It also happened in Alberta, Canada, a vast region of Siberia/China (Google ‘Amur River’ – the flooded area is equal to Germany and France combined), central Europe, and northeastern India.

And all these events were similar to Colorado in that they involved ‘average’ systems that simply got ‘stalled’.

I’m pleased to see you writing about this, Greg, because I’m seeing the very same thing. Floods from rapid snowmelt or hurricanes are to be expected. 1,000+ year events happening from typical (but stalled) systems are another sort of animal altogether.

BTW, Colorado’s rainfall amounts exceeded anything to be expected in a 1,000-year event – by more than 200%:

http://hdsc.nws.noaa.gov/hdsc/pfds/pfds_map_cont.html?bkmrk=co

But also, if we are entering an era of convoluted jet streams, we may not have settled in. It may be that as this transition progresses, standing waves end up standing in certain spots because of mountain waves or sea-land interactions (which in turn would probably be affected by major oscillations, so there might be an “El Nino Rossby Wave of Wetness” over the Rockies for five years, then it moves off and becomes the “La Nina Rossby Wave of Wetness” over Central Europe.

It would add a new and interesting dimension to the boring old seasonality thing.

I’m not so sure about that. Even if there were a strong preference for certain positions of the wave pattern, I expect it would take at least a decade if not more to establish this with confidence, and the high-amplitude standing wave configuration was rare until a few years ago. There is a reason the NWS uses 30-year baselines for determining climatology.

Even if the position is approximately random, however, certain positions will be worse than others. Mountains tend to enhance precipitation along the windward slopes. At Colorado’s latitude, this usually means the west side (if you have ever driven across the Rockies, you may have noticed a distinct difference in vegetation at altitudes above 7500 feet: deciduous trees west of the Continental Divide, evergreens to the east). In this case, there was a southeasterly flow tapping into the seasonal monsoon which normally stays further south; when this flow hit the Front Range, lots of rain fell. Shift that pattern east to Missouri, and you will probably have some flooding, but not the widespread devastation we saw in Colorado, because the rain won’t fall as quickly.