Swan, Indiana Weather Forecast Discussion

596
FXUS63 KIWX 271817
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
217 PM EDT Sat Sep 27 2025
.KEY MESSAGES...
- Dry and partly to mostly sunny through next week.
- Highs will be in the low to mid 80s through Tuesday cooling into
  the 70s for the middle and latter portions of the work week.
&&
.DISCUSSION...
Issued at 215 PM EDT Sat Sep 27 2025
A quiet weather pattern to be maintained through this forecast valid
period with seasonably warm and dry conditions persisting.
Primary short wave track tonight into Sunday will be across south
central Canada as an upper level wave moves into western Quebec by
daybreak Sunday. A weak frontal zone will drop across the southern
Great Lakes in response to this feature Sunday morning. Light
onshore winds are expected to develop across far NW IN/SW Lower
Michigan early Sunday morning which could promote some patchy fog
formation across the extreme northwest. Otherwise, clear skies and
light winds will promote another night of good radiational cooling
conditions and lows in the mid 50s.
Mid/upper level height rises will commence once again Sunday morning
with the departure of the northern Great Lakes/south central
Canadian negative upper height anomaly as a 590 dm ridge builds
across the MS Rvr Valley. Mid level subsidence and very weak
westerly low level WAA in wake of morning short wave should allow
for highs a few degrees higher on Sunday into the middle 80s for
many locations.
Little change in the day to day weather expected through midweek as
an omega block-like pattern develops. This stable wave pattern/blocking
should keep the upper ridge axis parked from the southern Great
Lakes into southwest Ontario. This pattern should produce
comparable highs in the mid 80s again on Monday with a
possibility of a few slightly warmer readings given potential of
superadiabatic lapse rates with continued dry soils.
For Tuesday into Thursday, guidance has been consistent in a more
substantial upper trough dropping southeast across SE Canada with
some backdoor-like cold advection building westward across the
eastern Great Lakes. Some of this cooler low level air should advect
westward in easterly low level flow regime for the end of the work
week with highs back into the mid 70s by Thursday.
The stagnant upper level pattern does still appear to break down
some by next weekend. Medium range deterministic/ensemble guidance
suggests a lead short wave should try to dampen central CONUS upper
ridging for first part of next weekend. This weakened upper ridging
could then be more conducive for better southward latitudinal
progression of next upper trough axis in the Day 8-10 period. This
would increase chances of more substantial cool front, but not until
well after this forecast valid period. Dry conditions were
maintained through this forecast as any moisture transport of note
ahead of the lead wave for Saturday will be hard to come by given
expansive southeast anticyclone at this time.
&&
.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1200 PM EDT Sat Sep 27 2025
Dry, stable air mass will continue to promote VFR conditions,
light winds and mainly clear skies through the TAF cycle.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...None.
&&
$$
DISCUSSION...Marsili
AVIATION...Steinwedel

NWS IWX Office Area Forecast Discussion