Weathercatch: Latitude, elevation don’t adequately explain why Deer Park has cooler temperatures

What’s with Deer Park? The community is located a short 23 miles north of Spokane, but its weather often runs notably cooler after the sun goes down.

In other words, whenever the Inland Northwest shivers, Deer Park shivers a little bit more. The cold front that recently swept across Washington state brought Monday’s overnight low temperatures to 38 degrees in Spokane, and yet a chillier 32 degrees in neighboring Deer Park.

The temperature difference tends to be greater at night than day, the largest during autumn, winter and into spring and more apparent when winds are light.

With Deer Park’s temperatures running an average of 5 to 10 degrees cooler at night, trees bud and flowers bloom about a week later than in Spokane and other outlying communities.

Not only does springtime arrive later, but autumn arrives earlier. The average first frost hits Deer Park on Sept. 11, compared to Oct. 7 in Spokane.

Getting back to spring, you may recall three weeks ago when a pulse of cold weather interrupted the season and challenged historical records across the region. While many locations broke or tied low temperatures for April 11, Deer Park’s record low of 15 degrees beat them all. Spokane bottomed out at 23 degrees, Coeur d’Alene, 24, and Sandpoint and Moscow-Pullman, 21.

Later that day, the National Weather Service Spokane informed the public on its Facebook page of the unusually cold temperatures. In response, one user asked: “Why is Deer Park always the coldest?”

It’s not because of the town’s higher latitude. After all, Sandpoint is located north of Deer Park, but still runs warmer at night. And it’s not due to elevation. At 2,123 feet above sea level, Deer Park is only 280 feet higher than Spokane and just 23 feet higher than Sandpoint. (In April, The average low temperature for Deer Park is 31.6 degrees, compared to 36.4 in Spokane and 34 in Sandpoint.)

The reason lies largely in the town’s topography, or the shape of its land surface. Located in a broad, shallow valley, cold air – more dense than warm air – sinks and then settles as close to the ground as possible rather than fanning out at a higher level.

Furthermore, Deer Park runs naturally cooler because it is a small town of 4,250. The more people, pavements and buildings, the warmer a populated area tends to get – a phenomenon scientists call the urban heat island effect. Spokane, with a population of 228,000, has a bigger concentration of asphalt, concrete and dark roofs. These absorb heat during the day and then radiate it back into the air at night.

If the annual pattern holds, this summer’s daytime temperatures in Deer Park will run a couple of degrees warmer than Spokane, but then run between 5-10 degrees cooler at night. Clearly, it’s a good place to sleep during a heatwave.

When the cold front dropped down from Canada last weekend, Deer Park, like all of the Inland Northwest, got much-needed rain following a stretch of unseasonably dry weather. Then a shift in the weather pattern early this week brought a comeback in springlike warmth and dry conditions. Expect temperatures to spike in the mid-70s today before a gradual cooldown into the 60s this weekend. And in typical Deer Park fashion, as we step into May, nighttime lows will run cooler in Deer Park than neighboring locations.

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Nic Loyd is a meteorologist in Washington state. Linda Weiford is a writer in Moscow, Idaho, who’s also a weather geek. Contact: ldweiford@gmail.com