Rockford, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

426
FXUS63 KLOT 291925
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
225 PM CDT Thu May 29 2025

.KEY MESSAGES...

- Strong thunderstorms with damaging wind gusts may move
  southward across the region Friday afternoon and evening. The
  Storm Prediction Center has a Level 1/5 threat for severe
  weather east of I-39.

- There is an increasing signal that smoke from wildfires in
  Manitoba will stream into the Midwest and Great Lakes as early
  as Friday, and potentially linger through the weekend.

- A pattern change is anticipated during the first week of June
  and will result in the arrival of more summer-like
  temperatures, followed by increasing chances for storms mid to
  late week.

&&

.DISCUSSION...
Issued at 225 PM CDT Thu May 29 2025

Through Friday Night:

A positively tilted mid-level trough shifting south-
southeastward into the Midwest this afternoon and evening will
drive an area of showers and thunderstorms eastward across MO
into southern IL later today into tonight. While most of this
activity will remain south of our area, we cannot rule out the
low possibility (~15%) for a few isolated late afternoon and
early evening showers, particularly across interior portions of
northern IL. Any showers that do develop are expected to
dissipate after sunset this evening.

On Friday, the mid-level short wave trough axis shifting across
the Midwest into tonight will shift out across the Ohio Valley.
In its wake, an enhanced belt of northerly mid and upper-level
flow setting up along the eastern periphery of a Canadian ridge
will drive another impulse southward across the western Great
Lakes Friday afternoon into the the early evening. While low-
level moisture will remain modest (in the low to mid 50s
dewpoints) in advance of this feature, steeping low-level lapse
rates within a deeply mixed boundary layer (0-3km lapse rates in
excess of 8.0C per km) during peak heating should support
MLCAPE of 500-1000 J/kg by late afternoon. Accordingly, the
expectation continues to favor the development of scattered
showers and thunderstorms by early to mid afternoon across parts
of eastern WI, before shifting southward into northeastern IL
and northwestern IN during the mid to late afternoon into the
evening hours (roughly 4 pm to 10 pm timeframe).

The kinematic envionrment in which these storms develop will be
supportive for organized severe storms. For this reason, the
SPC maintains a level 1 of 5 severe weather threat for eastern
WI and northeastern IL/far northwestern IN for late Friday. The
main concern is that these storms will promote strong downdrafts
and outflow as a result of the deeply mixed boundary layer
making for an inverted-V type sounding. Accordingly, instances
of strong damaging wind gusts may end up being the primary
severe risk with these late day storms. The storm threat will
wane later in the evening with the passage of a surface cold
front.

Outside of the threat for strong storms later in the day,
conditions on Friday will turn warmer and become rather breezy
in the afternoon. Mostly sunny skies and a deepening well mixed
boundary layer will help push afternoon temperatures into the
upper 70s to around 80 degrees. The well mixed afternoon
boundary layer will also foster gusty west-northwesterly winds
around 30 mph through the afternoon.

The final aspect of the forecast we will have to continue to
monitor is the threat of hazy/smoky conditions late Friday into
Saturday as a result of Canadian wildfire smoke being drawn
southward into the Upper Midwest. Strong north-northwesterly
flow aloft will be favorable for drawing some of this smoke
southward, possibly as far south as our region late Friday into
Saturday. While this appears to be a plausible scenario, it
remains a bit unclear how much of this particulate will reach
the near surface layer and impact the air quality. Nevertheless,
it appears at least some milky skies will be possible Friday
night into Saturday as a result of this smoke.

KJB


Saturday through Thursday:

Forecast thinking during this period has not changed. Please
reference the previous discussion below for more info.

Saturday`s weather will, in part, be dictated by how quickly a
backdoor cold front associated with the upper-level trough
diving from Canada into the Great Lakes cuts across our forecast
area Friday night into Saturday. Diurnal
heating/destabilization and low-level confluence could lead to
showers and perhaps a few storms developing along the front
Saturday afternoon wherever it is positioned. Thus, a slower
frontal passage should support shower chances in our forecast
area on Saturday, but a faster frontal passage would expel those
chances to our west and south. Similarly, temperatures will
also largely be governed by the southward and westward progress
of the front, with upper 50s to low 70s temperatures likely to
be observed behind the front (coolest near the Lake Michigan
shore), while locations that remain south/west of the front
through the afternoon may be able to make a run for the low 80s.

Sunday will likely remain dry across our forecast area as
surface high pressure begins to develop in the region ahead of
an approaching upper-level ridge. Daytime heating of the air
mass over the region should tend to favor slightly warmer
temperatures being observed relative to Saturday in most
locations, through continued, albeit weaker, onshore flow should
continue to support a lake shadow of cooler temperatures some
distance inland from Lake Michigan. One additional wildcard for
temperatures on both Saturday and Sunday will be the coverage
and opacity of any lingering Canadian wildfire smoke, as the
persisting northerly to northwesterly flow aloft should tend to
promote the continued transport of smoke particulates
originating from Manitoba and Alberta in our general direction.
If confidence increases in a relatively thick veil of smoke
hovering over the area on Saturday and/or Sunday, then up to a
few degrees may be need to be shaved off of our high temperature
forecast for the affected days.

Monday into Tuesday, the axis of the aforementioned amplified
upper-level ridge should slide eastward across the Midwest.
Both days look like they will be warm and dry (assuming that
the outlier 00Z GFS and GEFS solutions don`t verify), with
southerly flow and at least filtered sunshine allowing for high
temperatures to climb solidly into the 80s, and possibly even
into the low 90s in some locations. Eventually, a gaggle of
Pacific troughs will eject eastward into the central CONUS
during the mid to late week time frame, forcing the upper-level
ridge eastward. How all of these troughs will evolve and
interact with one another remains highly uncertain at this
vantage point, but the ensemble signal for a stormier period
occurring in the Midwest during the middle to latter part of
the upcoming workweek remains quite strong either way.

Ogorek

&&

.AVIATION /18Z TAFS THROUGH 00Z SATURDAY/...
Issued at 1240 PM CDT Thu May 29 2025

Key Messages:

- Weak lake breeze passage at ORD/MDW by early this evening

- Scattered thunderstorms may develop mid Friday afternoon into
  the evening

A developing lake breeze is expected to move inland this afternoon
and early evening causing northwest winds to shift
northeasterly/easterly behind it. Some uncertainty remains on timing
and how far inland the lake breeze will push. Opted to maintain a
lake breeze arrival time of 23Z for ORD, and 22Z for MDW. It`s
possible that the lake breeze may not reach ORD and MDW until the
late afternoon/early evening resulting in a much weaker wind shift.
Nonetheless, winds are likely to remain less than 10kts on either
side of the lake breeze. Winds will become westerly once again
overnight with VFR conditions expected through Friday morning.

After daybreak on Friday winds will increase through the morning out
of the northwest with gusts in the 20-25kt range expected by the
afternoon.

A weather disturbance diving south out of Wisconsin on Friday will
bring increasing chances for scattered thunderstorms to the area mid
Friday afternoon into the evening (some of which could be strong).
Accordingly, confidence was high enough to introduce PROB30s for
TSRA at ORD and MDW beginning at 20Z with this update. Additional
storms are then possible beyond the current 30-hr TAF window along a
subsequent cold front.

Lastly, wildfire smoke from Canada may drift into the region as
early as Friday afternoon aloft and mix down to the surface behind
the cold front Friday evening.

Davis/Petr

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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