NWS Forecast Discussion - Louisville, KY
387
FXUS63 KLMK 210605
AFDLMK
Area Forecast Discussion
National Weather Service Louisville KY
105 AM EST Thu Nov 21 2024
...Updated Aviation Discussion...
.KEY MESSAGES...
* There is high confidence for breezy conditions today through
Friday, with the strongest gusts on Thursday.
* Much colder weather on Thursday with wind chills in the 20s and
30s.
* Snow showers will be possible early Thursday morning through
Friday morning. The best chance for any local minor impact will
be from southeast Indiana to the Kentucky Bluegrass region.
&&
.UPDATE...
Issued at 944 PM EST Wed Nov 20 2024
Things are quiet across the CWA at this hour, although we`ll see a
change coming tomorrow. The anomalous closed low has a couple of
embedded shortwaves that will rotate into our area tomorrow. The
first wave is set to arrive around sunrise tomorrow across our NE
CWA, and will quickly scoot through by early afternoon with some
scattered light snow showers. Not expecting any real accums with
this first wave across our NE, although may get a dusting on some
roofs and/or grassy/elevated surfaces.
There should be a relative lull in activity from early afternoon
through late afternoon, although there are some signals that
steepened low level lapse rates and some lingering low level
moisture will be enough to squeeze out some more scattered snow
showers, especially across the bluegrass. These aren`t expected to
cause any real accumulations either, but they will be blustery with
perhaps some very brief moderate rates. So, just be mindful if
traveling across the Bluegrass this tomorrow.
The final wave set for late afternoon/early evening into the
overnight will be the most robust as the trop fold dips down around
500mb. This intense shortwave will have plenty of deep moisture with
forecast sounding showing saturation up through the DGZ. Surface air
temps and ground temps will still be a limiting factor to some
degree, however a good 6 to 7 hours of light to moderate snow will
likely result in some light accums across a good chunk of the area.
Like the current messaging of the highest probabilities of 1" of
snow across SE Indiana and through the Bluegrass region of east
central KY. Right now, think there will be fairly widespread amounts
of .5" to 1" on grassy surfaces, with some localized amounts over
1". This really is all dependent on rates and the ability to
accumulate with subpar ground temps. Given the first snow of the
season, and perhaps some minor impacts to roadways, at least some
consideration to a potential Winter Weather Advisory will need to be
given over the next 24 hours. Bottom line: Confidence is high in
snowfall for tomorrow, however confidence is much lower in just what
types of impacts we`ll see from it.
&&
.SHORT TERM /THROUGH FRIDAY/...
Issued at 347 PM EST Wed Nov 20 2024
An upper low spinning over the Upper Midwest is forecast to move
southeast over the Great Lakes and Upper Ohio Valley tonight and
Thursday. A lead mid-level vort max currently over IN/KY will
continue to swing off to the east this afternoon and evening. At the
surface, a cold front is draped south along the Appalachians. Clouds
continue to scatter out from west to east across KY as cooler, drier
air advects in from the west. With relatively steep low-level lapse
rates in place, winds will remain gusty into early evening with
gusts of 20-25 mph.
Skies will remain relatively clear this evening and into the early
part of tonight. Expect chilly, breezy conditions with temperatures
dropping quickly through the 40s. Temps will continue to fall
through the mid/upper 30s early Thursday morning. Clouds will
overspread the region from north to south during the early to mid-
morning hours on Thursday. A potent mid-level vort max wrapping
around the parent low is forecast to move right over southern IN and
central KY Thursday morning. This wave will briefly enhance moisture
depth and mid-level lift, especially from southern IN southeast
across north-central KY and the Bluegrass. Overall, moisture remains
fairly shallow, confined to roughly the 850-650 mb layer. This will
keep QPF pretty light, around 0.05 inches or less during the morning
hours. Due to ongoing CAA and much colder air aloft, fcst soundings
show a subfreezing cloud layer and saturated DGZ. Light snow is
likely to be the primary p-type due to extremely low WBZ heights.
However, impactful accumulation looks unlikely at this time due to
the light QPF and marginal near-sfc temps. Sfc temps slightly above
freezing will limit the accumulation potential. A deck/roof duster
looks possible from the Madison, IN area southeast to the northern
Bluegrass (Georgetown, Cynthiana, Carlisle, etc). But again, precip
in the morning will remain light and scattered in nature, so most
will not see any accumulation at all.
