textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Very cold mornings will continue through the first half of this week.

- Developing inversions will likely lead to fog, stratus and poor air quality.

Satellite is showing remnant subtropical moisture rotating around the ridge of high pressure currently building over the west coast. These high clouds will likely moderate expectations for a cold morning today, although most locations will still be quite cold. This will also slow the progression of deep cold pool development.

The models are still all in on the axis of high pressure moving over the Northern Rockies by Wednesday. This is when an expansion of valley fog and low stratus can be expected. We may also experience the beginnings of poor air quality due to stagnant valley air masses.

This was always forecasted to be a dirty ridge, the question now is will the clouds be at night, like today, and that keeps low temperatures slightly warmer or are the clouds during the day keeping high temperatures slightly cooler.

Ridge breakdown is expected by the end of the workweek, 75% of the models are in agreement it will happen by Friday evening. While the remaining 25% suggest overnight Friday. Depending on how strong the cold pools develop, there could be a period of mixed precipitation, freezing rain, in valleys. Snow levels initially will be elevated around 6000 feet and may slowly lower over the weekend. Better details will come as cold pools are analyzed mid- week.

AVIATION

Temperatures will begin to moderate as we progress through the coming week, with this morning likely being the coldest morning. As the ridge strengthens, so too will the valley inversions. Valley stratus and/or fog will become a concern by Tuesday morning.

MSO WATCHES/WARNINGS/ADVISORIES

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