Monday, January 30, 2006

The Baby Girl Needs to Learn

La-Nina continues to strengthen with anomalies of at least -2C and actual SSTs of about 24C, at around 140W. The event is now basin wide with anomalies of -1C and colder covering much of the eastern equatorial Pacific and -4C at ~150m below the surface.

The most significant tropical convective forcing is located near 5S/140E, a bit farther east than typical La Ninas. On roughly January 18, there was a convective flare-up at 0/140E in association with a convectively coupled Kelvin wave moving east at 15-20 m/s. Since then tropical convection has become quite intense across the South Pacific where SSTs are above normal and greater than 29C. Convection is also showing signs of increasing across both northern South America and South Africa. Even though some impacts from the Kelvin wave, when combined with existing SST anomalies, have been "MJO-like", the MJO signal continues weak.

During the past week westerly flow has increased substantially thoughout much of the equatorial and subtropical atmosphere. In fact, relative angular momentum has risen by roughly 2 standard deviations with respect to the 1979-1998 climatology. Much of this increase, the largest in about 6 months, has come simultaneously from several mountain barriers across the globe. In the posting I did January 25, there was discussion of retrogression across the north polar latitudes, and an ongoing sudden stratospheric warming (SSW). Feedbacks from the latter may also be a factor in explaining the recent changes in the high latitude zonal mean flow.

So, my thoughts are that the circulation is currently transitioning to SDM Stage 3, even though we have La Nina. That includes the continuation of a strong extended EAJ aimed at the west coast of the USA. There is a possibility the storm track may shift south by next week (timing is very uncertain), even though the greatest impacts are currently across the Pacific Northwest.

As has been the case for at least the past couple of weeks, many models have wanted to build a ridge off the North American west coast after about forecast day 5 (starting this upcoming weekend in today's case). I have wanted to believe some of those solutions, which would be suggestive of colder temperatures for much of the country for week 2, and a cessation of the frequent storms hitting the Pacific Northwest. Well, that has not happened. Furthermore, research suggests there may be lower predictability in La-Nina regimes as complicated as this one. Varying model solutions from day to day demonstrate that. Thus I would be cautious of model solutions that build ridges off the west coast after day 5. Instead, I expect a continuation of progressive synoptic systems to be more probable.

If there are to be adjustments to the circulation across the Asia-North American sector more consistent to La-Nina (SDM Stages 1 and 2), one behavior I would want to see is a rapid intensification of tropical convection across the Indian Ocean. I would also like to see an overall westward shift from it's current location to perhaps 100-120E. The above discussed Kelvin wave remains coherent and is approaching the Indian Ocean.

For southwest Kansas, other than progressive Pacific storm systems producing light precipitation from time to time, I see nothing substantial for at least the next 2 weeks. Given the seasonal cycle, temperatures may return to near normal during week 2.

Ed Berry and Klaus Weickmann

No comments: