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The upper airflow is bringing much colder air toward us both aloft and at the surface.  An arctic air mass is being pushed South by a strong jet stream (see airflow graphic above) and will move down behind a frontal system to our North. Another storm has pushed South through Northern California and Southern Oregon both adding up to the possibility of some snowflakes even reaching the Valley floor.

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Advisories: A WINTER WEATHER ADVISORY IS IN EFFECT UNTIL 10 PM MONDAY FOR THE NORTH AND CENTRAL COAST RANGE OF OREGON,   THE PORTLAND AREA, THE NORTH CASCADES FOOTHILLS AND THE FOOTHILLS OF LANE COUNTY, THE NORTH CASCADES AND THE CASCADES OF LANE COUNTY, AND THE UPPER HOOD RIVER VALLEY. A WINTER WEATHER ADVISORY IS IN EFFECT UNTIL 4 AM MONDAY ABOVE 1,000 FT. FOR THE CURRY COUNTY COAST AND CENTRAL DOUGLAS COUNTY,  AND ABOVE 1,500 FT. FOR EASTERN CURRY COUNTY, JOSEPHINE COUNTY,  THE EASTERN DOUGLAS COUNTY FOOTHILLS, AND JACKSON COUNTY. A WINTER WEATHER ADVISORY IS IN EFFECT UNTIL 8 AM MONDAY FOR THE SOUTH CENTRAL OREGON CASCADES.

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Here are your detailed forecasts. **

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Forecast for the Southern and lower Mid Willamette Valley including Eugene-Springfield and Albany-Corvallis: Mostly cloudy with showers this evening, showers (possibly mixed with snow down to the valley floor) likely (60%) tonight (0.25 in. of rain possible), mostly cloudy with showers likely (60%) Monday AM, showers in the afternoon (snow level 1,200 ft. up to 1 in. of snow possible down to that level) (0.25 in. of rain possible), rain and snow showers in the evening, a (40%) chance of  snow showers late Monday night and colder (up to 2 in. of snow possible), a mix of clouds and sun Tuesday and Wednesday, and partly cloudy each night lows 34-22 rising to near 30 Wednesday night highs 37-33-36. Mostly cloudy Thursday (Thanksgiving Day), mostly cloudy at night with a slight (20%) chance of rain, then mostly cloudy with a good (50%) chance of rain Friday and Friday night,  then rain likely (60%) Saturday through Sunday highs 42-46 lows 35-38. (seasonal averages highs 50 low 37)

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Forecast for the Umpqua Basin including, Roseburg: Cloudy with rain and snow showers and possible isolated thunderstorms this evening, rain and snow showers late tonight (snow level 2,000 ft. falling to 1,000 ft. late tonight 2-3 in. of snow possible),  rain and snow showers likely (60%) Monday AM, rain and snow showers in the afternoon (snow level 1,500 ft. 3-4 in. of snow possible), mostly cloudy with rain and snow in the evening, rain and snow likely (60%) late Monday night (snow level 500 ft.2-3 in. of snow possible), mostly cloudy Tuesday AM with  a slight (20%) chance of snow showers, sunny in the afternoon then partly cloudy Tuesday night lows 35-25 highs 42-33. Patchy AM fog Wednesday then partly cloudy in the afternoon, partly cloudy with patchy fog and freezing fog Wednesday night, patchy AM fog and freezing fog Thursday (Thanksgiving Day) then mostly cloudy, partly cloudy with a slight (20%) chance of evening rain, a slight (20%) chance of rain and snow late Thursday night, mostly cloudy with a (20%) chance of rain and snow Friday AM, a good (50%) chance of rain Friday afternoon through Saturday, rain likely (60%) Saturday night, rain and snow likely (60%) Sunday AM, then rain likely (60%) Sunday afternoon highs 32-47 lows 27-42. (seasonal averages high 53 low 39)

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Forecast for the South Oregon Coast including Coos Bay and North Bend: Cloudy with coastal showers and isolated thunderstorms this evening, then showers late tonight, rain and snow showers with isolated thunderstorms this evening inland,  then rain and snow showers late tonight (snow level 2,000 ft. falling  to 1,500 ft. late with no accumulation expected), AM coastal showers likely (60%) Monday then afternoon rain, AM rain and snow showers likely (60%) inland Monday then afternoon rain and snow showers (snow level 1,500 ft. 1 in. of snow possible, evening coastal rain, then rain likely (60%) Monday night  with rain and snow inland (snow level 500 ft. Monday night up to 1 in. of snow possible above 1,000 ft.) , breezy Monday night (wind: NW 15-25 mph), mostly cloudy Tuesday AM, mostly sunny in the afternoon, and partly cloudy Tuesday night lows 37-27 highs 47-40. Patchy AM fog and mostly cloudy Wednesday, partly cloudy with fog late Wednesday night, patchy AM fog Thursday (Thanksgiving Day) then mostly cloudy, partly cloudy Thursday night with a slight (20%) chance of rain, mostly cloudy with rain likely (60%) Friday, a good (50%) chance of rain Friday night, and mostly cloudy with rain likely (60%) Saturday through Sunday highs from 32-43. (seasonal averages high 55 lows 42).

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Forecast for the Cascades of Lane County:  Mostly cloudy with snow showers tonight (4-8 in. of snow possible), snow showers and breezy (wind: W 10-15 mph increasing to W 15-25 mph in the afternoon Monday (6-10 in. of snow possible), mostly cloudy with snow showers and colder Monday night (4-8 in. of snow possible) with wind chill temperatures falling to -15 to -20, a mix of clouds and sun with a slight (20%) chance of AM snow showers Tuesday, partly cloudy Tuesday night, a mix of clouds and sun Wednesday, and partly cloudy Wednesday night snow level at the surface through Tuesday, free air freezing level at the surface Tuesday night and Wednesday, and 2,000 ft. Wednesday night lows  22-9 warming 13-22 Tuesday and Wednesday highs holding near 22. Mostly cloudy Thursday (Thanksgiving Day), mostly cloudy  with a slight (20%) chance of rain Thursday night, a good (50%) chance of rain Friday and Friday night. rain likely (60%) Saturday and Saturday night, then mostly cloudy with a good (50%) chance of rain Sunday free air freezing level 2,500 ft. Thursday, and snow level 3,000 ft. Thursday night, and a snow level 2,500 ft. Friday, 4,000 ft. Friday night, 3,500 ft. Saturday and Saturday night, and 2,500 ft. Sunday highs 32-35 lows near 25.

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**Because weather forecasting is a combination of science, intuition, and timing there can be no absolute guarantees that individual forecasts will be 100% accurate. Nature is in a constant state of flux and sudden unexpected weather events can happen.