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Friday Afternoon Conditions:

Moisture from the remnants of a tropical storm, combined with abundant upper-level energy in the atmosphere, has contributed to frequent thunderstorms and even some flash flooding in canyon regions this week.

Our Lightning Risk Map has been very active this afternoon. The color shades in this map correspond to lightning risk over the next 60 minutes, and the dots represent recent cloud-to-ground lightning strikes. You can also use your current location or click anywhere inside the map to see distance rings from a point. 

Saturday (June 7) to Monday (June 9):

A strong ridge of high pressure will work its way into Western North America this weekend with the ridge becoming centered over the Pacific Northwest. The trough that has been located over the Eastern Rockies this weekend will slowly work its way eastward into the Central U.S.

A more subtle upper-level low-pressure area off the California Coast will also work its way into the Southwest early next week. 

The dome of high pressure will support well above normal temperatures from the Pacific Northwest to California and Nevada this weekend, and heat advisories have already been issued by the National Weather Service in some lower elevation areas. Welcome to summer!

Temperatures will also warm up across the Rockies to near seasonal levels for early June, which will be a change from the below-normal temperatures experienced in recent days.

In terms of thunderstorms and rainfall, coverage will decrease across the Southwest, Sierra, and Southern/Eastern Rockies compared to earlier this week as the high-pressure ridge pushes in, but lingering moisture and instability will still result in pesky afternoon storms.

Saturday – Lingering moisture and some weak wind convergence, along with terrain-enhanced lift, will support afternoon thunderstorms from the Sierra to the Southern Rockies. Storms will produce lighter rainfall compared to recent days, but some brief downpours are still possible.

A cold front will move through Eastern Montana and Wyoming late in the day, with moisture behind the front contributing to scattered thunderstorms during the evening hours, along and east of the Continental Divide. The Bighorns and the Black Hills will be the most favored areas in this pattern, with locally heavy downpours possible.

Sunday – Lingering moisture from the Sierra into the Southern Rockies (west of the Continental Divide) will once again contribute to isolated terrain-driven afternoon thunderstorms, with most storms producing light to moderate rain.

A cold front will slide from north to south down the east side of the Continental Divide, pushing into New Mexico. Behind the front, an increase in moisture combined with easterly upslope winds will contribute to scattered afternoon and evening thunderstorms near and east of the Divide.

Some storms in Colorado could be on the stronger side, with moderate to large hail possible along with heavy downpours.

Monday – The cold front will push southward, stalling near the Mexico border, with moisture behind the front supporting a more active day of thunderstorms across New Mexico and Southern and Central Colorado. Storms may initiate around or prior to noon over the higher peaks in this region. Moderate to heavy rainfall is also expected with thunderstorms.

To the west, a subtle area of low pressure will track across the Southwest, contributing to a relative uptick in thunderstorm coverage across the Southwest, Sierra, Great Basin, and Oregon Cascades. Most storms will produce light to moderate rain with brief downpours possible. 

The map below shows projected 3-day rainfall totals from Saturday through Monday from the European weather model. 

Tuesday (June 10) to Saturday (June 14):

Starting on Tuesday, a trough-dominant pattern will begin to take hold over the Pacific Northwest with a series of low-pressure troughs moving through.

These troughs are not expected to bring a great deal of moisture to the West Coast of the U.S. from the Central and Northern Pacific, as these moisture sources are starting to get cut off heading into the summer, and cool Pacific Ocean temperatures limit instability near the Cascades.

However, moisture and instability further inland combined with upper-level energy associated with the trough will contribute to an uptick in convective showers and thunderstorms east of the Cascades. 

Temperatures are still expected to be above normal throughout the West, and in fact, the Continental Divide region and areas east of the Divide will see further warming compared to prior days.

Thunderstorm coverage and rainfall amounts will favor the Northern Rockies in this pattern, with the heaviest amounts expected east of the Divide as these areas will have access to richer low-level moisture from the plains.

The North Cascades will see some lighter showers in this pattern, while the Colorado Rockies will see enough moisture and energy for thunderstorms on some days as well.

The map below shows projected rainfall for June 10-14 from the European Ensemble Model, which represents the average of 50 simulations of this model. 

June 14-20:

Heading into the middle of the month, a trough-dominant pattern is expected to become reinforced over the Pacific Northwest with higher rainfall potential across the Cascades and across the far northern Rockies.

Thunderstorm potential will also be greater over the Interior Northwest and Northern Rockies, where warmer temperatures and abundant moisture will support an unstable atmosphere on many days.

NOAA's 8-14 day outlook favors below normal temperatures near the West Coast and above normal temperatures throughout the Interior West, with lower terrain across the Rockies and adjacent plains potentially seeing their first real taste of summer heat.

June 21 to July 4:

NOAA also publishes a 3-4 week outlook every Friday.

Today's outlook has a high likelihood of above-normal temperatures throughout the West from June 21 to July 4, indicating an increased threat for heat waves during this window.

NOAA's outlook also favors a significant drying trend over the Northern Rockies, and is also hinting at some early-season monsoon moisture reaching the Southwest.

Thanks so much for reading and have a great weekend! Next update on Monday (June 9).

Alan Smith