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DISCUSSION

KEY MESSAGES: - Light Freezing Rain likely overnight tonight into Christmas Day for parts of Northeast Montana - Another round of mixed precipitation possible Friday into Saturday.

- Dangerous cold conditions could impact areas north of US-2 overnight Saturday into Sunday, with wind chills colder than 30 below zero. WEATHER PATTERN OVERVIEW:

Alaska low continues to push south over the next few days before rotating into the Pacific Northwest and crossing the northern Rockies early in the weekend. Moisture will continue streaming into Montana with the strong atmospheric river pushing over California and the Great Basin.

A shortwave lifting through the southwest flow will lift across the weak winter thermal boundary over central Montana with possible overrunning precipitation from tonight into Christmas Day. Thermal profiles with warm air aloft and a colder boundary layer will create conditions for freezing rain and ice pellets over mainly the northwest part of the CWA from any precipitation that occurs, intermittently from tonight through Saturday morning.

A stronger shortwave pushes through the ridge on Friday night for another chance for precipitation along with gusty winds and dropping temperatures. An arctic airmass will keep temperatures down below normal on Saturday and Sunday. A ridge is expected to move back in on Monday.

FORECAST CONFIDENCE & DEVIATIONS:

There was some decrease in ice accumulations overnight tonight into Thursday, but confidence remains moderate to high that northern and western parts of the region will see accumulating freezing rain. Confidence also remains moderate that there will be another round of light precipitation Friday into Saturday. While specifics with respect to deep cold is yet to be fleshed out, there is low to moderate confidence that dangerous wind chills can be felt across many parts of the region late Saturday night into Sunday morning.

Cliff

AVIATION

Updated: 2130Z

Expected Flight Category: As low as LIFR

Synopsis: Some patches of fog will continue to exist across northeast Montana this afternoon and into this evening. Overnight, a combination of very low clouds and some fog, along with an advancing front that likely will produce some freezing rain in parts of Phillips, Valley and Daniels Counties, will work to reduce the expected flight category to LIFR conditions through the morning hours Thursday, before conditions improve Thursday afternoon.

Winds: East winds of 15-30 kts across a wide area of northeast Montana will become light and variable by Thursday afternoon once the precipitation system moves away from the region.

Cliff

GGW WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory from 11 PM this evening to 11 AM MST Thursday for Central and Southeast Phillips-Central and Southern Valley-Daniels-Northern Phillips-Northern Valley-Southwest Phillips.