IND issues Area Forecast Discussion (AFD) at Jul 24, 1:38 PM EDT178
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
Source:
IND issues Area Forecast Discussion (AFD) at Jul 24, 1:38 PM EDT---------------
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