325
FXUS63 KIWX 150534
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
134 AM EDT Mon Jul 15 2024

.KEY MESSAGES...

- There are periodic chances for showers and storms (20 to 60%) tonight
  through Tuesday night, with one or more rounds of strong to
  severe storms possible during this timeframe.

- Best chances for severe weather will be on Monday late
  afternoon into the evening, when there is an Enhanced Risk
  (level 3 of 5) for severe weather. Damaging winds 60-75+ mph
  and a few tornadoes possible.

- Alongside the severe threat, flooding is also possible in any
  storms, especially in areas that remain saturated from the
  remnants of Beryl.

- Hot and humid Monday, depending on storm coverage, timing, and cloud
  cover. Afternoon heat indices mid 90s to near 100 degrees.

- Cooler, drier weather is anticipated midweek through next
  weekend.

&&

.UPDATE...
Issued at 919 PM EDT Sun Jul 14 2024

Previous forecast trends were maintained, with only small update
item of note to slightly increase PoPs across northwest half of
the area late evening into the overnight.

Compact convectively enhanced vortex continues to track east
across northwest/north central Illinois this evening with ring
of convection initiating over the past few hours from eastern
Iowa into southern Wisconsin and northern Illinois. Background
synoptic shear remains marginal, but RAP analysis suggests a
small pocket of 35-40 knot effective shear associated with this
small scale vort max. Despite this, convection has been rather
loosely organized up to this point with several storm
mergers/interactions across NW Illinois and some periodic signs
of some mid level rotation due to these mergers. Still
expecting these storms to congeal into a more linear feature
late this evening/early overnight as they track east. Upstream
00Z RAOBs from KILX/KDVN indicates very strong instability with
3000-3500 MLCAPEs.

Earlier stabilizing effects from northern Indiana early day MCS
will be eroded by westerly advection of this better upstream
instability axis along with eastward progression of some better
mid level lapse rates. Some low level CIN is expected to develop
this evening locally for mixed layer parcels however, so some
question as to the vigor of this convection as it tracks east
into a slightly less unstable environment locally. There could
be some tendency for more vigorous storms to develop upwind
across central/east central IL as northern portion of the storms
across southern Great Lakes become more outflow dominant. Some
isolated severe threat still appears to be intact west of US 31
locally in the 05Z-08Z period with a period of potential gusts
into the 40 to 60 mph range. Hail threat should be tempered with
eastward extent as storms congeal later this evening. Locally
heavy rainfall will be some concern across the west tonight,
especially considering recent heavy rainfall over the past week.

&&

.DISCUSSION...
Issued at 231 PM EDT Sun Jul 14 2024

Multiple rounds of storms are expected over the next 48 hours, with
one or more rounds being strong to severe. Our CWA is on the
periphery of a building ridge in the Plains, and with northwest
steering flow, this puts the Upper Midwest and Great Lakes regions
in a very favorable zone for storms. Several strong shortwaves that
drop into the Midwest in the coming days may help to sustain several
rounds of MCSs. SPC has us in a Day 1 Slight Risk (level 2 of 5), a
Day 2 Enhanced Risk (level 3 of 5), and a Day 3 Marginal Risk (level
1 of 5). The next 48 hours come with a lot of uncertainty in the
coverage, timing, and number of rounds of storms. Alongside the
severe threat, flooding is also possible with any of the MCSs. Many
locations, especially in the Wabash and St Joseph river basins, have
had 5 to 8 inches of rain this week. With saturated ground and
elevated rivers, it won`t take much for these areas to experience
more flooding. High PWATS of  and the potential for storms to
backbuild along outflow boundaries has me concerned about flooding
potential in addition to the multi-day severe threat.

As the initial round of storms today has now exited the area,
dry conditions will return for the next several hours before yet
another chance for storms. Hi-res models have yet to come to a
strong consensus, but it is looking more plausible (medium
confidence) that an MCS will develop over eastern IA/northwest
IL late this evening and move eastward into our CWA between 10
PM to 12 AM EDT tonight. With ample MLCAPE 2000-3000 J/kg and
DCAPE 1000+ J/kg, damaging winds would be the main hazard
overnight. The greatest confidence in severe weather is along
and west of US 31, as the MCS should weaken as it pushes
eastward overnight.

There is increasing confidence in severe weather Monday late
afternoon and into the evening. SPC has introduced 30% hatched wind
probabilities into the Day 2 Outlook, prompting the need for a
Enhanced Risk (level 3 of 5) upgrade across northern Indiana.
Another progressive MCS/bow-echo could develop upstream of a much
more favorable environment and ride along the highest theta-e axis
through southern WI, northern IL, and into northern IN. Strong
buoyancy, increasing vertical shear, and favorable thermodynamics
(dewpoints low 70s, highs upper 80s to low 90s, MLCAPE of 4000
to 5000 J/kg) could certainly yield a high-end impact damaging
wind event. A derecho is possible with organized damaging winds
60-75+ mph and a few tornadoes possible.

Heat and humidity build on Monday, with highs in the low 90s and
heat indices potentially in the upper 90s to low 100s. Heat Advisory
headline could be needed. Uncertainty in storm coverage, timing, and
lingering cloud cover could all result in temperatures being lower
than what is currently forecasted.

An upper level trough will pivot through the Great Lakes on Tuesday,
resulting in chances for storms ahead of and along the front. A
continental, cooler airmass from Canada will sink south midweek,
resulting in seasonable highs in the 70s, a stark decrease in
humidity, and dry conditions.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 121 AM EDT Mon Jul 15 2024

MCS...another is a string of systems...was just upstream of
SBN. Strong to severe wind gusts were associated with this
system over IL. Fairly robust support with this including a
slightly modified EML should help this system to move across
both terminals in the next few hours. Continued to extrapolate
ongoing movement to configure timing. Otherwise, yet another
system was well to the northwest near the Northern Plains and
Canadian border. Made an initial attempt to time this 2nd system
which appears stronger than the past two.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Flood Watch through late tonight for INZ012>015-020-022-103-
     104-203-204.
OH...None.
MI...Flood Watch through late tonight for MIZ078-177-277.
MARINE...None.

&&

$$

UPDATE...Marsili
DISCUSSION...Johnson
AVIATION...Skipper