Big Picture Weather Pattern (May 20-27):

A wet and chilly week is in store for much of the west as a series of low pressure troughs will drop in from the north and track across the Northwest and Northern Rockies. The Central Rockies will also be impacted by some of these storms.

On the map below, blue/purple colors and dips/troughs or circles in the black counter lines indicate areas of low pressure in the upper atmosphere, which are associated with cooler and more "stormy" conditions. We can see 4 storm systems across Western North America on the map for Monday (May 20), all of which will impact the Western U.S. during the next 7 days.

7-Day Precipitation Forecast (May 20-27):

The wettest areas over the next week include the Washington and Northern Oregon Cascades, a large portion of BC, Alberta, and Montana, and the northern half of Idaho. Favored mountain ranges could see 1-3+ inches of liquid-equivalent precipitation during this time. 

7-Day Snow Forecast (May 20-27):

Higher-elevation terrain will also receive significant snowfall this week, though melting of the new snow is possible in between storms given the time of year. The Northern Rockies (Wyoming, Montana, Idaho, BC, and Alberta) are favored for the highest snowfall totals, though accumulations will extend as far south as the San Juans in Southern Colorado. 

Forecast for Mon (May 20) to Tue (May 21):

On Monday, two storms will impact the Northern and Central Rockies with rain and snow showers expected from Canada to Utah and Colorado. The heaviest precipitation from this system will occur near and east of the Continental Divide in Wyoming (Wind Rivers, Bighorns, etc.). Isolated light showers will extend south and west into Southern Utah and the Sierra Nevada Range in California.

On Tuesday, a strong storm will impact the Northwest with heavy rain and high-elevation snow, favoring the Washington Cascades, Olympics, BC Coast Range, and Northern Oregon and Idaho.

Check out the zoomed-in precipitation forecast for the Pacific Northwest, with 1-2+ inch precipitation totals expected for the Washington Cascades and BC Coast Range.

The lower elevations in the Puget Sound region will see significant rainfall on Tuesday as well.

Forecast for Bellingham, WA:

Forecast for Wed (May 22) to Thu (May 23):

Lighter rain, snow, and chilly temperatures will continue across the Northwest, while the focus of heavy rain and snow will shift into the Northern Rockies. Montana, Idaho, and to a lesser extent, Northwest Wyoming, will see the heaviest precipitation. To the south, isolated showers will develop across Colorado.

Forecast for Fri (May 24) to Sat (May 25):

Another storm will move across the Northwest and Northern Rockies with more rain and snow expected. This storm doesn't look quite as strong as the last one, but cool and wet conditions will still prevail. A disturbance is also expected to move across Utah and Colorado with a better chance of scattered showers and thunderstorms, favoring the Front Range.

Outlook for Sun (May 26) to Thu (May 30):

High pressure will begin to build over the West Central U.S. during this period, resulting in a trend toward warmer and drier conditions for many areas. However, the Northwest will remain in a more unsettled pattern with cooler temperatures and periods of showers expected.

Thanks so much for reading! Next update on Wednesday (May 22).

Alan Smith