Tuesday, December 16, 2014
Now that the official and well-forecasted 19” storm total reported at mid-mountain is behind us (after the Steamboat ski area reported 2” this morning), attention turns to the unsettled pattern forecast to persist for at least the next week. Currently, light snow is falling and will continue through the early afternoon before ending. I expect accumulations of only an inch or two due to the brief duration of this first event.
Concurrently, a split trough has entered the west coast, and it looks like the southern part may produce precipitation over our area as soon as tomorrow and lasting through Friday. There is surprising disagreement between the American short-range NAM and the American medium-range AVN as to if this precipitation will occur for our area as the NAM is dry for us. I’m inclined to side with the moister AVN since that model tends to do produce a better forecast for our area in moist northwest flow with falling temperatures.
However, this model also tends to overpredict precipitation in the pre-frontal environment when southwest flow dominates, so I expect only minimal accumulations, if at all, during the day tomorrow. A weak front passes through near the end of the day, and that is when I expect snowfall to increase and become steadier.
Temperatures rise on Thursday during the day and this will lessen the snowfall. A trailing weak wave passes through Thursday night and should keep light snowfall going during the day Friday. At this point, I would expect around 4-8” between Wednesday and Friday afternoons.
A very brief break Friday night into Saturday morning before another splitting wave is forecast to bring another round of light snow starting Saturday afternoon and lasting through Sunday morning, likely leaving only several inches by noon Sunday.
Another very brief break that may only last Sunday afternoon before a period of moist northwest flow sets up over our area by Sunday night. Snows will be mostly light through Tuesday, though an enhancement may occur later Monday as some cool air moves over the area.
Models have been somewhat consistent in forecasting a major storm to cross the west coast midweek. This is another splitting storm, but this time the split occurs well off the coast and the dominant northern branch phases with some bitterly cold arctic air currently over northern Canada. The interaction between the Pacific and Canadian airmasses is forecast to lead to a major storm around Christmas for the northwestern US and Rockies. Current timing has heavy snows and plunging temperatures for us on Christmas Day, though of course that is subject to change as that forecast is a week away. In fact, the very latest European ECMWF has more interaction between the Pacific and arctic airmasses over the Gulf of Alaska early next week, and that might draw more cold air into the storm and change its trajectory.
Earlier model runs has this cold air remaining over our region for a while, but now, after forecasting a still cold post-Christmas weekend, they are forecasting warming temperatures by early in the next workweek.