Winds will remain breezy throughout Thursday due a sustained healthy
MSLP gradient. Favorable low-level mixing due to CAA will produce
wind gusts of 25-35 mph. Any light snow or flurries in the morning
may get blown around some by this wind, reducing visibility. This
may cause some spotty visibility issues on roadways. Wind chills
will also be in the 20s, so consider an extra layer or two Thursday
morning.
We`ll see a lull in precip activity during the afternoon hours, with
light snow in the Bluegrass winding down by midday or early
afternoon. The final shortwave disturbance takes aim at our region
Thursday evening, and snow shower chances increase from north to
south over southern IN and north-central KY during the 4-7 PM EST
window. Sfc temps should be very marginal in the mid/upper 30s at
onset. A brief mix will be possible at onset. Some minor
accumulations will be possible through 7 PM EST, mainly north of a
line from Brandenburg to Richmond. A dusting to around a half inch
looks possible, mainly on grass and elevated surfaces. Cannot rule
out a localized 1" report in southern IN, from French Lick/Paoli to
Madison.
&&
.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Issued at 347 PM EST Wed Nov 20 2024
Beginning Thursday night, an upper low will be near southwest
Pennsylvania with two surface lows circling around, one near Chicago
and the other near New York City. Throughout the night, the surface
low near Chicago is expected to dissipate as it get pushed southeast
towards Lexington while the surface low that was near New York City
becomes synced/stacked with the upper low over eastern Pennsylvania
Friday morning.
The surface low dropping into southern Indiana and central Kentucky
from Chicago is part of a larger shortwave rotating around the
aforementioned upper low. It`s these features that will likely lead
to enhanced forcing Thursday night, and with a surface low and upper
low in place, northwest flow and cold air advection is expected at
all levels. This can be seen in model soundings with no hint of a
warm nose. The warmest temperatures will be at the surface, so with
saturation of the DGZ, all precipitation is expected to fall as
snow. Surface temperatures at this time are expected to remain above
freezing for most of the night, but parts of southern Indiana and
central Kentucky east of Louisville, could see lows before freezing
before temperatures begin warming again on Friday. With warm
temperatures and borderline air temperatures, impacts are expected
to be limited. 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 have a better
chance of limited accumulations.
During the day on Friday, the shortwave bringing the heavier
snowfall will be well out of the area as the upper low continues
moving farther east towards New Jersey. This will bring an end to
the precipitation. The best chances of snow will be northeast of a
line from Dubois County to Clinton County with the highest totals
near Madison, Indiana and across the Bluegrass of Kentucky where
current values range from 0.5" to just over 2". This is what`s
expected to fall from the sky, not what will actually accumulate
given the warm temperatures.
&&
.AVIATION /06Z TAFS THROUGH 12Z FRIDAY/...
Issued at 105 AM EST Thu Nov 21 2024
Changes in the form of deteriorating weather conditions and flight
categories are still on schedule through this TAF cycle. VFR and
mainly clear skies remain but mid-level clouds are already working
in from the north as SDF CIGs are already around 7000ft. These
clouds are streaming in from the north and are associated with a
much larger and stronger weather system to our north. Main upper low
over Lake Michigan will continue to slowly work to the southeast
through the rest of the overnight and through the day today. A
deepening sfc low currently over far northern MI will rotate around
the upper low and start to work southward from Lake Michigan into
central IN. This will send two waves of precipitation in the form of
rain/snow to eventually all snow with the second and stronger wave.
The first wave will bring generally light precipitation. Mainly
light snow with some rain mixed in for even LEX. CIGS will lower to
high MVFR. With some of the precipitation, VIS could also drop to
around 5 miles. CIGS will remain MVFR until the second wave arrives
around 21-23z, this will bring a more vigorous burst of potential
snow and lower VIS and CIGS. Expecting IFR flight categories during
this time for several hours into the end of the forecast period. The
one exception to all this appears to be BWG where flight categories
remain VFR.
If the CIGs and precipitation wasn`t enough of an issue, winds are
also going to increase with gusts of 25 to potentially 30kts during
the day mainly out of the west. This is a result of the sfc low over
Michigan dropping south tightening the pressure gradient. Winds will
remain gusty and generally out of the west through the forecast
period.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
KY...None.
IN...None.
&&
$$
UPDATE...BJS
SHORT TERM...EBW
LONG TERM...KDW
AVIATION...BTN
NWS LMK Office Area Forecast Discussion
