Pineapple Express to bring flooding in Washington, British Columbia into Friday
Moisture from a Hawaii-connected atmospheric river will bring periods of heavy rain, rising rivers and flooding concerns across western Washington and southwestern British Columbia into Friday.
Floodwaters from a Kona storm in Maui, Hawaii, turned Iao Stream into a fast-moving river, eroding the ground beneath Tom and Carrie Bashaw’s home and causing the structure to collapse before strong winds swept away what remained.
Part of a storm that produced torrential rain and flooding in Hawaii this past weekend will impact parts of Washington and British Columbia through much of the week, resulting in a flood threat along small streams, rivers and urban areas.
A plume of moisture, known as an atmospheric river, will extend thousands of miles from Hawaii to British Columbia and Washington through Friday. Because this moisture originates near Hawaii, it is also referred to as a Pineapple Express.
Rain will drench the region through Friday as waves of moisture move through the Pineapple Express. During the heaviest periods of rain, ponding on highways and flooding of some city streets are possible.
As runoff accelerates down hills and steep mountainsides, small streams and river headwaters in higher elevations may surge and recede multiple times during the event. Larger rivers at lower elevations near the coast may experience somewhat delayed but longer flood cycles.
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Rainfall of 1-4 inches is expected across most lower elevations in western Washington and southwestern British Columbia. On west- and southwest-facing slopes of the Coast Mountains, Olympics and Cascades, 4-8 inches of rain is expected through Friday, with an AccuWeather Local StormMax™ of 13 inches.
There is a risk of moderate to major flooding along some rivers in northwestern Washington and southwestern British Columbia as snow levels rise above mountain passes. Some melting of high-elevation snow is likely due to this warmer pattern.
Some rain will spill over the Cascades and into eastern Washington, but the rain will be more sporadic and much less likely to lead to flooding.
This pattern is being fueled in part by a strong heat dome over the southwestern United States, which is steering storms and moisture northward around a zone of very warm, dry air. That heat dome will set daily, monthly and early-season high temperature records in dozens of locations in the western U.S. in the coming days.
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