If your travel plans are snarled this Thanksgiving holiday, perhaps being part of weather history will soothe the ensuing headaches?
Bearing witness to a storm that is forecast to come ashore at record strength and moving along an unprecedented track is about the only silver lining to be found in a powerful winter cyclone about to smash ashore near the California-Oregon border on Tuesday afternoon.
In the forecast stretching from Tuesday through Friday are plummeting temperatures, hurricane-force gusts that could reach or exceed 100 mph in some locations, giant waves of up to 37 feet, as much as four feet of snow in the Sierra Nevada and heavy rain in the lower elevations between San Diego and Salem.
It’ll be a big one, and the National Weather Service has posted a plethora of warnings, watches and cautionary advice in expectation of the storm system.
Despite the dangers, NWS meteorologists in the storm’s projected path couldn’t help but be a little giddy about the system’s historic nature.
The Eureka, Calif., NWS forecast office said the region may experience its lowest-ever air pressure reading, with the barometer forecast to fall to approximately 975 millibars off Cape Blanco, Ore., before landfall Tuesday afternoon. The previous record, 978 mb, was set in 2010. In general, the lower the pressure, the stronger the storm.
This is the work of a weather phenomenon known as bombogenesis, which creates “bomb cyclones.” Bombogenesis occurs when a mid-latitude cyclone rapidly intensifies, as measured by the pressure at the storm’s core dropping by at least 24 millibars over 24 hours.
Forecasts show that the storm could see air pressure in its center plummet by about 40 millibars in 24 hours, easily earning the “bomb cyclone” moniker.
“Models continue to show good agreement the low will strength to 972 mb this afternoon as it nears the Curry coast of Southern Oregon. This is lower than the 975 mb low of the historic Nov 9-10 storm in 1975,” the Weather Service forecast office in Medford, Ore., said Tuesday in an online forecast discussion.
“This is a unprecedented storm given the track and strength and will being very dangerous conditions to the area.”
With such steep pressure gradients come whipping winds, and places from Cape Blanco southward will endure gusts in excess of 75 mph — while exposed areas and headlands are blasted with high-end Category 1 hurricane-like winds of 100 mph, warns the NWS Medford, Ore., office. Areas north of the low-pressure area will see comparatively lighter winds of up to 55 mph or so out of the east. The unusual track of the storm could also bring high winds to valley areas in addition to high peaks, such as the Shasta and Rogue Valleys, the NWS noted.
These winds will kick up unusually large waves along the coast. “Seas will be incredibly high and confused during this stormy period with significant heights of 30-40 feet,” according to the Weather Service.
At exposed beaches along California’s North Coast, there could be breaking waves of 35 feet in the surf zone.
Storm’s track is also unique
“Rather than a deepening system moving from (southwest) to (northeast) inside 130 (west longitude), which typically bring our strongest coastal and inland windstorms … this one will be moving in from (northwest) to (southeast) as it moves onshore Tuesday evening,” forecasters said Monday afternoon.
Frigid temperatures are on tap, with a chilly Thanksgiving expected along the West Coast. While residents of usually gorgeous Pasadena, Calif., are tucking into the Thanksgiving turkey Thursday, the mercury outside will be more than 15 degrees below average, struggling to exceed the low 50s — and when the clouds clear, there should be a solid dusting of snow visible on the San Gabriel Mountains, as the snow level is forecast to drop to 3,000 feet if not lower. Mount Wilson, which overlooks the city, tops 5,700 feet.
Rain totals shouldn’t be excessive, a relief for those near fire-scorched areas, but thunderstorms are possible. The foothills of the eastern San Gabriels are predicted to get the most rainfall at 4 to 6 inches; at higher elevations, ski resorts could receive around two feet of snow. Los Angeles, Sacramento and San Francisco most likely won’t exceed 1.5 to 2 inches of precipitation.
Major winter storms along the West Coast are often connected to atmospheric rivers, which are pipelines of extraordinarily moisture-rich air that directs heavy rain and mountain snow at the West like a fire hose. It was just last winter when California got soaked by AR after AR funneling tropical moisture toward the Golden State — right after the Center for Western Weather and Water Extremes (CW3E) released a scale for measuring the strength of ARs.
For this storm, the CW3E said only the North Coast will be under AR conditions — and even then, it expected to be classified as a weak atmospheric river (AR1): “While the parent cyclone associated with this event is forecast to be strong, the AR is forecast to be fast moving and of relatively low moisture content, which will result in primarily beneficial instead of hazardous rainfall.”