Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 221645

Area Forecast Discussion
National Weather Service Louisville KY
1245 PM EDT Thu Mar 22 2018

...Updated Aviation Discussion...

.Short Term...(Today through Friday)
Issued at 244 AM EDT Thu Mar 22 2018

...Black Ice and Patchy Dense Fog This Morning...

Main concern going forward this morning is black ice and patchy
dense fog across areas that received several inches of snowfall
yesterday. So far, have not received a lot of reports of slick
roads, but imagine as the morning rush-hour picks up later today,
we`ll see some issues along secondary, elevated or untreated
roadways. Will continue to highlight these threats in an SPS.

Once the sun rises this morning, we should start to see temperatures
rebound quite nicely under clear skies. Afternoon highs will climb
into the low 50s across western Kentucky, while the Kentucky
Bluegrass area may struggle to get into the low 40s. High
temperatures in areas that received several inches of snow yesterday
will be a bit tricky, as some of the sun`s energy will either be
reflected (albedo effect) or go into melting the snowpack. Went
ahead and knocked a degree or two off guidance where the deepest
snowpack remains.

May have to keep an eye on black ice tonight into tomorrow morning.
While significant melting will occur today, areas that still hold
their snowpack into tonight will see temperatures drop near or below
the freezing mark, and any water that ends up on roadways could
freeze and make for slick spots on roads.

Deepening area of low pressure ejects off the Rockies into the
central Plains on Friday. A warm front will begin lifting up toward
Kentucky during the day on Friday, but will probably be just
southwest of the CWA by Friday evening. We may see some light
precipitation develop ahead of the low and warm front Friday, but
more than likely most areas will remain dry but just see increased

.Long Term...(Friday night through Wednesday)
Issued at 302 AM EDT Thu Mar 22 2018

The low pressure over the central Plains will move into the Midwest
Friday evening. The warm front associated with the low will also
begin lifting into southwestern parts of Kentucky, and create quite
a temperature gradient across the state. Isentropic lift ahead of
the warm front, as well as forcing from being located in the right
entrance region of a +140kt jet streak near the Delmarva Peninsula
will result in widespread precipitation developing over central
Kentucky and southern Indiana. Temperature profiles still support
the potential for wintry precipitation over parts of the Kentucky
Bluegrass and southeastern Indiana Friday night into Saturday,
though temperature differences of just 1 or 2 degrees in the lower
levels of the atmosphere or subtle changes to track of the low could
result in this being just a plain, cold rain... or a significant
snow/ice storm for northeastern parts of the CWA. The current
forecast is taking a blend of short to mid range model guidance for
temperatures to get the predicted p-types, which gives southeastern
Indiana and the Kentucky Bluegrass a period of snow/ice late Friday
night into Saturday morning with minor accumulations. The worst of
it still appears to be just northeast of the CWA near the KY/OH
borders at this time.

Will also have to keep an eye on thunderstorm potential Friday night
into Saturday as model soundings show some steep mid-level lapse
rates ahead of the warm front, and the potential that we could see
some surface based instability as the warm front lifts into parts of
southern Kentucky Saturday afternoon.

The surface low dives into the Southeast Saturday night into Sunday
morning. Precipitation may wrap around the northern side of the low,
but should taper off by Sunday morning. Some colder air wrapping
around the low may introduce some brief p-type issues. We`ll begin
drying out Sunday afternoon as upper level ridging builds in.

Active weather could continue into next week as the upper level
ridge parks itself over the eastern CONUS, while troughing occurs
over the southwestern CONUS. Flow aloft over the lower Ohio Valley
would be out of the southwest, and models show several perturbations
within the flow leading to multiple rounds of rainfall through much
of next week. Of course, the big concern with this setup would be
flooding, but there is still some uncertainty as to where the
heaviest axis of rainfall will end up. Plan to keep higher PoPs in
the forecast for the long term, and will continue to monitor the
setup for any potential flooding.


.Aviation...(18Z TAF Issuance)
Issued at 1245 PM EDT Thu Mar 22 2018

Clear skies and light NW winds are expected this afternoon. Cirrus
will start to spread in later in the evening as a warm advection
pattern aloft sets up, but sfc winds go light/variable if not calm.
Gradual lowering and thickening of clouds ahead of the next system,
so will bring in a mid-level ceiling by daybreak, and keeping it VFR
as it lowers, including in the afternoon at SDF. Could see enough
precip Fri morning to warrant a VCSH at BWG and HNB but even that
seems generous as we hold it off beyond the valid TAF period at SDF.




Short Term...DM
Long Term....DM
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