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Plummeting AO could offer some winter hints

As we’ve spoken about several times already this Autumn, our winter forecast doesn’t typically come out until the first week of November. Although some will bark at us for this — we’ve been hearing it already this Autumn — there are reasons for it. Mainly, our forecasters have recognized the importance of analyzing the pattern during October and the ideas moving into November. The recognition of the pattern during the next few weeks will be immensely important to understanding how things will shake down this winter. And our first “hint” could be offered during the next several days, as the AO — or Arctic Oscillation — is forecast to take a nose-dive.

The Arctic Oscillation is a large scale monitor of climate variability, also referred to as the Northern Hemisphere Annual mode. More simply, it’s a climate pattern characterized by winds circulating counterclockwise around the Arctic — typically at around 55°N latitude. In even more simple terms — the negative phase of the AO typically displaces cold air farther south in North America, while the positive phase keeps the colder air farther north, nearer to the poles and arctic regions. Forecast models are in good agreement that the AO will nosedive over the next several days — and not surprisingly, a major shot of below-normal temperatures is expected late this weekend into early next week. 

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Week begins with late season winter storm

NAM model forecast precipitation totals through Tuesday. Notice the sharp cutoff in precipitation totals from North to South near New York City.

NAM model forecast precipitation totals through Tuesday. Notice the sharp cutoff in precipitation totals from North to South near New York City.

Historically strong blocking, incredibly low Arctic Oscillation values, and a strong negative NAO have been in place for over 7 days. It was only a matter of time. A strong disturbance moving through the Central United States will move eastward towards the Mid Atlantic Coast, and eventually offshore. The surface low, which initially develops towards the Ohio Valley, will be forced to transfer and redevelop off the coast. However, the northward extent of precipitation will be extremely limited with a sharp cutoff likely. This will throw a serious wrench into the forecast — with a large discrepancy in snow possible over small areas.

Our Storm Total Snowfall Forecast, valid through Tuesday PM.

Our Storm Total Snowfall Forecast, valid through Tuesday PM.

Forecast models have been inconsistent with the developing gradient. As of Sunday evening, the GFS is the “wetter” of the model guidance — and farthest north with the precipitation shield. The NAM (which had previously shown extreme precipitation totals), Euro and SREF remain farther south. The precipitation amounts and intensity become an increasingly important issue due to the time of year. The warm ground and marginally cold low levels of the atmosphere suggest that light precipitation will not accumulate — and may even fall as rain in some locations on Monday.

Accordingly, the forecast remains highly uncertain as we move forward. We have laid out the expected snowfall totals in our Storm Total Snowfall map, but confidence remains extremely low. It is possible that many locations see light snowfall accumulations but only on grassy surfaces. The best chance for solid light to moderate snowfall totals appears to be over Interior Central and Southern New Jersey, where more persistent heavy precipitation is expected.

A Winter Storm Warning from the NWS remains in effect for Southern New Jersey, while a Winter Weather Advisory remains in effect for the remainder of the area.

The periods of snow, which will begin Monday, could linger into Tuesday throughout much of the area. For up to the minute updates on the upcoming storm system, stay tuned to our Facebook and Twitter accounts.