Bryan, thanks for this analysis. One lesson I have absorbed from you in the past is that it's not the surface-level winds that are important, but the wind up a bit higher where the birds are migrating. Why do you focus on surface winds this time?
thanks - Sandra Laursen On Monday, October 15, 2018 at 10:40:25 PM UTC-6, Bryan Guarente wrote: > > Cobirders, > when Ted beckons... you get a really long email... > > So the question is: > > 1. Why did this situation bring more birds to the Front Range? > > *TL;DR* (Too long; didn't read) -- Super-short snarky answer just for > Ted: it was the wind! The weather had a lot to do with it and which end of > the cold front Colorado ended up on helped dictate that flow of migrants. > Based on percentage of the total flow area behind the cold front compared > to the overall flow, it looked like a 30-40% chance that birds would end up > in the Front Range due to funneling or convergence. > > *Full version:* > > - *Why did this weather situation bring more birds to the Front Range?* > > Let's look through the computer models because it is sexier, and makes it > easier for everyone to understand because I can give you data everywhere on > the globe. One could also do this with satellite imagery, but it is harder > to get you to see what I want to see, so I will work with the easier > option. > > - > > https://earth.nullschool.net/#2018/10/14/0000Z/wind/surface/level/orthographic=-105,40,1706/loc=-105.000,40.000 > > That animation of a single time gives you the idea of what is going on > that made Colorado a hotspot for any migrants yesterday. Any bird trying > to make its way to the southeast from Canada may have started out with good > intentions, but depending on which side of the flow it started from or > ended up in over time, it had a strong chance of ending up heading toward > the Front Range. The cold front itself is the "blue" area with no wind > that curves from Lake Nipigon down through Iowa, Nebraska, then curving > into Colorado. All of the airflow behind that cold front (to the north and > west) is what we want to focus on. The flow had multiple possible end > points at that time: near Lake Nipigon, along the cold front just south of > Lake Superior, along the cold front in Iowa, or into the Colorado Front > Range. > > The highest likelihood location for the birds to end up was actually along > the Front Range. The percentage of the total area of that flow behind the > cold front that was showing a distinct convergence into the Front Range was > about 30-40% (guesstimated). So any birds within that 30-40 percentage of > the total area had a strong likelihood of ending up in Colorado's Front > Range. That means that birds ranging from Alberta through Montana, North > Dakota, Minnesota, and western Iowa and then everywhere southwest of that > behind the cold front, had a strong chance of ending up in the Colorado > Front Range. The door was wide open so to speak. The flow was broad > initially, then came crashing in on itself converging into a small area > (Colorado Front Range). So think of this as your funnel for bird > convergence. On the broad end, you put in any birds you'd like, then on > the other end, you get a stronger concentration of birds because the winds > they like to follow are forcing them together more over time. Other places > are getting lower concentrations of migrants due to the divergence of the > birds from their area into our area. > > This was only one snapshot of the winds at the surface though. For a > period of about 12 hours, this was still the case around this. Earlier it > was less convergent into the Front Range, but picked up, then maximized > around the time I showed you earlier, then tapered off a little. > Importantly though, the time I linked you to was right around sunset when > the snow started to pick up all along the Front Range. This was a bonus > for birders, hindrance for the birds. Both the sunset and the snowfall > made this more important for the birds to get to the ground, and then they > likely stayed the night to try their luck at adding some munchies in the > morning. > > This is the time for American Golden-Plover migration. It also happens > that the location this storm started from had a good chance of grabbing > some of those migrant AGPLs trying to make their way through the Central > Plains like they normally do. However, as luck would have it, they ended > up on the wrong side of