textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Saturday Arctic Push: Flash freeze potential as bitterly cold air moves west of the Divide Saturday morning. Strong northeast winds will develop in prone canyons and gap areas (e.g., Bad Rock Canyon).

- Building Ridge (Early Next Week): Cold and much drier conditions starting Sunday.

A few lingering showers are possible today, potentially forming bands during the afternoon. Impacts will be isolated to these showers if they develop and should not be long lasting as they will propagate rapidly southeastward.

An Arctic boundary is still on track to affect portions of northwest MT today. In fact, around 11:30 pm Friday the first hints of Arctic Air can be seen in weather stations just north of Cut Bank, MT where winds turned northerly. Its 'pick your favorite weather model Friday' on timing of the front but a middle of the road timing would be: 6 am - 9 am Marias Pass 10 am - 2 pm Kalispell MT 1 pm - 5 pm Lincoln MT

Sunday Morning low probability of reaching Missoula and Bitterroot Valleys

There is decent confidence that US-2 from Marias Pass into the Flathead Valley will have Arctic Front impacts such as gap winds up to 40 mph, rapidly dropping temperatures, enhanced snowfall rates, and potential for wet roads to freeze up. Elsewhere, the only effects from the Arctic may be the coldest temperatures yet this season. For instance, the coldest temperature yet this season for Missoula has been 17F on Nov 30th. There is a 50/50 chance the low temperature will be below 10F on Sunday in Missoula. North and east of Missoula, expect lows of single digits above zero. Continued winds and cloud cover will likely inhibit temperatures from lowering below zero except in higher elevations.

Now comes the difficult part of the forecast, a ridge will develop over the region on Sunday. Question is how does the ridge of high pressure play out? Valley locations that receive a few inches of snow by this evening, may quickly develop cold pools. These locations could see effects such as high temperatures remaining in the upper 20s for a few days, with low stratus or freezing fog for most of the mornings. In valleys that do not receive a few inches of snow, conditions will take longer to develop. Over a few days these locations will experience expanding areas of morning fog or low stratus, that lasts longer each day. High temperatures that quickly recover into the upper 30s Sunday, may slowly lower into lower 30s. It will be all about who gets a few inches of snow or not.

High pressure is expected to last through the end of the coming work week. This looks to be a dirty ridge, so there will be times with moisture moving through the ridge producing clouds with low probability of any precipitation beyond a few light showers in the mountains north of I-90.

AVIATION

An Arctic boundary is still forecast to impact KGPI between 27/1600 and 27/1900z. Expect winds to swing northeasterly with gusts 25 to 30 kts. A brief period of snow is possible with the front, temporarily lowering visibility and ceilings. Elsewhere, isolated showers are expected during the afternoon, they will also be capable of briefly lowering visibility and ceilings.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Winter Weather Advisory until 2 PM MST Saturday for Lower Clark Fork Region.

Winter Weather Advisory until 8 PM MST Saturday for Bitterroot/Sapphire Mountains...Flathead/Mission Valleys... Potomac/Seeley Lake Region.

Winter Weather Advisory until 5 PM MST Saturday for Kootenai/Cabinet Region...West Glacier Region.

Winter Weather Advisory until 5 PM MST Saturday for Missoula/Bitterroot Valleys.

Wind Advisory until 5 AM MST Saturday for Butte/Blackfoot Region.

Winter Weather Advisory from 5 AM to 8 PM MST Saturday for Butte/Blackfoot Region.

Wind Advisory until midnight MST tonight for Potomac/Seeley Lake Region.

ID...Winter Weather Advisory until 1 PM PST Saturday for Northern Clearwater Mountains.

Winter Weather Advisory until 8 PM MST /7 PM PST/ Saturday for Eastern Lemhi County...Southern Clearwater Mountains... Western Lemhi County.

Winter Weather Advisory until 10 AM PST Saturday for Orofino/Grangeville Region.