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KEY MESSAGES

- Cold rain and a wintry mix will flip to snow tonight before ending Friday afternoon through Friday night from west to east.

- Snow accumulations through Friday night will range from 1 to 3 inches for most of NE Montana, with 2 to 5 inches across the Yellowstone River corridor from Terry to Sidney areas. 4 to 6 inches are expected for portions of Wibaux County.

- A Lake Wind Advisory for Fort Peck Lake remains in effect until midnight tonight.

DISCUSSION

WEATHER PATTERN OVERVIEW: Low pressure will continue tracking from Wyoming into the Dakotas as a cold rain and wintry mix overtake much of NE Montana this tonight. Over time, precipitation will switch over to all snow. Snow will continue steady at times before ending west to east Friday into Friday night.

Headlines remain unchanged from prior shift with the exception of the entirety of Phillips county being added in this evening.

Much of NE Montana is expected to see a broad 1 to 3 inches of wet snowfall accumulation. Much of this accumulation will occur on grassy and elevated colder surfaces such as car tops or complex terrain such as the Little Rockies. Meanwhile, wet and/or slushy roads could become snow covered tonight. Evening radar trends show most of the rain snow mix to be occuring from about McCone to Daniels county and going west for the first wave.

A second wave begins farther southeast along the Yellowstone River corridor from Terry to Sidney starting around 3AM. Snowfall there will be steadier and more persistent. This is where a broad 2 to 5 inches are expected. Wibaux County is closest to the low track, and can expect 4 to 6 inches with a Winter Storm Warning there remaining in place.

Bottom line, wintry conditions from a late season system will bring a variety of impacts to the region from snow covered roads, low visibility, and stress to newborn livestock.

Secondarily, breezy E winds will continue through this evening and a Lake Wind Advisory remains in effect for Fort Peck Lake through midnight tonight.

Over the weekend, cooler and drier weather remain expected but ensembles show upper level ridging from the Pacific shore translating east over the Northern Rockies by early next week with milder temperatures expected, particularly by Tuesday which may have a more elevated fireWx conditions before a frontal passage and will be monitored.

FORECAST CONFIDENCE & DEVIATIONS: Deviations from NBM included the first 18 to 24 hours of PoPs and QPF which needed to be adjusted early on as radar trends are placing more snow over Phillips county than initially expected. A Winter Weather Advisory was added to this area as well based also on snow on MDOT webcams and local social media posts on traffic.

Confidence is HIGH n the wintry mix and snow through Friday.

But confidence is MODERATE on specific amounts due to precipitation type issues, warm ground complications, and April sun angle playing mitigating factors.

Confidence is HIGH on a general warm up by early next week with decent model consensus at larger time scales for now.

Confidence drops to MODERATE to LOW after Tuesday night frontal passage through the end of the forecast as ensembles begin to fray with each other from about this point on.

/GAH

AVIATION

LAST UPDATE: 0400Z

FLIGHT CAT RANGE: MVFR - LIFR

DISCUSSION: MVFR to IFR ceilings are expected through tonight with some LIFR ceilings possible. Low ceilings and a cold rain/wintry mix will transition to snow this evening which will drop visibility to IFR. Airport shutdown conditions cannot be ruled out. Worst conditions will be in between 03Z at KGGW and 10Z for the other terminals and last through roughly 16Z before snow thins or ceilings begin to rise.

WIND: E to NE and diminishing to 10 to 15 kts this evening. Becoming NE to N and reducing to 10 kts or less after midnight.

/GAH

GGW WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory until noon MDT Friday for Central and Southeast Phillips-Northern Phillips-Southwest Phillips.

Winter Weather Advisory until 6 PM MDT Friday for Central and Southern Valley-Daniels-Eastern Roosevelt-Garfield-McCone- Northern Valley-Sheridan-Western Roosevelt.

Winter Weather Advisory until midnight MDT Friday night for Dawson-Prairie-Richland.

Winter Storm Warning until 6 AM MDT Saturday for Wibaux.