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:

An unusually strong (for late June) trough of low pressure will impact the West this weekend, bringing chilly temperatures and significant precipitation to the Pacific Northwest and Northern Rockies.

On the southern side of this system, dry and windy conditions will develop across Utah, Colorado, and the Southwest, leading to a spike in fire danger through the weekend and into early next week.

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

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

COLORADO

Fri – One more day of active weather as monsoonal moisture remains in place. Thunderstorms will first develop over the San Juans, possibly before noon, with more widespread coverage of thunderstorms expected across all mountain ranges by early afternoon.

Storms will be fast-movers from WSW to ENE but will be capable of producing heavy downpours. 

As storms drift off the Front Range foothills into the I-25 corridor and adjacent plains, there is some potential for severe weather to occur, including 1+ inch diameter hail and 58+ mph wind gusts. StormNet is projecting 10-15% probabilities of 1-inch diameter hail in this area, so the threat looks to be fairly isolated.

Wildfire behavior in Utah has quieted down somewhat with the uptick in moisture, and as a result, smoke transport into Colorado is projected to be less compared to recent days.

Sat-Mon – A dry and windy pattern will take hold as a powerful low pressure trough tracks across the Northern Rockies. Colorado will be on the drier side of this trough, and the increased westerly flow will scour out the monsoonal moisture.

The downside is that the strong winds and decreased relative humidity will lead to a spike in fire danger on all three days. 

Also, there is a chance that the dry/windy pattern could exacerbate fire activity across Utah again. If this happens, then smoke could potentially return to Colorado, with SW flow likely "favoring" areas west of the Divide for more smoke than east of the Divide, but confidence is low. 

A significant warm-up is also expected east of the Continental Divide due to downslope winds (these have a warming & drying effect) with temperatures soaring into the mid/upper 90s on the plains, while areas west of the Divide will see more modest warming Sat-Sun followed by cooler temperatures on Mon.

The only threat of lightning during this stretch will be near the Wyoming border, with isolated activity at most.

Tue – Winds will calm down somewhat compared to prior days, though the afternoon still looks breezy, and fire danger will remain elevated. 

A weak backdoor cold front is projected to sneak into Northeast Colorado, leading to an increase in moisture and thunderstorm chances east of the Divide. Areas west of the Divide will likely stay dry. 

UTAH

Fri – Dry air begins to push into Utah from the west, and winds will also increase in response to a Pacific low pressure trough moving into the Northwest.

Fire behavior and smoke transport have settled down some compared to earlier this week. However, there is growing concern that fire activity could ramp back up this weekend as an increasingly dry and windy pattern takes hold, and there will also be an elevated risk of new fires.

Thunderstorm chances on Friday will be confined to the southeast corner of the state, where there will be some lingering moisture, while the rest of the state will see a drying trend.

Sat-Sun – A strong cold front will push into Northern Utah, leading to a significant cooldown across SLC and the Wasatch. Northern Utah will be right on the southern edge of the moisture with this system, with scattered showers and thunderstorms expected both days.

SLC and most of the lower elevations in Northern Utah will pick up a tenth to a quarter inch of rain over the weekend, but the higher humidity airmass will help with fire danger. Higher terrain in the Northern Wasatch and Bear River Ranges will see rain amounts of a quarter to a half-inch.

Southern and Central Utah will be a different story this weekend, as the cold front will only cool things off slightly (it will still be hot). Strong winds and low relative humidity will lead to a significant increase in fire danger.

Winds will be strong throughout Southern Utah on Saturday, while on Sunday, the strongest winds will be confined to Southeast Utah, while Southwest Utah will see a slight decrease in winds (it will still be windy, just not as strong compared to Saturday).

Mon-Tue – Temperatures will remain cooler than average across Northern Utah. Light showers are possible on Monday morning, then we should see a drying trend before a chance of isolated afternoon thunderstorms returns on Tuesday. 

Across Southern Utah, dry weather will persist with lighter winds compared to prior days, but fire danger will still remain elevated even if conditions are "less extreme" compared to Sat-Sun.

SOUTHWEST

Fri – Monsoonal moisture will shift eastward with drier conditions and reduced thunderstorm activity across Arizona, while an active day with more widespread thunderstorms can be expected across New Mexico. Storms in New Mexico will be capable of producing locally heavy rain.

Sat-Sun – A significant drying trend will occur as a trough pushes into the Rockies, scouring out monsoonal moisture across the Southwest. Strong winds will also develop over the weekend with low relative humidity, which will lead to an increase in fire danger.

Mon-Tue – Arizona will remain dry, while some monsoonal moisture will sneak back into Southern and Eastern New Mexico, resulting in a chance of thunderstorms. Gusty winds can be expected both afternoons, but it will not be as windy compared to prior days.

