Drought Continues and May Worsen in 2012
POSTED: Monday, January 2, 2012 - 6:13pm
UPDATED: Thursday, January 5, 2012 - 9:18am
SANTA TERESA - Forecasters are predicting only a few changes over the next several months to the general weather pattern. That is, the La Nina pattern which led to the overall dry and warm 2011 will likely continue for at least the winter months, and possibly longer. Index values created to estimate the strength of different La Ninas over the years put the La Nina of 2011 as one of the most pronounced in memory. This year, those same reference values put the intensity of our La Nina at about 3/4 of the one last year.
During a La Nina, circulation in the Pacific Ocean is altered and unusually warm ocean surface temperatures are observed in the parts of the Pacific. The warmer water has an influence over the atmosphere, helping to nudge the polar jet stream a bit further north. This keeps the storm track generally into the Pacific Northwest portion of the US, giving them higher rainfall and less rainfall for our region. The more northward polar jet stream also usually means warmer temperatures.
In a La Nina winter, there could still be intrusions of cold air and precip, but on average those winters will be warmer and drier. After winter, some indicators are pointing towards "neutral" or average rainfall and temperatures for spring. That may still be bad news for the drought, as spring tends to be very dry anyway. Beyond the spring, some believe that wetter, El Nino circulation could resume.