Back on December 17th, we referenced an upper level pattern that would develop over the Western US in late December. In this post (read more here), we discussed that this type of pattern is one that both frequently emerges over the Northern Hemisphere during the Winter months, and can persist for many days or even weeks. As this stable pattern has started to break down, we have returned to a more progressive setup, with frequent but fast moving storms as the atmosphere finally relents. As the atmosphere tries to figure out what’s next, we will continue to see the West remain stormy.
We hope you got out and got some deep turns in this last storm cycle though, as the next event is shaping up to be a warm one. While this event will start off cool thanks to the current airmass, temperatures will simply continue to ride throughout this event, without the typical cold frontal passage at some point during the storm. The we’ll get one final cool storm before we have another major pattern change. A similar setup to the one that’s dominated the last two weeks will develop in the upper atmosphere, however this time it will be shifted a bit. This will put a ridge over the Western/Central US and the trough out in the Pacific Ocean off the Aleutian Islands. Generally, this will put a stop to the storms and will lead to a drying/warming trend.
As mentioned, we have a few more rounds of snow to get through before the ridge sets in. There will be significant snow with these events, but with some alarmingly warm air at times. With cold air in place from the previous front, temperatures initially will be just fine. The first event will kick off this evening and favor Oregon, Southern Wyoming, Northern Utah, and Colorado, and last through the end of the day Thursday. You can see the precipitable water anomaly map below pointing towards the precipitation will fall during this storm.
(Image courtesy of Weatherbell)
This storm will also bring very strong winds to these areas, likely affecting lift operations and snow quality. Most resorts in the Oregon Cascades will see at least 10-20” tonight through midday tomorrow, while the volcanoes (Hood, Timberline, Bachelor) could approach 2 feet at upper elevations. Central and Southern Washington will see an additional 5-10” as well, on top of the 2-3 feet from the last few days. Check out our edit from Crystal here. The moisture will then target central/western Idaho, with Brundage and Tamarack receiving significant snowfall tonight through tomorrowl. Expect 5-10” by midday with the higher numbers near Brundage. We’re lacking the S/SE winds necessary for Sun Valley to get slammed, so expect only a few inches there. The Tetons will do well from this round of snow as well. Jackson and Targhee should see over a foot of snow by midday tomorrow, with perhaps slightly less winds than Oregon and Northern Utah, where they will be very strong. Still, heavy snow will spread across Northern Utah early Wednesday morning and last throughout the day, with the heaviest falling between 6am-6pm. By Thursday morning, the Cottonwoods (Alta, Snowbird, Solitude, Brighton) and Northern Wasatch (Powder Mountain/Snowbasin) should see 18-24”. NW flow will favor Little Cottonwood and PowMow where totals could approach 2.5 feet. Finally, this storm will impact northern Colorado from Wednesday to Thursday. Steamboat, A-Basin, Vail, Loveland, and Winter Park will all do well. Steamboat should be the winner with 2-3 feet, while A-Basin, Loveland, and Winter Park seeing 10-20\" during this period. Slightly less totals for Vail and Beaver Creek.
The next storm will be right on this one's heels, and will track a little bit farther north. Below is a snowfall map for the 24 hour period ending Thursday, followed by Friday. You can see the northward shift of the heavy snow compared to the first storm. We will have more details on storm #2 tomorrow.
After these two storms wrap up, we will enter a dreaded ridgy period. This pattern will be similar to the stormy one we've had the last two weeks, except with the stormy trough over the Pacific Ocean instead of the Western US. Compare the two patterns below. First is the upper atmospheric setup of the last few weeks.
A lovely deep trough over the West. Now look at the upper level setup about 10 days form now.
There are three troughs/ridges each, but with the ridge over the Western US this time. This forecast is backed up by the teleconnections as well, specifically the PNA. A negative PNA pattern, which we have had for the last few weeks, is associated with a trough (storminess) over the Western US. A positive PNA pattern is associated with the opposite, warm and dry. If you look at the forecast of the PNA index over the next month, the GFS and EURO agree that it will become positive (Western US Ridge) for 7-10 days starting next week.
(Images courtesy of Weatherbell)
The good news is that the models agree on breaking this pattern down mid month, with a possible return of a stormy setup.
Alright, we are about to touch down in SLC so that's all for today.