Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 171734
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1234 PM EST Wed Dec 17 2014
...Updated Aviation Discussion...
Issued at 1000 AM EST Wed Dec 17 2014
Issued an update to remove the drizzle wording from this morning`s
grids. Should remain cloudy for most of the day. Forecast soundings
show some breaking up of the saturation under the low-level
inversion, but then we`ll have clouds moving through aloft ahead of
the next system coming in from the Four Corners.
Issued at 640 AM EST Wed Dec 17 2014
Extended the drizzle from southeast Indiana to the Bluegrass for a
few more hours as light radar echoes continue over our region.
.SHORT TERM (Now through Thursday)...
Issued at 305 AM EST Wed Dec 17 2014
Light drizzle has moved mainly east of our region this morning
although some very spotty patches of drizzle may still be out
there. Very light radar echoes indicate some light drizzle may
still be reaching the ground. With temps expected to fall to or
below freezing this morning, a few slick spots aren`t out of the
question. Will need to keep an eye on this.
The rest of the day looks dry with sfc high pressure nudging in from
the NW. Cloud cover will be tricky today as the GFS scours out
clouds fairly quickly by mid to late morning and the NAM holds on to
low clouds for much of the day. The NAM has been right more times
than not with the low clouds hanging around so will keep a mostly
cloudy forecast for the day as low level moisture becomes trapped
under an inversion. With mostly cloudy skies and a colder airmass
in place, high temps will be limited to the mid 30s to low 40s.
The next forecast challenge will be a light precip event for mainly
south central KY late tonight into Thurs morning. Models continue
to indicate very light QPF in the form of a wintry mix may fall
during the pre-dawn hours through mid morning Thurs. However,
forecast soundings reveal a very dry layer just above the sfc which
may prevent mid level precip from reaching the ground. Most
high-res models indicate only a little precip would get into our
west central KY counties as the precip shield largely dries up over
our west central KY counties. Still feel that there is a slight
potential for a light wintry mix so left a 20-30% POP in for our
south central KY counties during the morning hours around sunrise.
With low temps expected to fall at or below freezing in this area, a
few slick spots may again be possible. Will need to monitor this
light precip event closely.
For the rest of the day, models indicate mid level saturation may
work to overcome dryness in low levels enough to produce sprinkles
or flurries over the entire area Thurs afternoon. High temps should
reach the mid 30s to around 40 Thurs.
.LONG TERM (Thursday night through Tuesday)...
Issued at 300 AM EST Wed Dec 17 2014
Thursday Night through Tuesday...
Late Thursday will feature a southern stream related trough at 500mb
across Arizona, with a fast westerly confluent flow across the
Tennessee Valley. A weak shortwave will move east of the
Commonwealth late Thursday, leaving extensive cloudiness for
Thursday evening, along with nearly calm winds. Forecast soundings,
especially the more saturated NAM, hint at some very light freezing
drizzle during the evening hours. However, the drier GFS has too
little low level moisture to produce drizzle. Towards Friday
morning, low level moisture does dry out a bit. Expect mostly cloudy
skies Friday with seasonably cool temperatures, but, possibly, the
sun may peak out from time to time. Lows early Friday will fall into
the upper 20s, with highs in the upper 30s to lower 40s during the
Guidance continues to trend farther south with a storm system
that potentially may produce some light snow or a wintry mix across
the Commonwealth on Saturday. A 500mb trough will de-amplify as it
moves across Arkansas very early Saturday. The NAM, GFS and the
latest ECMWF all agree with the development of a weak surface low
near Mobile, Alabama and an inverted surface trough extending
northwards into Tennessee. Central Kentucky will likely fall within
the very northern edge of an extensive precipitation shield
extending from Tennessee to the Gulf coast. Currently, very light
precip or none at all looks to fall northwest of the Ohio River.
The NAM has the coldest soundings, forecasting snow to develop
pre-dawn Saturday across Bowling Green and the rest of southern
Kentucky. The GFS is warmer, with its soundings forecasting rain for
the same area. The ECMWF is colder, closer to the NAM, and is
preferred. Think that light snow will develop across central and
north central Kentucky around dawn Saturday, with a rain/snow mix
possible right along the Tennessee border. This will continue
through much of the day Saturday prior to ending by evening. Some
light snow accumulations are certainly possible southeast of the
Ohio River if QPF is adequate. Highs Saturday will rise into the mid
to upper 30s. Partial clearing may develop Sunday with highs rising
a few degrees from Saturday`s peak temps.
A pattern change will begin Monday, as low pressure associated with
the northern stream of the jet strengthens over the Dakotas. This
will eventually carve a longwave trough centered over the upper
Mississippi River by Wednesday. Southerly winds will develop Monday
and continue Tuesday with several chances of light rain as a couple
of upper level disturbances rotate around this developing 500mb
trough. Showers are likely at some point Tuesday ahead of a sharp
front that will bring colder air Tuesday night.
.AVIATION (18Z TAF Update)...
Issued at 1235 PM EST Wed Dec 17 2014
Seeing evidence of cloud deck scattering out across KBWG and getting
closer to the SDF/LEX corridor this hour. With this change, have
gone more optimistic with the afternoon cigs. Next up will be an
upper-level disturbance crossing the region early Thursday. This
system will have to overcome some dry air above the current
inversion in order to produce precip, but think there`s enough of a
chance down south to warrant a PROB30 group with light rain or sleet
and MVFR cigs. Have increasing clouds again overnight at the other
terminals, but think they will stay VFR after the current deck