A mass of warm water in the northern Pacific Ocean known as “the blob” has returned, and it may have some profound implications for winter in the Lower 48 if it sticks around long enough.
Alaska’s fall to date has been strangely warm after an expansive dome of high pressure locked itself in place over the western part of the state. Because fall days are still long, extended warmth and sunny skies may have boosted ocean temperatures in the Northeast Pacific, causing them to rise significantly and forming the blob.
A similar patch of warm water formed several years ago in roughly the same location, together with a long-lasting zone of atmospheric high pressure called the Ridiculously Resilient Ridge.
There’s evidence that the Ridiculously Resilient Ridge caused that blob, compared to the reverse, wrote University of California climate scientist Daniel Swain.
“The blob has been a standout feature of North American climate this decade, but there is a chicken-or-egg aspect to it,” said Weather Underground meteorologist Bob Henson. “The blob warms the atmosphere above it, and the atmosphere can either nurture the blob with light winds or ravage it with strong winds that churn up cooler water.”
What scientists don’t know is just how long the blob plans on hanging around. If it manages to overstay its welcome long into winter, the Lower 48 could see some significant consequences.
“Earlier in the 2010s, the blob was part of a chain of events that extended from warmth in the western tropical Pacific all the way to cold and snow in the eastern U.S. The reemergence of the blob this fall gives us something to watch closely as a potential clue to how this winter may unfold,” Henson added.
In the past, the blob has been linked to development of extreme weather patterns across the Lower 48, including the intense California drought that peaked from 2013 to 2015. The blob has been associated with abnormally warm and dry conditions in the West and cold and stormy conditions in the East.
When the blob is in place, the jet stream, the divider of warm and cold air and a belt line for storms, is often arching north over the blob. This causes high pressure to build over the western part of the continent, allowing for mild weather and keeping storms away.
Cold air displaced by the blob and the atmospheric ridge typically moves into the East.
Despite a warmer-than-average finish to the month being forecast for Alaska by the National Weather Service’s Climate Prediction Center, the dome of high pressure fueling the blob is expected to shift and begin to deteriorate. This could allow in a stormier pattern, which may enable waters to blend where the blob sits, possibly weakening or destroying it.
The last time the blob appeared was in 2016, when multiple cold outbreaks were expected in its wake, but the blob was washed away.