December 1, 2018 – Mountain snow today with snow levels down to 4000 feet. Mountain travel difficulties likely through the evening hours. Dry Sunday and Monday with morning valley fog. Next chance of precipitation next Tuesday.
Pacific frontal band now moving on to the north coast. Scattered light showers in the diffluent flow ahead of the front have been falling through last evening and the morning hours with forecast area steadily filling in as the main cold front approaches. Mt. Shasta city showing light snow and about 34 degrees so snow probably sticking somewhere around 4000 feet over Shasta county. This goes along well with current snow advisory now in place for the Shasta lake area/northern Shasta county and coast range which is expecting up to about 4-8 inches of snow over the next 12-18 hours.
Light snow has reached the Sierra this morning as well. Snowfall totals still expected to reach heavy snow criteria today even though models have again edged back on expected snowfall amount. Breezy winds will also add to the equation with gusts up to 30 mph bringing hazardous travel conditions at times.
Without orographic aid, precipitation amounts in the valley will be fairly light and generally 1/2 inch or less through this evening including the recent burn areas. Therefore, significant debris flows are not expected with this system.
Main upper low shifts into the Great Basin tonight and by Sunday morning, any lingering showers should be confined to the Sierra Cascade range and northern mountains still under cyclonic flow. Over the central valley, there should be enough clearing to allow cooling and a real possibility of morning fog. Models do not indicate dense fog at this time.
By Sunday afternoon, northerly flow behind the retreating low will bring drying and precipitation should end all areas. Cool air filtering into the region will keep daytime highs several degrees below normal. Upper ridging will bring continued dry conditions on Monday with fair skies bringing another good chance of valley fog in the morning hours.
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Overall airmass warms a bit on Monday but cloud cover starts spilling in in the afternoon so not expecting much warming. Models fairly consistent in approaching next Pacific frontal system to the coast on Tuesday. Models differ on timing and positioning of this next system so still a lot on uncertainty in this time period but indications are that at least some overrunning precip will be spreading over the forecast area by Tuesday afternoon.
Extended Discussion (Wednesday through Saturday)
Wet weather pattern continues through next week with below normal temperatures. An upper low gradually moves inland Wednesday and Thursday, bringing continued chances for precipitation. Rainfall amounts are currently expected to be relatively light, with a few inches of snow currently possible in the mountains. Snow levels should be around 4500-5500 feet with this relatively cool system.
Light lingering showers are expected Thursday, mainly in the Sierra by later in the day. Drier weather returns Friday as shortwave ridging develops. There is some potential for wet weather to return Saturday, but this remains uncertain with continued model disagreement.