Hello. It’s the Snowy Hibbo back for another year of sub-seasonal forecasting for the Rockies and West Coastal ranges. This year, I will be producing model based outlooks, like last year. I will also be adding climate driver based outlooks to the outlooks, to give more meaning to the models, and the signals that they produce. Anyway today I will be reviewing all the information for the winter season forecast. I will be looking across the continent, at both the Western and Eastern ranges of North America. So let’s get into it!
We are currently in a Weak La Niña. Most models show that to continue until the end of winter, as a weak-moderate La Niña. A lot of forecasters, including the CPC or Climate Prediction Center at NOAA, have been using La Niña as a basis for their forecasts. With a La Niña, you often see more snowfall in the PNW and South BC regions. For the resorts in SoCal, NM and AZ, La Niña is associated with lower snowfall. However, ENSO is only a small part of the bigger picture here.
ENSO and PNA
The PNA or Pacific North American pattern and ENSO have a major correlation, that I need to address separately from the rest of this article that focuses on the AO. La Niña and a -PNA correlate, which means there is more chance of a -PNA. This involves more snowfall and lower pressure for the Western States of the USA.
Snow & Ice
We see three trends in the Arctic, as noted by this diagram.
You have lower than average ice in the Barents-Karas Sea, over October and November, higher than average snow cover in Siberia and Decadal high snow cover in North America. The first two have a correlation with a -AO and the last has a weaker correlation with a +AO. There is also has been quite a lot of high latitude blocking in the past two months, that also correlates with a -AO.
But what is the Arctic Oscillation or AO? It is basically a measure of the tropospheric vortex’s strength, whether the jetstream is weak (-AO) or strong (+AO). A -AO correlates with colder air and more snow for the Eastern US, and milder air and less snow for the Western US. The +AO does the opposite, favouring the West, with a strong Pacific jetstream.
CFS produces a forecast for the Arctic Oscillation. I wouldn’t pay too much attention to the values, just the trends.
After the major dip in the AO this coming week, you can see a relatively neutral AO, until late January, when it goes noticeably -AO until the end of the run in Mid February.
We currently are in a Easterly or negative QBO. This is correlated with more Sudden Stratospheric Warmings, which equals a weaker polar vortex, or a -AO. The QBO is the jet at the equator in the Stratosphere at about 30mb.
We are currently heading into a weaker period for our Sun, known as a solar minimum. We measure this using sunspots, that creates this map.
Less sunspots correlates with a -AO.
The AAM or Atmospheric Angular Momentum, which is basically a measurement of the relationship between the winds around the world and the earth’s rotation, has been in a negative phase for several months now. This trend may continue into winter. The GEFS 16 day forecast shows that the GWO is going into Phases 1 & 2, sending the AAM into it’s negative phase. This is correlated with a -AO.
Current GEFS Forecast
Recent GWO and AAM History.
MJO and more
One thing I haven’t touched much, while making these seasonal forecasts is the MJO or Madden Julian Oscillation. That is because the MJO isn’t a great driver to predict in seasonal timescales. However most people I have spoken to, suggests MJO might be coming back sometime in Winter, around late December or January. La Niña is often associated with a stronger MJO. Of course a stronger MJO is associated with more Atmospheric River events on the West Coast. So there is a chance of more precipitation than usual for the West Coast.
Firstly we are going to look at the new combo of models, from ECMWF, Met France and Met Office, in a MME product.
It shows ridging over most of the US, except much of the PNW and Southern BC as well, which have neutral anomalies.
Next the CFS…
This looks like a La Niña based run, with troughing over the PNW and Southern BC. It also features ridging over the Eastern and SW USA.
Finally the CanSIPS model run…
This is similar to the CFS run, with troughing over the PNW and Southern BC and ridging over the Eastern and SW US.
My personal thoughts on the AO situation are consistent with my assessments last week and two weeks ago. I am looking at a -AO, that will give more snow for the Eastern States, including New England. However the La Niña and MJO, plus the models suggests more snowfall and AR events for the PNW. I suggest the outlook for NoCal, Utah and Colorado will be neutral. And there will be less snowfall than normal for AZ, NM and SoCal.
Thanks so much for reading.
Seasonal outlooks tend to have bias and errors, due to the fact that these forecasts are so far out. So don’t use these outlooks to make important decisions. These outlooks is meant to be interesting information, that can help to see what the season might be like.
This took a lot of work, so I appreciate your support. Starting in December, my long range outlooks for Western North America will start! They will be produced every 2-3 weeks, looking out into the range of 10-30 days out. This season, I will explore climate Drivers as well, including the AAM, MJO and others. Stay tuned.
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