My Favorite Summer Weather Map Layers:

• StormNet Lightning Risk
• Current Lightning Strikes and 1-Hour Risk
• Current Radar
• Forecast Radar
• Forecast Total Precipitation
• Current Air Quality
• Smoke Surface Forecast (ground level)
• Smoke Sky Forecast (average smoke ground level to upper atmosphere)
• Forecast Air Quality (low-res 3-5 day smoke outlook)

5-Day Big Picture Overview:

Temperatures will generally remain above-average west of the Divide and below-average east of the Divide, though the warm anomalies west of the Divide will be only be slight as we see some heat moderation over the weekend.

There are two large-scale weather features to track over the next 5 days.

First, a Pacific shortwave trough will move from southwest to northeast across Northern California into the Northern Rockies this weekend, resulting in a good chance of thunderstorms across this region.

Second, low-level winds will shift to easterly on the east side of the Continental Divide, which will transport abundant moisture toward the Front Range of Colorado and Eastern Wyoming, fueling a more active thunderstorm pattern.

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

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

COLORADO

Fri – Some mid-level moisture will sneak into Southern Colorado from the west/southwest, resulting in a chance of afternoon thunderstorms, primarily over the Southern San Juans and Sangres. A slight chance of thunderstorms is also expected around Pikes Peak. Northern and Central Colorado look to stay dry.

Hazy skies are also possible at times on Friday and over the weekend due to smoke from wildfires in Utah, Arizona, and New Mexico, with increased west/southwest flow aloft. 

Sat – West of the Divide, dry conditions and gusty winds can be expected with only a slight chance of thunderstorms around Steamboat and the Park Range. 

East of the Divide, low-level moisture will arrive from the east, while energy and increased upper-level winds from a shortwave trough moving across the Rockies will pass overhead. This will favor an uptick in thunderstorms, some of which could become strong to severe.

Along the I-25 urban corridor, Ft. Collins looks most favored for storms right now, with the risk increasing further east on the plains. But sometimes these threats can shift further west as we get closer, so keep an eye on our StormNet Model.

StormNet is also picking up on a large hail (1+ inch diameter) risk across Northeast Colorado, including Ft. Collins, and inching very close to the Denver metro area. The Northern Front Range foothills could potentially see some hail risk as well.

StormNet is also picking up on a tornado risk across Northeast Colorado, mainly east of the I-25 corridor for now, but not by much.

Sun – West of the Divide will stay dry and winds will not be as strong as on Saturday. East of the Divide, deeper moisture will retreat further east, resulting in more of an isolated thunderstorm threat across Denver Metro and the I-25 corridor, along with a lower (but not zero) risk of severe weather.

Mon-Tue – Areas west of the Divide will stay dry, while moisture looks to increase east of the Divide, resulting in a better chance of thunderstorms over the eastern ranges (Front Range, Sangres), I-25 corridor, and adjacent plains.

The threat of severe weather (hail, wind) will also ramp up again east of the Divide (including the foothills and metro) both days as pulses of shortwave energy continue to track across Colorado from the west/northwest. 

UTAH

Fri – As a Pacific shortwave trough approaches from the west, isolated to scattered thunderstorms will develop across Central Utah around Ritchfield. This is a dry thunderstorm setup (very little rain and strong outflow winds), which increases the concern for wildfires. 

On Friday evening, the threat of isolated thunderstorms will shift into Northern Utah and will include the SLC Metro area. This is also a dry thunderstorm threat with very little rain expected.

Another thing to watch heading into the weekend is wildfire smoke. On Friday, varying levels of smoke are expected across Southern and Central Utah from regional wildfires. On Friday night, south/southwest winds aloft are projected to transport smoke into Northern Utah and SLC as well.

Sat – Northern Utah will see an increased threat of thunderstorms as a trough moves across the Central Rockies. Lighnting couldn't be ruled out in the morning, though the highest threat will be in the afternoon. Most storms will produce only light/spotty rain and strong outflow winds as low level moisture will remain limited.

Confidence in the smoke forecast for Saturday is low, although an eventual shift to westerly winds will likely clear most of it out of the SLC area at least (barring any new major fire starts upwind).

Sun-Tue – A drying trend is expected with temperatures heating back up. On Sunday afternoon, a low risk of thunderstorms is expected around the Wasatch and SLC, while on Monday and Tuesday, a low risk is expected over the Eastern Uintas.

SOUTHWEST

Fri – Arizona will see a significant drying trend, while scattered afternoon and evening thunderstorms will develop across New Mexico, favoring the eastern mountains and adjacent plains where moisture levels will be greater.

Sat-Sun – Conditions will be dry across most of the region with low-end thunderstorm chances confined to areas east of the mountains in Northeast New Mexico. Hazy skies can be expected at times through the weekend in both AZ and NM due to regional wildfires. 

Mon-Tue – There will be a little bit of moisture return from the east, which may be enough for a slight chance of afternoon thunderstorms, mainly around Taos and the Sangres in Northern NM.

