Maps by NOAA, based on NCDC climate division data provided by the Physical Sciences Division at NOAA ESRL.įor weak and moderate strength episodes (Figure 2), the relationship is even weaker, with approximately one-third of the events featuring above-average precipitation, one-third near-average precipitation, and one-third below-average precipitation.Įlsewhere over the United States, El Niño impacts are associated with drier conditions in the Ohio Valley, and there is a less-reliable dry signal in the Pacific Northwest and the northern Rockies. During strong El Niño events, the Gulf Coast and Southeast are consistently wetter than average. Years are ranked based on the maximum seasonal ONI index value observed. climate division during strong (dark gray bar), moderate (medium gray), and weak (light gray) El Niño events since 1950. DIfference from average (1981-2010) winter precipitation (December-February) in each U.S. However, strong events in 1991//10 only provided small surpluses in the southern part of the state, while precipitation during 1965/66 was generally average to below-average across the state.įigure 2. Median or above-median precipitation was recorded over the entire state during strong episodes in both 1957//73 (Figure 2). The stronger the episode (i.e., the larger the sea surface temperature departures across the central equatorial Pacific are), the more reliable the signal in this region has been.įor instance, during the two strongest events in the past 60 years (1982//98), much-above-median rainfall amounts fell across the entire state of California. Over California and the Southwest, the relationship between El Niño and above-average precipitation is weaker, and it depends significantly on the strength of the El Niño. This relationship has occurred during more than 80% of the El Niño events in the past 100 years. The most reliable of these signals (the one that has been observed most frequently) is wetter-than-average conditions along the Gulf Coast from Texas to Florida during this 6-month period. In general, El Niño-related temperature and precipitation impacts across the United States occur during the cold half of the year (October through March). However, they happen more often during El Niño than you’d expect by chance, and many of them have occurred during many El Niño events.Īverage location of the Pacific and Polar Jet Streams and typical temperature and precipitation impacts during the winter over North America. “Associated with” doesn’t mean that all of these impacts happen during every El Niño episode. So assuming El Niño develops, what can we expect across the United States and when can we expect it?īy examining seasonal climate conditions in previous El Niño years, scientists have identified a set of typical impacts associated with the phenomenon (Figure 1). But those two events were the 2 strongest El Niños in the past 60 years, and we’ve seen many other El Niño years where California didn’t experience those types of devastating impacts. As the region suffers through a devastating drought, it could be something of a relief if we knew for certain that El Niño would bring similar soaking rains. Many folks probably remember the heavy rainfall, flooding, and landslides that occurred in California in 1982/83 and again in 1997/98. Well, it turns out that El Niño often results in changes in the patterns of precipitation and temperature across many parts of the globe, including North America (Ropelewski and Halpert 1987, Halpert and Ropelewski 1992). After all, why should it matter if the tropical Pacific Ocean becomes warmer than average? That’s thousands of miles away from the continental United States. By this point, most of you have heard that it looks like El Niño is coming, and maybe you’re wondering why you should care.
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