Huge Gas Explosion Creates Pressure Wave over the Northwest PLUS a Powerful Storm Hits Our Coast

Around 1:45 AM today, a huge gas explosion destroyed a large building in the Greenwood neighborhood of north Seattle (see picture, courtesy of KOMO TV)

Folks throughout north Seattle and Shoreline was awakened from their sleep, some checking their homes for damage.  Heavy damage hit buildings near the explosion, including broken windows.

Large explosions produce very load sounds, which in reality are powerful pressures waves in the atmosphere.  Sound, as you learned in middle school, is associated with propagating pressure waves, with alternating areas of compression and rarefaction (see image).  A large explosion can produce an intense, rapidly increase zone of pressure called a shock wave that propagates away from the explosion.

After I heard about the explosion, I check the local barometers (microbarographs) used by meteorologists.   A microbarograph records pressure variations over time.   Here is the record from my department (the explosion happened about 0945 UTC).   Look at the first panel that says SLP.   Nothing, but that is not surprising considering the small amplitude of the expected signal and the long averaging time of most weather-related pressure sensors.

But then I got a message from Professor Steve Malone of UW's Earth and Space Sciences Department.  Steve is an expert in seismology and it turns out that many seismographs are paired with very accurate barometers.   Eureka!   A number of his microbarographs recorded the pressure signal, even ones 10s of kilometers away.   Here is a sample from a unit about 50 km distant from the explosion.  A pulse of roughly .17 Pascals (Pa) around 0948 UTC (1:48 AM), with some aftershocks/vibrations for about a minute after.

.17 Pascals (Pa) is a very small signal.    Average sea level pressure is about 1013 Hectopascal (hPa).   Hecto mean 100.   So average sea level pressure is about 101300 Pa.  Normal pressure variations are on the order of several hPa over a few hours...thus, the signal above would be in the noise level.    Of course, the signal would have been greater in neighborhood of the explosion.

You want a big pressure signal?  A very deep low center is now moving up our coast and will cross Vancouver Is. tomorrow morning.

At 10 PM this evening the WRF model shows a very deep low (972 hPa) off northern Oregon with a HUGE pressure gradient on he south and west sides.

 By 7 AM (1500 UTC), the low crosses northern Vancouver Island, with a very strong pressure gradient over the northern WA coast and northwest WA. Winds will gust to 70-90 mph along the coast and 30-60 mph over northwest WA. Expect power outages.

As of 9 PM, winds are gusting to 90 mph along exposed hills along the WA and southwestern WA coast, with 104 mph gusts at Naselle Ridge near Astoria, with a 97 mph nearby (see map  of max gusts over the past 24 hr)

And yes, lots of rain tonight.

Announcement: Public Talk: Weather Forecasting: From Superstition to Supercomputers

I will be giving a talk on March 16th at 7:30 PM in Kane Hall on the UW campus on the history, science, and technology of weather forecasting as a fundraiser for KPLU. I will give you an insider's view of the amazing story of of weather forecasting's evolution from folk wisdom to a quantitative science using supercomputers. General admission tickets are $25.00, with higher priced reserved seating and VIP tickets (including dinner) available. If you are interested in purchasing tickets, you can sign up here
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