IND issues Area Forecast Discussion (AFD) at Aug 18, 12:27 PM EDT046
FXUS63 KIND 181627
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
1227 PM EDT Mon Aug 18 2025
.KEY MESSAGES...
- Isolated to scattered showers and storms today and tonight
- Very warm to hot and humid conditions will be around into
Tuesday
- Showers and storms are expected to surround the frontal passage
Tuesday into Wednesday
- Dry and cooler late this week through early next week; Highs
falling into the upper 70s and low 80s by Sunday
&&
.FORECAST UPDATE...
Issued at 938 AM EDT Mon Aug 18 2025
Isolated showers extend from northeast Illinois southeast into
western portions of the forecast area along what appears to be a
boundary separating the drier air to the east with the much more
oppressive air highlighted by dewpoints in the mid 70s to the west.
The instability gradient also aligns near this boundary currently.
Elsewhere it was a hazy start to the day with temperatures at 13Z
already in the 70s with some locations across the Wabash Valley
already approaching 80.
There are a lot of moving parts that will influence the forecast for
the rest of the day...with a surface ridge to our east and the
continued expansion of the upper level ridge to our west. In
between...a narrow and low threat for convection will persist in the
vicinity of the boundary mentioned above with a focus across the
northern half of the Wabash Valley. As mid level heights rise by
later this afternoon...convection will likely have a harder time
developing with model soundings showing a developing capping
inversion despite the presence of limited instability.
The expansion of higher dewpoint air will make for an uncomfortable
afternoon for humidity across the western half of the forecast area
where heat indices will peak in the upper 90s to just above 100
degrees. Expect afternoon highs ranging from the mid 80s in
northeast counties to lower 90s in the Wabash Valley.
Zone and grid updates out.
&&
.SHORT TERM (Today and tonight)...
Issued at 233 AM EDT Mon Aug 18 2025
Early This Morning...
A surface boundary is across northeastern Illinois into northwest
Indiana. Weak isentropic lift along this boundary is creating some
light showers near the IL/IN border near the northwest forecast
area. Satellite shows some continued development of clouds in the
northwest forecast area as well.
This lift will continue through the early morning hours, so may have
to add some slight chance PoPs for parts of the western forecast
area.
Stronger lift farther northwest was producing convection across
areas closer to Chicago, but convection from this has weakened as it
moved closer to the local areas or has moved away from the area.
Feel this will continue and keep storms out of the area given little
change early this morning. Will monitor closely though.
Today...
The surface boundary will remain across the northwest forecast area
today. Weak isentropic lift will persist as well. Isolated showers
may linger this morning, so will have some slight chance PoPs.
Even though upper ridging remains this afternoon, the isentropic
lift may interact with increasing instability to bring isolated to
scattered convection to the northwest forecast area this afternoon.
Will add some low PoPs there this afternoon. Cannot rule out that
these will spread farther east, but confidence isn't high enough to
include. Severe storms are not expected given weak shear.
High temperatures will be middle 80s northeast to lower 90s
southwest. Dewpoints will be in the 70s most areas, making it feel
more like the middle and upper 90s over much of the area.
Tonight...
Any initial convection from this afternoon will diminish by early
evening. During the night. forcing from an upper wave north of the
area will generate more convection. This convection has the
potential to move into portions of the northwest half of the area.
Will go with some slight chance to chance category PoPs across the
northwest half, with the highest PoPs in the far northwest. Shear
increases some, but instability will be diurnally weakening. Thus
feel that severe storms are not likely.
Lows will be in the middle 60s to lower 70s.
&&
.LONG TERM (Tuesday through Sunday)...
Issued at 233 AM EDT Mon Aug 18 2025
Tuesday and Wednesday...
The greatest and only expected rain chances are early in the period
when an upper wave and cold front move through the region.
Southwesterly surface flow ahead of the system will help to pull
gulf moisture northward. This combined with increasing dynamics
favors scattered to numerous thunderstorms on Tuesday. The greatest
coverage is expected during peak heating when instability is
strongest. Weak deep-layer shear should mostly limit the threat for
severe, but an isolated strong to severe wind gust cannot be ruled
out given strong instability and steep low-level lapse rates.
Deeper moisture and forcing is expected to shift south on Wednesday
resulting in rain chances diminishing. However, daytime heating atop
lingering PBL moisture could promote isolated to widely scattered
convection. Look for hot and humid conditions to persist Tuesday
before temperatures slightly cool off into the 80s Wednesday.
Thursday onward...
Mostly quiet weather conditions are expected late this week through
early next week. Guidance depicts primarily N/NW flow with upper
ridging and surface high pressure providing dry weather through
Friday. An upper wave is then expected to push a dry cold front
through the region late Friday into Saturday. Precipitation is
unlikely due to marginal moisture ahead of the system though it
will bring a noticeable cooldown.
Expect highs generally in the 80s late this week with lower
dewpoints. A more substantial cooldown should occur behind the
aforementioned dry cold front. Most guidance suggest highs will fall
into the upper 70s on Sunday for portions of the area while
widespread highs in the 70s are possible by Monday. Dewpoints are
also likely to drop substantially as drier air advects into the
area, making it feel more like early fall.
&&
.AVIATION (18Z TAF Issuance)...
Issued at 1227 PM EDT Mon Aug 18 2025
Impacts:
- Isolated convection possible near KLAF this afternoon then again
mid evening into the overnight
- Scattered storms developing again by midday Tuesday
- Patchy fog possible primarily at KLAF predawn Tuesday
Discussion:
A persistent area of convection near KLAF may linger past 18Z but
the overall trend through the latter part of the afternoon will be
for limited to no impacts from storms as the ridge aloft builds in
from the west. By this evening however...a more robust convective
cluster will approach the region from the northwest and may again
impact KLAF into the overnight with restrictions and perhaps brief
gusty winds from storms as well. Any rain would contribute to an
increase risk for visibility restrictions in the predawn hours
Tuesday.
A frontal boundary will slide south into the region by early Tuesday
and will serve as a focal point for renewed convective development
by late morning Tuesday into the afternoon...especially for areas
near and south of I-70. Will carry PROB30s at KIND and KHUF after
14Z and may need to introduce one at KBMG with later TAF issuances.
&&
.IND WATCHES/WARNINGS/ADVISORIES...None.
&&
$$
UPDATE...Ryan
SHORT TERM...50
LONG TERM...Melo
AVIATION...Ryan
Source:
IND issues Area Forecast Discussion (AFD) at Aug 18, 12:27 PM EDT---------------
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