Climate and geography
Armed with an understanding of the climate and geography of the Pacific Northwest, we can define culinary regions based on shared characteristics. This article aims to explain those.
Geography
Major geographic features of the Pacific Northwest which affect the region’s climate:
Northern latitude
Western side of the continent
Coastal
Mountainous
Volcanic
Major geographic features of the Pacific Northwest.
Combined, the geographic features of the Pacific Northwest define the climate of the region and the flora and fauna it can support.
The first major feature is its latitude, or distance from the equator. The region ranges from about 40 degrees to 50 degrees latitude. Portland is right in the middle, at 45 degrees. This position is important because daylight patterns are affected by the distance from the equator. The tilt in Earth’s axis is responsible for the change in seasons over the course of the year; the further from the equator, the more extreme the effect. As a result of its latitude, the warm season in the Pacific Northwest is relatively short, which limits some plants’ ability to produce a worthwhile harvest, even though the region’s climate is exceptionally mild for how far north it is.
The second major feature is its location on the western side of North America, next to the Pacific Ocean. Due to the direction of Earth’s rotation, the western sides of continents have generally drier and milder climates than their eastern counterparts. In addition, the region is located along the Pacific Ocean, which has a moderating effect on temperature extremes. Temperature extremes are greater inland due to the lack of this moderating effect.
The final feature to examine is the region’s topography. Like much of the western United States, the geography of the region is highly varied and mountainous. It’s also volcanically active: this volcanic activity is responsible for the region’s fertile soil, which was further enhanced by massive floods at the end of the last Ice Age.
Mountains have a large impact on local climates by blocking prevailing winds, which results in precipitation concentrating on one side of the range and reducing on the other. The area with reduced precipitation is known as a rain shadow. In the Pacific Northwest, this effect is especially evident with the Cascade Mountains, which create a rain shadow on the eastern side of the state and concentrate rainfall on the western side.
Climate
Broadly speaking, the Pacific Northwest can be divided into two distinct areas: a wet, mild coastal climate in the west, and an arid, continental climate in the east.
Both areas are characterized by dry summers and wet winters. If you travel south, the climate trends warmer and drier. Travel north, and it becomes cooler. Closer to the coast, the climate is cooler and milder, and precipitation increases significantly.
The western side of the Pacific Northwest receives high annual precipitation. Temperatures are moderated by the Pacific Ocean, with few temperature extremes. The area supports extensive temperate coniferous rainforests.
The eastern, inland side of the region is affected by greater temperature extremes and receives very little annual precipitation, with much of it falling as snow. Precipitation increases in mountainous areas. The area features deserts, plains, and open conifer forests.
To best understand our region’s climate, it’s important to look at several different sources of data. All classification systems have their limitations. By looking at several together, we can make up for these shortcomings and get a more complete picture of the region.
We’ll be looking at the following information:
Köppen climate classifications
USDA hardiness zones
Precipitation patterns
Temperate rainforests
Köppen climate classifications
The Köppen system was designed in the early 20th century by German-Russian climatologist Wladamir Köppen. Because the classification system was based in large part on Köppen’s experience as a botanist, it provides us with insight on ecosystems, and in turn, on what grows in our region.
Under the Köppen system, climates are divided into five main groups, then further differentiated according to precipitation and temperature patterns.
The five groups are:
A - tropical
B - arid
C - temperate
D - continental, and
E - polar
These main groups are then assigned a second letter according to precipitation patterns, and a third letter according to temperature patterns. There are 30 climate types in total.
Of the 30 climate types, 14 of them are found in the Pacific Northwest. Of these 14, the 5 most common are: warm-summer mediterranean (Csb), hot-summer mediterranean (Csa), temperate oceanic (Cfb), cold semi-arid (BSk), and warm dry-summer continental (Dsb).
The 14 climate types are listed in the table below, with the 5 most common in bold.
| Arid | BSk | cold semi-arid |
|---|---|---|
| BWk | cold desert | |
| Temperate | Cfb | temperate oceanic |
| Cfc | subpolar oceanic | |
| Csa | hot-summer mediterranean | |
| Csb | warm-summer mediterranean | |
| Csc | cold-summer mediterranean | |
| Continental | Dsa | hot, dry-summer continental |
| Dsb | warm, dry-summer continental | |
| Dsc | dry-summer subarctic | |
| Dfb | warm-summer humid continental | |
| Dfc | subarctic | |
| Polar | ET | tundra |
| EF | ice-cap |
Main climate types of the Pacific Northwest
Mediterranean: Csb and Csa
The dominant climate type in the Pacific Northwest is warm-summer mediterranean (Csb).
