Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 251851
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
251 PM EDT Sat Jul 25 2015
.SHORT TERM (Now through Sunday Night)...
Issued at 245 PM EDT Sat Jul 25 2015
The synoptic pattern on this Saturday afternoon features a strong
and persistent ridge across the southern and south-central CONUS.
The Ohio Valley will be on the periphery of this ridge through the
short term period, meaning rather warm and humid conditions along
with the chance for some convective activity Sunday into Sunday
All is quiet across central KY and southern IN this afternoon thanks
to surface ridging. This ridge is helping to keep dewpoints in the
low to mid 60s in place currently, making for rather pleasant
humidity values despite the warmer temps. Higher dewpoints have
entered portions of western KY and southern IL where values have now
risen into the low and mid 70s.
This surge in dewpoints marks the edge of the instability axis,
which should set up across portions of eastern IL and western KY
tonight. Therefore, expect convective activity to remain west of
the LMK CWA tonight as high pressure keeps a slight hold on the
region. There may once again be some patchy fog tonight in southern
and eastern KY where the surface ridging will be most prominent.
A weak complex of showers and a few embedded thunderstorms may
attempt to dive into areas west of I-65 Sunday morning along the
instability axis as it slowly nudges northeast into our area
throughout the day. Other than this potential activity, actually
think the majority of Sunday will end up dry as the main convective
focus will remain off to the north along a weak cold front.
Soundings also indicate capping around 800mb as the upper ridge
attempts to build in. Therefore, will slow the arrival of pops into
southern IN and northern KY, with the best chance coming Sunday
evening into the overnight hours as the front sags into the region
and the instability axis sets up near the I-65 corridor. The latest
hi-res GEM/NAM depict a bit stronger signal in a mid-level wave and
associated low-level jet response Sunday night, so have upped pops a
bit in this timeframe. However, guidance is not in very good
overall agreement on the timing and convective coverage of this wave
so confidence is a bit below average through the end of the short
Have gone with highs in the upper 80s to low 90s on Sunday, once
again ignoring the raw GFS numbers mid 90s) as it continues to
struggle with mixing the boundary layer way too deep in the
afternoons. Overnight lows will be in the low to mid 70s.
.LONG TERM (Monday through Saturday)...
Issued at 224 PM EDT Sat Jul 25 2015
An upper ridge over the southern Plains will swell northeastward
Monday through Wednesday, and then shrink back to the west as a
Canadian trof digs into the eastern United States late in the week.
Monday we will have a weak east-west surface boundary over Kentucky
plus perhaps outflow boundaries from MCS activity to our northwest
the previous night. In addition we`ll still be far enough away from
the heart of the upper ridge, with sufficient moisture in place,
that scattered showers and thunderstorms will be a possibility.
Rain chances will decrease on Tuesday as that ridge builds in more.
An isolated pop-up storm can`t be ruled out, but at this time it
appears most locations should remain dry.
Even going below the GFS`s overdone temps, heat index readings will
still be in the 95 to 100 degree range each afternoon Monday through
Wednesday night into Thursday that upper trof will enter the
picture, preceded by a surface cold frontal passage. With
precipitable water amounts pooling ahead of the front around two
inches and deep moisture showing up on sounding progs, the storms
will be capable of some heavy downpours. The better upper dynamics
will remain to our north and right now the front is progged through
here at a climatologically unfavorable time of day for strong
storms, so it`s appearing that heavy rain is a bigger threat than
Surface high pressure will move through the Ohio Valley Thursday
night through Saturday, along with a marked decrease in atmospheric
moisture, so dry conditions are expected along with seasonable
.AVIATION (18Z TAF Update)...
Updated 1248 PM EDT Sat Jul 25 2015
A rather benign TAF period is in store as VFR conditions will
largely prevail at all three sites. The only exception is at KBWG
and KLEX early Sunday morning, where some light MVFR fog will be
possible. Otherwise, winds will continue to remain rather light and
variable with just some passing upper-level cloudiness through the