Tuesday, December 19, 2017

A little mild weather and rain late Saturday but Christmas forecast continues to improve and includes plenty of cold weather

Lots to discuss today with it being a busy finish to 2017 weather-wise and a certainly a busy part of the ski season given the upcoming holidays. Generally the news today is pretty good. The mild weather Tuesday was tame relative to many  thaws we've experienced the past few years and we hope there's only one brief additional difficult window to get through before another extended stretch of winter begins.

A colder push of weather will be accompanied by snow showers and maybe a squall or two Tuesday night. The snow will only amount to a few inches and accumulations will generally be confined to the high country, but winter will be back with temperatures in the 20's Wednesday along with a chilly wind. The Rocky Mountains have gotten off to a difficult start this winter with balmy temperatures and a glaring lack of snow. Resorts in both Utah and Colorado will pick up a bit of snow Wednesday and this represents our next storm and in this particular case, our next concern. Fortunately, a healthy area of cold will continue to build across the region Wednesday night and allow temperatures to plummet back into the single numbers and subsequently remain in the teens on Thursday. This airmass will provide a nice foreground for an approaching system that is not poised to track in a favorable direction. The result is what I think might be a healthy overrunning thump of snow late Friday and Friday night. As of late Tuesday, it looks like much of this snow falls very late in the ski day Friday, Friday night and into early Saturday before changing to freezing rain/drizzle early Saturday. Temperatures will remain in the teens through Friday and are likely to be in the 20's early Saturday. Powdery turns are possible early Saturday before the ice begins in earnest. Several inches of snow are possible but I can't say that I have the timing or the exact amounts of  snow nailed down. I could use another day or two on that.

 Milder air will slowly make its northward push Saturday and the aforementioned ice will turn to a bit of rain. Temperatures will make climb toward 40 but will have a limited window to do so before colder air arrives by the morning of Christmas Eve. Arctic cold will be beating against a rather stubborn ridge in the jet stream - positioned just off the southeast U.S. coast. The front marking the advance of the arctic cold will thus remain active and capable of generating a 2nd east coast weather system in time for Christmas Day. As this is happening, extremely cold arctic air will make a giant southward advance. It all makes for a rather delicate situation. It won't take much to move this potential Christmas storm offshore and it also won't take much for the cold to be somewhat delayed and allow for precipitation to be something other than snow. For now, snowfall on Christmas Day appears to be a legitimate possibility as opposed to a far-fetched one and within a few days, we should be able to pin this storm down as well.

Coldest air of the winter season so far will consume the region after Christmas and send temperatures well below zero. There might even be a day between Tuesday and Thursday where readings fail to break 10. Snow showers and squalls are possible Tuesday although the intensity of the arctic air will likely limit available instability.  I expect the cold to persist through the New Years holiday however thanks to the blocking structure which is expected to drift westward very slowly across the Alaskan Peninsula and the EPO which will keep the Pacific loose and friendly. The setup looks conducive for another big east coast system around December 29th and 30th but it is very early and there have been only occasional hints of such an outcome right now.

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