Could it be True? Lowland Snow in March?

A few social media sites are predicting as much as a foot of snow in Seattle next week.

Why such excitement?

Some weather prediction systems are predicting something quite unusual for mid-March:  lowland snow.

Not everywhere, but in favored locations.  And not every weather modeling system.

Consider the predicted snow total from the NOAA/NWS model for the 24-h  ending 2 AM on Thursday (below).  Lots of snow in the mountains, with a snow band across Puget Sound, probably from a Convergence Zone.

Plotting the GFS model snowfall prediction for Seattle from its ensemble system of many forecasts shows that several of the predictions included several inches of snow, although there is a lot of disagreement.  Disagreement means uncertainty.

 

Now, let me prove that I lack promise as a YouTube channel host.  

I suspect that such forecasts of bountiful lowland snow are problematic.    

Let me start by noting that the climatology of significant snow in Seattle plummets after the first week of March, as shown below.  Yes, late March snow has occurred, but it has never been significant.

Another issue is the temperature of the air, as shown by the forecast for Tuesday morning below.  The air over us will be cool, but not the primo Arctic air required for serious lowland snow in our region.   And there is onshore flow from off the mild Pacific.   But cold enough for PLENTY of snow in the mountains.    Get your skis out!.

The US GFS model has a long history of overdoing lowland snow in our area....its forecasts are generally too cold.   In contrast, the UW WRF model shows substantial snowfall in the mountains, but essentially nothing in the lowlands (accumulated snowfall through 5 PM Wednesday shown below).

The European Center's predictions are similar:

In short, plenty of snow in the mountains (which should address many concerns about this issue), but virtually nothing in the lowlands, although a few of you might see some melting snowflakes.

Precipitation totals during the next weeks should be impressive, providing water exactly when it is most valuable before the dry season starts in 2-3 months.

Announcement

I will hold a special online Zoom session at 10 AM on Saturday for Patreon supporters.  Will answer questions and talk more about the snow situation.

The Most Valuable Precipitation of the Year

Precipitation at some times of the year is more valuable than at others.

Here in the Pacific Northwest, March and April precipitation is by far the most prized and valued.

Fortunately, the latest forecasts suggest we will enjoy bountiful amounts during this period, which should be a relief to those worried about the water supply.

Why is spring precipitation so important?

It can moisten the soil and help fill the rivers before our dry summers.

It can build up water behind our dams and in our reservoirs, providing water and power during the summer.

For years without good snowpack (e.g., 2024), it can provide needed water.   

It doesn't make much difference if we fill our reservoirs with melted snow or spring precipitation.

As you can see from the average cumulative precipitation at Olympia (below), quite a bit of the annual precipitation at this station occurs in March and April (between the red bars).  

Bottom line:  it is not too late to get substantial precipitation, even in a normal year.

Although there has been a lot of gnashing of teeth about this year's precipitation, the water year totals (from October 1 to now) are actually near normal, something shown by the cumulative precipitation at Seattle and Yakima below (red is normal and green is this year).

The issue is that the snowpack is about 50% of normal as of today.  However, reservoirs are in very good shape, with some well above normal (e.g., the Yakima reservoir system).

As I have noted before, the prediction models have been emphatic about our progression into a far wetter pattern.

To illustrate, below is the total precipitation forecast from the European model through Friday, March 20th, over the Northwest.   Quite a lot over the Cascades!

Much of that will be snow, as shown by the totals through March 19th

The latest extended forecast from the NOAA Climate Prediction Center is for wetter than normal conditions for the second half of the month.

With La Niña rapidly weakening, there is no reason to expect that we will get a persistent dry pattern, as in January.  

I suspect our summer water situation will be fine.