Monday, September 16, 2013

Biblical Floods in Colorado

You've probably been hearing about the epic-Biblical-thousand year floods that Boulder, Colorado is experiencing. The cause is record rainfall - as you can see from the chart, above, developed by Climate Central. In fact, according to Weather Underground and Climate Central, Boulder, which normally gets 1.7 inches of rain in September and 20.68 for the year, got half a year's rain in less than half the month of September. (The forecast has a small chance of rain today, and then sunshine for the next few days.)

What might be causing all the rain? The Pacific. According to Climate Central:

During the past couple of weeks, the weather across the West has featured both an active Southwest Monsoon and a broad area of low pressure at upper levels of the atmosphere, which has been pinned by other weather systems and prevented from moving out of the region. It was this persistent low pressure area that helped pull the moisture out of the tropics and into Colorado. Signs point to the tropical Pacific being the source of the abundant moisture according to the University of Wisconsin’s Cooperative Institute for Meteorological Satellite Studies. From there, the moisture plume was transported northeastward, over Mexico and into Texas, and then northward by upper level winds.

This tropical air mass, which is more typical of the Gulf Coast than the Rocky Mountains, has been forced to move slowly up and over the Front Range by light southeasterly winds. This lifting process, known as orographic lift, allowed the atmosphere to wring out this unusually bountiful stream of moist air, dumping torrents of rain on the Boulder area for days on end.
That's a screen shot of the satellite images loop CIMSS released showing the tropical air mass. (I couldn't find it to embed it, but click on the link to Climate Central - you can see it moving there.)

Is climate change involved? No one weather event can be traced back easily to climate change, but there is at least one suggestive factor: the magnitude of the change from past events. And, of course, temperatures are rising around the globe. Generally, warmer temperatures mean more water vapor in the air, which means more extreme rain or snowfall. Stay tuned.



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