264
FXUS63 KLMK 311924
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
324 PM EDT Fri May 31 2024

.KEY MESSAGES...

*   Rain and storm chances return for the weekend and continue into
    next week. Temperatures and dewpoints will also be on a steady
    increase into next week.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 323 PM EDT Fri May 31 2024

High pressure over the central Appalachians will keep our weather
generally quiet and dry for most tonight. A small area of weak low
pressure moving eastward out of the Ozarks may introduce showers
well after midnight west of I-65, but any showers would be scattered
and very light. Low temperatures by sunrise will vary widely from
the lower 50s in the Blue Grass closer to the high...to the lower
60s in southwestern portions of central Kentucky closer to the low
and under thicker, more widespread cloud cover.

On Saturday a 500mb shortwave trough will slowly move into the Ohio
Valley from the west. Precipitable water values will be only
slightly above normal, and afternoon dew points should only be from
the mid 50s in eastern sections of central Kentucky to low 60s west.
In addition, instability will be very weak. So, we`re expecting
primarily showers with perhaps a few embedded rumbles of thunder.
High temperatures should be in the middle to possibly upper 70s,
depending on how widespread the clouds and showers are.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
Issued at 323 PM EDT Fri May 31 2024

Synopsis...The medium-range forecast will see a return of warmer and
wetter conditions than the past several days. The period will start
off with a weak, mid-level shortwave trough and attendant surface
low moving across the Lower Ohio Valley while the formerly-placed
upper ridge and surface high pressure weaken and relocate to the
Eastern Seaboard. This will lead to scattered showers and isolated
storms the second half of the weekend. For next week, attention
turns to a powerful, northern-stream trough approaching from the
Pacific Northwest accompanied by a large upper-level anticyclone on
its southern flank. The anticyclone is eventually expected to stall
and build from Texas to the Northern Rockies, allowing the trough to
amplify and potentially close off over the Great Lakes vicinity with
broad cyclonic circulation covering portions of the Eastern CONUS.
At the surface, main low will occlude as it meanders over the Upper
Midwest and southern Canada pushing a cold front to the Ohio Valley
on Wednesday that will enhance regional storm chances.

Model Evaluation/Confidence...Deterministic models agree fairly well
on the large-scale pattern evolution through Monday with usual
uncertainties regarding the mesoscale environment and its
interaction with smaller wave energy. The latter will play a role
defining onset and ending times of rain chances as well as best
storm coverage. On the other hand, model confidence decreases on
Tuesday and onwards regarding the progression and downstream
amplification of the powerful, northern-stream trough while
questions still remain with the strength of the blocking ridge to
the west. Overall, the consulted deterministic guidance
(GFS/ECMWF/CMC) show the amplifying wave over the Great Lakes but
the Canadian remains on the faster and weaker end of the spectrum as
it closes off and ejects the upper low quicker than the rest of the
guidance. On the other hand, the GFS and ECWMF offer similar
solutions with a slower and stronger trend during the last several
runs. Last but not least, ML-based guidance is hinting at low
chances of severe weather next Wednesday with the frontal passage;
however, low confidence is placed in any severe weather based on
current model variability.

Sat Night - Sunday...Presence of weak, mid-level shortwave trough
and attendant surface low will provide sufficient synoptic/mesoscale
forcing to increase precipitation chances, especially Saturday night
and Sunday morning when a modest 850-mb jet enhances moisture
advection over the region and the profile saturates. Most of the
shower activity appears to be stratiform with some embedded messy
convective elements, judging by poor mid-level lapse rates, stable
surface to 850-mb layer, and weak deep-layer shear. Severe weather
is not anticipated at the moment. In addition, areal and river
flooding concerns are low during the weekend as 48-hr rainfall is
progged to be around an inch and soils have been able to dry during
the past several days. That being said, some ponding and minor
flooding issues could arise if convective training occurs. Best
storm chances might be present Sunday midmorning and afternoon over
south-central KY where potential instability and better mid-level
lapse rates should promote stronger updrafts. Drier airmass will
arrive Sunday evening.

Monday - Wednesday...Still expecting warmer temperatures and
increased humidity given theta-e advection amid southerly low-level
winds. Brief and weak southern-stream vort waves will provide
intermittent sources of lift during Monday and Tuesday to maintain
daily rain chances in the forecast. As mentioned above, there is
lower confidence in timing and coverage of precipitation and storm
chances early in the week, even though the late afternoon and early
evening periods are favored considering lack of strong lifting
mechanisms and generally weak steering currents. Some of the diurnal
convective activity could become strong Tuesday afternoon based on
GFS forecast soundings showing strong moderately high SB-CAPE and
steep mid-level lapse rates. As a result, if updrafts are able to
overcome the low-level cap, the pulse convection cannot be ruled
out. For Wednesday, strong to potentially severe storms appear
possible as the cold front moves through the region, but there is
still too much uncertainty to place sufficient confidence in this
scenario.

Thursday - Weekend...Very low confidence in weather elements during
the period as model uncertainty increases substantially. All in all,
forecast indicates slow lowering trend in rain chances towards the
weekend with slightly cooler temperatures.

&&

.AVIATION /18Z TAFS THROUGH 00Z SUNDAY/...
Issued at 114 PM EDT Fri May 31 2024

With high pressure over the upper Ohio valley this afternoon surface
winds will continue to come in from the ESE around 10kt with a few
higher gusts. VFR conditions will continue with cirrus as the
predominating cloud type.

Tonight a 500mb shortwave trough will approach from the west.
Borderline LLWS may materialize at HNB and BWG as a compact low
level jet forms over the Tennessee Valley. Ceilings will gradually
lower and thicken from west to east, with showers moving into the
region by early Saturday morning. Showers will overspread the area
during the day, with some scattered thunder possible especially in
the afternoon. Will stick with mostly VFR conditions although some
MVFR ceilings and vsbys may form once the showers move in tomorrow.

&&

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

&&

$$

SHORT TERM...13/CJP
LONG TERM...ALL
AVIATION...13