Active Period Ahead for the Sierra, Great Basin, and Rockies

A trough of low pressure will set up along the West Coast for the remainder of this week and into the Memorial Day holiday weekend. A dominant ridge of high pressure over the plains will "block" the trough from moving inland at all.

As a result, a consistent southwest flow can be expected, while will transport abundant moisture into the Great Basin and Northern/Central Rockies.

The moisture combined with warm air and instability across the Intermountain West will result in daily rounds of showers and thunderstorms with stronger storms capable of frequent cloud-to-ground lightning and heavy rain.

Shower/thunderstorm chances will be greatest in the afternoon and evening hours with the morning hours looking more favorable for outdoor activities in most instances. However, we always recommend that you check the hourly forecasts for specific locations on OpenSnow to help you time your adventures. 

We offer hourly forecasts for precipitation probability, temperature, wind, and cloud cover for any location under the Weather tab. On the OpenSnow website, we now display hourly lightning potential as well. Hourly lightning potential is not yet available on the OpenSnow app, but it will be added to the app in the near future so stay tuned.

Example Forecast: Buffalo Creek, Colorado

Forecast for Wednesday:

Numerous thunderstorms can be expected across Nevada, Idaho, Wyoming, Montana, and Colorado, especially in the afternoon and evening hours. Check out the lightning percentages from a blend of high-resolution weather models for lightning strikes within 12 miles of any given point on Wednesday. 

The morning hours will feature scattered showers in Montana and Southern Canada with mainly dry conditions elsewhere. However, by Wednesday afternoon, our Forecast Radar is looking colorful with numerous thunderstorms projected across the Great Basin and the Rockies.

Keep in mind, the forecast radar is based on a single weather model and should be used to get a general idea of coverage/timing, but should not be taken literally.

In addition, be sure to use our Current Radar and Lightning Density map overlays to track thunderstorms as they happen throughout the summer. These map overlays are great resources if you need to check on current conditions before heading out on an afternoon run or bike ride.

Here is a rainfall projection from Wednesday morning through Thursday morning. Locally heavy rainfall will be possible under stronger storms across the Rockies and Great Basin, and some storms could also produce moderate to large hail along with gusty winds. 

Forecast for Thursday:

Thunderstorm activity on Thursday will favor the Northern Rockies including Idaho, Wyoming, and Montana as well as the Colorado Front Range and Northern New Mexico. The Sierra Nevada Range is also looking more active with scattered thunderstorms expected. Locally heavy rain will be possible in all of these regions, which could potentially result in flooding of small streams that are already running high due to snowmelt.

Forecast for Friday:

A similar pattern can be expected with showers and thunderstorms favoring the Sierra, Great Basin, Northern Rockies, Colorado Front Range, and Northern/Eastern New Mexico. Once again, stronger storms will be capable of producing locally heavy rainfall. Showers and isolated thunderstorms will also be possible across Western Canada and the Northern Washington Cascades. 

Forecast for Memorial Day Weekend (Saturday to Monday):

An active pattern will continue right through the holiday weekend with showers and thunderstorms favoring the same general regions, including the Sierra, Great Basin, and Northern Rockies. Northern Utah is also looking a bit more active compared to recent days. Further south, thunderstorm activity will be more isolated in Colorado and New Mexico.

If you have holiday outdoor plans, keep in mind that showers and thunderstorms will be off and on in nature and will favor the afternoon and evening hours. In most instances, there should be some good weather windows early in the day.

Outlook for Tue, May 30 – Sat, June 3:

Next week's pattern is looking awfully similar to this week with a strong ridge of high pressure located just east of the Continental Divide, while a relatively weak trough near the West Coast will keep a southwest flow in place.

Temperatures will be cooler than average across much of California and near to below average across the Southwest, while the Northwest and Northern Rockies are expected to be warmer than average.

A fairly active pattern is expected to continue across the West with the wettest signal (showers & thunderstorms) projected to shift southward a bit into Wyoming, Colorado, and New Mexico. Shower/thunderstorm potential also looks fairly high from the Sierra into parts of Nevada and Utah.

Thanks so much for reading! Next update on Friday (May 26).

ALAN SMITH