The strongest storm forecast to affect the area so far this winter season is beginning to take shape in the northern Gulf of Alaska as seen in the latest IR satellite image. This storm will pull in a significant amount of cold air and moisture as it moves to a position just off the northern California and southern Oregon coast by Thursday. Ahead of the storm, clouds and some afternoon winds will increase by Wednesday afternoon. By Thursday, snow will develop and become heavy in the Sierra by Thursday, with snow being almost continuous through Saturday. The snow may let up at times as there appears to be three distinct shortwaves moving through the longwave trough over the three day period. In the valleys of western Nevada, pattern recognition and the position of the low would suggest that significant snows may occur in the Reno-Carson City-Minden-Gardnerville areas as well with possibly a mix of rain and snow to start the event by Thursday afternoon.
Looking at precipitation amounts, forecast models have been in very good agreement on the amount of liquid precipitation expected to fall. The WPC 5-day precipitation forecast shows higher amounts of 4-7 inches of liquid equivalent along the Sierra. Amounts of ½ to 1 inch are shown for far western Nevada. The GFS, ECWMF and GEFS are in excellent agreement showing 2-4+ inches along the Sierra and similar amount like the WPC in far western Nevada. A quick look at the SREF forecast (not shown), which only goes through 06Z Saturday morning shows around ½ of an inch of liquid equivalent for Reno, which typically receives the lower end of the precipitation forecast due to the location on the eastern side of the Truckee Meadows.
What will this mean for snow fall potential? Snow fall ratios of 15:1 are likely above 6,000 feet, with ratios closer to 10:1 in the lower valleys of western Nevada. If the forecast precipitation amounts are realized in the Sierra 3-5 feet are likely along the Sierra crest. The Lake Tahoe area will see 1-3 feet with the higher amounts along the west shore of the lake. For the metro areas of far western Nevada, anywhere from 4 inches to a foot (especially above 5,000 feet) are possible. The main issue for the valleys is how much shadowing occurs, time of day the precipitation falls, where the heaviest snow bands occur and some of the precipitation may fall as rain initially, which could limit the amount of snow fall accumulation to the lower end of the range noted above. A plus is with the amount of cold air already in place and expected cold air aloft; it shouldn’t take long for snow levels to fall to the lowest valley floors on Thursday. As a result of the snow fall potential, the Reno NWS has issued a Winter Storm Warning from 10 PM Wednesday through 10 AM Saturday morning for the Sierra and Carson Range. A Winter Storm Watch remains in effect from Thursday afternoon through Saturday morning.
More updates later if forecast thinking and models change as we get closer to this potentially major winter storm.
Weather graphics are courtesy of Weatherbell Analytics and Tropical Tidbits.com.