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DISCUSSION

KEY MESSAGES:

- Wintery mix with snow and ice accumulation is expected along and near the Hi-Line into this afternoon.

- A strong winter storm with significant snow accumulation is possible for early Friday morning through Saturday morning.

- Bitter cold temperatures are expected tonight through Saturday night.

WEATHER PATTERN OVERVIEW:

Strong atmospheric river spreading moisture across the northern Rockies and encountering a warm front over central Montana this morning. A band of light to moderate precipitation extending from north central Montana into east central Montana has been slowly moving to the northeast overnight. Colder air beginning to filter south, and rain is changed over to snow along Hwy 2 while to the south rain is occuring. With the rain earlier and the overlying snow, very slick conditions are still expected, and will continue with the current advisory/warning.

As the arctic air continues to filter south, a significant overrunning snow event is expected from Friday morning through Saturday morning. Significant snow accumulation are anticipated and a watch is in effect. Models have pushed back the start time slightly so left watch in place but adjusted the timing by several hours. Greatest snow amounts are expected to be southwest of a Glasgow-Glendive line. The arctic airmass will also push temperatures to near or below zero for highs on Friday and Saturday, leading to wind chill values below the -25 criteria for a cold weather advisory through the weekend.

The upper pattern shifts quickly by Sunday, with a chinook pushing the arctic air eastward. Fresh snow pack could slow the warm up especially in the lower Milk and Missouri Valleys, depending on the strength of the wind, but overall will see warmer temperatures and melting next week.

FORECAST CONFIDENCE & DEVIATIONS:

Average to high confidence on the accumulating heavy snow in the SW half of the forecast area between from Friday through Saturday with lower confidence in the specific snow amounts for the NE corner zones and the boundary between warning and advisory snow amounts.

High confidence on the bitter cold temperatures tonight through Saturday night. Lower confidence on the rebound of temperatures next week.

AVIATION

IFR to MVFR as a mix of rain and snow lift north across the region this morning. Some freezing rain is also possible with the wintry mix, along with falling temperatures creating ice on wet surfaces. Another round of snow along with near to sub-zero temperatures are expected from early Friday morning through Saturday morning.

GGW WATCHES/WARNINGS/ADVISORIES

Winter Storm Warning until 8 PM MST this evening for Central and Southeast Phillips-Central and Southern Valley-McCone-Northern Phillips-Richland-Western Roosevelt.

Winter Storm Watch from late tonight through Saturday morning for Central and Southeast Phillips-Central and Southern Valley- Dawson-Garfield-McCone-Northern Phillips-Petroleum-Prairie- Southwest Phillips.

Winter Weather Advisory until 8 PM MST this evening for Daniels- Dawson-Eastern Roosevelt-Garfield-Northern Valley-Petroleum- Prairie-Sheridan-Southwest Phillips-Wibaux.