest Missouri near the
front. Values taper off to the east where the jet is working into
our area. This is pushing northwest to southeast waves of rain
showers to the east into and across the CWA. Model soundings show a
slight increase in the amount of elevated CAPE, above the inversion,
with MUCAPE values of around 500 J/kg making it into our area.
Farther west there are values over 1,000 J/kg. This is producing
ongoing lightning in the strongest cells. This could still cause a
few rumbles of thunder in our area, but nothing severe is expected.
The best chances of lightning in the coming several hours will be
along the Ohio River as the precipitation gets pushed to the
northeast.
As we look at the day, there are the couple of isentropically driven
waves of showers that are pushing through the CWA currently. They
will continue working across the CWA during most of the morning.
Behind this, the northeast to southwest oriented precipitation ahead
of the cold front will begin working into our western southern
Indiana counties later this morning. The line should get to
Louisville around midday before taking the rest of the day to reach
the Lake Cumberland area. This line will likely get ahead of the
front enough that a second narrower line of showers just ahead of
the front will push through the region this evening through the
first half of the night before exiting the CWA.
The first waves of rain are expected to combine with the main line
of precipitation near the Ohio River, this will likely keep rain
showers over southern Indiana for most of the day without much of a
break, but farther south in southern Kentucky, a dry period will be
more likely during the middle of the day.
It's going to be windy. Winds are currently out of the south but are
expected to veer towards the southwest this afternoon ahead of the
front. Winds will likely reach 15-18 mph with gusts expected to
reach around 30 mph. This will lift temperatures into the 60s across
the CWA.
As the cold front moves through tonight, winds will quickly veer
towards the northwest. Even though winds ease to 5-10 mph, cold air
advection will drop temperatures into the mid 30s to low 40s.
&&
.LONG TERM /TUESDAY THROUGH SUNDAY/...
Issued at 342 AM EST Mon Dec 16 2024
Tuesday through Thursday Night...
At the start of this period, fairly zonal flow is expected across
the CONUS. Dry conditions are expected across the region on Tuesday
with afternoon highs warming into the low-mid 50s over southern
Indiana and the northern half of Kentucky. Highs across southern
Kentucky will be in the upper 50s.
By Tuesday night, a shortwave trough axis will move out of the inter-
mountain west and amplify over the central Plains. As this occurs,
a surface frontal boundary draped across the deep south will lift
northward as a warm front. Scattered rain showers are expected to
develop within an increasing warm advection scheme with fairly
decent isentropic lift. With the warm front lifting northward,
we'll see a gradient of low temperatures for Tuesday night. Readings
will range from the upper 30s/lower 40s over southern Indiana and
the northern half of Kentucky. Low-mid 40s will be found over
southern Kentucky.
Moving into Wednesday, the amplifying upper level wave is expected
to induce cyclogenesis over northwest Tennessee by Wednesday
morning. This surface wave will move northeastward during the day
and reach West Virgina by the afternoon. Widespread rain will
accompany this system with rainfall amounts of around 1 inch in many
places. Some isolated rumbles of thunder will be possible across
far southern KY as model proximity soundings show some steeper lapse
rates aloft supporting some elevated instability. The rainfall from
Wednesday will be falling on ground that has already received some 1-
2 inches of rain from earlier in the week. So, some isolated hydro
issues may occur in some spots. Highs on the day will be in the
lower 50s across southern Indiana and northern Kentucky. The
warmest spots will be along and south of a line from roughly Bowling
Green to Richmond where highs will reach the upper 50s/lower 60s.
Precipitation will quickly move off to the east during the afternoon
with cold advection bringing in a much colder airmass during the
evening and overnight hours of Wednesday. Lows Wednesday night will
drop into the upper 20s to the lower 30s in many areas. Thursday
continues to still look dry across the region with highs in the
lower-mid 40s. Thursday night lows will drop back into the upper
20s/lower 30s.
Friday through Sunday...
Moving into the medium range period, the upper level pattern looks to
feature a large ridge over the western US with a downstream trough
axis across the east. Modeling over the last several days indicates
that a clipper system will push through the southern Great Lakes and
northern Ohio Valley on Friday. Model soundings continue to be
fairly dry here, but we'll probably be able to squeeze out some snow
flurries during the day. As expected, the blended guidance
continues to trend downward but is likely still too warm here. HIghs
on the day will likely only reach the low-mid 30s across southern
Indiana and portions of northern Kentucky, but southern Kentucky
will probably warm into the mid-upper 30s. Clearing skies and a
continued northwest flow aloft will result in a cold night for
Friday night as temps drop into the lower-middle 20s.
For the weekend, deep upper trough axis will remain in place across
the eastern US but that trough axis will shift eastward on Sunday.
We'll remain in a strong north/northwest flow with below normal
temperatures. Again, NBM blend here is a bit too warm and we'll go
closer to the raw temps. Highs on Saturday will be in the upper
20s/lower 30s with overnight lows in the upper teens to lower 20s.
Highs Sunday will be similar with readings in the 30s.
Extended Forecast Discussion...
Moving into the Christmas holiday period, early December signal
analysis has performed quite well through the month of December.
We've been tracking an increasingly stronger signal passage that
looks to occur around the 24th. In recent days, the deterministic
models have started to pick up on this. The Canadian was first to
do so, but the GFS and Euro have come on board as well. An upper
level shortwave trough axis is forecast to move through the Great
Lakes with a boundary pushing through the region on Christmas Eve.
As this system pushes through, we'll be on the verge of a return
flow pattern. Precipitation Christmas Eve morning may start out as
a wintry mix of rain/snow with temps in the lower 30s. Temps look
to warm during the day which will change this over to a cold rain
with highs in the mid 30s. Drier and milder weather looks
increasingly likely for Christmas day with highs in the low-mid 40s.
Looking ahead after Christmas, an overall milder period of weather
is expected. Signal analysis suggests another strong signal passage
occurring around 12/27-12/28 followed by another signal around 12/29-
12/30. Both of these signals will need to be monitored as we'll be
in a warmer pattern. In fact, some of the longer range Euro and GFS
runs suggest that these signals may result in a severe weather
threat over portions of the deep South including the Ohio Valley.
&&
.AVIATION /12Z TAFS THROUGH 18Z TUESDAY/...
Issued at 710 AM EST Mon Dec 16 2024
As a cold front approaches the region, rain showers have moved
across southern Indiana and central Kentucky. HNB will see a few
flashes of lightning, but this isn't expected to remain in the area
too long. BWG is now seeing a a break in the showers before the main
line of rain reaches them this afternoon. Generally ceilings are at
IFR levels, and that's where they will remain until the front passes
tonight. Heavy rainfall should be expected to reduce visibilities
throughout the day. Still believe the heaviest/longest duration of
heavy rainfall will be closer to the Ohio River which would affect
HNB and SDF maybe a little more than BWG, LEX, and RGA. South winds
around 10-15 knots are expected to gust to near 25-30 knots as they
veer towards the southwest this afternoon.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
KY...None.
IN...None.
&&
$$
UPDATE...ALL
SHORT TERM...KDW
LONG TERM...MJ
AVIATION...KDW
Source: LMK issues Area Forecast Discussion (AFD) at Dec 16, 9:51 AM EST (https://mesonet.agron.iastate.edu/p.php?pid=202412161451-KLMK-FXUS63-AFDLMK)
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