Pineapple Express to unleash a torrent of rain and snow on the western US
Over a months' worth of rain and snow will fall in a matter of days in a portion of the West this week, as deep tropical moisture from the Pacific flows ashore.
Wintry weather led to both flooding and snow across the Pacific Northwest from Feb. 2-3.
An atmospheric river originating from near Hawaii known as a 'Pineapple Express,' will send copious amounts of moisture into a large portion of the Northwest and California this week, resulting in heavy rain and waist-deep snow, warn AccuWeather meteorologists.
The Pineapple Express, already evident on weather maps this weekend, will bring a variety of hazards to the West over the next few days, such as major flooding, avalanches, strong winds and travel delays. The heavy precipitation marks a dramatic change to begin February, after what was a relatively dry January.
Meanwhile, lowland areas in the Pacific Northwest, away from the direct discharge of moisture from the atmospheric river, are expected to see slippery accumulating snow—many for the first time this season—through early week.
Rounds of soaking rain and feet of snow in Northern California
The region expected to be hardest hit by the atmospheric river event through Tuesday will be northern portions of California, where not only snow can be measured in feet, but rain as well, say AccuWeather meteorologists.
"Locations like Redding and San Francisco can receive a month’s worth of rain just alone from this event," said AccuWeather Meteorologist Elizabeth Danco. "Across the rugged terrain of Northern and Central California, heavy rain can cause landslides which could lead to road closures and travel disruptions."
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AccuWeather meteorologists are forecasting a large part of the northern third of the Golden State and far southwestern Oregon to measure several inches of rain. This includes the San Francisco Bay Area and cities such as Chico and Santa Rosa, California; and Eugene, Oregon.
The heaviest rain, amounting up to 12 inches, with an AccuWeather Local StormMax™ of 24 inches, will be centered over Northwestern California and a portion of the northern Sierra Nevada mountain range. For many even outside the area of highest rain totals, the atmospheric river can easily deposit at least a months' worth of rain in a matter of days.
"San Francisco's historical average rainfall for the month of February is 3.96 inches, while Redding's is 5.48 inches," added Danco. The Golden Gate City is forecast to receive 2-4 inches of rain through Tuesday, while rain in Redding can total 4-8 inches.
Such eye-popping rain totals are common with Pineapple Express atmospheric river events that last for days. "Since the Pineapple Express starts thousands of miles to the west of Washington, Oregon and California, there is plenty of time for excessive moisture to gather," explains AccuWeather.com Managing Editor Monica Danielle.
In the Sierra range, as much as 3-6 feet of snow can fall through Tuesday, especially above 7,000 feet, making travel nearly impossible. Gusty winds are also expected across the lee side of the range in western Nevada, resulting in localized wind damage, including around Reno.
While AccuWeather meteorologists expect the worst of this atmospheric river to wane by Tuesday night, a storm following the path of rich moisture can arrive Wednesday night into Thursday, bringing one last round of rain and snow.
The precipitation is also expected to shift south toward Southern California, which would be good and bad news in the wake of last month's historic and deadly fires around Los Angeles. While any rain would be helpful in preventing new fires in the near future, downpours can trigger mudslides and debris flows.
Rare lowland snow on tap for the Pacific Northwest
While the Pineapple Express looks to avoid directly impacting northwestern parts of Oregon, western Washington and far southwestern British Columbia, Canada, an influx of cold air from the Arctic region combined with Pacific moisture can lead to accumulating snow outside of the mountains, warn winter weather experts at AccuWeather.
"Portland and Seattle [had] yet to record any measurable snow so far this winter," said Danco on Saturday. By Sunday, a few tenths of an inch had been recorded in both places, with more snow showers expected on Monday.
Meanwhile, over two million people in the Vancouver, Canada, metropolitan area will have to prep their snow removal equipment, with a whopping 6-10 inches (15-25 cm) forecast through Monday night. Much higher amounts can fall in the nearby mountains, which can impact travel through the passes.
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