Coppess Corner, Indiana Weather Forecast Discussion

824
FXUS63 KIWX 201040
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
640 AM EDT Sat Sep 20 2025
.KEY MESSAGES...
- Chances (30-60%) for showers and a few thunderstorms
  increasing through the day and into tonight, especially west
  of I 69. Mostly cloudy with highs in the 80s. Lows overnight
  in the 60s.
- A more active pattern ahead, with daily chances (20-60%) for
  showers and storms through next Saturday. The best chances
  will be Sunday and Monday. A few stronger storms are possible
  Sunday afternoon and evening, with gusty winds the primary
  threat.
- High temperatures Sunday will be in the upper 70s and low to
  mid 80s, then remain in the 70s through the remainder of the
  work week. Lows will be in the 50s and low 60s.
&&
.DISCUSSION...
Issued at 440 AM EDT Sat Sep 20 2025
Showers and thunderstorms just along our western border,
particularly near White County, IN. Left pops around 20-30 percent
there through the day, eventually expanding to the remainder of the
CWA through the afternoon and overnight and increasing to around 30-
60 percent depending on location (best chances west of I 69). A
stalled boundary draped from MN into the Chicago area and southeast
into Portland, IN lingers-with east flow to the north of it, and
nearly calm to light E-SE/S winds to the south. The showers/storms
are focused along a trough/axis of moisture convergence-with decent
moisture transport and elevated instability at 850-925 mb.
Eventually our stalled front will lift northeastward this morning as
a warm front before stalling again this evening roughly from Van
Buren Co, MI through Fulton/Defiance/Henry, OH and into Lake Erie. A
500mb trough swings through extending from low pressure over the
northern plains/upper MS valley towards the afternoon into the
overnight, providing better forcing (especially west) for
showers/storms to develop-especially along the frontal boundary.
Flow is pretty weak aloft so don`t expect any severe weather today.
Highs will rise into the mid-upper 80s, with lows dropping to around
60 degrees overnight.
Late tonight into Sunday we have a couple stronger waves move
through, especially in the afternoon and evening. With better
forcing, decent afternoon instability (500-1000J/kg sfc cape/mid
level lapse rates around 6.5C/km), and a belt of mid level flow to
35-40 knots or so--we could see some stronger storms develop. SPC
has our area in a marginal risk, which is reasonable. Main threat
would be gusty winds in the 40-50 mph range with any downbursts in
stronger cells, with isolated gusts to around 60 mph. Chances for
rain max out in the 60-80 percent range, which is welcome given
drought/abnormally dry conditions around the area. Highs will be in
the upper 70s and low to mid 80s, warmest in NW OH.
Monday and beyond confidence lowers, as much will depend on the
evolution of the upper level pattern which is still in question.
Have the best potential Monday-Monday night (55-70% max) tied to the
strongest waves rippling through the flow along the trough/Upper low
(afternoon/evening hours). Tuesday into Friday we could have an
upper low centered right over our CWA and the Great Lakes (favors
better rain chances), or if solutions like the ECMWF are right-the
low dives southward towards the gulf and we end up with more of an
elongated low/trough (and lesser chances). Have 20-50% chances from
Tuesday into next Saturday, which is reasonable given expected
pattern. Overall, temperatures with a low/trough overhead and
probably more extensive cloud cover will likely be in the 70s, with
overnight lows dropping into the 50s.
&&
.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 640 AM EDT Sat Sep 20 2025
An initial dampening lead short wave will continue to lift
across northwest Indiana this morning. This forcing has started
to outrun the better elevated instability across northeast
Illinois and would expect that coverage of the showers/isolated
storms across far northwest Indiana will have a difficult time
maintaining over next several hours. By late morning and
especially this afternoon/early evening, a larger scale upper
trough will begin to acquire more negative tilt across the Corn
Belt allowing instability to gradient to shift slightly
eastward into far northwest Indiana. This mid/upper forcing
combined with broad low level confluent flow should allow for
scattered showers/isolated storms to develop during the
afternoon. Best chance of showers and storms still appears to be
in place for KSBN vicinity closer to this instability gradient.
Steep low level lapse rates and fairly large low level dew
point depressions could support some gusty winds of 25+ knots
with any showers or storms but confidence in this scenario is
low given uncertainty in the extent of available instability
this afternoon which will depend on cloud breaks and depth of
mixing. Scattered showers will likely persist into tonight but
loss of sfc based instability should make thunder coverage more
limited through late evening.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...None.
&&
$$
DISCUSSION...MCD
AVIATION...Marsili

NWS IWX Office Area Forecast Discussion