textproduct: Chicago

KEY MESSAGES

- On and off lake effect showers will continue overnight and through Friday across eastern Porter County.

- Breezy and cool conditions are expected on Friday.

- Freezing temperatures likely for much of the area Friday night, and possible again Saturday night and Sunday night in some locations.

- Dry and warmer than average weather returns early next week.

DISCUSSION

Issued at 125 PM CST Thu Nov 5 2026

Recent GOES-19 water vapor imagery depicts an upper-level trough propagating southeastward through the Great Lakes region. Per surface observations from regional airports, a cold front is also racing southward across the Great Lakes today tied to a parent low pressure system centered in central Quebec. Expansive low-level stratus blankets the Great Lakes regions on either side of the front within the cyclonic shear axis of the trough, which is leading to a muted diurnal temperature response (current readings locally are in the lower 50s). Meanwhile, a secondary upper-level wave anchored by seasonably cool low- to mid-level temperatures (around -5C at 850mb per a 00Z sounding from Churchill, Manitoba yesterday evening) is evident diving southward over Lake Superior at press time. Increasing low- level isentropic ascent ahead of the cold front and secondary upper-level trough is maintaining spotty showers and drizzle this afternoon primarily near and north of I-80. Taken altogether, the synoptic picture across the Great Lakes today is quintessential of November.

This evening (especially after sunset), coverage of showers and drizzle should increase across the area ahead of and immediately behind the cold front. Breezy northerly winds will follow the front and continue through the overnight hours thanks to mixing forced by the initial bout of cold air advection and modest pressure rises (3hr rises of 3 to 4mb). Toward daybreak, breaks in stratus may allow for temperatures to tumble with overnight lows favored to reach the mid 30s north of I-88 to around 40 elsewhere.

As the sharp secondary upper-level wave races through the central Great Lakes throughout the day tomorrow, relatively warm waters of Lake Huron and lingering baroclinicity along the frontal boundary will induce the development of a secondary center of low pressure somewhere near the thumb of Michigan. A relatively packed pressure gradient between the developing low and a building 1020mb high pressure system in the Upper Mississippi River Valley will establish a healthy pressure gradient centered on Lake Michigan leading to breezy northerly winds across our area. Associated robust low-level cold air advection will thus lead to a somewhat chilly day with highs poised to remain in the 40s to perhaps around 50. As the core of the upper-level wave should pass largely toward Michigan, do anticipate a good deal of clearing in our local area (outside cyclonic shear axis). The exception will be in northwestern Indiana downstream of Lake Michigan where building 850mb to water temperature differentials will afford expansive stratus and lake effect rain showers. Based on the orientation of the wind field, currently anticipate a majority of lake effect showers to stream into LaPorte and Berrien counties just to the northeast of our forecast area of responsibility.

Friday night, the aforementioned surface high will build while moving southward through the Mississippi River Valley. Assuming stratus doesn't overstay its welcome, the combination of light winds, a dry airmass, and mostly clear skies should afford rapidly falling temperatures after sunset with overnight lows poised to reach the upper 20s to lower 30s away from Lake Michigan.

The pattern turns rather banal this weekend onward as a cut- off low pressure system atop a surface high pressure system over the southern US effectively forces a Rex Block across the central US. The eastward spread of Pacific air toward the Great Lakes will allow for daily temperatures to warm from this weekend into early next week with highs poised to return to the lower 60s by Monday. Ensemble guidance is hinting at a period of cooler temperatures tied to amalgamation upper-level troughs over the eastern US by the end of next week, though am noting quite a bit of spread on the areal extent of any associated cold pocket (850mb temperature spread reaches nearly 20C by Friday). Will note a pitiful signal in ensemble guidance for meaningful rainfall locally anytime soon, consistent with CPC Day 6-10 and 8-14 day outlooks favoring below average precipitation in our area. Of course, this in tandem with above average temperatures also translates to no opportunities for snowflakes in our area anytime soon.

Borchardt

AVIATION /06Z TAFS THROUGH 12Z SATURDAY/

Issued at 1125 PM CST Thu Nov 5 2026

Forecast concerns include...

Possible mvfr cigs through the overnight hours. Gusty north/northwest winds through Friday afternoon.

The cold front is well south of the terminals late this evening with showers and drizzle ending from north to south and cigs lifting through mvfr with even vfr cigs across parts of northern IL. Sct/bkn mvfr level clouds are still expected through the overnight hours, but the overall trend will be for cigs to gradually become prevailing vfr which will continue through much of Friday and then are expected to scatter out by Friday evening. There will be a chance for lake effect rain showers across northwest IN overnight into Friday but these should remain east of GYY.

Northerly winds will slowly turn to the north/northwest through the overnight hours and remain north/northwest for the rest of the period. Gusts into the 18-20kt range will be possible through Friday afternoon when gusts will slowly end and then speeds will diminish under 10kts with sunset Friday evening. cms

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until 9 AM CST Saturday for the IL nearshore waters.

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