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207
FXUS63 KIND 262258
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
658 PM EDT Fri Apr 26 2024

.KEY MESSAGES...

- Showers and a few thunderstorms at times this evening into
  Saturday.

- Warm through much of the period, particularly Sunday, when record
  highs may be threatened.

- Active weather, with multiple chances for showers and storms next
  week.

&&

.SHORT TERM (This evening through Saturday)...
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Issued at 313 PM EDT Fri Apr 26 2024

Latest GOES-16 visible satellite loop was showing a few breaks in
the mid and high deck over east central Indiana. Meanwhile, radar
was showing light returns over the upper Wabash Valley and lower
White River Valley, but the lower levels are currently dry leading
to no ground truth. Breezy southeast winds have allowed temperatures
to rebound into the 60s.

Surface high pressure will remain anchored over the east coast as
low pressure moves from the central Plains to Lake Superior on
Saturday. Meanwhile, a wave will form over the High Plains as a
front stalls over the Upper Midwest and High Plains. This will
result in a very warm and moistening air mass as the flow returns
off the Gulf of Mexico. Warm advection/Isentropic upglide will occur
at the 300-305 K levels and Hi-Res soundings and lowering
condensation pressure deficits support the column saturating from
top down. This will bring shower chances to the area the remainder
of the afternoon through Saturday. Although thunder can not be ruled
out tonight, better chances for thunderstorms are in the offing for
Saturday. In addition, tight surface pressure gradient will mean
gusty southerly winds with gusts to 30+ mph mainly Saturday
afternoon. Finally, a few strong storms are possible during the
afternoon, mainly over the upper Wabash Valley where SBCAPE gets
closer to 1000 J/kg and deep shear approaches 30 knots.

The combination of a few breaks in the overcast along with the
breezy return flow will allow temperatures to climb all the way to
the upper 70s to lower 80s Saturday afternoon. This is around 10-15
degrees above normal. Meanwhile, temperatures will not drop much at
all tonight due to the influx of the Gulf air.
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&&

.LONG TERM (Saturday night through Friday)...
Issued at 313 PM EDT Fri Apr 26 2024

A warm and active period is expected this week, with multiple
opportunities for showers and thunderstorms.

Large scale troughing will predominate over much of the CONUS this
week, with mean ridging of various intensity over the eastern CONUS.
Lee cyclogenesis later in the weekend will produce a fairly strong
low pressure system that will move from the central Plains into the
Great Lakes early in the week, though a fairly amplified flow
pattern will keep the bulk of the precipitation associated with this
system in a fairly narrow zone along the primary baroclinic zone,
which will keep the forecast largely dry across central Indiana
tomorrow night into Sunday, though depending on evolution of
upstream convection, cannot completely rule out some weakening
convection sneaking into the area, mainly late Saturday night.

The vast majority of activity associated with this first system will
come late Sunday night into Monday evening as the front gradually
pushes eastward through the area. The overall pattern, weak
instability and mostly weak shear, along with the rest of the
parameter space appearing unimpressive as the front passes, suggests
mostly rain with isolated/widely scattered embedded thunderstorms,
with little to no severe threat.

Uncertainty increases as multiple additional waves develop along the
remnant baroclinic zone later in the week as the tail end remains
draped across the central/southern CONUS, and model differences keep
predictability/confidence limited. PoPs will be limited to low-
middling chance at the highest the remainder of the week, and
several dry periods are likely.

Analogs and experimental machine learning guidance suggests at least
a low mid-week severe threat (Tuesday into Wednesday), with the
maximum threat well to our west/southwest in a much more robust
parameter space, but this will require close monitoring as details
become clearer with time.

Will also have to keep an eye on hydrologic threats given the
elevated streamflow continuing along area waterways, particularly in
the Wabash Valley, though at this time a significant flood threat is
low probability, and will obviously be dependent upon mesoscale
environment/convective evolution. At a minimum, given multiple
rounds of rain, streamflows may remain elevated into the first week
of May, if not necessarily in flood.

Temperatures will be warm much of the week, especially Sunday, when
widespread highs in the 80s are expected, perhaps threatening some
daily records. NBM is concentrated much of the week toward the low
end of the envelope, though given its tendency to struggle in warm
advection regimes, particularly during the transition seasons, have
made some occasional upward adjustments to highs.

&&

.AVIATION (00Z TAF Issuance)...
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Issued at 658 PM EDT Fri Apr 26 2024

Impacts:

-LLWS 04Z to 12Z
-Isolated RA/TSRA through TAF period, highest confidence at LAF
tonight
-Southerly wind gusts to 25kts

Discussion:

Generally dry conditions expected through much of the TAF period,
but isolated showers will continue through tomorrow afternoon.
Coverage will be greatest around LAF tonight with shower chances too
low past 12Z for any specific TAF mention at this time. LLWS is
expected with a 40kt wind difference between the surface and 020
from 04Z to 12Z with wind gusts gradually increasing after daybreak
tomorrow. Cigs will remain VFR through the period with MVFR vsbys
during heavier showers.
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&&

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

$$

SHORT TERM...MK
LONG TERM...Nield
AVIATION...White