140 
FXUS63 KLMK 030453
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
1253 AM EDT Wed Jul 3 2024

...Updated Aviation Discussion...

.KEY MESSAGES...

*   A heat advisory is in effect Wednesday afternoon and evening for 
    areas primarily along and west of the I-65 corridor. Heat 
    indices within the advisory area could be as high as 107 
    degrees. 

*   Unsettled weather expected Wednesday afternoon through Friday 
    with daily chances of showers/storms.  Strong storms will be 
    possible each day with potential for isolated flash flooding. 
    Isolated damaging wind gusts, torrential rainfall, and intense 
    lightning will be the primary hazards.

&&

.UPDATE...
Issued at 929 PM EDT Tue Jul 2 2024

Things are quiet across the CWA this evening with light S winds and 
mild temperatures ongoing. Overnight lows are expected to stay 
pretty mild tonight given surface wind staying up a bit and keeping 
the low levels a bit mixy. Some variable upper cloudiness later 
tonight could also help a bit. As a result, lows are only expected 
to settle in the 70s for most. 

Some model data shows a few blips of QPF toward sunrise across our 
area, and although can't completely rule that out will elect to keep 
a dry forecast going as coverage would likely be less than 20% 
anyway. There is enough of a LLJ around that time to at least 
warrant raising the "silent" pops a bit. Still, values will be less 
than 10% for this forecast update.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 340 PM EDT Tue Jul 2 2024

Summertime temps and humidity are slowly making a return to the 
region today. Southerly return flow on the back side of a ~1025mb 
high centered near the Mid-Atlantic has helped to push temps well 
into the 80s and even some low 90s at this hour, with dewpoints 
climbing into the low 70s (southern KY) to ~60 (southern Indiana). 
Despite a cu-field developing where dewpoints are higher, warmer air 
aloft has helped to suppress any sort of vertical convective 
development so storm chances should be near 0% for the remainder of 
the day. 

Except for some passing high clouds, skies will clear out overnight. 
The region will be on the outer fringes of a LLJ that will develop 
and stretch from the central Plains into the upper Ohio Valley, 
which will help to keep surface winds steady but generally light 
(<10kts). This will also result in overnight lows not falling to 
more typical climo values, and it's possible some urban areas could 
stay in the 80s for the majority of the overnight period. 

The forecast for tomorrow is a bit complicated and will be heavily 
influenced by how convection evolves over the Midwest. Some high-res 
models indicate that a decaying line of showers/storms may push into 
the region tomorrow morning, leaving an outflow boundary lingering 
across portions of southern Indiana and/or central Kentucky for 
additional development later in the day. Additionally, a weak 
frontal boundary across southern IL into central IN will likely 
serve as a focus for more convective development tomorrow afternoon, 
and those showers/storms will likely drift into the region by late 
afternoon or early evening. 

These showers and storms will be moving into an environment with 
marginal deep layer shear (20-30kts effective bulk shear) but modest 
instability and DCAPE to support wet microbursts in the stronger 
convection. Therefore, the greatest severe risk tomorrow will be 
damaging winds in the strongest storms. On top of the wind threat, 
PWATs will be quite high (>2") so torrential rainfall is likely in 
many of the showers/storms. The orientation of storm motions to the 
projected outflow/frontal boundaries do raise some concern, as they 
are nearly parallel which would result in localized training of 
storms that may drop several inches of rain in a short amount of 
time. Where these boundaries set up still remain a bit uncertain, 
and the scope of the threat doesn't look large enough to support a 
flood watch, but localized flash flooding does look possible in this 
setup. 

