207
FXUS63 KIND 051311
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
911 AM EDT Wed Jun 5 2024

.KEY MESSAGES...

- Showers and scattered to numerous thunderstorms today into early
  this evening. A few strong storms cannot be ruled out.

- Cool with below normal temperatures Thursday through Tuesday

- Numerous shower/storm chances Saturday through Tuesday

&&

.FORECAST UPDATE...
Issued at 653 AM EDT Wed Jun 5 2024

Made minor forecast adjustments to speed up arrival of higher PoPs
in the western forecast area a bit, as an axis of convective
development either side of the Mississippi valley has produced a
small complex of strong storms in the past couple of hours that is
currently moving through central Illinois. This complex appears
strong but subsevere, but may arrive in the western forecast area as
early as about 9-10 AM. Additional upscale growth is possible owing
to the juxtaposition of frontal forcing, pooled pre-frontal
moisture, and a maximum of upper level jet divergence, which may
overcome fairly minimal instability this early in the diurnal cycle.

On its current trajectory, this initial round would arrive into Indy
metro by about 11 AM, and into the eastern forecast area by around 1
PM, barring any acceleration that may occur if a more robust cold
pool can become established.

&&

.MESOSCALE UPDATE...
Issued at 910 AM EDT Wed Jun 5 2024

Keeping a close eye on a bowing segment of thunderstorms nearing the
Upper Wabash Valley that has a history of gusts as high as 40-50
mph.  Satellite is showing some warming in the cloud tops which
lines up with the poor thermodynamic environment these storms are
moving into.  The system has developed a cold pool robust enough to
mitigate the poor thermodynamics and weak shear, so expect that it
should remain near steady state as it crosses the state line.

What meager instability that is available is on the northern end of
the bowing segment, so expect that to be where the stronger portion
will remain through 12 PM.

Focus then will shift to the potential for additional showers and
storms later this afternoon with outflow boundaries from the morning
convection being where convective initiation is most likely to occur.
Widespread cloud cover will limit the instability but shear becomes
slightly more favorable by 20Z which should allow for at least some
additional marginally severe storms.

&&

.SHORT TERM (Today and tonight)...
Issued at 304 AM EDT Wed Jun 5 2024

Showers and thunderstorms are expected today across central Indiana
as a cold front sweeps through the area in the late morning to early
evening time frame - a bit slower than previously expected.

Ample moisture is in place ahead of the boundary, with precipitable
water values as high as 1.6-1.9 inches, close to climatological max.
Modest destabilization is expected despite increasing cloud cover,
and weak though potentially sufficient deep layer shear values will
exist for at least a low threat of an isolated strong to severe
storm, primarily in the eastern half to third of the area where
frontal passage will be occurring near peak heating. Primary threats
today will be damaging winds, heavy rain/localized flooding, and
perhaps some marginally severe hail given the distribution of the
forecast CAPE profiles.

Showers and storms will come to an end early this evening as the
front exits the area, and dry weather is expected for the rest of
tonight. Some midlevel moisture will accompany the primary upper
level wave as it slides through the Great Lakes tonight, but dry low
level air will likely prevent anything from reaching the ground,
instead manifesting as some midlevel cloud overnight - this should
help prevent any significant fog formation tonight, though some
patchy fog will be possible due to the rainfall today.

Diurnal range will be limited somewhat today and tonight by the
precipitation and cloud cover, and expect highs to max out around 80
today, and drop to around 60 tonight.

&&

.LONG TERM (Thursday through Tuesday)...
Issued at 304 AM EDT Wed Jun 5 2024

An active weather pattern appears in store for the end of the work
week through early next week. Models are in good agreement regarding
the general trend of the overall upper pattern, but differ with some
of the timing and forcing details.

Thursday and Friday...

Starting on Thursday, strong ridging is expected to develop over the
western CONUS leading to a deep, negatively tilted  trough over
Ontario and the Great Lakes. This is expected to be the prevailing
pattern through early next week.  Cooler northwest flow within the
lower levels will be expected as the deep trough aloft allows
Canadian air to arrive across the Ohio Valley and Central Indiana.
Moisture will remain a problem for this system on Thursday and
Friday. The gulf will be effectively cut off, and continental air
will be in place. Forecast soundings on Thursday through Friday show
mainly a dry column as a mid level inversion aloft caps any CU
development. Furthermore, best forcing and moisture looks to remain
wrapped in the main cyclonic flow aloft over the Great Lakes. Thus
will try to trend toward a dry forecast on Thursday and Friday amid
cooler highs. However some low chance pops may be needed across the
northeast parts of the forecast area due to proximity to the better
forcing/moisture.

Saturday and Sunday...

Better chance for showers will be in place through the weekend.
Overall the upper pattern will remain the same, with northwest flow
in place aloft and a deep upper low over western Quebec. However
models suggest a few short waves within the flow aloft to push
across Indiana. Forecast soundings also point toward saturation as
these features pass, although confidence is often low in timing
these waves at this time range.  Models also suggest a weak surface
trough/cold front to pass also as it pivots around the low to the
northeast. Thus for now, at least some low chance pops will be
warranted through the weekend. A washout weekend appears unlikely
and many dry hours appear to be expected, but a few passing showers
or storms cannot be ruled out.

Monday and Tuesday...

Models differ a bit here with an unresolved upper pattern. On
Monday, One model suggests the arrival and passage of a upper low
while another suggests ridging aloft amid continued northwest flow.
This is then followed by the upper low departure with ridging
arriving on Tuesday, while the second model allow the arrival of a
short wave on Tuesday afternoon. Thus lots of uncertainty here,
mainly due to the uncertain evolution of the previous upper trough.
For now, low rain chances each day appear quite reasonable until a
higher level of confidence can be achieved.

&&

.AVIATION (12Z TAF Issuance)...
Issued at 625 AM EDT Wed Jun 5 2024

Impacts:

- Widespread MVFR ceilings developing mid morning.

- Showers and thunderstorms, particularly in a 3-6 hour period
  starting around 14-17Z depending upon the site.

- Wind gusts approaching 20KT around this time ahead of frontal
  passage from 210-240 degrees.

Discussion:

Passage of a frontal system later today will cause an increase in
coverage of showers and thunderstorms, particularly from around mid
morning into mid afternoon, along with gusty pre-frontal winds and
deteriorating ceilings and possibly visibilities, particularly in
precipitation.

Widespread MVFR conditions are expected, with occasional drops to
IFR possible, mainly in precipitation. A small patch of IFR
conditions may continue to impact IND during the first few hours of
the period.

Winds will become gusty ahead of the front, gusting as high as 20KT
from 210-240 degrees. These gusts will subside in the evening as the
front departs.

Have concentrated thunder mentions at each site to the most likely
time frame for scattered storms.

VFR conditions will return this evening, though depending upon
rainfall amounts, sky cover, and winds behind the front, some fog
cannot entirely be ruled out late tonight.


&&

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

$$

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