Snowpack Update:

The melt is on across the West as we have seen a recent transition to above-average temperatures following a colder-than-average winter season that persisted through April. The warm-up has been substantial enough that snowpack has fallen below average for mid-May across portions of the Pacific Northwest and Northern Rockies.

Snowpack still remains well above average across California, Utah, and much of the West Central U.S.

Areas that received record snowfall this winter in Utah and California have seen a recent uptick in snowmelt rates. But there is still a lot of snow on the ground and it's going to take a while before entirely melting out.

Check out the snowpack versus average graphs at Alta (UT) and Sugar Bowl (CA) to see how the melt has ramped up recently. 

Be sure to check our Snow Depth Map as the spring progresses to keep tabs on when your favorite trails or peaks melt out. Or to get an idea if backcountry areas/peaks still have enough snow to ski on.

Big Picture Weather Pattern:

A tall ridge of high pressure will remain in place across the West this week, resulting in unseasonable warmth across the Pacific Northwest and Western Canada in particular.

However, an area of low pressure will remain located over the Southwest, which will help to draw in subtropical moisture from the Eastern Pacific and the Gulf of Mexico. The result will be a wetter-than-average pattern for this time of year across the Southwest and Southern Rockies.

A "backdoor" cold front will also slide down the eastern side of the Continental Divide this week, with an associated disturbance resulting in frequent shower/thunderstorm chances across the Central and Eastern Rockies. Moisture will be most abundant along the eastern slopes of the Continental Divide in Colorado and New Mexico.

Over the next 5 days, temperatures will be above average across the Far West, Great Basin, and Northern Rockies, and near to below average across Colorado, New Mexico, and Arizona.

Forecast for Tuesday (May 16):

Showers and thunderstorms will be common across much of the West, especially during the afternoon hours. This is due to a disturbance moving across the Northwest and Northern Rockies, as well as a moist southerly flow across the Southwest. 

While showers and storms will be hit or miss in nature, locally heavy rain, and isolated flash flooding will be possible across northern portions of NE Washington, Idaho, and Montana, as well as Northern Arizona.

Forecast for Wednesday (May 17):

Showers and thunderstorms can be expected across a large portion of the West once again, with the focus shifting to Southern Montana and Northern Wyoming while the Four Corners states will also remain favored. Showers will be more isolated across the Cascades and Sierra.

Forecast for Thursday (May 18):

A cold front will slide down the eastern side of the Continental Divide in Colorado and New Mexico on Thursday. Upslope easterly winds will transport Gulf of Mexico moisture to the east side of the Divide, resulting in a good chance of showers and thunderstorms with locally heavy rain possible. 

Isolated showers and thunderstorms can also be expected across Arizona, Utah, and Wyoming. The Northern Rockies will start to dry out, while a weak disturbance will bring a chance of showers and thunderstorms to Washington and British Columbia. 

Forecast for Friday (May 19) to Saturday (May 20):

A wet and active pattern will continue across the Four Corners region during this period with showers and thunderstorms expected along with locally heavy rain, especially on Friday. The Southern Colorado Front Range, Northern New Mexico, Sangre de Christos, and parts of the San Juans look the most favored.

Shower and thunderstorm activity is also expected to extend westward into Nevada and California, while the Pacific Northwest could see some showers/storms as well. The Northern Rockies is looking like the driest area during this period.

Outlook for May 21st-27th:

The ridge of high pressure over the Western U.S. should weaken a bit compared to the prior week, but will still remain the dominant pattern, resulting in above-average warmth for most areas.

However, stubborn low pressure over the Southwest along with disturbances sneaking through the high pressure dome should keep frequent shower and thunderstorm chances going across the Southwest and West Central U.S. including California, while the Pacific Northwest is looking comparatively drier. 

Thanks so much for reading! Check back in for my next update on Wednesday, May 24th.

ALAN SMITH