Updated Migration Advisory: Wed Night into Thurs

[Bryan Guarente]

Previously, the forecast looked like it would be good for build-up of birds all along the Colorado Rockies.  Today's model runs look different though, and you may have noticed a change in your weather app's forecast as well because of it.  Here is what it looks like now for tonight at midnight:

https://earth.nullschool.net/#2020/04/16/0600Z/wind/isobaric/850hPa/orthographic=-105.0,40.0,2421/loc=-105.000,40.000

The front came through earlier than expected, and has cut-off the possibility of good overnight migration further north in CO along the Front Range and has now limited down the good migration area to further south (along the Arkansas River).  The best bet for overnight migration is along a line from La Junta to Holly, CO (and into KS).  The flow looks more convergent over La Junta than over Holly, so the further west on that line you can go the better.  

With the frontal passage happening earlier than expected, the entire possibility of good migration into CO has changed with more northerly winds throughout (until the Arkansas River).  This has also driven the possibility of good migration farther south and east on this side of the system, but driven the eastern portions of the good migration flyway farther north and east into IA/IL at daybreak tomorrow.  

Here is daybreak tomorrow (with Boulder highlighted as the Green Circle):

https://earth.nullschool.net/#2020/04/16/1200Z/wind/isobaric/850hPa/orthographic=-105.0,40.0,2421/loc=-105,40

So major differences in CO migration compared to what we saw yesterday as a good possibility of migration throughout the region overnight.  Sorry to those of you in the now-not-so-good areas (CO Front Range north of Pueblo) and bonus to those of you in SE CO who could expect some intrigue out of this system.  

Best of luck out there.  

Bryan

Bryan Guarente

Meteorologist/Instructional Designer

UCAR/The COMET Program

Boulder, CO

[Steven Rash]

Bryan,

The overnight Birdcast seems to agree with your prediction, though it looks like the bulk of the movement was full on northward. I bet there were some wayward flocks on the fringe that made it into the southeast corner as well. Cool to see the correlation between datasets! Thanks for your post.

https://birdcast.info/live-migration-maps/

Steve Rash
Denver Co.

[Bryan Guarente]

Steven,

The interesting things that you are noting are dataset problems in SE CO.  The closest radar (what birdcast is based on) is probably Pueblo (but the radar is along the El Paso/Pueblo county borders).  The further away from a radar you get, the higher up in the atmosphere you are and the less likely you are to encounter birds since they like to fly about 1-1.5km above the ground (if possible).  By the time you reach that far out on a radar beam, you are usually 4-6km off the ground, so you are missing the bulk of the birds if there are any.  The green dots on the birdcast map are where the radars are, and you will see quite clearly that there aren't radars very close to SE CO.  

I love the folks at Cornell and appreciate what they are trying to do on a localized scale with the radar data.  It is a great dataset for correlating with local upticks in birds.  It isn't, however, a large-scale indicator of bird movement.  They can only be reactive, not proactive to the weather patterns.  Getting a deeper look into forecasting is what I am trying to do.  I hope my forecasts can help in a different way than the birdcasts can.

Thanks for the info.

Bryan

Bryan Guarente

Meteorologist/Instructional Designer

UCAR/The COMET Program

Boulder, CO

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[Steven Rash]

Bryan,

Thanks for pointing out the flaws in the system. Limitations of radar technology is not something I would have considered given my extremely limited knowledge of how the whole thing works. Your perspective is greatly appreciated! 

It’s kind of a bummer that one of the largest areas in Colorado for migration is sort of in a black hole down there... 

The whole thing makes me think about sensitivities and specificities. Seems like the Birdcast info is decently specific, but the network definitely lacks sensitivity, particularly in our case. 

Much like medical testing, nothing beats the gold standard of getting your eyes directly on whatever it is you’re looking for. As you pointed out, the real value is going to be correlating weather data and birdcast info with observational reports. 

To that end, a quick romp around my “patch” here in SE Denver turned up a couple of odd-balls. Wayward loggerhead shrike, lesser yellowlegs, Wilson’s snipe, and Lincoln’s sparrows were the highlights and first records for the species at this park for me. Along with those, a group of black crowned night herons flying overhead and a continuing Western Grebe were also interesting. “Bad weather, good birds,”wins again. 

I’m sure there will be many other reports to the same effect over the next couple of days. 

Happy (social isolation appropriate) Birding!

Steve Rash

Denver Co. 

On Apr 16, 2020, at 7:55 AM, Bryan Guarente <bryan.g...@gmail.com> wrote: