Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 270812

Area Forecast Discussion
National Weather Service Northern Indiana
412 AM EDT Tue Jul 27 2021

Issued at 412 AM EDT Tue Jul 27 2021

Dry again today with highs near 90. Humidity will increase on
Wednesday and storms are expected Wednesday night into Thursday.
Severe storms with damaging winds and heavy rain are possible but
confidence is low. Cooler and drier to end the week.


.SHORT TERM...(Today and Tonight)
Issued at 412 AM EDT Tue Jul 27 2021

Decaying MCS over northern Lake Michigan and secondary MCS to
the west still expected to dissipate before reaching our CWA as they
far outpace parent forcing and intersect a very dry, subsident, and
stable airmass over the Ohio Valley. Anticipate just some increasing
high clouds mainly across our northern zones. Overall setup remains
very similar to yesterday with highs expected to be very near 90F
though clouds may limit that slightly. Dewpoints may creep up a bit
more today given some weak return flow late in the day and
increasing influence of agricultural evapotranspiration this time of
year. Still, only expecting mid to perhaps upper 60s for most
locations which only equates to low 90s for heat indices. Still
watching weak frontal boundary that pushes into our area late
tonight into Wed. Still prefer to keep tonight period dry given
almost complete lack of mid/upper support for ascent and still a
very dry/stable airmass locally per latest forecast soundings. A bit
more clouds and increasing dewpoints in light but steady WSW flow
will add a few degrees to overnight lows (upper 60s-70F).


.LONG TERM...(Wednesday through Monday)
Issued at 412 AM EDT Tue Jul 27 2021

Situation does begin to change on Wed though. Front will stall
across our area early in the morning and then try to lift back north
as a warm front. However...latest models are suggesting more NW low
level flow with some embedded shortwaves that could support precip.
First chance is during the early morning but prefer to hold with
silent 10 PoP given tenuous vort signal and still poor instability.
Another wave possible during the late afternoon and this is where I
have added some slight chance PoP`s mainly because forecast
soundings now indicate decent instability (around 2000 J/kg MLCAPE)
with very little cap. Lack of strong forcing will keep coverage in
check but a few isolated storms are possible. If storms develop
there is a low severe risk given moderate instability and around 25
kts of 0-6km shear. Note that is not what is driving the SWODY2 for
our area. That is driven by nocturnal convection Wed night discussed

Better precip chances still anticipated overnight...particularly by
late overnight. Strong MCS expected to develop over WI given extreme
moisture convergence and instability (near 4000 J/kg MLCAPE) on nose
of 50 kt LLJ. Shear and MUCAPE profiles are supportive of nocturnal
MCS maintenance with 7-8 C/km midlevel lapse rates folding into the
southern Great Lakes by early Thu AM and around 60 kts of deep layer
shear over MI. Potential exists for widespread and/or significant
damaging winds and heavy rain to our north through the overnight
period but question for our area will be exact track and timing.
Several guidance sources indicate track of primary MCS will be just
to our N/NE while some models do clip our NE half. Further
complicating things for our area is very late timing. Could be
around 09Z before MCS reaches our CWA and it`s very tough to
maintain severe convection that late when it is so far removed from
initial forcing and best instability. Unfortunately tough to nail
down any specifics at this time range but will continue to monitor
very closely. Heavy rain and damaging winds are the main concerns
for our area with heavy rain being the more likely hazard given late
timing and some signal for upwind propagation Thu AM.

Attention then turns to corresponding cold front passage during the
day Thu. Once again timing is key with uncertainty compounded by
questions about nocturnal convection. If our area is largely missed
by MCS early AM then suspect enough recovery to support strong
(potentially very strong) instability over our far southern zones
that could support severe convection by early afternoon. If however
we are hit with strong MCS, expect enough stabilization and
southward surge of outflow boundary to keep severe chances south of
our CWA. Again very tough to nail down specifics this far out but
hope to have more clarity in the next 24 hours.

Only other item of note is building heat/humidity Wed. Temps remain
near 90F but dewpoints will climb into the low to perhaps mid 70s
yielding heat indices near 100F in our southwest half. Think we will
fall short of advisory criteria but something else to watch. Rest of
the long term is quiet. Cool and pleasant weather returns Fri. A
weak wave and cold front passes Sat night/Sun with some low precip
potential and reinforcing shot of cool/dry air for early next week.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday Night)
Issued at 118 AM EDT Tue Jul 27 2021

VFR Conditions are expected at the TAF sites through Tuesday
evening, with light southwest winds and mostly clear skies. Low-
level moisture will be increasing, but BR is not expected tonight
at the terminals given large dewpoint depressions. Mid-level
clouds may develop Tuesday evening, in advance of the next
disturbance that is set to arrive Wednesday night.





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