Mundelein, IL Weather

Key Messages

- Generally well above normal temperatures will continue, albeit with a modest cool-down on Monday near and north of I-80, and particularly near Lake Michigan.

- There are periodic low/uncertain rain chances in the mid to late workweek period, with the best chance of any meaningful rainfall not until next Saturday (Halloween) night.

Discussion

Issued at 250 AM CDT Sun Oct 25 2026

Conditions are again nice and quiet as we welcome the new week. Temperatures early this morning are in the 40s and lower 50s with some high clouds passing overhead. Some light rain showers and sprinkles developed over southern and central WI last evening associated with a low-mid level jet max downstream of a surface cold front. The precip has stayed safely to our north thus far and that will remain true as it now starts to move over central Lake Michigan. Today will be very similar to yesterday with afternoon temperatures in the lower and middle 70s and sunshine filtered by scattered high cloud cover.

That aforementioned cold front currently stretching from central IA, up across far SE MN and into northern WI won't make a ton of eastward progress during the day. But it will pivot to become more zonally-oriented across central WI before dropping south across our area overnight tonight through tomorrow morning. Weak forcing for ascent, both along the front and from neighboring synoptic features, and a lack of layer moisture will keep any mentionable rain chances out of the forecast with this frontal passage. It will, however, have a noticeable influence on temperatures as the timing is diurnally favorable for a good gradient in afternoon temps tomorrow. High temperatures are forecast in the lower and middle 60s in our north where the front will have passed by early morning, while lower and middle 70s are expected near and south of the Kankakee and Illinois river valleys where the front won't make it across until later in the morning.

Upper 60s to lower 70s are expected on Tuesday with 70s forecast areawide on Wednesday. Another weak cold front looks to drop into northern IL Thursday night and is then favored to stall nearby into the weekend. The latest NBM came in with slight chance and low-end chance PoPs in our north and northwest ahead of the front Wednesday night into Thursday. However, forecast soundings suggest that may be difficult to achieve until some better layer moisture works in closer to the end of the week. Chances are seemingly better toward the weekend near the stalled baroclinicity. There is uncertainty in the exact evolution of this front/baroclinic zone which lowers confidence in temperature trends late in the week. Generally warmer- than- normal conditions are favored to continue through the end of the week, but a consistent signal among ensembles is for more seasonable temperatures for the early part of November.

Doom

Aviation

Issued at 557 AM CDT Sun Oct 25 2026

Quiet weather continues with VFR conditions persisting into tonight. South-southwesterly will prevail today, but speeds will generally remain under 10 kt. Winds will ease to 5 kt or less this evening in advance of an approaching cold front. This cold front will shift across the terminal airspace during the predawn hours of Monday morning, resulting in a north- northeasterly wind shift. We will also have to keep an eye on the potential for a period of IFR CIGs with the passage of this front early Monday morning. For the 12Z TAFs we maintained the northerly wind shift mention after 10Z Monday morning (slightly early at RFD). I also hinted at the possibility of some lower clouds (SCT008) around in the wake of this frontal passage. Any lower CIGs that develop should improve by mid to late morning.

KJB

Lot Watches

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