Wind Uncertainty

The confidence in weather forecasts is not always the same.

Sometimes all the models lock onto a forecast, suggesting uncertainty is low and meteorologists can have confidence in their predictions.

But in other situations, uncertainty is large, with large differences among the forecast guidance.

The wind forecast for tomorrow over central Puget Sound is a good example of such an uncertain forecast.

One of the key tools of meteorologists for exploring uncertainty is viewing the forecasts from many weather model simulations, something called an ensemble. 

Below is the ensemble of forecasts for wind gusts in Seattle for forecasts starting early Friday.  

The predictions for Saturday are all over the place!

A low confidence prediction, at least for Seattle winds.

The key issue producing uncertainty is the path and intensity of a weak low-pressure center approaching the region.

The updated American model solution on Friday evening has a low approach coast and then passes across northern Puget Sound  (see below for forecast at 5 AM Saturday. 

Earlier today, both the European Center and NOAA HRRR models had a stronger low passing to the north, which would have produced much stronger winds (up to 50 mph) over western Washington, but they have backed off that solution.

I suspect very few will lose power tomorrow.  However, the approaching low will dump ever more rain over the region on Saturday morning.   Showers will greatly decline on Sunday and Monday, and Tuesday should be mainly dry.

Talking of rain, today's moist southwesterly flow produced profound contrasts for precipitation across the Olympics (below).  For the period from midnight through 8 PM Friday, there were 2-3 inches on the southwest side of the barrier and only .01 in Port Townsend.    That is quite a rain shadow.

Note that the largest rainfall totals are not at the high elevations but in the lower foothills of the mountains, where the moist air was initially forced to rise.