Severe Thunderstorm Warning 44, NWS Northern Indiana

Area Forecast Discussion
National Weather Service Northern Indiana
128 PM EDT Sun Jun 25 2023

.SYNOPSIS...
Issued at 1000 AM EDT Sun Jun 25 2023

A round of strong to possibly severe storms is expected during the
mid to late afternoon hours today. Cooler weather is expected
Monday and Tuesday with periodic showers.

&&

.UPDATE...
Issued at 1000 AM EDT Sun Jun 25 2023

Rain associated with a decaying MCS should clear our far eastern
counties by 11 am leaving dry and increasingly hot/humid
conditions through mid afternoon (2-3pm). This will promote a
favorable environment for strong to severe convection to develop
along an incoming cold front near the US-31/IN-15 corridors around
19-20z, possibly growing upscale into a linear segment or two
once reaching I-69 and east between 20-00z. SPC's latest day1
update did cap probs in the Enhanced range, though did extend
the higher hail/wind/tornado probs north to include south-
central MI. Thoughts on shear/instability profiles and favorable
deep forcing remains unchanged from what was described in the
short term discussion. Confidence continues to increase for strong
to severe storms to develop, however, when convection initiates
and how quickly said convection can grow upscale into a more
organized wind machine does remain the lingering question mark at
this juncture.

&&

.SHORT TERM...(Today and Tonight)
Issued at 345 AM EDT Sun Jun 25 2023

...Increasing confidence for at least scattered severe storms later
today....

Nocturnal MCS is currently knocking on our doorstep, being supported
by impressive low level theta-e advection on the nose of a 30-40 kt
LLJ. This moisture advection is anticipated to weaken with time and
eastward extent this morning as low level flow backs more westerly
and best theta-e plume is pinched off to our south. Mean flow and
placement of moisture/instability gradient should favor more S/SE
propagation of this cluster with time. Local environment is
currently very dry/stable but there will still be some decent
moisture advection in the next few hours. Hi-res guidance shows a
weakening trend as convection crosses our CWA in the next 4-6 hours
but wouldn't be surprised if a few strong storms survive into at
least our southwest quadrant based on forecast soundings/instability
profiles and tendency for this type of nocturnal convection to
sustain itself longer than anticipated. SPC/RAP mesoanalysis
supports this possibility with some non-zero MLCAPE's in our far SW
by 12Z. Severe threat still appears low however given very stable
conditions near the surface (limiting damaging wind) and overall
modest midlevel lapse rates (limiting large hail).

Do expect morning convection to dissipate/exit by 15-16Z with a gap
before primary cold front arrives roughly 18-19Z. That is not a
large gap but virtually all of the latest guidance is in agreement
that deep convection will develop along the cold front in our CWA by
mid-late afternoon. Synoptic forcing is impressive for June with
good upper level divergence in left exit region of a 100+ kt jet at
250mb. Strong CVA/height falls noted with closed midlevel low and
this will drive a sharp cold front through the area providing ample
lift. Instability continues to be the main question given morning
clouds/precip and limited gap but models persist in indicating at
least 2500 J/kg of SBCAPE due to impressive moisture pooling ahead
of this strong front. NAM CAPE values are much higher but driven by
unrealistic mid 70s surface dewpoints. Prefer surface dewpoints just
below 70F. Still...midlevel lapse rates are expected to be near 7
C/km and 87/68 surface T/Td still yields around 2000 J/kg 0-1km
MLCAPE. Kinematics are also supportive of organized convection,
particularly in our southern CWA closer to primary midlevel jet. 30-
40kts of 0-6km bulk shear is anticipated in our far south tapering
to 20-30 kts in our north. 3km winds will also be SW around 35 kts
with decent veering/helicity given southerly surface winds. This
would support the potential for a few supercells when storms
initiate (roughly 18-19Z along/just east of the US-31 corridor)
transitioning to a more linear mode with upscale growth. All hazards
remain on the table with initial storms with large hail likely due
to steep midlevel lapse rates. Anticipate eventual growth into a
QLCS with damaging winds and a few embedded tornadoes becoming the
main threat. Storms will be moving very quickly across our CWA with
storm speeds up to 50 mph possible. Hi-res CAM's suggests storms may
exit our eastern border by 23Z.

Coverage of severe storms is one lingering question though,
particularly at/just after initiation. There is a mismatch between
best synoptic forcing in our north and better moisture/instability
in our south. This coupled with lingering concerns over exact degree
of destabilization leads to some subtle but important differences in
hi-res CAM's regarding exact location of initiation, coverage in the
early hours, and whether initial storms will develop on the northern
end of the front or the southern. Eventually expect a more solid
line to develop but coverage of strong/severe storms in our central
CWA is a lingering uncertainty. There is higher confidence in
greater coverage of severe storms east of I-69 and south of US-24
where SPC has placed greatest severe probs.

&&

.LONG TERM...(Monday through Saturday)
Issued at 345 AM EDT Sun Jun 25 2023

With plethora of potential hazards in the short-term did not make
too many changes to the going forecast for the long term. The
overall story remains much the same with upper low moving into the
Great Lakes and supporting two days of cool, cyclonic flow. This will
yield cool, cloudy, and windy conditions with periodic showers Mon-
Tue. Dry weather is expected midweek with some potential for
additional rain to end the week, though details remain highly
uncertain at this range.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday Afternoon)
Issued at 110 PM EDT Sun Jun 25 2023

Another round of storms will move through with a cold frontal
passage this afternoon. Storms have developed over northwest IL
and are moving east to northeastward and will likely begin
affecting KSBN around 19-20z period but then move east of the
terminal by 21z Sun. There is a bit more uncertainty to the exact
evolution and initiation further eastward however latest HRRR
guidance has a linear convective feature moving into the KFWA
vicinity around 21z. Strong gusty winds and hail will be possible
with these storms, some look to become severe. Storms should exit
the area after 23z Sun. Scattered showers behind the frontal
boundary with lowering cigs with MVFR conditions after 06z Mon
for KSBN and around 07z for KFWA.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...Small Craft Advisory until 8 PM EDT this evening for LMZ043-046.

&&

UPDATE...Steinwedel
SYNOPSIS...Steinwedel
SHORT TERM...AGD
LONG TERM...AGD
AVIATION...Andersen

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