La Niña is a component of the natural see-saw of oceanic and atmospheric conditions in the tropical Pacific characterized by anomalously cold ocean temperatures in the central and eastern tropical Pacific. These anomalously cold temperatures are evident in sea surface temperature anomalies from earlier this month. Note in particular, the tongue of anomalously cold water extending along the equator from South America to the dateline.
Source: Climate Prediction Center |
Another way to look at this is in terms of hight anomalies at upper levels. Areas in warm colors below correspond to anomalous ridging, and areas in cool colors anomalous troughing. At upper-levels, the primary circulation features are an anomalous trough near Hawaii, ridging in the North Pacific, and troughing over northwest North America.
Source: NOAA/ESRL |
Source: NOAA/ESRL |
Thus, this is a pattern that doesn't fit the average La Niña pattern all that well. That isn't to say La Niña isn't playing some role. It could be playing an important role, with our use of relationships based on averaging past events the real problem. On the other hand, it is also possible that we need to look at what is happening from a broader, global perspective. Some discussion of this topic is provided by the California Weather Blog. This is an area of active research, and one that will probably get even more attention after this winter, which has generated some remarkable weather extremes across the United States.
Thanks for linking to that California Weather Blog. Lots of good info there, though not exactly encouraging. Our only hope at this point might be for you to take a trip.
ReplyDeleteI have tried to find correlations between some of the other indices (such as the NAO, AO etc) and winter precip in parts of the western U.S. but have not found much of any significance. There is some definite correlation (plus or minus) with ENSO of course, but even so this correlation is relatively low with R values between 0 and 0.25 for most areas (1.0 would be a perfect correlation). For California, positive phase (El Niño) seems to be associated with greater variability in winter precipitation, with the La Niña phase more "predictable", e.g. less variable, and having a lower seasonal mean in southern half of the state. In Utah, areas roughly north/west of I-70 appear slightly favored by La Niña but this correlation is really only significant in the far north (R value ~ 0.20). Southern and eastern Utah are slightly favored by El Nino for winter precip but with a low correlation (< 0.10). The bottom line is that any season really can bring any given type of pattern.
ReplyDeleteIn Colorado, neither La Nina nor El Nino conditions produce statistically decipherable impacts to snowpack. Its spaghetti.
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