By Rod Hill on 2010-12-23
Cool water temperatures in the equatorial Pacific continue to be 1.4 to 1.7 degrees centigrade cooler than normal, which is classified as a moderate to strong La Nina. About ten days ago, I mentioned Portland would enter a period of heavy rain and would likely see 10.00" this month. We know now, the rain I was talking about moved into California. In fact, the dominate jet stream pattern over the past 30 days or so has been to our south. Not only have we not been seeing heavy rain, but only a few storm centers have pushed inland into the Northwest, most have stayed offshore and dropped south.
Heaviest moisture in terms of season averages have been mostly across California, Nevada, Idaho, Wyoming and Montana. This area is representative of a jet entrance into California and the leading trough northeast into Montana. This pattern is not what you would expect with La Nina. A typical El Nino flow would enter California, but would stay more south and run across Colorado or New Mexico, Missouri or farther south into dixie.
So, the point is, the flow pattern has not been what was expected. It is true, that our total rainfall has been above normal each month since September and is expected to continue into March, but the surplus will likely not be as high as predicted. To date, PDX has a water year total (since Oct. 1st) of 16.37". The total is above normal by 3.80 inches.
THE UPDATED FORECAST: Near normal to slightly cooler temperatures will continue into March. Precipitation will continue to be above normal, but not significantly so. I do expect a stretch of wet weather much of next week. I remind you that the Willamette valley is due for a strong windstorm. I continue to believe we will not see a heightened chance of valley snow.
Wettest weather through March is expected to be to our north, across northern Washington, Idaho and Montana. I am sure the folks in California are glad to hear this! As I always say....we'll see.
Rod Hill
Fall Headlines of 2010