textproduct: Glasgow

DISCUSSION

KEY MESSAGES: - Isolated rain and snow through this evening.

- A wintry mix including freezing rain possible on Christmas Day. - Another round of mixed precipitation possible Friday into Saturday. WEATHER PATTERN OVERVIEW: A weak push of moisture from the south has resulted in a weak band of precipitation occurring, with very little accumulation expected. The band will move from south to north across the area before ending late this evening. A broad ridge across the CONUS is expected to become more amplified through the week, with the east Pacific trough digging southward along with the Gulf of Alaska low. This will lead to a slow increase in moisture streaming into Montana as the atmospheric river pushing into southern California spreads across the Great Basin.

With the weak winter thermal boundary over central Montana, as slight ripples occur in the flow and moisture increases, overrunning precipitation is possible. Thermal profiles with warm air aloft and a colder boundary layer will create conditions for freezing rain and ice pellets over mainly the central part of the CWA from any precipitation that occurs, intermittently from Wednesday night 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: Increased pops on Day 1 to account for the weak band of precipitation moving through the area. Increased winds for the area for Day 1 and 2, especially around Glasgow and Vandalia. Increased PoPs slightly for Days 2 and 3 since there is decent agreement among CAM models of freezing rain and ice pellets occurring.

There is moderate to high confidence in temperatures for the next 6 days of the forecast. There is high confidence of less than 0.02 hundredths of precipitation occurring through this evening. There is moderate to high confidence in freezing rain occurring Wednesday night into Thursday night west of HWY 24, with low confidence in precipitation accumulation. There is moderate confidence of a wintry mix occurring on Friday. There is high confidence a winter weather headline being issued for Wednesday night into Thursday, but the uncertainty lies in freezing rain accumulation amounts and surface temperatures getting above freezing at the time the precipitation moves through.

Moderate to high confidence for widespread freezing rain on Thursday, with lower confidence for the QPF amount.

AVIATION

UPDATED: 2030Z

FLIGHT CATEGORY: VFR, Isolated IFR.

DISCUSSION: Widely scattered precipitation is moving through the region from south to north along a stationary surface front. There is high confidence of VFR conditions remaining in place through 10Z. There is low to moderate confidence in a surface east and southeast wind aiding in isolated IFR conditions developing between 10Z and 18Z.

WINDS: For KGGW, southeast winds at 7 to 15 knots, becoming northeast after 6Z, becoming southeast again after 18Z. For all other sites, east at 6 to 12 knots, becoming light and variable after 4Z, becoming east at 7 to 13 knots after 11Z.

GGW WATCHES/WARNINGS/ADVISORIES

None.