Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 161847
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
247 PM EDT Tue Sep 16 2014
.SHORT TERM (Now through Wednesday Night)...
Issued at 245 PM EDT Tue Sep 16 2014
The synoptic pattern this afternoon features a broad trough across
the eastern 2/3rds of the CONUS, with an upstream ridge across the
West Coast. This regime will remain in place through the short term
period, as another weak shortwave will reinforces the mean trough
over the Ohio Valley on Wednesday.
Clouds continue to mix out quickly this afternoon given they were
rather shallow to begin with and we still have a pretty good sun
angle here in mid September. This trend will continue through the
remainder of the afternoon hours, with most areas going partly
cloudy by the evening hours. Highs may vary quite a bit across the
region given the sporadic nature of the clouds, but upper 60s to
lower 70s still looks like a good bet.
For tonight, the clouds will continue to dissipate, leaving mostly
clear to partly cloudy skies overnight. A surface ridge will nudge
into the region from the northwest, causing winds to go light.
Light winds coupled with a clearing sky means the potential exists
for some fog development overnight. Think enough dry air has mixed
down and advected into portions of southern IN and northern KY to
limit the fog threat in these areas. Still may be some fog in the
more prone locations near bodies of water. Further south across
south-central KY, especially near the Lake Cumberland region, skies
continue to remain cloudy with dewpoints in the upper 50s to lower
60s. Without any strong dry air advection into this region
overnight, think fog will be a bit more likely. Given the favorable
radiational cooling conditions, lows will be cool tonight as they
fall into the upper 40s and lower 50s.
On Wednesday, a quick-hitting PV anomaly will slide through the
northwest flow aloft. Soundings show a thin layer of saturation in
the mid-levels, thus have upped cloud cover a bit for tomorrow. May
even see some virga across southern KY as this system slides
through. Otherwise, expect temperatures to top out in the low to
Wednesday night will once again be clear to partly cloudy.
Overnight lows will bottom out in the lower 50s.
.LONG TERM (Thursday through Tuesday)...
Issued at 245 PM EDT Tue Sep 16 2014
A dry northwest flow aloft will dominate the end of the work week,
with a ridge moving into the OK/AR border area by Friday evening.
Surface ridging will keep us on the dry side as well. Increasing
low-level thicknesses will mean a warming trend each day. The
remnants of TC Odile look to be just west of the ridge by Friday
Previous model runs have been showing the moisture
associated with this system merging into a trough dropping through
the Plains this weekend, but the latest GFS and even the new Euro
just coming in is backing off some, having part of the moisture
linger over TX/OK. This split really does not affect the pop
forecast that much, as we still expect a healthy trough to move into
the region Sunday and bring a good shot at rain. Total amounts would
be lesser though in this scenario, which would also mean better rain
chances for a part of the nation that needs it. Temperatures ahead
of this front will be pretty warm Saturday, likely flipping us from
below normal temperatures Thursday to above normal by Saturday.
Rains Sunday should bring us back to near normal.
Models diverge a bit at this point on just how cold we get to start
the next work week. Will undercut statistical guidance here, which
trends back toward climatology at Days 6 and 7. Tuesday could end up
much cooler than what I have in the forecast, should the 00Z Euro
.AVIATION (18Z TAF Update)...
Issued at 100 PM EDT Tue Sep 16 2014
MVFR stratus deck continues to erode early this afternoon as some
peeks of sun are now filtering through. This trend will continue
over the next several hours, with KSDF likely going VFR first early
this afternoon, followed by KLEX and KBWG later on. Winds will
remain out of the NNE at 4-8 knots.
Skies will go mostly clear tonight and winds will go calm as a
surface ridge builds in. Will have to keep an eye on dewpoints this
afternoon to see if we can mix drier air down and help avoid fog
potential overnight. Current thinking is that KSDF will remain VFR,
but KLEX and KBWG likely won`t have as much time to mix down their
dewpoint this afternoon resulting in fog development overnight.
Will keep KLEX at MVFR BR for now and hit KBWG hardest with some
IFR vsbys, but confidence in this occurring is rather low given some
uncertainty in the cloud cover and associated dewpoint evolution