Forecast Headlines:

• Showers and thunderstorms for the Rockies, Sierra, and Great Basin with moisture having a moderating effect on temperatures.
• Rain and lightning potential will be highest during the afternoon and evening hours, but overnight and morning activity is also possible at times. 
• Dry in the Pacific Northwest with temperatures heating up late in the week.
• Seasonally dry but cooler than average across the Southwest.

Tuesday Afternoon Update:

An area of low pressure is located near the Central/Southern California Coast on Tuesday with south/southeast winds transporting moisture into the Sierra Nevada Range with storms developing on the eastern slopes and slowly tracking westward.

Meanwhile, a trough of low pressure is approaching the Pacific Northwest, and energy associated with this system is interacting with an abundance of "leftover" moisture from previous systems to trigger widespread thunderstorms from the Great Basin into the Northern Rockies. 

Our Current Radar and Lightning Density Maps indicate widespread thunderstorm activity across a large portion of the West on Tuesday afternoon. These maps are interactive and "zoomable" with terrain overlays, which are ideal for tracking thunderstorms at both regional and highly localized scales.

Forecast for Wednesday:

The trajectory of moisture and resulting shower/thunderstorm will favor the Sierra Nevada Range of California, the Great Basin in Nevada, Southeast Oregon, Central Idaho, and Southwest Montana. Locally heavy rainfall will be possible in these areas as well. More isolated storms are expected across Utah and Wyoming.

Scattered thunderstorms can also be expected across the Colorado and New Mexico Rockies on both sides of the Divide.

Abundant Gulf moisture and favorable wind shear (change in wind speed/direction with altitude) will also result in a severe weather threat just east of the Rockies and I-25 corridor in Colorado and New Mexico. Large hail and damaging straight-line winds will be the primary threats with storms on the CO/NM plains, but a tornado couldn't be ruled out either.

Forecast for Thursday:

Another active thunderstorm day can be expected across the Sierra, Great Basin, and Rockies with more widespread coverage expected across Montana, Wyoming, and Northern/Western Colorado compared to prior days. 

Heavy rain will be a possibility across the Northern and Central Rockies, especially along the eastern side of the Continental Divide in Southern Montana and Wyoming.

Forecast for Friday:

A wet and stormy day can be expected across the Central and Northern Rockies, with coverage favoring Central Montana, Wyoming, Eastern Idaho, and Northern Utah. Locally heavy rain will be possible across all of these regions, with the highest potential for heavy rain and flash flooding expected along the eastern side of the Divide in Montana and Wyoming.

Forecast for Saturday to Sunday:

The Central and Northern Rockies will remain favored for showers and thunderstorms with locally heavy rainfall possible, especially across the Northern Rockies. An uptick in shower/thunderstorm activity can also be expected across the Great Basin, Sierra Nevada Range, and Colorado/New Mexico Rockies.

One region that will see dry weather this weekend is the Pacific Northwest. Following a relatively cool week, temperatures will warm up significantly for the PNW this weekend with well-above-average values expected east of the Cascade crest.

Outlook for June 5th-9th:

The pattern for early next week will largely remain the same with above-average rainfall and thunderstorm activity expected for a large portion of the West, except for perhaps the Washington Cascades. 

A similar temperature pattern is also expected with above-average temperatures for the Northwest and below-average temperatures for the Southwest.

Aside from the east side of the Cascades where temperatures could be well above average, significant heat waves are not anticipated for the other regions where above-average temperatures are projected.

The reason is that cloud cover from the uptick in moisture should have a moderating effect during the afternoon hours, with overnight low temperatures likely to deviate further from average compared to highs. 

Thanks so much for reading! Next update on Friday (June 2).

Alan Smith