Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 290246
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
946 PM EST Fri Nov 28 2014
Issued at 940 PM EST Fri Nov 28 2014
Adjusted sky cover and temps to current conditions. Adjustments
resulted in only minor forecast changes. Low temps in the upper 20s
to upper 30s still look on track for tonight. These lows will occur
earlier in the overnight period as strong WAA will hold temps steady
for the most overnight hours.
.SHORT TERM (Now through Saturday Night)...
Issued at 305 PM EST Fri Nov 28 2014
High pressure has retreated east of the Appalachians, giving way to
southerly return flow. Clouds this morning held temps back, but we
have recovered to around 40 along the I-65 corridor, with warmer
temps poised to our south and west. Expect a warming trend in temps
through the weekend, but with the pattern becoming a bit unsettled
in the persistent warm advection.
Return flow is still not that strong, so will not carry much of a
non-diurnal temp curve tonight. Still expect a fairly quick drop
this evening, with temps flatlining from late evening onward. Will
lean on the warmer NAM MOS guidance for mins tonight, but could
still see decent radiational cooling in the Bluegrass, so will open
a bit more of a range in temps there.
The warm advection on Saturday looks quite strong, especially in the
mid levels. This complicates the forecast because we expect an
inversion to develop, and trap low-level moisture at least to some
degree. Raw model progs are quite cool as they develop a goalpost
sounding, but with 900mb winds pushing 50 kt, would expect
boundary-layer stability to be a bit limited. Still look for skies
to become mostly cloudy, but lean on the warmer GFS MOS temps as we
see a slow climb toward late-day highs. Will also bring a slight
chance POP into southern Indiana and north central Kentucky as weak
isentropic lift develops.
Will increase POPs to chance on Sat night, mainly north of the
Parkways, as the warm advection continues. Depth of moisture is
limited so QPF should be quite light. More pronounced non-diurnal
temp curve as we expect only a slight evening drop, then steady or
rising temps toward Sunday morning.
.LONG TERM (Sunday through Friday)...
Issued at 300 PM EST Fri Nov 28 2014
Unseasonably mild temperatures are expected for Sunday into Sunday
evening. At this time brisk southwesterly flow is expected over the
Commonwealth, as Kentucky will be sandwiched between strong 500mb
ridging over Florida, and a cold front expected to stretch from
Chicago to near Missouri. Despite widespread low cloudiness, highs
will reach the lower to mid 60s Sunday. Surface winds will range
from 10 to 20 mph with some higher gusts Sunday afternoon. Although
some numerical guidance is calling for likely showers Sunday, not
sure that this will really happen. Forecast soundings show
saturation below around 9k feet with an inversion around 9k feet and
quite dry air above this inversion. Any showers that develop in that
environment would be quite light and actually be little more than
sprinkles. Will undercut precip guidance Sunday and call for just a
chance of a very few light rain showers.
A shallow arctic airmass will begin to filter south into Kentucky
Monday morning. Weak lift associated with from an exiting jet max
and overrunning will likely bring some light rain Sunday night into
Monday morning. Light precipitation will linger, especially across
our south well into late Monday. Precipitation Monday may end up as
a light wintry mix with possibly freezing rain or even some light
sleet. At this time amounts will likely stay too light to bring
travel problems, but this will have to be watched.
Monday`s highs will occur at midnight, and fall through the upper to
mid 30s during the afternoon hours, depending on the exact timing of
this cold air`s arrival. After a cold morning, highs Tuesday will
rebound well into the mid to upper 40s.
As has been the case over the past several days, quite a bit of
uncertainty still remains for the middle of next week. In general, a
flat zonal flow will traverse the northern half of the country in a
pattern that frequently spells a relatively mild period for the
Lower Ohio Valley. Even as early as Wednesday the most recent runs
of the ECMWF are vastly different: the ECMWF has cool temperatures
Wednesday with light northerly winds, while the GFS is much warmer
with a frontal boundary established well north of the Ohio River.
Both models are also different in their forecasts of a series of
weak disturbances embedded within westerly flow over the
Commonwealth. Our forecast will be basically a compromise, a safe
bet until guidance comes into better agreement. In general though,
temperatures look warm enough after Tuesday for any precipitation
to stay as rain.
.AVIATION (00Z TAF Update)...
Updated at 615 PM EST Fri Nov 28 2014
VFR conditions will prevail tonight with southerly winds between 5-8
kts increasing toward sunrise. Return flow will be in full swing
for tomorrow with low level moisture on the increase. This will
result in deteriorating TAF conditions to MVFR levels tomorrow with
southerly winds of 10-14kts gusting to around 20 kts during the
afternoon hours. There is still uncertainty as to how quickly an
MVFR cig will become established. Therefore kept the TAFs on the
conservative side introducing a low VFR cig just after sunrise and
then taking flight conditions down to MVFR by mid afternoon as
moisture increases and rain or drizzle begins reaching the ground.