textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Strong cold front Friday will bring snow, especially in the mountains, through Saturday.

- Behind the cold front Saturday, expected wind gusts 20-35 mph across the region.

- Sunday through early next week a ridge builds over the region causing stable conditions.

Lots of moisture over the last 24 hours has left the boundary layer saturated causing a lot of fog and mist. With rising pressure level heights and increasing stability this morning, expect some of that to linger for a while today. An increasing easterly pressure gradient will prevent it from remaining dense all day, but it won't be enough to clear it out much until this afternoon.

Another cold front is headed our way for Friday into Saturday. As with all the systems so far this winter, there is considerable uncertainty in the snow levels and snow amounts at area passes range from 2 to over 9 inches of snow in 24 hours. Even on the high end of the range of forecasts, valleys are expected to pick up less than an inch of snow by Saturday morning. This front will also bring another round of wind behind it with Saturday afternoon gusts ranging from 20 to 35 mph in the valleys across the region. Some of the typically windier locations like Grangeville will see gusts approaching 40 mph.

Sunday into early next week a ridge builds over the region again. It will be a dirty ridge, which just means there will be quite a bit of moisture flowing through the ridge, so there will be plenty of cloud cover. Still, it will cause increasing stability at a time when the sun angle is very low, so if there's much moisture available in the boundary from melting snow, fog will once again return early next week.

AVIATION

The remnants of the atmospheric river that has been impacting California are moving through our region in southwest flow. Due to recent rains and melting snow, the boundary layer is saturated and this is causing some fog and mist. An easterly pressure gradient this morning is helping to break it up and preventing the fog from becoming dense, but with rising heights, a low sun angle, and plenty of mid and high cloud cover it will be mid-afternoon before it can clear out the larger valleys around most terminals. And then, with so much recent moisture in the boundary layer, fog and mist will most likely return again tonight.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Dense Fog Advisory until 8 AM MST this morning for Missoula/Bitterroot Valleys.

ID...Dense Fog Advisory until 5 AM MST /4 AM PST/ early this morning for Eastern Lemhi County...Orofino/Grangeville Region.