Western US Daily Snow
By Alan Smith, Meteorologist Posted 3 years ago August 27, 2021
Relatively quiet pattern this weekend, but smoke issues persist
Summary
A storm system moving across the Northern Rockies will bring showers and thunderstorms to Northern Idaho and Montana on Friday followed by a less active pattern over the weekend. A weak monsoon will maintain daily thunderstorm chances across the Four Corners, while smoke from California fires will affect the Sierra, Great Basin, and parts of the Rockies.
Short Term Forecast
The last of a series of disturbances will move across Montana on Friday, resulting in cool and windy conditions along with widespread showers and thunderstorms.
Check out the forecast radar for 4 pm on Friday for Montana, Idaho, BC, and Alberta.
A weak ridge of high pressure will build over the West this weekend with generally isolated thunderstorms across the Four Corners with a weak monsoon in place.
Then, early next week a trough of low pressure will set up over the Pacific Northwest. Southwest flow ahead of this feature will lead to increasing monsoonal moisture across Arizona, Nevada, and Utah, and energy from the trough will interact with the moisture to result in increasing thunderstorm activity.
Temperatures over the next five days will be cooler than average across the Northwest and warmer than average for the remainder of the West.
A shift to west/northwest winds aloft is pushing the main smoke plume from California fires southward on Friday, and this will lead to increasing smoke across Utah, Southern Wyoming, and Northwest Colorado.
By Saturday morning, smoke will have further settled across much of Utah as well as Northern and Western Colorado and could shift farther south as the day progresses.
Heading into Sunday and early next week, the heaviest smoke will initially impact Utah and Colorado but will gradually shift northward again as winds aloft shift back to southwesterly.
Forecast for Friday, August 27th
Showers and thunderstorms will be most numerous across the Idaho Panhandle, Montana, BC, and Alberta with lingering early morning showers in the Cascades tapering off later in the day. Isolated thunderstorms can also be expected across Colorado, New Mexico, and Arizona.
Forecast for Saturday, August 28th
Areas along/east of the Divide in Montana and Wyoming could see some lingering showers early with a drying trend later in the day. A similar pattern will remain in place farther south with isolated afternoon thunderstorms in Colorado, New Mexico, and Arizona.
Forecast for Sunday, August 29th
Isolated thunderstorms can be expected across Colorado, New Mexico, and Arizona once again as a weak monsoon pattern remains in place. The rest of the West is looking dry.
Forecast for Monday, August 30th
Moisture will begin to increase across the Southwest with an uptick in thunderstorms expected across Arizona and Southern Utah. Colorado and Northern New Mexico will initially be on the "drier" side of this pattern and will see decreasing thunderstorm chances on Monday compared to prior days.
A few isolated storms couldn't be ruled out across the Northern Rockies, but most of this region will stay dry.
Forecast for Tuesday, August 31st
Southwest flow associated with a deepening trough of low pressure over the far west will result in a more impressive surge of monsoonal moisture into the U.S. on Tuesday with more numerous thunderstorms and wetting rains expected across Arizona, Southern Utah, Nevada, and the SoCal Mountains. Thunderstorm activity will remain very isolated across Colorado and New Mexico.
Farther north, a disturbance moving across Canada will lead to an uptick in showers and thunderstorms across BC and Alberta and areas just south of the border (such as Glacier) could potentially get in on the action as well.
Extended Forecast
Outlook for Wed, Sept 1st - Sun, Sept 5th
The beginning of this period is looking quite active with Pacific energy interacting with monsoonal moisture to result in increased thunderstorm activity and wetting rains across Arizona, Utah, Colorado, and New Mexico. Parts of Wyoming could get in on the action as well.
As we head later into the week, the focus of moisture and thunderstorm activity will shift eastward with a drying trend for Utah and Arizona. Across Colorado and New Mexico, elevated thunderstorm activity could potentially linger into the start of Labor Day weekend, though confidence is low.
Rainfall is generally expected to be above-average for this 5-day period across the Four Corners states. Farther north, lighter showers/thunderstorms will be possible at times across the Northern Rockies.
Thanks so much for reading! Next update on Wednesday (9/1).
ALAN SMITH
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