Soggy November and a Big Pattern Change

 Are you tired of the rain?  We have good news if you are looking for some drier weather.  Will lowland snow arrive anytime soon?  In this blog we will take a look at the soggy November and the big weather pattern change ahead.

Let's start with how wet November has been.  Here is a map showing total precipitation amounts for the month so far (through Nov 26th).

Total precipitation as measured by area gauges from Nov 1st - Nov 26th, 2024.

The wettest locations have been along the Cascade crest, Northeast Washington, and the Idaho Panhandle with amounts in excess of 6-8" in some spots.  Please note that not all gauges are heated so precipitation that falls as snow may not be captured by some gauges (especially mountain areas).  How do these amounts compared to normal?

The area that stands out the most when compared to normal is Central Washington including Omak, and Ephrata.  

Omak is in 2nd place, and just .05" shy of breaking the record for the wettest November.

Omak top 5 wettest November's

Ephrata is also in 2nd place, but has a long ways to go to get to 1st place.

Ephrata top 5 wettest November's

For Spokane, it's the wettest November since 2006.

Much of this precipitation has fallen as snow in the mountains.  It's very early in the season, but mountain snowpack is running above normal across the region.

Snow Water Equivalent Percent of Normal - Nov 25th, 2024

So what lies ahead?  A much drier pattern with the 7 day precipitation forecast favoring dry conditions in Central Washington, with light precipitation limited to mainly the Cascade crest and ID Panhandle.

Weather Prediction Center forecast precipitation amounts Nov 26th-Dec 3rd, 2024

And what about beyond that?  Models are showing a mild pattern setting up over western North America as broad southwesterly flow develops.  This is the forecast weather pattern from the European Ensemble for December 6th, with other models showing a similar scenario.

ECMWF Ensemble 500mb height anomaly valid 00z Dec 7th (4 PM PST Dec 6th)

And a look at the temperature anomaly for Dec 6th from this same model is impressive, with above normal temperatures dominating all of western North America.  

ECMWF Ensemble 2 meter temperature anomaly valid 00z Dec 7th (4 PM PST Dec 6th)

A ridge this strong can take a while to break down.  There is also the potential for some precipitation given the southwesterly flow and offshore trough, but with the mild pattern don't expect much in the way of lower elevation snow.  Here is the latest 8-14 day outlook from the Climate Prediction Center favoring above normal temperatures, with around normal precipitation.

So for most of the region you likely won't need your snow shovel through at least December 10th.  But your sunglasses probably won't be needed much either, as this type of pattern leads of lots of low clouds and fog, especially given how wet the ground is with all the rain this month.

La Nina Update - Winter Outlook 2024-25

Have you been wondering what kind of winter the Inland NW will be granted with this year?  In this blog post we take a look at what a possible La Nina Winter will bring.

Our partners from the Climate Prediction Center wrote a fantastic blog about the influence of La Nina on snowfall across the region, that we highly recommend checking out.  The link to their blog can be found here.

As the blog states, for La Nina winters there is a tendency for above normal snowfall.  Indeed, local research we've conducted for several cities across our region show a tendency for above normal snowfall.  As shown below, on average snowfall ranges from 110-125% of normal for La Nina Winters.

% of normal snowfall for all La Nina winters from 1950-2017

For the interactive version of this map, where you can view charts for individual locations, click here.  Unfortunately the map isn't mobile friendly, so it is best viewed from a computer.

The latest probability for a La Nina this winter is around 70% according to the chart below.

% chance of La Nina (blue), Neutral (gray), El Nino (red) for each 3 month period.  DJF would be the chances for this upcoming winter

What do some of the latest climate models suggest for the winter?  The NMME (North American Multi-Model Ensemble) shows what one would typically expect for La Nina, cooler and wetter than normal conditions for the northwest.

NMME temperature and precipitation anomaly forecast for Dec 2024-Feb 2025

What about the official outlooks from the Climate Prediction Center?  These are weighted towards cooler and wetter than normal as well.

CPC Temperature Outlook valid Dec 2024 - Feb 2025

CPC Precipitation Outlook Valid Dec 2024 - Feb 2025

We have said this in previous blogs and will say it again in this one.  La Nina is only one piece of the puzzle, and while the outlooks favor increased odds for above normal snow, it is certainly not a guarantee.  This is because other oscillations in the atmosphere impact the weather pattern that sets up.  For instance, take a look at Spokane snowfall for all La Nina Winters since 2000.

My oh my!  Anywhere from 27"-98"!  And interestingly, those two winters (2005/06 and 2008/09) were both weak La Nina events.  So, while the average La Nina snowfall for Spokane is between 55-60", the precise number Spokane ends up with this winter may be much higher or lower.  

But given that a weak La Nina is favored and latest outlooks side towards the cooler and wetter, it would be best to prepare now if you haven't already.