the flow behind that cold front. They got stuck on > the Colorado Front Range side, and then we got lucky to see them here. The > number of AGPLs that migrate through this corridor in a short period of > time is HUGE. That also gives us a higher chance of getting them here in > CO. I remember from my days in Illinois that this time of year would > produce fields upon fields of AGPLs numbering in the thousands easily. > They would take off in huge flocks and migrate quite broadly through the > area during the day. You could easily go a day with seeing 20-40 flocks > numbering 500-1000 birds a piece. It is kind of surprising that there > weren't more AGPL found along the Front Range when you think of it that > way. > > Yes, you may say as a counterargument to my arguments about the wind that > birds have wings, and they don't have to follow the winds. True. They > don't have to follow the winds. If you ended up on the wrong side of that > flow though (the west side closer to Montana or Alberta), the chances of > you covering enough ground to not end up in Colorado was pretty slim > without a LOT of extra effort to cross the flow. Ask your pilot friends > which way they spend more fuel with a tail wind or with a cross wind and > you will get some idea of why they ended up here instead of Iowa like they > were "supposed" to. > > Hope that helps. This was my quick response. If you want to hear more, > just ask and I will see what I can do to respond. If you get to this email > soon after I sent it, you can see the same type of wind pattern play out in > the satellite imagery here: > > https://www.ssec.wisc.edu/data/geo/#/animation?satellite=goes-west&end_datetime=latest&n_images=all&coverage=conus&channel=03&image_quality=gif&anim_method=javascript > > This is real-time data though, so you won't be able to watch that loop for > too much longer as it purges the old stuff. > > Hope that helps, Ted. And I hope others gleaned some knowledge from this > as well. It was a fun situation to analyze and even more fun to bird. > > Bryan Guarente > Meteorologist/Instructional Designer > UCAR/The COMET Program > Boulder, CO > > > On Mon, Oct 15, 2018 at 10:42 AM Ted Floyd <tedfl...@hotmail.com > <javascript:>> wrote: > >> Hey, everybody. >> >> American Golden-Plovers were reported from eleven (11) sites in Colorado >> yesterday, Sunday, Oct. 14. To put that in perspective, there were two (2) >> previous reports for Colorado in 2018: one (1) in Washington County, Sept. >> 4-8, and one (1) in Kiowa County, Sept. 18. >> >> The previous analysis is based on eBird data-mining. >> >> When one ponders such matters, one's thoughts turn instantly to Bryan >> Guarente. Bryan, what caused this? The snow, obviously. But why this >> particular snowfall? And why this particular species? >> >> Ted Floyd >> Lafayette, Boulder County >> >> P.s. Other than an American Golden-Plover, goodies yesterday in the >> general vicinity of Waneka Lake, Boulder County, included an Eastern >> Bluebird, hundreds of southbound Sandhill Cranes, two Hermit Thrushes, FOS >> Gray-headed and Pink-sided juncos, FOS Townsend's Solitaire, a Long-billed >> Dowitcher, Wilson's and Orange-crowned warblers, a getting-latish flock of >> 15 Lesser Goldfinches, and a Wood Duck. >> >> P.p.s. This Monday morning, Oct. 15, a quick stop at the Legion Park >> overlook revealed the Valmont Reservoir complex to be very birdy, harboring >> a Sanderling, a Semipalmated Plover, a couple dozen Mountain Bluebirds, and >> distant gulls, geese, and grebes galore. It would be very much worth the >> effort, I suspect, to walk in from Red Deer Drive and watch from the Open >> Space tract beyond the end of the road. >> >> -- >> You received this message because you are subscribed to the Google Groups >> "Colorado Birds" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to cobirds+u...@googlegroups.com <javascript:>. >> To post to this group, send email to cob...@googlegroups.com >> <javascript:>. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/cobirds/0a1e3b67-bb68-4da0-824c-1e4a43b36048%40googlegroups.com >> >> <https://groups.google.com/d/msgid/cobirds/0a1e3b67-bb68-4da0-824c-1e4a43b36048%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> For more options, visit https://groups.google.com/d/optout. >> > -- You received this message because you are subscribed to the Google Groups "Colorado Birds" group. 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