In a major study released today by the National Center for Atmospheric Research, scientists identify a climactic mechanism that increasingly appears to be blocking the kinds of storms that carry the most rain and snow from reaching California and the Southwest.
From NCAR’s press release:
“For the study, the researchers analyzed 35 years of data to identify common weather patterns—arrangements of high and low pressure systems that determine where it’s likely to be sunny and clear or cloudy and wet, among other things. They identified a dozen patterns that are typical for the weather activity in the contiguous United States and then looked to see whether those patterns were becoming more or less frequent.
“The weather types that are becoming more rare are the ones that bring a lot of rain to the southwestern United States,” [researcher Andreas] Prein said. “Because only a few weather patterns bring precipitation to the Southwest, those changes have a dramatic impact.'”
Prein said that the nature of drought itself has changed in our region.
From Climate Central’s story by Brian Kahn:
“Nowadays, the droughts are not the same as 30 years ago. They can be more intense and last longer than we would expect 30 years ago,” Prein said.
While Prein did not look directly at whether the current drying was driven by climate change or natural forces, the main climatic driver is an increase in high pressure in the northeast Pacific Ocean that essentially steers stormy weather away from the region. (You might recall a feature called the ridiculously resilient ridge doing something similar and driving the California drought. That’s kinda what’s happening in the Southwest.)”
Maybe a high pressure ridging pattern that looks something like this?
Not really what we want to see during severe #CAdrought @ climatological peak of wet season:big W. Coast ridge.#CAwxpic.twitter.com/CbFiGplmOF
— Daniel Swain (@Weather_West) February 5, 2016
That reddish high pressure area is sure to block all of California from the kind of low pressure systems that bring us water in the winter for at least the next week. The meteorological map was posted by Stanford researcher Daniel Swain, the man who first identified and named the “ridiculously resilient ridge.”
But most “ominous” of all, another study from 2015 found an 80% chance that we will soon find ourselves in a megadrought. Alarmingly, yesterday Prein suggested that we’re already in one.
“We see a very intense trend in the Southwest,” Andreas Prein, a postdoctoral researcher at the National Center for Atmospheric Research, said. “The Southwest might already have drifted into a drier climate state.”
Kit Stolz 
Nice piece, Kit.
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