884
FXUS63 KLMK 051455
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
1055 AM EDT Wed Jun 5 2024

.KEY MESSAGES...

*   Scattered showers and storms likely again today. A few strong to
    severe storms are possible. Gusty winds and torrential rainfall
    will be the main threats.

*   Drier weather and cooler temperatures are favored late week into
    the first half of this coming weekend.

&&

.UPDATE...
Issued at 1055 AM EDT Wed Jun 5 2024

Morning satellite imagery showed mostly cloudy skies across southern
IN and central KY.  Temperatures were in the low-mid 70s across the
region.  WV imagery shows a few MCVs moving across the region.  One
was down near the BWG area and moving east which will help drive
additional convection across our eastern forecast area this morning.
A second MCV was noted across far western KY.  Latest CAMs show this
feature moving eastward and generating additional convection across
the I-65 corridor later this morning and into the afternoon hours.

Mesoscale analysis shows rather low values of MLCAPE this morning
with rather meager lapse rates.  PWAT values range from 1.6 to 1.9
which indicate a pretty rich moisture environment.  Shear isn`t
overly impressive this morning with 20-25kts.  So storm this morning
and into the early afternoon will likely be torrential rain
producers once again with some gusty winds and frequent lightning.
Main question is after this wave moves through this afternoon, will
we see some partial clearing and additional destabilization?
Uncertainty remains here with that and we`ll continue to monitor.
Overall thinking is that clouds and precip may end up keeping our
temps down, hence instability may end up being a bit more muted.  A
second line of showers/storms is likely to come into the region
later this evening and will also be capable of producing torrential
rainfall, gusty winds, and frequent lightning.

Current forecast has this well in hand at the moment.  We did make
some minor adjustments to the weather elements and local products
have already been published.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 324 AM EDT Wed Jun 5 2024

Things are pretty quiet across the CWA at this hour, outside of a
few lingering showers along and east of the I-75 corridor. These
will continue to push slowly east and exit our area in the pre-dawn
hours. Continuing to monitor for some early morning fog potential,
but still think this threat will be mostly mitigated by variable
cloudiness and light winds/subtle low level jet keeping the near
surface areas a bit too mixy.

Expecting a couple of distinct rounds of convection for later today.
The first wave should enter our SW just before sunrise and looks to
mainly be associated with a remnant MCV. Seeing a clustering of
convection with this feature currently across western TN, and it
should work SW to NE across our CWA through the morning and early
afternoon hours. Most of the coverage is expected to travel along
and south of the Parkways, but honestly a stray shower or storm
could trigger anywhere around this feature as it moves through. For
now, have the highest pops with the first wave across the center and
southern portions of the CWA. The main threats with this first wave
of storms will be locally heavy rainfall, cloud to ground lightning,
and some gusty winds. Most concerned about some isolated flooding
spots given that PWATs are currently pooling around 1.7-1.9" with
the MCV, and it will only slowly push NE through early afternoon.
Noticed that some localized areas have 1 hour FFG values below
1.25", and any repeated t-storm activity could lead to some problems
pretty quickly. These "hot spots" are pretty localized, however and
more widespread issues are not anticipated.

First wave pushes E by early to mid afternoon, and then focus will
shift upstream for shower and storm redevelopment just ahead of the
approaching cold front. Morning wave may have an impact on how we
destabilize ahead of the next wave, but overall it doesn`t take long
this time of year. Highs should still reach the low to mid 80s
pretty easily. HREF shows similar probabilities to yesterday of ML
CAPE values reaching up around 1000-1500 J/KG. Best probabilities
are across our northern CWA, which makes sense given where the wave
1 MCV is expected to track earlier in the day. Overall, deep layer
shear looks to be weak, but perhaps a tick stronger than yesterday,
and just a bit closer to values that are more supportive of weakly
organized updrafts. Given what we`ve seen the past couple of days
with water-loaded downdrafts, can`t rule out a couple strong to
severe storms (wind), especially across our north CWA through the
evening hours. The better likelihood is for more typical
thunderstorms with gusty winds, locally heavy rain, and lightning.
Like the Marginal Risk just to our north, where the slightly better
dynamics look to reside. Also like the WPC Marginal Risk for
excessive rainfall, as we have seen localized instances of flooding
each of the past 3 nights. That threat is also still on the table
until frontal passage late this evening.

We dry out W to E later tonight with frontal passage. Temps are
expected to fall into the 60-65 range by dawn on Thursday.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 324 AM EDT Wed Jun 5 2024

Thursday through Friday Night...