Another concern going into tomorrow is heat potential. While the 
convective evolution and any potential clouds from leftover morning 
storms may limit or slow down heating during the day tomorrow, there 
is enough confidence to go with a heat advisory for portions of the 
CWA (mainly along and west of I-65) tomorrow afternoon. Confidence 
is lowest across the north where convection would have the greatest 
impact on temperatures.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Issued at 340 PM EDT Tue Jul 2 2024

Looking into the long-term, beginning Wednesday night, an upper high 
will cover the southeastern US while a shallow upper trough, 
centered over the Rockies, directs west-southwest flow from the 
Central Plains towards New England. This places southern Indiana and 
central Kentucky in the area in-between the main flow and the high 
to the south. This also lines up with where a southwest to northeast 
or west to east oriented front will be located, and with surface 
high pressure sitting just off the Atlantic Coast, lots of Atlantic 
and Gulf moisture will be funneled up the Mississippi and Ohio River 
Valleys, into the CWA and along the front. This front will sit near 
or over the CWA until the upper trough begins to amplify and 
generates a cold front that pushes east across the Lower Ohio Valley 
Friday afternoon. 

Timing is still impossible to lockdown, but don't think the period 
will be a total washout. Currently, it looks like Wednesday night 
into Thursday morning could be more active with a break sometime on 
Thursday before the heating of the warm air mass causes more 
convection to develop during the afternoon and evening hours. Expect 
isolated to scattered storms for period before the passage of the 
cold front on Friday, but it's not going to non-stop rain. It's 
summer time convection. There will be winners and losers.  

Precipitable water values could increase up to around 3" along this 
front, according to the NAM. Most of the ensembles have this values 
around 2.25" spread out over a larger area, and some of the global 
models are sitting a little higher than the ensembles. Generally, 
north of the front to near Indianapolis values tend to be higher 
than south of the front. PWATs over 2" could cover Indiana up to 
around Indianapolis while south of the front, PWATs drop off 
quicker, but not by much. PWATs could still be around 1.8" or so 
near Clinton County, and when PWATs are over 2" around here, it 
doesn't take much to be concerned with intense rainfall. 3" PWATs 
are unheard of, so if this materializes and depending on where the 
front sets up, we could see some areas of flash flooding or at least 
ponding of water.

The severe threat appears to be limited. During Thursday and Friday, 
models soundings show deep saturation with lots of "long skinny 
CAPE", and with temperatures in the upper 80s to 90 for highs, 
believe heavy rainfall will be the main concern. MLCAPE values are 
slightly over 1,000 J/kg. Some gusty winds with isolated to scattered 
storms will be possible, but with the likelihood of precipitation 
riding along the front from west to east, the risk of training 
convection concerns me more than the wind threat.

In general believe this system has trended farther south towards the 
Interstate 64 corridor. Yesterday, it appeared more of the activity 
would be slight farther to the north over south-central Indiana. 

Behind the front, high pressure will bring mostly clear skies with 
lower dew points in the mid 60s. With temperatures in the mid 80s to 
near 90, this will feel slightly better.

&&

.AVIATION /00Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1252 AM EDT Wed Jul 3 2024

The pre-dawn hours will be quiet with mostly clear skies and a light 
breeze out of the south. A low level jet is expected to develop from 
BNA to CMH but should remain weak enough to stay below LLWS 
threshold.

Today will be a hot and muggy day as a cold front approaches from 
the northwest. Scattered summertime thunderstorms are expected to 
develop by late afternoon and continue into tonight. Very heavy 
downpours and gusty winds will be possible with the storms. 
Confidence is low in the exact location of convection, but high 
enough to include PRO30s at all sites, and went ahead with a VCTS at 
SDF late tonight as the front approaches the Ohio River. Winds may 
be somewhat chaotic tonight with thunderstorms and various outflow 
boundaries.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...Heat Advisory from 1 PM EDT /noon CDT/ this afternoon to 8 PM 
     EDT /7 PM CDT/ this evening for KYZ023>031-034-038-045-
     053-061>063-070>074.
IN...Heat Advisory from 1 PM EDT /noon CDT/ this afternoon to 8 PM 
     EDT /7 PM CDT/ this evening for INZ076>078-083-084-
     089>092.

&&

$$

UPDATE...BJS
SHORT TERM...DM
LONG TERM...KDW
AVIATION...13