Mediterranean climates are temperate and characterized by dry summers and cool, wet winters. The overwhelming majority of annual precipitation is received in the cool season (winter and adjacent months). This simple fact makes an large impact on agriculture and the seasons. For example, the Northwest has a productive growing season in late fall and winter due to mild conditions and plenty of rain.
This is a rare climate type, even less common than the also rare hot-summer mediterranean climate (Csa). Mediterranean climates are only found in about 2% of the world.
The hot-summer mediterranean climate is the "typical" mediterranean one - think California, Italy, Greece, etc. The warm-summer mediterranean climate is found in the northern reaches of mediterranean zones, and at higher elevations. They are cooler overall, especially in summer. The Pacific Northwest is unique in that it is the largest single area in the world to feature this climate.
Oceanic: Cfb
As you move further north into Washington and British Columbia, the climate becomes more oceanic and similar to the western side of Europe. Oceanic climates are characterized by consistent precipitation throughout the year, cool summers and mild winters. Temperatures are also consistent, and stay within a relatively narrow annual temperature range with few extremes.
Many coastal parts of the Pacific Northwest can be considered transition areas between mediterranean and oceanic climates.
Semi-arid: BSk
Inland, the climate changes to a cold semi-arid one due to the rain shadow created by the Cascade Mountains and the greater distance from the Pacific Ocean. Defining characteristics of the climate are low year-round precipitation and larger temperature variations between night and day. The climate features dry, warm to hot summers and most precipitation is received in winter, often in the form of snow. This climate provides a fertile environment for growing cool-season legumes such as chickpeas and lentils, and for growing unirrigated wheat.
Continental: Dsb
The warm, dry-summer continental climate is generally found in mountainous areas of the inland Pacific Northwest. Without the moderating influence of the ocean, temperature differences between summer and winter are more extreme.
In many ways, this continental climate is just an extension of the mediterranean climate into higher altitudes, and exhibits similar rainfall patterns (most of it falling in the cool season). This climate type is very rare.
USDA hardiness zones
The USDA hardiness zone system is used in horticulture to determine what plants can be grown in an area. It has its limitations, though, because it’s based only on the average extreme minimum temperatures found in an area over the course of a year and does not take into account other climatic differences. That said, it makes a good starting point for researching plants, since many can be ruled out simply based on their hardiness.
USDA hardiness zones.
There are 13 hardiness zones under this system, with “a” and “b” subdivisions added for further detail. The Pacific Northwest as a whole ranges from zones 3b to 10a.
Oregon: 4b to 9b
Washington: 4a to 9a
Northern California: 5b to 10a
Idaho: 3b to 7b
Because the USDA hardiness system uses averages, it can paint an inaccurate depiction of the lowest temperatures that may affect an area. In Portland, for example, we are subject to a cycle of extreme low temperatures that occur intermittently. Cold snaps like that don’t affect the average much overall, but they can still kill a plant that would otherwise be OK. With regards to commercial agriculture, no producer will be willing to grow a perennial plant that might get wiped out in a decade.
For the Portland area, I look for perennial plants which can handle about 0°F to 5°F, since these are temperatures which have historically hit the area. Of course, climate change will likely raise these numbers, but as it currently stands, this is a good gauge.
Precipitation patterns
Annual precipitation in the Pacific Northwest is actually lower than it would appear, since the region as a whole is more arid. The distribution of precipitation is very unequal, with some parts of the western side of the Pacific Northwest receiving the highest precipitation levels in the lower 48 states.
Annual US precipitation totals.
One impact of the difference in precipitation between the arid and temperate parts of the Pacific Northwest is expressed in the acidity or alkalinity of the soil (pH balance). The soil is more alkaline in arid climates than the soil in the forested, temperate climates, which can be very acidic due to the leaching of minerals caused by elevated rainfall. Plants have varying soil pH preferences which can affect their success in different regions.
Dry-summer climates
Many parts of our region are affected by dry summer conditions. Because of this, plants that succeed best here are often those that can handle some amount of drought and dry weather in summer. In the coastal areas, those plants must also thrive in wet to very wet weather. Evergreen plants do very well thanks to their ability to photosynthesize in cold weather, which is when they also receive plenty of water to grow. It’s one of the reasons conifers do so well in the Pacific Northwest.
