Plain Language Summary: Extreme heat is responsible for the most weather-related deaths in the United States (US). Using observations and numerical model experiments, this study investigates the potential predictability of heat waves determined by the state of the tropical Atlantic sea surface temperature (SST). During boreal summer (June-July-August), a larger than normal area of warm SST produces an atmospheric response over the US Great Plains, leading to increased clear-sky conditions, rainfall deficits, surface temperature, and heat wave events. The results of this study suggest a potential seasonal predictability of high-impact extreme heat events, owing to the longer prediction skill of SST.

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The post Modulation of North American Heat Waves by the Tropical Atlantic Warm Pool appeared first on NOAA's Atlantic Oceanographic and Meteorological Laboratory.

Abstract: This study presents an experimental model for Seasonal Probabilistic Outlook for Tornadoes (SPOTter) in the contiguous United States for March, April, and May and evaluates its forecast skill. This forecast model uses the leading empirical orthogonal function modes of regional variability in tornadic environmental parameters (i.e., low-level vertical wind shear and convective available potential energy), derived from the NCEP Coupled Forecast System, version 2, as the primary predictors. A multiple linear regression is applied to the predicted modes of tornadic environmental parameters to estimate U.S. tornado activity, which is presented as the probability for above-, near-, and below-normal categories....

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The post A Seasonal Probabilistic Outlook for Tornadoes (SPOTter) in the Contiguous United States Based on the Leading Patterns of Large-Scale Atmospheric Anomalies appeared first on NOAA's Atlantic Oceanographic and Meteorological Laboratory.

This study investigates the impact of the Madden–Julian oscillation (MJO) on U.S. tornadogenesis using atmospheric reanalysis and model experiments. Our analysis shows that the impact of MJO on U.S. tornadogenesis is most significant in May–July and during MJO phases 3–4 and 5–6 (P3456). These MJO phases are characterized by anomalous ascending motion over the Maritime Continent (MC) and anomalous subsidence over the northeast Pacific (EP), generating anomalous diabatic heating and cooling, respectively. These in turn generate large-scale atmospheric conditions conducive to tornadogenesis in the United States, enhancing the North American low-level jet (NALLJ) and thus increasing the influx of warm and moist air from the Gulf of Mexico to the United States and increasing the low-level wind shear and convective available potential energy along its path...

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The post Madden–Julian Oscillation–Induced Suppression of Northeast Pacific Convection Increases U.S. Tornadogenesis appeared first on NOAA's Atlantic Oceanographic and Meteorological Laboratory.