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000
FXUS63 KIND 280521
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
121 AM EDT Sun Apr 28 2024

.KEY MESSAGES...

- Warm and active weather expected throughout the next seven days,
  with above normal temperatures and multiple opportunities for
  showers and thunderstorms.

- Organized severe storms appear unlikely, though multiple rounds of
  rainfall may allow redevelopment of minor flooding along some
  rivers.

&&

.FORECAST UPDATE...
Issued at 917 PM EDT Sat Apr 27 2024

No major changes needed to the ongoing forecast with conditions
generally evolving as expected. Did make some minor adjustments to
POPs during the overnight hours to better delineate where the higher
expected coverage for showers will be across the northwestern
counties based on ongoing rain in east central Illinois.

These showers are expected to continue to increase in coverage as
the LLJ ramps up. Instability should be sufficient for occasional
rumbles of thunder, but don`t expect any other hazardous weather
outside of lightning. With strong southerly flow, expect a pretty
flat diurnal temperature curve through the night with lows in the
low to mid 60s.

&&

.SHORT TERM (This evening through Sunday)...
Issued at 254 PM EDT Sat Apr 27 2024

Not much going on at the moment as Hi-RES soundings are showing some
dry air  mixing in aloft. There were only a few showers over east
central Illinois and southwestern Indiana seen on radar moving
northeast around 35 mph per the AWIPS distance speed tool.
Meanwhile, satellite data indicated warm cloud tops associated with
weakening convection over southern Illinois. Earlier their had been
a decent amount of lightning strikes with this activity, but latest
ENTLN data was no longer showing any strikes. That said, LAPS data
was showing over 1200 J/KG CAPE over the upper Wabash Valley, where
a DAY1 SPC Marginal Severe Risk is residing. With deep shear not
that impressive there at less than 30 knots and little upper
support, not expected much development this afternoon.

Hi-RES soundings show the column saturating again tonight and deep
shear increasing a bit to the point where if enough instability can
be present a few storms may become strong or marginally severe with
hail and thunderstorm gusts the main threat. Despite the lack of
synoptic forcing, 305K isentropic lift and saturating column will
result in some showers with the best coverage over the upper Wabash
Valley where the lower condensation pressure deficits will be
residing and slightly better deep shear and instability.

Would not rule out a storm or two again on Sunday. This will depend
on whether or not a weak impulse in southwest flow aloft can combine
with projected weak instability to trigger isolated convection. The
bigger story will be temperatures and continued breezy southwest
winds will support near record in the lower 80s. With the tight
surface pressure gradient hanging around and some breaks in the
clouds permitting mixing, will once again see gusts to 30 plus mph
Sunday afternoon.

&&

.LONG TERM (Sunday night through Saturday)...
Issued at 254 PM EDT Sat Apr 27 2024

A warm and active period continues to be the expectation for this
coming 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 or just off the
eastern/southeastern CONUS. The strong surface cyclone currently
bringing a regional severe weather outbreak to the central and
southern Plains will swing northeastward into the Great Lakes early
this week and weaken. The associated surface frontal zone will
weaken as well, as it is stretched/washed out with time.

Significantly boundary-parallel flow throughout the depth of the
troposphere will keep the bulk of precipitation associated with this
system in a relatively narrow zone along and near the boundary,
which will concentrate the highest rain chances mainly early Monday
morning into the early evening hours. With the main forcing for
large scale ascent displaced well to our north and a secondary
shortwave displaced to our south, as well as limited opportunity for
destabilization given early arrival of precipitation, little to no
severe threat is expected, though some very modest instability will
necessitate low thunder probabilities.

Another weak system is expected to follow in quick succession mid-
week, before a third, stronger system develops in the lee of the
southern Rockies late in the week, with potential for additional,
perhaps somewhat higher precipitation chances late week into the
weekend, though uncertainty increases with time both due to a
complex evolution of these systems and model differences. Though
precipitation chances will be frequent this week, several dry
periods are likely.

Analogs and experimental machine learning guidance suggest the area
will be on the fringes of a low threat for strong to severe storms
mid to late week, though the overall parameter space is much more
robust well to our west and southwest during this time frame - an
organized severe threat appears unlikely at this time.

Ongoing and prolonged elevated streamflows, particularly in the
Wabash valley and lower White River valley, will necessitate
monitoring of hydrologic conditions and threats with time, as
capacity is relatively low at the moment. That said, there is little
to no signal for significant rainfall in any one period, but
multiple potential rounds of convective precipitation could steadily
worsen the hydrologic situation over time in the right mesoscale
circumstances. At a minimum, streamflows will likely remain elevated
well into early May, with some areas in the Wabash and lower White
valleys rising back into minor flood. This is well-supported by
hydrologic ensembles.

Temperatures will be warm much of the week, with highs in the 70s to
lower 80s at times, and lows in the 50s to mid 60s - running about a
month ahead of time relative to climatology. Deterministic NBM
remains concentrated much of the week in the lower half of its
guidance envelope, though given its tendency to struggle in warm
advection regimes, particularly during the transition seasons, have
made some occasional upward adjustments to temperatures,
particularly highs, where merited.

&&

.AVIATION (06Z TAF Issuance)...
Issued at 120 AM EDT Sun Apr 28 2024

Impacts:

- Mainly VFR this TAF period.
- VCSH possible through the night, mainly at HUF and LAF
- Southerly wind gusts to 25 kts mainly during daylight hours.

Discussion:

Southerly surface flow will remain in place across Central Indiana
through this TAF period. Convection from storms over the plains is
expected to continue to drift north and west of much of Central
Indiana through the period as upper ridging continues to steer flow
that direction.

Some weak showers may be possible overnight at LAF and HUF as seen
on radar, but these showers will be VFR based, weak and short-lived
as they progress northeast. Thus have used a VCSH mention for now.

On Sunday, Indiana will remain within the warm sector, with limited
forcing available, similar to Saturday. thus have again trended to
VFR cigs, but confidence remains too low for any precip mention.
Moderate pressure gradient across the area will allow gusts to near
25 mph when heating and mixing resumes.

&&

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

$$

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