Marine Weather and Tide Forecast for Lakeside, MT

FXUS65 KMSO 300830 AFDMSO

Area Forecast Discussion National Weather Service Missoula MT 230 AM MDT Wed Apr 30 2025

DISCUSSION

KEY MESSAGES:

- A ridge builds briefly Thursday and Friday with Friday temperatures 10 to 20 degrees above average, though they'll still be roughly 5 degrees below records.

- A cold front this weekend will bring the potential for thunderstorms, especially on Saturday.

A trough of low pressure with its axis just east of the Northern Rockies will continue east today as high pressure begins to build.
Showers and cloud cover will linger today over western Montana until the remainder of the moisture from Monday’s disturbance can move out, which will be by this evening.

A potent ridge builds in overnight on tonight and through the day on Thursday. This will bring a very dry air mass with it, causing relative humidity to drop below 20 percent in many valleys, especially south of Interstate-90. Along with the dry air comes temperatures 10 to 20 degrees above average, but temperatures will still remain about 5 degrees below record levels. Winds under the ridge will be light and variable. That means poor smoke dispersion for any local burning.

On Saturday evening, the ridge breaks down, and a deep trough of low pressure digs along the West Coast, sending Pacific moisture into the Northern Rockies from the south. At the same time, a shortwave will traverse the Canadian border, bringing a cold front across the Idaho Panhandle and into western Montana. The result will be rain showers across the Northern Rockies on Saturday afternoon and evening. There will be enough instability to fuel thunderstorms capable of producing small hail and gusty outflow winds to about 40 mph. Rain will continue on Sunday as the Pacific moisture plume remains in place. Enough instability will remain to keep thunderstorms in the forecast for Lemhi County and southwest Montana on Sunday afternoon and evening.

Looking into early next week, ensemble outcomes have changed all together and are now in good agreement for the West Coast low to cut off and dive well south of the Northern Rockies. This sets up a split flow pattern over our region, which means only light precipitation. So the chances for a very wet rain event in early May are waning.
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