textproduct: Chicago

KEY MESSAGES

- Frost is possible tonight away from the more urbanized areas, with localized freezing temps possible.

- While the majority of the time will be dry, there will be a few opportunities for showers Thursday through the upcoming weekend.

- Other than a possible brief warm up Saturday, temperatures will remain mostly near to below average through early next week.

DISCUSSION

Issued at 251 AM CDT Wed May 6 2026

Large scale pattern across North America will be dominated by sprawling, deep Hudson Bay trough. Our area will generally remain in the northwest flow on the southwestern flanks of this large trough. This will provide us with a steady feed of seasonably cool air and multiple clipper-like northwest flow low amplitude disturbances bringing occasional shower chances through the weekend. The northwest flow will also keep richer Gulf moisture bottled up well to our south, so despite multiple chances of rain, rainfall amounts should be on the lighter side.

While there will likely be some breaks at times, mid and high cloudiness looks to be pretty extensive today. Source region for our air mass saw dewpoints in the upper teens to mid 20s Tuesday afternoon and even with the cloud cover potentially throttling back the depth of mixing slightly, still anticipate some very low dewpoints/afternoon RH today and have continued trend from previous shift going with the low end of the guidance spectrum.

Tonight's temperatures and frost/freeze potential are tricky. Models continue so suggest large patches of mid-high level cloudiness will traverse the area tonight. Given the expected light winds, any meaningfully large hole in cloud cover could allow temps to locally tank. In fact, we could see temps fluctuate at times tonight dependent on the state of the cloud cover. If mid-high clouds end up not as big of a factor, then low temps could end up lower than forecast with even temps near/slight below freezing possible in the typically colder areas. In addition to uncertainty about temps and cloud cover, given the light flow, dewpoints may not recover much tonight, possibly remaining in the 20s and lessening the frost threat. Seems like the course of least regret will be issuing a frost advisory for sizable portion of our CWA (away from the urban corridor), but given the uncertainties, will defer to the day shift for issuance of a frost advisory. Hopefully by this afternoon, cloud cover trends may be more apparent, leading to higher confidence in temps and subsequent frost or even localized freeze threat tonight.

A pair of low amplitude northwest flow shortwaves will move across the region, the first late Thursday and the next about 24 hours later late Friday. As mentioned earlier, these systems will be somewhat moisture starved, but most guidance does support some light QPF as forcing squeezes out what little atmospheric moisture is available. Dry low levels may also tend to eat away at some of the potential precip as low levels will require some top down moistening. Given the recent trends in guidance to latch onto the Thursday shortwave, coordinated with surrounding offices to introduce some chances pops Thursday afternoon/early evening. NBM pops for Friday looked reasonable and no changes were needed.

There still looks to be an opportunity to sneak in one rather warm day Saturday with robust warm air advection driven by gusty southwest winds in advance of the next shortwave trough. As is often the case with these lower amplitude waves, there is some spread in ensembles regarding timing, but generally looks like that trough will bring another chance of showers to the area sometime in the Saturday night or Sunday time frame. That looks to be followed by another shot of below average temps to end the weekend and into Monday of next week.

- Izzi

AVIATION /12Z TAFS THROUGH 18Z THURSDAY/

Issued at 630 AM CDT Wed May 6 2026

There are no significant aviation forecast concerns for the current TAF period. Sustained 10-15 kt west-northwesterly winds with gusts to around 20 kts are expected to develop by the late morning amidst VFR cloud cover.

The one exception to this may be GYY, which will be in close enough proximity to the lake breeze for winds to be a bit lighter and possibly variable there if the lake breeze boundary ends up positioning itself over the GYY airfield. If the lake breeze ends up setting up/progressing farther inland/westward than currently expected, then northeasterly winds may prevail there instead this afternoon, but the most likely outcome at this time is that the west-northwesterly winds to the west of the lake breeze end up being strong enough to keep it just east or over the airfield.

Winds will become light or calm again at all TAF sites after sunset as the boundary layer decouples and surface high pressure settles into the region, though they will pick back up again with regular gusts to around 20 kts after sunrise tomorrow morning. Scattered showers may also move in to the area just prior to 18Z tomorrow, though will let the potential introduction of a SHRA mention into the TAFs be handled in forthcoming TAF issuances.

Ogorek

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...None.