+AAM Causes High Wind Events

Super Cold Midwest to Northeast Mid-to-late Next Week
01/24/2019, 2:39 pm EDT
Atmospheric Angular Momentum Contibutes to U.S. (and Elsewhere) High Wind Events
01/27/2019, 12:55 pm EDT
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An unusually strong +AAM regime will cause over-achieving high wind events in the U.S. well into February.

Atmospheric Angular Momentum Exceptional Increase

Caused excessive wind New England yesterday

Next up: Nebraska and Ohio Valley MON to NY/New England TUE.

Midwest/Great Lakes high wind event Feb. 2.

Fig. 1: Using all models the atmospheric angular momentum is forecast to increase into early February. +3 to +4 AAM is unusually strong.

Discussion: Exceptionally high wind ahead of a cold front affecting New England yesterday caused widespread power outages. Wind gusts exceeding 80 mph were observed at Blue Hill just south of Boston. The exceptionally high wind ahead of a conventional cold front is likely linked to strong positive phase atmospheric angular momentum (+AAM) present the past week or so and forecast to continue through the end of January and strengthen further in early February according to the GFS model (Fig. 1).

+AAM represents the presence of stronger than normal westerly flow aloft in the middle latitudes. Stronger wind aloft can extend to the surface ahead of strong cold fronts or during intense storms. Yesterday’s high wind event across the northeast was an example (Fig. 2).

Fig. 2: The 850 MB wind speeds yesterday afternoon were over 100 mph across Cape Cod and reflected at ground level with gusts to 81 mph at Blue Hill, MA.

So where is the next high wind event? We use the 850 MB wind forecast to best project where surface wind will be strongest. Next Monday morning the 850 MB wind forecast implies wind gusts of 50-60 mph across Nebraska (Fig. 3). Similar wind gusts are generated in northwest Arkansas Monday near dawn. The high wind belt strengthens across the Ohio Valley Monday afternoon when wind gusts to 60 mph affect Indiana and Ohio (Fig. 4).

Fig. 3-4: The 850 MB wind forecast is used to project damaging wind gust areas early next week.

More high wind events are expected next week. As the early week Midwest high wind shifts east the affected area expands affecting New York and New England Tuesday morning where gusts exceed 70 mph (Fig. 5). The next storm emerges late next week and brings borderline hurricane force wind gusts to the Great Lakes region Saturday (Feb. 2) evening (Fig. 6).

Fig. 5-6: The 850 MB wind forecast is used to project damaging wind gust areas next Tuesday and next Saturday.