National Weather Service Raw Text Product

178 
FXUS63 KIND 241738
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
138 PM EDT Wed Jul 24 2024

.KEY MESSAGES...

- Scattered PM thunderstorms are expected today, a few of which 
  could be strong to potentially severe

- Locally heavy rainfall and isolated damaging wind gusts are the 
  main threat today from storms, but marginally severe hail cannot 
  be ruled out

- Wildfire smoke at times which may reduce visibility and air 
  quality

- Seasonable temperatures in the 80s through this weekend gradually 
  warming to near 90 early next week

&&

.FORECAST UPDATE...
Issued at 1038 AM EDT Wed Jul 24 2024

Only minor updates needed to the forecast as of 1030am. We have a 
small area of showers and embedded thunderstorms moving 
southeastward out of Illinois. These should be entering our far 
northwestern Counties shortly. Bumped up PoPs across the northern 
third of our CWA to account for this activity. CAMs tend to diminish 
it very quickly, which may not be entirely realistic given the 
presence of a weak cold pool and modest CAPE in the downstream 
environment.

&&

.MESOSCALE UPDATE...
Issued at 137 PM EDT Wed Jul 24 2024

A thunderstorm complex is currently moving through the northern part 
of our CWA, and just recently passed through the Lafayette area. 
These storms developed over northern Illinois, and have been 
traveling southeastward throughout the morning hours. They have 
either maintained or even slightly increased their intensity in the 
past hour or so.

The downstream environment is beginning to destabilize, as noted by 
increasing low-level lapse rates and surface-based CAPE. 
Additionally, cumulus development is now beginning to occur across 
much of the area. ACARS soundings out of IND show a rather deep CAPE 
profile with no notable inversions/capping. Mid-level lapse rates 
are still poor (5-6 C/Km) and there exists a fair amount of dry air 
in this layer as well. Observed storms are not quite gaining the 
height that the CAPE profile would otherwise suggest, and this may 
be due to weak forcing and/or dry air entrainment.

CAM guidance has consistently shown these storms quickly 
dissipating, which was not been the case. Observations and 
appearance on radar suggest that a weak cold pool is present. This 
cold pool is sufficiently strong/deep to keep the system going. 
Since the downstream environment is destabilizing, continued 
propagation is likely, at least for now. Little shear exists 
downstream to there is also potential for this to become outflow 
dominant and weaken. CAMs will continue to struggle regarding these 
storms and their subsequent evolution.

In terms of hazards, the mid-level dry air may promote a downburst 
threat. Currently, storms have not been gaining enough strength for 
this to be realized. We will continue monitoring the system for 
further development.

&&

.SHORT TERM (Today and tonight)...
Issued at 253 AM EDT Wed Jul 24 2024

Current observations show a few showers are still ongoing across 
southern portions of the area. While overall forcing is negligible, 
a weak remnant boundary continues to promote a few showers. Any 
ongoing showers are expected to diminish over the next few hours as 
the boundary becomes diffuse. Light winds and mostly clear skies 
should allow for patchy fog to develop before daybreak. Only a few 
spots are currently reporting minor visibility reductions, but 
coverage should continue to increase over the next few hours. 

Look for any fog that develops to quickly mix out after daybreak. 
Quiet weather conditions are then expected during the morning before 
an approaching cold front leads to increasing rain/storm chances 
later today. The best chance for storms should be from late this 
afternoon into the early overnight hours. Forecast soundings show 
steep low-level lapse rates, moderate instability, and sufficient 
effective bulk shear for the potential of a few strong storms. The 
main threat would be isolated damaging wind gusts though there is a 
non-zero threat for locally heavy rainfall or marginally severe 
hail. The aforementioned front will likely linger across central 
Indiana overnight which will keep rain/storm chances in the 
forecast.  

