Alta Chasing History

Posted March 13 7:15 am PT 6:15 am MT

Pattern Discussion

Alta Chasing 748

We are at day 14 of cycle 4, of this year’s pattern. As we all know, it has been an incredible, record breaking, year. Alta has received 664 inches so far and are presently 9th on the all-time list, chasing 748 that happened in 1981-82 season. Four of the top six seasons were in the 2000’s, with number 1 and 3 occurring in the 80’s. Alta’s staff has put together a great breakdown of the month-by-month snowfall to date. You can find that link here.

Pattern Comparison

I have put together this year’s version of the MSLP (Mean Sea Level Pressure) surface compilation to show the pattern in action. It is not difficult to see, but I do want to point out that there are differences, teleconnection wise, between the two cycles.

The compilation lasts the entire length of the cycle, 50 days. The actual cycle length is closer to 49.3 days, which we have taken into account for 0ur next set of predictions that will be out Wednesday.

Seasonal Differences

Upper Pane

In the upper pane is from the fall, from Oct 30 thru Dec 18th. the lower pane is winter, Dec 18- Feb 6th. There are seasonal differences between fall and winter, that is obvious, but the main point is the strength of the jet stream is strongest as we get into February. It is expected that storms in October and November will generally be weaker than storms December thru February.

I choose these dates because it is easier to see the pattern when it is amplified. There are 3 types of patterns, weak, regular and amplified. In the upper pane, the pattern is amplified until November 10th and then turns weak. You will notice weak storms following the jet stream, those are pattern storms and come through regardless of the strength of the pattern.

The pattern switches back to “amplified”, Nov 30th. When the pattern is amplified, the storm door to Lake Tahoe is opened and the pattern storms that normally follow the jet stream are bigger and storms (waves) that are 3-4 days apart grow together.

Lower Pane

In the very beginning of the clip, the pattern is regular, but quickly becomes amplified within a few seconds, as wave after wave of atmospheric rivers (AR) flow into the west coast. This is full-on winter with an amplified pattern and strong jet stream.

Jan 20th, the pattern flips to regular, then weak by Jan 23rd. You will notice the position of the High-pressure area during the weak point. The High is part of the Artic Oscillation (AO). When the AO is strong positive, the jet stream steers storms northward, allowing for warm air to move in. The storms are squeezed of moisture but still flow on time.

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GFS Surface Map

All Snow High Res HRRR

500 millibar and Jet Stream (click to animate)

Forecast Summary

Snow today in the Pacific Northwest, through this afternoon with heavy snow at times. after 4-8 inches fell overnight at Crystal, Stevens Pass, and Timberline with Mt Baker reporting 10. Snow levels will be falling throughout the day settling around 1000 feet by this evening, along with the current storm.

Scattered snow showers over the next few days for the northern Cascades, snow continues, albiet with light totals for the southern Cascade resorts. Expect 1-2/2-4 thru Wednesday. Temperatures around 30 degrees at 5000 feet for Washington resorts and low to mid 30’s for Oregon.

Lake Tahoe, heavy snow is expected to continue throughout the day and evening until Tuesday night. Record breaking amounts are likely through the week where relentless heavy snow will continue through Wednesday mooning. Temperatures remain warm with snow levels around 6000 feet today, rising to 8000 feet tomorrow, before we get some colder air overnight tomorrow. The storm continues through Wednesday, with Wednesday the best day to ride.

In Utah, the next system moves in tomorrow afternoon with the stronger part occurring overnight. Expect a nice powder day Wednesday, if you want to ride the storm. Heavy snow will fall throughout the day with 1-2 feet expected during the day. Temps on the warm side at base level but should be really nice above 8000 feet.

The Utah storm arrives in Colorado Wednesday. I will have expected totals tomorrow, but the early numbers are looking like generally 5-10 for northern, central and resorts along 1-70 with 1-2 feet for southern resorts. Powderhorn, in the west, may get double digit totals.

Lake Tahoe

Utah

Colorado

Daily Snow Stakes

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Long-Range Prediction Chart

We are on storms 60-64 that will occur this week. Presently, we are in a lull with the strength of the storm systems, but that is predicted to energize in the coming days. We are seeing this energy on the models, around storm 64, for Lake Tahoe, with the aforementioned AR that is setting up now.