Stratospheric Warming Trigger A “Polar Vortex” February in U.S? Maybe! But Expanding Snow Cover is Guide to A Colder February Ahead!

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Fig: 1-3: NOAA/CPC arctic oscillation history (since late September) and the 16-day forecast yielding a wide array of forecast possibilities (above). The mega-cluster ensemble day-15 most likely and caveat forecast for temperature anomalies across North America.

Discussion: Climate analog forecasts for North America did a good job at forecasting the January thaw. Climate analogs follow-up the January warmth with a February chill. Will that cold pattern happen? The atmosphere is shifting in that direction as stratospheric warming is widening from the Eurasia side of the North Pole into North America by early February. But! Will the troposphere (where weather occurs) respond to produce arctic air and mid-latitude chill normally associated with stratospheric warming? The 16-day arctic oscillation (AO) forecast from NOAA/CPC replies to that question with “I don’t know!”. I add the exclamation point due to the gigantic range in AO possibilities according to the ensemble members of the 16-day forecast. The mega-cluster ensemble interprets that AO forecast with a day-15 solution that has a “most likely” (64% chance) of cold over Canada and the West U.S. OR the “caveat forecast” (36% chance) of widespread cold in the U.S. So, from a model standpoint, early February is most likely marginally cold. However, left out of the model interpretation is the invitational character and influence of expanding snow cover has on cold air masses. Climate Impact Company expects a significant increase in snow cover across the northern half of the U.S. the next 2-3 weeks which will (eventually) favor the colder model solutions heading into the last month of meteorological winter.