Wednesday, January 7, 2009
Just a little change in angle makes all the difference
A look at the current radar shows a major change from this morning...the rain shadow protection of Seattle is gone and now the rain shadow is NE of the Olympics. Moderate to heavy rain is now spread over the entire region from the Olympics to the Cascades. Why the change? The flow direction on the coast has shifted slightly from nearly westerly to southwesterly. You can see this by looking at the observations in the vertical (called a "sounding") at Quillayute on the coast (see figures). These observations are taken by balloon-launched weather observations (radiosondes) twice a day (4 am and 4 PM).
The first sounding is for 4 AM and you can see the winds (blue pennants) are nearly westerly at low levels...the second one is 4 PM this afternoon....a turn to the SW. The Y axis is pressure...850 (millibars) is about 5000 ft and 700 is about 10000 ft. The red line is temp and the blue dashed is dew point. The x axis of the plot is temperature in C.
The storm total precipitation from the local radar is shown below...pretty amazing..with some values over 15 inches! Note..this is uncalibrated and the radar could be high...but this is a major event and some rivers are hitting record amounts.
Interestingly the computer simulations were indicating record streamflows yesterday...these are from combining atmospheric and hydrological models...that is why the National Weather Service was hitting it so hard. I could hardly believe what they were saying...now I do.
Posted by Cliff Mass at 10:33 PM