Pineapple Express hits with a fury

When I was brainstorming the topic for this article last Saturday, I really thought I’d be writing about snow. The weather maps at the time were lit up with all sorts of heavy snow warnings, morning low temperatures were in the teens, and it looked like area ski resorts would finally get the wintry bonanza they had been waiting for. I failed to look at some of the forecast charts, however, which would have showed the ominous signs of a moist and mild subtropical fetch headed right our way.

It is known as the Pineapple Express, and this particular one hit the Northwest with a fury earlier this week. Strong winds, heavy rains and record high temperatures in the middle 50s made their way into the Idaho Panhandle. This snow eating monster of a storm melted away piles of the white stuff just as quickly as it had fallen. But soggy, barren hilltops at places like Mount Spokane Ski Resort were nothing compared to the destructive forces of nature seen on the west side of Oregon and Washington, especially on the coasts. Pictures and reports have been all over the national news during the past week, but most of these numbers are worth repeating, they are so staggering. Winds in excess of 100 mph hit many locations in coastal Oregon and Washington. The highest winds were measured in the Tillamook area in Oregon, including 104 mph at Rockaway Beach, 114 mph at Cape Meares, an incredible 129 mph in Bay City, and 125 mph farther south in Lincoln City. These wind speeds are comparable to those found in a Category 3 hurricane. These winds were not the result of any hurricane, tornado, or even severe thunderstorm though. They were the result of a strong pressure gradient, caused by a deep low-pressure system. In the atmosphere, winds always move from higher to lower air pressure. The change in air pressure over a specific area, is called the pressure gradient. The tighter the gradient is, the stronger the winds will be.

It was not just the winds that came though. Torrential rain followed a record-breaking 1.1 inches of snow in Seattle. Snow was being measured in feet in the mountains locally. Then the warmer air arrived, and melting snow along with heavy rains caused flooding in parts of the Inland Northwest, but much more so west of the Cascades. Storm total precipitation across North Idaho amounted to an average of 2 to 4 inches in the valley locations, with remote mountain weather stations measuring between 7.5 and 8.5 inches in a couple of spots. The Seattle airport measured a record-breaking 3.77 inches of rain on Dec. 3, while 7.76 inches were measured near Bremerton in one 24-hour period.

Now the “Pineapple Express,” occurring most often in November and December, is a type of storm that is known for bringing heavy precipitation and mild temperatures to the Northwest. The strong winds are not usually part of the package, but this time around made the event even more destructive. The air mass from these storms originates near the Hawaiian Islands, hence the subtropical nature and name. In this particular storm, the air mass was particularly heavy with moisture picked up from the remnants of a typhoon off the coast of Japan. The jet stream provided the transport system, and the moist, mild air was carried to the Pacific Northwest.

As a result of the past week’s storm, Coeur d’Alene has picked up 2.62 inches of precipitation as of Wednesday. Snowfall this season has so far totaled 15.8 inches. December is normally a wet month with an average of 3.92 inches of precipitation, 19.3 inches falling as snow.