Aside from convection, increasing wildfire smoke may lead to reduced 
air quality at times today. High resolution smoke models continue to 
indicate that a plume of denser smoke will arrive from the northwest 
later this morning. While much of the smoke may remain aloft, 
diurnal mixing could help mix some of this down leading to reduced 
visibilities at times, especially north of the I-70 corridor.

&&

.LONG TERM (Thursday through Tuesday)...
Issued at 253 AM EDT Wed Jul 24 2024

A highly amplified pattern aloft will persist into the upcoming 
weekend...with a ridge focused over the Four Corners region and a 
trough on either side...over the eastern part of the country and 
across the Pacific Northwest. The presence of the upper trough in 
tandem with a frontal boundary dropping south through the region 
will keep a lingering convective risks over southern portions of the 
region Thursday before high pressure settles in with dry and 
seasonable weather. The ridge will slide east into the Great Lakes 
and Ohio Valley by the weekend bringing warmer temperatures and an 
increase in humidity levels by early next week. 

Thursday through Saturday

The frontal boundary will be located across southern Indiana by 
daybreak Thursday and should gradually push south into the Tennessee 
Valley as the day progresses. Isolated convection will remain a 
possibility across southern portions of the forecast area until 
drier air associated with high pressure to the north can advect into 
the region by late afternoon.

The high pressure will settle over the Great Lakes for late week 
then gradually shift east into the weekend. A predominant E/NE flow 
will pump drier air into central Indiana with dewpoints once again 
returning to more comfortable levels in the upper 50s and lower 60s 
for Friday and most of the day Saturday. Return flow on the back 
side of the high will begin transporting deeper moisture back north 
into the Ohio and mid Mississippi Valleys by late Saturday... 
enabling humidity levels to start creeping back up. Highs in the 
lower and mid 80s Thursday and Friday will nudge back up into the 
mid and upper 80s for Saturday in response to the expanding upper 
level ridge into the area.

Sunday through Tuesday 

Model guidance continues to show a subtle wave aloft tracking into 
the Great Lakes by Sunday afternoon which will buckle heights aloft 
and force the ridge back to the south. The presence of an increasing 
moist and unstable environment across the Ohio Valley interacting 
with a series of subtle waves aloft riding along the quasi-zonal 
flow will generate scattered convection at times Sunday into Monday. 
Even with the greater risk for storms...temperatures will climb into 
the upper 80s to possibly low 90s both days with a noticeable rise 
in humidity levels as dewpoints rise into the lower 70s.

The retrogression of the upper ridge back into the High Plains and 
southern Rockies by early next week will place the Ohio Valley and 
Great Lakes W/NW into the northern Plains on the periphery of the 
ridge. Signs continue to point at a more active regime taking shape 
as next week progresses with convective clusters riding along the 
edge of the ridge and interacting with the deep moisture and modest 
instability likely to be present across the region. Details are 
murky at this point but the overall pattern remains supportive of a 
return to hot and humid conditions with periodic impacts from 
convective clusters by the middle of next week.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 137 PM EDT Wed Jul 24 2024

Impacts

- Scattered showers and storms possible as a front sags into the 
  area late in the day. Brief MVFR restrictions possible.

- Potential for transient visibility reductions from smoke transport 
  into the region.

Discussion: 

Haze from wildfire smoke may limit visibility today.

Scattered showers and a few thunderstorms are developing across 
central Indiana as of 130pm. These should continue on and off 
through the evening and into the overnight hours. Shower/storm 
activity is possible until a cold front sweeps through around 05z. 
Should a shower/storm impact a terminal, then brief reduction to 
MVFR conditions or lower is possible.

Gradually clearing skies with northeasterly surface winds can be 
expected after the front passes. Lingering wildfire smoke should 
also diminish. VFR conditions are expected after 10z.

&&

.IND WATCHES/WARNINGS/ADVISORIES...None. 

&&

$$

MESOSCALE...Eckhoff
UPDATE...Eckhoff
SHORT TERM...Melo
LONG TERM...Ryan
AVIATION...Eckhoff