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:

Most of the West will see a dry pattern this week with a ridge of high pressure in place over the West Coast, while a trough will be centered further east near the Great Lakes. There are a couple of exceptions, however, such as lingering subtropical moisture over the Southwest.

This large-scale setup will favor hot temperatures across the far western states, while areas east of the Continental Divide will see fluctuating temperatures with an early-week warm-up and a late-week cool-down.

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

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

COLORADO

Mon – Moisture is retreating southward, which will lead to an overall decrease in thunderstorm activity. Storms will still develop early afternoon over the Southern San Juans and Southern Sangres, while only some isolated activity is expected from the Northern Sangres into the Southern Front Range Mtns. There is a minimal threat of lightning north of I-70.

Tue-Thu – Thunderstorms are not expected as conditions dry out statewide. Temperatures will heat up substantially on Tue-Wed, with low elevations getting well into the 90s. A cold front will bring some relief on Thu.

Winds will also be strong above treeline throughout the week, with a strong jet stream (by June standards) setting up just north of CO. Peak winds are expected on Wed just ahead of the cold front.

Fri – Flow will shift from NW to W/SW, which will bring a little bit of subtropical moisture back into Colorado. This will lead to a chance of afternoon thunderstorms, which, for now, looks to favor areas south of I-70.

UTAH

Mon-Thu – Hot and dry conditions will prevail overall. Isolated thunderstorms couldn't entirely be ruled out across Southern Utah on Monday afternoon, but our StormNet Model is projecting lower than 10% probabilities. 

Fri – A shortwave trough will approach from the west, resulting in a chance of afternoon or evening thunderstorms across Northern Utah. For now, this looks like a mainly dry thunderstorm setup initially with strong outflow winds. There is somewhat better potential for measurable rain with showers/storms on Saturday, but confidence is low.

SOUTHWEST

Mon – An early-season monsoon-like pattern remains in place with abundant subtropical moisture for this time of year. 

A few thunderstorms are already developing across Southern Arizona on Monday morning. Heading into Monday afternoon, more widespread coverage is expected mainly along and south of I-40, with Phoenix possibly even getting in on the action.

This looks to be a mixed wet/dry thunderstorm setup (some storms produce local downpours, others more wind than rain). Our StormNet Model is actually picking up on a small risk of damaging wind gusts with thunderstorms around Phoenix on Monday afternoon, and thus a risk for dust storms as well.

Across New Mexico, isolated to scattered afternoon storms can be expected across all major mountain ranges, with locally heavy downpours possible.

Tue – Moisture will retreat southward, with thunderstorm activity favoring Southeast Arizona and, to a lesser extent, the Prescott area and the Western Mogollon Rim. Most storms will produce light/spotty rain, but isolated downpours are possible under stronger storms. 

New Mexico looks to dry out entirely with little to no thunderstorm activity except along the southern and southwestern borders.

Wed – A somewhat similar setup is expected with thunderstorm activity favoring Southeast Arizona and Southwest New Mexico. Most storms will produce light/spotty rain, but isolated downpours are possible under stronger storms. 

Thu-Fri – Moisture will gradually shift eastward with thunderstorm chances favoring New Mexico, while Arizona should dry out completely by Friday. Storms on Friday will have a better chance of producing meaningful rain in NM as low-level moisture increases. 

CALIFORNIA/SIERRA

Mon – Lingering subtropical moisture will result in isolated afternoon thunderstorms across the Sierra again, with the main threat expected north of Mt. Whitney but including Yosemite and the Mammoth Lakes area.

Tue – Thunderstorm potential will decrease across the Sierra with just a slight (<10% chance) of thunderstorms. However, thunderstorm activity will increase a bit across SoCal, mainly in the foothills and deserts east of LA and San Diego. These will be dry thunderstorms with gusty outflow winds and little to no rain.

Wed – A subtle shortwave will approach the Sierra from the east/southeast, resulting in a better chance of afternoon/evening thunderstorms. Activity looks to favor the Yosemite and Mammoth areas per the latest StormNet projections, but the threat extends from roughly Mt. Whitney to the south shore of Tahoe.

Low-level moisture will be lacking, so these will mainly be dry thunderstorms with gusty winds and only light/spotty rain.

Thu-Fri – A stronger Pacific shortwave trough will approach from the southwest, bringing a chance of more widespread showers and thunderstorms to the Sierra and NorCal, along with a better chance of meaningful rains.

The Central and Southern Sierra will be favored initially on Thu, then on Fri, activity looks to favor the Northern Sierra, including Tahoe, as well as Shasta, Trinity Alps, and points eastward toward the NV border. 

A cold front will also accompany this system and will move through on Friday, bringing some relief after a hot week.

