Incoming Pacific jet stream to battle the arctic airmass
Thursday, December 8, 2016
The arctic airmass currently entrenched over most of the US will be pushed eastward on Friday as a moist Pacific jet stream slams into the West Coast.
A persistent ridge over the Bering Sea is largely responsible for our current and future weather. Very cold air from Siberia has been shunted over the North Pole by the ridge, bringing the sub-zero temperatures observed this week. Additionally, a moist Pacific jet stream has undercut the Bering Sea ridge and is currently bringing precipitation to the northern half of the West Coast. A battle will ensue between the warm Pacific jet and frigid arctic airmass, with temperatures first warming aloft tonight before the warming makes it’s way to the lower elevations on Friday.
This is a difficult short-term forecast since there will be a lot of moisture around, but Steamboat Springs usually does not do so well when there is warming aloft. In fact, we had our notorious freezing rain event around this time two years ago that also involved warming aloft, and I can’t discount the possibility that there may be some of that again. However, it is relatively rare so I won’t include it in the forecast, but I do expect that snow amounts will be tempered from tonight through Saturday morning while this is occurring. I would expect 2-4” overnight with another 1-3” during the day Friday.
Snow on the mountain and a possible rain-snow mix in the valley will taper off during the day Friday but likely not completely stop before they pick up again by Saturday afternoon as an embedded cool wave in the west-northwest flow moves over northern Colorado by Saturday night.
Snowfall will become moderate to heavy by midnight and continue through the morning hours before substantially decreasing by later in the day and overnight. I would expect 6-12” by the Sunday morning report with another 3-6” during the day, likely making travel conditions quite difficult or even impossible for a time.
Meanwhile, another wave traveling down the east side of the Bering Sea ridge will send more cold air south and west Sunday night, though the still strong Pacific jet stream will keep the coldest air to our north and eventually east. While the westward moving air will invigorate another storm in the Gulf of Alaska, the re-introduction of the relatively dry arctic airmass over our area will keep lighter snow showers off and on from Monday through Wednesday.
There are a lot of moving pieces that will likely change in future forecasts, but by Wednesday night, a piece of the Gulf of Alaska storm is forecast to be carried over our area by the Pacific jet stream and could make Thursday a snowy day with possibly significant accumulations as another round in the battle of the airmasses begins.
