NWS Area Weather Forecast Discussion
Louisville, KY

FXUS63 KLMK 150150

Area Forecast Discussion
National Weather Service Louisville KY
850 PM EST Sat Dec 14 2019

.Forecast Update...
Updated at 847 PM EST Sat Dec 14 2019

Current radar is showing some very light returns moving through
portions of south central Indiana and north central Kentucky.
Louisville Muhammad Ali International Airport carried light drizzle
for roughly 40 minutes, which had no impact to visibility. Have
updated the next couple of hours of PoPs and Wx grids to show this.
Also refreshed the near term grids to blend in the latest
observations. Otherwise, forecast remains on track. Updated products


.Short Term...(This evening through Sunday)
Issued at 254 PM EST Sat Dec 14 2019

Now - Early Sunday Afternoon...

Seeing dry conditions across the CWA at this hour as lingering
drizzle has pushed east of the CWA. Did want to mention the light
radar returns across our western CWA, where it appears precipitation
is not hitting the ground. Latest Kentucky Mesonet obs show no
measurable precipitation across western counties recently, so will
mostly continue a dry forecast into tonight. Suppose a few drops
could fall, but overall the chance of anything measurable seems too
low to mention at this time. Temperatures will hover in the low to
mid 40s for a few more hours under variable but mostly cloudy skies.

A dry cold front does pass through the region by late this evening,
with temperatures falling off into the upper 20s and low 30s in most
spots by dawn on Sunday. Surface high pressure briefly settles into
the area behind this front, so dry conditions continue for the good
part of Sunday with temps struggling to get out of the 30s across
southern IN and north central KY. Across far southern KY, the
boundary hangs up where temps could be in the mid to upper 40s.

Later Sunday Afternoon - Dawn Monday...

...Wintry Mix Across Southern Indiana, Light Snow Accumulations...

An interesting setup occurs later Sunday into Sunday night, that
will likely bring a wintry mix and some light snow accumulations to
portions of our southern Indiana counties. The right entrance region
of a 120-130 knot upper level jet will be noted over the Ohio River
Valley with good frontogenetical forcing tilting back toward the jet
core showing up on time height cross sections Sunday evening. The
cross sections along with forecast soundings do show favorable lift
and saturation up into at least portions of the DGZ, along with a
favorable low level thermal profile, at least across the northern
tier of our southern Indiana counties. The farther south you go,
there should be a pretty sharp cutoff as temps will be notably
warmer. The window for wintry precipitation across our far north
should close pretty rapidly in the pre-dawn hours of Monday as warm
advection wins out with the aid of a 40-50 knot low level jet nosing
into the area. So, any light accumulations will likely turn to slush
and melt pretty quick Monday morning.

Overall, think there could be a swath of 1 to 2 inches of snow
mainly along and north of a line from French Lick to Salem, IN over
to Bedford, KY with lesser amounts quickly going to zero down to the
I-64 corridor. Given the potential for some frontogenetical banding
briefly producing moderate to heavy snow rates (a little bit of
elevated negative EPV showing up on cross sections) suppose that a 3
inch amount can`t be ruled out north of Madison, IN. Overall, this
will be a wet/slushy snow as snow ratios will likely go from at or
just below 10:1 down to 5:1 in the pre-dawn hours. Given the evening
hours on a Sunday combined with temps at or just above freezing for
most of the event and temps rising well above freezing for the
Monday morning commute think that impacts will be pretty limited.
That being said, a Winter Weather Advisory seems like it could be on
the table along and north of the line mentioned above due to the
snow accums. After collaborating with neighbors, not quite ready to
go with one yet but will issue a Special Weather Statement as a
heads up for that area.

Did also want to mention that a glaze of ice from freezing rain
can`t be ruled out along and north of the same line mentioned above.
The warm nose working into the area could briefly create a marginal
temp profile capable of a glaze. Overall, not overly worried about
that threat as roads likely wouldn`t be impacted and the main threat
looks just north of our area.

