Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 200243
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
943 PM EST Tue Feb 19 2019

...Forecast Update...

.Forecast Update...
Issued at 940 PM EST Tue Feb 19 2019

After analyzing some of the incoming 00z model and observational
data, plan to keep the advisory in place for the overnight hours. KY
Mesonet and ASOS/AWOS obs show temperatures in the advisory area
ranging from 33-35 degrees, with T/Td spreads around 10 degrees.
Precipitation currently in central KY will overspread the advisory
area within the next hour or two, and will likely start out as sleet
and quickly transition to rain. Evaporative cooling in the low
levels of the atmosphere will help drop surface temperatures some,
and most 00z model guidance shows a 1-3hr window where temperatures
in the advisory area could fall to 32 degrees or colder. Any rain
falling during this time could freeze on elevated surfaces (i.e.,
freezing rain). Everything is then expected to turn over to a plain,
cold rain as surface temperatures warm above freezing in response to
strong WAA. The odds for snow continue to look slim... but some snow
may be possible in parts of northern KY and southern IN where
slightly cooler temperatures aloft remain, but think any snowfall
accumulations in those areas will be very limited due to its brief
duration.

Issued at 750 PM EST Tue Feb 19 2019

Some of the latest observations and high-res model guidance
indicates we may be in for a less wintry night than earlier thought.
AMDAR soundings from SDF show a pretty stout warm nose in place
(~3C), and several high-res models show this warm nose remaining
intact through the overnight hours across much of the region. Dual-
pol data from regional radars show melting of snowflakes aloft along
the leading edge of the precipitation band that is currently in
southern KY, marching northward. Precipitation being observed on the
ground has been all rain thus far.

The AMDAR soundings, dual-pol data, and recent high-res model
guidance would suggest that as this band of precipitation moves
northward, p-type will primarily be rain, with pockets of sleet
along the leading edge of the precipitation. A brief period of
freezing rain may be possible at sites where temperatures remain at
or below freezing. Snow chances, at this time, look pretty slim
everywhere due to warm temperatures aloft, except perhaps the far
northern tier of southern Indiana counties where a small window of
snow may be possible. Updates have been made to the forecast, and
snow totals have been dropped considerably across most of the area.

There was some consideration for dropping some counties from the
winter weather advisory along and near the I-64 corridor, given that
snow looks very unlikely now. The concern now, though, is that
surface temperatures in these areas could be close to freezing when
precipitation begins, and even brief periods of freezing rain could
result in slick elevated roadways. Will hold off on any advisory
cancellations for a little bit and keep a close eye on KY Mesonet
temperatures while analyzing 00z data as it comes in. Expect another
forecast update before 10pm.

&&

.Short Term...(This evening through Wednesday)
Issued at 309 PM EST Tue Feb 19 2019

Tonight...

Precipitation will spread throughout the region this evening and
continue through the night with strong isentropic lift and a very
moist column ahead of a deep upper trough over the Plains.

While southern and much of central Kentucky will be all rain, a
light wintry mix will be found on the leading edge of the
precipitation shield. Road temperatures are mostly in the 40s and
surface air temperatures are expected to hover just above freezing.
Soundings in north central Kentucky and southern Indiana support
mostly a rain/snow mix with perhaps a brief period of snow for a
couple of hours this evening when temperatures hit their minimum and
dew points are still in the 20s. Best chances for any wet snow
accumulation will be north of the Ohio River where an inch...maybe
2...will be possible. Accumulations elsewhere should be light. Slick
spots will be possible on elevated untreated surfaces with the
possibility of some very brief light icing as the precipitation
changes to rain and bridge/overpass temperatures lag and remain
cold. Will drop a few southern counties from the Winter Weather
Advisory where impact should be minimal, but hold on to it over most
of southern Indiana and the Kentucky Blue Grass where colder
conditions will linger the longest.

Temperatures will bottom out in the lower and middle 30s this
evening, then rise into the upper 30s - mid 40s by morning.

On the heavy rain side of things, 0.75-1.25" of precipitation looks
like a good bet tonight, especially after midnight with a 60kt low
level jet nosing in with increased theta-e ridging and precipitable
waters. Will add just a few counties on the Indiana side of the
Louisville metro into the Flood Watch where QPF and FFG numbers are
similar to areas where the watch is already out.

Wednesday...

Significant moisture will remain in the area...K Index in the mid
30s...though there is some weak mid-level drying in the afternoon.
The 5H trough over the Plains will lift northeastward, but its
surface low will travel from KC to the Twin Cities and pivot an
occluded front into the Ohio Valley by evening. Rain will continue,
though likely in a more showery fashion, as opposed to the large
area of steady rains we see tonight. A few rumbles of thunder will
be possible, especially in the Lake Cumberland region. An additional
.5-1" of rainfall will be possible.

