903
FXUS63 KLMK 012338
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
738 PM EDT Sat Jun 1 2024

...Updated Aviation Discussion...

.KEY MESSAGES...

*   Shower and storm chances Sunday and each day Tuesday through
    Friday. A few strong to severe storms may form Tuesday, with
    slightly better chances for a few severe storms on Wednesday.

*   Highs in the 80s Tuesday through Thursday. The highest
    daytime relative humidity will be on Tuesday and Wednesday.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 312 PM EDT Sat Jun 1 2024

The upper wave that brought us clouds and showers today will
deamplify as it moves overhead tonight. Clouds and showers will
persist through the night, but shower coverage should slowly
decrease as the wave moves through and precipitable waters decrease
slightly, especially after midnight with rainfall amounts between
sunset and sunrise less than a third of an inch. With very weak
instability it continues to appear that any thunder would be
isolated. Widespread cloudiness and a south breeze will keep
temperatures from dropping much, with morning lows in the 60 to 65
degree range.

There`s good model agreement on higher instability tomorrow, though
morning clouds will have an effect on how much instability can
develop. Today`s wave will be off to the east and shear will be very
weak. So, at this time more widespread patchy light rain is expected
in the morning followed by scattered showers and a few thunderstorms
with destabilization in the afternoon ahead of a broad surface
trough. Any storms that do get going should rain themselves out
quickly. Precipitation loading, and some dry air present aloft, may
lead to some slightly enhanced wind gusts, but organized severe
weather is not anticipated.

&&

.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
Issued at 312 PM EDT Sat Jun 1 2024

Discussion...Quasi-zonal and relatively slow flow aloft will be
present over the Lower Ohio Valley at the beginning of the extended
period. Furthermore, subtle wave energy will cross the Mid
Mississippi Valley towards the east as mid-level ridge and surface
high pressure build over the Northeast US. A more dynamic and
unsettled pattern is in store by the middle of next week as a strong
northern stream trough moves from the Pacific Northwest to the
Northern Plains and eventually the Upper Midwest. Additional
upstream Canadian energy interacting with the shortwave trough and
large blocking anticyclone over the Rockies will lead to the
development of a deep, occluded low over the Great Lakes vicinity.
As a result, the Lower Ohio Valley will likely experience increasing
rain and storm chances Wednesday and onwards as a cold front
translates through the region. Lastly, the upper low and occluded
surface cyclone complex will meander into the weekend with some
potential of amplifying southward into the Southeast US.

Model Evaluation/Confidence...Confidence is relatively high for most
of the forecast elements through Tuesday except for precipitation
coverage and convective intensity given the absence of defined
synoptic lifting mechanisms and dependence on mesoscale and smaller
scale factors difficult to predict at this time. Confidence in the
rest of the extended period continues on the low side as
deterministic model guidance shows model-to-model and run-to-run
variability with the pattern amplification/blocking across the
CONUS. All in all, the GFS and ECMWF seem to handle the mid-level
wave pattern somewhat similar while the CMC follows a weaker and
faster trend more in line with the EC-AIFS. Such variability
potentially leads to timing differences with the frontal passage
and, therefore, uncertainty in the rain and storm coverage and
intensity. As for severe weather probabilities, the latest CSU ML
algorithm maintains a low chance for Wednesday with notable chances
in the placement of the outlined areas, in agreement with ongoing
uncertainty.

Sun Night - Tuesday...Lowering rain chances will follow Sun night
into Monday morning as dry low- to mid-level air is advected into
the area behind the departing weak surface low. GFS model soundings
show near-surface saturated conditions amid weak low-level winds and
some mid-level subsidence, so fog/stratus event is possible Sunday
night into Monday morning across central Kentucky and portions of
southern Indiana. A quick transition towards a wetter profile will
occur during the day on Monday as Mid Mississippi shortwave energy
favors theta-e transport over the Ohio Valley. Although the role of
these waves as triggering mechanisms is not guaranteed, they will
probably enhance any convective development early in the week. So,
deep convective initiation will depend on mesoscale interactions in
the afternoon after convective temperatures are met. That being
said, the presence of moderately strong instability, weak steering
currents, and decent low-level lapse rates could spark pulse
convection with a threat of gusty winds and hail as the main
hazards. In this regard, Tuesday appears to have better chances of a
conditional threat of strong to marginally severe weather as well as
minor flooding issues if storms become stagnant as PW values soar
above 1.5 inches, according to GFS.

Wednesday - Thursday...As mentioned above, higher rain and storm
chances exist for Wednesday and ultimately Thursday as the cold
front moves through the region. Best chances of strong to
marginally severe weather next week are focused around Wednesday, as
shown by ML-based guidance, given strong instability and additional
convergence ahead of the front. Nonetheless, confidence in organized
severe weather remains low as deep-layer shear remains muted and
displaced to the north. Therefore, main severe hazards on Wednesday
could be gusty winds and hail associated with individual convective
elements or poorly-organized multicell clusters. Storm and rain
chances will decrease on Thursday, but still anticipating lingering
showers under breezy conditions.

Friday - Weekend...Forecast exhibits low confidence as models
disagree on the large-scale pattern. Overall, expect lowering rain
chances towards the weekend with slightly cooler temperatures.

&&

.AVIATION /00Z TAFS THROUGH 06Z TUESDAY/...
Issued at 737 PM EDT Sat Jun 1 2024

Weak sfc low and associated upper wave over the Upper Mississippi
Valley will slowly move eastward overnight into tomorrow. Bulk of
the light showers are tapering off from west to east with the bulk
of the rain over LEX/RGA. There`s some activity firing across
southern IL and far western KY this evening but a lot of that
activity should diminish some with the loss of daytime heating. Will
start to see more MVFR CIGs through the overnight with even a period
of IFR CIG closer to the start of the day tomorrow. We should see an
improvement by the end of the period from west to east with a
gradual CIG rising from the IFR in the morning to MVFR to VFR by the
afternoon. The only thing of note would be the possible development
of isolated storms in the afternoon from SDF-LEX-RGA. For now left
them out for the most part as confidence is not all that high.

&&

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

&&

$$

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