August 10, 2019

Saturday Morning "Deluge" Shows the Limitations of Modern Weather Prediction

This morning was very wet around Puget Sound, with some locations getting 3/4 of an inch or more.  And eastern Washington is being hit quite hard today with vigorous thunderstorms.

To illustrate, here is the total precipitation over the past 24 hr, ending 4 PM Saturday (click on figure to expand).  About 2/3rds of an inch in Seattle...close to the usual amount for the entire month of August.   Several locations in the southern Cascades and the eastern slopes of the mountains got over an inch.

Over western Washington, precipitation was associated with a deformation band north of a land-falling low center to our south.  What is a deformation band?  It occurs then two streams of air converge together, often north of a low center, resulting in upward motion--and thus clouds/precipitation.  Here is the forecast winds for 8 AM this morning at 700 hPa (about 10,000 ft) can see the deformation pattern.

The result was a band of precipitation that hung over Seattle for several hours, thoroughly wetting the area.  A radar image around 7 AM  shows the band very well.

Unfortunately, although the models had shown that a band would set up somewhere in western Washington, they universally got the timing and location wrong.  For example, the 24h precipitation forecast from the NOAA/NWS HRRR model, their best at the short-range, kept the band too far south, with less than .25 inches over Seattle.   Clearly, the models lacked sufficient information to define the initial conditions of the forecast, or there is some issue with model physics.

This afternoon the action moved to eastern Washington, where surface heating released a great deal of instability, resulting in strong thunderstorms, lightning, and lots of rain.   Take a look at the radar for 5 PM.  Wow.  The red areas are very heavy rain or hail. Lots of places over the eastern Cascade slopes are getting hit hard.

These storms are really impressive in the visible satellite imagery at the same time (see below).   You see the high high ice clouds extending northwestward from the storms?  These are anvils--the high cloud blow off from the thunderstorms.     Some of this anvil cloudiness is spreading into western Washington!

The big issue, of course, is the potential for lightning from these storms causing more fires.  Will have to be watchful.

Sunday should be a bit drier, but eastern Washington will get more thunderstorms, and a few showers might well drift over the west.


  1. Thank you Professor for elucidating such a curious weather event! (bit of a deluge in August)

  2. Just maybe a trace over 0.75 in our rain gauge in Wedgwood in NE Seattle. Impressive for an August morning. By the time we were seated for the Sounders match it was sunny, dry and trying to get too warm.

  3. Do you have the rain totals for the governor's mansion?

  4. Here in Bow, Wa the total rainfall to now, at the Friday Creek station since the beginning of the water-year in October, is below any of the past 7 years that are displayed. Often well below. Stream flows such as the Samish River are also well below their averages. It is a difficult year for natures water needers.

  5. As you stated, "Clearly, the models lacked sufficient information to define the initial conditions of the forecast, or there is some issue with model physics." And you were summarizing only a short term forecast. As such, you've defined exactly why I, like so many others, seriously question the 12, 20, or 50 year "end-of-the-earth" predictions that have been heard for decades about man-made global warming and our ability to use computer models to predict the future.

  6. Considering their massive presence next to Magnuson Park, why doesn't the NOAA facility have a weather data website on weather underground? I know they have a weather station there.

  7. I'm surprised nobody, especially Cliff, recognized that the energy of this is the remnants of a hurricane that misssed Hawaii.

  8. Widely scattered in Portland, some areas received over two inches in less than two hours(!), while others saw less than scant.

  9. Skeptic517: current observations of climate change are not computer model predictions. Not to mention Iceland, Europe etc.

  10. My weather station captured .6" in under 15 minutes. Moses lake. Thunder, lightning wind

  11. Well I was disappointed. I was out on the boat on the Sound. I saw no lightning, and heard no thunder.

    Trouble is, I was prepped to expect it. It is all the more disappointing if you are prepped and then it doesn't deliver.


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