510
FXUS63 KLMK 070715
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
315 AM EDT Fri Jun 7 2024

.KEY MESSAGES...

*   Pleasant weather expected today with mostly sunny skies and low
    humidity.

*   Showers and a few thunderstorms this weekend. Locally heavy
    downpours possible late Saturday night into early Sunday morning
    across western and southern Kentucky.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 313 AM EDT Fri Jun 7 2024

Across the region this morning, mostly clear skies are observed on
nighttime microphysics satellite imagery as a swath of deep dry air
is continuing to work into the Ohio and Tennessee valleys from the
north and west. A broad upper level trough axis stretches from
central Ontario down into the southern Appalachians, with deep layer
NW flow present over the region helping to advect in significantly
drier and marginally cooler air. Satellite imagery also shows valley
fog developing over eastern KY at this hour; while some isolated
valley fog may develop between now and sunrise (especially in the
Cumberland River valley), a more persistent light westerly wind and
drier air should limit fog overall. Light winds, clear skies, and
dry air has allowed for efficient cooling thus far this morning,
with lows expected to fall into the 50s in most locations outside of
the Louisville heat island.

Today should feature excellent weather across central KY and
southern IN, as the dry air mass over the region brings us mostly
sunny skies and low humidity values. It will still be a bit breezy
late this morning and into the afternoon hours as diurnal mixing
allows for 20-25 kt NW flow around 850 mb to mix down to the
surface. Expect W/NW winds of 10-15 mph with gusts to around 20 mph
today, with winds once again slackening off by around sunset
tonight. Temperatures should only be slightly below climatological
norms with highs expected to reach the upper 70s and lower 80s;
however, afternoon dewpoints in the upper 40s and low-to-mid 50s
will make things feel quite pleasant.

Tonight, the dry air mass overhead will begin to give way as sfc
high pressure and ridging aloft over the lower Mississippi Valley
flattens, with moisture from the Great Plains beginning to work over
the top of the ridge and into the Ohio Valley after midnight.
Additionally, an MCS which is expected to develop over Nebraska late
this afternoon will promote the development of a convectively-
enhanced shortwave which will eject southeastward overnight into
early Saturday morning. Significant instability will remain well
west of the Mississippi Valley, so any convective complex which
develops later today will be much weaker by the time it enters our
area. The forecast late tonight will be strongly influenced by the
evolution of the upstream MCS, with latest convection-allowing
guidance showing the remnants reaching northwestern portions of the
CWA as some light-to-moderate rain showers by around sunrise
Saturday. Before moisture and clouds increase early Saturday
morning, temperatures should be able to cool into the 50s and lower
60s, with temperatures likely remaining fairly steady or even
slightly increasing toward dawn Saturday morning.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Issued at 313 AM EDT Fri Jun 7 2024

The Weekend...

MCS development is expected tonight over MO/IA/IL ahead of a strong
low level jet across Kansas and Missouri. Remnants of that complex
will slide ESE into the lower and middle Ohio Valley Saturday
morning, bringing mostly showers and a few embedded rumbles of
thunder. Given these morning clouds and showers, it may be difficult
to destabilize much in the afternoon, resulting in the best rain
chances on Saturday occurring in the morning.

Saturday night a WSW-ENE oriented cold front will slip in from the
northwest and will likely be draped somewhere along Kentucky by dawn
Sunday. The LLJ Saturday night is expected to be much weaker than
tonight`s, but fairly impressive precipitable water air of 1.75-2"
will pool along the front, resulting in widespread rain from Kansas
to Kentucky. Deep layer shear vectors oriented from WNW to ESE
suggest that showers/storms will move off the boundary, rather than
parallel to it, and models & WPC are progging the heaviest rainfall
amounts to our west over southern Missouri. Still, with such high
PWATs and the QPF pattern stretched out linearly along the surface
boundary, locally torrential downpours and minor flooding issues may
still arise, primarily after midnight into early Sunday morning
across western and southern Kentucky, especially if any training
occurs.

Instability has increased slightly for the weekend, primarily
Saturday evening through Sunday morning, so will continue to
advertise the possibility of scattered thunder.

Next Week...

Three runs ago the operational GFS was dry on Monday-Tuesday...and
now has about 2/3" of rain in southern Kentucky Monday afternoon,
and more Monday night-Tuesday, as a wave of low pressure rides up
the weekend front, which by Monday should be over the Southeast.
However, looking at GEFS plumes with regard to QPF, the operational
GFS is a significant outlier. Looking at the individual
perturbations of the GEFS, about half of the members are still dry.
The 07/00Z runs of the CMC and ECMWF are dry with the front being
pushed farther southeast by Canadian high pressure invading the
Great Lakes, and most members (though not all) of the Euro ENS are
dry. Given the operational GFS`s outlier status and the sudden jump
from dry to wet, will refrain from buying totally into that
solution. However, still shouldn`t discount it completely, so will
go ahead and hold on to the 20-30% PoPs suggested by the NBM.
Confidence, however, is very low for Monday-Tuesday.

Confidence increases a bit for Wednesday-Thursday with a lack of
storm systems in the region and dry weather the result. By Thursday
temperatures will moderate into the middle and upper 80s, with 90
degrees possible Friday into the weekend as an upper ridge spreads
eastward from the Plains into the Great Lakes and Ohio Valley.

&&

.AVIATION /06Z TAFS THROUGH 12Z SATURDAY/...
Issued at 1254 AM EDT Fri Jun 7 2024

VFR conditions are expected through the current forecast period.
As expected, winds have slackened considerably compared to this
afternoon as a nighttime inversion has set in across the region.
Light westerly winds will continue through a few hours after
sunrise, when stronger winds aloft begin to mix down to the surface
with the help of daytime heating. Would expect to be able to mix
into 20 kt NW flow about 5 kft AGL by late morning through the
afternoon hours, with sfc wind gusts around that magnitude expected.
A dry air mass in place should limit cloud cover to a 5-7 kft FEW-
SCT cu field during the afternoon hours.

Tonight, moisture will start to return from NW to SE across the
region after 06Z, with an increase in mid and high clouds expected
initially. Winds are expected to go light and variable quickly after
sunset tonight.

&&

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

&&

$$

SHORT TERM...CSG
LONG TERM...13
AVIATION...CSG