Weather

Weather and climate refer to patterns of changes in the environment, and differentiate in terms of time. Weather is the atmospheric conditions in a relatively short period of time, whereas the climate is how the atmosphere changes over time, creating long-term patterns. When we look at climate change, we look at various lengths of time with weather patterns.

The jet stream is a horizontal rapid air corridor created from temperature differences around the globe. It circulates cold air from the poles and warm air from the equator, carrying storms and other weather systems in its west-east path. It affects the weather we experience in Oregon due to the positioning of the stream in summer and winter. Summer experiences a hotter climate due to the tilt of the earth and position of it around the sun, moving the Jetstream north during the summer and south during the winter. Local weather patterns, especially in the Willamette Valley, depend on placement of weather patterns over mountains, and thus give the WV its extraordinary climate.

Rainfall is generally split along a north-south line, separating east and west climates on different sides of the Cascades, typically turning mountains into rain-producing regions. The ability to carry water depends on temperature; the cooler air holds more moisture than the hot air. With the jet stream moving air over mountains (which subsequently warm and cool in changes in elevation), it allows condensation to form when air moves through different systems of pressure and temperature, and when it crosses mountain peaks, the air warms and expands, decreasing cloud coverage. Depending on the amount of water carried, showers can be prevalent going down a mountain.

With global climate pattern circulation, the sun becomes the main force that heats the air, moving air from the tropics to the poles, and vice-versa. As the air rises from becoming heated, it cools toward a dew point, reverses course, and begins to precipitate. There are three ‘cells’ going around the latitude of the earth, and each one has a different climate pattern associated with it. Oregon’s climate is very unique, with siblings in Chile, Scotland, Japan and Norway, all have 1 ½ times the amount of precipitation in the wettest winter months than in the driest summer months. In the Cascades we attribute it with a cold polar air mass, polarized against a warm subtropical mass, creating a massive front roughly 20° latitude wide.

A desert is a geographic region that typically receives ten or fewer inches of rain per year. More specifically, other characteristics include a higher percentage of sunlight, low humidity and high temperatures/extreme fluctuation, higher mineral soil and rough erosion on the ground. Isolation from an oceanic coast is also a contributing factor, as the area won’t get moisture from the ocean (like the west coast gets with fog). Deserts also don’t benefit from cold ocean currents, which quickly warm up when travelling eastward over the Cascade mountain range and the Willamette Valley.

Low-pressure systems have the ability to create storms and lift areas of warm air, and can be formed from thunderstorm events. This lifting can bring clouds, which can bring precipitation. The air doesn’t rise as much and different winds can move air through monsoon-like circulations.  High-pressure systems are usually associated with lighter winds, and dry out air through heating, and can produce clearer skies. Since the absence of clouds prevents reflection of sunlight, radiation of the earth is reduced and heat isn’t as present.

Microclimates are miniature geographic areas that have very different weather patterns from surrounding ‘macroclimates.’ Closer toward the ground, microclimates are affected by several factors. One reason they occur is due to the physics of hot air rising, and cold air falling. Cold air in small pockets can follow a stream or find the floor of a valley. This is an explanation for why some places hold snow longer than other places.

Another reason they occur is because of temperature differences in the ground and in lakes, and how they are susceptible to radiation. Since darker areas heat more than light ones, a cloud covering could become a potential area for heat collection. High peaks of mountains are closer and more exposed to radiation, and the same goes for south-facing slopes versus north-facing slopes.