Flight Check
Weather Delay Guide

Fog delaying your flight?
Here's exactly what's happening.

The most predictable disruption in US aviation — and most travelers have no idea how to handle it. Updated October 16, 2026.

SFO — The Worst Fog Airport in America

Summer morning numbers

50%

Runway capacity
reduction in fog

35%

Summer mornings
affected by fog

10am–1pm

Typical fog
clearing window

The fix: Book afternoon flights when possible. Fly into OAK or SJC instead. Set up flight alerts to know instantly when your status changes.

Flight delayed by fog? Here's what to do.

  1. 1

    Check the delay, not just your flight

    Look at what time the fog typically clears at your departure airport. SFO fog usually lifts by noon. If your 8am flight is delayed, the 11am flight may be fine.

  2. 2

    Don't rush to the airport — wait for updates

    Unlike cancellations, fog delays are usually temporary (1–4 hours). Check your flight status before leaving for the airport.

  3. 3

    If cancelled — demand cash, not vouchers

    Fog cancellations are rare but happen. Federal law requires a full cash refund to your original payment method if the airline cancels.

  4. 4

    For SFO specifically: book afternoons in summer

    This is the only fog-related disruption that's highly predictable. If you're flying SFO June through September, morning flights are a gamble.

Set up flight alerts — free

Know immediately when your gate or delay status changes — no app needed.

Why fog is so disruptive — the aviation science

Fog isn't just low visibility. It's a systems problem that multiplies through the entire airport — and creates delays that can last all day even when the fog itself lasts only a few hours.

The landing rate problem

In clear conditions, airports use visual separation — pilots can see and avoid each other. In fog, they switch to instrument approaches, which require aircraft to be spaced much further apart. This can cut landing capacity by 30-50%, meaning fewer planes land per hour — and the backlog grows.

Why SFO is uniquely bad

SFO has two parallel runways (28L and 28R) that are only 750 feet apart. In good visibility, they can be used simultaneously for simultaneous instrument approaches. In fog below a certain visibility minimum, they can only use one at a time. This immediately halves capacity.

The ripple effect lasts all day

A 3-hour morning fog delay doesn't go away at 10am. Every plane that was delayed is now late for its next flight. Crew hours are ticking. By afternoon, flights that had nothing to do with the fog are delayed because their aircraft are somewhere they weren't supposed to be.

Why afternoon is safer

Marine layer fog burns off as the sun heats the ground. Most coastal fog clears by noon. Booking a 1pm or later departure when flying through SFO in summer dramatically reduces your fog exposure.

Airports most affected by fog — by severity

SFOSan Francisco

The worst fog airport in the US. Marine layer fog on 30-50% of summer mornings cuts runway capacity by 50%. Avoid morning flights Jun–Sep.

Extreme
SEASeattle-Tacoma

Low visibility events are common Oct–Mar. SEA handles it better than SFO but morning fog regularly causes 30–90 min delays.

High
LAXLos Angeles

Morning marine layer affects LAX departures May–Aug, especially before 10am. Usually clears by noon.

Moderate
OAKOakland

Less fog-prone than SFO despite being across the bay. A viable alternative when SFO is socked in.

Low
PDXPortland

Willamette Valley fog traps air Nov–Feb. Portland fog is lower-altitude and more persistent than coastal fog.

High
BOSBoston

Coastal fog is common spring and fall. Less frequent than SFO but can cause significant delays when it hits.

Moderate
JFKNew York (JFK)

Atlantic sea fog affects JFK spring through early summer. Dense fog events can delay departures by 2–4 hours.

Moderate

Your rights during fog cancellations

Fog delays vs. fog cancellations

Most fog events cause delays, not cancellations. For delays, airlines are not required to compensate you for food or hotels in the US. If your flight is actually cancelled, you're owed a full cash refund under federal law.

Fog delays — no automatic compensation

US law doesn't require airlines to compensate for delays, including fog delays. Check your credit card benefits — many premium cards cover meals and hotel during delays over 6 hours.

Fog cancellations — full cash refund required

If the airline cancels your flight due to fog, you're owed a full refund to your original payment method within 7 business days. Don't accept vouchers.

File a DOT complaint if refund is delayed

airconsumer.dot.gov — free, takes 5 minutes, airlines must respond in 60 days.

Common questions

Why does fog cause flight delays?

Fog reduces visibility below the minimums required for visual approaches. When visibility drops below roughly 3/8 mile or 200-foot ceiling, airports switch to instrument landing system (ILS) approaches — which require more spacing between aircraft. This cuts the number of landings per hour by 30-50%, creating a backlog that ripples through the entire day's schedule.

Why is SFO so bad for fog?

San Francisco International sits on the edge of the San Francisco Bay, surrounded by the Pacific Ocean on three sides. Every summer morning, cool marine air pushes inland and condenses into thick fog — the famous 'Karl the Fog.' SFO's runway configuration (two parallel runways used simultaneously) only works in good visibility. In fog, it drops to one runway at a time, cutting capacity by half. This happens on 30-50% of summer mornings.

Do I get a refund if my flight is cancelled due to fog?

Yes. Under 14 CFR Part 260, you are entitled to a full cash refund if your flight is cancelled — even for weather, including fog. The airline must refund to your original payment method within 7 business days for credit cards. You do not have to accept vouchers or travel credits.

When does SFO fog clear?

SFO's morning fog typically clears between 10am and 1pm local time as the sun heats the land. However, in peak summer months (June–August), it sometimes persists all day. Afternoon flights are generally safer than morning flights if you're traveling through SFO in summer.

What can I do about fog delays?

Unlike hurricanes and blizzards, fog usually isn't severe enough to trigger weather waivers. Your options: (1) Book afternoon flights when flying SFO in summer — fog usually clears by noon. (2) Use OAK (Oakland) or SJC (San Jose) as alternatives to SFO — they're less fog-prone. (3) Set up flight alerts to know immediately when your flight status changes. (4) If your flight is cancelled, demand a full cash refund.

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