IWX issues Area Forecast Discussion (AFD) at Sep 9, 6:27 AM EDT570
FXUS63 KIWX 091027
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
627 AM EDT Tue Sep 9 2025
.KEY MESSAGES...
- Temperatures in the mid to upper 70s and low 80s will climb
into the mid-upper 80s by Friday, possibly persisting through
the weekend.
- Dry with variable cloud cover through the work week. There are
low chances (20-30 percent) for rain showers this weekend.
Isolated thunderstorms are possible.
&&
.DISCUSSION...
Issued at 353 AM EDT Tue Sep 9 2025
High pressure/increased ridging persists over the coming days, with
an upper level trough moving through Wednesday-Thursday that may
lead to some increased cloud cover. As the trough moves eastward and
another ridge extending from the SW US and TX builds into our west
Thu afternoon-evening, it's possible we see some light rain showers
along the edge of the ridge...but confidence was way too low to
include in the forecast at this point. High temperatures today will
be in the mid-upper 70s, then hover around 80 degrees Wed-Thu. By
Friday as the ridge builds in we will see high temperatures into the
mid-upper 80s.
This weekend forecast is a little more challenging as models
continue to show large scale pattern differences with regards to the
strength of the ridge and the path of the 554dam low pressure system
that moves into Hudson/James Bay around Friday afternoon. The trough
extending from this closed low will make a run at breaking down the
ridge over our CWA--its success dependent on it's strength and the
path of the low. Some models carry the low into northern Quebec,
others keep it closer to the Ontario/Quebec border just northeast of
Lake Huron/Georgian Bay. Either way, our CWA will likely be on the
border of the ridge/trough, thus susceptible to any waves riding the
ridge (585 to 590 dam). The first of these arrives either Friday
night or Saturday morning, crossing through our CWA into Sat
evening, followed by an additional wave Sunday. On Saturday, we'll
have a low level jet (albeit not crazy strong) aiming into our NWS
CWA (near Lake MI) through the morning/afternoon, which will bring
in some moisture for us to work with. Some models bring the trough
axis through earlier in the 6-12z time frame, others more in the 15-
18z time frame. Mid level lapse rates look to be around 6.5-7C at
times-especially further west...so did keep the 20-30 percent
chances for rain showers with isolated thunderstorms possible
(especially with later timing where we can build up more daytime sfc
instability. The timing of this wave and that on Sunday will impact
temperatures--the more precip/cloud cover the less likely the upper
80s are (probably more like upper 70s, low-mid 80s in some areas).
Adding to the complexity, as the war between the ridge/trough to the
east continues, another low pressure system enters off the western
CONUS and slowly drifts eastward--impinging on the western side of
the ridge. An omega-blocking pattern sets up and strengthens through
Sunday (low over the north/central plains and then the other in the
Northeastern CONUS). The upper level ridge is amplified as this
western trough builds in--extending from the southern US into
northern Ontario and possibly Manitoba by Sunday-depending on where
it sets up as previously discussed. The ECMWF really holds this
pattern as it keeps the stronger/more elongated western trough
further east until Tuesday and the eastern coast low further south
and stationary, with the "neck" of the ridge over us becoming more
and more narrow with time. It also sets up a frontal zone from the
Dakotas southeastward into MN/WI/IL (possibly western IN). This
solution keeps the potential for precipitation over our area
(especially west) Sunday into Monday/Mon eve.
Alternatively, more progressive solutions like the GFS keep the
ridge broader as the trough to the east moves out into the Atlantic
(by 18z Mon) and western trough/frontal zone lifting further
northeast into Saskatchewan/Manitoba/northern Ontario. This solution
would keep us mostly dry from Sunday afternoon into Tuesday.
For now, kept the low 15-20 percent chances for showers and possibly
a few storms over the CWA Sunday and then in the west on Monday.
&&
.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 625 AM EDT Tue Sep 9 2025
High pressure sliding east allows more warm air advection to come in
on its west side into the area and this brings in high clouds.
However, plenty of antecedent dry air in the mid to low levels
allows for VFR conditions and a weak gradient limits the low level
jet strength keeping winds weak.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...None.
&&
$$
DISCUSSION...MCD
AVIATION...Roller
Source:
IWX issues Area Forecast Discussion (AFD) at Sep 9, 6:27 AM EDT---------------
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