One Week Forecast: Odds for Storms are Dwindling

Posted Thursday, December 13th, 2018 by marcelcaron
TLDR: Models converge toward mild and unexciting weather…but give mother nature a chance before scoffing at the 7+ day forecast. Weekend forecast and a nod to storms before Christmas toward the end of this post.

Did you see this today?

mountain cam
Hidden Peak Camera, 10:19 AM MT December 13 2018. Courtesy snowbird.com

Yeah no real complaints considering only yesterday a storm brought the goods.

But odds for more have dwindled with every forecast run. Short range probabilistic forecasts like the NAEFS have very low chances for any precipitation over the next 5-7 days.

Three-Day Forecast

Dominating recent forecasts for the next several days has been high pressure aloft extending down to the surface. This usually accompanies milder temperatures and an inversion over the western US, and that’s what we’re going to get. Over the next three days expect warmer temperatures in the valleys and similarly warm temperatures at high elevations. Due to the inversion layer, resort-goers will feel mild temperatures in the upper 30s on the mountain during the daytime, and perhaps lower 20s overnight.

Next chance for a Storm

Beginning this past Monday night, deterministic runs have shifted to the less exciting scenario–a domineering high pressure system–over the next week or so. Currently, there isn’t any powder dump in the works before Christmas, but maybe the shiftiness of this week’s forecasts was enough to convince you that deterministic forecasts over a week out are wildly misleading. See the two forecasts for early morning December 26 below for example:

GFS-FV3
GFS-FV3 Simulated Precipitation 5AM MT 12/26, initialized this morning December 13. Courtesy tropicaltidbits.com
GFS-FV3
GFS-FV3 Simulated Precipitation 5AM MT 12/26, initialized last night December 12. Courtesy tropicaltidbits.com

The first plot has a big snowstorm over UT the morning after Christmas, this one’s fresh off the press. The second plot has a dull set up over UT, also the morning after Christmas. The latter was produced by the same modeling system just 12 hours earlier than the first. These are deterministic or “one solution” runs, and demonstrate the importance of considering probability when locking in a forecast, especially when you’re looking over 5 days out. That said, I’m leaving that period alone until the models begin to settle on something.

All in all, I’m leaning toward a mild next 7 days with maybe a weak system around Tuesday, but more likely nothing. I’m giving the 7-12 day period a chance for a storm or two. Balmy bluebird days are great, but I’m hoping for a few more layers will bulk up the snow that already exists before Christmas.

-marcel

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