Weather topic #5

 Snow in the Puget sound lowlands

Section 1: Why it is hard to get Puget sound snow

Sometimes in the Puget sound lowlands, we can go very long periods of time without snowfall, even during winter. This is because of multiple terrain features that are nearby, and these features make it very difficult to get cold air down to surface level at lower elevations. The first of these features is the Puget Sound itself. Water is a temperature moderator, because it stays at a relatively stable temperature. Due to this, typically the further you get from a large body of water, the more variability there is in temperature. A personal experience of this phenomena taking place was when I drove from the Tacoma area to Portland. It was 36 degrees and raining by the Puget sound in Tacoma, but during the portion of the drive just south of Chehalis, the temperature dropped to 29 degrees, and heavy snow was falling. This was because Chehalis was further from a large body of water to act as a moderator. The Pacific Ocean can also amplify this principle. 

A second reason that it is hard to get sea level snow around the Puget Sound is that we have a multitude of mountain ranges that bottle up cold air off to the east, and don’t allow for it to seep out into the lowland areas. The first of these is the Rockies, because when the polar lobes come, the arctic air comes from the northeast, and moves toward the Pacific Ocean. Below the highest peaks, the cold air is blocked, and cannot get down to the surface level. The second operates at a smaller degree, and it is the cascades. The cascades generally block less cold air, but they are still a key factor in keeping western Washington too warm for snowfall. 

Section 2: Cold Air conduits

I previously mentioned that much of the cold air that tries to get into Washington gets trapped by the various mountain ranges. However, there are some paths that cold air can take to seep its way into Washington. The first way, and main way, is the Fraser river outflow.When this occurs, strong winds start at the surface in the Fraser river valley, which empties out north of Bellingham, WA. This brings cold air from B.C and Alberta into the northern Puget sound, and this cold air can rip down the sound via northerlies. 

A second conduit of cold air that brings Arctic air into places west of the Cascades is the Columbia river gorge. This is the event of colder air from eastern Washington and Oregon spilling into the Portland metro area from the Columbia River gorge via strong Easterlies. This cold air is then pushed by Northerlies south into the Willamette Valley.

A final cold air conduit flows into eastern Washington, and it is called the Okanogan River outflow. This is cold air that pushes southward out of the Okanogan river valley from B.C into eastern Washington. This outflow has many similarities to the Fraser river outflow, but it is a much smaller scale conduit of cold air. 

Section 3: Pacific Ocean snow Machine

One way that snowfall amounts can be enhanced is by the Pacific Ocean snow effect. This occurs when a low from B.C swings out over the Pacific Ocean, and brings moisture with it. As long as the low is substantially cold, the moisture that the Pacific Ocean contains can evaporate up into the levels of the atmosphere, and condenses, causing it to all fall back the the surface after it crashes inland, leading to heavier snowfall because of the excess of moisture in the atmosphere. This can lead to drastic snow totals. However, if the low is not cold enough, the relatively warm Pacific Ocean can warm the air too much and put too much moisture into the air, causing the precipitation to fall as rain.