Long Range Overview - March 13, 2013

6-10 Day 500mb height anomalies from European (left) and American (right) model guidance.

Discussion: Medium range model guidance differs moderately in how the pattern will take shape over the Northern Hemisphere in the next couple of weeks. Both model systems agree in unusually strong high pressure over the Northern Hemisphere. This strong dominance of high pressure will allow low pressure anomalies to form and remain stagnant in perts of the globe. European model differs from American model in potential formation of low pressure in Canada. The American model is much more enthusiastic and allows for low pressure encompassing Canada and bringing about a very zonal (jet stream is west-to-east, no big cold blasts or warm shots) pattern. The European model prefers two centers of considerably stronger low pressure in the Gulf of Alaska and New England. This sort of pattern would allow high pressure to attempt to form in the Plains and Midwest, possibly able to connect to the dominant high pressure over the Arctic Circle.

Negative West Pacific Oscillation index will be provoked in either scenario with strong high pressure in the Bering Sea. The tendency of high pressure in the Bering Sea allows a pattern more supported by the European model, with lower pressure placed in a portion of Canada and not elongated throughout the entire region. Additionally, high pressure instigated by the negative WPO in the Southwest US is more enhanced by the European model, and it is this solution I favor for the next little while. Regardless of which model guidance prediction is correct, a weakly amplified pattern appears to be in store for the United States, and this should allow for a more stagnant pattern- not many sudden temperature swings due to a wild jet stream.

Andrew