Rexford, MT 59930 Weather

Discussion

KEY MESSAGES:

- Valley rain and mountain snow Sunday into Monday morning, focused along and south of I-90. Northwest Montana stays mostly dry.

- High pressure bringing stable conditions and valley fog next week.

- Late Week Shift: A return to unsettled pattern and potential for mountain snow by next weekend.

Low pressure continues to spin in place over the Pacific Northwest this morning. This feature brought sporadic showers to the region yesterday and due to the breaks in clouds, some locations have developed fog or low stratus clouds. For Halloween festivities later today, expect dry conditions and partly cloudy skies.

Looking further upstream over the northeastern Pacific Ocean, a very large trough has been shifting eastwards over the last 24 hours. As a result, our Pacific Northwest trough will begin to move and split into two separate systems. This second system will draw up subtropical moisture over the western United States, with our area receiving the northern edge of it, generally south of I-90 during the day on Sunday, and pulling away Sunday night. There is a high probability for at least a tenth of an inch of precipitation east and south of a line from McCall, Idaho to Sula, Montana to Great Falls. The mountains could see 0.25 to 0.50" of precipitation. Northwest Montana may avoid most of the precipitation Sunday, and sunshine could actually peek out between high clouds!

Snow levels will be around 7000 feet to start but lower to 5000 feet late Sunday. This will bring a chance for snow at mountain passes and locations including Lost Trail, Georgetown Lake area, Homestake Pass, and passes along the Divide in Lemhi County (i.e. Lemhi Pass), where lows by Monday morning will be at or below freezing. Impacts will primarily be slushy accumulations at these locations.

High pressure builds by Monday morning, but fog and low clouds could again be impactful, especially areas that received rain the day before: West-central and southwest Montana, parts of central Idaho, and Lemhi County. Clouds give away to sunshine on Monday due to a transient ridge.

Chances for fog or low clouds continue Tuesday and Wednesday mornings, while daytime temperatures climb to slightly above- average readings. The pattern becomes progressively more unsettled by the end of the week. Late week mountain snowfall will depend on how much energy can break off from the huge trough over the northeast Pacific and move onshore, similar to what we have been experiencing lately. The latest NBM forecast snow levels next weekend range from 3000 to 5500 feet.

Aviation

Fog and/or low clouds are possible across the region this morning through 31/1500Z or 0900 MDT. Lemhi County Airport (KSMN)has been able to consistently receive mid-level clouds which has prevented further reduction in ceiling or visibility. After clouds dissipate, expect mainly VFR conditions today with periodic high clouds. Rain showers develop by daybreak Sunday over Lemhi County and then spreads north and east during the day. Expect mountain obscuration and lower ceilings generally south of Interstate 90.

Watches, warnings and advisories

MT: None. ID: None.