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After a long winter that’s seen record-setting warmth, a couple of rounds of the polar vortex, and a constant barrage of rain and snow out West, the U.S. could use a break as we head into spring. Unfortunately, it doesn’t look like we’re going to catch much of a reprieve from the atmosphere’s tantrums.
How El Nino's Played Out So Far
The pattern we’ve seen over the last couple of months is typical of a year influenced by a mild El Niño in the Pacific Ocean. An El Niño occurs when the water of the eastern Pacific Ocean is abnormally warm for many months at a time. The warmer-than-normal water in this part of the Pacific can warm the air over the ocean, altering upper-level jet streams that cross the country.
Jet streams largely exist because of the temperature gradient between the warm tropics and cooler air at higher latitudes. The northward expansion of warm air during an El Niño strengthens the subtropical jet stream over the southern U.S. and shoves the polar jet stream farther north toward the Canadian border, changing weather patterns across the country.
El Nino’s effects on U.S. weather are most pronounced in the winter. The hallmark of an El Niño winter is heavy rain and snow in the western U.S. and warmth in the southeast. We’ve seen that in abundance so far this year. After a slow start to the rainy season, storms started washing over the West Coast with a vengeance last month, bringing almost weekly bouts of flooding rains and torrential mountain snows from Washington to California.
There's plenty of upside to moisture like this, of course. Increased mountain snow has been a boon to the ski industry. Farmers will benefit from the snowmelt in the warmer months, and the drought situation across the region has improved. California began February with 76 percent of the state experiencing abnormal dryness or full-on drought conditions, then that number plummeted to just 32 percent after three weeks of steady rainfall. The Four Corners region of the Southwest has also seen relief from its exceptional drought—the worst category on the U.S. Drought Monitor—over the last couple of months thanks to wetter weather resulting from the El Niño pattern.
Here’s What Kind of Weather Pattern You Can Expect This Spring
Taking a look back at the weather we’ve seen this winter helps put into context the weather coming up this spring. Seasonal precipitation in California comes to a dramatic halt between April and November, while cities like Las Vegas and Phoenix historically see little precipitation between the start of spring and the onset of the summer monsoon season. The seemingly-endless precipitation out West—including the healthy snowpack in the mountains—will serve as a nest egg once the rainy season comes to an end.
It’s not just the West that’s seen plentiful precipitation. Many areas east of the Rockies have seen so much rain and snow that their soil is oversaturated for this time of the year. The above map shows soil moisture for February 18, ranked by percentiles. The darkest green shows soil moisture in the 99th percentile, which tells us that the ground is about as wet as it can get for the middle of February.
This has big implications for the coming spring rains. Showers and thunderstorms can produce more and heavier precipitation because the air can hold more moisture with spring's warmer temperatures.The combination of saturated soil from recent rains and the opportunity for heavier precipitation will dramatically increase the risk of flooding as we head into the warmer months.
The latest long-term forecast from the Climate Prediction Center shows a general ridge-trough-ridge pattern across the U.S. this spring. A setup like this would place ridges of high pressure—fostering drier, warmer weather—over the coasts while the center of the country experiences troughing, leading to an active and stormy pattern. A ridge of dry air parked over the West, could cut the rainy season short, allowing groundwater to evaporate and snowpack to melt more quickly than under normal conditions. However, the extensive precipitation the region received this winter will help delay the ill-effects of abnormally dry stretches for several months longer than we would have seen otherwise.
Upper-level troughs moving over the center of the country will allow frequent low-pressure systems to develop at the surface, leading to regular bouts of stormy conditions east of the Rocky Mountains. Thunderstorms can develop if the cold and warm fronts extending off of these lows have enough instability to work with. Not only would that heighten the risk for flooding from even modest amounts of heavy rain, but an active pattern would crank up the risk for severe storms as we get into the peak months for dangerous wind, hail, and tornadoes.
We’ve already seen one such storm tear through Alabama this month, killing a reported 23 people. That storm was an EF-4 on the Enhanced Fujita Scale, the first storm of that magnitude since 2017 and the deadliest since 2013.
Start Preparing for Spring Weather Now
The dry and warm weather that’s likely out West isn’t inherently dangerous—it’s a slow-motion pain that’s easy to ignore until you fall into a water crisis. The best thing folks out West can do is to conserve water as if there was a raging drought. Preemptive water conservation is a surefire way to help a region prepare for extended periods without precipitation.
Folks east of the Rockies can prepare for the potential for severe thunderstorms and flooding by making emergency plans for hazardous weather. Make sure you have plenty of emergency supplies at home and in your vehicle. It’s important to know in advance where you would take shelter from threats like tornadoes, destructive winds, or large hail if you’re at home, work, on the road, or caught outdoors. If you have to go out during flooding, it’s a good idea to plan out multiple routes between home, work, and school so you’re not caught off-guard by water-covered roadways.