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Wednesday Afternoon Conditions:

A robust shortwave trough moved across the Northern Rockies on Wednesday with numerous thunderstorms developing. Utah and Colorado have also seen plenty of thunderstorms with remnant energy on the southern fringe of this system. 

Storms impacted Eastern Oregon and Western Idaho during the morning hours on Wednesday, with thunderstorm activity ramping up eastward heading into the afternoon.

Here was our Lightning Risk map at 2:08 PM mountain time:

Big Picture Pattern - June 12 to 16:

A trough-dominant pattern over the Pacific Northwest will result in below-normal temperatures near the West Coast, while most of the Interior West will see above-normal temperatures. The jet stream will be stretched across the Northern Rockies and will tap into a moist and unstable atmosphere to support frequent thunderstorms.

Thursday (June 12):

Wednesday's trough will exit eastward onto the plains, while another trough will push into the Interior Northwest.

This trough will interact with lingering moisture to result in another active thunderstorm day across the Northern Rockies, with locally heavy rain possible, especially east of the Continental Divide in Montana.

The Central and Southern Rockies will see a decrease in moisture compared to prior days, with more isolated thunderstorm activity expected along with lighter rainfall. Storms could still fire up by midday over the higher mountain ranges, however, especially in Colorado. 

Friday (June 13):

A surface low will develop over Southeast Colorado, and counterclockwise (cyclonic) winds to the east of the low will transport rich Gulf of Mexico moisture into the high plains and Northern Rockies, leading to increasing instability, or "thunderstorm fuel".

Meanwhile, another shortwave trough will track across Montana, which will also support thunderstorm development, especially east of the Divide, where more abundant moisture will be present.

Storms could become strong to severe along the eastern ranges of the Rockies and the adjacent plains, with the potential for large hail, damaging winds, and heavy rain. Denver Metro looks to be just inside of this risk area, with a higher potential for severe weather east of the metro area. 

Isolated to scattered thunderstorms can also be expected west of the Divide in the Northern Rockies and Interior Northwest, including the Northern Washington Cascades. Storms west of the Divide will generally produce light to moderate rain. 

Saturday (June 14):

A very similar setup is expected on Saturday, though richer moisture and greater instability look to shift further north and east of the Denver metro area, with the primary threat over the eastern plains and along and east of the Divide in the Northern Rockies in Wyoming and Montana.

Storms will be capable of producing large hail, damaging winds, and heavy rainfall east of the Divide, with fewer and weaker storms west of the Divide. A notable decrease in thunderstorm coverage is expected across Colorado, though a few stray storms couldn't be ruled out over the higher peaks. 

Here is a 3-day rainfall projection from the European weather model from Thursday through Saturday:

Sunday (June 15) to Monday (June 16):

The pattern will not change much during this period, with a trough remaining over the Northwest, while jet stream energy will continue to stretch into Montana. Gulf moisture will also remain entrenched east of the Divide in Montana and Wyoming, where a threat of strong to severe thunderstorms will continue each day.

Elsewhere, only some isolated late-day thunderstorm activity is expected at best over the higher mountain ranges with light and spotty rainfall.

Here is a 2-day rainfall projection for Sunday-Monday:

Outlook for June 17 to 21:

A trough-dominant pattern will remain over the Northwest next week, and we may actually see a deeper trough push into the Northwest, which could bring some moisture into Oregon and Washington. 

Temperatures are expected to be below-normal across the Pacific Northwest and above-normal across the remainder of the West.

The next image is a rainfall projection from the European Ensemble Model, which represents the average of 50 simulations of this model.

Washington and Oregon could potentially pick up some beneficial rainfall in this pattern, while the Northern Rockies (Idaho and especially Montana) will continue to see higher chances of thunderstorms.

A much drier pattern is expected to the south, including over Colorado and New Mexico, where only some isolated thunderstorm activity is expected at times near the Divide with light and spotty rainfall.

Thanks so much for reading! Next update on Friday (June 13).

Alan Smith