CALIFORNIA/SIERRA

Fri – A strong cold front will move through, resulting in windy and chilly conditions across the Sierra and higher terrain of NorCal. Scattered light rain showers will also develop from Tahoe northward, but the lightning threat is minimal.

Sat – Another chilly and windy day is expected with scattered light showers possible. Two-day rain totals will range from a trace to a tenth of an inch around Tahoe, while higher elevation areas north of Tahoe and areas along the northwest coast could see a tenth to a quarter inch (and some areas of NE Cal more than a quarter inch).

Sun – Winds will still be breezy but lighter compared to prior days, and temperatures will remain well below average for the end of June.

Mon-Tue – A gradual warming trend will ensue with moderate winds. Temperatures will remain below average in the Sierra and in Tahoe, but it will be warmer compared to prior days.

PACIFIC NORTHWEST

Fri – Widespread rain showers will develop across the Cascades, West Coast, and Western Lowlands as a Pacific trough arrives, with the Northern Cascades and BC Coast Range favored for the heaviest rain. The Inland Northwest will also see moderate to heavy rain showers, along with a chance of PM thunderstorms.

Sat – Rain showers will continue with the focus of heavier rainfall shifting to the Oregon Cascades. The Inland Northwest will see more variable rain showers, but with locally heavy rain possible. 

Sun – Showers will be more terrain-driven, favoring the Cascades and eastern ranges of WA/OR, while the western lowlands will see a drying trend but with continued low clouds and cool temperatures.

Mon-Tue – A secondary trough will arrive, which will keep rain showers going over the Cascades, BC Coast Range, and Inland NW ranges, while temperatures will also remain chilly. Afternoon thunderstorms are also possible across the Inland NW.

Total rainfall through Tuesday will range from 1-2 inches across the Cascades, Olympics, BC Coast Range, and eastern ranges of Washington & Oregon.

NORTHERN ROCKIES

Fri – As a powerful Pacific trough approaches, widespread rain showers and isolated thunderstorms will develop across Western and Central Idaho, while Eastern Idaho, Montana, and Wyoming will see more isolated to scattered showers and thunderstorms. 

Sat-Sun – The trough will continue to track inland with more widespread showers developing throughout Idaho, Western Montana, and Western Wyoming, with significant amounts expected. Colder air will also arrive with snow levels dropping to 8,000 to 9,000 feet. The best chance of thunderstorms will be across Eastern Idaho and Western Wyoming. 

Mon-Tue – The main trough will begin to lift north and east out of the Northern Rockies, while a secondary trough will arrive, keeping shower chances going both days, while temperatures will also remain chilly. Northern Idaho and Western Montana will be favored for the most widespread and heaviest showers.

Total precipitation through Tuesday will range from 1-3 inches across Northern/Central Idaho, much of Montana, and Northwest Wyoming. Areas above 9,000 feet will also pick up a few inches or more of snow.

BC INTERIOR & CANADIAN ROCKIES

Fri – A cold front will move through with widespread rain showers developing across Interior BC, while the Canadian Rockies will see only light and isolated showers, though an uptick in cloud cover is expected. Thunderstorm chances will primarily be limited to the Okanagan region.

Sat – Scattered showers will continue and look to be more evenly distributed across Interior BC and Alberta, and there is also a slightly better chance of lightning compared to Friday.

Sun-Mon – A secondary cold front will slide into the Canadian Rockies from the north, resulting in heavy rain across the Alberta Rockies, including Banff-Jasper, and across eastern portions of BC, though the entire region looks wet. Flooding concerns could arise in this pattern, especially on the Alberta side of the Divide.

Tue – Rain showers will continue as a secondary disturbance arrives. All regions have a good chance of showers and will see continued wet conditions, but the BC side looks favored for heavier rainfall than the AB side on Tuesday, at least for now.

Total rainfall through Tuesday will be substantial, ranging from 1 to 2+ inches across Interior BC and 1.5 to 3+ inches across Alberta. 

Wednesday (July 1) to Sunday (July 5):

Heading into the Fourth of July holiday period, a trough-dominant pattern looks to remain over the West Coast, leading to continued below-average temperatures from California to the PNW. Additional periods of showers are also possible from the PNW into the Northern Rockies, including a chance of thunderstorms across the Northern Rockies. 

Further south, a weak monsoon will attempt to re-emerge across New Mexico and possibly into Colorado, which could result in thunderstorm chances, though this setup would favor only light rain.

In between these features, dry conditions and gusty winds may continue to be an issue across Utah, unfortunately. 

Beyond the holiday weekend, longer-range models continue to hint at a possible uptick in monsoonal moisture across the Southwest, along with additional "troughiness" across the PNW with at least some occasional shower chances. 

Thanks so much for reading, and have a great weekend! Next week, I'll post updates on Monday and Thursday, and will take Friday off for the holiday.

Alan Smith