Chili, Indiana Weather Forecast Discussion

837
FXUS63 KIWX 211042
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
642 AM EDT Sun Sep 21 2025
.KEY MESSAGES...
- Scattered to numerous showers expected at times today, with
  chances for thunderstorms. A few strong to severe storms are
  possible, with damaging winds the primary threat.
- Rain is likely with scattered thunderstorms Monday and
  Tuesday (40-80%), highest chances on Monday. Daily chances
  (20-40%) for showers and a few storms Wednesday through next
  Saturday.
- High temperatures will be in the upper 70s and low to mid 80s
  today, then fall into the 70s through next weekend. Lows will
  be in the 50s and low to mid 60s.
&&
.DISCUSSION...
Issued at 427 AM EDT Sun Sep 21 2025
Complex forecast this week in terms of narrowing down the exact
time/location of precipitation chances, though expect the best
chances will be today into Tuesday. Our area is on the border of the
upper level ridge to the east and an incoming closed low to the
northwest (over Dakotas/MN this morning). A broad trough extends
down into the central/even southern plains, with convection
developing at various points along shortwaves that ripple through
mid level flow. The more synoptically driven shortwaves and
convectively driven impulses will impact our area through the next
week, particularly as the low migrates eastward into upper Michigan
with the associated trough over our CWA by Monday/Tuesday. By Wed-
Friday the upper low could be either south of our CWA or slightly
west (some overhead). If it`s further south (towards Dixie Alley)
then we`ll see a drier forecast after Wed, but if solutions like the
ECMWF (slightly west/overhead) verify, we`ll see a surface low
develop in the central plains Wed night that lifts northeast into
our CWA by Thursday morning...lingering through Friday and Saturday.
Overall, decided to keep the highest pops today into Tuesday (40-
80%), then left the consensus 20-40 percent chances from Wednesday
into next Saturday (dry Sun), with highs in the 70s and lows in the
50s, low 60s.
This morning we have a pair of stationary fronts draped from
southern Lake MI--one heading into IL (west of our area) and another
through South Bend down into Portland, IN. Convection this morning
is in between these two features thanks to increased moisture
transport/convergence from the LLJ and a shortwave moving through
aloft. Right now have numerous showers (~60%) with chances for
thunderstorms in the white County, IN to Grant County, IN area all
the way up to Rochester, lifting northeast and likely diminishing
through the morning. Otherwise, lower chances persist as the
stationary front over IN lifts northeast as a warm front through the
afternoon and evening. There may be a period of lesser coverage (20-
40%) or even dry conditions late this morning into early afternoon
before the next shortwave arrives for the late afternoon-evening
period. Have higher chances (40-60%) to account for this.
Additionally, given the later afternoon timing (better surface
instability), mid-level lapse rates around 6.5-7C/km, and 25-40
knots of bulk shear at times--SPC has our area in a Marginal Risk
for isolated strong-severe storms. Given yesterday`s overperformance
with less favorable conditions-it`s definitely a possibility.
Damaging winds would be the primary threat, though I wouldn`t be
surprised to see a few small hail reports (up to 1 inch max).
Forcing is stronger tonight into Monday along yet another wave/weak
surface cold front (especially with some increased support from an
upper level jet), so have rain (60-85% range) with scattered
thunderstorms in the forecast through Monday evening, diminishing
gradually through Tuesday (outside of a slight uptick during the
afternoon with extra heating/instability available). Confidence is
much lower on Tuesday as a lot depends on how today into Monday
develop. High temperatures today will be in the upper 70s, low-mid
80s (a few upper 80s possible if more sun can break through cloud
cover over NW OH-especially near Lima). With more widespread rain
chances and cloud cover expected Monday into Tuesday, have highs in
the 70s.
&&
.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 640 AM EDT Sun Sep 21 2025
The combination of broad isentropic upglide and what appears to
be convectively enhanced short wave kicking out of northern
Illinois has been sufficient for large area of rain showers
across northern Indiana early this morning. Some weak elevated
instability is noted per RAP analysis soundings for 850 mb based
parcels, but still expecting thunder coverage this morning to
be very limited. Rain showers should tend to diminish after 14
or 15Z this morning with a possible lull in rain shower coverage
through early to mid afternoon. Forecast confidence on
convective trends remains low given a complex mid/upper level
pattern. Upstream short waves are being modified by ongoing
convection early this morning across southern IL/MO and also
across KS/OK. This leads to low predictability in forecast
details regarding the track and strength of these short waves.
Both of these areas of convection may allow for some
convectively enhanced short wave to lift northeast into northern
Indiana later this afternoon into tonight.
Low level southerly flow will be a bit stronger today in
advance of these forcing mechanisms, which should also help
sustain advective forcing into this evening. Have included TEMPO
SHRA mention from mid afternoon into early evening hours
coincident with peak diurnal instability, but iso-sct thunder
remains a distinct possibility given steep lower level lapse
rates and most guidance indicating 1000-1500 J/kg of sfc based
instability by later this afternoon. Will remain conservative
with precip mention after 01Z, as forecast confidence remains
low given the uncertainty in upstream short wave track/strength.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...None.
&&
$$
DISCUSSION...MCD
AVIATION...Marsili

NWS IWX Office Area Forecast Discussion