402
FXUS63 KIWX 181426
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
1026 AM EDT Sat Oct 18 2025

.KEY MESSAGES...

- Showers and scattered thunderstorms will develop over
  northwest Indiana this morning then spread across the entire
  area this afternoon.

- Thunderstorms today may become marginally severe and produce
  strong to locally damaging wind gusts this afternoon into
  early tonight.

- Rain will be heavy at times tonight through Sunday. Total
  rainfall amounts may exceed 2 inches in some areas northwest
  of Fort Wayne.

- Becoming breezy today with wind gusts up to 30 mph. Windy Sunday
  with wind gusts to 40 mph Sunday.

&&

.UPDATE...
Issued at 1026 AM EDT Sat Oct 18 2025

There continues to be the marginal risk of severe thunderstorms this
afternoon and the overall forecast remains on track. Start time for
thunderstorms is within the 2pm to 5pm EDT window, with a slight
preference toward the 5pm start time. Compared to 24 hours ago, it
appears north of US 24 may be the area of interest, even as far
north as South Bend and Angola. Isolated thunderstorms may develop
in those areas on a lingering outflow boundary from morning showers
that fizzled out. Upper-level support this afternoon comes from a
departing 500-mb jet (right entrance region) and an incoming 850mb
jet (left exit region). Cloud cover is thin upstream which ought to
permit ample destabilization. 60-degree dew points are already seeping
in along the IN-IL line. Southern areas have the risk of severe
storms closer to sunset from any lingering activity existing west-
central IN.

Hodographs appear linear in nature and LCLs remain high (1500m)
which lessens confidence in any tornado risk. Thus, damaging wind
gusts remain the primary severe weather hazard amid this highly
sheared environment and steep low-level lapse rates.

&&

.DISCUSSION...
Issued at 108 AM EDT Sat Oct 18 2025

A pair of upper level trofs will approach from the west today
and then merge just upstream of the forecast area. This new
merged system will have a lot of energy in the base of the upper
level trof with 500 mb winds > 100 kts. Mid level lapse rates
do not appear very steep; however, low level shear and very
strong upper level winds should create an environment for
marginally severe storms. Wind gusts from 45 to 55 mph with at
least the stronger storms this afternoon into this evening
appears reasonable. Locally heavy rainfall is likely with most
of the storms. The PWAT anomaly will be around +1.00" for an
extended time from this morning through most of tonight. While
the antecedently dry conditions do not favor flooding, it looks
like the chances for any flooding should be confined to mainly
urban areas - especially those that are more prone to flooding.

Low level moisture at the surface was meager early this morning
with dew points almost exclusively in the 40s. Winds had
already become south around 10 mph ahead of the front and
associated developing surface low pressure area. Low level
moisture will surge north of the Ohio River and east of the
Mississippi River today as the system approaches. The latest GFS
BUFKIT has CAPE values this afternoon < 200 J/Kg; however, the
00Z NAM is much more unstable with afternoon CAPEs topping 1000
J/Kg. In light of the GFS and SREF soundings, the NAM does
appear to have a better handle on afternoon low level heating
with surface temperatures southeast of the front around 80
degrees to the lower 80s. All considered, the chance for
marginally severe storms appears reasonable given the changes
expected in the low level thermal environment and wind fields.
This environment should be able to support strong to locally
damaging wind gusts by late this afternoon.

Chilly air will spread across the forecast area behind the main
system. High temperatures Tuesday and Wednesday are expected to
only be in the 50s. There is a good chance for frost Wednesday
night before temperatures recover closer to normal.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 647 AM EDT Sat Oct 18 2025

A broken line of showers and thunderstorms is lifting north-
northeast through Chicago. Time of arrival yields a glancing
blow to KSBN around 13z. Lightning is sparse south of Chicago
due to weak instability. After this passes, low confidence in
some scattered showers in the vicinity. Improved confidence in
the advertised PROB30 group, followed by a period of steady
rain overnight and decreasing flight conditions.

At KFWA, there is a low likihood the current IL activity
survives due to the NNE trajectory. Instead, a period of -TSRA
remains in the cards for the late afternoon followed by a period
of rain. The start time of steady rain and decreasing flight
conditions is a little uncertain due to the NNE trajectory of
the low which delays the onset time there. Have split the
difference by offering 09z.

For both sites, wind becomes northwesterly just beyond this TAF
period. Will need to monitor the LLWS threat later today, but
for now appears to be brief and marginal.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...Gale Warning from 8 AM to 11 PM EDT Sunday for LMZ043-046.

&&

$$

UPDATE...Brown
DISCUSSION...Skipper
AVIATION...Brown