Northeast Pacific Horseshoe SSTA Pattern Forming

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The Gulf of Alaska has cooled off considerably this autumn season and is cooler than normal for the first time since 2012. More recently, the cool waters have evolved off the U.S. West Coast. The California Ocean Current is up-welling subsurface cool waters causing a horseshoe cool anomaly to form from the Gulf of Alaska to the California Coast and southwestward toward Hawaii.

Highlight: North Pacific Horseshoe Pattern Forming; Super GOA Low-Pressure

Fig. 1-2: Northeast Pacific Ocean SSTA and the 15-day upper air forecast for the northern hemisphere by the 12Z GFS.

Discussion: The Gulf of Alaska has cooled off considerably this autumn season and is cooler than normal for the first time since 2012 (Fig. 1). More recently, the cool waters have evolved off the U.S. West Coast. The California Ocean Current is up-welling subsurface cool waters causing a horseshoe cool anomaly to form from the Gulf of Alaska to the California Coast and southwestward toward Hawaii. The cool horseshoe pattern is characteristic of La Nina episodes. The cool SSTA in the Northeast Pacific foreshadows a developing upper trough that intensifies over the next 15 days from the Gulf of Alaska toward the California Coast (Fig. 2). Just downstream, the atmosphere compensates by producing an amplified upper ridge over West-central Canada. And consequently, a new longwave trough is indicated on the U.S. East Coast. Another example of strong middle latitude SSTA patterns outweighing ENSO on the prevailing climate.

Gas Population weight HDD discussion: Heading into the weekend, the bottom line is that the national limited heating demand for mid-autumn is going to shift toward normal for the last 10 days of October and early November (Table 1).

DatesHDD Forecast12-Hr Change24 Hours Ago10-year NML30-year NML
Oct 15-2144.8-0.446.258.866.1
Oct 22-2882.5+18.392.676.181.7
O 29-N 489.1+0.194.395.197.5

Table 1: The 12Z GFS gas population weight HDD forecast compared to the 30-year/10-year normal and 12 and 24 hours ago.