Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 070043

Area Forecast Discussion
National Weather Service Louisville KY
743 PM EST Tue Dec 6 2016

.Forecast Update...
Issued at 745 PM EST Tue Dec 6 2016

Rain has exited the area to the east, leaving behind plenty of low
stratus and still a fairly brisk NW wind. Cold advection will
continue through the night, but winds will die down after midnight.
With that, forecast lows around 30 seem to be on track even though
clouds should hang in for most of the night.


.Short Term...(This evening through Wednesday night)
Issued at 215 PM EST Tue Dec 6 2016

Potent shortwave now east of the area, after having brought over an
inch of rain in many locations across southern IN and central KY,
will continue east northeast the rest of this afternoon. In its
wake, one more vortmax, now over northern Arkansas, will cross the
region this evening. Forecast soundings from the GFS/RAP and to a
lesser extent the NAM show this feature, via a saturated layer at
500 mb and above. There is plenty of dry air underneath this layer,
save for near the surface. Any ice crystals aloft should sublimate
through this dry air.

High pressure will ridge in from the west during the day Wednesday,
under partly cloudy skies, with more upper clouds all from making us
sunny. Wednesday night cloud cover will increase again as a
reinforcing cold front approaches. Models have continued the trend
of showing a dry passage with this front. Even the NAM joined that
dry party, reversing its trend from the 00Z run. The SREF spreads
show a little more uncertainty, with some higher values near the
KY/TN border late Wednesday night. Thus will keep in slight chance
for light snow, but no accumulations, down there.

.Long Term...(Thursday through Tuesday)
Issued at 215 PM EST Tue Dec 6 2016

...Unseasonably Cold Later This Week...

Reinforcing cold shot moving in Wednesday will allow Arctic high
pressure to spill southward into our region.  Expect temperatures
Thursday through Saturday to run some 10-20 degrees below normal,the
first time we`ve run with average temperatures that far below normal
was back in mid May. Surface high pressure should be right over the
area Saturday morning, so our cold spots easily could see mid teens
or lower for lows.

The slightest chances for precip in this cold regime are possible
just northeast of our area Friday, in the flow off Lake Michigan. A
few models hint at light QPF in this plume, but with this package we
are forecasting that plume to stay out of our area.

By Saturday night the surface high will push east of the area,
allowing a return flow to start warming us up. Flow aloft will be
zonal but should back to southwesterly Sunday, as the next cold
front approaches. Models have slowed the timing of precip a little
since this time yesterday`s runs, now keeping the bulk of the rain
during the daytime period...which more than likely would be rain.
Still given uncertainty in timing, will be continuing our rain/snow
mix wording.

High pressure building in behind that front should make us cold and
dry again by Tuesday.


.Aviation...(00Z TAF Issuance)
Issued at 635 PM EST Tue Dec 6 2016

Main challenge overnight is how quickly the stratus deck will
scatter out, which will depend on the battle between trapped low-
level moisture and incoming dry air. Ceilings are on the rise, with
BWG into MVFR but still fuel-alternate, and SDF will be a last-
minute call on fuel-alternate status. LEX will remain IFR until late

Model soundings and hi-res guidance suggest that low clouds may
scatter out after midnight but prior to daybreak. Just enough N-NW
flow above the top of the boundary layer to support this, though it
opens up fog potential at BWG. Not highly confident in losing the
stratus, but if it does break, visibility is likely to drop. For now
will play the middle with lower-end MVFR happening on either cig or
vis, but likely not both. If LEX and/or SDF can scatter, they will
remain unrestricted due to a lingering mid-level ceiling.

Light NW winds expected on Wednesday with only cirrus cover.
Planning period at SDF could see the return of a mid-level ceiling
as the next disturbance is ready to bring the arctic front into the
Ohio Valley.


.LMK Watches/Warnings/Advisories...


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