Cold Stormy Week Ahead

Posted Tuesday, February 20th, 2018 by marcelcaron
TLDR: In short, the general large-scale setup through mid next week favors frequent cold frontal systems through Northern Utah. It seems that the week will end with a couple moderate orographically-enhanced (high-elevation) precipitation events. More events are likely through next Wednesday.

Hey guys! Given yesterday’s great wrap up of the cold and snowy weekend, I’ll focus mainly on the late-week forecast for this post.

First, a quick recap.


The Recap

As filling as the President’s day storm was, snow-lovers might credit the strength of the storm’s cold front for our big snow, rather than orographic (terrain-induced) effects. As rankings go, this was the 2nd largest snowfall this season at Salt Lake City Airport. In comparison, this doesn’t even make the top 5 storms at Alta-Collins this year. The minimal difference in snowfall between upper and lower elevations tells me that there was minimal orographic-enhancement in the highlands.

The storm left behind lingering lake-effect precipitation (see Taylor’s post for details) and cold temperatures. Tomorrow morning, temperatures could rival some of the coldest temperatures we’ve seen this season (14 degrees F at SLC airport occurred in late December 2017).


cold air mass
GFS 2m temperature anomaly 5PM Friday, February 23, 2018 (blues and dark purples indicate anomalously cold air near the surface). (courtesy tropicaltidbits.com)
Currently…

Furthermore, we seem to be in an isolated period of cold weather and frequent cold frontal systems. Why the sudden change after warm temperatures and few snow storms?

It does have much to do with the Pacific ridge, in two ways: First, the big guy drifted west quite a bit and is currently being held in its position. Why? I wouldn’t be able to answer that, not without wandering into mysterious theory land. Storms traveling eastward will avoid this ridge, moving up and over, then straight down to the western US. In contrast, earlier this month the ridge was further east, pushed storms past us to our northeast, and brought some love to the midwest and northeastern US. Second, the entire continent is under the influence of high amplitude waves. This means that both the ridge to our west and the trough to our east are digging deeply north and south, thus shuttling either very cold arctic air (into western US) or very warm tropical air (eastern US). See the map below for a visualization.

Cold Snowy Set-up
GFS 500 mbar heights (black solid) and relative vorticity (shaded) over North America at 11 AM Tuesday Feb 20th 2018. Note the large amplitude trough axis cutting through UT, and a large amplitude ridge axis far into the Pacific. Labeled are the center of this ridge (“H”), the current storm track (red arrows), and potential late week systems (circled in blue). (courtesy tropicaltidbits.com)

The Forecast

If we maintain this setup, and with some luck, we can anticipate seeing more cold and snowy weather over the next few days. Here’s what the forecast looks like:

I’m seeing at least three events before next Monday, all varying in strength. Furthermore, at least one could be moderately orographically-enhanced. Finally, each system would be cold enough to bring snow to the valley floor.


Wednesday night into Thursday

A weak shortwave (moderate confidence) seems to be a conditionally unstable prefrontal event, and as result should be enhanced as it pushes into the mountains. It’s a weak system, but I think we will see at least a few inches in most ski resorts.

Friday

A cold front will pass through, bringing a few inches of snow (moderate confidence). I think we will see a minimal difference in snowfall between low and high elevations with this storm. I don’t think this will outperform last weekend’s cold front.

Saturday Night into Sunday

Another weak shortwave could pass through during this timeframe (low confidence).


In combination, between Wednesday and Friday, ski resorts might see another 5 to 10 inches of snow (moderate confidence), with locally lower or higher amounts. In short, it’s one of a select few times this year we could expect frequent bursts of pow in the mountains. Enjoy!

Also stay tuned this week as we narrow down the details for each storm. In particular, check Wednesday night-Thursday snowfall forecasts in tomorrow’s post.

Happy skiing,

-marcel

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