Pattern Change Next Week

A ridge of high pressure is going to build over the Eastern and US once again late this week into this weekend, causing temperatures to moderate (warm) across much of the region.

However, all indications are that a flip in the large-scale weather pattern will occur by the early to middle half of next week.

NAO and PNA

The North Atlantic Oscillation (NAO) is forecast to go negative next week, and the Pacific North American Pattern (PNA) is forecast to go positive next week.

GEFS NAO forecast initialized 00z October 17, 2017.

Both support troughing in the Eastern US in the aforementioned phases.

Typhoon “Lan”

Additionally, a typhoon in the West Pacific (“Lan”) will strengthen into a super typhoon this week and get absorbed into the polar jet stream, which also favors troughing in the East/Central US in about 7 – 10 days.

The last time this occurred during a similar set-up was with Typhoon “Nuri” in November of 2014.

What Does it Mean?

When troughs drop down into the Continental US during the fall and winter months, they bring cold fronts with them, which cause outbreaks of arctic air, and generally stormy weather (including severe weather) at times.

GEFS 850 millibar temperature anomaly forecast initialized 18z October 17, 2017, valid October 25, 2017.

Therefore, a change to a much colder — and possibly somewhat wetter — weather pattern is likely across the Central and Eastern US, including the Gulf Coast region, starting next week.

How Long Will it Last?

It is not clear how long this pattern change will remain in place. Although, extended-range guidance suggests that it will last through the end of the month, and potentially into early November.

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