[californiadisasters] La Nina Diagnostic Discussion (February 2012)

Synopsis: La Niña is likely to transition to ENSO-neutral conditions during March-May 2012.

A mature La Niña continued during January 2012, as below-average sea surface temperatures (SST) persisted across the equatorial Pacific Ocean (Fig. 1). The weekly SST indices remained near -1.0^oC in the Niño-3.4 and Niño-4 regions (Fig. 2). However, the negative SST anomalies weakened in the far eastern Pacific, indicated by warming in the Niño-1+2 and Niño-3 regions. The oceanic heat content (average temperature in the upper 300m of the ocean) anomalies also weakened slightly (Fig. 3), but continued to reflect an extensive area of below-average subsurface temperatures east of the Date Line (Fig. 4). Also, anomalous low-level easterly and upper-level westerly winds persisted over the central and west-central Pacific. Convection remained suppressed in the western and central Pacific, and enhanced over Indonesia (Fig. 5). Collectively, the oceanic and atmospheric patterns reflect a weak-to-moderate strength La Niña.

A majority of models predict La Niña to weaken through the rest of the Northern Hemisphere winter 2011-12, and then to dissipate during the spring 2012 (Fig. 6). Also, there is evidence of a downwelling phase of an eastward-propagating oceanic Kelvin wave (red shading, Fig. 4), which may increase temperatures across the Pacific in the next couple of months. The combination of a weakening subsurface temperature anomaly, the historical seasonal evolution, and forecaster preference for the average dynamical model prediction favors a return to ENSO-neutral conditions during the Northern Hemisphere spring, which are likely to continue into the summer. Therefore La Niña is likely to transition to ENSO-neutral conditions during March-May 2012 (see CPC/IRI consensus forecast).

Because the strength of impacts in the United States is not necessarily related to the exact strength of La Niña in the tropical Pacific, we expect La Niña impacts to continue even as the episode weakens. Over the U.S. during February - April 2012, there is an increased chance of above-average temperatures across the south-central and southeastern U.S., and below-average temperatures in the northwestern U.S.  Also, above-average precipitation is favored across most of the northern tier of states (except the north-central U.S.) and in the Ohio and Tennessee Valleys, and drier-than-average conditions are more likely across the southern tier of the U.S. (see 3-month seasonal outlook released on 19 January 2012).

Source: http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.html

--
Check out http://groups.yahoo.com/group/californiadisasters/
Read my blog at http://eclecticarcania.blogspot.com/
My Facebook: http://www.facebook.com/derkimster
Linkedin profile: http://www.linkedin.com/pub/kim-noyes/9/3a1/2b8
Follow me on Twitter @DisasterKim

__._,_.___

Be sure to check out our Links Section at http://groups.yahoo.com/group/californiadisasters/links
Please join our Discussion Group at http://groups.yahoo.com/group/californiadisasters_discussion/ for topical but extended discussions started here or for less topical but nonetheless relevant messages.

Your email settings: Individual Email|Traditional
Change settings via the Web (Yahoo! ID required)
Change settings via email: Switch delivery to Daily Digest | Switch to Fully Featured
Visit Your Group | Yahoo! Groups Terms of Use | Unsubscribe

__,_._,___