The San Juan Islands weather is better than you might think. For starters, these islands off the Washington coast get about half the rain that Seattle and other regional cities tend to get on an annual basis. In fact, there are more than 240 sunny days a year on average. You might also be interested to know that the mean high temperature only varies about 28 degrees between the coldest month of January and the warmest month of July, and the low only eighteen degrees. The Cascade Mountains, the Olympic Mountains, Vancouver Island, and the area waters are largely responsible for the wonderful San Juan Islands weather. The mountains help to block cold weather systems from Canada, and together with Vancouver Island, they also help to keep the rain at bay in the San Juans. As for the area waters, the average temperature is 45 degrees in the winter and 52 degrees in the summer. This in turn influences the air temperature. There is a warming effect in the winter and a cooling effect during the warmer summer months.
Summer: For many travelers, summer is the best time to travel to San Juans WA. While it's warm outside during the day in the summer, the temperatures rarely top 80 degrees Fahrenheit and rain is sparse. Clear skies are very common, and the area waters tend to be at their calmest. Boaters flock to the San Juans in greater number during the busy summer season, and you can bet that the hotels, vacation rentals, and campsites fill up fast. It should be noted that the summer nights in the San Juan Islands tend to be cold. Once the sun goes down in the summer, the temps drop to around 50 degrees, so you'll want to pack accordingly.
Fall: Fall is a wonderful time to visit the San Juan Islands, as the skies are often clear and the days warm. The average temperatures drop a little from summer, and they continue to cool the closer that you get to winter. Highs in the 50s and 60s can be expected during the day, and the average lows range from around 50 to 40 degrees. The list of things to do in the San Juans is a healthy one during the fall months, and if you need extra incentive to plan an autumn visit, the summer crowds are gone and the lodging rates decreased.
Winter: The winter season in the San Juan Islands is moderate. The highs during the day tend to hover in the mid and upper-40s, with the nighttime temps falling to around 37 degrees on average. Winter is the rainiest season in the San Juans, and every once in a while, an arctic cold front blasts down from the Yukon. Snow falls on rare occasions, but it is rarely heavy. Fishing, kayaking, and a host of other fun activities can still be enjoyed during the winter months in the San Juan Islands, and this is when lodging rates are at their very lowest.
Spring: Spring in the San Juan Islands is very akin to fall. The temperatures are similar, for example, and while it does rain more than in the summer season, clear skies are common. Springtime markets add some extra flair to the shopping and dining scene, and you can expect the lodging rates to be lower than they are in the summer. If this isn't enough to convince you to plan a spring visit, then maybe the blooming flowers will seal the deal. Gardens around the islands burst into bloom, and you are likely to encounter more than your fair share of sweet-smelling roses.