200
FXUS63 KLMK 152308
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
708 PM EDT Thu Aug 15 2024

.KEY MESSAGES...

*   Scattered thunderstorms are expected tonight through Friday
    morning. Some locally heavy rainfall is possible, but the risk
    for severe weather is low.

*   Unsettled weather is likely Saturday and Sunday with scattered
    showers and thunderstorm being possible each afternoon/evening.

*   Dry weather is expected for much of next week, with well below
    normal temperatures for late August.

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 301 PM EDT Thu Aug 15 2024

Conditions remain dry under partly sunny skies this afternoon. A
vertically stacked low pressure system will rotate ESE over the
Upper Midwest through tomorrow, with multiple smaller-scale
shortwave disturbances wrapping eastward across portions of the
Midwest and Great Lakes. Deep-layer flow will be fairly weak
tonight. Friday, the northern CWA will be on the southern periphery
of moderate (40+ kt) mid-level westerly flow as the parent trough
translates eastward.

This afternoon, a large moisture gradient remains in place from west
to east across the Ohio Valley. Deeper moisture lingers just off to
our west, with 2+ inch PW values noted in western KY and IL.
Therefore, the atmosphere locally remains fairly stable. Convective
initiation appears likely upstream across portions of eastern MO and
southern IL later this afternoon and evening. Shower and
thunderstorm chances then increase across central KY and southern IN
late this evening and overnight as upstream activity evolves
eastward. Notable moisture advection takes place tonight with the
development of a 25-30 kt southwesterly LLJ. Activity should be
somewhat scattered/spotty early in the night, with rainfall chances
peaking during the early to mid-morning hours of Friday.

Both instability and deep-layer shear will be marginal at best, and
the severe weather risk is rather low. Cannot rule out a stronger
storm or perhaps a stronger cluster of storms this evening in the
western CWA. The main hazard would be locally gusty winds. However,
any weak instability overnight will be elevated in nature. The only
concerns overnight would be lightning and locally heavy rainfall.
Locally heavy rainfall may be a concern through Friday morning, and
spotty 1-2+ inch amounts look possible. Significant flooding is not
expected, so the main impacts would be ponding of water on highways
and perhaps localized standing water in low-lying areas.

Low temperatures Friday morning will be in the upper 60s to lower
70s. Friday will start off cloudy and fairly wet. However,
conditions will gradually dry out during the afternoon and evening
as the front moves through the region and drier air filters in from
the west. Some late day sun looks probable in most areas, with the
exception of perhaps the far southeastern CWA. Highs will be in the
mid/upper 80s.

&&

.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
Issued at 301 PM EDT Thu Aug 15 2024

Friday Night through Sunday Night....

Trailing surface cold front is forecast to be in the vicinity of the
Midwest Friday evening.  Scattered thunderstorms will be possible
across the region, though it looks like the most concentrated area
of storms would be over central OH ahead of the approaching mid-
level trough axis, and then across southern TN on the remnant
outflow from the earlier day activity.  Some additional convective
development is possible late Friday night and into early Saturday
morning as the cold front approaches our region.  The frontal
boundary looks to cross the Ohio River in the 17/10-12Z time frame
and then into southern KY during the afternoon. Lows Friday night
will be in the upper 60s to the lower 70s.

The upper trough axis will remain in place across the region on
Saturday with additional convective redevelopment likely Saturday
afternoon and evening.  Convergence along the frontal boundary
continues to be rather modest.  However, diurnal heating and
marginal shear will be in place to produce some amount of organized
convection, likely in clusters or small linear segments.  Heavy
rainfall, gusty winds, and lightning would be the main threats with
this activity.  Overall, the scenario advertised here supports at
least a marginal risk of severe given uncertainties on instability,
cloud cover and convective evolution.  Highs on Saturday carry a bit
of uncertainty given potential cloud cover and ongoing convection.
Highs in the mid-upper 80s seem reasonable here, though a few spots
that get a bit more sunshine could touch 90.

Some scattered convection will likely persist into the evening hours
before gradually winding down due to the loss of heating and
increased CINH during the evening.  Overnight lows will drop into
the mid-upper 60s.

A closed upper low will remain in the vicinity of the Great Lakes on
Sunday and will slowly move into southern Ontario through the day.
Associated upper level trough axis will pivot slowly eastward into
eastern KY during the afternoon.  Diurnal heating and expected
destabilization will result in additional convection firing during
the afternoon with the greatest coverage in areas east of I-65.
Temperatures will likely be held down by convection and
ongoing/existing cloud cover with highs in the low-mid 80s.  The
upper trough axis will continue to migrate eastward Sunday night
with drier conditions pushing in from the west. Sunday night lows
will be in the lower-mid 60s.

Monday through Thursday...

Moving into next week, the upper level flow across the CONUS will
become quite amplified again with a trough axis along the NW Pacific
coast and a large trough axis along the east coast.  In between
these features, another ridge axis is forecast to develop across the
high Plains.  This ridge does not appear to grow that much to the
east during the week, and the Ohio Valley looks to remain in a deep
northerly to north-northwesterly flow through the period.  Overall,
much of the synoptic guidance has little in the way of perturbations
coming around the ridge in the Monday-Wednesday period.  However, we
may start to see that change by late Wednesday/Thursday.  For now,
plan on going with a dry forecast for the period.

Given the sharp northerly flow and the core of the ridge remaining
west of the region, temperatures will average well below late August
normals through the period.  In fact, much of next week will feel
more like September.  Daytime highs Monday and Tuesday will range
from the upper 70s to the lower 80s, warming into the low-mid 80s by
Wednesday/Thursday.  Overnight lows will generally be in the mid-
upper 50s.  However, there is a rather strong signal that good
radiational cooling setups may occur, especially in the Tue night-
Wednesday night period.  Here, our typical radiational cooling spots
and valley locations could easily see temps drop into the upper
40s/lower 50s.

&&

.AVIATION /00Z TAFS THROUGH 06Z SATURDAY/...
Issued at 707 PM EDT Thu Aug 15 2024

Showers and storms have started to develop in portions of the Plains
and Midwest; depending on how these evolve and grow upscale, some
TAF sites may be impacted by them tonight into tomorrow morning.
Confidence in their exact track remains low, but there is a decent
signal for a more widespread wave of rain and embedded storms to
impact the area in the 08z-14z timeframe. As such, have carried SHRA
with prob30 thunder mentions for time being. Any site impacted by a
heavier shower or storm will see brief reductions in cigs/vis.

We should steadily dry out tomorrow by late morning or early
afternoon, with partial clearing expected by the afternoon. More
showers and storms may fire off in the afternoon, though confidence
in where those may form remains too low to warrant mention in TAF.

Outside of showers/storms, ceilings and visibilities are expected to
be in the VFR range.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...None.
IN...None.

&&

$$

SHORT TERM...EBW
LONG TERM...MJ
AVIATION...DM