Chicago Lake Plain

The last 30 days at Chicago Northerly Island station (3 km from Chicago Lake Plain) averaged 2.5°F above normal for daily highs and 4.4°F above normal for daily lows. Warmer-than-normal conditions have been consistent through mid-October.

No part of Cook County is currently classified in drought as of the week of October 20-26, 2026. Drought classification was lifted the previous week after a brief classification of abnormally dry conditions the week of September 15-21, indicating water stress has eased in the region.

Multiple damselflies were observed at Goose Island on 2026-10-10, including unidentified narrow-winged damselflies of the family Coenagrionidae. Damselfly presence indicates adequate water quality in occupied sites.

A threatened gray treefrog was observed in Cook County on 2026-09-24, and threatened green frogs were recorded on 2026-10-10 and 2026-10-05, with spotted salamanders and plains leopard frogs also appearing in recent weeks. These federally protected species show active movement in fall as cooler temperatures drive seasonal behavior shifts in wetland-associated amphibians.

Silver-haired bats, a state-threatened migratory species, have been documented in seven separate observations in Cook County from late October through early October, including records from Grant Park and downtown Chicago. These solitary bats are actively passing through during autumn migration, a seasonal movement pattern preceding hibernation.

A Tule Bluet, a state-threatened damselfly, was observed on 2026-08-24 in Chicago. Damselflies are indicator taxa requiring well-oxygenated freshwater habitats, and their presence in the ecosystem suggests adequate conditions in occupied sites.

An Eastern Massasauga rattlesnake was observed in Cook County on 2026-09-06. This Threatened species, found in wetlands and open prairie habitats, indicates persistent habitat quality in the region and demonstrates its presence within the ecosystem's range.

Red maple, bur oak, and northern red oak displayed colored leaves and falling leaves on September 21. The past 30 days averaged 2.9 degrees Fahrenheit above the normal high temperature, with a peak of 96 degrees on September 2. Fall color timing aligns with the normal start of the season in this region.

Fifty chimney swifts were reported at Horner Park on September 21. In the Midwest, chimney swifts depart in early October after gathering in large numbers to roost and feed before the long migration to South America. This is peak staging season when flocks congregate at traditional chimneys.

A Hooded Warbler was confirmed at Montrose Point Bird Sanctuary on September 22, part of the southbound movement of this eastern breeder to Central American wintering grounds. This neotropical migrant's presence here on the Great Lakes represents its expected fall passage through the region.