Sunday, December 13, 2020
The skies have cleared behind the storm on Saturday in Steamboat Springs, with cold temperatures in the single digits both in town and at the top of the Steamboat Ski Area as of 11 am this Sunday morning. Though temperatures will warm under sunny skies for most of the day, they will stay cold and five to ten degrees below our in-town average of 28 F. Clouds will increase ahead of our next storm timed to begin by Monday afternoon, with another significant storm forecast for the end of the work week.
7” was reported on the Steamboat ski report this morning, with 11” observed on the Steamboat Powdercam at the top of Sunshine Peak. Of those 11”, 4” fell between 4:10 pm and 4:40 pm Saturday afternoon as a storm cell passed overhead, which is an 8” per hour snowfall rate! The snow that fell was comprised of planar dendrites, which are the familiar two dimensional branch-shaped snow crystals. Conversely, when the branches spread out in all three dimensions, they are referred to as spatial dendrites, and both crystal types can lead to rapidly accumulating snowfall. So we had that elusive combination of heavy snowfall rates comprised of fluffy, low-density snowfall; exactly the type of snow Steamboat is famous for.
Our next storm has crossed the northern West Coast with precipitation already occurring in Nevada. Clouds will increase as the storm moves to the southeast, with generally light snowfall rates expected over our area from Monday into Tuesday. This will be another cold system, though we will likely see warmer overnight low temperatures than last night as the clouds will act like a blanket to insulate the surface of the earth. I would expect 3-6” by the Tuesday morning report with another inch or two falling Tuesday morning before the snowfall becomes more showery in the afternoon and tapers off by sunset.
Though a transient ridge of high pressure is forecast over our area early on Thursday, ripples of moisture and energy will move down the east side of the approaching ridge on Wednesday, possibly leading to some light snowfall that would leave minimal accumulations.
Any sunshine on Thursday will be short-lived as a significant storm crosses the northern West Coast Wednesday night and moves over our area on Friday. Clouds should increase by Thursday afternoon with snowfall commencing soon after that and lasting through the day Friday before tapering off Friday night. There is uncertainty with respect to the evolution of the storm, with the European ECMWF keeping the storm stronger and more consolidated than its American GFS counterpart. Let’s see how this storm develops in the weather forecast models over the work week and I’ll have a snowfall guess by my next regularly scheduled weather narrative on Thursday afternoon.
At this point, longer range weather forecast models have a break in our active weather pattern through the weekend and into the following work week, though we will remain close enough to the jet stream and resultant storm track so there will likely be periods of sun and clouds. There is agreement among these models that some sort of significant storm will be around by midweek as we head into the Christmas holiday.
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.
Sunday, December 6, 2020
Another bluebird day is over the Steamboat Springs area this Sunday noon with temperatures in the mid-thirties, on their way to over ten degrees above our average high of 31 F. More of the same is expected through midweek before the atmosphere undergoes a pattern change which brings wintry weather back to our area by Friday.
A storm currently over the Oregon - Nevada border has formed an eddy cut off from the main jet stream, and is forecast to move to the south-southwest through the day Monday before vacationing for a few days off the coast of the Baja peninsula. Meanwhile, a piece of a strong storm currently near the Aleutian Islands is forecast to move through the Gulf of Alaska and cross the Pacific Northwest coast on Wednesday, followed by the main part of the Aleutian storm on Thursday.
All three of these storms will interact to some degree, bringing an end to our warm and sunny weather which is expected to last through the day Wednesday. Even as the lead part of the Aleutian storm moves across the northern Rockies on Thursday, it will also force the vacationing eddy to to move along the southern U.S. border with Mexico. There was hope in my earlier forecast that some moisture rotating around the eddy would be pulled northward into the northern storm as it approached our area, but it appears now that we will only see some clouds and cooler temperatures on Thursday as that northern storm will be quite weak.
However, there will be a strong interaction between that eddy and the northern storm as the two storms move to our east; in fact the storms are forecast to merge into a single stronger storm that consolidates around Kansas. Interestingly, moisture originally from that eddy is then forecast to rotate counterclockwise around the merged storm and move over our area by Friday ahead of the bulk of the Aleutian storm. Colder temperatures and snowfall of generally light intensity are expected for Friday into Saturday morning as the main storm moves through. It’s probably too early to throw numbers around for forecast snow amounts at this point due to the complicated interaction between all of these storm pieces, but I should have a good idea of snow accumulations by my next regularly scheduled weather narrative on Thursday afternoon.
A transient ridge of high pressure is then forecast to move over the West behind the storm complex after Saturday, though weather forecast models disagree on the amplitude of the ridge and whether we will see light snow for a time on Sunday. Both agree on a dry start to the following work week, but also agree on a currently good-looking storm for our area around midweek. And for what it’s worth, the longer-range forecasts are predicting an active and wintry weather pattern to continue after mid-month.
Thursday, December 3, 2020
After the storm on Opening Day, a cold and dry air mass has settled over the Steamboat Springs area, bringing cold nights and sunny days. There won’t be much change to our weather for the upcoming week, though we can look forward to warming daytime highs closer to our average of 31 F. There is hope, however, that our area will see snow chances return in about a week.
That Opening Day storm was far more productive than advertised, with 6” reported at mid-mountain on Wednesday morning and 11” shown on the Steamboat Powdercam at the top of Sunshine Peak behind Patrol Headquarters, most of which fell during the day Tuesday. Snow density was very low thanks to the cold temperatures which encouraged the formation of dendrites, which are the classic and familiar branch-shaped snow crystal. The branches of the dendrites allow lots of space to separate each fallen crystal which inflates the depth of accumulated snowfall.
With clear sunny days and cool nights, the most interesting aspect of our upcoming week’s weather will be the temperatures, specifically the formation of night time temperature inversions. These occur when cold air pools at the lower elevations, becoming colder than the air aloft, which is the opposite of the normal atmospheric temperature profile which cools with height. For example, the low temperature this morning was -2 F at the Bob Adams airport, -6 F at my house near the base of the mountain (lower in elevation than the airport) and 4 F at the top of Mt. Werner. The conditions that support the formation of temperature inversions, mainly snow cover (the fresher the better), clear night skies, light winds and low sun angle will persist this upcoming week so expect the cold starts to the morning with warmer temperatures found higher on the mountain to continue.
A pattern change may be in the offing though, as a storm traveling across the Gulf of Alaska makes landfall in the Pacific Northwest mid-weekend and forms an eddy cut off from the jet stream. This eddy is forecast to dive through the western Great Basin early next work week, taking up residence near Baja and southern California, before another Gulf of Alaska storm makes landfall, again in the Pacific Northwest, around midweek.
Eventually, these storms will interact, with the southern storm possibly transporting subtropical moisture northward that can be incorporated into the northern storm or perhaps being ejected out ahead of the northern storm. As might be expected this far out, there is a lot of uncertainty as to how these storm will interact, though longer-term weather forecast models agree that a ridge of high pressure builds in the Gulf of Alaska behind that second northern storm. This may allow favorable and moist northwest flow to set up over our area around the next weekend, though it is unclear for how long that may persist
Enjoy what will likely be a gorgeous upcoming week of weather, and I should know more about this pattern change in my next regularly scheduled weather narrative on Sunday afternoon.