By sunrise Thursday morning, the last of the showers and
thunderstorms should be clearing into the central and southern
Appalachians as the primary sfc frontal boundary pushes east of the
region. While the bulk of the deep moisture will clear with this
initial frontal passage, there should be a little bit of lingering
low-level moisture, especially south of the Ohio River. A secondary
frontal boundary is expected to dive through southern IN and central
KY Thursday afternoon, with a more substantial fetch of dry air
arriving behind this front. As this front crosses the region, a
narrow plume of higher PWAT values may be just sufficient when
combined with frontal lifting to support isolated showers or even a
shallow thunderstorm. Since the ingredients look fairly marginal at
this time, will only advertise a 10 PoP for most of the region, with
locations east of US 127 seeing the best chance for a shower
Thursday afternoon.

Otherwise, as the secondary FROPA occurs, winds should veer from WSW
to WNW, beginning the process of advecting cooler and drier air over
the region. Highs on Thursday will be near normal (low-mid 80s) with
much of the diurnal heating occurring before FROPA and the onset of
CAA occurs.

Cooler and drier air will continue to filter into the Ohio and
Tennessee valleys Thursday night through Friday night, setting up
what should be quite pleasant weather for the end of the week. Both
the NAEFS and EPS ensemble mean PWAT values are around the 10th
percentile of model climate Friday into Friday night, with
forecasted dewpoint temperatures settling into the upper 40s and
lower 50s on Friday. Breezy NW winds should continue on Friday as a
nearly stacked low meanders across southeast Canada, leaving much of
the eastern CONUS in a NW flow pattern. Temperatures Thursday night
though Friday night should be below climo, with highs in the upper
70s to near 80 and lows in the 50s and lower 60s.

This Weekend into Early Next Week...

Large-scale pattern agreement remains relatively high through this
coming weekend, with negative height anomalies stretching NW-SE from
the Canadian Prairies into the northeast CONUS while upper ridging
remains in place across the intermountain west. Brief blocking
pattern over the Canadian Maritimes should abate by the first part
of next week, allowing for some eastward progression in the overall
pattern. This should allow for some de-amplification in the pattern
by the middle of next week, with the magnitude of negative height
anomalies across the eastern half of North America expected to
gradually decrease.

The main source of forecast uncertainty over the weekend centers
around how much moisture return makes it into the region as the
upper low contorts to our north, with a secondary upper trough
expected to drop south through the eastern CONUS for the second half
of the weekend. The GFS favors faster/more moisture return on
Saturday, which would lead to a return of precipitation chances
Saturday afternoon and evening, with higher chances the farther
southwest you go. On the other hand, the ECMWF solution is slower
with moisture return, keeping Saturday dry. However, by the time the
secondary upper trough dives into the region on Sunday, this
solution shows enough moisture return to facilitate precipitation
chances for Sunday and Sunday night. In contrast, the GFS shows the
moisture suppressed well into the TN Valley by Sunday, leading to a
drier solution for the second half of the weekend. As a result,
confidence in any one day this weekend being wetter versus drier is
fairly low at this time. For now, will advertise a general chance
PoP through the weekend, with the expectation that the weekend
should by no means be a washout.

For the start of next week, the secondary trough should bring a
reinforcing shot of cooler and drier air. ECMWF Extreme Forecast
Index values for MaxT are around -0.7 next Monday, indicating medium-
high confidence in below normal high temperatures. With the pattern
turning more progressive, a gradual return to warmer temperatures
would be expected through the middle of next week as higher heights
and layer thicknesses overspread the Ohio and Tennessee Valleys.

&&

.AVIATION /12Z TAFS THROUGH 18Z THURSDAY/...
Issued at 644 AM EDT Wed Jun 5 2024

Tricky forecast cycle ahead as low ceilings, periods of showers and
storms, and some visibility restrictions could all come into play at
times. Later this morning, a better chance for low MVFR ceilings is
expected as a stratus deck briefly sets up, however a return to VFR
ceilings is expected again by early to mid afternoon.

Do expect scattered showers and thunderstorms to develop in a couple
of waves. One will be this morning, and another later this afternoon
into the evening ahead of an approaching cold front. Given a moist
and unstable atmosphere, some locally heavy rain could easily reduce
vis briefly into the IFR range with any storm. Also have a period of
fairly strong S gradient winds between 10 and 15 mph, gusting up
around 20-25 mph at times. Cold front passes later tonight with
conditions drying out and light W winds taking hold.

&&

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

&&

$$

UPDATE.......MJ
SHORT TERM...BJS
LONG TERM....CSG
AVIATION.....BJS