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:

On Wednesday and Thursday, a ridge of high pressure will remain over the West Coast with a trough over Central North America. This will lead to above-average temperatures across the Far West (especially California) and cooler temperatures east of the Continental Divide.

On Friday PM and Saturday, the pattern turns a bit more active for some areas as a shortwave trough will undercut the West Coast Ridge and will track from Northern California into the Northern Rockies. To the north, a trough will also move through BC, Alberta, and Northern Montana, and this will include a shot of cooler air.

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

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

COLORADO

Wed-Thu – A warm, dry and brisk northwest flow pattern will be in place. Wednesday will feature the strongest winds ahead of an approaching cold front, which will bring some heat relief on Thursday, especially east of the Divide.

Fri – Flow aloft will shift from NW to W, and this will bring in enough mid-level moisture to result in isolated to scattered thunderstorms. The best chance of lightning will be across the Sangres north to Pikes Peak, with more isolated activity expected across the San Juans, Central Colorado, and Front Range.

Low-level moisture will be lacking, so this will primarily be a dry thunderstorm setup with storms producing only light/spotty rain and gusty outflow winds.

Along the I-25 corridor, easterly low-level winds will lead to a gradual increase in moisture, and depending on how quickly this moisture arrives, there is an outside chance of strong to severe thunderstorms. 

Our StormNet Model is picking up on a slight risk of large hail (1+ diameter), mainly along and south of the Palmer Divide from Castle Rock to Colorado Springs to Pueblo.

One other wild card to keep an eye on with the shift from NW to W flow is the potential for wildfire smoke transport from new wildfires in Northern Arizona and Southern Utah. This is highly conditional depending on how these fires behave (and if new fires start) in the coming days, but it's something to keep an eye on, especially across Southwest Colorado. 

Sat-Sun – Big differences in the weather pattern west vs. east of the Divide this weekend. West of the Divide, mainly dry and breezy conditions are expected, though some isolated thunderstorm activity is possible near and north of I-70 as shortwave energy moves through.

East of the Divide, low-level moisture will continue to increase from the east, while shortwave energy aloft moves through via upper-level W/SW winds. This will favor a higher threat of thunderstorms, including the potential for strong to severe thunderstorms. The threat of large hail will be greatest out on the plains, but it couldn't be ruled out in the Front Range cities and suburbs either. 

UTAH

Wed-Thu – Hot and dry conditions will prevail statewide with gusty winds on Wednesday giving way to lighter winds and slightly cooler temperatures (at least for Northern Utah) on Thursday.

Wildfires have developed across Southern Utah and Northern Arizona, so this could result in smoky/hazy conditions at times in Southwest Utah depending on fire behavior over the next couple of days.

Fri – Conditions will likely stay dry during the day, and a big warm-up is also expected. On Friday evening, a shortwave trough will move into Northern Utah from the southwest, resulting in scattered evening to overnight thunderstorms. The best chance of storms will be north of SLC, and also east of SLC in the Wasatch and Uintas.

Low-level moisture will be lacking, so this will be a dry thunderstorm setup with storms producing only light/spotty rain and strong outflow wind gusts. In fact, our StormNet Model is picking up on the potential for localized severe wind gusts with thunderstorms in excess of 58 mph.

Sat – Lingering instability on Saturday will result in another chance of afternoon thunderstorms across Northern Utah, including the Wasatch, Uintas, Bear Rivers, and SLC Metro. Low-level moisture will be slightly higher than Friday night, but still limited, resulting in mainly dry thunderstorms with locally very strong outflow winds possible. 

Sun – Conditions will stabilize with little thunderstorm threat for most of the state, except perhaps around the Eastern Uintas and Vernal.

SOUTHWEST

Wed – Thunderstorm activity will favor mainly central and eastern portions of Arizona and southwest portions of New Mexico, where moisture levels remain above average for this time of year. Much drier air will hold over the remainder of New Mexico. 

Wildfire activity has also increased across Southern California, Northern Arizona, Southern Utah, and Western New Mexico, which could lead to hazy skies and areas of reduced air quality at times.

Northern Arizona looks to be the most vulnerable to smoke, but keep in mind this outlook will likely evolve based on fire behavior in the coming days, so I would recommend checking our smoke and air quality maps frequently for updates.

Thu – We start to see a gradual decrease in moisture in Arizona with a gradual uptick in moisture across New Mexico. As a result, thunderstorm chances will increase throughout NM with mainly isolated to scattered coverage.

Fri – Arizona looks to be storm-free on Friday as areas west of the Divide continue to dry out. However, the eastern ranges and adjacent plains of New Mexico will likely see an uptick in thunderstorm coverage as low-level moisture increases from the east.

Storm coverage looks to favor the Sangres, including the potential for stronger storms (1"+ hail threat being noted by our model just east of the Sangres).

