textproduct: Chicago

KEY MESSAGES

- Lake effect rain showers may periodically affect portions of Porter County, IN through tonight.

- Below freezing temperatures may be observed across a large portion of northern Illinois tonight. Near or below freezing temperatures may then be observed once again Saturday night and Sunday night in some locations.

- Dry conditions and a warming trend are expected this weekend into early next week.

DISCUSSION

Issued at 259 AM CST Fri Nov 6 2026

Early morning GOES water vapor imagery loops show a well- defined upper-level trough/cut-off low sinking southward towards the Lower Peninsula of Michigan. As the associated cold pool of air continues to spill into the lower Great Lakes, a surface low meandering around the eastern Great Lakes and an elongated surface ridge extending from the central Plains up through Hudson Bay will enforce breezy northerly surface winds across the region today. The respectable magnitude of this cold air advection should largely keep temperatures mired in the 40s today with any low 50s readings likely to be few and far between this afternoon.

The cooler air mass settling into the region will also yield 15-17C water surface-850 mb temperature differentials and 6000-9000 ft equilibrium levels over southern portions of Lake Michigan today, which will lead to a steady stream of lake effect rain showers into portions of southwestern Michigan and northwestern Indiana. The predominantly 330-350 degree fetch over Lake Michigan should keep most of this activity focused to the east of our CWA into La Porte and Berrien counties, but may still allow for these lake effect showers to affect portions of Porter County (and possibly far northeastern Jasper County) at times through tonight. The aforementioned parameters are also marginally supportive of some potential for waterspouts over Lake Michigan, though again, the greater potential for this should remain focused to our east/northeast along the main lake convergence axis.

The Great Plains surface ridge will slide eastward over the course of the day today and should be in close enough proximity to our area tonight for winds to turn light/calm across a good chunk of our CWA after sunset. With temperatures already expected to be in the low-mid 40s around sunset and dew points progged to mainly be in the low 30s and upper 20s, below freezing temperatures will very much be in play for areas outside of the core of the Chicago urban heat island and the footprint of the lake effect stratocumulus in northwest Indiana tonight into Saturday morning. However, some uncertainty remains with just how much temperatures will fall tonight owing to questions about the coverage of any non-lake-induced stratus across the area. Most of the latest model guidance favors skies clearing out over most our area by the overnight hours, which would yield optimal radiational cooling conditions and allow for temperatures to quickly tank to near or below freezing. However, it's not uncommon for stratus to stick around longer than depicted in model guidance in these cold cyclonic flow regimes during the cool season, and some model solutions, namely the latest runs of the RAP and UKMET, do favor an expansive blanket of stratus lingering over our forecast area through the night and keeping temperatures propped up a bit higher than what is depicted in our forecast grids. Note that frost/freeze headlines for our area have been discontinued for the remainder of this fall, but anyone who may still have sensitive vegetation outside should consider taking the necessary precautions to protect it from the cold conditions tonight.

The weather pattern for our area will become fairly benign from this weekend through at least the first half of next week with a split jet stream pattern keeping any real disturbances of note displaced to both our north and south. A gradual warming trend is expected during this time frame with high temperatures likely to reach the 60s once again early next week before a cold frontal passage halts that trend sometime mid-week. Ensemble guidance then favors aggregate longwave troughing developing over the northeastern quadrant of the CONUS during the latter half of the week. If this were indeed to materialize, then that could bring about our next chances for precipitation sometime mid-late next week, though there is very little ensemble consistency at this time with exactly where and when any opportunities for precipitation may materialize.

Ogorek

AVIATION /12Z TAFS THROUGH 18Z SATURDAY/

Issued at 555 AM CST Fri Nov 6 2026

- Lower confidence in ceiling trends today and tonight

MVFR stratus from overnight has since shifted south of I-80 and the terminals early this morning. Winds remain NNW to NW around 10 kt with occasional gusts in the upper teens to near 20 kt, highest near the lakeshore.

A separate area of low stratus ongoing over portions of eastern Wisconsin and over Lake Michigan is expected to drift down into northeast Illinois this morning and likely persist through the afternoon and evening hours. The main question is whether this stratus remains MVFR or lifts slightly to low-end VFR as it approaches the Chicago terminals. Have maintained a SCT020 BKN035 mention with this update given lower confidence in the inland extent of the MVFR CIGs but the introduction of prevailing MVFR may become warranted with later updates this morning based on observational trends.

Cloud coverage overnight also remains lower confidence with model guidance mixed as to whether the low stratus persists all night, particular near the lake, or fully clears out after midnight. Winds will trend WNW and ease with sunset to around and under 5 kt.

Petr

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until 3 AM CST Saturday for the IL nearshore waters.

Small Craft Advisory until 3 PM CST Saturday for the IN nearshore waters.