The calendar can’t turn to December fast enough for the Pacific Northwest — but even that offers little promise of respite. Residents there have been blitzed by a series of November storms that have driven widespread flooding and destruction.
A snap of moisture is ushering the month out with flood watches and warnings blanketing Washington and British Columbia. Warm conditions have boosted snow levels to 3,050 metres, meaning rain will fall at high elevations and melt out what little snowpack there is, sending more water rushing into rivers and racing over already soggy soil.
The reason those soils are so waterlogged is because of the absolutely stunning rainfall totals seen over the course of this month. The National Weather Service’s Seattle office tweeted a graphic on Tuesday that made me do a double-take. It shows that a large swath of the Cascades and Olympics, the two main mountain ranges in Washington, have seen 50 inches (127 centimeters) or more of rain in November. As the office helpfully notes, that’s 13 years of annual rainfall for Las Vegas. The colour scale on the map below includes such a wide range due to those monster totals — the areas that are light-grey are actually where the heaviest rain fell, not gaps in data of rainfall. (Hence, my double-take.)
The Northwest is generally known as a damp place in the winter when the jet stream sends storms streaking over the region. The Cascades and Olympics both act as major rain catchers, wringing that moisture out as snow on the high peaks and rain in the lowlands. The Olympics are the first mountain range any storms hit when they come off the Pacific. Areas to the west of the range receive so much rainfall, they’re home to the only temperate rainforest in the Lower 48. (Side note: It’s one of the most incredible places on Earth and home to the quietest place in the U.S.)
The Cascades are the next barrier storms hit and do an efficient job of wringing most of the rest of the moisture out of storms. The east side of both mountain ranges sit in relative rain shadows, particularly the east of the Cascades; parts of eastern Washington wouldn’t look out of place in the desert Southwest.
The map from the NWS Seattle office shows this pattern clearly, but the magnitude of rainfall is on another level. Even by the region’s soggy standards, this November has been absolutely shocking. A major atmospheric river ushered moisture from the tropics to the region mid-month. Up to 0.6 metres of rain fell and, combined with wildfire scars leftover from this summer, unleashed widespread flooding and debris flows on both sides of the U.S.-Canada border. At one point, every road connecting Vancouver to the rest of Canada was closed due to damage, and farmers resorted to jet ski rescues for their cattle herds.
Another major atmospheric river hit the region over the Thanksgiving long weekend and hasn’t let up, with Tuesday’s pulse of rain being the latest in that string of storms. At one point, the Trans-Canada Highway was shut down this weekend so authorities could build a dam across it. Seattle has already set the record for its wettest November and the rain on the month’s last day will only pad it further. Numerous daily rainfall records have also been set across the region.
A natural climate phenomenon that forms every few years in the tropical Pacific known as La Niña is also another major driver of wetter-than-normal weather in the Pacific Northwest. La Niña formed this year, which could be a contributing factor. Climate change has increased the odds and intensity of the heaviest downpours, much like the ones that have hit the Northwest recently. Burning fossil fuels has also increased the odds of extreme heat, including the record-smashing heat wave this summer. It’s this one-two punch that shows just how much we need to be ready for all types of hazards that also intersect.
The good news is that November is ending. The bad news is the region’s rainy has many more months to go.