textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Stream and creek flooding concerns tonight into Wednesday for northwest Montana, especially Lincoln and Sanders counties

- Well above normal temperatures and gusty winds at times into Friday, especially I-90 southward

Deep moisture from an atmospheric river will be directed into the Northern Rockies throughout the week. The heaviest precipitation is expected tonight into Wednesday, with a secondary surge arriving on Friday. High-resolution guidance indicates mean precipitation amounts ranging from 1.50 to 2.50 inches over the higher terrain of the Cabinet, Whitefish, and Swan ranges through early Thursday. Conversely, valley locations will see significantly less precipitation, generally around 0.10 to 0.30 inches. With snow levels remaining unusually high at 7,000 to 8,000 feet, accumulating snowfall will be restricted to the highest peaks of Northwest Montana.

Hydrological & Temperature Impacts: The combination of rain and warm temperatures will accelerate melt from a primed snowpack in Northwest Montana. There is concern for rapidly rising streams and creeks, especially in Sanders and Lincoln counties as rain rates pick up by late this evening. Also watch for ponding of water and rock/snow slides along roadways. Both daytime highs and nighttime lows will warm to near-record levels by late week, running 10 to 20 degrees above seasonal normals, especially from I-90 southward. The combination of anomalous warmth and rain-on-snow potential will likely degrade the snowpack, leading to worsening avalanche conditions. Backcountry recreationists are strongly encouraged to monitor local avalanche centers for the latest updates this week.

Winds: Breezy to locally windy conditions will persist, with gusts of 25 to 35 mph, especially during the afternoon/evening hours. Localized higher gusts are possible in areas prone to the mountain wave activity favored by this pattern. These winds may create choppy conditions on area lakes and could occasionally disrupt outdoor activities. Fire weather concerns will also be heightened in southwest Montana due to a combination of low humidity and gusty winds the latter half of this week.

Changes by Saturday: A cold front is forecast to sweep through the region on Saturday. This will bring a return to cooler, more seasonable temperatures, along with a round of light precipitation and gusty winds. At this time, impacts from this weekend frontal passage appear minimal.

AVIATION

An atmospheric river will direct moisture across the region through Wednesday, bringing precipitation primarily to areas north of I-90. This precipitation will be largely terrain- focused, with snow levels remaining unusually high near 7,000 feet, resulting in frequent mountain obscurations across Northwest Montana.

Surface winds from the west and southwest will become gusty each afternoon and evening throughout the week, occasionally exceeding 25 knots at valley terminals. While these surface winds will generally decouple and diminish overnight, ridgetop winds will remain elevated at 25 to 35 knots. This will introduce localized low-level wind shear concerns during the overnight and early morning hours.

Finally, lingering low-level moisture presents a slight risk for patchy morning fog. However, abundant cloud cover and continued boundary layer mixing should significantly limit its overall coverage and operational impact.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Flood Watch from 6 PM MDT this evening through Wednesday afternoon...Kootenai/Cabinet Region.

ID...None.