Fog in Portsmouth, NH

daily fog outlook & 2016–2026 climatology
Fog unlikely through Monday (peak 3%). August typically brings about 8 hours of dense fog here.forecast cycle 2026-08-16T00:00:00Z · page rebuilt daily · live layers below update hourly

Measured at Portsmouth International Airport at Pease (KPSM). Forecast percentages for this station have passed live verification.

Measuring station

stationairportfog hours/yrforecast
KPSMPortsmouth International Airport at Pease129 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 Portsmouth fogs in

Fog here concentrates in October and September — about 129 hours in a typical year at KPSM, usually lasting ~2 h once it forms. Hour-by-hour patterns, live conditions and the forecast strip live on the KPSM station page.

Fog season

January: ~8 hJanFebruary: ~10 hFebMarch: ~13 hMarApril: ~8 hAprMay: ~11 hMayJune: ~11 hJunJuly: ~10 hJulAugust: ~8 hAugSeptember: ~16 hSepOctober: ~17 hOctNovember: ~5 hNovDecember: ~14 hDec
Fog season is year-round, peaking in October; fog is mostly a 11 PM–7 AM phenomenon; typically thinning out by 10 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.