Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 081045

Area Forecast Discussion
National Weather Service Louisville KY
545 AM EST Fri Dec 8 2017

...Updated Aviation Discussion...

.Short Term...(Today through Saturday)
Issued at 255 AM EST Fri Dec 8 2017

Dry but cold today and tonight as a Canadian air mass maintains its
hold on the Ohio Valley. Not looking for much of a temp gradient
this afternoon as cirrus from the southern jet will keep south-
central Kentucky mostly cloudy. Highs generally in the mid/upper 30s
this afternoon.

Fast-moving impulse currently over northern Manitoba will be our
main weather player in the short term, as it dives into the Great
Lakes late tonight. Surface reflection will swing through southern
Michigan on Saturday, but there will be just enough dynamical
support to squeeze out at least scattered snow showers over southern
Indiana and north central Kentucky. QPF is quite modest, and a good
chunk of that will be lost to evaporation in a very dry boundary-
layer, but low-level lapse rates are quite steep and there will be
saturation through much of the dendritic growth layer. This will
open a small window of opportunity for a quick half inch of
accumulation, which during daylight hours will require some healthy
snowfall rates. Believe most if not all accumulation will occur on
grassy/elevated surfaces, and any impacts beyond that will be brief
as this is the type of snow that will melt quickly once snowfall
begins to taper off. Snow accumulation grids reflect the potential
for snow accumulations around a half inch along and north of I-64,
but it`s worth noting that even these totals will be quite spotty.
Little or no accumulation is expected farther south, and there may
even be some mixing with rain in the afternoon.

.Long Term...(Saturday night through Thursday)
Issued at 255 AM EST Fri Dec 8 2017

Weather pattern through the period will be defined mainly by upper
trofiness over the eastern CONUS, which will maintain a generally
chilly and somewhat unsettled regime over the Ohio Valley.

Once Saturday`s snow system departs the rest of the weekend will be
transitional as weak shortwave ridging works on the SW side of the
broad trof. Temps won`t really bottom out any night as a westerly
sfc gradient persists between a ridge along the Gulf Coast and the
parade of lows swinging through the Great Lakes. By Sunday night and
Monday temps recover to near normal for early/mid December.

A couple stronger waves will deepen the upper trof again on Tuesday,
bringing another slight chance for snow to the Ohio Valley. Another
wave on Thursday sets up enough of a low-level trajectory off Lake
Michigan to warrant at least flurries over the Bluegrass region.
Latest model runs are less amplified overall with the pattern,
keeping most of the forcing well to our north, which will limit our
precip chances with these moisture-starved systems.


.Aviation...(12Z TAF Issuance)
Issued at 545 AM EST Fri Dec 8 2017

Plan on VFR conditions through the TAF period. High clouds will
persist over the area, especially across southern Kentucky. Westerly
winds will prevail for much of the period and will remain light
under 10 kts. The next weather system arrives late in the period,
likely after 12z Saturday. Look for an increase in cloud cover,
especially at HNB and SDF where snow showers will be possible
starting after 12z.




Short Term...RAS
Long Term...RAS
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