It will be a quiet night and a nice start to Saturday though clouds will increase through the day. There could be a light shower or sprinkle, mainly west of Puget Sound during the day but most of us will stay dry. Highs will top out around 60 in Seattle.
Rain sweeps in Saturday evening near and just after dark and rain will be heavy on Saturday night into the pre-dawn hours of Sunday morning as a cold front sweeps through. Rainfall totals will be over a quarter-inch in most areas and with leaves down, we could have some brief urban flooding Saturday night and early Sunday, so drivers should use caution as there could be standing water in darkened streets and intersections.
On Sunday, expect showers, sunbreaks and cooler temperatures with highs only in the low 50s. We could have an isolated thunderstorm on Sunday afternoon, particularly if a Puget Sound Convergence Zone develops north of Seattle. In the mountains, snow levels will be above 5,000 feet while the heaviest precipitation occurs, but by Sunday afternoon going all the way into Monday morning, snow levels will drop to below 4,000 feet. It will likely remain too warm during the day Sunday for snow at Snoqualmie Pass but conditions could change if precipitation is unusually heavy in spots, as that can drag the snow level lower.
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So how much snow? Right now, the forecast is for up to three inches of snow at Stevens Pass from Saturday afternoon through Monday morning and an inch or less (possibly none) at Snoqualmie Pass, with that primarily more likely Sunday night.
But we are dealing with a Puget Sound Convergence Zone, so to mention again, if the convergence zone is aimed at Stevens or Snoqualmie passes and has heavier precipitation, more snow could fall. It will be a situation that will just have to be watched hour-by-hour Sunday and early Monday.
Rain showers and mountain snow will taper off through the morning Monday and it stays chilly. Monday night will be the coldest night of the season thus far with widespread Tuesday morning temperatures in the 30s (my forecast for Tuesday morning low is 39°.) There will be some frost and some of the coldest spots, particularly south of Puget Sound could get down close to freezing to start Tuesday.
Some chances for rain and mountain snow return Wednesday and Thursday of next week.
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