“The weather when I leave the house and when I get to work can be a night and day difference,” he said.
There isn’t much of an elevation change in his commute, Prothero said, and he wants to know if I-205 is such a large structure that it actually impacts weather around it.
The short answer is no, said Amanda Bowen, a meteorologist with the National Weather Service in Portland.
“Interstates don’t have any impact on weather,” Bowen said. “What he’s probably seeing is that when we have east winds that are blowing through the Gorge, (I-205) tends to be a convenient separator for us to talk about weather differences, like east of (I-205) and west of (I-205).
“If he’s seeing rain on one side and not the other, it can be sometimes because those east winds that are blowing; they’re blowing harder generally further east toward the Gorge. …You can have it so that the really dry wind that’s stronger east of (I-205) is actually making it so that really light rain is evaporating before it’s reaching the ground,” she said.
That’s not the case in every situation, Bowen said, but it is one way to explain how weather can differ on either side of I-205.
“It’s not always the same spot every time, where it’s like, ‘Oh, it’s snow east and rain west, or it’s dry east and rain west,’ or something like that,” she said. “But in general, with I-205, people know it and are familiar with it, so it’s an easy thing to talk about in making generalizations about what’s going to happen east of (I-205) and west of (I-205).”
County microclimates
Scott Weishaar, a forecaster with the National Weather Service, said there can be microclimates in Clark County depending on where you are, and how much of a deep cold air layer there is in that area. Places closer to the Gorge, such as Washougal and Camas, have a little bit deeper cold air layer, he said, which can cause more snow and freezing rain.
Just a couple weekends ago in Clark County, some parts of the county got 8 inches of snow, while others only got about an inch.
“The main issue is terrain,” he said. “If you happen to be in a valley area that is sheltered and cold air is trapped in there, then you have a higher chance of seeing freezing rain or snow, whereas you’re away from that valley or in an exposed area, the cold air may have mixed out and you may just have rain.”
In general, he said, there isn’t necessarily one side of Clark County that gets much more precipitation than the other. But Weishaar said “south-facing or west-facing slopes are going to have better lift and more efficiency for rain.” Those areas get higher amounts of rain than sheltered areas of south-facing or east-facing slopes, he said.
“The farther east you go in the county, the more varied the terrain is,” Weishaar said. “That’s where you’re going to have the more likelihood of seeing those higher precipitation amounts.”
