Unsettled week ahead with a Sunday night storm and a long-duration event starting mid-week

Friday, February 17, 2017

A storm from the central Pacific that is currently inundating California will split as it crosses the West Coast on Saturday. Some energy ejecting out ahead of the storm will bring the chance of light showers to the Steamboat Springs area tonight and again later Saturday, but the bulk of the storm will stay south of our area.

 A trailing wave of energy  strengthens the northern part of the split later Sunday and brings some cool air and the best chance of accumulating snowfall through Monday morning. Due to the split flow and additional upstream energy, the snowfall forecast for Monday morning is uncertain, but at this point I would expect 4-8” for the President’s Day report as there is some cool, moist and unstable northwest flow for a time.

Unsettled weather will persist after a brief clearing later Monday behind the cool front as waves in the relatively warm Pacific airmass move over the area on Tuesday and early Wednesday.

Meanwhile, a central Pacific ridge builds somewhere around the Bering Sea and the Gulf of Alaska, similar to patterns observed earlier in this winter season.  Cold air from Siberia and the North Pole is forecast to slide southward along the east side of this ridge and begin a likely long-duration winter storm event starting later Wednesday and lasting into the weekend.

The specifics are highly uncertain as some of the cold air is forecast to move southwestward underneath the eastern Pacific ridge and merge with the branch of the Pacific jet stream that undercuts this ridge. If this pattern evolves similar to the pattern observed earlier in the season, which seems likely, then significant snows are possible as the moist Pacific jet stream once again battles the cold air from the northern latitudes over the western states. Current long-term forecasts have March arriving like a lion as this active period looks to last through at least the first week of March.

Active weather returns after a beautiful work week

Monday, February 13, 2017

The disappearance of the Bering Sea ridge has allowed cold air from Siberia and the North Pole to surge into the central Pacific and re-energize the jet stream. A ridge of high pressure that has built off the West Coast in response to the strong Pacific jet stream will translate over the western U.S. during the work week, bringing warm and mostly sunny conditions through Thursday.

Starting around Friday, energy from the Pacific jet will force the ridge of high pressure eastward and bring showers to the western U.S. There are a number of waves of energy that will move through the area for the long President’s Day weekend, and the forecast timing, strength and duration of the precipitation will almost certainly change as we get closer to the weekend. Hopefully, better model agreement and more details will emerge for my late-week forecast.

Right now, the first wave is forecast to move over the Continental Divide on Friday, bringing mostly light snow showers to the Steamboat Springs area during the day.

Another Pacific wave splits as it crosses the West Coast on Saturday, and this may bring some more showers to the area mid-weekend if the parts of the storm are close enough to Colorado. 

A third wave quickly follows the second, and this may bring a better chance of snows to the Steamboat Springs area around Monday before a brief break is advertised ahead of another stormy period that is forecast to close out the month.

Friday night rain turns to Saturday snow ahead of a warm and dry work week

Friday, February 10, 2017

A splitting wave is currently crossing the West Coast and will affect our weather this weekend. The southern portion of the split will form a closed low and dive south to Baja by Sunday as the northern portion of the split screams across the northern U.S. this weekend as an open wave.

Before the Steamboat Springs area feels the effects from the northern part of the storm, energy ejecting out of the southern part of the storm will bring rain showers to elevations below around 9000′ by this evening.

The precipitation will increase in intensity overnight as temperatures begin to cool due to the approach of the northern portion of the storm. Snow levels will drop overnight and into tomorrow morning before the Yampa Valley sees snow, but the timing of that switch is uncertain. Models have trended a bit faster with the arrival of cool air, and current forecasts have the switch to snow occurring early Saturday morning for the valley.

Temperatures will continue to cool through Sunday morning as the northern portion of the storm moves east of our area, but snows should end by later Saturday as moisture quickly erodes behind the diffuse cool front. Snow forecasts for the hill are tough due to the timing of the switch and the temperature-related density of snow, but right now I expect 3-6” of dense snow for the morning report and and additional 3-6” of lighter and fluffier snow during the day Saturday, most of which will occur before noon.

While the main part of this storm ends later Saturday, and some dry air works into northern Colorado by early Sunday, moisture from the Baja low is forecast to move northward and bring some clouds with the chance of light showers later Sunday as it combines with some left-over energy from the northern part of the storm.

