Another Windstorm Tomorrow

This is almost getting routine.   Another wind event will occur tomorrow (Saturday), but with a bit of a different meteorological twist:  no major cyclone, but a warm front passage, followed by a strong cold front.

Today, I will show you some advanced meteorological technology for wind prediction, something developed at the UW with funding from Seattle City Light and the Northwest Modeling Consortium.   
This figure shows the peak wind gust forecast over the city of Seattle predicted by the National Weather Service (green line), a super-high resolution numerical model prediction  run at the UW(red line), and a collection of high-resolution forecasts (gray lines and blue line).    Showing many forecasts (or an ensemble), each slightly different in their initialization, provides a way of estimating the uncertainly in the prediction. All these predictions were started at 4 PM Thursday.

These forecasts are the gusts (short-term wind maxima), based on a calibration from historical periods.  Virtually all the models are going for a significant wind event on Saturday, with maximum gusts over Seattle getting to 40-50 mph (most places in Seattle will experience less) between 10 AM and 4 PM.    Note how the wind continuously ramp up starting this afternoon....this is associated with a warm front passage.

The latest high-resolution (1.3 km grid spacing) run is in (below).   At 1 PM Saturday, it is windy around central Puget Sound (gusts of 35-40 knots), and if you look carefully you will notice the windshift on the NW coast associated with the cold front.

 Three hours later, the cold front has reached Hoquiam, on the central WA coast, and and strong westerly winds have pushed into the Strait of Juan de Fuca.

Considering all the stress put on trees during the past two windstorms, I would expect for less damage this time, but I am sure there will be some power outages.

To give you a better view of what is going on, here is a plot of sea level pressure (solid lines), low level temperature (colors--yellow is warm, blue is cold) and surface winds.  The situation at 4 AM this morning, shows cold air over the interior and the warm front offshore (transition from green to yellow, and significant wind shift).

 By 10 AM Saturday, warmer air had spread over Washington and Oregon, leaving us in the warm sector.    Note the large north-south pressure difference--that is what will produce strong winds.

The winds should weaken Saturday evening, with cooler and partly cloudy conditions on Sunday.

New Year's Eve should be dry!

from Cliff Mass Weather and Climate Blog http://bit.ly/2RkKWzF