FXUS63 KLMK 162007

Area Forecast Discussion
National Weather Service Louisville KY
307 PM EST Sun Dec 16 2018

.Short Term...(This evening through Monday)
Issued at 305 PM EST Sun Dec 16 2018

The clearing line has slowly pushed east today and is now roughly
along the I-65 corridor. The Louisville metro may still get an hour
or two of sunshine before setting this evening. Meanwhile, areas
over our eastern CWA will stay socked in clouds until later in the
evening with afternoon temps staying in the mid 40s. Locations along
and west of I-65 will likely still top out in the low 50s.

The biggest concern overnight will be the potential to fog,
especially in our south and east CWA where clouds have stuck around
through peak heating. The inability to mix some of the low level
moisture out, combined with good radiational cooling overnight once
clouds do clear should result in Patchy/Areas of coverage. Don't
have enough confidence to go with widespread or dense mention at
this time as a couple of mitigating factors are hurting confidence.
First off, it looks like a steady W surface wind will hang around
overnight which could keep things just mixy enough from completely
tanking. 925mb winds also stay up in the 15-20 knot range. In
addition, the steady W wind will also bring dry advection as dew
points steadily fall into the low 30s by dawn on Monday. Can't
really rely on the crossover T method in this environment given the
dry advection component. For now, will just mention in the zones and
see how evening trends progress. Lows tonight mostly fall into the
30-35 degree range.

Dry NW flow aloft and surface high pressure will control the region
on Monday. Expect plenty of sunshine with highs in the upper 40s and
low 50s.


.Long Term...(Monday night through Sunday)
Issued at 250 PM EST Sun Dec 16 2018

Monday Night - Wednesday...

Plentiful low level moisture as well as light winds and a stout
inversion under sfc high pressure should result in patchy fog over
the region Tues morning. With lows in the upper 20s, there is a
small chance for freezing fog should fog get thick enough to
actually accrete ice. Right now will just mentioned patchy fog and
remain on the conservative side. The rest of the day Tues should be
mostly sunny with highs in the mid to upper 40s.

An upper level ridge will pass through the region Tues night with
flow turning more southerly behind the ridge on Wed. This will
result in increased clouds and temps. Highs on Wed will range
through the 50s.

Thursday - Sunday...

A strong low pressure system will bring plentiful moisture to the
Ohio Valley Thu - Sat morning. Rain will spread from southwest to
northeast of the area Wed night into Thu morning as the low pressure
system deeps over the lower Mississippi Valley. Rains will continue
Thu-Fri with long range models varying in amounts. The most
aggressive with precip totals is the GFS as it wraps up the low
pressure system quite quickly and pushes northeast through KY. The
ECMWF isn't quite as strong with the system over KY but GFS
ensembles do show a similar solution as the Op GFS. While soundings
remain quite warm through much of the event, they do show a chance
for some snow to mix in on the back side of the system Fri evening
and Fri night before precipitation comes to an end completely.

Expect high temps in the 50s for Thu and then dropping back into the
40s for highs into the weekend.


.Aviation...(18Z TAF Issuance)
Updated at 1247 PM EST Sun Dec 16 2018

Conditions are finally improving at HNB/BWG, and will be over the
next 1 to 3 hours at SDF. However, LEX is expected to stay under IFR
conditions for the remainder of the afternoon and into the evening
hours before improvement. Have their ceilings improving around 8 PM
EST. Expect steady WNW winds between 5 and 10 mph the rest of the
afternoon and evening.

One concern overnight is that we could see some pretty good fog
potential in areas that didn't clear out in time and mix out the low
level moisture. This would be most likely over toward LEX, although
have also hinted at BWG because their low looks to fall 3 to 4
degrees below the crossover T tonight. The only problem with the
crossover T method is that dry air advection will also be
occurring. Will go with 2SM toward dawn at LEX early Sunday
morning, but wouldn't be surprised to see some vis below 1SM
either. Otherwise, expect a VFR Monday after any fog lifts.




Short Term...BJS
Long Term...AMS
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