Marine Weather and Tide Forecast for North Riverside, IL

DISCUSSION
Issued at 212 AM CDT Wed Jun 17 2026

Through this evening:

Complex set-up today with difficult to predict mesoscale details regarding early day convection and its impacts on surrounding environment likely to play a key role in the magnitude and location of severe potential this afternoon and evening. Significant regional severe weather outbreaks are often a result of mesoscale "accidents" happening withing an otherwise favorable synoptic scale environment for severe weather.

Synoptically, today fits that bill well with an unseasonably strong 120kt+ 250mb upper level jet nosing east-southeast into the mid-Mississippi Valley this afternoon. A rather sharp and vigorous 500mb trough will reach the Upper Mississippi Valley later this afternoon, with a remarkably strong (for mid June)
80kt+ H5 jet streak rounding the base of this trough. At the sfc, a near record deep (for June) double barreled low pressure system is progged by 00z to have one low over southern Lake Michigan east of the IL/WI border with a trough extending northwest to a second low over northwest Wisconsin. From a large scale perspective, this set-up looks exceptionally favorable for a regional severe weather outbreak including the potential for intense tornadoes, however the devil may end up being in the mesoscale details that unfortunately just cannot be accurately predicted this far in advance.

A strong low level jet over the eastern Plains is rapidly transporting deep moisture northward into the lower Missouri Valley. This process can be seen well on GOES TPW imagery. The combination of strong large scale ascent associated with the upper level jet and strong isentropic ascent with the aforementioned low level jet has already led to the development of showers and scattered thunderstorm from northern IA west- northwest across South Dakota and southern Minnesota. Convective allowing models have a pretty strong signal depicting more vigorous, potentially severe, convection developing over eastern IA just prior to dawn this morning as this strong forcing encounters a rapidly northeastward expanding axis of elevated instability driven by the strong low level theta-e advection from the low level jet. The severe threat with this convection looks like it will be confined more to areas south and west of our CWA, closer to the expected elevated instability axis, but cannot rule out a severe threat later this morning creeping into our far southwestern CWA

There is considerable spread in guidance in how this convection evolves, but with low level jet remaining strong through the day as the nose shifts east into Illinois, it is certainly plausible that this convection will increase in coverage and organize into an MCS. Depending on the track, longevity, and intensity of the potential MCS, the synoptic scale environment will be disrupted heading into the afternoon. Again, there's considerable spread in guidance with respect to the placement of what will likely become the effective boundary, a composite of the synoptic scale warm front and outflow boundary from this MCS. A number of models indicate an extremely rapid northward surge of low level moisture and result instability in the wake of this MCS, while other guidance indicates that the effective boundary may struggle to even reach the Highway 24 corridor across our far southern CWA

Normally it is safe to expect a farther south than progged location of the effective boundary in the wake of an early afternoon MCS, however today's set-up features an unseasonably deep surface low for mid June with a near peak high sun angle.
These factor make it difficult to write off the models that depict this boundary and unstable air mass surging rapidly north in the wake of the MCS, possibly making it to nearly the Wisconsin border later this afternoon. The northward extent of the boundary should be demarcation between a more substantial severe weather and tornado threat, and a potentially more muted (but still existent) severe weather threat to the north.

Several of the CAMs are depicting convective initiation along a pre-cold front trough in the warm sector. Given the expected shear, should air mass recovery actually be sufficient, then this would create an exceptionally favorable environment for discrete, fast moving tornadic supercells. Given how quickly these cells will tend to propagate off of the initiating boundary, their ability to survive and thrive will hinge on them traversing a sufficiently unstable/weakly capped environment.
Where and whether this type of environment will exist, will hinge on how the difficult to predict mesoscale details play out this afternoon. Also, the magnitude of instability will play a role in how quickly these storm develop along the boundary as low level convergence along the prefrontal trough isn't progged to be terribly strong. So if weak convection quickly moves off the boundary to even a weakly capped air mass, it could struggle to mature. Where and whether this type of environment will exist, will hinge on how the difficult to predict mesoscale details play out this afternoon.

Forecast hodographs within the warm sector feature an amazingly strong low level shear profile with 0-1km SRH well over 300 m^2/s^2, maximized closest to the composite warm front/outflow boundary where some backing of the low level flow is likely.
Given that LCLs and LFCs will be quite low, there could be rather strong low level CAPE despite the progged abysmal low level lapse rates (less than 6C/km).

