November 9, 2017 – Rain, high elevation snow, and breezy winds through Friday. Dry weather for Saturday and Sunday. Another system will bring additional precipitation Sunday night and Monday.
Quick update to adjust overnight low temperatures upward. The slow moving system will help to keep temperatures very mild tonight with lows in the mid to upper 50s for many locations in the valley. Mountain valley lows will be warm as well in the upper 30s to mid 40s. Have also adjusted winds along the crest upward for the overnight period with wind gusts up to 75 mph already being reported at one of the higher peaks near Tahoe. Snow levels are staying high overnight and will not be a problem. During the day on Thursday the models are slightly different in the amount of cold air. The GFS is slightly colder than the NAM. The difference would be in when snow levels will drop below I-80. Currently snow levels may drop to around pass levels by late Thursday morning then a little below for the afternoon. This may cause some travel issues for the afternoon and evening hours. Slightly warmer air expected down around US-50 may results in no travel problems during the day.
Large low pressure center is currently off the coast on the Pacific Northwest. A weak band of prefrontal showers moved across the area this morning through early afternoon. Main batch of precipitation associated with the cold front is moving onshore in NW portions of the state this afternoon. This will continue to drop southeast across the area this evening into Tuesday morning with light to moderate rainfall. Rainfall amounts still look on track so only minor changes made. Southerly winds will also increase as front moves through with gusts to around 30 mph in the valley and 60 mph across mountain ridges. Snow levels look to remain above pass levels so expecting minimal travel impacts, though a heavier shower could briefly drop snow levels.
Secondary wave moves across the area Thursday night into Friday with additional light precipitation. Winds will not be quite as breezy as today or Thursday. Snow levels may drop to near or just below pass levels with this wave, but only expecting an inch or two of accumulation on affected roadways. Still may be enough to cause a few delays.
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Ridging briefly builds into the area on Saturday, allowing for dry weather and temperatures a few degrees warmer. Next system looms for the start of next week.
Extended discussion (Sunday through Wednesday)
A Pacific frontal boundary will move across interior NorCal early next week bringing widespread precipitation and mountain snow. Early precipitation estimates suggest about 1-3 inches of precipitation over the mountains, and 0.25-0.75 inches at Valley locations. Snow levels will start out rather high, but accumulating snow will be possible down to pass level by Monday night as the cold air mass aloft moves in. Breezy winds will be possible as the system moves through.
Another system is expected to bring light precipitation across the northern mountains and the northern Sacramento Valley late Tuesday into Wednesday. Forecast remains the same, but the latest model guidance has slowed the onset of precipitation. Therefore, have lowered PoPs and slowed precipitation timing to reflect current model solutions.