Learn · Conditions & Decisions

Fox River Season Tracker

Where is the Fox River right now in its normal annual thermal progression?

Current thermal position

Thermal progression is about 10 days behind normal.

Through September 14, 2026 · Latest complete local day

Reference temperature
69.5°F
Historical median
71.7°F
Current anomaly
−2.2°F
Historical position
20th percentile

The reference daily mean was 69.5°F on September 14, 2.2°F below its historical median.

The reference temperature fell 3.7°F on the latest complete day, but the five-day thermal position remains behind normal.

Annual progression

This year against the historical reference

The shaded range appears only where at least six historical years support the P10–P90 envelope. Winter gaps are left unfilled.

Fox River reference-temperature annual progression Historical median, supported historical range, current-year reference temperature, 60 and 65 degree reference lines, and latest complete day. 20° 30° 40° 50° 60° 70° 80° 90° Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 60°F thermal reference 65°F thermal reference Latest complete day Reference temperature (°F)
Current-year reference Historical median Historical P10–P90 60°F / 65°F thermal references

Thermal references

Typical and current-year transitions

These are seasonal landmarks, not Water Safety thresholds.

Typical seasonal transition

Spring 60°F
May 10P10–P90: May 3–May 14
Spring 65°F
May 26P10–P90: May 18–May 30
Fall 65°F
October 5P10–P90: September 27–October 9
Fall 60°F
October 14P10–P90: October 5–October 23

2026 transition status

Spring 60°F
May 14
Spring 65°F
May 16
Fall 65°F
Not yet established
Fall 60°F
Not yet established

How to read this

One seasonal clock, not one temperature everywhere

Season Tracker compares a completed-day reference temperature from three Fox River USGS stations with as many as 15 prior completed years. It uses local calendar days, so partial readings from today never enter the comparison.

Historical evidence supports treating the Fox mainstem from New Munster through the Illinois River confluence as one coherent annual thermal progression. Absolute water temperature still varies by place and season. The reference temperature is not the exact temperature at every location.

Weather and Water Safety are separate products. This seasonal context does not determine whether conditions are safe.