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:

Another surge of monsoonal moisture will push into the Western U.S. this week, with precipitable water levels (the amount of water vapor in the atmosphere) ranging from 200 to 250 percent of normal from the Sierra to the Great Basin to the Rockies at times this week, while a shortwave slowly moving from the Southwest into the Central/Northern Rockies will trigger more widespread showers and thunderstorms at times. 

The Northwest will remain under the influence of a high-pressure ridge, leading to hot, dry, and smoky conditions with wildfires burning across the region, though shower/thunderstorm chances (spotty rainfall) will sneak into the picture at times. 

COLORADO

Mon – Thunderstorms will develop over the high country by early afternoon, with storm chances favoring areas west of the Divide. The Elks, Gores, Flat Tops, and San Juans look favored for the highest thunderstorm coverage.

East of the Divide, we could see some storms develop over the Northern Front Range foothills, but storm chances will be limited across the I-25 corridor, where hot and dry conditions will prevail.

Storm motions will be from east to west across the San Juans, while Central and Northern Colorado will see slow/erratic movement. Stronger storms west of the Divide will be capable of producing heavy rain, and flash flooding is also a possibility in vulnerable terrain. 

Tue – Thunderstorm coverage will favor areas west of the Divide again, with StormNet highlighting the greatest risk for lightning across the Park Range/Steamboat and Flat Tops, as well as the San Juans. During the daytime, storm coverage will be limited east of the Divide, though we may see some isolated activity in the Front Range foothills, Palmer Divide, and Pikes Peak. 

Storm motions will generally be ESE to WNW across Southern Colorado, S to N across Central Colorado, and SW to NE across Northern Colorado, as the high-pressure ridge over the plains begins to shift southward.

Strong storms will be capable of producing heavy rain, with localized flash flooding also possible. 

On Tuesday evening, low-level southeast winds across Eastern Colorado will lead to an uptick in moisture east of the Divide, with storm chances increasing mid to late evening across the Northern Front Range urban corridor, especially around Boulder and Ft. Collins. Locally heavy rain will be possible with any storms that form in this region.

Wed – High pressure will continue to shift further south and east of Colorado, opening up the door for a deeper surge of monsoonal moisture. A shortwave moving through will also help to trigger more numerous showers and thunderstorms both west and east of the Divide.

StormNet is currently projecting storm coverage to favor Central and Northern Colorado, both west and east of the Divide. But all areas of the state have a good chance of showers and thunderstorms, with an increased potential of heavy rain and localized flash flooding.

Thu – Another active day is expected with more numerous showers and thunderstorms possible, including a good chance of morning showers in the mountains, which could potentially disrupt "routine" summer outdoor plans when mornings typically offer the best weather window. Afternoon thunderstorm coverage is currently projected to favor Southern Colorado, but storms are possible statewide.

Fri – The pattern should quiet down a bit compared to Wednesday/Thursday with more of a routine afternoon thunderstorm setup. But storm coverage could still be fairly widespread across the higher elevations along/west of the Divide, with stronger storms capable of producing heavy rain.

Our PEAKS Model is projecting 5-day rain totals to range from 0.75 to 1.5 inches across most of the high country, except for the Sangres where rainfall will be lower due to fewer storms early in the week. The I-25 corridor is projected to receive 0.25 to 0.5 inches of rain.

Keep in mind that rainfall is often hit or miss in thunderstorm setups, so locally higher amounts are possible due to stronger thunderstorms.

UTAH

It was a tough weekend for the outdoor community in Utah, and our hearts go out to those affected by the lightning and flash flooding tragedies that occurred. 

Mon – Storms could develop over the higher elevations in Southern and Northern Utah prior to noon, with additional isolated to scattered thunderstorms expected through the afternoon. Storm motions will be from SE to NW across Southern Utah and S to N across Northern Utah, with stronger storms producing heavy rain. Slot canyons, dry washes, and burn scars will be at risk of flash flooding once again. 

Tue – Another surge of monsoonal moisture will arrive, resulting in an uptick in thunderstorm coverage throughout the state, along with an increased risk of flash flooding in vulnerable terrain across both Southern and Northern Utah. Similar to Monday, storm motions will be SE to NW across Southern utah and S to N across Northern Utah.

Wed – This will be the most active day of the week as a shortwave moves through, resulting in more widespread afternoon and evening showers and thunderstorms. An elevated threat of flash flooding will exist again for most of the state, with slot canyons, dry washes, and burn scars being the most vulnerable.

Thu-Fri – A more routine isolated to scattered afternoon thunderstorm setup will resume, with activity favoring Southern Utah more so than Northern Utah. Isolated flash flooding risk will remain a concern in canyon country.

Our PEAKS Model total rainfall forecast through Friday is projecting 0.5 to 1.5 inches across the mountains of Northern Utah, and 0.75 to 2.0 inches across the mountains of Southern Utah. But isolated higher totals are possible anywhere depending on where stronger thunderstorms develop. 

SOUTHWEST

Mon – Late morning to early afternoon thunderstorms will develop across New Mexico and Eastern Arizona, with more widespread mid to late afternoon thunderstorm coverage favoring Arizona. Rain amounts and flash flooding risk will be greatest across Arizona and Eastern New Mexico, with more scattered coverage across Northern New Mexico. Storm motions will be from east to west.

Tue – Another active day is expected with storms favoring Arizona and Northwest New Mexico, while Taos and North Central New Mexico will see more scattered coverage. Storms could produce locally heavy rain anywhere in the region, but the highest threat of flash flooding will be in Arizona. Storm motions will be from east to west. 

