Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 242334
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
634 PM EST Sat Jan 24 2015
...Updated Aviation Discussion...
.SHORT TERM (Now through Sunday Night)...
Issued at 257 PM EST Sat Jan 24 2015
Temperatures are ranging in the low and mid 40s acorss the south and
west, meanwhile readings are stuck in the low and mid 30s across the
snow pack and the northeast. These temperatures are expected to only
gradually fall off this evening as a steady S wind holds over the
area, and upper level clouds increase. Actually, temperatures may
reach their lowest point around Midnight and then slowly rise toward
dawn. Overall, expect lows around freezing in most places, with
temps in the upper 20s over the remaining snow pack. Its possible we
could see some fog in this area as well.
A clipper will dive into the area tomorrow and quickly depart to the
east by dawn on Monday. Ahead of this system, a steady warm
advective component will persist with temperatures reaching into the
mid and upper 40s in most spots. This will help keep the boundary
layer warm enough for all rain during the daytime hours. The lead
batch of rainfall is expected to arrive around late morning to
midday across the center part of our CWA, working to the east
through the afternoon. This initial surge will be associated with
H85 moisture transport and isentropic lift aided by a 30 knot low
level jet. The best moisture/lift will be across the northern CWA
where 80 percent chance is mentioned, these chances will taper to
60-70 across the south. Overall, a tenth to a quarter of an inch of
rainfall is expected.
Did want to quickly mention that we will have to watch arrival of
precipitation on Sunday morning as it will be a race to get surface
temps above freezing ahead of time. Most concerned over lingering
snow pack, however at this time feel temperatures will make it north
of freezing before rain arrives.
The upper PV anamoly and its associated surface low will pass
through Sunday night, with colder air crashing in behind it. At this
time, it still appears enough low level moisture will linger to
allow for rain showers to change over to snow showers. Best coverage
of these showers should be along and east of I-65, with special
emphasis also along and north of I-64. A bit concerned that some
minor accums less than a half an inch could develop in this area
toward dawn. With temperatures falling rapidly into the mid and
upper 20s, a few slick spots can`t be ruled out for the Monday
morning commute. Will continue to monitor the latest data, as the
model trends are recently pointing to a more southern solution. If
the low tracks much more south, snow becomes more of a concern
through the overnight hours across our north.
.LONG TERM (Monday through Saturday)...
Issued at 300 PM EST Sat Jan 24 2015
We`ll begin the long term period with some snow showers/flurries
Monday morning behind an exiting clipper system. Although
precipitation is expected to be on the light side (perhaps a few
tenths of an inch of snow accums), will need to watch the exact
timing of these light accums and if they may potentially have
negative impacts on the Mon morning commute. Monday morning lows
will start out in the lower 20s to lower 30s with temps increasing
to the mid to upper 30s for highs Mon afternoon.
We`ll then enter a sharp NNW flow pattern for Mon night/Tues with a
few weak upper level disturbances potentially sparking snow shower
activity especially over southern IN, north central KY, and east
central KY. This may amount to more light accums Mon night into
Tues morning. Any precip that persists into the afternoon hours
Tues may be more of a rain/snow mix as temps warm into the mid 30s
to lower 40s for highs.
A dry period is expect Tues night-Wed as upper level ridging works
into the Ohio Valley. Expect temps to moderate into the low to mid
40s for highs on Wed.
Another clipper system looks to bring precip to the Ohio Valley from
very early Thurs morning through Thurs night. The exact time of day
that this precip rolls through the region will have an effect on
p-type. As it stands now, precip could start as a rain/snow mix,
transition to all rain during the day Thurs as we warm into the mid
to upper 40s, and then end as rain or snow Thurs night. Again
precip with this system is expected to be on the light side. Winds
should turn gusty from the SSW on Thurs ahead of the front
associated with this clipper.
We`ll have another dry day on Friday before models diverge greatly
on the upper level pattern and associated storm systems for next
weekend. The GFS would favor a less amplified pattern with another
potential southern stream winter weather maker while the ECMWF
favors a cold NW flow with another clipper system to impact the Ohio
Valley. Will continue low POPs, with rain or snow chances for next
weekend for now until the pattern becomes more certain in coming
.AVIATION (00Z TAF Update)...
Issued at 630 PM EST Sat Jan 24 2015
Only concern first half of the period will be if any fog develops
because of the snow around LEX. Some clouds moving in by daybreak as
well as moderate winds through the night should help the situation
out. Will monitor through the night and amend as needed. The second
half of the period should see increasing clouds as a clipper system
approaches the region from the Northern Plains. Will see cigs lower
through the afternoon, with showers briefly reducing vsby`s as well.
By late afternoon we should see at least MVFR conditions, if not
IFR. The lower cigs will persist into the evening as well, and we
may see some snow mix in late in SDF`s TAF period.