LA NINA, WINTER, AND THE ITCZ
Written by: Bob Metcalfe
This post will answer (somewhat) the question posed in the blog I wrote yesterday. Someone asked "What effects do La Nina have here in the winter?". Clearly a snow lover I take it!
The graph I've included at left is a study done by the NWS Buffalo on EL NINO effects on temperatures in the winter months since 1950. You can see that moderate to strong El Ninos typically mean noticeably warmer winters here in Rochester. Unfortunately they didn't do a similar study with La Nina effects. And no, the exact opposite does not occur during a La Nina.
This image shows the relationship between a La Nina (cold) occurrence and how the world fares. You can see "dry and warm" weather in the southern US, with cooler air indicated somewhat near the Great Lakes. La Nina's effects are usually much less of an effect than El Nino in our neck of the woods.
Some people ask "Well why is it that el nino/la nina have global impacts on the weather?" It all has to do with wind patterns along the axis of the equator where these waters lie. There is a line called the intertropical convergence zone (itcz), where the trade winds converge. It divides the southeast and northeast trade winds. Because of the coriolis effect, the typical motion of these winds is east to west in the northern hemisphere. When el nino occurs, there is a fight against these easterlies, which is why we usually associate el nino years with less tropical activity. But in a la nina, these fighting winds are relaxed, or even help increase the easterlies near the equator, which would of course alter the location of precipitation and temperature norms.
Thanks, Bob. And yes, I definitely am a snow lover. Hopefully we can return to a triple digit snow year for 2010-11. And we're still due for that big one.
ReplyDeleteSo is there no clear correlation between la ninas and how snowy we get? When looking back at la nina years, do you know if we tend to average more or less than normal? I seem to remember Scott saying once that with a la nina we tend to see more great lakes cutter storm tracks. I might be recalling incorrectly, though. But if thats the case, wouldn't it tend to favor us being on the warmer side of storms? Are there any big, historical snowstorms that have happened here during strong la nina winters?
ReplyDelete