Forecast Highlights:

• Warming trend throughout the West this week.
• Scattered thunderstorms across the Rockies on Monday.
• Isolated thunderstorm chances near/east of the Continental Divide most days this week.
• Unseasonably wet system to bring heavy rain to the Pacific Northwest Thursday-Saturday.
• Showers/thunderstorms increase across the Northern Rockies this weekend.

Synopsis:

A trough of low pressure responsible for wet conditions and extensive shower/thunderstorm coverage over the weekend is working its way eastward across the Northern Rockies with lingering moisture and continued unsettled weather on Monday.

A ridge of high pressure will build over the Great Basin and Intermountain West heading into the middle of the week with warmer and drier conditions for most areas. Late in the week, an unseasonably moist trough of low pressure will approach the PNW with significant rain expected starting Thursday and continuing through Saturday.

Forecast for Monday:

Cool and unsettled conditions will linger across the Northwest and the Northern and Central Rockies on Monday as lingering moisture combined with instability and support from the jet stream will contribute to showers and thunderstorms.

Showers will be more isolated/less numerous over the Cascades for a change, while the Northern Rockies from Idaho to Montana and Northern Wyoming will see the most widespread coverage. The Black Hills of South Dakota are also at a risk for strong to severe thunderstorms.

Further south, thunderstorm chances will also be on the increase across a good portion of Colorado on Monday afternoon.

The Storm Prediction Center has highlighted the Black Hills region of South Dakota for a Slight (level 2 out of 5) risk for severe weather. The main threat across this region will be very large hail of 1 to 2 inches in diameter, but an isolated tornado also couldn't be ruled out. 

Outside of the Black Hills, the severe weather threat on Monday should remain confined to the plains with mountain areas experiencing more standard thunderstorms with dangerous cloud-to-ground lightning along with brief downpours and gusty winds. 

Rain amounts on Monday will be spotty and heaviest under stronger thunderstorms with the Northern Rockies, Black Hills, and Colorado expected to see the most widespread activity with lighter/more spotty showers (and a lack of thunderstorms) across the Cascades. 

Forecast for Tuesday:

The Pacific Northwest will see a welcome break in the rain on Tuesday as lingering moisture continues to shift further east. Thunderstorms on Tuesday will be more isolated and generally confined to areas along/east of the Continental Divide in Montana, Wyoming, Colorado, and New Mexico with any strong/severe storms occurring well east on the plains.

Rain amounts on Tuesday will be lighter along and east of the Continental Divide. On Tuesday night, a minor disturbance will result in light showers developing across the Cascades. 

Forecast for Wednesday:

Another relatively quiet day is expected on Wednesday. The Cascades will see another break in the action following Tuesday night's disturbance, while spotty/light showers will be possible across the Northern Rockies, mainly in Idaho and Montana.

The isolated thunderstorm threat will shift southward into the Southern Front Range/Sangre de Christo Range of Colorado and New Mexico with only light rain expected from any storms.

Outlook for Thursday-Friday:

A strong storm system will impact the Pacific Northwest late this week, and the amount of water vapor in the atmosphere will be unusually high for this time of year. The image below shows the moisture plume extending from well out in the Pacific toward the Cascades and has an atmospheric river look to it – something we don't often see in June. 

Two-day rainfall amounts are likely to be significant across the Cascades and Olympics on Thursday and Friday with lighter amounts expected south of Mt. Hood and east of the Cascades, though the Idaho Panhandle also looks quite wet. Flooding may be a concern across the Northwest during this period, especially on Friday.

Elsewhere, Thursday and Friday are looking dry except for some spotty thunderstorms across Colorado, New Mexico, and Arizona. 

A heatwave is also expected to take hold across the interior of California as well as Arizona and surrounding desert regions during this period with temperatures topping the century mark in many areas. 

Outlook for Saturday (6/11) to Sunday (6/12):

The low pressure system over the Northwest will move inland this weekend with lingering rain across the Cascades and PNW on Saturday, while the latest trends suggest these rain-soaked areas should see a break on Sunday.

Shower and thunderstorm chances will increase across Idaho, Montana, and Wyoming on Saturday and Sunday with hotter and drier conditions persisting further south. Areas along the Continental Divide in Colorado and New Mexico could see some isolated thunderstorm activity, however.

Outlook for Monday (6/13) to Monday (6/20):

Next week, additional low-pressure troughs are expected to move across the Pacific Northwest resulting in continued cooler than average temperatures, while high-pressure further south will result in hotter and drier conditions across Southern California and the Four Corners states.

Despite the cooler pattern, we're not seeing much of a wet signal across the Northwest for next week. Still, the overall pattern will likely be conducive to periods of showers and thunderstorms across the Northwest and Northern Rockies, but perhaps with lesser rainfall amounts compared to the past couple of weeks. 

Thanks so much for reading! Next update on Wednesday (6/8).

ALAN SMITH