Forecast Highlights:

• Quick Memorial Day storm system recap
• Isolated thunderstorms Colorado/New Mexico (mainly foothills/eastern plains) Wed-Fri
• Showers/thunderstorm coverage expands across Northwest and Northern Rockies Wed-Fri
• Warm but active pattern with showers/thunderstorms for much of the West this weekend & early next week

Synopsis:

A slow-moving storm system that impacted a large portion of the West over the holiday weekend is finally exiting to the east out across the plains. A weak ridge of high pressure will build over the Great Basin over the next couple of days, resulting in a significant warm-up following a stretch of unseasonably cool conditions. Meanwhile, a trough of low pressure will set up off the Pacific Northwest coast late this week and over the weekend and a series of embedded disturbances will move across the Western U.S.

Quick Memorial Day Storm System Recap:

It was a wet, cold, and in some cases, snowy holiday weekend across a large portion of the West with significant precipitation totals for many areas.

Here is a 7-day estimated precipitation analysis ending on Tuesday morning, which gives an idea of the wet pattern experienced recently across the Northwest and the Rockies. Mountain areas across these regions received well over an inch of precipitation and favored areas in Southwest Montana received over 4 inches of precipitation. 

Here is a 3-day estimated snowfall analysis from Saturday morning (5/28) through Tuesday morning (5/31). First-hand snow reports are limited this late in the season, but based on estimates, substantial amounts of snow fell across higher elevation areas of Oregon, Idaho, NE Nevada, Montana, Wyoming, Utah, and Colorado.

The heaviest amounts of snow fell in the Beartooth, Absaroka, and Big Horn Mountains of Montana and Wyoming.

According to OpenSnow Utah forecaster Evan Thayer, Alta picked up 16 inches of snow from the weekend storm and many skiers were out hiking for turns on Memorial Day. 

 

Slightly unsettled weather for Colorado & New Mexico, mainly east of the Divide

The tail end of the Memorial Day system is moving east of the Rockies on Wednesday, but the Front Range of Colorado will see some lingering snow through the morning hours on Wednesday morning before tapering off by midday. Areas of the Front Range above 8,000 feet were expected to pick up several inches of snow.

By Wednesday afternoon, an overall drying trend will occur but some residual moisture along with daytime heating could fuel some isolated showers and thunderstorms across portions of Colorado and New Mexico, mainly along and east of the Continental Divide with drier conditions west. 

Heading into the later part of the week, easterly winds at the surface will gradually transport more abundant Gulf of Mexico moisture from the Southern Plains westward toward the Front Range of Colorado and New Mexico.

The best chance of thunderstorms associated with this moisture uptick will occur over the plains of Eastern Colorado and New Mexico, but isolated thunderstorms will likely develop across the foothills as well on Thursday and especially Friday.

Taking a look at the image below, we can see increasing moisture (40+ degree dewpoints) reaching the eastern slopes of the Rockies on Friday afternoon, which is a key ingredient for thunderstorm development.

Convective available potential energy (CAPE), a measure of instability in the atmosphere, will be elevated throughout Eastern Colorado and New Mexico on Friday afternoon, extending westward toward the Front Range foothills. 

Upslope winds in combination with increasing moisture and instability will likely trigger some thunderstorms on Friday afternoon (and perhaps Thursday as well), so be prepared if you plan to hit the trails in the foothills. 

Shower and thunderstorm chances increase across the Northwest/Northern Rockies

While a reprieve from the unseasonably cold temperatures and widespread rain will occur over the second half of the week, a series of Pacific disturbances associated with a strengthening trough of low pressure off the coast of Washington will result in daily rounds of showers and thunderstorms.

Moisture and instability will be present across this region as well in the warmer airmass, resulting in higher odds of thunderstorms (as opposed to strictly showers), even across the Cascades.

Wednesday will be the tamest day of the week with only isolated showers and thunderstorms associated with a weaker disturbance. Any rainfall will be light, and most areas across the Northwest/Northern Rockies will see plenty of sunshine as well.

Shower and thunderstorm chances will increase across Washington, Oregon, British Columbia, Idaho, and Western Montana on Thursday, while Utah and Wyoming should mainly stay dry.

Here is a look at projected lightning activity on Thursday afternoon with the Blue/Wallowa Mountains and Idaho Panhandle being favored, while the Cascades could see some isolated lightning strikes pop as well. 

On Friday, rain will become more widespread and heavier across Oregon, Washington, BC, and Idaho, while shower/thunderstorm coverage will increase across Montana and Wyoming as well.

Lightning activity should also be more widespread throughout the Northwest and Northern Rockies on Friday afternoon.

Outlook for Saturday (6/3) to Monday (6/6):

A more robust disturbance is projected to move across the West over the weekend and into early next week with increasing shower/thunderstorm chances and more widespread rainfall expected across the Northwest and the Rockies, while the Sierra could see some activity on the southern fringe as well. 

There are still some model differences regarding the timing and geographic coverage, but right now, Saturday and Sunday look to be most active across the Cascades, Sierra, and Northern Rockies (ID, MT, WY), while Colorado should stay relatively dry for most of the weekend with an uptick in showers/thunderstorms possible on Monday.

Northern Utah will see its best chance of rain on Sunday and/or Monday, while the Southwest (AZ, NM) should stay mostly dry through the weekend.  

Temperatures will be mild enough through the weekend that widespread snow is not expected at this time, except maybe on some higher peaks. 

Outlook for June 7th-12th:

The rest of next week and into the weekend of June 11th-12th looks relatively unsettled across the Northwest and the Rockies with a northwest flow pattern in place allowing frequent disturbances with showers/thunderstorms to drop into these regions with temperatures running near to below average. 

A ridge of high pressure is expected to develop over California and the Great Basin/Southwest, resulting in hotter and drier conditions.

Thanks so much for reading! Next update on Friday (6/3).

ALAN SMITH

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

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