July 25, 2011

Heavy Showers and Thunderstorms

I wasn't going to blog today...but had to mention the convection--heavy showers and thunder--that rolled through on both sides of the Cascades.  The radar showed it nicely---here are a few samples.

And all of this during one of the climatologically driest weeks of the year.  A number of locations along the eastern slopes of Cascades, around the Tri-Cities, and over the south Sound got .15 to .20 inches in the downpours.

And I hate to admit it, but the forecasts were not good regarding these thunderstorms--both the human predictions and computer models.   The NWS forecast yesterday was correct about a major cool down today as the upper trough pushed in, but pretty much missed the heavy showers.  The models also did not do well.  At least we have plenty to work on!

Now this was a classic convective pattern, with a sharp trough moving in:

But clearly some ingredient was missing in the models--either how the models were initialized or their descriptions of the physical processes.

Perhaps a hint of the origin of the failure can be found from the infrared satellite sequence today.  Here are images from last night through this afternoon.  My eye sees two features:  one associated with the trough moving in from offshore and another feature initially over Oregon.  It is when they join that the convection blew up in a way that Friday's computer runs missed.  My own examination of the model output suggests that the eastern convection was associated with a weak upper trough over land that the models underplayed....but I only looked at the situation briefly.  It takes some detective work to conclusively discover what is behind such forecast failures.


  1. I was at my dentists office in Ballard having work done when the thunder started.

    What I could hear of it ( through the drilling :-( ) it sounded like heavy equipment being dropped outside, rather than rolling thunder I more typically hear.

    Driving in from the eastside at 630 am the sky became ominous pretty quickly.

  2. Cliff. Always love your blog, you were a great instructor, the UW meso models are cool....But what in the world!

    Are agrimet guage here NW of Yakima picked up .82 inches. We had 3 thunderstorms! One at 3, 7, and 9am. The one at 9 was two hours of thunder.

    150 acres of hay down and 80 acres of cherries ready. Insurance agent estimated 6 figures damaged. Everybody took a hit today.

    People wanting to cut funding on weather/climate research so vital to every sector of the economy are the ones I disapprove of tonight, not the meteorologists.

  3. We were staying at McMenamin's Edgefield in Troutdale and were awoken at 6:15 am by what I seriously thought was a bomb! Car alarms started going off, dogs barking, everyone in the hotel woke up and ran outside - some yelling - and then ran right back in because the lightning was hitting on the property! The thunder and lightning continued with sharp banging sounds (no rolling thunder - explosive gunshots) and bright lightning - within 1-2 seconds of lightning more thunder - like a violent explosion! - for about 10 minutes, and then a huge downpour. I'd never seen (or heard) anything like it. Quite a wake up on Monday morning!

  4. The weather is very atypical this year, at least along the inner coast of BC.

    Is it possible that forecast models are having difficulty because there is little in the data record that resembles the weather patterns this year?

    I notice that the forecasting for this area has consistently underestimated the amount and extent of precipitation when one of these troughs moves through?

    Do the models 'heal'? If we get several years of this pattern does the modelling get better? Just wondering ...

  5. Cliff,
    Speaking of forecast models I have been following the UW Probability forecast for Anacortes where I live. It seemed that the forecast was very often low for the forecast high temperature so I've tracked it for the past month and a half. The high temperature at the Anacortes ferry terminal (which should include the water influence here) exceeded the 50% forecast high on 44 of the 47 days. And it equaled or exceeded the 90% probability high on 25 of the 47 days (53%). Seems the model can use some tweaking.

  6. Cliff, I'm sorry I missed most of the show- the famous "convergence zone" where I live (north Bothell) does NOT seem to be a thunderstorm "hot spot"- which seems counter-intuitive! Since I have lived here it seems like there are less of them here than in Gig Harbor (where I lived for some years). Is my impression correct? And looking at the west side in general, I know they're uncommon, but where are the thunderstrom hot spots, if any?


  7. A question regarding snow remaining in the mountains. I use the SNOTEL sites to get an idea of what remaining snow pack is and one of the sites I track is Alpine Meadows. I noticed the snow water content getting closer and closer to snow depth over the last weeks. Ok, its consolidating and taking on additional rain. But on 7/25 snow water content was 15.5 inches and snow depth was 15 inches! Wait a second. How can that be? And Marten Ridge started showing negative snow water. Any thoughts?

  8. Digger,

    The instruments that a SNOTEL uses to measure snow depth and snow water equivalent (SWE) are two different sensors. You can see an example of them at: http://www.or.nrcs.usda.gov/snow/about/sensors.html

    The snow pillow measures the weight of the snow pack on it, and converts this to the amount of water in the snow pack. The snow depth sensor is an ultrasonic instrument on a tower pointing downward.

    Since these are two different and independent instruments, there's nothing to ensure that they're consistent (e.g. more SWE than snow depth). The instruments are typically least accurate when the snow pack is very small, and in general, the SWE measurement is more accurate than the snow depth. Hope this helps.

  9. I live in Pasco, and the forecast had been for thunderstorms; I don't think the meteorologists got it wrong. The "scientific forecaster discussion" seemed right on for what actually happened. My only complaint is that the main storm in the area went north of us and we missed out: no lightning,no thunder, just a few sprinkles.


Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

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