Thursday, 13 October 2016

Extreme weather in Pacific NW

Four Thousand Mile Long River of Moisture Could Dump 2 Feet of Rain on The Pacific Northwest

11 October, 2016

As the U.S. East Coast is still reeling from impacts associated with Hurricane Matthew, the Pacific Northwest is just now confronting its own potential extreme climate event. For a 4,000 mile long river of moisture streaming off ex super typhoon Songda in the Pacific Ocean is now firing a barrage of storms at Northern California, Oregon, Washington, and British Columbia. A series of storms that could, over the next five days, dump as much as two feet of rainfall over parts of this region.

Powerful Atmospheric River May Produce 2 Feet or More of Rainfall This Week

(A powerful atmospheric river is forming over the record hot Pacific Ocean in a record hot atmosphere. Typhoon Songda is delivering a great deal of tropical moisture to this flow — which is expected to impact the Pacific Northwest and produce very heavy rainfall this week. Image source: Weatherbug.)

Jet stream winds running across the Pacific now range between 180 and 220 mph. These strong winds are producing a powerful storm track even as they are tapping a vast plume of tropical moisture over the Eastern Pacific. Embedded in this moisture plume is the rain-rich ex supertyphoon Songda. As the strong upper level winds pull in Songda and draw on the extreme moisture bleed rising up off the record-hot waters of the Pacific Ocean, forecasters expect a resulting atmospheric river to run 4,000 miles across the Pacific Ocean and deliver storm after powerful storm to the Pacific Northwest.

NOAA model forecasts now show as much as 22 inches of rain falling upon parts of this region over the coming 7 days. However, with so much moisture loading up the atmosphere, it’s possible that locally higher amounts of rainfall will occur.
(Very heavy rains in the range of 7-22 inches or more are expected to fall over the Pacific Northwest this week in associate with a powerful river of moisture streaming off the record-hot Pacific Ocean. Image source: NOAA.)

Conditions in the Context of Climate Change — Here We Go Again

Over the past year, a record hot atmosphere has helped to generate extreme moisture levels aloft. Such record to near record moisture levels have helped to produce 500 to 1,000 year flood events in places like Louisiana, Texas, North Carolina, Maryland, Virginia and in other parts of the US and around the world. This week, record high moisture levels contributed to flooding rains falling over Virginia and North Carolina in association with Hurricane Matthew. Now, a similar extreme moisture pattern is taking aim at the Pacific Northwest.
So this is kind of a ‘here we go again’ situation. And, unfortunately, these types of extreme weather events are now more likely due to the fact that a world now in the range of 1-1.2 degrees Celsius warmer than 1880s averages is one in which a higher volume of water evaporates from the land and ocean surfaces and into the Earths atmosphere. Such a physical dynamic related to human-forced warming is one that increases rainfall even as it provides more fuel for powerful storms.
Hat tip to Colorado Bob
Hat tip to DT Lange
Hat tip to Greg

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