May 12, 2010

The Secrets of Staying Dry While Biking

May is national bike to work month and next week is bike to work week. Here in Seattle a big concern is staying dry while bike commuting or during recreational runs.

Now there are two ways to stay dry while biking. The first is shown in the image above--mounting an umbrella on your bike. Perhaps this would work if you went REALLY slowly and there was little wind, but for most of us another solution is needed...and I can offer it. Use the weather radar!

I commute by bike every day roughly five miles each way. Ever since a weather radar was installed in western Washington (early 1990s), I rarely get seriously wet. I mean...this has really changed my life.

You all have seen weather radar images on TV or the web (see one below).

Weather radar basically shows you where it is raining. The units shown on the image are actually something called reflectivity, the amount of the radar signal scattered back to the radar. The higher the reflectivity, generally the heavier the rain. A rough scaling is 5-10 (gray above) for very, very light rain (drizzle), pinks (15-25) for light rain, greens (30-35) for moderate rain, yellows for heavy rain (40-45), and you don't want to know about the reds and blues. I will bike in greys and pinks, particularly if I am wearing a Gortex (or similar type of material) jacket. I avoid greens and will take the bus with yellow and reds. The National Weather Service radars provide a new image every 6 minutes. And you can view both single time and animated radar imagery on the web, using a smart phone app, on an internet-equipped cell phone, or on tv.

Here is an example of a radar animation:

An interesting and critical fact about rain is that it is rarely uniform. There are heavy areas and light areas and breaks. By viewing radar animations you can spot the light areas, or make a good estimate when one will be at your location. So if you have some flexibility of when you bike, delaying or advancing your trip by a 10-15 minutes, you can nearly always avoid the real heavy stuff or secure a dry ride even on a supposedly rainy day. The more flexibility you have the better your chance of staying dry.

And radar helps in another way. If you are just looking for recreation, the radar can tell you where it is dry now and will continue to be dry for a while.

Trust me....using weather radar can revolutionize your biking life.

So where do you go to get this information? Lots of web sites offer great radar access.
Some examples for Seattle and vicinity:

Seattle NWS office site:

The UW: (click on radar loops)

All the major TV stations in town have radar links. And many more.

For those in Seattle I will be giving a talk on this topic:

"You Can Avoid the Rain! Weather Tips for Biking" on May 20th,12:00pm-1:00pm,Gerberding Hall room 142, on the UW campus

Happy biking.


  1. Why is it that at night the radar frequently shows rain when it's dry and cloudless out? For example right now (at 2:17 AM) is showing dBZ 5-25 (light rain) for the entire Puget Sound region, with the heaviest reflectivity just east of Everett.

    During the day, the radar is definitely a great tool for figuring out if/when you'll have a rainless window to make it from X to Y. But I do a lot of riding and walking at night, and it's annoying to not be able to rely on the radar at those times.

  2. Weather Underground has a nice full-screen map with an animated radar overlay:

  3. night, those light echoes are BIRDS! ...more on that later

  4. I have an iPhone. Which app would you recommend? Thanks!

  5. For iPhone users, Weather Underground has an iPhone friendly site at This site also has an animated radar display, it's lower res than the main site but still very useful.

  6. Hey Cliff,

    If you go the national radar here:

    The radar sites seem to have lots of clutter that seem to be related to humidity or moisture levels in the atmosphere. Dryer areas , or areas behind front seem to have less of the reflectivity, and radar sites in fron of the frontal systems, or in more humid areas such as the south seem to have more clutter. Is it because of the humidity/Moisture?

  7. I like both the my-cast app and website. Satellite and radar info is easy to access for your unique location. One of the other radar apps is supposed to be pretty good as well but it's $10 and I don't want to pay that much.

  8. the other way to stay dry is to invest in a decent bicycling rain coat. I happen to like the one's made by ShowersPass (available at a bicycle store near you...)

    I have a 14 mile commute and I find it's harder to find a full weather window even using the radar.


Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

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