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.

Wintry weather forecast by next weekend

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.

Next chance for snow about a week away

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.

Some snow and cold for Opening Day

Sunday, November 29, 2020

Bluebird skies and temperatures in the upper thirties are over the Steamboat Springs area this Sunday afternoon. After another day like today on Monday, a storm will cross the Pacific Northwest coast Monday morning and affect our area starting Tuesday with low intensity snowfall and colder temperatures. The cold will hang around for Wednesday, along with some likely non-accumulating afternoon showers, and most of Thursday before we see warming and drying heading into and through the weekend.

Lift-served skiing is back in Steamboat Springs this weekend as the local Howelsen Hill, which is the the oldest operating ski area in North America, opened on Saturday and offered free skiing on Sunday. Opening weekend was graced by warm days and brilliant blue skies, with more of the same weather forecast for Monday. The Steamboat Ski Area will open on Tuesday with the opposite weather as an incoming storm is forecast to bring cooler temperatures and some light snowfall.

That storm is forecast to cross the Pacific Northwest coast early Monday before splitting as it first travels across the northern Rockies and then over our area by Tuesday. Splitting storms are always a forecast challenge due to the uncertainty of how the energy is partitioned between the two branches of the storm, and the storm for Opening Day is no different.

Even at this close range, the weather forecast models disagree on how strong the southern part of the split storm will be and whether it passes over our area or drifts to our west. Of course, we’ll see the most snow if the storm passes overhead, but even then the storm lacks much moisture and only an inch or two are expected at the lower elevations with twice that much possible up high. A stronger split storm traveling further west would further decrease even those meager accumulations.

Regardless, it looks like cooler temperatures will be in store for Tuesday, Wednesday and possibly Thursday as the northern branch of the split storm eventually passes close enough to keep the cold air around. There may be some light snow showers that accompanies the northern branch when it moves by later Wednesday, but again accumulations, if they occur, would be meager.

We’ll start cold Thursday morning, and whether we stay cold through the day will be determined by the evolution of this complicated storm. By Friday, it appears all of the forecast uncertainty will be for areas to our west, south and east as an amplifying ridge of high pressure moves overhead and brings dry air and warming temperatures.

This gorgeous weather is expected to continue through next weekend and into the beginning of the next work week. For those anxious for more winter weather, longer-range weather forecast models have been indicating some sort of storm and a pattern change starting around the following weekend. I should have a better idea about this possible return of winter weather by my next regularly scheduled weather narrative on Thursday afternoon.

Nice weekend of weather ahead

Thursday, November 26, 2020

It is snowing lightly this Thanksgiving afternoon in Steamboat Springs, with 3” of what looks like low-density, fluffy accumulations on the Steamboat Powdercam and about an inch on my deck. Snows will taper off by midnight after several more inches fall at the higher elevations before a chilly Friday morning is followed by sun and warming temperatures that will persist through Monday. And it now looks like we have cooler temperatures with some snow chances to commemorate our rescheduled Opening Day at the Steamboat Ski Area on Tuesday, 1 December.

Our current wintry Thanksgiving is courtesy of a splitting storm that is bringing enough moisture and energy over our area for some persistent snowfall of light intensity. Cold air will continue to infiltrate our area overnight behind the storm for a chilly Friday morning with low temperatures around zero, which is about ten degrees below our average of 11 F. But a ridge of high pressure that has built behind the storm moves over our area starting on Friday for warming temperatures and sunny skies.

More gorgeous weather is forecast for Saturday before a a grazing storm moving through the top of the ridge of high pressure may be close enough to bring some cooler air and clouds for Sunday. But if any clouds do appear, they will be chased away by a warm and sunny Monday.

There has been a lot of uncertainty in the weather forecast models starting around Tuesday, and the latest consensus is that a storm moving through the Gulf of Alaska will make landfall along the Pacific Northwest coast early Monday before moving first to the east and then the southeast before it eventually passes overhead on Tuesday. That early easterly trajectory looks to allow the Cascades to grab most of the moisture from the storm, though the storm stays cold and several inches of snowfall is now looking possible through the day Tuesday and overnight.

The storm is forecast to form some sort of eddy nearby or overhead, and it may not be completely cut off from the jet stream which makes predicting its movement difficult. And that eddy may itself split, leaving some of the storm near our area and some migrating to the southwest. Right now, it looks like precipitation ends early Wednesday as the cold air sticks around for the day before we see a cold Thursday morning give way to sun and warming temperatures.

And though there is an active jet stream forecast over the Pacific during this time frame, our weather is looking quiet as we head into the following weekend. Stay tuned to my next regularly scheduled weather narrative late on Sunday afternoon for an update to our Opening Day weather, and enjoy the beautiful upcoming weekend.

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