Sat-Sun – A dry and thunderstorm-free weekend is expected for most of the region, save for some isolated thunderstorm chances on the northeast plains of New Mexico. 

CALIFORNIA/SIERRA

Wed – Easterly flow aloft associated with a weak area of low pressure over SoCal will generate enough instability over the Sierra for isolated to scattered mid to late-afternoon thunderstorms. Activity will primarily favor the Eastern Sierra. 

Skies may also be hazy at times as some wildfire smoke tries to sneak into the Sierra from SoCal and Arizona/Utah thanks to southerly and easterly winds aloft. 

Thu – Flow aloft turns S/SE ahead of an approaching Pacific shortwave trough, and this will lead to a better chance of thunderstorms throughout the Sierra in the afternoon, including Tahoe. Most storms will produce spotty rain and gusty winds initially in the afternoon.

The SSE winds aloft could potentially transport some wildfire smoke into the Sierra, though confidence is low and will partially be a function of fire behavior over the next couple of days.

Thu Night – An overnight threat of thunderstorms is expected across NorCal as the shortwave approaches, with the best chance of storms expected from Tahoe northward to Lassen National Forest. Rain totals overnight are projected to be light and spotty in most areas, but localized downpours are possible as low-level moisture increases. 

Fri – Scattered showers and thunderstorms will favor NorCal and Nevada as a cold front moves through, and gusty winds can also be expected. The highest threat of lightning will be from roughly the east side of Tahoe into Northern Nevada and Northeast Cal, though storms are also possible further west toward Redding and Eureka.

Most areas will pick up around a trace to a quarter inch of rain, though isolated higher amounts couldn't be ruled out under stronger storms.

Sat-Sun – Conditions will dry out with temperatures remaining cooler compared to the past week, though lower elevations will start to heat up again on Sunday.

PACIFIC NORTHWEST

Wed-Thu – The pattern will stay quiet overall with cooler temperatures compared to earlier this week, though interior areas will start to head up again on Thursday. There are some wildfires burning around the PNW, but smoke transport has settled down compared to a couple of days ago. Most areas should be ok in terms of air quality in the near-term.

Fri-Sun – Washington, Southwest BC, and Northern Oregon will stay dry, but a shortwave will bring showers and thunderstorms to Southern Oregon on Friday night and Saturday. A slight chance will extend about as far north as Bend.

NORTHERN ROCKIES

Wed-Thu – Isolated to scattered showers (and a slight chance of thunderstorms) can be expected mainly east of the Divide in Montana and into the Bighorns of Northern Wyoming. West of the Divide, warm, dry, and breezy conditions will prevail. 

Fri-Sat – Most areas will be dry during the day on Friday. However, a shortwave trough will approach from the southwest on Friday night, with overnight thunderstorms possible across Southern Idaho and Southwest Wyoming.

During the day on Saturday, more numerous showers and thunderstorms are expected, with favored areas for lightning including the Tetons, Yellowstone, Northern Winds, and Bighorns.

Showers/storms will produce meaningful rain across the Tetons and Yellowstone, where rain totals will generally range from a quarter to a half-inch. The Madison, Gallatin, Beartooth, and Bighorn Ranges could see a half to three-quarters of an inch, with isolated higher amounts possible.

Sun – A drying trend is expected aside from some lingering light showers east of the Divide.

BC INTERIOR & CANADIAN ROCKIES

Wed-Thu – Scattered showers and isolated thunderstorms can be expected mainly along and east of the Divide on the Alberta side, with drier conditions in BC. Rain amounts of a quarter inch (7+ mm) or more are possible around Jasper and in the foothills east of Canmore, with lighter amounts around Banff.

Fri – A break in the pattern is expected with dry conditions for most of the region.

Sat-Sun – A low pressure trough will slide in from the northwest along with a cold front, bringing widespread rain showers. The Alberta Rockies just north of Lake Louise are currently projected to see the heaviest rain (an inch or more possible) with lighter totals for the Southern Alberta Rockies and BC Interior.

Still, a cool and wet weekend should be expected, at least to some extent. Light snow is also possible above 8,000 feet at Banff Sunshine, which is reopening for summer skiing this weekend.

Monday (June 22) to Friday (June 26):

Next week, the pattern will feature above-average temperatures west of the Divide and below-average temperatures east of the Divide. This is in response to a ridge-dominant pattern along the West Coast, while a trough-dominant pattern will be centered over the Great Lakes.

Low-level easterly winds associated with post-frontal airmasses east of the Divide will favor moisture transport and shower/thunderstorm chances along the eastern slopes and adjacent plains of the Rockies. This includes the CO Front Range and Denver Metro, which could be looking at an active thunderstorm pattern.

A subtropical high pressure ridge will also build over the Southwest, with a weak early-season push of monsoon moisture expected into the Southwest around mid-week, which should lead to an uptick in thunderstorm chances. 

Thanks so much for reading! Next update on Friday.

Alan Smith