Fog in Chicago/Rockford, IL

daily fog outlook & 2016–2026 climatology
Some chance of fog — peaks at 31% around 6 am Sunday.forecast cycle 2026-08-16T00:00:00Z · page rebuilt daily · live layers below update hourly

Measured at Chicago Rockford International Airport (KRFD). Forecast percentages for this station have passed live verification.

Measuring station

stationairportfog hours/yrforecast
KRFDChicago Rockford International Airport37 h/yrlive forecast

Fog is measured where instruments live — airports. Hours/yr = time below CAT I approach minima (visibility under ~½ mile or ceiling under 200 ft), the aviation definition of seriously dense fog.

When Chicago/Rockford fogs in

Fog here concentrates in December and January — about 37 hours in a typical year at KRFD, usually lasting ~2 h once it forms. Hour-by-hour patterns, live conditions and the forecast strip live on the KRFD station page.

Fog season

January: ~8 hJanFebruary: ~5 hFebMarch: ~3 hMarApril: ~1 hAprMay: ~1 hMayJune: ~1 hJunJuly: ~1 hJulAugust: ~2 hAugSeptember: ~2 hSepOctober: ~1 hOctNovember: ~4 hNovDecember: ~9 hDec
Fog season runs November through March, peaking in December; fog is mostly a 4 AM–9 AM phenomenon; typically thinning out by 11 AM; a typical event lasts about 2 hours once it forms local time · 10-yr average

Machine access: data.json · llms.txt · forecast verification. Not for operational use.