You Ain' t Seen Nothin' Yet

We begin this Monday
The first day of spring break
With a little from BTO
Because as I look at the forecast
All I can think is
You Ain't Seen Na-Na-Nothin' Yet

The numbers for the past season, each month of the season, the past month, the past week, and even the past two days are astounding.  600+ inches of snow at Alta.  Another 15" last night.  Alta-Colllins snow depth at 7 am: 185 inches!

And our friends upstream in California?  The Central Sierra Snow Lab near Donner Pass reported yesterday that the've had a season total of 562", within a foot of the epic 2016/17 year total, with 2-4 feet in the forecast.  

We have a deep 30.5" (77.5 cm) of new #snow that has fallen over the last 24 hours. Our season total is now 562" (14.29 m) and we're now within one foot of the 2016/2017 winter snowfall total.

We're expecting another 2-4 feet through tomorrow and more this week!#CAwx #CAwater pic.twitter.com/eQE40GPSvS

— UC Berkeley Central Sierra Snow Lab (@UCB_CSSL) March 5, 2023

But as crazy as you think this season has been, it's about to get crazier.

The recent pattern has been dominated by high-amplitude ridging over the north Pacific and a deep trough along the Pacific coast.  This has resulted in a series of cold storms across California, Nevada, Utah, etc.  The GFS analysis for yesterday morning (1200 UTC 5 March) shows this well.

That pattern will bring more snow for both California and Utah this coming work week, but change is coming.  As shown in the GFS forecast, by 1200 UTC 10 March (5 AM MST Friday), the subtropical Pacific Jet will extend across the eastern Pacific and onto the Pacific Coast where it merges with the polar jet dropping down from Alaska.  

This is an important shift in the pattern and the corresponding GFS regional forecast below shows a potent atmospheric river, what we would have once called the Pineapple Express, directed right at California with the parent cyclone making landfall over the Pacific Northwest and trailing cold front across California.  So, after all of this snow, we transition into a windy and warm storm pattern with 700-mb temperatures in the Tahoe area of -1˚C on Friday morning.  Sorry Tahoe, no more blower pow for you!

That system ultimately spreads into Utah giving us wind and warmth Friday night with a big system potentially following.  

It's a bit early to talk confidently about details, but let's take a look at what the GEFS ensemble is doing.  At the Central Sierra Snow Lab, after the snowfall during the work week, the downscaled NAEFS shows the action picking up around 6Z 10 March (11 PM MST Thursday).  There are, however, a wide range of forecasts.  Some only generate an inch or two of water equivalent (which when added to the precpitation since last night adds up to about 3" of water for the week) but some go off.  The mean for the week is about 7 inches of water and, this will be a warm storm.  Our snow-to-liquid ratio algorithm suggests ratios certainly less than 10:1 and some ensemble members call for rain at this 7000' elevation.  Batten down the hatches!

For Alta-Collins, one can also see significant spread after 6Z 10 March as much depends on the track of the storm and atmospheric river.  Regardless, over the 7-day period (including last night), most of the downscaled ensemble members are producing between 2 and 5 inches with a mean of just over 3. 

The low-end scenario is that the system tracks to the north and we get wind and warmth but not as much snow.  We still get a decent amount of snow.  2" of water equivalent and 20-25" of snow this week (including last night) would be at or just above what we would expect from climatology.  High end scenarios are more than double that.  

So, insanity to continue this week, but expect a change to a warmer pattern later in the week.  You ain't seen nothin' yet.