Pacific Extreme Pattern

The development of the Pacific Extreme Pattern from 50 days (a) to 0 days (h) in 10 day increments. Contours indicate the height of 300 mb, an indicator of a warm air mass (ie. more contours closer together = hotter). (McKinnon et al. 2016)
The development of the Pacific Extreme Pattern from 50 days (a) to 0 days (h) in 10 day increments. Contours indicate the height of 300 mb, an indicator of a warm air mass (ie. more contours closer together = hotter). (McKinnon et al. 2016)

Would you still book that summer vacation if you knew there was going to be an extreme heat wave during your trip? This is a question you may soon ask yourself with last months revelation of a new Pacific Extreme Pattern that has the capability to accurately forecast a heatwave (>6.5 degC, 11.7 degF) up to 50 days in advance. The pattern relates the sea surface temperatures of the central subtropical Pacific to the air temperature anomalies in Midwestern US states during the hottest days of the year (June 24 – August 22).

The area of the US with the strongest correlation to the Pacific Extreme Pattern. Purple and red colors indicate weather stations that were most closely linked to the oceanic conditions. (McKinnon et al. 2016)

The oceanic conditions leading up to the heat wave require warmer than normal waters butting up against anomalously cool waters (deviations from normal >0.5 degC). When this pattern is particularly pronounced, the likelihood of an extreme heat wave during a certain week or day can triple.

The exact mechanism for the connection remains a topic of further research, but initial thoughts are that the oceanic pattern causes waves in the atmosphere whose energy accumulates into a ‘heat dome’ over the Midwestern states. Alternatively, there could be an external third factor that triggers both the oceanic and atmospheric patterns.

This coming summer will serve as a proving ground for this new technique to see if it really holds up in practice. Currently, the oceanic pattern is flipped, suggesting cooler summer weather, but this contrasts more traditional seasonal forecasting methods which predict one of the hottest summers in recent years. We’ll have to see how the summer plays out to determine the predictive capabilities of this new pattern.

If the Pacific Extreme Pattern proves to be a valuable mid-range forecasting tool, it could help farmers, utility operators, and others in the US heartland better prepare for the crippling heat that is becoming more common with a changing climate. It is also possible that similar patterns may exist for other regions, but further research will be required to tease out these relationships.

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