Friday, October 16, 2009
A very wet Saturday (and the Green River will not flood)
The latest high resolution forecast model runs are in. As are the new ensemble predictions (running many lower-resolution versions to determine the uncertainty of the forecasts). The bottom line...it will be quite wet during the next 24-36h...including the central Puget Sound region, the Olympics, and the Cascades.
Lets start with the latest satellite picture (attached)--you can see the plume of moisture that is approaching us. You can also see a wave in the clouds--that is a developing weather disturbance that will move through tomorrow and enhance the rain.
I will show you a graphic now I have never shown before...from the new RAINWATCH system my group is developing for Seattle Public Utilities (who are very concerned and proactive about heavy precipitation and flooding in the City). This shows you the rainfall over the past twelve hours based on combining the local radar and surface rain gauges. You can see the rain shadow NE of the Olympics and the heavier rain over Seattle and the central Cascades (keep in mind the blockage of the radar SE of the Olympics and over portions of the Cascades). Many locations have gotten over .5 inches in the later regions, some with well over an inch. But there will be a lot more.
Next the latest information from the high resolution forecasts. The precipitation may back off a bit tonight and then hit hard tomorrow as the disturbances comes in. The 24h totals ending tomorrow at 5 PM (Saturday) show a drenching...with 1.26-.2.5 inches (pink) over many locations (like central Puget Sound), with some places getting 2.5-5 inches. The subsequent 24 hours (ending 5 PM Sunday) brings precipitation, but far less (graphic). A frontal passage late on Saturday will transition us to a drier regime on Sunday with scattered showers. So that is the day to get out (and dry out). Maybe a hike in the Olympics.
So lets talk about the Green River...there should NOT be flooding from this. The river is very low now and this event is not the equal of the big ones. There is plenty of room behind the dam to store water right now.
Around the urban core there could be some localized street flooding...particularly if leaves clog the drains...so it is a very good idea to clean the drains in front of where you live or work.