Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 242001
Area Forecast Discussion
National Weather Service Louisville KY
301 PM EST Tue Jan 24 2017
.Short Term (Now through Wednesday Night)...
Issued at 300 PM EST Tue Jan 24 2017
Low clouds are quickly clearing as the 925 thermal ridge builds in
from the SW at this hour. Temps currently in the mid to upper 40s,
should jump a few degrees and may end up in the low 50s in some
spots before they begin to fall off this evening.
Otherwise, the remainder of today and tonight will be dry as
progressive upper ridge axis slides overhead. Meanwhile at the
surface, pressure gradient will tighten between surface high
pressure off the mid Atlantic and surface low moving into the upper
Midwest. Temperatures should fall off initially this evening until
around Midnight EST, and then begin to rise toward dawn as the
of increasing winds and cloud cover help to warm. Look
for lows in the upper 30s NE to low 40s SW before the warming trend
Strong SSW flow by Wednesday ahead of a cold front will help temps
to rise to around 60 by mid afternoon, before dropping off
dramatically behind the front into Wednesday night. Overall,
moisture is lacking with this frontal passage so will go with small
chances for a measurable rain shower through the day. Best chances
will be in our eastern CWA Wednesday afternoon and evening.
Temps drop to the low and mid 30s through Wednesday night with the
aid of some gusty NW winds. Some gusts may be around the 30 mph
range. Most of the rainfall should push east by Wednesday night as a
dry slot works into the area. Low level moisture then works back
into the area from the north, but will not re-introduce precip
chances until after dawn on Thursday (see long term).
.Long Term (Thursday through Tuesday)...
Issued at 230 PM EST Tue Jan 24 2017
...Colder Air and Light Wintry Precipitation Return...
Thursday - Saturday...
The cold front will have pushed east of central Kentucky and
southern Indiana by 12z Thursday, ushering in a much cooler airmass.
There is good agreement between the 12z GFS/00z ECMWF on the
placement of the mid-level trough axis right over the forecast area
around 12z Thursday. 500-300 mb potential vorticity advection then
becomes negative through the rest of the day. Without any
significant lift, any precip Thursday will be light. Decent
saturation in the DGZ does exist between 12-18z Thu, especially
across southern Indiana and northern Kentucky (closer to upper low).
There is a 20-30% chance for very light snow, or a light mix as
surface temps recover slightly toward midday. Impacts do not look
likely given surface temps in the mid to upper 30s for much of the
day. Otherwise, expect a cloudy Thursday with temps holding in the
With an upper level trough in place across eastern North America, a
series of shortwaves will rotate down in the northwest flow aloft
late this week through the weekend. There is a chance for some
wintry precip on Friday, but it again looks light. Temperatures will
be cooler to start the day, with lows falling into the mid to upper
20s Friday morning.
Sunday - Monday...
The best chance for winter weather impacts arrives on Sunday. The
main upper trough finally swings down, and deeper moisture will
coincide with better forcing. Snow is more likely Sunday morning,
with a mix possible in the afternoon (especially in southern KY).
Accumulations and travel impacts are possible Sunday, but not
certain at this point. The 12z ECMWF is less amplified with the
upper trough and pushes it east instead of down into the Ohio
Valley. Consequently, the Euro is much drier than the GFS for
Sunday, keeping the best snow chances across eastern KY.
Monday into Tuesday looks fairly quiet, with highs in the 30s on
Monday and low 40s on Tuesday.
.Aviation (18Z TAF Update)...
Issued at 1240 PM EST Tue Jan 24 2017
Stratus deck is persisting early this afternoon, although seeing
some signs of improvement as 925b mb thermal ridging begins to build
in from the SW later this afternoon and this evening. BWG will be
the first to see improvement in the next hour or two. Expect SDF to
go back into VFR by around sunset, and LEX a couple hours before
Midnight EST. Any MVFR until then will be above fuel-alternate at
SDF/BWG, and mostly below fuel alternate at LEX.
Another concern for the overnight will be LLWS as a 45 to 50 knot
low level jet moves over the area. Seeing a bit more directional
shear in the lowest 2 K feet than we are used to, combined with a
strong inversion so feel LLWS is warranted.
LLWS threat ends by late morning with expected MVFR ceilings moving
back into the region, along with a few showers. A steady SSW wind
will be going through the remainder of the day. Cold front begins to
pass at the end of this cycle.