A Look At Winter And Our Next Shot of Precipitation

Factors Affecting The Upcoming Winter.

Since I moved to the area 12 1/2 years ago I have tried to determine the best recipe for a good, bad, or average winter snow season. I am still trying.

What has become very apparent is that you cannot generalize the conditions that accompany ENSO (La Nina, El Nino, Neutral). That is true everywhere, but it is more important in our area. The other thing that is apparent is summer and fall conditions have very little correlation with winter conditions.

October is historically the worst month of the year for weather model forecasting. Fortunately, in November historically the modeling is more successful. That continues until April or May the other “shoulder season”. The reason is because of the northern branch of the jet stream and the pressure gradient between the cooler air mass to the north and the warmer air masses to the south.

Eventually, the western ridge buckles and often puts the trough where the ridge was in fall. We are due for that to happen before long, more on that later.

This season we have started experiencing La Nina conditions and they are expected to continue into a moderate La Nina. Weak, strong, and moderate La Ninas, depending on what other factors are present, all can lead to below, above, or average precipitation amounts as well as below, above, or average temperatures.

All of this is true with El Nino as well as neutral Enso conditions. If you are starting to get confused, join the club.

The other cast of characters that you have to take into consideration are the “teleconnections”. These are the drivers for the large scale pattern that are the true drivers of our weather.

These teleconnections are in positive or negative phases. For now, I don’t want to dig too deep of a hole into weather nerd land so I won’t get too technical.

The three major teleconnections for us to look at are the Madden Julian Oscillation (MJO),  the Eastern Pacific Oscillation(EPO), and the Pacific North American index (PNA).

We have talked about the MJO and I will revisit the explanation and implications later, for now, remember there are 8 phases to the MJO, and what phase we are in can have an effect on precipitation and temperatures. The MJO is most influential from December through March.

The EPO in its negative phase generally results in below-average temperatures for most of the lower 48 states and above-average temperatures in the Gulf of Alaska.

The PNA in its negative phase is common in a La Nina. It can lead to cold temperatures especially in the west, where the trough usually sets up for the winter. With a positive PNA, the opposite is true-warmer temps in the west with a trough in the east.

Other factors I am looking at are the cooling sea surface temps (SST) north of Hawaii. If this continues the cooler temps will spread east towards the west coast of the US. This could result in a cooler pattern as well.

I will revisit all of these factors in mid-November and we will look at how the November pattern evolves and hopefully get a better handle on long term modeling.

Possible Pattern Change Around 10/25

I know I just mentioned that October is statistically the worst month for weather model performance. But all of the models for the last 48 hours or so have been showing the possibility of the northern jet dropping at least a small storm far enough west to affect our weather on the or about the 25th-26th. If it were one model, I don’t think I would mention it. In this case, the GFS, Euro, and Canadian all show this. I responded to an email I got yesterday about this by saying I am not yet even cautiously optimistic it will happen. The more solutions and agreement among the models I see, the more optimistic I will become. At this point, I find the model agreement worth mentioning, but for today, I will leave it at that.

With the possibility of a ripple developing in the pattern, I will be posting more frequently this week. Thanks for following and supporting the page while we wait for winter to kick in!

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