919
FXUS63 KIWX 072235
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
635 PM EDT Sun Jul 7 2024

.KEY MESSAGES...

- Low chances of showers and thunderstorms (20%) for NW IN/SW
  Lower Michigan tonight and Monday. Scattered showers and
  thunderstorms are possible Monday night, especially west of
  I-69.

- Remnants of tropical system Beryl will bring showers and
  thunderstorms to the area Tuesday afternoon through Thursday
  with heavy rain at times.

- Warmest conditions this forecast period expected on Monday
  (mid and upper 80s), and possibly again next weekend.

&&

.DISCUSSION...
Issued at 400 PM EDT Sun Jul 7 2024

Scattered showers and thunderstorms have developed this afternoon
from eastern Iowa into northeast Illinois. This appears to be at
interface of modest low level theta-e gradient. Several small scale
short waves are also progressing through the southwest upper flow
across the Mid MS Valley. There also appears to be a weak MCV across
eastern Iowa that will lift northeast into this evening. Some
question as to the eastern extent of this convection through the
remainder of the afternoon in the early evening with a strong west
to east instability gradient expected to remain anchored from
northeast Illinois into SW Lower Michigan and northwest Indiana.
Some potential should exist for isolated showers and thunderstorms
across far west/northwest portions of the area into early this
evening. Cannot completely discount some additional isolated showers
and thunderstorms late evening into the overnight as the stronger
convectively enhanced short wave works across the western Great
Lakes. However, developing low level CIN this evening should limit
these chances.

A stronger upper level trough lagging back across the Dakotas this
afternoon will dig across the Corn Belt Monday afternoon before
beginning to shear out across the western Great Lakes Monday night.
Modest southwesterly low level flow will allow for low level
warm advection during the day Monday, and Monday should feature
the warmest conditions of this forecast period with highs in the
mid 80s to around 90. Not expecting heat indices to be much of
a concern however as richer near sfc moisture remains upstream.
Through the day Monday, best coverage of scattered showers and
thunderstorms is expected back across northeast Illinois, but
weak surface based instability and approach of some weak pre-
frontal forcing may allow of isolated to scattered
shower/thunderstorm development west of IN-15. A negative factor
for convection on Monday is a possible lull in better/mid upper
level forcing.

On Monday evening will carry low chance PoPs into the area as
primary upper level short wave shears out across the western Great
Lakes, and axis of weak 925-850mb moisture/mass convergence shifts
across the southern Great Lakes. While severe weather is not
expected Monday night, there could be a few storms capable of some
gusty winds given some increase in low/mid level flow and low level
moisture.

Tuesday through Thursday looks to be the primary period of concern
for this forecast valid period as remnants of Beryl may impact the
western Great Lakes and/or Ohio Valley. A rather complicated
synoptic pattern makes predictability on the low side regarding
finer details with exact track. An upper low in northwest upper
flow is expected to eventually merge with remnants of Beryl
later Tuesday with this consolidated upper level trough lifting
northeast across the southern Great Lakes on Wednesday. The
exact track/strength of the low/mid level height minimum remains
of low confidence as initial warm core/latent heat dependent
nature of this system is hard to pin down at this forecast
distance. Ensemble spread appears to increase sharply with track
of low level features after 00Z Wednesday. Scattered showers
and storms may fill in during the day Tuesday well north of low
center as low/mid level fgen axis extends north into southern
Great Lakes.

While details will need to be refined, the possibility of at least
portions of the area getting into heavy rainfall Tuesday
night/Wednesday still appears intact as PWATS may increase to 2+
inches late Tuesday/Wednesday. Antecedent conditions have been on
the dry side most locations which could alleviate some of the
concerns, but if higher end rainfall amounts in excess of 3 or 4
inches are realized in deformation forcing zone, some hydro issues
are possible. Have issued an ESF this afternoon highlighting the
late Tuesday-Wednesday evening period for some heavy rainfall
potential. Possible northward advection of mid level dry slot
midweek could sharpen up the axis of heaviest rain to a greater
degree than current guidance indicates. If a slower/westward
trend ends up verifying, there is some low possibility that a
marginal severe risk could evolve in a brief window across the
far southeast during this period.

Additional chances of storms may arrive for next weekend as area may
be on strong low level theta-e gradient. A transition to hot and
humid conditions is possible toward late next weekend into early
next week as eastward progression of upper level ridge allows this
strong theta-e gradient to shift eastward.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 630 PM EDT Sun Jul 7 2024

Showers moving along the southeast Lake Michigan shoreline may
move over KSBN within the next hour or two. No lightning is
present at this time, thus -SHRA is favored over -TSRA. Late
in the TAF period, additional showers and storms are possible
at KSBN but the coverage of these storms is questionable.

Otherwise, at KFWA, tranquil conditions through Monday.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...None.

&&

$$

DISCUSSION...Marsili
AVIATION...Brown