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Winter is officially over, and spring is here! March 20 was the spring equinox, when the sun moved north across the celestial equator and day and night were approximately equal length. The wet weather season, which kicked off on October 1st, was cool and wet. For extended periods of time this winter, the longwave pattern over the Eastern Pacific remained highly amplified, allowing frequent moisture rich storm systems to impact the state. We experienced both ‘warm’ and ‘cold’ systems this winter. The ‘warm” systems had atmospheric rivers tapping into moisture and warm air from the tropics. One of our ‘cold’ systems in February originated from the frigid reaches of Canada, bringing rarely seen snow accumulation across Southern California with snow levels all the way down to roughly 1,200 feet. And for the first time in recorded history (140+ years), downtown Los Angeles did not reach 70 degrees or higher for the entire month of February. The good news is that the above normal precipitation spanned across the entire Southwest, including most of the Colorado River Basin (Figure 1).
 Figure 1. Percent of Average Precipitation Since October 1, 2018 (Credit: NOAA Regional Climate Center) What a difference a year makes. Last year, precipitation across the entire Southwest was 25-50% of average and the drought expanded. This year’s wet winter resulted in significantly reduced drought conditions and many areas are now no longer in drought (Figure 2). And it wasn’t just Southern California, the succession of storms in January and February 2019 blanketed the Sierra Nevada mountain range (Figure 3). Snow reports were being reported in feet, not inches. The summit at Mammoth Mountain has recorded over 50 feet of snow since the beginning of winter and the main lodge has received over 35 feet.  Figure 2. Southwest U.S. Drought Monitor (Credit: Western Regional Climate Center)  Figure 3. Sierra Nevada Snow Coverage from February 2018 and 2019 (Credit: NASA) ALTA Environmental is a Weather-Ready Nation Ambassador (WRN) with the National Oceanic and Atmospheric Administration (NOAA). As a WRN Ambassador, ALTA supports NOAA’s initiatives to inspire others to be better informed and prepared, helping to minimize or avoid the impacts of natural disasters by educating employees and the business community on workplace preparedness. More information about WRN and weather preparedness can be found at http://www.nws.noaa.gov/com/weatherreadynation/.
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