Cooler Than Normal Water Off the Northwest Coast

One of the reasons Northwest weather is so temperate in summer is the cool coastal waters off our coast.

And this year, we start the summer with surface waters cooler than normal.

This is illustrated by the sea surface temperature anomalies (differences) from normal (below), with blue indicating cooler than normal water.

Below is a map of sea surface temperatures off the U.S. West Coast (°C).   The purple and blue colors indicate the coldest temperatures.   You will need a sweater to enjoy a coastal stroll!

Why such cold water along the coast? 

One reason is the upwelling of cold water from below, as illustrated by the figure below. Such upwelling is forced by northerly (from the north) winds along the West Coast.

Importantly, these northerly winds have been stronger than normal for the past month.

Why? 

Because of stronger-than-normal surface high pressure offshore of the northwest.  This is demonstrated by the figure below, which shows the sea-level pressure anomaly (difference) from normal over the past month.

The red area indicates a much higher-than-normal high-pressure area offshore.

Since winds move counterclockwise around high-pressure areas in the Northern Hemisphere, this implies enhanced northerly flow along the coast, something shown explicitly in the figure below (which shows the wind differences from normal of the past month).

With this persistent pressure/wind pattern in place, the current 5-day forecasts are for colder than normal conditions over western Washington, Oregon, and British Columbia (blue and green indicate colder than normal conditions)

Keep your sweaters handy!

Wind and Fireworks Brings A Fast-Growing Wildfire Near Lake Chelan

 The  Chelan Hills fire, reported to have been started by some irresponsible fireworks Saturday morning, has now spread to over 10,000 acres (see map below).

A high-resolution visible satellite image this morning shows the burnt area (dark color), and the satellite imagery shows some still-active fires (red dots).  Smoke from  another (smaller) fire is apparent to the southwest.

The fire started in grass and range vegetation, not forest.  

Importantly, this vegetation was NOT unusually dry, as shown in the figure below, which provides 100-h fuel moisture levels on the eastern slopes of the Cascades.  Red is observed moisture level, and the shading shows the normal range.  

Current moisture levels were above normal.

So "climate change" can not be blamed.

What can be blamed was strong winds.  

Winds that were skillfully forecast by the UW WRF modeling system and the NOAA models.  To illustrate, below is the wind forecast for Saturday afteroon be the UW WRF weather model....strong winds were predicted around Chelan!

Below are the strongest observed winds yesterday around the fire area.  A 36 mph gust was observed near the fire start.

Winds at this location really revved up during the afternoon and early evening (see below).

At the same time, relative humidity plummeted to less than 20%--the result of drying of air moving downslope on the eastern side of the Cascades.

There is reason that wildfire starts are maximized on July 4th.  

The ignitions are there, the grasses/range vegetation are dry enough to burn, and it is early enough in the summer so that strong onshore flow produces powerful winds.