Wednesday, March 4, 2015

Long Range Outlook for March, Early April 2015

This is the Long Range Outlook for the period of March 2015 into early April 2015.

Paul Roundy
The above image is pretty complicated, but bear with me and it won't be so bad. This chart shows a longitude-by-time forecast for tropical convection anomalies (colored shadings) between 7.5º North and 7.5º South latitude, centered on the Equator. Blue colors correspond to enhanced tropical convection (thunderstorms), while yellows are indicative of suppressed convection. There are a lot of lines here, but the only ones we need to worry about are the red lines, which show the active phase of the Madden-Julian Oscillation in solid (dashed is the suppressed 'phase'), as well as the Kelvin Wave, which is in thin pink.

We currently see an MJO wave evolving from about 75 degrees East, as the red lines in that longitudinal sector show. It is expected that this wave will strengthen in the next week or two as an Equatorial Rossby Wave moves over the region, shown as a light-green delineation. The placement of tropical convection in this part of the world is equivalent to a Phase 4 MJO event. As shown in the image below, temperatures during a Phase 4 event will tend to lean warmer than normal for much of the country, but a deep snowpack across much of the North and Central parts of the US tells me this warm-up could very well be muted around March 12th.

A Kelvin Wave then forms around that March 12th period, and this convectively-coupled Kelvin Wave traverses the Pacific in time for the final days of the month. This very progressive tropical forcing theme tells me the country is likely in for some roller coaster weather patterns for the remainder of the month, despite the MJO wave signal only shifting eastward slowly in contrast to the Kelvin Wave movement. This particular chart has us reaching Phase 5 of the Madden-Julian Oscillation by the final days of March, which would typically favor a cooler than normal pattern for the Northern US.

However, this cold outlook for the end of March is working in contrast to a projected pattern shift in the Pacific, in which ensemble guidance sees a trough positioning itself along the west coast of North America to permit warmer weather in the Central and East US. With warm signals coming from the Typhoon Rule as Japan undergoes a generally-warm pattern in the next two weeks-plus, and tropical forcing not really being effective this past month due to such dominance from the Pacific pattern, I'll opt for a warmer outlook to close March.

To summarize:

- An overall cool pattern should remain in place through about mid-March.
- Model guidance is then indicating, at the very least, the synoptic (overall) weather pattern will undergo some changes for the last half of March. I see this as being a good shot for a warmer pattern.
- This warmer pattern could continue into early April.