Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 082342
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
642 PM EST Sun Dec 8 2013
...Updated Aviation Discussion...
.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. Further north, convective bursts of
sleet/snow dropped around an inch of quick accumulation before
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 light
freezing drizzle overnight, but impacts from this should be rather
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 (00Z TAF Update)...
Updated at 630 PM EST Sun Dec 8 2013
Precip has pushed well off to the south and east, but low clouds and
advection fog have become the main players as warmer but still moist
air comes in and starts to melt some of the accumulated ice and
snow. LIFR ceilings have been observed at all three terminals with
visibilities solidly into IFR. BWG has improved a bit as the temps
have risen far enough above freezing.
Expect BWG to drop back into LIFR late this evening as another wave
rides NE, roughly along the Appalachians but close enough to
generate some patchy drizzle into the pre-dawn hours of Monday. Will
keep this activity south and east of SDF.
Temps may not actually rise enough to take care of the ice at SDF
and LEX, in which case we will have to wait for the westerly
gradient to set up behind a low that will deepen over the Great
Lakes. This should happen after midnight, and bring ceilings up out
of LIFR. Gradual improvement is expected later in the morning but
cigs will remain in fuel-alternate MVFR most of the day. West winds
will stay under 10 kt...which is not much help in scouring out low
clouds under a meager December sun.