Spring has definitely arrived here in the Pacific Northwest--the trees are blooming, leaves are starting to appear, and high temperatures are consistently in the 50s. However, with spring comes bouts of heavy rain which continue the feel of winter well into June.
The jet stream is on its way north and with it, lots of moisture. Here's the water vapor satellite image from this morning:
|Fig 1 -- GOES-W WV satellite image at 17Z, March 29, 2011. From the HOOT website.|
|Fig 2 -- 250mb winds (colors) and geopotential height (contours) at 12Z, March 29, 2011. From the HOOT website.|
How much rainfall are we looking at? Here is this morning's 24-hour rainfall forecast for the end of the day on Wednesday from the 12km UW WRF model.
|Fig 3 -- Previous 24-hours of rainfall at 00Z, Thursday, March 31, 2011. From the UW Modeling page.|
|Fig 4 -- Previous 24-hours of rainfall at 00Z, Friday, April 1, 2011. From the UW Modeling page.|
Such extended rainfall events being forecast often raises the specter of flooding in the mountain rivers. The Northwest River Forecast Center (NWRFC) runs many hydrologic models using the input from atmospheric models (like the ones we've been looking at) to try and predict how much water will enter each river basin. They can use this information to try and forecast river height. Here's a chart from the NWRFC showing the observed and predicted levels of the Snoqualmie River near the city of Snoqualmie east of Seattle.
|Fig 5 -- Observed (blue line), model forecast (green line) and extended trend (cyan line) of river stage level for the Snoqualmie River near Snoqualmie, WA. From the NWRFC.|
It's going to be a wet week in Seattle.