We’re getting closer to the positive pattern change. If you look down the right sidebar at the maps you can see that the precipitation forecast for the next 5 days and next 15 days are looking much better, and so is the MJO forecast. Your iphone forecast should even have much colder air and a few flakes showing up by next Wednesday.
We continue to wait out the retrogressive pattern that will slowy open up the storm door. Starting first with cold and light snow by Wednesday and next weekend, then progressing into bigger cold storms for week 2 around the 18th and into Christmas as the long wave pattern retrogrades and opens the storm door.
Even though the system for Wednesday is pretty dry we could see some decent snowfall with the cold temperatures. Model output is around .25-.5 inches of liquid. At lake level that should be a quick 3-6 inches but up above 7000 ft. in the colder air with higher snow:water ratios we could see 6-9 or even 9-12 above 8000 ft. Especially along the crest where up to .75 inches of liquid could fall. Here is the GFS snowfall forecast in inches by Thursday.
For next weekend there is some disagreement in how much moisture will be pulled in off the Pacific. The GFS would double down on the Wednesday storm but Euro is show enough precip for 1-2 feet of fluffy powder.
I’m getting excited about the long-range forecast possibilities. As the ridge retrogrades back out towards 150w-160w week 2 we could see some bigger storms that are plenty cold and could add some feet of new snow before the Christmas holiday. The operational models have been consistent with this all week. The CFS v2 climate model is forecasting the storms to start week two and last through week 4. You can see below the dry start here in week 1 and then the big change.
I have also been talking about how the blocking over the Arctic has been displacing and building some really cold air over Alaska and that will spread into Canada, then will start pushing South into the U.S. over the next few weeks. Here is the CFS forecast for week 3 temperature departures with the blue being the coldest air, and you can see how much cold is over Alaska and Canada pushing South into the U.S. and right down the West Coast.
We have plenty of teleconnection support with a -PNA pattern forecasted to continue. We look to continue into a triple crown of negatives with a -PNA, -NAO, -AO pattern. That pattern is more rare as when the NAO is negative along with the AO the block over Greenland usually holds the trough and cold in the East and ridges the West and creates a +PNA pattern. With this pattern we should see cold for the nation as well as coast to coast storms.
We saw a triple crown of negatives pattern back in 78/79 so I ran the snowfall analog for that season. That was a 105% of average snowfall season for Donner Summit. The MJO is also forecasted to become more active and in a neutral Nino season like this its affects can be much greater on the pattern. The forecast is strengthening into phase 1 then progressing into phases 2 & 3. What does that look like in December? Cold and Snowy!
I also promised you a November recap this week. With all of the warm storms and cloud cover at night November was a warm month at 1.8 degrees above average. The bright side is that for hydrology it was also a very wet month with lots of high elevation snowfall. The Truckee River Basin ended up with 129% of average precip while the Tahoe Basin ended up with 137% of average. That brings them to 120% and 130% respectively so far this water year which we are 2 months into now.
I gave you lots to chew on today. I will be doing lots of work on the merge with opensnow.com over the next couple of days. Stay tuned for updates on the Wednesday system. BA