Christmas Day storm brings snow and cold temperatures
Tuesday, December 23, 2014
This last storm was disappointing for us, as most surrounding areas received snow in the 18-36” range. I mentioned in the last forecast that any warming aloft is cause for concern. Indeed, freezing rain started on the hill about 2pm Sunday afternoon after a morning of heavy snowfall, which was eerily similar to the Opening Day Ice Storm. Luckily, there was minimal damage to the snowpack this time around, though the lack of accumulating snowfall surely hurt.
Unfortunately, I don’t have a good explanation of why we are getting these very unusual freezing rain events. I’ve sent emails to the National Weather Service and Colorado Avalanche Information Center asking for their opinions, but they are so concerned with future operations that the resources to investigate past events are scarce. I mentioned in the last storm forecast that warming aloft causes my forecasts to lean pessimistic, and apparently I need to increase that negative bias in the future.
After unsettled weather for today and tomorrow, attention turns to the impending Christmas Day storm, currently located in the Gulf of Alaska. This storm splits as it enters the west coast late Wednesday, but a considerable amount of energy is forecast to be in the southern branch as this portion of the storm traverses the Great Basin. Light snow should start around midday on Christmas and we should have a burst of heavy snow when the front moves through later that afternoon or evening. Most of the energy will remain south of our area, but we should continue to receive lighter snow behind the front, leading to 4-8” by the Friday morning report.
It does appear the flow will eventually turn to the northwest sometime on Friday, and that may allow for snowfall to keep accumulating through the day under much colder temperatures. Coincidentally, after the just-passed storm earlier in the week inundates the East Coast, it will help form the Hudson Bay vortex, which is one lobe of the Polar Vortex which received much media attention last year. The counter-clockwise rotation around this vortex allows the bitterly cold arctic air in the Canadian Plains to move southward, enhanced by energy entering the west coast from the Pacific.
Some of this Pacific energy will trail the Christmas storm and move west of us later Friday night, keeping snow showers going through early Saturday morning and leaving another 2-5” for the morning report before a break later in the day. Additional minor waves keep the unsettled and cold weather present from Sunday through midweek, leading to a general forecast of 1-4” for the Monday through Wednesday morning reports.
Current forecasts have a more significant wave bringing a threat of heavier snows around New Years Eve day, but the models are struggling with the westward and southern extent of the cold air, lending uncertainty to that forecast.
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