789
FXUS63 KLMK 091947
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
247 PM EST Sat Nov 9 2024

.KEY MESSAGES...

*  Widespread rain and isolated storms are expected tonight through
   Sunday afternoon. Between 1.0 to 1.5" of rain expected for most
   with higher localized amounts.

*  Breezy non-thunderstorm winds Sunday afternoon.

*  Rain tapers off Sunday night. Mostly dry week ahead other than
   scattered showers Wednesday night. Temperatures slightly warmer
   than normal.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 246 PM EST Sat Nov 9 2024

Synopsis...Weakening upper-level low will translate from the Central
Plains to the Great Lakes in the next 24 hours as it drags an
occluded surface low and attendant fronts in a similar fashion.
Meanwhile, the currently reigning mid-level ridge and surface high
pressure will be displaced to the east and south allowing theta-e
advection and increasing rain/storms chances over the region during
tonight and tomorrow.

Model Evaluation/Confidence...There is medium to high confidence in
rainfall amounts through Sunday evening given large model agreement.
Most of the latest deterministic guidance (NAM/ICON/GFS/CMC) have
the greatest accumulations (1.0-1.5) focusing on a swath oriented SW-
NE across central Kentucky. Nonetheless, a tendency for a secondary
maximum of rainfall is observed along the Ohio River in models such
as the ECMWF, UKMET, RRFS, and HRW-FV3. Otherwise, probabilities of
organized severe weather are negligible based on the CSU ML Severe
Guidance and Nadocast.

Afternoon/Evening...Isentropic lifting/moisture ahead of a warm
front surging across the Deep South is contributing to overcast
skies and high-based radar echoes already streaming into central
Kentucky. Surface observations over northern Tennessee and KY
Mesonet are reporting light rain or sprinkles, with heavier
precipitation rates not expected until later this evening and
tonight when top-down moistening via evaporational cooling and
horizontal moisture advection saturate the low levels. No lightning
is expected this afternoon or early evening based on the lack of
forcing and mixed-phase hydrometeors as well as poor mid-level lapse
rates.

Tonight...GFS forecast soundings and several model outputs depict
better support for increasing coverage moderate rainfall showers
after 10/3Z given an almost complete saturated profile with PW
around 1.5-1.6 inches, arguably due to moisture transport from the
outer periphery of TC Rafael in the Gulf of Mexico. In addition,
enhanced forcing thanks to DCVA ahead of the ejecting upper low and
a developing 40+-knot low-level jet across central Kentucky could be
sufficient for isolated thunder chances overnight. This activity
will be elevated in nature as a strong near-surface inversion
emerges with the LLJ, limiting any momentum transfer from the winds
aloft. As for flooding issues, precip. accumulation before sunrise
should be close to 1.0 inch in some places which is below FFG at the
moment while HREF probabilities of 1"/hr are extremely low.
Therefore, widespread flooding is not expected with perhaps minor
localized ponding issues.

Sunday...Low-level jet will continue during the morning and
afternoon hours as it slightly strengthens and slowly lifts to the
northeast. Light to moderate elevated showers and isolated thunder
will still be ongoing during the first morning hours; however, there
might be an opportunity for breaks after 10/14Z as the activity
reorganizes to the west and best forcing moves to the east. Limited
daytime mixing will slowly erode the near surface inversion and some
gusts between 20-30 mph could be reported by midmorning and
especially during the afternoon. Persistent, thick cloudiness will
block any attempts of destabilization, so instability will be rather
meager in the afternoon. Then, hi-res guidance suggest a semi-broken
line of convection, that according to GFS soundings, has a better
chance to be surface based. If such a line materializes, then brief
heavy rainfall and lightning would be the main threats as weak
instability, poor lapse rates, and dry air entrainment will inhibit
severe weather once again.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Issued at 246 PM EST Sat Nov 9 2024

Sunday night the rain will taper off from west to east as the cold
front pushes through the region. Additional rainfall amounts will be
light, from little if any in southern Indiana to around a quarter of
an inch in the Lake Cumberland region.

Monday and Tuesday still look like very pleasant fall days with
plenty of sunshine and seasonable temperatures as high pressure
advances from the northern Plains to the Great Lakes. Though winds
will be light and mixing won`t be particularly deep, soundings
showing some very dry low level air so went on the low side of
guidance for afternoon dew points, especially Tuesday.

Wednesday and Thursday low pressure will weaken as it crosses
Ontario and drags its cold front through the Ohio Valley Wednesday
night. Gulf moisture attempts to return northward but the front is
progged to push through just as that moisture is about to arrive.
The better dynamics will be to our north as a sharp 5H shortwave
trough crosses the Lakes. As a result, just some scattered showers
are expected with this system from Wednesday evening into Thursday
morning. If the current fropa timing holds, total rainfall will
likely be around a tenth of an inch, if even that much.

We`ll return to dry weather Thursday and Friday as high pressure
moves right over us on its way from the Ozarks to the southern
Appalachians. This air mass will be Pacific (as opposed to Canadian
or Arctic) in origin, so temperatures will continue to be mild by
mid-November standards.

The next weather maker will begin to approach from the west this
weekend, especially by Sunday and into the early part of the
following week. CPC has outlooked a slight risk for heavy
precipitation November 17-19, which agrees with a local large-scale
signal analysis that was done, though there are some indications
that the corridor of heaviest rainfall will be off to our west. Stay
tuned.

&&

.AVIATION /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 1234 PM EST Sat Nov 9 2024

Impacts/Confidence:
- High confidence in MVFR CIG/VIS tonight as rain spreads the area
- High confidence in gusty southerly winds tomorrow
- Increasing confidence in non-convective LLWS later tonight through
Sunday morning if convection delays.

Discussion...Current VFR conditions will continue across the TAF
area until at least this evening. Then, a warm front approaching
from the Deep South will progressively increase rain chances and
lower the cloud base to MVFR thresholds. Heavier rain showers would
be strong enough to reduce visibility to MVFR levels, and perhaps
IFR at times. At the same time, a 50-knot LLJ will develop and
bisect the Lower Ohio Valley starting around 9Z and depart late
Sunday afternoon. Current concern is that given inversion in place
and low confidence in storm chances, moderate non-convective LLWS
would develop late tonight and during the morning hours. For the
time being, decided to leave out any storm or non-convective LLWS
mention in the TAF and let the next shift take a better look at it.
For Sunday, ceilings will gradually lower to IFR while south winds
turn gusty amid augmenting low-level mixing.

&&

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

&&

$$

SHORT TERM...ALL
LONG TERM...13
AVIATION...ALL