Ultimately, today is going to require close monitoring of the mesoscale environment to determine if and where the greatest tornado threat will exist this afternoon and early evening. The current SWODY1 placement of the MDT risk highlights the most likely area within our CWA to face this potential, however it also wouldn't be hard to envision a scenario where early convection results in the more favorable environment developing farther south/east than the current MDT risk. Given these uncertainties, not planning any significant change to our messaging for the severe potential at this time, however as observational trends begin to shed a light on the ultimate evolution of the mesoscale environment, some changes to today's severe whether forecast may be needed.

Finally, the influx of richer Gulf moisture combined with the strong synoptic forcing continues to look favorable for locally heavy rainfall totals today. While storm motion will be fast, rainfall efficiency will be high, so localized totals in excess of 3" (most of it falling in a very short time) are certainly well within the realm of possibility. Flash flood guidance remains low, so in coordination with neighboring offices will be issuing a Flood Watch for today.

Beyond this evening:

Gusty westerly winds are expected overnight as the deep low pulls away. Dry and pleasant weather is expected Thursday and Friday. Another strong shortwave trough is progged to move across the Midwest later this weekend, likely resulting in another round of potentially heavy rainfall and/or severe weather in the general region. Too soon to say how much, if any of our CWA will be impacted, but our area is certainly well within the proverbial cone of uncertainty and pops are very high Sunday accordingly.

- Izzi

AVIATION /06Z TAFS THROUGH 12Z THURSDAY/
Issued at 1250 AM CDT Wed Jun 17 2026

Forecast concerns include...

Scattered thunderstorms from mid morning through early evening.
Ifr cigs late morning through late afternoon.
Wind directions mid/late afternoon.

The primary focus for this period is thunderstorm timing. Models are in general agreement with a thunderstorm complex moving southeast from eastern IA around daybreak through north central IL in the late morning/early afternoon, with showers and embedded thunder on the north side of this complex. Prob thunder for this potential seems reasonable at this time but did include a few hours of mvfr vis/cigs with moderate rain. There may not be much of a break/lull between this first wave and additional thunderstorm development in the early/mid afternoon.
Previous forecast tempo from 19z-23z seems reasonable and there is some potential for thunder to be occurring during most of this time period at the Chicago terminals. The thunderstorms are expected to move southeast of the terminals by early this evening with a few lingering showers possible into this evening.
Any of the thunderstorms today will be capable of producing torrential rainfall which could briefly lower visibilities under 1sm.

Cigs are expected to lower through mvfr during the mid/late morning and into ifr by early afternoon, which may continue through late afternoon before lifting and scattering out by early this evening.

Light southwest winds overnight will become southerly by daybreak and then southeasterly during the mid/late morning.
Speeds and gusts will increase with gusts potentially into the mid 20kt range by late morning/early afternoon. Then there is quite a bit of uncertainty for wind directions during the mid/late afternoon. Some of the guidance lifts the warm front as far north as ORD, which would shift winds back to the south/ southwest. For now, maintained southeast winds at ORD and MDW and turned winds southwest at GYY. Changes to the wind forecast during this time period can be expected with later forecasts.
Winds will become west/southwest by early evening and then more westerly early Thursday morning as speeds/gusts increase. cms

LOT WATCHES/WARNINGS/ADVISORIES
IL...Flood Watch from 10 AM CDT this morning through this afternoon for ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011.

Flood Watch from 10 AM CDT this morning through this evening for ILZ006-ILZ012-ILZ013-ILZ019-ILZ020-ILZ021-ILZ023- ILZ032-ILZ033-ILZ039-ILZ103-ILZ104-ILZ105-ILZ106-ILZ107- ILZ108.

Beach Hazards Statement from this afternoon through Thursday morning for ILZ006-ILZ103-ILZ104.

IN...Flood Watch from 10 AM CDT /11 AM EDT/ this morning through this evening for INZ001-INZ002-INZ010-INZ011-INZ019.

LM...Small Craft Advisory from 1 PM this afternoon to 1 AM CDT Thursday for the IL nearshore waters.

Small Craft Advisory from 1 PM this afternoon to 7 PM CDT this evening for the IN nearshore waters.