Wed-Fri – An active monsoon will continue throughout Arizona and New Mexico with scattered to widespread storms expected each day. Stronger storms will be capable of producing heavy rain.

Our PEAKS Model total rain forecast through Friday favors the higher terrain of Arizona and Western New Mexico with 1-3 inches of rain expected, while the remainder of New Mexico will see more scattered coverage and lighter amounts, though isolated higher totals are possible anywhere in the Southwest depending on where stronger thunderstorms develop.

SIERRA/CALIFORNIA

Mon – Monsoonal moisture is increasing across the Sierra, and this will result in a good chance of afternoon showers and thunderstorms, some of which will produce locally heavy rain. Lightning potential will be greatest across the Eastern Sierra.

Tue – This will be the most active day of the week with isolated showers possible over the Sierra in the morning, giving way to more widespread showers and thunderstorms in the afternoon with locally heavy rain possible. There is also some risk of localized flash flooding in steep/narrow terrain and small streams. 

The highest threat of lightning is expected across the High Sierra, Eastern Sierra, and east side of Tahoe.

Wed-Fri – The deepest moisture will exit to the east, but there will be enough lingering moisture for daily chances of isolated showers over the High Sierra and Eastern Sierra, along with a slight chance of thunderstorms. The Tahoe area should stay dry during this stretch.

Our PEAKS Model is projecting 5-day rain totals to range from 0.5 to 2 inches across the High Sierra and Eastern Sierra. 

PACIFIC NORTHWEST

Wildfire has exploded across the Interior Northwest in recent days. Lightning triggered many of these fires during a widespread thunderstorm outbreak last week, which was followed by hot and dry weather that supported fire growth.

Smoke will likely be an issue across the Interior Northwest throughout the week, with southwest winds aloft transporting smoke to the northeast of individual wildfires. 

Mon – Mostly dry conditions can be expected, though scattered light showers are possible along the eastern slopes of the Cascades in Southern Oregon as some monsoonal moisture sneaks in.

Tue – Mostly dry conditions are expected, but some isolated thunderstorm activity could not be ruled out over the Southern Oregon Cascades, from Bend southward.

Wed – Monsoonal moisture will increase across Oregon from the south, resulting in an uptick in thunderstorm coverage across the Oregon Cascades and Central Oregon. While stronger storms could produce locally heavy downpours, this setup will also lead to continued fire weather concerns due to lightning and gusty outflow winds.

Thu – Remnant moisture will move into Washington from the south, resulting in a chance of light showers west of the Cascades, along with isolated thunderstorms along and east of the Cascades as well as across Northeast Oregon. This looks like a dry thunderstorm setup, which will keep fire danger elevated. 

Fri – Dry conditions can be expected throughout the region, but smoke will likely remain an issue across the Inland Northwest.

NORTHERN ROCKIES

Mon – Mostly dry conditions are expected aside from some isolated to widely scattered thunderstorm activity across Southern Wyoming and Far Southern Idaho.

Wildfire smoke from Interior Northwest wildfires will also impact much of Montana and Northern/Western Idaho on Monday, and likely for much of the week ahead with consistent west to southwest flow. 

Tue – Increasing monsoonal moisture from the south will result in an uptick in thunderstorm coverage across Western and Southern Wyoming with stronger storms capable of producing heavy rain. More isolated thunderstorm coverage is expected in Southern Idaho.

Wed – This will be the most active day of the week as a shortwave arrives from the south along with increasing monsoonal moisture. As a result, more widespread showers and thunderstorms can be expected across Wyoming, Southern/Central Idaho, and Southwest Montana. Heavy rain will be possible with stronger storms, and there will even be an elevated risk of flash flooding in vulnerable terrain.

Thu-Fri – The pattern will calm down a bit with more routine isolated to scattered afternoon thunderstorms. Stronger storms will still be capable of producing heavy rain.

Our PEAKS Model rainfall forecast through Friday is projecting 0.75 to 2.0 inches of rain across the higher mountain ranges of Wyoming, and extending into the Beartooths of Southern Montana. The Central Idaho mountains and Southwest Montana mountains are looking at 0.25 to 0.75 inches. Isolated higher totals are also possible anywhere in this region where strong thunderstorms develop. 

BC INTERIOR & CANADIAN ROCKIES

Mon-Fri – A mostly dry weather pattern is expected, but isolated afternoon showers and thunderstorms are possible over the higher elevations and eastern Alberta foothills each day. 

Periods of wildfire smoke can also be expected from fires burning in the Fraser River Valley and across the Northwest U.S. The smoke will likely come in waves with periods of cleaner air in between waves, so be sure to check out our Smoke Forecast Map ("regular" instead of high-res is best for Canada), and Air Quality Forecast Maps to plan around the smoke.

Saturday (July 25) to Wednesday (July 29):

A high pressure center will set up around the Four Corners with monsoonal moisture rotating around the high, favoring Utah, Colorado, New Mexico, and Arizona for thunderstorm coverage. Limited amounts of monsoonal moisture will continue to result in periodic thunderstorm chances across the Sierra, Great Basin, Wyoming, and Greater Yellowstone region as well. 

A trough-dominant pattern will set up over British Columbia and the PNW Coast, resulting in cooler temperatures across the coastal regions. A series of Pacific disturbances will also lead to increasing rain chances across the BC Coast Range, and possibly the Northern WA Cascades and Olympics at times. 

Thanks so much for reading! Next update on Wednesday (July 22).

Alan Smith