Forecast Triumph

Yesterday, a strong front, associated with strong winds gusting to 40 mph or more, moved through the region, resulting in numerous power outages.

As I will describe below, numerical weather models predicted this event with great skill, something we could not have done 20 years ago.   

This is a triumph of modern weather prediction technology.

Let me demonstrate this to you.  

Below is the radar image around 4 PM Saturday, based on the radar observations from the Langley Hill radar near Hoquium.  An intense radar return was apparent offshore (the thin yellow and red line, indicated by the red arrow).   This is the front.

Fronts associated with a narrow, cold frontal rainband were first described by  UW researchers, such as Professor Peter Hobbs and associates.

Even more impressive is a video of the cold front approaching the coast (from a wonderful phone app called RadarScope).

Here is a forecast of a simulated radar image, made 24 hours (from 4 PM) before the event is shown below.  It was made by the UW WRF model run by my group.  

Almost perfect.  Very strong simulated front.

A closer-in view is below.

A forecast made 60 hr before the event was virtually the same.  Strong front in the same location

A forecast made on Thursday evening, showing the strongest near-surface wind gusts, indicating strong winds over the region.  Strong enough to worry about.

The winds for Seattle made for Seattle City Light as part of the UW WindWatch system were clearly accurate, showing the threat of strong wind (the black dots are the strongest observed with the city; the gray and colored lines indicate model forecasts)

The models were very, very clear.  

There was a prediction of 30-45 mph winds over the city.  And that means power outages, particularly early in the storm season.

Such an emphatic forecast by the models was the reason I blogged about it on Friday, making it clear that some would lose power.

In fact, over 100,000 customers lost power over western Washington last night (see below).

And over 46,000 customers in Seattle lost their lights.

This kind of skillful forecasting occurs time and time again, based on highly skillful weather model forecasts.

Another reminder that it is no longer appropriate to make fun of forecasters and weather models.   😀

No longer appropriate

A SuperFront Will Cross the Northwest This Weekend

Most weather fronts that cross the region are unremarkable due to their passage over the relatively warm, uniform waters of the northeast Pacific.  

This weekend will be different:  a  SuperFront will make landfall late tomorrow (Saturday).  

Some of you will lose power.

Let me show you simulated radar images for three times:  10 AM, 4 PM, and 9 PM on Saturday from the UW high-resolution forecast system (from the 4-km grid-spacing domain).  Red indicates very strong winds, followed by yellow.  The arrows point to the frontal locations.

Wow. Very intense, sharp front.  Very heavy rainfall.

The high-resolution 1.3 km simulation run by my group at the UW produced an even more intense front (forecast around 8 PM shown).  Very impressive.

What about the predicted winds?

The City of Seattle supports the most high-tech wind prediction system in the country (called SeattleWindWatch, run at the UW), which includes an ensemble of many wind predictions for estimation of the uncertainties.  

The forecast below is for the winds over Seattle.  Several of the simulations predicted winds reaching 40 mph. Over the water, winds could be stronger,

 Winds will rev up after dinnertime and peak overnight.

Such strong winds, this early in the wind season when some leaves are still on the trees, mean power outages.  

As noted above, wind will be strongest over the water (see forecast below for 4 AM).   I suspect most of the power outages will be in such areas.

For the whole region, the strongest winds will be on the coast (see map of strongest wind gusts below).  Importantly, there will be areas of intense gusts on the lee/downstream side of some of our highest terrain, including the eastern slopes of the Cascades.

In addition to wind, the front should bring substantial ( and welcome) precipitation to the region, with the total through 4 AM Sunday shown below

So, if you live west of the Cascades,  get your meteorological popcorn out and be prepared for a dramatic meteorological show later tomorrow and early Sunday.