 Meanwhile, the Bering Sea ridge present these last few weeks is forecast to collapse, allowing cold air from Siberia and the North Pole to surge into the central Pacific. Initially, a ridge of high pressure will build off the West Coast as the Pacific jet stream is re-energized. This ridge is forecast to translate over the western U.S. during the work week, bringing warm and mostly sunny conditions. However, the re-energized Pacific jet will likely bring more stormy weather sometime around President’s Day weekend or soon thereafter.


The storm that stayed away

Thursday, February 9, 2017

It’s hard to believe that we received so little snowfall from this storm, especially since all guidance pointed to significant accumulations.

I’ve prepared a loop of the Western U.S. IR satellite from 1pm Tuesday, 7 Feb 2016 MST through 7am Wed when numerical models indicated the Steamboat Springs area would have the heaviest snowfall. Colorado is outlined in red, and there is a red dot in northwest Colorado that represents the location of Steamboat Springs. My 6-12” forecast was woefully wrong as we only received about 2” during the afternoon on Tuesday and some rain early Wednesday morning.

Time series of western U.S. IR from 1pm Tue 7 Feb 2017 to 7am Wed 8 Feb 2017

I’ve annotated some of the images in the loop to roughly outline the Pineapple Express snaking through the Great Basin. I’ve also highlighted a large dry area that appeared later Tuesday in yellow.

Rather than Pineapple Express, meteorologists have started calling these wet events with a tropical and/or subtropical connection Atmospheric Rivers, as that descriptive term better captures the sometimes thin and wavy moisture feed.

Two features that likely doomed snowfall for the Steamboat Springs area were the large dry area highlighted in yellow that moved over our area late Tuesday afternoon, and the thinning Atmospheric River of moisture that passed just south of us Tuesday evening.  The southern movement of the Atmospheric River was due to the passage of a correctly forecast weak cool front. There were periodic enhancements along the I-70 corridor that contributed to some 10” reports as the Atmospheric River moved south, but the big winner was Monarch that reported 17” and was the result of the Atmospheric River loitering over that area before it became diffuse and moved back north as a warm front overnight. The passage of this warm front brought the rain and gusty winds observed very early Wednesday morning.

But still, how could the models have gotten it so wrong? This Atmospheric River event was relatively narrow in width and I believe that made it’s measurement problematic. Upper air moisture is measured by balloons released every 12 hours, but their locations are several hundred miles apart or more. It becomes difficult to accurately measure and resolve a narrow band of moisture, and all of the numerical models were initialized with a broader extent of moisture than was actually present.

The result was that snowfall produced under the Atmospheric River was narrower and spottier in areal extent than forecast. This was exacerbated by the narrowing of the Atmospheric River in the latter half of the storm.


Early and late-week storms on tap

Sunday, February 5, 2017

The re-emergence of a strong Bering Sea ridge, which was observed earlier this winter season, has directed cool air from Siberia and the North Pole southward into the Gulf of Alaska while also routing moist Pacific energy underneath in another incarnation of the Pineapple Express.

A complicated weather forecast ensues as the warm Pacific airmass battles the cold northern-latitude airmass for about the next week. Models have trended toward a more diffuse solution with less cold air for the Steamboat Springs area, bringing snow showers to the hill and a rain/snow mix to the valley by Monday afternoon.

Mainly light precipitation should turn to all snow and continue overnight, leaving 1-4” on the Tuesday morning report until a cool front passes on Tuesday, increasing snowfall rates and decreasing snow densities during the day Tuesday in breezy west to northwest flow. Temperatures warm again later Tuesday into early Wednesday ahead of another wave of energy that will graze our area during the day Wednesday, again increasing snowfall rates under continued breezy conditions.

Snowfall estimates for the hill are tough due to the varying temperatures and it’s affect on the snow density, but I would expect 6-12” of snow by Wednesday morning and another 2-5” during the day that will be reported Thursday morning.

Currently, Thursday looks like a precipitation-free day with some clouds, before another warm Pacific storm spreads showers over our area around Friday ahead of the Steamboat Springs Winter Carnival weekend. Temperatures will be even warmer, with rain likely in the valley and snow showers above mid-mountain during the day Friday before cooler air arrives by nightfall, turning the rain to snow.

Significant accumulations are expected by Saturday morning before cooler and drier air ends the snows by later Saturday. There is some trailing energy that gets left behind in the southwestern US for Sunday, and our weather may or may not be affected by that late in the weekend or early next week before a western ridge is advertised to bring warming and drying to the area for most of the following work week.


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18 May 2018

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