Western US Daily Snow
By Alan Smith, Meteorologist Posted 3 years ago September 20, 2021
New snow for parts of the Cascades and Rockies
Summary
A storm system accompanied by a strong cold front last weekend resulted in heavy precipitation across the Pacific Northwest along with the first widespread accumulating snowfall for higher elevations in the Cascades as well as the Northern/Central Rockies. A trend toward warm and sunny conditions will occur this week for most areas, along with some late week showers for the Southwest.
Short Term Forecast
The weekend storm system delivered impressive precipitation to much of the West, with the heaviest totals across Western Washington and Western Oregon. Rain totals in excess of 4 inches were estimated or recorded across portions of the Cascade and Olympic Ranges. Northern California also saw some beneficial rainfall.
Check out the 3-day precipitation totals ending Monday morning:
A cold front also moved across the West over the weekend, and snow fell behind the front across the higher elevations of the Cascades and Rockies.
Check out our estimated 24-hour snowfall totals from Sunday morning through Monday morning. The heaviest snow fell across the mountain ranges of Northwest Wyoming and Southwest Montana, with snow accumulations extending southward into Northern Colorado as well.
Our estimated snow depth map shows plenty of new snow cover across the mountainous regions in and around Yellowstone and Grand Teton National Parks as of Monday morning.
The good news if you have hiking plans in these areas later in the week is that the new snow should melt off quickly with warmer and drier weather expected to return.
The OpenSummit forecast page for Paintbrush Divide in Grand Teton National Park does a good job of highlighting the recent snowfall under the "Estimated Trail Conditions" section. You can also see on the 5-day forecast that warmer temperatures and a lack of precipitation will allow the new snow to melt off.
As of Monday afternoon, the storm system is moving east of the Rockies with backside valley rain showers and mountain snow showers developing along and east of the Divide in Montana and Wyoming.
Most of the West will see a drying trend for the remainder of the week with warmer temperatures as high pressure returns.
A weak system from the Pacific will split as it reaches the BC/Washington Coast. The northern piece of energy will track north of the Canadian border, while the southern piece of energy will develop into a cut-off low (meaning an area of low pressure that separates itself from the main jet stream and often exhibits slow/erratic movement) as it meanders into Southern California. This feature will result in a chance of showers over parts of the Southwest later in the week.
The 5-day departure-from-average temperature map reveals a warming trend throughout the West over the course of the week. This will be most notable along the West Coast and more delayed near and east of the Continental Divide where chilly temperatures will persist early in the week.
Forecast for Monday, September 20th
Backside showers will favor areas near and east of the Continental Divide over the Rockies on Monday, including snow for higher elevation areas. Light rain amounts showing up on this map over the Cascades occurred earlier this morning and shower activity has since cleared out with sunshine returning.
Forecast for Tuesday, September 21st
Tuesday is looking dry across the entire Western U.S. with rain chances confined to areas well north of the Canadian border as a weaker system approaches.
Forecast for Wednesday, September 22nd
The previously mentioned weak system will split as it reaches the U.S. Coast on Wednesday with only some light showers for the Cascade and Sierra Ranges. Snow levels will remain high over these areas with a warmer airmass in place compared to last weekend's storm.
Forecast for Thursday, September 23rd
Shower and thunderstorm chances will increase across Southern California and Arizona as an area of low pressure sets up over the region. Confidence is low at this time regarding the location and intensity of shower activity, but hopefully, this area will pick up some needed rainfall.
Forecast for Friday, September 24th
A similar pattern will remain in place on Friday with shower and thunderstorm chances across Southern California and Arizona and drier conditions elsewhere across the West.
Extended Forecast
Outlook for Sat, Sept 25th - Wed, Sept 29th
The previously mentioned weak area of low pressure over Southern California is expected to remain a factor this weekend and into early next week with additional shower/thunderstorm chances across the Southwest. High pressure will dominate the pattern farther east and north across the Rockies.
The SoCal Mountains, Sierra, Great Basin, and Desert Southwest will see the best chance of showers during this time. Confidence is low on how much rain potential and if we see any noticeable fire relief in California, but every little bit helps.
A little bit of shower activity could also reach areas farther east in the Rockies by early next week.
However, temperatures will be warmer than average throughout the Rockies during this time and any shower activity will occur with high snow levels.
Thanks so much for reading! Next update on Wednesday (9/22).
ALAN SMITH
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