Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 112253
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
653 PM EDT Fri Jul 11 2014
...Updated Aviation Discussion...
.SHORT TERM (Now through Saturday Night)...
Issued at 305 PM EDT Fri July 11 2014
High pressure ridge at the surface and aloft will continue to
influence our weather over much of the short term period.
Currently, partly to mostly sunny skies were noted across the
region. Highs were generally in middle to upper 80s. A few 90
degree temperatures were noted in the urban areas and a few Kentucky
Mesonet sites. Expect diurnally driven cumulus field to fade
towards sunset with skies becoming mostly clear. Temperatures this
evening will cool down into the lower 80s. For the overnight
period, some mid-high level cloud cover upstream will stream into
our area. This will not have a sensible impact on our weather.
Lows should be similar to what we saw this morning, with readings in
the upper 50s to the lower 60s in our far eastern counties and
lower-middle 60s elsewhere.
Latest guidance continues to suggest mainly dry conditions across
the region on Saturday. Upper air data suggests that 850 temps will
warm a little more than on Friday which should support temperatures
in the 85-90 degree range. Though some 90-92 degree readings can
not be ruled out. The only fly in the ointment here is that if we
see more significant upper level cloud cover pass through the
region...temperatures may be 2-3 degrees too high. So this will be
something to watch in later forecasts. Mainly dry conditions are
likely for Saturday night, though some shower and thunderstorm
activity may be approaching our northwest sections by early Sunday
morning. Lows will be quite warm under a strong southwesterly
flow. Readings should average around 68 to 73.
.LONG TERM (Sunday through Friday)...
Issued at 312 PM EDT Fri Jul 11 2014
The synoptic pattern at the start of the long term period will
feature a highly amplified western CONUS ridge, leading to a
downstream trough across the the Great Lakes region. This trough
will amplify substantially into the Ohio Valley through the long
term period, leading to unseasonably cool conditions for mid-July by
the middle of next week.
Before the cool air arrives, the Ohio Valley will have to deal with
the heat and humidity on Sunday. Given good southwesterly surface
flow and rather dry ground conditions, think Sunday has the
potential to get quite warm. However, it appears as if convection
will develop to the north across central IN during the early
afternoon near a surface front, then drop south toward southern IN
and northern KY along its outflow by Sunday evening. Depending on
the exact timing/coverage of this convection, clouds and precip
could hold highs down a bit more than currently forecast in these
areas. With this convection expected to hold off until later in the
day, will continue to advertise highs in the lower to even mid 90s.
Dewpoints in the upper 60s and lower 70s will push heat indices near
100 degrees at times Sunday afternoon.
After Sunday, quite a bit of uncertainty creeps into the forecast
Sunday night through the Tuesday. It is certain
that the aforementioned strong trough is going to dig into the Ohio
Valley, but guidance is struggling with just how it`s going to
happen. The 11/12Z GFS is quickest with the trough, inducing a
surface low and blasting its associated front through the region by
Monday evening. The 11/12Z ECWMF is much slower with the trough and
associated surface front, not pushing it through KY until early
Tuesday afternoon. The operational GFS has support from its
ensemble, which only muddles the picture a bit more. Will lean
toward a general blend until the details become more apparent, which
falls pretty much in line with the 11/12Z GEM. Depending on the
time of day, there appears to be at least some potential for
stronger storms Monday (maybe into Monday night if ECMWF solution is
correct) given the rather strong mid-level flow and synoptic-scale
ascent. However, will not play this potential up at this time given
the overall uncertainty in the general pattern evolution.
After precip potential Sunday night into Tuesday, all guidance
points to dry conditions through the remainder of the long term
period as a strong Canadian surface ridge builds in. Much cooler
air of Canadian origin will filter into the region, meaning highs
likely won`t get out of the 70s in most places Tuesday and
Wednesday! Overnight lows will be in the mid 50s to lower 60s. By
Thursday, the high will slowly being to shift east, meaning
temperatures will start to creep upwards. Highs Thursday will be in
the lower 80s.
.AVIATION (00Z TAF Update)...
Issued at 650 PM EDT Fri Jul 11 2014
VFR conditions will persist through the valid TAF period. High-based
diurnal cu should dissipate early this evening, and may even be able
to initialize with no more than cirrus. Wave passing to our north by
Saturday morning may be close enough to push a cirrus ceiling into
SDF and LEX. Light/variable winds overnight will pick up out of the
SW by mid/late morning, but speeds remain below 10 kt.