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KEY MESSAGES

- Winter Weather Advisory for blowing snow and visibility reduction is in place across parts of the Hi-Line from late this evening into Thursday morning

- High Wind Warning in effect from Thursday morning through Thursday afternoon for all of northeast Montana.

- A Winter Storm Watch is in effect for Petroleum, Garfield and southwest Philips counties late Thursday night through Saturday. This system could bring a significant impact to newborn livestock.

- Wind chills could possibly drop to near or below zero Saturday and Sunday morning.

DISCUSSION

WEATHER PATTERN OVERVIEW: With a light round of snow exitng the area this evening. The snow on top of a semi-moist atmosphere early this morning along with clear skies and light winds has begun to form up fog. This will likely last into 6 to 9 AM where it forms and then clear.

Temperatures will moderate some the next 2 days. The northern high plains will remain under the influence of northern stream zonal flow, which will send Pacific moisture our way late in the week and the weekend.

A disturbance in the nearly zonal flow tonight could bring some light snow along the Canadian border. Up to 2 inches is possible(20-30%) in the first band, but significant winds ramping up from the incoming chinook will take any light snow and reduce visibility harshly. There is also an outside chance(5-15%) that high winds could arrive early generating near white out conditions with this bands passage mid to late morning.

A warm front/chinook will move into NE Montana late Thursday morning with overrunning pacific moisture and transition snow to rain briefly through mid-day. Confidence in this transition in low to moderate as temperatures while snowing may not warm enough to pass the freezing line and run back into rain.

Complicating this mid-day transition is the High Winds. HREF soundings are almost universal in the strength/intensity of the wind speeds and gusts, while the NBM ensembles has to be raised to it absolute limit (NBM90) just to mimic the cams. Therefore NBM was thrown out for straight NBM90 speeds and gusts during this time. Using KJDN as a proxy, the lowest ensemble sounding member from the HREF is 30 kts at the surface with with all other members showcasing 40 kts at the surface and 70 kts at the top of the mixed layer. This will further intermix with precip for HIGH uncertainty in precipitation type... and while rain is a possibility snow along with it could also lead to blizzard like conditions popping up unexpectedly (5-10% chance). The High wind should begin to wind down Thursday evening.

Thursday night into Saturday: As the chinook shuts off a cold front will drag modifying arctic air into the region. Overrunning pacific moisture will bring in snow. Between Friday and Saturday, the front will become quasi-stationary to the south and west close enough to the forecast area that overrunning moisture will generate significant accumulations, mainly in the southwestern 3 zones of the CWA. A Winter Storm Watch has been issued to amounts up to 12 inches.

This has the potential to be a long duration significant event with impacts to travel and may cause stress on newborn livestock. Those with travel plans or interests in the area will want to monitor for forecast updates in the coming days as this late winter season storm takes shape.

FORECAST CONFIDENCE & DEVIATIONS: Blended NBM90 with winds and gusts for Thursday morning into the evening.

Confidence in snow amounts have increased slightly starting Thursday night but the confidence level is moderate at best. Amounts and placement will continue to be tweaked through this week.

TFJ/GAH

AVIATION

UPDATED: 0715Z

FLIGHT CAT RANGE: VFR - IFR

DISCUSSION: Early morning snow showers could impact KSDY and KGDV and exit by 08Z. The snow on top of an already semi-moist atmosphere early this morning along with clear skies and light winds has begun to form up fog. This will likely last into 12 to 15 Z where it does form and then clear at sun-up. Conditions could drop as low as MVFR or maybe IFR before exiting at sun-up and leaving VFR conditions through the rest of the cycle.

Some snow showers could pop up around or after 06Z Wednesday night. These would bring ceilings and maybe visibility down for KGGW right at the end of the cycle before slowly spreading east.

WIND: W and light this morning. Increasing to 10 to 20 gust 25 kts this afternoon. Then calming to SW and variable in the evening hours.

GAH

GGW WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory from 10 PM this evening to noon MDT Thursday for Central and Southeast Phillips-Central and Southern Valley-Daniels-Northern Phillips-Northern Valley-Sheridan- Southwest Phillips.

High Wind Warning from 5 AM to 9 PM MDT Thursday for Central and Southeast Phillips-Central and Southern Valley-Daniels-Dawson- Eastern Roosevelt-Garfield-McCone-Northern Phillips-Northern Valley-Petroleum-Prairie-Richland-Sheridan-Southwest Phillips- Western Roosevelt-Wibaux.

Winter Storm Watch from late Thursday night through Saturday afternoon for Garfield-Petroleum-Southwest Phillips.