CALIFORNIA/SIERRA

Fri – As a shortwave trough an associated cold front move through, scattered thunderstorms will primarily favor Northeast California and the east side of Tahoe, with more isolated activity on the west side of Tahoe.

Moisture levels will be high enough for a mix of wet and dry thunderstorms, but the fast-moving nature of storms means that most areas will only see light rain, and this poses an elevated risk of lightning triggered wildfires.

Sat-Tue – Dry conditions will prevail as high pressure rebuilds over the West Coast. Cooler temperatures on Saturday will give way to a significant warm-up Sunday-Tuesday.

PACIFIC NORTHWEST

Dry conditions will prevail overall with temperatures cooling off briefly on Saturday before warming up signfiicantly from Sunday to Tuesday.

The only exception to the quiet pattern will be some isolated thunderstorm activity across southern and southeast Oregon on Friday-Saturday, mainly south of Bend and east of the Cascades. 

NORTHERN ROCKIES

Fri – Dry conditions will prevail during the day, but we could see some isolated thunderstorms develop across Southern Idaho late Friday night, mainly across the Snake River Plain and points southward, as a Pacific shortwave trough approaches from the southwest.

Sat – A substantial uptick in thunderstorm chances is expected as the shortwave moves across the region, with thunderstorms favoring Eastern Idaho, the Tetons and Yellowstone in Western Wyoming, and areas east of the Divide in Central and Eastern Wyoming.

Scattered thunderstorms will also develop across the southern mountains of Montana, while isolated storms are possible as far west as the Sawtooths and Salmon Rivers in Idaho, and as far north as Glacier Park in Montana.

The highest threat of lightning will be during the afternoon and evening hours, but there is at least some threat for morning lightning as well.

Some thunderstorms in these areas could also be on the stronger side, with localized areas of large hail and damaging wind gusts possible.

Our StormNet Model is also picking up on a risk of large hail (1+ in diameter) across Southeast Idaho, while the threat of damaging wind gusts (58+ mph) covers the same area but also extends into Western Wyoming. A more significant threat for severe thunderstorms and large hails is anticipated across Eastern Wyoming.

Storms across Central/Eastern Idaho, Wyoming, and Southern Montana will generally produce rain amounts of 0.1 to 0.5 inches, with isolated higher amounts possible.

Sun – On the backside of the trough, thunderstorm activity will favor areas along and east of the Divide in Montana and Wyoming, with isolated activity west of the Divide. Overall, storms should be less intense compared to Saturday, though some isolated large hail couldn't be ruled out east of the Divide in Montana.

Mon-Tue – Thunderstorm chances will be confined to areas east of the Divide in Montana and Wyoming with dry conditions west of the Divide. Areas east of the Divide in Wyoming will see a risk of severe thunderstorms (large hail, damaging winds) on Monday and possibly Tuesday as low level moisture increases from the east.

BC INTERIOR & CANADIAN ROCKIES

Fri – Mostly dry conditions are expected other than some isolated showers along the foothills and adjacent plains in Alberta.

Sat – The weekend storm system has trended further north since my last post. Jasper will still pick up 0.5-0.75 inches of rain, while showers will be more intermittent further south with areas along the Hwy 1 corridor from Revelstoke to Golden to Banff with rain totals ranging from 0.05 to 0.25 inches.

Lightning potential will largely be confined to areas east of the mountains in Alberta, with only some isolated activity in the mountains of Eastern BC and Western Alberta.

A cold front will move through from the north during the day on Saturday, bringing a noticeable cooldown to all areas.

Sun – A chilly airmass will remain in place with scattered showers developing. Southern areas such as Fernie and Waterton Lakes will see a better chance of showers compared to Saturday, and an increased risk of lightning is also expected in the afternoon. More isolated activity is possible further west toward Nelson.

Mon-Tue – A drier pattern is expected overall with just some isolated afternoon shower and thunderstorm activity in most areas. However, the Okanagan region could potentially see an uptick in storm chances on Tuesday afternoon as a shortwave trough approaches. 

Wednesday (June 24) to Sunday (June 28):

The pattern is trending more unsettled for the second half of next week.

Initially, from June 24-26 (approximately), a weak push of monsoonal moisture into the Southwest will bring an increased threat of thunderstorms to the Four Corners region (west of the Divide), while low-level easterly flow will keep elevated moisture levels and thunderstorm chances going east of the Divide in CO/WY. 

However, late next week (June 26-28), models are catching onto the idea of a deeper trough moving into the Pacific Northwest and Northern Rockies, potentially bringing cooler temperatures and appreciable rain chances following a hot stretch during the middle of the week.

If it verifies (remember, we're still 6-10 days out), this trough would likely bring another period of strong winds to much of the West, continuing the theme of what has been a windy month of June thanks to a stronger and more persistent jet stream than what we typically see at this time of year.

Thanks so much for reading, and have a great weekend!

The next update on Monday will be written by my colleague, Zach Butler, while I'm out of town.

Alan Smith