Overall confidence is medium to high in the light snow accumulations
along and north of the French Lick to Salem to Bedford line.
Confidence is also pretty high in the early Sunday evening to early
Monday morning time frame for wintry potential.

A heavy rain threat starts to develop across the warmer southern
portions of the CWA early Monday morning. See the long term
discussion for more details on that threat going into Monday.

.Long Term...(Sunday night through Saturday)
Issued at 245 PM EST Sat Dec 14 2019

...Heavy Rainfall Expected Monday Across Kentucky...

Monday through Tuesday...

Still expecting a quasi-stationary front to guide a sfc low from WSW
to ENE across Kentucky on Monday, serving as the focus for a swath
of excessive rainfall. Compared to previous runs, the low track a
bit farther south, but forecast soundings continue to show too much
low-level warm air for anything but rain...and a lot of it.

With the sfc low tracking along a nearly stationary front, there
could be a narrow swath of 3-4 inch rainfall amounts. However, such
high QPF will be fairly localized and it remains a bit uncertain
where that will set up. Best chance appears to be in a corridor near
or more likely just south of the Western Kentucky and Bluegrass
Parkways, but will key our messaging on widespread 1-2 inch amounts
and more of a broad scope for localized 3+ inch rainfall totals. The
rainfall could be heavy enough at times to result in some minor
flooding in the typical low spots and poor drainage locations.
Window of opportunity for thunder and heavy rain will continue into
Monday evening, especially across the Lake Cumberland area. Based on
collaboration with neighboring offices, we will hold off on a Flash
Flood Watch at this time, but will highlight heavy rain potential in
most of our messaging this afternoon. Embedded thunder is a decent
bet in the warm sector, but not impressed with SVR potential at this
time as sfc-based instability remains lacking.

Later Monday night into Tuesday the low-level jetting will translate
off to our east, and precip chances and intensity will diminish from
west to east.  Temps will crash in strong cold advection, so there`s
a good chance for precipitation to end as snow, mainly across
southern Indiana. As usual, cold air will be chasing the moisture
out of the area, so little or no accumulation expected.

Precip shield will be departing by Tuesday morning, but much of the
day could remain cloudy and unsettled until the upper trof axis
pushes to our east. Slight chance POPs will continue into Tue
afternoon across the Bluegrass region with a possible Lake Michigan
plume, but temps are just warm enough and moisture just shallow
enough for mainly light rain showers.

Tuesday Night through Saturday...

Cold sfc high settles overhead by Wednesday, pushing temps a good 10
degrees below mid-December normals.  However, upper ridging wins out
for the remainder of the week, so expect dry weather and seasonable
temps Thu-Sat. A cutoff low developing over the Plains near the end
of the week appears to remain beyond the scope of this forecast.


.Aviation...(00Z TAF Issuance)
Issued at 653 PM EST Sat Dec 14 2019

A broad area of Fuel Alternate MVFR stratus will drift southeast
over central KY and southern IN 00-12z tonight. SDF/BWG/LEX will
start briefly at VFR before lower ceilings move back in from the
west. A very narrow/brief period of IFR ceilings will also be
possible tonight, mainly between 04-10z. WNW will remain somewhat
breezy at 8-9 kts overnight.

The low stratus gets scoured out Sunday morning, so expect VFR
conditions from mid to late morning through the afternoon hours.
MVFR ceilings could linger near the I-75 corridor into the early
afternoon hours. Winds diminish quite a bit after 12z due to sfc
high pressure building in from the northwest. The daytime period of
Sunday looks dry.

For the planning period, conditions will deteriorate Sunday evening
into Sunday night. Precipitation looks to begin as a wintry mix near
and north of I-64. HNB/SDF/LEX could all see brief SNRA, but
accumulations look to be pretty limited. Accumulations of an inch or
two look more likely along a FRH to IMS axis.




Short Term...BJS
Long Term...RAS

Forecast Discussion from:
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