Active weather pattern on our doorstep

Thursday, December 10, 2020

Temperatures a few degrees above our average of 29 F and cloudy skies are over the Steamboat Springs area this Thursday noon. A well-advertised pattern change is on our doorstep, with several chances for snow over the upcoming week, and likely beyond.

An eddy that was off the Baja Coast earlier this week has been forced eastward into the Desert Southwest ahead of a storm currently crossing the Pacific Northwest. The Pacific Northwest storm will elongate and weaken as it moves southeast across the Great Basin today, forcing the eddy to move across southeast Colorado tonight, first bringing precipitation to the southern Colorado mountains and then the Colorado Plains, including the Front Range.

Interestingly, and as discussed in last Sunday’s weather narrative, moisture from that eddy will move counterclockwise around the eddy and be incorporated into the Pacific Northwest storm as it approaches our area on Friday. We should see a good chance for some light snow on Friday and Friday night as the weakened Pacific Northwest storm moves overhead, with 1-4” expected at mid-mountain by the Saturday morning snow report.

There seems to be some confusion as to what I mean by light snowfall, and I am referring to the intensity of the snowfall, or the rate at which it falls. Technically, the National Weather Service classifies intensity by its affect on visibility, so that heavy snowfall limits visibility to under a half kilometer, moderate snowfall limits visibility to between one half and one kilometer and light snowfall allows visibility of one kilometer or greater. Practically, heavy snowfall usually coincides with snowfall rates of about an inch per hour or greater, moderate snowfall of around a half inch to an inch per hour and light snowfall less than that.

Note that the rate at which the snow falls is not necessarily related to the density of the fallen snow, which is how much moisture the snow contains, or how much it weighs, and ultimately how it skis. To keep things clear, I will attempt to use light, moderate and heavy to refer to the intensity of the snowfall, and refer to the weight of the snow through density, or perhaps a descriptive term like fluffy.

So, after the light snowfall on Friday, another storm is forecast to cross the Pacific Northwest coast Friday night and begin heavier snowfall across our region starting Saturday afternoon that will extend into the evening. Colder air will be associated with this storm, so not only will we see moderate to perhaps heavy snowfall at times, but the snow will be lower-density and fluffier than what occurred on Friday. Depending on how far into the evening the snowfall continues, we could see as much as 4-8” of fluffy snow by the Sunday morning ski report at mid-mountain. Travel may be difficult at times during the heavier showers, especially over Rabbit Ears pass from about Saturday afternoon through midnight.

A transient ridge of high pressure then translates over our area on Sunday ahead of another storm that crosses the Pacific Northwest coast on that day. After our recent string of unseasonably warm days, with the high temperature yesterday reaching 49 F, twenty degrees above average, expect a cold-feeling day on Sunday with some sun and temperatures around or below average.

Snow looks to begin again on Monday, becoming moderate to heavy at times in the afternoon as the cold front associated with the storm passes through. Snow showers will continue overnight before tapering off during the day Tuesday in the favorable, moist and unstable northwest flow. This looks like another moderate event, though I’ll refrain from guessing the snowfall amounts until my next regularly scheduled weather narrative on Sunday afternoon.

There is a fair bit of weather model forecast uncertainty starting midweek with regards to another approaching storm, and it is not clear if we get a weak storm around Wednesday or a stronger storm for later in the work week. I’ll know more about the Monday storm and the following weather by my next weather forecast on Sunday.