Western US Daily Snow
By Alan Smith, Meteorologist Posted 1 year ago May 9, 2023
Showers favoring the Central and Eastern Rockies
Summary
The main weather focus across the West this week will be a slow-moving trough of low pressure that will move across the Central Rockies during the middle to latter half of the week. This system will draw in moisture from the Gulf with a good chance of t-storms for parts of CO & WY on Wed, followed by more widespread rain & high elevation snow on Thu-Fri favoring areas near & E of the Divide.
Short Term Forecast
Big Picture:
A lingering trough of low pressure will be located over the Northern Rockies on Tuesday as it weakens and eventually exits the region. Attention will then turn to another trough of low pressure approaching from the Pacific that will track across the Sierra, Great Basin, and Central Rockies over the coming days.
There will be limited Pacific moisture to work with as this trough moves ashore, therefore widespread precipitation is not expected from California to Utah. However, this system will be tapping into moisture from the Gulf of Mexico as it moves into Colorado with heavier and more widespread precipitation expected across portions of Colorado and Wyoming from Wednesday to Friday.
By the weekend, a significant pattern change is expected as a tall ridge of high pressure will build over Western North America, extending way up into Canada. This will result in above-average temps across the West Coast and especially the Northwest.
However, an area of low pressure will undercut the ridge further south, drawing in more abundant moisture from the Gulf into New Mexico and portions of the Southwest. This will mark the beginning of a wet pattern across the Southwest.
Forecast for Tuesday:
Lingering moisture from a departing low pressure system will result in numerous rain showers and high-elevation snow showers across northern portions of Idaho and Montana as well as BC and Alberta. Isolated thunderstorms will also be possible.
Further south, the next trough of low pressure moving ashore in California will result in light to moderate rain and high-elevation snow showers across the Sierra.
Forecast for Wednesday:
Showers and thunderstorms will become more numerous across the Central Rockies with lighter showers also possible across the Pacific Northwest. Strong to severe thunderstorms are also possible along the eastern slopes of the Divide in Wyoming and Colorado and especially out onto the adjacent plains.
On Wednesday night, increasing moisture from the Gulf will result in more widespread rain and high-elevation snow developing east of the Divide, with the Big Horns in NE Wyoming looking the most favored at this time. Winds blowing around the center of low pressure from the northwest and west should also result in rain and high-elevation snow for areas west of the Divide in Colorado.
Forecast for Thursday:
This shaping up to be a wet and snowy day (depending on elevation) along and east of the Divide in Wyoming, Southern Montana, and Northern Colorado. Areas west of the Divide in Northern Colorado will also be favored.
Heavy snow will be possible across the higher elevations in these favored zones, while heavy rain and possible rain-on-snow flooding will be possible along the eastern slopes of the Divide in Wyoming.
Forecast for Friday to Saturday:
Lingering moisture on Friday will result in additional rain and snow showers near and east of the Divide in Colorado, Wyoming, and Southern Montana, at least early in the day.
Much of the West will undergo a warming and drying trend on Saturday. However, the exception will be parts of New Mexico and the Southwest where an area of low pressure will help to draw in moisture from the Gulf, resulting in an uptick in shower and thunderstorm chances.
5-Day Snowfall:
Snowfall will be dependent on slight fluctuations in the track of the low as it moves across the Central Rockies. However, the Front Range and many of the central and western ranges of Colorado stand a good chance of receiving heavy snow from Wednesday night through Friday. The eastern slopes of the Wind River, Absaroka, Beartooth, and Big Horn Ranges in Wyoming will also be favored for heavy snow.
Extended Forecast
Outlook for May 14th-21st:
Next week's pattern will feature a strong and stubborn ridge of high pressure across Western North America, while low pressure will continue to undercut the ridge with moisture favoring the Southwest.
Temperatures are projected to be well-above-average across the Northwest during this pattern, while the Northern Rockies and California/Nevada will also be on the warmer side with enhance snowmelt rates expected. Cooler than average temperatures can be expected across New Mexico during this period.
The Four Corners region, especially New Mexico, will be favored for above-average rainfall during this pattern. May is climatologically-speaking a drier time of year for the Southwest with increased fire risk, so the fact that we are expecting so much moisture at this time of year is great news, though flash flood risk could be a concern in vulnerable areas such as dry washes and slot canyons.
Thanks so much for reading! Next update will be in about a week from now (May 16th-18th timeframe).
ALAN SMITH