044
FXUS63 KIWX 021938
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
338 PM EDT Tue Jul 2 2024

.KEY MESSAGES...

- A Marginal Risk of severe storms for Wednesday afternoon and
  early evening mainly east of Interstate 69 across northeast
  Indiana and northwest Ohio. Isolated damaging wind is the
  potential main threat.

- Warmer and more humid for Wednesday with peak afternoon heat
  indices in low to mid 90s south of US Route 24.

- Isolated severe weather is also possible on Friday, but low
  confidence at this time.

&&

.DISCUSSION...
Issued at 335 PM EDT Tue Jul 2 2024

Broad positive mid-level theta-e advection across the western Great
Lakes has shifted across southern Lower Michigan this afternoon.
This elevated moisture return combined with small scale vort max
tracking across southern Great Lakes has allowed for rain showers,
primarily north into central Lower Michigan. Passage of this vort
max and axis of better mid level moisture will cut-off additional
rain chances for the remainder of the day. Focus for the rest of the
day into this evening will be upstream as renewed convection
develops across the Corn Belt in a zone of stronger
frontal/moisture convergence. The upstream short wave helping to
initiate this convection will shear out as it ejects northeast
into the UP of Michigan, and low level convergence will weaken
as this axis shifts into the southern Great Lakes Wednesday
morning. Still some uncertainty as to the coverage of rain
showers/embedded storms into west/northwest portions of the area
early Wednesday morning, but overall trend should be weakening
through the late morning hours.

Convective potential for Wednesday remains a challenge as residual
cloud cover will likely be accompanying primary low-mid level
theta-e ridge as it sags into the southeast half of the
forecast area Wednesday afternoon. Weak sfc cool front will also
likely be lagging back across the western Great Lakes early
Wednesday afternoon, and strength of low level convergence in
guidance progs looks to be relatively weak. At this forecast
distance, it remains difficult to differentiate whether actual
cold front, or pre-frontal confluence zone across the Ohio River
Valley will be more favorable for convective initiation. This
pre-frontal area southeast of the local area may also be
characterized by some pockets of differential heating Wednesday
afternoon. Have not made many changes to previous forecast with
NW to SE PoP gradient Wednesday afternoon. Westerly deep layer
shear on the order of 30-35 knot and potential of some SBCAPES
on the order of 2000 J/kg could yield a small window of isolated
severe risk in the 18Z-00Z timeframe, mainly along and south of
US Route 24. Weak mid level lapse rates and marginal westerly
shear would point to main threat as isolated strong wind gusts
with precip loaded cores.

Lull in the greater rain chances still looks to set up Wednesday
night into early Thursday as this low level theta-e gradient stalls
out south of US 24. It is possible there may not be much impetus for
return advection and northward retreat of this boundary until later
Thursday night as next convectively enhanced vort max lingers back
across the Mid MS Valley during the day Thursday.

On Friday, guidance still points to a stronger synoptic upper
level trough affecting the area with flow backing to the
southwest allowing for better northward moisture transport. Some
Dprog/DT trends have indicated a slight tendency to a more open
wave, with perhaps a slightly faster progression of SLP minimum
and sfc cold front. Shear will be a bit more robust by Friday
downstream of this more vigorous wave which leaves the main
ingredient of uncertainty as instability. There could be a good
deal of cloud cover from advective forcing to begin the day
Friday which could limit destabilization. If some moderate
instability can be realized, some strong/severe potential is
possible given expected background shear.

Passage of this trough will lead to cooler and less humid conditions
for Saturday. Maintained some slight chance PoPs across the
northeast Saturday as departing upper level trough across the Great
Lakes allows for slightly cooler upper level temps and weak pocket
of lingering MUCAPE.

Predictability in the finer details diminishes post-Saturday as
medium range guidance depicts additional waves in western CONUS
northwest flow aloft dropping into the region with additional fropa
potential.  At this forecast distance, have just maintained
broadbrush low PoPs late Sunday into Tuesday along with seasonable
temps.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1240 PM EDT Tue Jul 2 2024

Dry low levels will maintain VFR/dry conditions through most of
tonight. A frontal boundary will then weaken southeast into
KSBN toward daybreak tomorrow, and around midday at KFWA. A few
showers may survive into KSBN, though chances for measurable
rain remains on the low side. Low level moisture does stream in
advance of the front with high MVFR to low VFR cigs expected to
fill in tomorrow.

&&

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

&&

$$

DISCUSSION...Marsili
AVIATION...Steinwedel