On Monday, I was contacted by Scott Beason, Park Geologist at Mount Rainier, who was looking for precipitation data.
Why?
Because of a serious debris flow down "Dry Creek" on the southwest side of Rainier, that closed the Westside Road on Saturday evening. Look at the pictures of the aftermath (below).
Just to orient you, in the image below, the area of interest is shown by the red circle and is just east of Mount Wow.
The debris flow, driven by very heavy rain, was even evident on local seismic data (see below). Note that the slide action started around 0515 UTC Sept 7 (10:15 PM PDT Saturday, Sept 6).
It turns out this event was caused by VERY heavy rain on Saturday evening associated with potent thunderstorms.The regional radars showed substantial thunderstorm/heavy rain activity moving across the Rainier area (an image around 8 PM is shown below)
Looking closer at the weather radar at 9:15 and 10:30 PM below, you can see some heavy rain over the "dry creek" area. Remember, weather radar can provide a measure of precipitation rate.
What were the rainfall totals in the debris flow areas? There were no nearby observation stations.
We can add up the radar precipitation rates over time to secure the answer (see below). By 10:28 PM, some locations in the area received as much as 2 inches, at least according to the radar.
So we know what produced the heavy rain that led to the debris flow: potent thunderstorms.
Did the forecast models predict them?
To help answer this question, below is the rainfall total covering the period from the high-resolution UW forecast model for the 24-hour period ending 5 AM on Sunday. The circle shows the area in question.
Moderate rain was predicted, but clearly the precipitation was underpredicted.
Getting thunderstorm precipitation right is very, very hard, and accurate local forecasts of such localized heavy rain may never be as skillful as we would like.
Talk about skillful. Professor Mass frequently uses that word to describe accurate forecasts. This post represents vital analysis of past extreme weather events, analysis which can help mitigate future damage caused by extreme weather.
ReplyDeleteHere's an unrelated question. In recent years it has become common for my Yakima Valley farmer friends to run short of late season irrigation water..Especially those on the Roza irrigation district. Is this a global warming phenomenon that will be ongoing, or mere coincidence? Certainly hope coincidence.
ReplyDeleteOne of my early (July 2007) Washington Trails Association trips to Mt. Rainier was to work on the Kautz Creek Trail that is in the drainage just east of your photos. The flood that did so much damage was in November 2006. There was so much destruction that other more prominent places got the media attention. I suspect WTA will find work in that area in 2026. The Park is an amazing place, and I'd love to go, but the body says no-more.
ReplyDeleteCliff, the models really have struggled with the recent convection. Looking at the Euro, HRRR, NAM, etc., the bullseyes showing heavy precip make it look like the model has things nailed down -- until one realizes that none of the models are making similar predictions. And none of them end up hitting the mark..
ReplyDeleteLately, the HRRR won't even initialize correctly, so of course it's all downhill from there. I end up following hunches when I go out to take photos, and my ideas about where convection will fire aren't much better (or worse) than the models. Very frustrating, indeed.