Extreme Winter Weather?
An impressive late winter storm moved across the Southwest earlier this week dropping over two feet of snow across higher elevations and over half an inch of rain to much of the low desert areas across Arizona. A highly amplified (loopy) jet stream guided the storm directly from the Gulf of Alaska to the Southwest, along with an ample supply of cold air tailing the storm system (see image of jet stream below). This combination of jet stream energy and cold air were the ideal ingredients for a late winter storm across the desert Southwest.
Was this type of late winter storm an unusual outlier in terms of extreme weather? Not really. Very few records fell across Arizona over the past week. A handful of record low high temperatures fell across northern Arizona as the storm system passed, but no precipitation records fell anywhere in the state. This storm system stood out as unusual because it punctuated a string of unusually warm and dry days that characterize the dominant weather pattern that has gripped the region for much of this winter. Tucson has already experienced several days with above-average temperatures well into the 80s over the past thirty days and has observed only 0.56” inches of precipitation (with most of it falling with this latest storm) since the beginning of the calendar year. This total is about 1.5 inches below average for this time of the year. What’s more, Phoenix had seen no traceable precipitation since the beginning of the year until this latest storm.
The current, but waning, La Niña event has been implicated in driving this recent (and temporary) highly amplified jet stream pattern that brought winter weather to the Southwest and early summer and record temperatures to the eastern U.S. More importantly, La Niña is the most likely culprit behind the exceptionally dry weather pattern we have observed across the Southwest during the January-February-March season for two years. With fewer than average winter storms like the one this past week, much of the Southwest has been bogged down in moderate to severe drought for over a year now with the expectation that drought conditions will continue to expand and intensify across the region through the rest of the spring. We seem to be getting used to warm and dry winters in our region…as maybe we should.