Fog in Chicago/Prospect Heights/Wheeling, IL

daily fog outlook & 2016–2026 climatology
Fog unlikely through Sunday (peak 5%). August typically brings about 1 hour of dense fog here.forecast cycle 2026-08-16T00:00:00Z · page rebuilt daily · live layers below update hourly

Measured at Chicago Executive Airport (KPWK). Forecast percentages for this station have passed live verification.

Measuring station

stationairportfog hours/yrforecast
KPWKChicago Executive Airport20 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/Prospect Heights/Wheeling fogs in

Fog here concentrates in January and December — about 20 hours in a typical year at KPWK, usually lasting ~1 h once it forms. Hour-by-hour patterns, live conditions and the forecast strip live on the KPWK station page.

Fog season

January: ~7 hJanFebruary: ~1 hFebMarch: ~1 hMarApril: ~1 hAprMay: ~1 hMayJune: ~0 hJunJuly: ~0 hJulAugust: ~1 hAugSeptember: ~1 hSepOctober: ~0 hOctNovember: ~1 hNovDecember: ~4 hDec
Fog season runs December through January, peaking in January; fog is mostly a 8 PM–5 AM phenomenon; typically thinning out by 10 AM; a typical event lasts about 1 hour once it forms local time · 10-yr average

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