Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 181142

Area Forecast Discussion
National Weather Service Louisville KY
642 AM EST Mon Feb 18 2019

...Updated Aviation Discussion & Forecast Update...

.Forecast Update...
Issued at 642 AM EST Mon Feb 18 2019

...Light Snow At Times For The Morning Commute...

A few light streamers have been hanging around southern IN and
northern KY early this morning, producing flurries. However, a
slightly more impressive and organized band of light snow is
developing over south central Indiana. This feature will slide
southeast down through our southern IN and and northern KY counties
through the next several hours. Given that some light to possibly
brief moderate snow can create a quick dusting and some slick spots
for the morning commute, will elect to go with a Special Weather
Statement mainly along and north of I-64. Any accumulations should
be a dusting to a few tenths of an inch of snow. This is already in
the forecast from the morning issuance so will just issue the SPS to
raise awareness a bit more.


.Short Term...(Today and tonight)
Issued at 315 AM EST Mon Feb 18 2019

...Light Wintry Precip Across Southern IN/Northern KY Today...

Satellite imagery this morning shows an elongated band of upper
clouds stretching SW-NE across the entire eastern CONUS. These
clouds are associated with an intense upper jet streak (180Kt core).
Seeing a few light returns on radar from this, but given the height
of the clouds don`t expect anything to hit the ground. Other light
returns across southern IN and northern KY associated with the
lingering stratus deck are hitting the ground in the form of mainly
sprinkles, light drizzle, and brief snow/snow grains at the moment.
This is occurring where temps are in the mid 30s so not expecting any
issues with these.

With cold air continuously advecting in behind the cold front,
temperatures will steadily drop below freezing from W to E as we
move toward dawn. This is expected to change any light precipitation
over to flurries, or perhaps a few light snow showers north of I-64.
A look at the low level thermal profile shows steep low level lapse
rates to the point where saturation up near - 8 to -10C should occur
by the time surface temps fall below freezing. Therefore, don`t
expect freezing drizzle to be an issue because it should be cold
enough for ice nucleation by the time the surface temps would be
supportive. So, will go with mainly flurry mention along and north
of I-64 this morning into the afternoon, with small chances of a
dusting from measurable light snow showers across southern Indiana
and north central Kentucky. Will continue to message a few slick
spots possible in the HWO and monitor.

Otherwise, temperatures will struggle today under steady cold
advection and cloudy skies. There could be a few breaks in the
clouds by late afternoon and evening, but it looks like we don`t
completely scour things out until after sunset as surface high
pressure builds in. Given that that we should see mostly clear skies
and light and variable surface winds, a pretty good radiational
cooling setup should occur. As a result, expect a cold Monday
night/Tuesday morning as lows dip into the low and mid 20s in most
spots. The southern CWA could hang onto upper 20s.

.Long Term...(Tuesday through Sunday)
Issued at 305 AM EST Mon Feb 18 2019

...Heavy Rainfall AND Minor Snow Accumulations Tuesday Night...
...Additional Waves of Rain through Sunday...

Strong upper level ridge off the southeast U.S. coast will continue
to feed moisture into our area from the Gulf of Mexico through most
of this period. Expect periods of rainfall as disturbances cross
within that flow. The first wave looks to come Tuesday afternoon and
night, as a warm front lifts across the Tennessee Valley. Expect
precipitation to become enhanced by the presence of a 60-70 knot low-
level jet crossing the KY/TN border before daybreak Wednesday. Peak
rainfall totals could exceed 3 inches in spots with this first wave.
For this package will carry 2-2.5 inches along and south of the KY
Pkwys. The axis has shifted just slightly north with this set of
model runs. Given some uncertainty in where the heaviest rains could
fall, and after coordinating with the TN offices, will hold off one
more model cycle before issuing a Flood Watch. Fairly certain a
watch will be issued later today, just want to see if the northward
trend continues. Current ESF, Hydrologic Outlook, area still looks
good...and a Flood Watch later today likely would cover most if not
all of that region.

Another hazard that continues to pop up in the models is with the
onset of precipitation. Soundings indicate as moisture builds into
the region from aloft, the column will cool with it and bring a
brief period of snow. The best chance for this snow/sleet to occur
would be along a Hartford to Liberty line in KY late this
afternoon...with the focus shifting northward as precip starts
northward. As we get into the evening hours, brief accumulations are
possible as far south as an Etown to Danville line, but think the
best chances are in the I-64 corridor. Anything on the ground should
be brief though as we transition over to all rain with that low-
level jet helps to bring in some warmer air. Crazy to think we could
have both a Winter Weather Advisory and Flood Watch in place at the
same time!

As we get deeper into the day Wednesday we should see a breather in
the heavier precip rates. From Thursday through Sunday however, that
faucet will turn back on in waves as a quasi-stationary boundary
remains in the region and we have that southwest flow aloft. This
setup very likely will bring continued flooding concerns. Looking at
areal average rainfall totals Tuesday through Sunday, our southern
Indiana counties look to see 2-4 inches, whereas central Kentucky
likely will have 2-6! We are starting to see some hints that by
Sunday the pattern could the southeast ridge starts to
flatten out. So there is some hope on the horizon for at least a
brief chance to dry out.


.Aviation...(12Z TAF Issuance)
Updated at 630 AM EST Mon Feb 18 2019

LEX/HNB are hanging onto fuel-alternate range ceilings at this hour,
and expect improvement into the high MVFR range in the next few
hours. Meanwhile, SDF/BWG have currently found a VFR patch, but will
likely fall back into MVFR shortly. Persistent stratus has been
enough to even squeeze out some light snow flurries at the northern
sites so will also mention VCSH and P6SM/-SN for the morning into
the afternoon hours. Expect a steady W and then NW wind through the
day. Perhaps a few gusts around 20 mph will be possible at times.

Expect a return to VFR conditions mostly by late afternoon and early
evening at the northern sites, and possibly by early to mid
afternoon at BWG. Ceilings will then scatter out into mostly clear
skies overnight with light and variable winds taking over as high
pressure settles in.




Short Term...BJS
Long Term...RJS
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