The Australian Bureau of Meteorology has officially declared the start of an ENSO event with sea surface temperatures (SST) across the tropical Pacific colder than normal (-0.8 °C) and consistent trade winds. The current La Niña is expected to be moderate in strength through midsummer (2020/21) for the Southern Hemisphere. Typically, these events bring above-normal precipitation across Australia during spring and summer and drier conditions across the Pacific coast of North and South America.
La Niña’s impact can be more far reaching, and there is a general belief that La Niña tends to favor cocoa production across West Africa. The effects of these climate phenomena are hard to establish scientifically and are not as well understood, however. Overall, the intensity of the ENSO event seems to determine the overall impact, so the current situation will need further monitoring as it progresses.
Closer to home, the influence of cooler ocean temps along the equator and pockets of warmer SST in the north Pacific is influencing weather patterns across the U.S. The position of the jet stream has shifted far to the north along western Canada, dipping down across the Midwest as it makes its way across the country. This pattern is causing warm temperature anomalies to dominate in the western half of the U.S. and bringing down a cooler dry air mass across the northern plains in the Midwest.
We have already witnessed warmer than normal temps across the Pacific Northwest and California that contributed to the active wildfire summer season similar to 2018.
The U.S. drought monitor is showing increasing moisture stress across the western U.S. on poor precipitation. Meanwhile, cooler, dry, fall-like conditions are aiding farmers across the Midwest as harvest is underway for many crops. Should the pattern continue into winter, the chance increases for an extreme polar vortex for the Midwest, carried down from Canada by the deep trough of the jet stream.
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