Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 082000
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
300 PM EST Sun Dec 8 2013
.SHORT TERM (Now through Monday Night)...
Issued at 239 PM EST Sun Dec 8 2013
The synoptic pattern this afternoon features a rather impressive
deep trough across much of the central and western parts of the
country. This trough will slowly deamplify and shift east into the
Ohio Valley through the short term period.
The steadier wintry mix that we saw early this morning has shifted
northeast of the region this afternoon. The worst conditions with
the highest ice accumulations were on a line from about Logan County
northeast to Madison County. In this this band, around 1/4" of ice
accumulated mainly on trees and elevated surfaces, causing a few
scattered power outages before temperatures rose above freezing. Further
north, convective bursts of sleet/snow dropped around an inch of
quick accumulation before moving out.
Temperatures should continue to rise through the rest of the
afternoon into the early evening hours as winds go more southerly,
with the freezing line slowly making northward progress. As of 2PM,
this line was located on a track from about Clark County southwest
to Ohio County. Much of Kentucky will likely go above freezing at
some point this evening, but southern Indiana will likely remain
just below due to the deep snowpack in place. As these warmer
temperatures and higher low-level moisture run into the deeper
snowpack, fog is likely to continue to form. With light winds in
place, it should not become too dense but will go ahead and add
patchy fog wording into the grids.
Another PV anomaly will ride along the arctic front tonight. This
will spread precipitation back into southeastern KY, but it should
fall as all rain with temperatures well above freezing. Further
northwest across central/northern KY and southern IN, moisture may
become deep enough to support some light drizzle. Depending on
surface temperatures, some of this precip may fall as a very light
freezing drizzle overnight.
On Monday, the arctic front slides just enough east that conditions
look as if they`ll dry out across the region. Temperatures will
vary from northwest to southeast, with southern Indiana topping out
in the lower 30s and southern KY climbing into the middle 40s.
The last hoorah of this expansive upper-level trough will come on
Monday night, as the trough axis finally swings through. Guidance
has been really inconsistent with it`s placement of a potential
snowband, with the latest model suite depicting this band somewhere
near the Ohio River. The forcing will remain mostly in the
midlevels, and with a rather dry layer beneath it, don`t expect much
QPF to reach the ground (less than a tenth of an inch).
Nonetheless, with cold profiles through the atmospheric column and
much of the mid-level ascent residing within the DGZ, a quick burst
of dendritic snow seems possible, perhaps dropping an inch or so in
a few locations. Will need to pin down the exact placement in the
band in coming forecasts, and adjust pops upwards when confidence in
the area begins to increase.
.LONG TERM (Tuesday through Sunday)...
Issued at 251 PM EST Sun Dec 8 2013
The upper trof that has been to our west will finally pass overhead
during the day Tuesday. Models have been trending wetter with the
trof passage, and the GFS and EC have come into remarkable agreement
for Tuesday morning. It appears a stripe of snow may form in
association with a band of weak mid-level frontogenesis and weak
isentropic upglide ahead of the trof...as well as being near the
right entrance region of the upper jet. Any snow Tuesday morning
will be light, but there is the chance that a heavier band or two
could set up, and could come through the Louisville metro right
around the morning rush. Just something to watch.
A couple domes of Canadian high pressure will keep us dry Tuesday
afternoon through at least Friday. Temperatures will be chilly,
possibly into the single digits over the snow pack Wednesday morning
and Thursday morning.
The models diverge, of course, by the weekend. Right now will lean
more toward the EC ensemble mean solution which suggests a drier
forecast and less progressive upper pattern. Even so, a small PoP
will be warranted as we sit under zonal flow ahead of an approaching
western trof. Precipitation type in the grids will be rain/snow
depending on surface temperature.
.AVIATION (18Z TAF Update)...
Updated at 1218 PM EST Sun Dec 8 2013
The wintry mix has become very light across the region this
afternoon, but a prolonged period of IFR cigs or even LIFR cigs
appears increasingly likely overnight. These LIFR ceilings have
already moved into KBWG, and will likely affect KLEX as well. As
another disturbance pushes in from the southwest overnight,
additional low-level moisture will work into the region. This will
cause ceilings to remain IFR or LIFR through the overnight period,
with even a few light showers possible around KLEX or KBWG. KSDF
will be further removed from the deeper moisture overnight, so just
expect IFR cigs and perhaps some isolated drizzle. Winds will be
shifting from easterly to southerly to westerly by Monday morning.
Wind speeds will be generally light, around 7 knots or less.
Ceilings should slowly improve throughout the day on Monday, lifting
to MVFR thresholds by the mid to late morning hours.