textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Snow showers today and tonight will be heavy at times.

- Near record or record cold temperatures forecast for Saturday morning.

- Cold lasts into early next week.

A broad, cold closed low over central Canada this morning is causing a cold, northwest flow across the northern Rockies and helping to push a cold front across the region. This is a very cold air mass, and as it interacts with the warmer and very moist air mass currently over the region, it is causing some heavy snow showers. MTDOT web cameras today have shown whiteout conditions at times on some of the roads in northwestern Montana. Minimal snow accumulations are expected in the valleys today due to warm ground temperatures and the warming effects of the daytime sun. Mountain locations, however, will continue to see accumulating snow, especially on unpaved roads. That all changes this evening when we lose the sunlight and the cold air pushes further south, with even valley locations potentially picking up some snow by Friday morning. This is mainly a concern in areas where the leaves have come out on the trees, since the leaves will hold onto the snow and cause tree limbs to break, potentially causing power outages.

Another potential hazard is snow melting on the warm ground and then refreezing into ice overnight as the air temperature continues to drop. Any ice formation this way would be patchy, and difficult to spot, so if traveling this evening or overnight use caution and be on the lookout for ice.

After the cold air moves into the region, models are currently forecasting record lows for Saturday and Sunday morning in Missoula, and near record lows for central Idaho including areas like Riggins and Orofino. The Missoula and Bitterroot valleys are expected to drop into the low 20s and teens for morning temperatures this weekend. We've recently been as cold as the mid-20s, so while a freeze shouldn't be too much of a shock, this will be a very hard freeze and has the potential to damage fruit trees that have started to bud or bloom. Also, for any areas that have started irrigation already this year, a freeze this hard may damage equipment. Temperatures will trend warmer each morning, but we do not expect them to return to average morning temperatures until Tuesday or Wednesday of next week, so the cold will last a few days at least.

AVIATION

A broad, very cold upper level trough over the northern Rockies is causing widespread convection today that will last through the night. With colder air moving into the region, precipitation has turned to snow already at terminals KGPI, KMSO, and KBTM. We expect it will turn to snow at KHRF this evening and early tomorrow morning at KSMN. Due to the high solar angle and warm ground temperatures, snow accumulation is not expected on paved surfaces until tonight, though it will vary by terminal and will start accumulating first at KBTM this evening. This air mass is very unstable, and despite the cold temperatures occasional lightning has been observed. Visibility and ceiling restrictions will last half an hour to about 3 hours as showers move through.

Snow melting on the pavement due to the warm ground this evening could refreeze and become black ice as the temperatures drop tonight.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Winter Weather Advisory until noon MDT Friday for Bitterroot/Sapphire Mountains...Butte/Blackfoot Region... Potomac/Seeley Lake Region.

Winter Weather Advisory until 6 PM MDT this evening for West Glacier Region.

ID...Winter Weather Advisory until noon MDT /11 AM PDT/ Friday for Eastern Lemhi County...Southern Clearwater Mountains... Western Lemhi County.