West U.S./Europe Colder Pattern Change

Turning Very Cold & Snowy Across Europe To Close February
02/16/2018, 2:38 pm EDT
Intense Negative Phase of the North Atlantic Oscillation Deliveres Historic Cold/Snow to Europe
02/19/2018, 5:20 pm EDT
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Discussion: Normally, a La Nina winter is cold and snowy in the Northwest U.S. The 15-day forecast for the western states reveals and evolving, strengthening and long-lasting cold to very cold pattern (Fig. 1). The first serious cold of winter despite La Nina’s presence. Accompanying the cold and helping to enhance the amplitude and duration is a heavy snowfall forecast (Fig. 2).

The La Nina climatology for JAN/FEB/MAR (according to NOAA) of anomalous temperature across the U.S. favors the cold West, warm East (Fig. 3) currently forecast to close meteorological winter. From Dec. 1 to middle February the U.S. pattern has been very non-La Nina-like with warmth in the West and a cold pattern for much of the eastern half of the U.S. (Fig. 4).

The thermal pattern is changing in Europe as well. A mild winter closes very cold and similar to the Northwest U.S. as a blanket of snow (Fig. 5) precedes the cold to very cold air mass spreading from Western Russia across Europe (Fig. 6).

Cause of the late winter chill? A stratospheric warming event evolving over the polar region (Fig. 7) and likely to last through early March.

Fig. 1: La Nina temperature anomaly climatology for JAN/FEB/MAR according to NOAA.

Fig. 2: La Nina temperature anomaly climatology for JAN/FEB/MAR according to NOAA.

Fig. 3: La Nina temperature anomaly climatology for JAN/FEB/MAR according to NOAA.

Fig. 4: Dec. 1 to Feb. 16 U.S. temperature anomalies.

Fig. 5: Day 6-10 temperature anomaly forecast for Europe by the ECM ENS model.

Fig. 6: Day 11-15 temperature anomaly forecast for Europe by the ECM ENS model.

Fig. 7: Stratospheric warming is indicated on Thursday Feb. 22. The patter will persist into early March.