PACIFIC NORTHWEST

Mon – Hot and dry conditions will prevail with a ridge of high pressure in place along the West Coast, though some thin/high cloud cover is expected.

Also, several large wildfires ignited across South Central Washington over the weekend, and smoke from these fires has settled into the Columbia River Gorge and Portland on Monday morning, leading to poor air quality.

 

Low-level smoke is projected to gradually disperse later in the day around Portland, but areas close to the fires, such as Yakima and Pasco, will likely see smoke issues throughout the day.

Tue – A cold front will move through, bringing much cooler air and gusty winds. Scattered light showers will also develop during the day across the WA Cascades and Olympic Peninsula, as well as the North Shore Mtns around Vancouver, BC. However, this is not expected to be a major event, with most areas receiving a trace to a tenth of an inch. The Puget Sound Lowlands will see little to no rain.

Strong wet/northwest winds aloft will push any lingering smoke out of Portland and the Columbia River Gorge, while smoke transport downwind of these fires will likely produce periods of hazy skies and/or reduced air quality across Southeast WA and Northeast OR.

Wed-Fri – Conditions will dry out again with occasional high-level cloud cover favoring Oregon. Temperatures will be cooler and more refreshing on Wednesday before gradually warming up on Thursday and Friday.

There is a chance of afternoon or evening showers and thunderstorms across Southeast Oregon on Friday as a shortwave approaches from the southwest.

NORTHERN ROCKIES

Mon – Shaping up to be a beautiful day with warm and dry conditions.

Tue – Warm, dry, and windy conditions will prevail ahead of an approaching shortwave from the northwest.  With the increased WNW winds, NOAA's high-res smoke model is also projecting some smoke to reach Southern/Central Idaho and Southwest Montana from wildfires in Washington.

On Tuesday night, scattered showers will develop mainly near and east of the Divide in Glacier National Park and Northern Montana (i.e. Logan Pass eastward).

Wed – Scattered showers and thunderstorms can be expected near and east of the Divide in Montana, with the best chance in the afternoon. The east side of Glacier NP looks to be the most favored.

Temperatures will also cool off a bit in most areas as a cold front slides through, even in areas west of the Divide that miss out on the shower activity. Winds will also remain gusty on Wednesday.

Thu-Fri – Warmer and drier conditions will prevail during the daytime hours. Then on Friday night, a shortwave will approach from the southwest and will lead to a chance of overnight showers and thunderstorms from Southern Idaho to Western Wyoming and Southwest Montana. This overnight activity currently looks to favor Southwest Idaho, including Boise.

BC INTERIOR & CANADIAN ROCKIES

Mon – Mostly dry conditions are expected, but cloud cover will be on the increase, with isolated light showers possible, mainly near the Trans-Canada Highway corridor from Revelstoke to Golden to Banff.

Tue – More numerous showers and perhaps a few thunderstorms can be expected as a cold front moves through. Shower activity will favor the central/northern BC Interior Mountains (Revy, Golden, etc.) as well as the Canadian Rockies and adjacent plains in Alberta, with drier conditions in the BC Kootenay Boundary region.

Wed – Afternoon showers and thunderstorms will favor the Canadian Rockies and areas along and east of the Divide (BC/AB border). BC will see a drying trend with just some isolated light shower activity at most.

Thu-Fri – A similar setup is expected with afternoon shower/thunderstorm chances favoring areas east of the BC/Alberta Divide, though coverage and rain amounts will be less compared to Tue-Wed. 

A cold front will approach from the northwest on Friday night and it's possible we could see heavier and more widespread rain develop overnight, though confidence in the timing is low with some models holding off the action until Saturday.

Saturday (June 20) to Wednesday (June 24):

A more active weekend is expected for some parts of the West, while the general temperature pattern will continue to favor above-average temps west of the Continental Divide and below-average temps east of the Divide.

In terms of active weather, a shortwave trough will move from the Great Basin into the Northern Rockies over the weekend, bringing a good chance of showers and thunderstorms to Idaho, Western Wyoming, Southwest Montana, and, to a lesser extent, Northern Utah.

This shortwave will come into phase with a larger trough deepening over Western Canada, which will bring more widespread showers and thunderstorms to BC and Alberta, along with the potential for heavier rain, especially inland. The North Cascades and northern most potions of WA, ID, and MT will likely see some of this action as well, though it's a closer call.

Next week, low-level easterly flow is projected to increase across Eastern Colorado, which should bring enough moisture for the Front Range to get back into a routine afternoon thunderstorm pattern, while areas west of the Divide will be drier.

Thanks so much for reading! Next update on Wednesday.

Alan Smith