Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 151916

Area Forecast Discussion
National Weather Service Louisville KY
316 PM EDT Tue Aug 15 2017

.Short Term...(This evening through Wednesday night)
Issued at 314 PM EDT Mon Tue 15 2017

Expecting a relatively quiet evening across the CWA with only a very
small chance of a shower across our far SE CWA, and across our KY/TN
border. A convective complex is currently ongoing across western TN,
and will slowly lift ENE over the next few hours. However, the
complex will encounter much drier air the further north it works,
and will ultimately struggle. Hi-res models have this handled well,
and will only mention small chances for a shower across the far
south into the evening. The bulk of the activity will stay to our

As we move toward dawn tomorrow, do expect scattered showers and
storms to develop with a remnant MCV that moves into the area.
Pockets of moderate instability will combine with weak shear to
create a pulse storm mode. However, the strongest updrafts will be
capable of some brief heavy rainfall, lightning, and perhaps some
gusty winds. Overall, most areas should see between 40-50% coverage
at some point tomorrow so chances of getting rain are pretty decent.
If you miss out tomorrow, Thursday/Thursday night will carry a
better chance.

As we move into Wednesday night, isolated to scattered shower and
storm chances continue across the area, especially up near the warm
front across southern IN and northern KY. The further south you get
into KY, it should be drier as it becomes more established in the
warm sector of an upper Midwest storm system.

Temps during this time will feature highs Wednesday in the mid to
upper 80s, perhaps a tick or two below normal. Lows each night will
be in the upper 60s to low 70s, more so on Wednesday night.


.Long Term...(Thursday through Tuesday)
Issued at 314 PM EDT Tue Aug 15 2017

Thursday - Thursday Night...

A shortwave trough and it`s associated surface low will move from
the upper Midwest into the Great Lakes region during this period. By
this time, our CWA will be established in the warm sector ahead of a
cold front trailing from the Great Lakes system. As we move into the
day, expect to destabilize as a warm moist boundary layer sets up
beneath slowly steepening mid level lapse rates. Scattered to
numerous showers and storms are expected as we move into the
afternoon and evening hours as better forcing arrives to set off an
unstable atmosphere. Taking a look at forecast soundings and shear
profiles, parameters appear supportive of a few strong storms as 0-6
km shear values peak around 30 knots over southern IN/northern KY.
In addition, pockets of moderate to even strong instability can be
expected with areas that see better heating. SPC Marginal Risk
Outlook looks pretty good to cover where the best forcing will be
located. Strong storm threat could carry into the overnight ahead of
the cold front, so will keep shower and storm mention in for this

Look for highs in the mid to upper 80s with mild lows in the upper
60s and low 70s.

Friday - Sunday Night...

Shortwave trough axis and cold front are slowly pushing through on
Friday morning, and will keep light rain shower mention mainly in
the eastern CWA for a time. Most spots should remain dry, however.
Highs Friday top out in the mid to upper 80s.

Expect a dry Friday evening/night as we hold between two shortwave
troughs in the overall weakly amplified parent broad trough. Expect
slightly cooler lows in the mid to upper 60s.

By Saturday and Saturday night, another shortwave dives into the
parent trough with some deep moisture return ahead of it. This is a
bit of a trend toward wetter and faster as models didn`t have much
in the way of measurable precipitation with yesterday`s runs. So,
will include mention of some shower or storm chances Saturday
afternoon into the evening hours. We`ll continue with highs just
below normal in the mid to upper 80s.

Dry conditions return Sunday and Sunday night in the wake of the
shortwave trough, and upper ridging beginning to build over the
southern CONUS. Highs recover to normal, mostly in the upper 80s.

Monday (Solar Eclipse Day)...

Upper ridging begins to take hold of the southern CONUS by Monday,
with the stronger westerlies displaced north over the Great Lakes
and New England. This should be a mostly dry and warmer
setup/pattern but the models depict a bit of "dirty ridge" solution
where some afternoon/evening showers and storms could develop in an
unstable, but mostly uncapped, environment. Coverage in these
situations is usually isolated in nature, and I wonder to myself
whether we would be able realize enough heating (only triggering
mechanism available) to fire off showers/storms if the sun is
limited during near peak heating hours? Will consider throwing in
some slight chances for a shower or storm, but prefer to lean toward
the overall pattern this far out, and the overall pattern/setup
suggests mostly dry. In fact, forecast soundings that far out show a
subtle cap around 600-700 mb adding confidence that depicted QPF in
the models might be overdone. Like the idea of partly cloudy
wording, seasonal temps, and a small chance at rain (~15-20%).

Monday Night - Tuesday...

The forecast for Monday night into Tuesday will be dependent on how
well the upper ridge holds in strength vs. another shortwave trying
to dig into the upper westerlies over the lower Great Lakes. May
have to include some low chances as current solutions suggest the
ridge breaks down a bit. Highs near 90 should be expected.


.Aviation...(18Z TAF Issuance)
Issued at 145 PM EDT Tue Aug 15 2017

A precipitation complex to the south of our region this afternoon
will slowly lift northward toward the TAF sites tonight as a
strengthening warm front lifts north.  Light showers should make it
into BWG shortly after 6Z and SDF/LEX closer to 12-13Z.  A better
chance for showers exists at all TAF sites from mid morning onward
with perhaps a rumble of thunder.  Did not include t-storms in the
TAF yet as probabilities are too low for inclusion at the end of the
TAF forecast. So a VFR TAF is in place but any showers/storms could
drop conditions to MVFR or lower.  Also, models hint at some light
br formation late tonight into tomorrow morning, but conditions
aren`t that favorable given potential mid-level clouds and/or precip
overnight as well as only a very weak inversion if any.  So will
leave any br related restrictions out of the TAFs for now.  Westerly
winds will turn light or calm tonight and then predominantly from
the south tomorrow.




Short Term...BJS
Long Term...BJS
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