textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Patchy fog and low stratus less likely tonight in western Montana due to developing easterly winds.

- Unsettled weather pattern next week with multiple systems capable of mountain and mountain pass snow.

Areas of fog and low stratus have been slow to erode today, particularly for the valleys of northwest and west-central Montana. Satellite imagery reveals gradual eroding occurring from east to west, with most of this low level cloud cover expected to be dissipated by late afternoon. Western Montana and north central Idaho will remain under a weak area of high pressure through Sunday night, bringing generally benign weather conditions.

An easterly wind gradient sets up across the region tonight, which should allow for light winds to persist into the overnight and early morning hours. This should keep additional fog and low stratus from forming once again, especially across western Montana. These winds will also likely keep temperatures from reaching as cold as previous forecasts indicated. The east winds are anticipated to strengthen through the day Sunday, likely peaking Sunday evening with localized areas seeing gusts 25 to 35 mph, including over the eastern side of Flathead Lake.

On Monday, a low pressure system is expected to dive into the Pacific northwest, tracking through central Idaho and western Montana Monday night into Tuesday. This will allow for another round of precipitation to develop Monday night, generally along and south of Interstate 90, then spreading northwards into northwest Montana Tuesday afternoon into Wednesday morning. Forecast models indicate snow levels will lower to between 5000 to 6000 feet, which will allow for accumulating snow in the higher terrain and may bring periods of slick travel over mountain passes, especially in the overnight and early morning hours.

Forecast models are coming into better agreement on another, potentially colder, low pressure system moving over the region Thursday into the weekend. While the overall details remain murky, there is potential for snow level to lower further, especially in northwest Montana and along the COntinental Divide, where its not out of the question to see periods of snow even into valley locations.

AVIATION

Persistent low clouds and valley fog has been stubborn to clear today across lower valleys of northwest and west central Montana. However, current satellite imagery shows a gradual improvement from east to west, and likely will be fully eroded by 25/0000z. The threat for fog and low stratus again tonight look less likely due to an anticipated easterly wind gradient developing between 25/0300z and 25/0900z. Airfields such as KGPI and KMSO are expected to have enough wind to keep fog and low stratus at bay. However, more sheltered locations such as KHRF may see some localized fog develop towards sunrise. Easterly winds will continue into Sunday, likely strengthening through Sunday morning.

MSO WATCHES/WARNINGS/ADVISORIES

MT...None. ID...None.