A closer look at coastal fog

An interesting new study from UC Santa Cruz (Go slugs!) about coastal fog asks “what is in fog?” and “how will fog change as the planet warms?” It's part of the larger Pacific Coastal Fog Research project. Fifteen locations along the length of California will be tested.

Point Reyes is the perfect place to conduct the study! It has the distinction of being the second foggiest place in North America with 200 foggy days a year — only 6 days behind foggy winner Grand Banks Newfoundland, and here’s why:

  1. Geography & Exposure
    – Point Reyes juts far out into the Pacific Ocean—about 10 miles west of the main California coastline. That makes it the first piece of land that incoming marine air and fog hit, so it gets blasted more than neighboring areas.

  2. Cold Ocean Current
    – The California Current brings cold water south from Alaska. When warm inland air rises in summer, it pulls in cool, moist ocean air. As this air cools further over the cold water, the moisture condenses into fog.

  3. Summer Pressure Systems
    – High pressure over the Pacific and low pressure inland set up a strong draw of moist air toward the coast in summer. Point Reyes acts like a “catcher’s mitt,” snagging the fog before it can disperse.

  4. Topography Traps Fog
    – The peninsula’s ridges and valleys (like Bear Valley and Olema Valley) funnel and hold fog, sometimes keeping it around for days while other parts of Marin clear up.

  5. Frequency
    – Some years, Point Reyes sees fog more than 200 days annually. It’s common to start the morning socked in, only to have it burn off late in the day—then roll back in by evening.

This is why Point Reyes is legendary among photographers and naturalists for its mysterious, moody atmosphere. For the insatiably curious, read more about climate and weather in Point Reyes

Fog in Point Reyes: Sources & References

This bibliography lists sources that describe the causes, frequency, and ecological significance of fog in Point Reyes and along the California coast.

• National Park Service — Point Reyes Oceans & Upwelling

https://www.nps.gov/pore/learn/nature/oceans.htm

• National Park Service — Fog, Redwoods and a Changing Climate

https://www.nps.gov/articles/000/fog-redwoods-and-a-changing-climate.htm

• Dawson, T.E. (1998). Fog in the California redwood forest: ecosystem inputs and use by

plants. Oecologia, 117(4): 476–485.

https://atmos.uw.edu/~breth/PCC/Au2009Readings/dawson98fogredwood.pdf

• Johnstone, J.A. & Dawson, T.E. (2010). Climatic context and ecological implications of

summer fog decline. PNAS, 107(10): 4533–4538.

https://www.pnas.org/doi/10.1073/pnas.0915062107

• Ewing, H.A. et al. (2009). Fog Precipitation in Coastal California Forests. Ecology, 90(12):

3353–3360.

https://esajournals.onlinelibrary.wiley.com/doi/10.2307/1940364

• Public Policy Institute of California — The Future of Fog

https://www.ppic.org/blog/the-future-of-fog/

• Golden Gate National Parks Conservancy — How does fog contribute to Bay Area

ecosystems?

https://www.parksconservancy.org/article/how-does-fog-contribute-bay-area-ecosystems

• Scholl, M.A. & Murphy, S.F. (1994). The importance of fog-drip water to vegetation: Point

Reyes Peninsula, California. Journal of Hydrology, 164(1–4): 269–285.

https://www.sciencedirect.com/science/article/abs/pii/002216949402538M

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