First off, congratulations to Cathy Sheeter on the great find! Just wow!
-- Whenever a mega like this shows up in Colorado, I always have to check the recent weather patterns to see what might have made this bird show up where it did. Winds play such a huge role in these mega sightings, but I feel like it doesn't get enough coverage, or isn't understood well.
Over the last five days, there has been a persistent, slow-moving, low pressure system headed east out of Colorado (back on the day the Summer Tanager was found in Boulder, coincidence?) that parked itself over the middle of the US. This has essentially cut off most of the eastern portions of the US from bird migration except for maybe Florida (until today). The tornado outbreaks in the Deep South are from this same system. The flooding in Pensacola, same system. The "landslide" in Baltimore, same. You get the picture. Whenever there is a nearly stationary system, someone gets the good fortune and someone gets the bad. In this case, anything west of the system has gotten the goods (bird-wise). It turns out, Colorado and Kansas got the goods.
Beginning back on April 25th, this low pressure system began to form right on top of Colorado. Here is a map that helps you understand (if I explain it well).
http://earth.nullschool.net/#2014/04/27/0300Z/wind/surface/level/orthographic=-104.3269,40.6347,2133
This wind map is centered on Crow Valley Campground and is the surface wind streamlines. These are close to the winds at the level of bird migration, but not exactly. Aside from the map being centered on Crow Valley Campground, you may notice something that also points directly to Crow Valley Campground: the wind pattern. Track those winds backwards (go opposite the flow) and see where they are coming from. Low and behold, Arizona and Mexico are on that track. So does this account for the Painted Redstart (CVCC), Summer Tanager (Boulder), Hepatic Tanager (Lamar), Hooded Oriole (Kansas), and other rarities recently? Maybe... As the track of this low moved east it also moved south probably passing close to over the location of the Hooded Oriole (haven't looked too hard).
The low is mostly out of the way now and the flow is returning to a more normal pattern, so don't expect anything else to make its way up here (but we still might find something where people haven't been looking). Hopefully you get out to get a piece of the action.
Again congrats to Cathy Sheeter on the great find!
Bryan Guarente
Instructional Designer/Meteorologist
UCAR/The COMET Program
Boulder, CO
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