Special Marine Warning 25, NWS Northern Indiana

Area Forecast Discussion
National Weather Service Northern Indiana
337 PM EDT Tue Sep 7 2021

.SYNOPSIS...
Issued at 336 PM EDT Tue Sep 7 2021

A line of storms will move through the region this evening into
early tonight. Some of the stronger storms may have damaging wind
gusts and large hail. Cooler and drier air will move in for
Wednesday and Thursday.

&&

.SHORT TERM...(This Evening through Wednesday)
Issued at 322 PM EDT Tue Sep 7 2021

Strong mid level shortwave translating eastward through northern
Lower Michigan this afternoon. Strong, elevated, linear-segmented
convection ongoing from central Lower Michigan into north central
Illinois at this time. Strong diabatic heating across CWA early
afternoon with surface temperatures into the middle 80s that will
aid in maintaining upstream thermal instability and allow storms
to become surface based with increased wind threat. This
morning/early afternoon convection was driven more by theta-e
plume/middle to upper 60s surface dewpoints immediately in advance
of attendant cold front and collocated eastern periphery of
EML/higher mid level lapse rates with elevated storm mode. Veered
low/mid flow continues to strengthen with resultant deep/effective
layer shear on order of 40-50 kts. Forcing depth accentuated amid
40-60m/12 hour 5H height falls. Setup should aid in maintaining
strong to severe convection into northwest CWA around 20-21 UTC.
While primary concern is damaging wind gusts with DCAPE on order
of 900 J/kg, strong helical low level flow could give rise to
leading edge mesovorticies that, when tied to rear inflow
jet/notch, could lead to brief tornado. Million dollar question
will be how far southeast strong/severe convection can maintain.
Shallow nature of theta-e upstream and mixout into the upper
50s/lower 60s presently points to short duration with southeast
extent MLCAPE waning. Suspect convection to dwindle/become
outflow dominant by about 00 UTC across northern Indiana.

&&

.LONG TERM...(Wednesday Night through Tuesday)
Issued at 322 PM EDT Tue Sep 7 2021

Few changes to long term. Steep low level lapse rates and minor
shortwave could yield some showers downstream of southern Lake
Michigan. Otherwise long duration dry period as Great Basin mid
level ridge retrogrades eastward with building heights across
southern Great Lakes. A weak frontal boundary sags southward into
northern CWA late Sunday, associated with shortwave within high
belted westerlies. A better chance for showers/storms late
Monday/Tuesday with stronger northern stream wave in advance of
deepening warm sector.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday Afternoon)
Issued at 1239 PM EDT Tue Sep 7 2021

VFR conditions through 20Z. Winds remain strong from the
southwest between 15 and 25 kts. Occasional gusts to 40 kts cannot
be ruled out. LLWS does not appear to be a concern at this time
as the flow is uniform through the boundary layer.

For KSBN - After 20Z the situation changes dramatically as the
front and associated convection charges out of the WI/MI and
sweeps into the KSBN area. Expect IFR CIGS/VSBY with along and
behind the front/convection. Additionally, high confidence that
there will be LLWS / significant turbulence associated with this
convection at onset. Timing of LLWS is still uncertain...but don't
expect it to persist for more than a couple of hours.

CIGS/VSBY improve by the latter part of the forecast period.

For KFWA - Continued VFR through 00Z. Strong southwest winds will
create a very turbulent boundary layer but LLWS is not expected.

After 00Z conditions begin to deteriorate and expect a short
lived period of convection to pass through the area. ISOLD
MVFR/IFR CIG/VSBY with the convection/frontal passage...and could
have isold LLWS during the passage. Some lower CIGS possible in
the wake of the cold front...however do not anticipate widespread
impacts to flight operations.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Beach Hazards Statement through Wednesday evening for INZ003.

MI...Beach Hazards Statement through Wednesday evening for MIZ077.

OH...NONE.
LM...Small Craft Advisory until 8 PM EDT Wednesday for LMZ043-046.

&&

SYNOPSIS...Murphy
SHORT TERM...Murphy
LONG TERM...Murphy
AVIATION...Lewis

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