Model Skill & The 15-Day Forecast

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ALERT: Strong MJO Influence Clashes With Stratospheric Warming

Discussion: Much discussion the past week or so regarding the persistent influence on climate by an immense Madden Julian oscillation now centered in the central (southern) tropical Pacific Ocean (Fig. 1) and an evolving stratospheric warming event also forecast to become unusually intense. The stratospheric warming event is likely linked to the MJO in that heat emitted by convection in the tropics has surged pole ward and into the stratosphere. Have the forecast models decided what the influence on North America climate will be in February? To determine the answer to that question we review the CWG/Storm Vista model skill scores for the past 30 days predicting 500 MB heights. Indicated is the ECM ensemble is the best model (Fig. 2).

Fig. 1: Current location of Madden Julian oscillation tropical convection is intense in the central and west Pacific tropics.

Fig. 2: The model skill scores calculated by CWG/Storm Vista of 500 MB forecasts for the northern hemisphere the past 30 days.

The ECM ensemble identifies above normal 500 MB heights produced in-part by tropical influences caused by the MJO presence into the northeast North Pacific and western North Atlantic (Fig. 3). The strong polar vortex located over central Canada in early February splits (due to stratospheric warming) with a new center near Iceland and the old center continuing over north-central Canada. The new polar vortex over Iceland is intense! However, the reflection of the warming in the stratosphere to produce cold at ground level is across the open water of the northern North Atlantic defeating arctic air development.

During the medium-range (days 6-10/11-15) the warm influence into the middle atmosphere by tropical/MJO influences remains suggesting the MJO stalls in the Pacific (rather than shifting east to the Atlantic as indicated by most models). Meanwhile the polar vortex persists but slowly loses intensity as stratospheric warming occurred in the wrong place to produce new arctic air. Consequently, the eastern U.S. trend warmer while the West is cooler and in-between Texas to the Northeast U.S. (Fig. 4-5) is stormy (helping to ease soil moisture shortages).

Fig. 3: The ECM ENS 500 MB forecast for the northern hemisphere for days 1-5 with MJO and stratospheric warming influences annotated.

Fig. 4: The ECM ENS 500 MB forecast for the northern hemisphere for days 6-10 with MJO and stratospheric warming influences annotated.

Fig. 5: The ECM ENS 500 MB forecast for the northern hemisphere for days 11-15 with MJO and stratospheric warming influences annotated.