LMK issues Area Forecast Discussion (AFD) at Dec 28, 3:28 AM EST090
FXUS63 KLMK 280828
AFDLMK
Area Forecast Discussion
National Weather Service Louisville KY
328 AM EST Sat Dec 28 2024
.KEY MESSAGES...
* Mild highs today in the low-mid 60s. A few lingering showers or
drizzle. Main chances for rain will hold off until early evening.
* 1-1.75" of rain possible tonight into Sunday for most. Localized
amounts of 2" possible. Embedded thunder will be possible tonight
but severe storms are not expected.
* Another period of rain is forecast for Monday night into Tuesday.
By this time area rivers may be running high, though confidence is
low on whether or not there will be any flooding. Interests along
streams will want to monitor the waves of rain as they pass
through the district this weekend and early next week.
* A turn towards colder weather is outlooked for early and
especially mid-January.
&&
.SHORT TERM /THROUGH TONIGHT/...
Issued at 328 AM EST Sat Dec 28 2024
Things are relatively quiet at this hour as we sit in the wake of
the lead shortwave, and await the arrival of a second and more
intense system later this evening. We do have some lingering 1000-
850mb moisture, and are seeing some light returns on radar. So, will
keep mention of patchy drizzle and/or light rain chances through the
morning hours. Temperatures should stay mostly flat through the
remainder of the early morning hours thanks to heavy cloud cover and
steady S winds. As a result, expect a mild start to the day with
temps in the low and mid 50s around sunrise. We aren't too far from
challenging the record warm mins, but it looks like we're already a
bit too cool.
As we move through the daylight hours, heavy cloud cover and a few
light precip (drizzle or light rain) chances will linger. Most folks
will stay dry with mild highs in the low and mid 60s.
An intense shortwave will eject out of the lower Mississippi River
Valley tonight, reaching the Ohio/Wabash River Valley confluence by
sunrise Sunday. An associated surface low will follow a similar
trajectory as it strengthens beneath a favorable right entrance
region of the upper level jet. Given the strong upper divergence,
we'll see a good low level jet response as it ramps up above 50
knots. Poleward moisture transport associated with this jet will
result in PWATs climbing to near the climatological max for this
time of year. The end result will be a widespread rain shield
overspreading our CWA from south to north on the nose of the low
level jet this evening into the overnight. As a result, will
continue with 100% chances for rainfall tonight, along with some
embedded thunderstorms thanks to some meager MUCAPE and the strong
mid level forcing. The good news is that forecast soundings continue
to show a low level stable layer, which should help to mitigate the
severe potential. It appears that we have been helped by yesterday's
lead wave, at least from an instability be suppressed to the south
standpoint. Latest HREF data continues to show virtually no
probabilities for ML CAPE into our area as it is kept well to our
south, despite a very favorable surface low track for severe weather
for this time of year. Good thing, because the low level hodograph
would be quite concerning with even a little bit of surface or near
surface based instability. We'll still have to monitor through the
overnight as some of the stronger wind energy just off the surface
could still cause some issues if it is able to be brought down by
any stronger convection. Can't completely rule out an isolated
instance of damaging winds.
Another threat with the overnight system will be rainfall amounts.
Overall, expecting a pretty widespread 1 to 1.5" range for most
folks. However, do think there is some potential for isolated
amounts over 2". Latest HREF 6 hour PMM data seems to agree with the
idea that some higher totals could be embedded within the widespread
1 to 1.5" range. Right now, it looks like the heaviest rain could
fall down near the Lake Cumberland region. Overall, HREF rates don't
look to exceed the 1,3, and 6 hour FFG values, but some localized
spots could. As a result, can't rule out the need for some flood
advisories or an isolated Flash Flood Warning. Didn't quite have
enough confidence in more widespread flooding to go with a Flood
Watch, but won't completely take that off the table either.
A third threat could materialize through the overnight in the form
of gradient winds over 40 MPH, however think the likelihood of this
would be more into the day on Sunday with the arrival of the dry
slot (see long term discussion below). The aforementioned stable
layer should keep most of the wind energy aloft through the
overnight outside of stronger convection. It is worth noting that
HREF probabilities of winds over 40 MPH do reach into the 40-60%
range along and south of the parkways. However, there is no support
from the LREF or NBM in that category. Will tend to side with the
latter two suites of data given how hard it is to realize Wind
Advisory criteria overnight in many cases.
&&
.LONG TERM /SUNDAY THROUGH FRIDAY/...
Issued at 328 AM EST Sat Dec 28 2024
===== Sunday =====
Very mild temperatures are expected for Sunday morning due to strong
WAA and moisture transport as we will be underneath a 60kt LLJ.