Southeast winds in the morning will turn to the south in the
afternoon and push temperatures into the 50s.

.Long Term...(Wednesday night through Tuesday)
Issued at 345 PM EST Tue Feb 19 2019

...Additional Heavy Rainfall and Thunderstorms This Weekend...

Sfc cold front is forecast to push east to the Appalachians by 06z
Thu, so have showers exiting off to the east late Wednesday night. A
1022 mb sfc high quickly builds east from Missouri Thursday morning,
diminishing the westerly winds. Morning lows should range from the
lower 30s in southern Indiana to the upper 30s/low 40s along I-75.
Thu/Thu night still look mainly dry for a good chunk of the area as
a warm front lifts north through the Deep South. Partly sunny skies
for Thursday with highs ranging from the mid 40s north to mid 50s
south. Low chance PoPs for some light rain seems reasonable for
areas south of the Cumberland Parkway Thursday night.

=============================
Friday through Saturday Night
=============================

Friday into Friday night, a deep upper trough will swing east across
the Four Corners. SW moisture transport and isentropic ascent over a
sfc warm front will result in widespread light rain by Friday
morning into early afternoon. Lift and theta e advection continue to
increase late Friday through Friday night, resulting in heavier
showers. May see elevated convection develop by the early hours of
Saturday.

The heaviest rainfall in the long term will fall in the 24-hour
period from early Saturday morning through early Sunday morning. On
Saturday, a very dynamic system rotates northeast from the Plains to
the Midwest. Central KY/southern IN will be favorably located in the
exit region of the increasing 140-150 kt upper jet. Strong moisture
transport will aid in the development of widespread showers and
scattered elevated storms during the first half of the day. This may
play a role in limiting sfc based instability during a potential
window for severe weather later in the evening. Certainly not seeing
much opportunity for sunshine with this forecast.

Still, a strong, fast-moving cold front will approach from the west
late Saturday evening. BL moisture return should be healthy in the
warm sector, with sfc dewpoints in the neighborhood of 60 degrees.
Sfc LIs are forecast to be slightly negative, perhaps -1 to -2. 3-6
km lapse rates look pretty good actually, but a low level inversion
will linger most of the day (until perhaps right before fropa). So
the instability looks modest, but it really won`t take much to
produce significant convection.

SW winds of 75 kts will be seen as low as 700 mb. Deep layer shear
will be more than sufficient, and right-curving hodographs suggest
some potential for low-topped supercells. Based on the 12z run, CIPS
analog guidance shows 30 to 40 percent of the top 15 analogs exceed
5 severe weather reports.

We will of course monitor the severe weather potential closely for
this weekend. Confidence is highest, however, in flooding. PW values
will climb to around 1.5 inches ahead of the cold front Saturday
evening. Additional heavy rainfall through the weekend will
exacerbate ongoing flooding and prolong/extend rises on the rivers.
Minor to potentially moderate river flooding will be an issue well
into next week.

Sunday and Monday...

Even outside of convection, it will become quite breezy on Saturday
afternoon in the warm sector. It will become downright windy
Saturday night and Sunday with CAA developing. There`s potential for
advisory-level gusts on Sunday. The weather turns cooler and dry for
Sunday and Monday.

&&

.Aviation...(00Z TAF Issuance)
Updated at 614 PM EST Tue Feb 19 2019

Ceilings will continue to lower this evening and overnight as
moisture advects in from the south. Expect to see conditions quickly
go from VFR to MVFR/IFR as the stratus and precipitation move
northward. Widespread IFR with isolated LIFR ceilings will be
possible by early tomorrow morning. Precipitation will continue
through much of the day tomorrow.

As the precipitation moves northward, we could see a brief period of
wintry precipitation along and north of the I-64 corridor. This is
expected to quickly change over to rain as we head into the early
morning hours.

Low level jetting will rev up after midnight and continue into
Wednesday morning. At this time it appears that the strongest winds
will remain above 2000 feet, with a steady 10-15kt breeze sustained
at the surface, which should only result in borderline LLWS within
the restrictions of the TAFs. As a result, no LLWS will be mentioned
in the TAFs at this time.


&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...Winter Weather Advisory until 4 AM EST Wednesday for INZ077>079.

     Flood Watch through Thursday morning for INZ090>092.

     Winter Weather Advisory until 2 AM EST Wednesday for INZ076-083-
     084-092.

KY...Winter Weather Advisory until 4 AM EST Wednesday for KYZ032-036-
     037-042-043.

     Flood Watch through Thursday morning for KYZ023>031-033>043-
     045>049-053>057-061>067-070>078-081-082.

     Winter Weather Advisory until 2 AM EST Wednesday for KYZ031-
     033>035-040-041-048-049.

&&

$$

Update...DM
Short Term...13
Long Term...EBW
Aviation...DM


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