IND issues Area Forecast Discussion (AFD) at May 21, 1:48 AM EDT752
FXUS63 KIND 210548
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
148 AM EDT Wed May 21 2025
.KEY MESSAGES...
- Widespread showers and storms expected through this evening
with convection diminishing overnight.
- Below normal temperatures through the week with light rain chances
continuing tomorrow and Thursday
- Increasing chances for precipitation Sunday into early next week
&&
.FORECAST UPDATE...
Issued at 1017 PM EDT Tue May 20 2025
Forcing is producing a couple of lines of convection across central
Indiana this evening. Northern convection has weakened, but
convection across the southern half continues.
There remains some instability from the warm sector in the southern
forecast area that will help maintain the convection as it moves
southeast. However, odds of severe convection are lowering as
heating has been lost. Some gusty winds and small hail remain
possible, but the most likely threat looks to be locally heavy rain
and resultant flooding.
Adjusted PoPs to reflect current trends seen on radar, with likely
or higher PoPs where current line is and to where it's expected to
end up. Some showers may move into the north late tonight so kept
low PoPs there late.
Adjusted low temperatures a bit and changed hourly forecasts to
reflect latest obs.
&&
.SHORT TERM (This evening through Wednesday)...
Issued at 258 PM EDT Tue May 20 2025
Current Satellite and radar observations depicts clouds have cleared
considerably across IL and western portions of IN as a warm front
associated with a low pressure system lifts northward. Despite
scattered showers ongoing across northeastern counties, there is a
lack of convective coverage. Satellite imagery does already show
agitated cu with convection initiating over portions of IL. Look for
the convection to become more widespread further east into Indiana
as daytime heating and deeper moisture surging north promotes
greater destabilization. Stronger diffluence aloft should also
provide greater forcing for ascent.
Strengthening mid-level flow supporting stronger deep-layer shear
and moderate instability supports the potential for severe
thunderstorms later this afternoon into the evening. Damaging wind
gusts, severe hail, isolated tornadoes, and localized flooding are
all possible. The isolated tornado threat may be more localized to
areas near the warm front boundary where surface winds become
backed. This looks most likely across the southern half of central
Indiana. Shear vector orientations generally favor a more linear
storm mode or storm clusters, but there is some potential for
discrete or semi-discrete supercells.
Stronger forcing shifting eastward overnight will lead to decreasing
coverage of convection. Overall weak forcing should lead to mostly
dry conditions overnight though broad cyclonic flow may keep a few
light showers around at times. The aforementioned low pressure
system and parent trough will likely linger over the region through
the period resulting in dreary conditions for most.
Expect extensive clouds and scattered showers around during the day
Wednesday due to broad cyclonic flow in place. This will greatly
limit daytime heating with highs remaining in the low-mid 60s. A
tight pressure gradient will also result in breezy conditions making
it feel colder. Expect gusts around 25-35 mph through the day.
&&
.LONG TERM (Wednesday night through Tuesday)...
Issued at 258 PM EDT Tue May 20 2025
Wednesday night through Saturday...
Clouds and scattered light showers at times will likely linger
through Thursday as a surface low slowly moves out of the region.
The best chance for precipitation is across east or northeastern
counties where deeper moisture and stronger forcing align. Upper
troughing and northwesterly flow should also remain over the region
through the end of the week providing seasonably cool weather. Highs
are expected to remain mostly in the 60s with lows in the 40s or low
50s. Northern portions of central Indiana may even stay in the 50s
during the day Thursday due to extensive clouds.
Drier air and greater subsidence from high pressure building in
towards late week should allow clouds to finally decrease in
coverage. Increasing subsidence will also likely provide quiet
weather conditions Thursday night Saturday. While cloudy conditions
are expected across much of central Indiana, latest guidance does
suggest drier air filtering in across the south which would lead to
more sunshine.
Saturday night through early next week...
There are low chances for precipitation (30% or less) towards the
latter half of the weekend, but there is still uncertainty due to
diverging model solutions. Most guidance shows a few complexes of
storms developing over The Plains and weakening as they propagate
ESE. While there are discrepancies between models, the general
agreement is for the storm track to favor the southwest half of
central IN or locations further south around Sunday morning. Will
continue to watch for trends as this track is slightly further
northeast compared to yesterday. It is also worth noting a sharp
gradient in precipitation chances or amounts are likely from SW-NE
due to lingering subsidence induced dry air.
By race day, temperatures should rebound slightly into the upper 60s
to low 70s thanks to increasing heights aloft. Rain chances increase
further early next week with another system expected to move in, but
exact details remain uncertain due to even larger model differences.
&&
.AVIATION (06Z TAF Issuance)...
Issued at 148 AM EDT Wed May 21 2025
Impacts:
- MVFR/IFR ceilings at times through the period
- Winds becoming westerly, increasing to 15-20 kts after 14z
Discussion:
Satellite and radar imagery shows the majority of the showers and
storms weakening and pushing south of the region at this hour. ACARs
sounding shows a weak nocturnal inversion setting up just above the
surface, which may trap leftover moisture in the boundary layer and
result in low stratus. Cigs widely vary over Central Indiana tonight
with a few locations already reporting IFR cigs. Lower confidence in
how widespread low ceilings will be; however satellite is showing
more widespread MVFR/VFR stratus already developing. Keeping cigs at
Bkn035 at the moment as upstream observations indicate the stratus
deck around this level. Would not be surprised to see lowering cloud
bases by sunrise to MVFR levels or lower.
Central Indiana remains under the influence of an area of low
pressure over the next 24 hours, which will keep lower clouds and
scattered showers around. Expect another wave to rotate into the
state within the 13-15z timeframe this morning, bringing widespread
MVFR cigs and scattered showers. This pattern should persist through
the day. Brief periods of MVFR or worse cigs and vis possible under
any shower, however coverage of shower activity should be far less
than what has been observed the past few days.
Forecast soundings indicate steepening low level lapse rates as cold
air moves in aloft later today. With a strong low level jet
overhead, expect westerly wind gusts of 25-30 kts to mix down to the
ground beginning shortly after sunrise and persisting into the
evening hours.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...50
SHORT TERM...Melo
LONG TERM...Melo
AVIATION...CM
Source:
IND issues Area Forecast Discussion (AFD) at May 21, 1:48 AM EDT---------------
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