Temperatures will likely be in the 50s to start the forecast period,
and should peak in the low 60s during the late morning. A deepening
sfc low will be located in the Wabash River Valley, with widespread
rain and embedded thunder pushing off to our east as a dry slot
works into the area. This will coincide with the eastward-shifting
LLJ and moisture transport axis as this sfc low continues to deepen
while it moves northeast. HREF cloud cover probs keep low level
clouds over the dry slot, which will help limit mixing to an extent.
However, the tight sfc pressure gradient will promote gusty sfc
winds during Sunday morning, with east of I-65 more favorable for
wind gusts over 30 mph due to the LLJ shifting east. HREF
probability of sfc winds exceeding 35 mph is roughly 50% or greater
east of I-65. Additionally, there is a 20-30% prob of exceeding 40
mph wind gusts east of I-65, with a 40% probability along and east
of the I-75 corridor. It appears we may need at least a SPS for wind
gusts on Sunday, but could see the need for a Wind Advisory
somewhere in the east if confidence grows. A decision on this will
come in future forecast packages.
Wrap-around precip will bring another round of rain to the region
for the afternoon, which should be lighter than the early morning
round due to weaker moisture transport and CAA taking over. Temps
are still expected to be above freezing, so all precip will remain
liquid for Sunday. The upper shortwave axis will swing through by
the evening hours, leading to drier air filtering in with NW flow and
PoPs tapering off from west to east. For Sunday night, temps will
cool to the low 40s, which will still be above normal for late
December.
===== Monday - Tuesday =====
Dry weather is in store for the first half of Monday as the upper
flow briefly takes on a zonal component. Upper level clouds will
linger for most through the day, though some clearing will be
possible in our southeastern forecast area where slightly better
subsidence will be. Southwesterly flow will promote another day of
WAA for us, with temps reaching the 50s again. The dry weather will
be short-lived though, as another deepening shortwave ejects across
the Plains and brings another sfc low into the mid-Mississippi River
and Wabash River Valleys by Monday night and into Tuesday morning.
Forcing will begin to increase Monday night as the shortwave tracks
across the Midwest, and will continue to strengthen as we become
located underneath the left exit region of the upper jet structure.
A LLJ will swing around the 850mb low, which will bring a tongue of
moisture transport into the lower Ohio Valley, though PWs peaking
around 0.70" is not the most impressive. PWs will be near the 75th
percentile of BNA sounding climatology. The best precip chances and
moisture content appears to be on the nose of the LLJ and across
Indiana, though light precip will also be possible this far south
for Monday night and into Tuesday. During this time, the sfc
pressure gradient will be fairly tight too as the sfc low rides up
the Ohio River, so some breezy conditions will be possible. There is
uncertainty on the magnitude of wind gusts given late night
stability and the LLJ weakening, but it's something to keep an eye
on.
Light rain will linger into the evening hours on Tuesday, with a
gradual clearing from west to east as the upper wave continues an
eastward progression. Some light rain will be possible in our east
for the end of 2024.
===== Wednesday - Friday =====
PoPs will be exiting our eastern corner during the early morning
hours of Wednesday, and region-wide dry weather will be around at
the first sign of daylight in 2025. However, clouds will be hanging
on as an upper jet streak sits overhead. Temps will take on a colder
trend for the first of the new year, with daily highs in the 40s or
cooler for late next week.
&&
.AVIATION /06Z TAFS THROUGH 12Z SUNDAY/...
Issued at 1253 AM EST Sat Dec 28 2024
Pretty complex forecast for the next 24-30 hours as lingering low
level moisture will initially create some patchy drizzle and low
ceiling issues. Later in the TAF period, a surface low will track
into our region, bringing widespread rainfall, a few thunderstorms,
and a LLWS threat.
Early this morning, expecting widespread ceilings in the low MVFR
range with perhaps a few patches of drizzle at times. Not real
confident in any one timeframe for drizzle, so mostly left it out of
the forecast. Will amend as necessary for any more prominent drizzle
that shows up on obs. Surface winds will be steady around 10 mph and
mostly out of the south this morning, however expect them to back to
a more SE and the ESE direction late afternoon and early evening as
the surface low approaches. During this time, also expect some brief
improvement to ceilings into the high MVFR or even VFR range.
However, ceilings/vis will quickly diminish again through the
evening as widespread rain and a few thunderstorms move into the
area.
Have also mentioned a LLWS threat at SDF late in the planning period
as a 40-45 knot low level jet overspreads light SE surface winds.
Low level inversion is also expected to be in place at this time.
Left thunder mention out of all but BWG for this TAF cycle, however
may still have to add this potential at some point in future
forecasts.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
KY...None.
IN...None.
&&
$$
SHORT TERM...BJS
LONG TERM...CJP
AVIATION...BJS
Source:
LMK issues Area Forecast Discussion (AFD) at Dec 28, 3:28 AM EST---------------
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