Strong Positive Phase Pacific North America/North Atlantic Oscillation Indices Bring Hot Risk

Updated August 2021 North Atlantic Tropical Cyclone Season Outlook
08/01/2021, 6:53 pm EDT
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A strong positive phase Pacific North America index brings excessive heat peaking Wednesday in the Pacific Northwest while an equally impressive strong positive phase of the North Atlantic oscillation later this week causes extreme heat by early next week in the Mid-Atlantic region.

Highlight: +PNA/+NAO spikes = More extreme heat! Heat spike Wednesday Pacific Northwest and Mid-Atlantic region early next week!

Discussion: Spiking Pacific North America (Fig. 1) index associated with an amplified upper-level high-pressure ridge over the Northwest U.S. causes excessive heat peaking on Wednesday when 100-105F is likely for parts of Oregon, Washington and Idaho (Fig. 2). The PNA pattern flips to negative phase early next week.

Meanwhile an evolving amplified positive phase of the North Atlantic oscillation develops this week (Fig. 3). The associated anomalous heat associated with this pattern spikes early next week when the Washington, DC area reaches 100F (Fig. 4).

Fig. 1: The 15-day Pacific North America index forecast indicates a spiking positive phase driving excessive heat in the short-term for the Northwest U.S. reversing somewhat cooler early next week when -PNA generates.

Fig. 2: Excessive heat in the Northwest U.S. this week peaks on Wednesday.

Fig. 3: The 15-day North Atlantic oscillation index forecast indicates a spiking positive phase later this week and positive phase lasting into next week.

Fig. 4: +NAO-driven excessive heat peaks in the Mid-Atlantic next Tuesday.