5-Day Big Picture Overview:

A ridge of high pressure will strengthen over the West Coast this weekend, resulting in the first heatwave of the summer for the far western states. A trough over the Central U.S. will reinforce a cooler airmass along the eastern side of the Continental Divide.

In between these two features, an unsettled northwest flow will continue across the Northern Rockies (mainly east of the Divide). To the south, subtropical moisture (let's call it a "pre-monsoon" pattern) will sneak into the Four Corners states, favoring NM and CO, and leading to weekend thunderstorm chances. 

5-Day Regional Forecast Breakdown below as follows...

• Colorado
• Utah
• Southwest
• California/Sierra
• Pacific Northwest
• Northern Rockies
• BC Interior & Canadian Rockies

COLORADO

Fri – Dry conditions will prevail for one more day, with only the southeast corner of the state (plains) expecting any thunderstorms. Temperatures will also warm back up to above-average levels for mid-June.

Sat – Moisture begins to sneak in from the south, resulting in mainly isolated afternoon thunderstorms across southern parts of the state. The best chance of storms will be over the Sangres, while there is also some potential for the Pikes Peak Area and San Juans. Temperatures will also cool off across Northern Colorado as a cold front arrives, but this area should stay dry for one more day.

Sun – This will be a more active day with more widespread coverage of showers and thunderstorms across Southern Colorado. The San Juans, Sangres, Southern Sawatch, and Pikes Peak will be the most favored areas, with more isolated activity to the north along the I-70 corridor and into Denver/Boulder. Temperatures will also be cooler statewide. 

Here is a map of projected rain totals through the weekend from our PEAKS Model. The Southern Front Range, Pikes Peaks, and Sangres are projected to receive 0.25 to 0.50 inches of rain with isolated higher totals possible. The San Juans into Central Colorado will generally see 0.10 to 0.25 inches, but again, with isolated higher totals possible under thunderstorms. 

Mon – Moisture begins to decrease statewide with isolated afternoon thunderstorm chances mainly confined to the southern and eastern ranges from Pikes Peak to the Sangres. Temperatures will be warmer than Sunday but still relatively cool for this time of year. 

Tue – Dry conditions are expected statewide, and temperatures will also warm up significantly.

UTAH

Fri – An overall quiet day is expected with dry conditions and warm to hot temperatures statewide.

Sat – Mid-level moisture will sneak in from the south, but the lower levels of the atmosphere will remain dry, resulting in scattered dry thunderstorms across Southern Utah. The highest threat of lightning is projected from Grand Staircase-Escalante to Canyonlands. Gusty outflow winds, cloud-to-ground lightning, and limited potential for meaningful rain will pose an elevated fire risk across this region.

On Saturday night, an overnight threat of thunderstorms is expected across Southwest Utah, including Zion, Bryce, and Brian Head. These storms will also produce more wind than rain due to dry low levels.

Sun – Low-level moisture will increase somewhat, resulting in a more widespread thunderstorm threat across Southern Utah. Storms will have the potential to produce brief and localized downpours and at least some potential for canyon flash flooding, but the dry thunderstorm-fueled wildfire risk will also remain critical. 

Thunderstorm activity will favor Southwest Utah on Sunday with only some isolated activity expected around Moab. 

Mon-Tue – Moisture will retreat southward, leading to dry conditions statewide. Temperatures will also heat up as high pressure builds in from the west. 

SOUTHWEST

Fri – The onset of this "pre-monsoon" moisture will favor scattered thunderstorms across the northern and eastern ranges of New Mexico, while some isolated activity is also expected across Western Arizona as moisture from the Gulf of California sneaks in.

An increase in hazy skies is also expected across Central New Mexico due to smoke from the Bear Fire. Smoke will gradually push eastward through the day, reaching Albuquerque later in the afternoon and possibly Santa Fe by the evening.

Sat – This is shaping up to be a more active day, and we're actually picking up on a threat of morning thunderstorms around Flagstaff and the South Rim of the Grand Canyon.

By early afternoon, an uptick in thunderstorm activity is expected across the board with storms capable of frequent cloud-to-ground lightning, strong outflow winds, and locally heavy downpours.

Albuquerque could see some wildfire smoke sneak in at times, though the overall trajectory of the smoke plume will be a little further south compared to Friday. One thing to keep an eye on this weekend is how the fire will react to any thunderstorm activity in the area. 

Sun – Another active thunderstorm day is expected, with similar coverage (compared to Saturday) across Arizona, and higher coverage expected across New Mexico. Albuquerque will remain at risk for periods of wildfire smoke, though plenty of uncertainty exists in terms of how the fire behavior will change based on the weather pattern this weekend. 

