La Nina and Snow Expectations for this Winter

A number of you have asked about this coming winter and the status of La Niña.  

Will the snowpack continue to increase? Will those worried about flooding and drought get the answers they are looking for?   

The only useful meteorological tool for predicting more than a few weeks ahead is the correlation of our weather with El Nino and La Niña.

La Niña occurs when the central tropical Pacific sea surface temperatures are cooler than normal.  El Nino conditions occur when the water is warmer than normal (the area considered---called the Nino 3.4 area--is shown below)

We are now in a weak to moderate La Niña, as shown by the sea surface temperature differences from normal (called anomalies) below:

The Nino 3.4 temperatures over time are shown below.  Since August, they have been below normal, ranging from 0.5 to 0.9 °C below normal.  This is a weak to moderate La Niña.

Interestingly, such cold water periods have an impact on the weather in our region.

The latest predictions are that La Niña will remain in place through February and then weaken (see below).

During weak to moderate La Niña winters, we tend to be a bit cooler than normal, modestly wetter than normal, and the snowpack is modestly enhanced.

I know everyone is interested in the snow outlook, so let me get right to it.  For all La Niña years, our snowpack tends to be above normal in January through March (see below).

But what about weak La Niña years here in the Northwest?   The excellent folks at the Northwest Avalanche Center have examined this issue, with the results shown below.

For moderate and strong La Niña years, all the major ski areas have substantially above normal snowfall.  Weak La Niña years are a bit above normal at Mission Ridge and Timberline.  Near normal at Baker,  Paradise, and Snoqualmie.

Based on these and other statistics, a projection of slightly above normal snowpack in the Cascades is probably a decent prediction.

The European Center seasonal precipitation prediction for January through March is for wetter than normal conditions.

And the temperature prediction for the same period is near normal conditions for western WA and Oregon:

The official NOAA season forecast is for colder than normal and wetter than normal conditions:

At this point, there is little reason to expect to have low snowpack going into the summer.

Announcement

I will hold a special online Zoom session at 10 AM on Saturday for Patreon supporters.  Will answer questions and talk in detail about the outlook for the remainder of the winter, and perhaps cover some "controversial" topics. 

Massive Mountain Snow and Flakes Down to Sea Level

For those worried about below-normal mountain snow, your worries are over..... a major snow dump is ahead.

You can also expect great skiing, and there could be some travel delays in the mountain passes. 

 Today, the Seattle NWS office noted the snowy threat....and they are right.

As I discussed regarding the windstorm forecast failure of last week, a good forecaster needs to examine the predictions of multiple forecast systems and ensembles of many forecasts from the same system in order to judge the reliability of a prediction.    

Let's do exactly that.

For the period ending Sunday at 11 AM, the European Center snowfall total is impressive,  reaching 4-5 feet.  You read that right.  5 feet.

The U.S. model has similar depths for that period.

Next, let's look at the ensemble of many snow forecasts at Stampede Pass (on the drier side of the Cascades) from the UW WRF model (only for the initial period through Thursday morning)--see below.

All the forecasts are calling for snow, which is steadily accumulating at that location.  We can have some confidence that substantial snow will fall there.

Now, let's turn to the latest run of the high-resolution UW WRF model.  Below are the snowfall totals through Thursday at 11 AM.  Up to three feet in the mountains!

Note there are a few areas of VERY, VERY light snow reaching near sea level.  This represents a few flakes mixed into the rain.

Temperatures will be relatively cool on Thursday morning at 4 AM, with very low freezing levels.  Here is a forecast map of the temperature around 2500 ft.  White and blue indicate below-freezing temperatures.   Precipitation will obviously be snow at that level (2500 ft) for the entire region, melting as it approaches sea level.  

I don't want to hype this (I don't run a YouTube channel 😋), but just don't be surprised to see some flakes on Thursday morning if you are near sea level.   The mountains will be hit hard...pretty much guaranteed.