The Windstorm That Never Came: A Failure of Communication

Last week, there were strident warnings of a strong windstorm from the National Weather Service, which were amplified by conventional and social media.      

The storm never happened.  

Instead, we had a short period of winds gusting to 30 mph or so, producing little damage and few power outages.  I received dozens of emails about the errant forecast.  Folks were not happy.

As I will describe below, the problem was not the technology of weather prediction, but the poor communication of forecasts and their uncertainty.  

The Problematic Prediction

Last Tuesday, the National Weather Service put out a high wind warning for the western Washington lowlands for Wednesday (see below).

According to the official definition, a High Wind Warning means that dangerous winds (sustained 40+ mph or gusts 58+ mph) are imminent or occurring, requiring action.

A warning should only be provided when a forecaster is absolutely sure that the threat will occur.   This was NOT the case for this event.  Not even close.   I describe why below.

This problematic warming was then amplified by the traditional media and further hyped by social media "influencers" and local weather enthusiasts, few of whom have degrees in meteorology.  A sampling below:

The day before, I tried to deflate the hype in my blog since it was clear the forecast was excessive and wrong.

Below are the maximum winds observed last Wednesday.  Most locations had gusts of only about 30 mph.  A few in their 30s.  Only near the water were higher gusts noted (46 mph near the Tacoma Narrows Bridge and 59 mph on southwestern Whidbey Island).

This time of the year, after the leaves are down and following earlier wind events, there are very few problems with gusts under 30 mph.  Very minor problems for 30-40 mph.   Only when winds gust to above 50 mph do series power outages become apparent.  

No wonder this "event" was a big disappointment for those looking for intense weather.

Are you ready for some inner baseball of the weather forecasting business and to view some state-of-the-science tools?

On Tuesday, of the major international weather prediction centers, only the American was producing a strong, very small-scale low-pressure center moving up the Northwest coast.  

To illustrate, here are the 36h forecasts for sea level pressure and surface winds for the American GFS model and the European Center (ECMWF) model, both valid at 4 PM Wednesday.  The GFS had an intense mini-low, and the ECMWP had a weak inland low.

I was immediately suspicious of the GFS storm.  First, the GFS is far less skillful than the European model.  And I have learned from experience that such small features are often bogus or poorly predicted. 

But there were more reasons to be worried.  The National Weather Service runs ensembles of many forecasts, each a little different, to get a handle on the uncertainties of the forecast.   The NWS ensemble forecasts made Tuesday morning for Wednesday were ALL OVER THE PLACE, indicating great uncertainty.  

Earlier on Tuesday, the NWS forecast seemed to recognize this uncertainty in a graphic they produced (see below).  Very nice.

But later that day, they literally threw caution to the wind and put out the high wind warning:

Next, let me show you a graphic from the  Seattle Windwatch site, which my group provides to the city.  

This graphic presents the maximum gusts predicted over Seattle by the NWS and several modeling systems for the forecast cycle starting at 4 PM on Tuesday.

The observed winds are shown in black (with a high of around 35 mph).  The shading shows the range of forecasts by the US model (GFS). 

The NWS forecast wind (yellow color) was at the extreme top of the ensembles, showing they were gambling on a low-probability solution.  The UKMET forecast (light red) and Canadian model forecast (dark red), both consistently more accurate than the American model, were almost perfect.

So we had a situation in which the NWS forecasters did not properly consider uncertainty, nor did they recognize that historically better forecasting systems had a very different (and more benign) forecast.

The conventional media, like the Seattle Times (see below), went with the poor NWS forecast, and the weather amateur YouTube channels, Facebook, and X outlets exaggerated the event even more.

Let me be honest, perhaps too honest.  A major problem is the deterioration in the forecasts of the National Weather Service. 

Their global model, which drives almost their entire forecast system, is inferior to the best (e.g., the European Center).   This event is a good illustration of that.

Many of the local forecasters in the Seattle NWS office are relatively new to the region and lack experience with the local meteorology and model performance.   They also depend too heavily on the NWS models and don't use ensembles sufficiently.  And this is not the only local forecast failure...the December ice storm a few years ago is another one--and there are several more.

A real warning sign is that objective verification of forecast quality has consistently shown that Seattle NWS forecasts  (NWS Digital Forecasts) are inferior to totally objective forecasts, such as those from the Weather Channel (see below).  

The National Weather Service needs serious reform and reorganization.  The American people deserve state-of-the-science weather prediction.  They are not getting it now, and last week was a good example of the persistent failure mode.

North Puget Sound Lowland Snow from the Other Type of Convergence Zone

 The first significant lowland snow over western Washington occurred last night, ranging from a trace to about an inch.

How it happened is quite interesting....let me explain. 

The snow started falling late yesterday evening and was associated with a narrow convergence band that was evident in the weather radar (see below).  The band stretched northwest to southeast and started near Sequim.

The band brought heavy precipitation in places and extended into the Cascades.

Why Sequim?  The driest location in western Washington!

As we will see, this precipitation band was associated with a convergence zone, in which low-level air streams came together, forcing upward motion and precipitation.

But it was different from the "classic" Puget Sound convergence zone we often talk about.

The figure below shows a schematic of the typical Puget Sound convergence zone. Northwesterly winds from off the Pacific are forced around the Olympics and then converge over Puget Sound, producing upward motion, clouds, and precipitation.   

Most of the time, this is the convergence zone we are talking about.

But there is another way to get low-level convergence over the western interior:   air moving southward down the Strait of Georgia can converge with air moving eastward in the Strait of Juan de Fuca, producing a band of clouds and precipitation.

Something like this occurred last night.  A strong, sharp upper trough moved through, causing the northerly winds in the Strait of Georgia to be particularly strong.   That air converged with air moving eastward down the Strait to create a low-level convergence zone that stretched from Sequim to north Everett.

Want the proof?  Here are the winds late last evening.  You can see the two air streams coming together.

The high-resolution UW WRF model predicted this situation (see the model forecast winds for yesterday evening below).  Shading is wind speed (in knots), and wind vectors are plotted.

You can see the converging airflows.

 

The precipitation band was narrow and well defined, as shown by the 24-h precipitation totals (below), with some locations in Snohomish County receiving over an inch of liquid precipitation.

The heaviest precipitation was associated with light snow (see totals below).

Why such modest snow?  

Because temperatures were very marginal (too warm) for snow.  Only in places with a lot of precipitation (and thus a lot of cooling from melting and evaporation) could the snow level be driven down to the surface.  Initially, precipitation fell as rain and then gradually evolved into snow and snow pellets.