Jan 25, 2012 5:12 PM by Erin Yost (StormTracker Weather Center)
Freezing rain & sleet were major weather threats across western Montana Wednesday morning along with very breezy conditions.
The reason for the freezing rain, though? After cooling down considerably Monday night (single digits for many), it was hard to warm up Tuesday (along with valley inversions developing). While that happened, warmer air aloft began moving into the region as our system approached.
Think of it this way: all precipitation starts off as snow in the U.S.. This moisture falls into a thick, warmer layer of air which melts it into a raindrop. Now, when it reaches the surface (where there's colder air that up high or where temps are below freezing), that super-cooled raindrop freezes instantly onto whatever object is sub-freezing - hence freezing rain.
Sleet, on the other hand, forms when that super cooled raindrop has enough time to try to get back to the original "snowflake" form because the warmer layer isn't as thick. Instead, we end up seeing ice pellets, grauple or sleet!
We have another system moving in beginning late Wednesday night into Thursday, however, I don't think freezing rain will be an issue again. We just won't have enough time before our next warm/cold front combination to see those cold pools develop like they did Monday night. STILL, there will be that transitional period of a rain/snow mix Thursday morning, so drive safely!
Wednesday night, light valley snow is likely as temps drop into the mid 20s to low 30s. Mountains will continue to see snow with a few Winter Weather Advisories issued:
Lower Clark Fork Region (Lookout Pass): Until 5 p.m. Thursday for 6"-10" with windy conditions reducing visibility.
West Glacier Region (Marias Pass): Until 5 p.m. Thursday for 5"-9" with windy conditions reducing visibility. Lower elevations could see 2"-4".
Bitterroot/Sapphire Mountains (Lolo & Lost Trail Passes): Until 5 p.m. Thursday for 5"-8" with windy conditions reducing visibility.
Potomac/Seeley Lake Region: Until 5 p.m. Thursday for 6"-10" with windy conditions reducing visibility. Lower elevations could see 2"-5".
Thursday, anticipate the mixed precipitation again with valley rain eventually. Things will begin to quiet down by the afternoon/evening. Highs will be in the upper 30s to low 40s again, but cooler Friday after a second (& slightly stronger) cold front moves through.
Friday into the weekend, high pressure will begin building into the west allowing for drier conditions with a mix of clouds & sun. Highs Friday into the weekend will be in the low to mid 30s.