Weather and El Nino Update from
July 16, 2009
Most of the western U.S. is scorching this week under the influence of a strong ridge of high pressure, and Tahoe is no exception. Temperatures are forecast to remain well above normal into the weekend, with highs in the 80s around the Lake and the 70s near the mountain passes.- The basin has been- dry for most of this week, but by Friday the chance of thunderstorms will increase as moisture from Tropical Storm Dolores in the Eastern Pacific begins to be pulled northward. Thunderstorms are possible Friday and Saturday afternoons, especially along the Sierra Crest. By Sunday a low-pressure system sweeping across the Northwest should begin to have at least a slight influence on our weather, cooling temperatures a few degrees but still above normal for this time of year. Next week the high pressure rebuilds and the heat continues.
El Nino Update Sea Surface Temperatures were .8 degrees above normal in the week ending July 13, and the Oceanic Nino Index for the April-May-June period was .2 and rising.- This index, which measures the temperature change from normal in either direction,- must- be at least- a positive .5 for five- consecutive, overlapping- three-month periods before an official El Nino can be declared,- so we still- have a ways to go. But all signs are pointing to at least a moderate El Nino for the winter of 2009-10.