Mon-Tue – A decrease in thunderstorm activity is expected as moisture starts to retreat southward. On Monday, storm chances will favor the southern half of AZ and NM (more isolated activity Flagstaff to Santa Fe and Taos), while on Tuesday, only isolated activity is expected near the AZ/Mexico border and perhaps the Southern/Eastern Mogollon Rim.

CALIFORNIA/SIERRA

The first major heatwave of the season will take hold over the next 5 days across the lower valleys, while a marine layer will keep temperatures cooler along the coast. Also, we will see some thunderstorm chances enter the picture across the Sierra.

Fri – A late afternoon and evening isolated thunderstorm threat will emerge over the Southern Sierra, including Mt. Whitney, as a little bit of subtropical moisture sneaks in.

Sat – Isolated thunderstorms are possible over the Southern Sierra again, and coverage should be a bit greater compared to Friday. The threat will also emerge earlier in the afternoon, with chances ramping up from 2pm onward. Mt. Whitney is included in this risk again, though StormNet is picking up on higher coverage near the CA/NV border.

Sun – Moisture will increase a bit, leading to an expansion in thunderstorm chances northward to Yosemite and to just south of Tahoe. Coverage also looks a bit higher compared to prior days, and stronger storms will be capable of producing localized downpours.

Mon-Tue – Moisture will gradually decrease, but we will still hang onto some isolated thunderstorm potential across the Central and Southern Sierra (mainly from Yosemite southward). 

PACIFIC NORTHWEST

Dry and sunny weather will prevail from Friday through Tuesday, and temperatures will also heat up significantly across the lower-elevation interior areas as high pressure strengthens. 

The only exceptions to this outlook are Northeast Washington and the Northern Idaho Panhandle, where scattered showers and thunderstorms can be expected on Friday afternoon. Also, a few light showers couldn't be ruled out over the BC Coast Range on Tuesday afternoon.

NORTHERN ROCKIES

Fri – A cold front arriving from the northwest will bring showers and thunderstorms to Northwest Montana and Northern Idaho during the day, and to Southern Montana and Northern Wyoming on Friday night.

StormNet is picking up on a high threat of lightning from the Idaho Panhandle to Glacier National Park by early Friday afternoon.

 

Snow levels will dip to 7,000 to 8,000 feet across Northern Montana on Friday afternoon, and to 8,000 to 9,000 feet across Southern Montana and Northern Wyoming on Friday night, with Beartooth Pass expected to pick up a few inches of snow.

Sat – Montana will begin to dry out, while rain and high-elevation snow will continue across the Absarokas and Bighorns in Wyoming. The Bighorns will see the highest precipitation totals, and this includes significant snow totals above 9,000 feet (with minor accumulations possible down to 8,000 feet).

Sun-Tue – A warming and drying trend is expected, which will lead to beautiful weather. A cold front will reach the central and eastern plains of Montana on Tuesday night with showers possible, but this activity looks to stay east of the mountains. 

BC INTERIOR & CANADIAN ROCKIES

Fri – A cold front moving through from the northwest will favor showers across Southeast BC (such as Fernie) and across the Canadian Rockies, with the highest rain totals across the Southern Canadian Rockies around Waterton Lakes. Fernie to Waterton Lakes also has a good chance of thunderstorms early on Friday afternoon.

Sat-Mon – A warming and drying trend is expected, with the only exception being some isolated shower/thunderstorm activity across Southeast BC (Nelson to Fernie) on Saturday afternoon.

Tue – A cold front will arrive from the northwest, resulting in a good chance of showers. For now, lightning potential looks limited to the foothills and plains of Alberta. 

Wednesday (June 17) to Sunday (June 21):

The high pressure ridge should weaken and retreat somewhat later next week, though models have backed off on this some since my last post when we discussed a potentially more widspread cooldown (that now looks less likely).

Instead, above-average temperatures are expected to hold from Oregon and Northern California through the Central Rockies, with near-to-below-average temperatures across the northern tier near the U.S./Canada border.

Shower/thunderstorm chances will continue to favor Western Canada and areas east of the Divide in the Northern and Central Rockies and adjacent plains as disturbances and cold fronts track through from the northwest periodically.

There are some hints of limited moisture sneaking into the Southwest around June 18-19, and perhaps interacting with better dynamics to produce a higher threat of t-storms from the Sierra into the Northern U.S. Rockies next weekend (June 19-21), though confidence in this setup is low.

June 22nd and Beyond:

From June 22nd-26th, model spread increases, indicating a relatively low confidence forecast, though I don't see anything right now that catches my attention in terms of "interesting" weather. 

For what it's worth, the ECMWF (European) Weekly Model and the ECMWF Seasonal Model have been consistently on board with the idea of a robust start to monsoon season across the Southwest and the Rockies heading into early July. 

Confidence is inherently low this far out, and it's far from a guarantee, but it's worth keeping an eye on as we get closer.

Thanks so much for reading, and have a great weekend! Next update on Monday. 

Alan Smith