Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 060711
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
311 AM EDT Mon Jul 6 2015
.SHORT TERM (Now through Tuesday)...
Issued at 305 AM EDT Mon Jul 6 2015
Surface pressure pattern remains quite sloppy, while an upper low
continues to retreat slowly eastward into the Appalachians, giving
way to shortwave ridging. In spite of SW flow and a warm and moist
boundary-layer, deep moisture will be on the decrease with
precipitable water dropping to just over an inch. Soundings will
still be unstable, making it hard to rule out an isolated pop-up
over south central or east central Kentucky, but this only warrants
the slightest of slight chances. Afternoon highs will recover to
near climo for the first time in July.
Tonight will see clouds increasing and a more mixy SSW flow as a
front approaches the area from the NW. A fairly vigorous shortwave
trof will be pushing across the upper Great Lakes late tonight and
Tuesday, and should drive the front well into the Ohio Valley, where
it will hang up. POPs late tonight will be limited to slight chance
west of I-65, but will increase sharply Tuesday with the front in
the area. Forcing for SVR will remain well to our north, but heavy
rain threat will ramp up as the front lays out parallel to the flow
.LONG TERM (Tuesday Night through Sunday)...
Issued at 308 AM EDT Mon Jul 6 2015
The synoptic pattern at the start of the long term period will
feature weak zonal flow across the Ohio Valley. This regime will
amplify through the period, as a Southeast ridge strengthens and
builds into the Ohio Valley. This large-scale ridging will bring
warmer temperatures to the region, along with less in the way of
The 00Z suite of guidance has come in with general agreement on a
more amplified regime through the long term period, which is now two
model cycles in a row (00Z, 12Z) that has shown this. Therefore,
have trended the forecast quite a bit drier Wednesday night-Sunday,
as it appears this large-scale ridging will win out, especially
across southern and central KY.
A cold front will sag into the region Tuesday night, but will be
stalling as it becomes parallel to the upper-level flow. Therefore,
showers/thunderstorms will have a tough time making it into southern
KY, so have confined the better pops to the northern half of the
The upper-level flow then turns more southwesterly by Wednesday,
which will allow what`s left of the boundary to lift north as an
effective warm front. Given this boundary exiting the area, little
focus will remain for thunderstorm coverage on Wednesday, especially
across southern KY. With less expected convection, have upped
temperatures quite a bit for Wednesday which puts highs in the mid
to even upper 80s.
The remainder of the long term will be characterized by the main
front residing north of the region, which will keep the better focus
for convection off to the north of the forecast area. There may be
outflow boundaries and differential heating boundaries that spark
convection at times Thursday through Sunday, especially during peak
heating, but the signal just is not there for anything widespread as
the upper ridge will be in place over the Ohio Valley. This is
certainly welcomed news as the region needs some time to dry out
from the recent soaking we`ve seen as of late.
Given the ridge building in and expected sunshine, temperatures will
be quite warm by the end of the week into the upcoming weekend as
readings push into the upper 80s and lower 90s. This heat coupled
with dewpoints in the 70s will help push heat indices near 100
degrees at times.
.AVIATION (06Z TAF Update)...
Issued at 105 AM EDT Mon Jul 6 2015
Minor restrictions to vis already showing up in LEX and BWG, and
that will be our challenge overnight. Calm winds, clearing skies,
and plenty of low-level moisture all support fog formation. However,
the night is very short, there is some slightly drier air trying to
filter in, and even the usually pessimistic NAM MOS guidance isn`t
hitting it that hard. Other bit of uncertainty in LEX is how much of
an influence the lingering mid-level clouds associated with the
upper low will be. All that said, will initialize with MVFR
visibilities and go with at least a TEMPO IFR for a few hrs around
daybreak. SDF is already a bit drier and always more mixy, so will
stay unrestricted there.
Should mix out any fog/stratus by late morning, with light SW winds
and just diurnal cu expected for the rest of Monday. Any return of
precip Monday night is a low probability, and most likely beyond the
valid TAF period.