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DISCUSSION

KEY MESSAGES:

- First winter storm of the season to impact northeast Montana.

- Accumulating snowfall expected tonight.

- Wintry travel impacts possible for Thanksgiving holiday travelers.

WEATHER PATTERN OVERVIEW:

Upper trough moving across the Pacific Northwest this morning will push a low pressure system through eastern Montana today. Warm front will lift north today, followed by the low pressure in the afternoon, and cold front tonight. Main concern is precipitation type with the warm front, as sounding suggest a slow moistening of the atmosphere, delaying precipitation until mid levels cool enough to support ice in the clouds for rain or snow instead of freezing rain. The current observations east of divide also support a delays start of precipitation. During the afternoon, temperatures will warm across most of the area for rain, with a wet snow possible to the north of Hwy 2.

By this evening, as the colder air moves south from Canada, precipitation will change to all snow, with increased chance for accumulations. Blowing snow is also possible with the increasing northwest winds.

Tuesday morning will see the system exiting to the east with some lingering light snowfall across the Big Sheep Mountains east into North Dakota. Tuesday afternoon will be cold (highs below freezing for most locations), but the sun should peak out by the afternoon.

Ensembles continue to indicate potential for more snow for Thanksgiving and beyond with colder temperatures for next weekend. There continue to be significant variations in precipitation potential in the models and ensembles at this time.

FORECAST CONFIDENCE & DEVIATIONS: Deviation from NBM are limited to increasing winds for Mondays storm system.

Confidence for the rain/snow event today into Tuesday is high. However confidence in snow amounts remains moderate with snow amounts ranging from zero to 5 inches.

Later in the week, the wider model spread increases uncertainty regarding snowfall.

AVIATION

VFR dropping to MVFR/IFR from late morning into the afternoon. Ceilings and visibility will lower from west to east as an upper trough punches in through the day on Monday, bringing a mix of rain and snow during the day, turning to all snow overnight. Increasing west winds will also produce blowing snow during the early morning hours on Tuesday.

EQUIPMENT: KOLF and SDY will remain AMD NOT SKED until repairs can be made.

GGW WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory until 5 AM MST Tuesday for Central and Southeast Phillips-Central and Southern Valley-Daniels-Dawson- Eastern Roosevelt-McCone-Northern Phillips-Northern Valley- Richland-Sheridan-Southwest Phillips-Western Roosevelt-Wibaux.