We are currently entering a weak La Nina period, meaning cooler than normal Equatorial waters off the Peruvian Coast. Also, indications are that the North Atlantic Oscillation is entering a negative phase. The NAO refers to the east-to-west movement in the upper-level high across the North Atlantic. Typically, this works in tandem with the Arctic Oscillation. In a negative phase, we see a blocking pattern setup over Greenland, forcing the polar jet farther south across the eastern third of the U.S. La Nina further amplifies this trough, by setting-up a ridge of high pressure in the North Pacific.
Outlook:
Indications are we could see deep trough of low pressure setup across the eastern U.S. by December, accompanied by below-average temperatures. A record setting Lake Erie water temperature this past summer would provide for an active lake effect season across the snowbelt, at least to start. This is also the time in which we could see some big synoptic players (i.e. Nor'easters) for the Mid-Atlantic and New England states.
Climatologically speaking, January is the coldest of the winter months. This year, however a large upper-level high may anchor itself over the southeast U.S. This would keep the polar jet and thus, the bulk of the colder air farther north. A good portion of the eastern U.S. may see above-average temperatures and below-average precipitation during this month.
Summary:
December... Negative NAO & AO... Temperatures: Below-Average/ Precipitation: Above-Average (especially for the snowbelts)
January... Positive NAO... Temperatures: Above-Average/ Precipitation: Below-Average
February... Temperatures: Average/ Precipitation: Average
**La Nina should be in a weakening state at this time. February starts dry, but trends wetter heading into March.
JFB
