Forecast Highlights:

• Strong and slow-moving storm system to impact much of the West from Friday to Monday
• Significant precipitation expected across the Pacific Northwest and Northern/Central Rockies
• Thunderstorms possible each day across the Rockies from Friday to Sunday
• Heavy snow for the Cascades on Saturday and the Northern/Central Rockies on Sunday and Monday
• Well below-average temperatures for most of the West by Sunday and Monday
• Elevated fire danger throughout the weekend across the Southwest

Synopsis:

A slow-moving trough of low pressure will move into the Western U.S. over the Memorial Day holiday weekend, resulting in multiple days of active weather along with a transition to colder-than-average temperatures. The Northwest and the Northern and Central Rockies will see the greatest weather impacts this weekend and any outdoor activities should be planned with caution or postponed depending on the activity and location. 

Precipitation - Timing and Amounts (Friday to Monday):

Showers and thunderstorms will become more numerous as the day progresses on Friday and into Friday night across the Pacific Northwest and the Northern Rockies. Colorado could see some isolated thunderstorms on Friday afternoon but any rainfall will be very light. 

On Saturday, precipitation will become heavier and more widespread across the Pacific Northwest and Central Rockies. Oregon, Southern Idaho, Western Wyoming, Northern Utah, and Southern Montana will be favored for the heaviest rainfall, and high elevation snow can also be expected.

The Sierra, Great Basin, Southern Utah, and Western Colorado will also see some shower activity on Saturday.

On Sunday, the heaviest precipitation (valley rain and mountain snow) is expected across the Northern and Central Rockies, especially across Southwest Montana and Northern Wyoming, including the Madison, Gallatin, Beartooth, and Big Horn Ranges along with Yellowstone National Park.

The Wasatch Range in Utah will also see heavy precipitation, and precipitation potential is looking greater across Western and Northern Colorado than previously expected.

The Cascades will remain in a cool and wet pattern with additional rain and mountain snow expected.

On Monday, areas east of the Continental Divide in Wyoming will be favored for the heaviest and most widespread precipitation while rain and snow showers will continue west of the Divide across the Central Rockies and, to a lesser extent, the Pacific Northwest.

Bottom line, Memorial Day weekend is shaping up to be wet and chilly (and for higher elevations, snowy) across much of the West.

Here is the projected 4-day precipitation total from Friday through Monday via the European Model. Notice how Southern Montana is in the bullseye with widespread liquid-equivalent precipitation totals of 3+ inches projected.

Thunderstorm Potential:

We're at the time of year where strong solar radiation and surface heating lead to increased instability in the atmosphere, and as a result, thunderstorms will be possible across most of the West, at least east of the Cascades, this weekend.

On Friday, the combination of moisture and instability along with the presence of wind shear will result in more numerous clusters of thunderstorms across Northern/Central Wyoming while activity will be more isolated elsewhere, including Colorado where instability will be present but moisture will be limited.

There is also a marginal to slight threat of severe thunderstorms across Eastern Idaho and Northern Wyoming, where straight-line wind gusts of 60 mph will be possible under strong thunderstorms. The highest threat (level 2 out of 5) for severe wind gusts is expected across the Black Hills of NE Wyoming and Western South Dakota.

On Saturday, the highest threat for thunderstorms across the Intermountain Region will be across Oregon and Utah with more isolated activity across Idaho, Montana, and Wyoming. Stronger thunderstorms are likely east of the Rockies across Eastern Wyoming, South Dakota, and Nebraska. Colorado should largely stay lightning-free on Saturday.

On Sunday, the lightning threat will decrease somewhat across Idaho and Montana as a colder airmass settles into place, while Colorado is expected to see a noticeable uptick in thunderstorms throughout the state, with the strongest storms likely across the Front Range. 

Thunderstorms will remain possible across the Rockies on Monday, but will be more isolated and weaker as a colder airmass will be entrenched across the West with well below average temperatures (less surface heating available to "fuel" t-storms as a result). Still, there could be some occasional lightning strikes so don't let your guard down if you plan to spend time outside. 

Heavy snow for higher elevation areas this weekend:

We will see a downward trend in temperatures across the West throughout the holiday weekend, and as a result, snow levels will gradually lower over time and a significant winter storm is expected for higher elevations of the Cascades and Northern/Central Rockies.

On Saturday, snow levels will begin to lower across the Cascades with snow levels dropping to 4,500 feet. The Oregon Cascades will be favored for the deepest totals with 6-12 inches expected above 4,500 feet while the Washington Cascades will see amounts ranging from 2-8 inches.

Snow levels will remain relatively high (above 9,000 feet or so) across the Northern and Central Rockies on Saturday, but will drop on Sunday and Monday as colder air arrives with heavy snow expected down to 8,000 feet and light snow extending to even lower elevations at times. 

The combination of moisture, colder air, and favorable wind directions will result in very heavy snow accumulations across the Beartooth, Absaroka, Big Horn, and Wind River Ranges in Montana and Wyoming in particular where snow totals of 2-3 FEET are likely above 8,000 feet.

Elsewhere, heavy snow (6-12+ inches) is also likely from the Sawtooths to the Beaverhead and Bitterroot Ranges in Idaho and Montana as well as the Tetons in Wyoming and Wasatch and Unitas in Utah, while the western and central ranges in Colorado should also pick up some decent snow totals. 

Fire Danger Continues for the Southwest:

Once again, the Southwest U.S. will remain on the dry and windy side of this upcoming storm system, and fire danger will remain elevated to critical as a result. The map below shows the current Red Flag Warnings (for high fire danger) in effect:

Large fires continue to burn across New Mexico and the Lost Lake Fire is also burning near the Arizona/California border. Smoke from these fires could creep into Colorado and Southern Utah at times over the weekend, so be sure to check our Smoke Forecast Map and Current Air Quality Map for the latest. Also, see the announcements section below for an exciting new feature we've added related to air quality. 

Outlook for Tue (5/31) to Thu (6/2):

Overall, we should see a warming and drying trend across most of the West heading into the middle part of next week. Lingering unsettled/showery weather is likely across the Central Rockies on Tuesday with decreasing rain chances and warmer temperatures on Wednesday and Thursday.

The Pacific Northwest should dry out on Tuesday and Wednesday with increasing shower chances by Thursday as the next storm system approaches.

Meanwhile, low-level moisture from the southern plains drifting westward is expected to reach New Mexico on Wednesday and Thursday with increasing thunderstorm chances along with the potential for some much-needed rain. This pattern may be a double-edge sword, as any rain would be welcome, but if thunderstorms develop with limited moisture then there could be a threat for lightning-triggered fires. 

Outlook for June 3-9:

Models are in relatively poor agreement regarding the overall evolution of the pattern by next weekend and into the first full week of June.

However, I'm expecting a fairly active pattern to continue across most of the West with fluctuating temperatures and frequent shower and thunderstorm chances, especially across the Pacific Northwest and the Rockies. I also don't see any significant heatwaves (or cool spells) on the horizon at this time. 

I suspect we'll see more numerous thunderstorms during this period across the Rockies. Also, we'll be heading into the heart of severe thunderstorm season across the high plains so keep this in mind if you live east of the Continental Divide in New Mexico, Colorado, Wyoming, Montana, or Alberta.

Thanks so much for reading! Next update on Wednesday (6/1).

ALAN SMITH

NEW: Global Air Quality Forecast Map

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Click the "Maps" tab and select the "Air Quality Forecast" overlay.

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