Smoky End of Summer

After a relatively smoke-free summer, the region is now engulfed in smoke from a series of fires caused by dry lightning.  Fortunately, major changes are coming, including cooler temperatures and precipitation that should decrease the smoke during the next few weeks.

The visible satellite image this morning was stunning (see below), with much of eastern Washington in smoke, some of it moving aloft across the Cascades into western Washington.

As a result, the sunrise in Seattle was very reddened:

We can see the fires from satellites, and the satellite imagery from last night is shown below (red dots).  The Bear Creek fire is not evident (it is just smoldering), but several fires are apparent east of the Cascade crest.  Unusually few fires in California.  It has been a very low fire year so far to the south of us.

The eastern WA fires have degraded air quality there (see Purple Air map this morning, red and purple are the bad air locations).  With most of the smoke aloft, western Washington generally has decent air quality, with the worst around Bellingham.  

We are about to see a major weather transition, as the persistent ridge of high pressure aloft finally weakens and moves eastward.

Temperatures will greatly decline on BOTH sides of the Cascades to normal levels as shown by the forecast at Seattle and Pasco below.

Precipitation will return as illustrated by the accumulated total through Monday at 5 PM.

The most interesting challenge during the next few days is the potential for thunderstorms, which could start rolling in tomorrow and will continue over the weekend.

To illustrate, below is the simulated radar imagery from the ultra-high resolution UW weather model.

For Friday at 5 PM, a major area of thunderstorms/convection is over Oregon.

For Saturday at the same time,  Oregon thunderstorms, plus some getting into Washington, on both sides.

Such thunderstorms will bring rain and the potential to start a few more fires where dry lightning occurs.  Will talk more about such issues in my next blog.

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Announcement

I will hold a special online Zoom session at 10 AM on Saturday for Patreon supporters.  Will answer questions and talk in detail about the end of summer and the wildfire situation.

Warm West and Cold East

 It has certainly been warmer than normal over the Northwest during late summer, but what you might not know is that the eastern U.S. has been far cooler than normal.

Consider the plot of the temperature anomaly (difference from normal) for the past two weeks over the entire U.S. from the NOAA/NWS Climate Prediction Center.  WAY colder than normal from the Rockies to the East Coast.

Here is a high-resolution view of the temperature anomaly at 5 PM PDT on Sunday. 

Amazing.  Some portions of the eastern U.S. were 10-20°F below normal!  Very warm over SW Canada.

Why this anomaly pattern?   A persistent, perturbed upper-level  (500 hPa pressure, about 18,000 ft)  pattern with a ridge (higher pressure) centered over SW Canada and a trough (lower pressure) over the eastern US. (see below, and anomaly from normal for the last week below).

But all good things have to end.

The large-scale pattern will be changing over the weekend, with rain and cooling temperatures over the west and moderation of the cool temperatures over the east.

Tonight, we see the previous pattern with a ridge in the west and a trough in the east.

Same story on Thursday afternoon. 

But BIG CHANGES by next Wednesday with a massive trough of low pressure over the western U.S..  It will feel like autumn.  And that pesky, West Coast ridge moved into the central part of the U.S.

Going out even farther (and, of course, with less skill) for Sunday, 14 Sept, the forecast model shows a broad trough (blue colors) over the NW Pacific and the ridge moving into NE Canada.

Consider the latest precipitation forecast total through the same time (next Sunday).  Several inches in the mountains and light rain in the lowlands.  I suspect this will essentially end the wildfire season.

 

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