Migration Advisory: Wednesday Night into Thursday

[Bryan Guarente]

Let's start this post off with two quotes:

• "Go Birding in Bad Weather."  -- Bill Schmoker ("Good Birders Don't Wear White")
• "Thursday, April 16th: Snow. High near 33. Northeast wind 7 to 11 mph, with gusts as high as 18 mph. Chance of precipitation is 90%" -- National Weather Service Boulder

Thanks to Bill and the NWS for making this post possible/easier.  Bad weather is coming on Thursday... so expect some good birds.  Let's look more carefully though to be clear.

https://earth.nullschool.net/#2020/04/16/0600Z/wind/isobaric/850hPa/orthographic=-105.,40,1600/loc=-105.000,40.000

That link has a green circle centered on Boulder, Colorado just for reference.  So what do we see on this wind map?  Winds (in greens and yellows) that are coming from the south in the Rio Grande valley into southeastern CO then curving into the mountains where they abruptly slow down or stop.  If you were a northward-migrating bird, you might want to jump onto this train since it is the best show in town (by that I mean the only southerly winds [blowing FROM the south]) in all of the US.  This map is for Wednesday night/Thursday morning at 12 am.  It is also the winds right near ground level here in CO, but about 1km off the ground in Texas.  

This pattern looks great for bird migration.  It also looks great for precipitation in the eastern half of CO, more in the north than in the south.  With precipitation comes clouds, and in this case lower clouds.  Due to the timing of these winds, it might be good to get out overnight to listen for low-altitude migrant overflights.  They love to chip, chirp, tseep, and zeep when flying at night, and with low clouds that they won't love to fly through (a dry flight is a safer flight), they will likely be going below cloud base where we get a chance to hear them.  

Here is the tricky part though... https://earth.nullschool.net/#2020/04/16/1200Z/wind/isobaric/850hPa/orthographic=-105.,40,1600/loc=-105.000,40.000

Six hours later, it doesn't look like the pattern is as conducive for birds dropping into CO as much as it looks good for NE/KS/MO/IA, especially near the nexus of all those borders.  Birds riding that south wind won't end up in CO before the winds are no-longer advantageous for their northward movement.  

So with a grain of salt, we can take Bill Schmoker's advice and go locally birding on Thursday.  There should be some movement of birds, but maybe not as much as we would "want" during bad weather to prove Bill's thesis.  I can say with confidence there will be plenty of movement on Thursday and some people will get new birds for their year lists or yard lists if you are lucky.  Expect some new influx on Thursday.  

If the precipitation and temperatures aren't exciting for you, just wait for the reports to come in on Thursday, then go out locally on Friday to hunt those down.  They should still be around... check out the winds for 6 am Friday... https://earth.nullschool.net/#2020/04/17/1200Z/wind/isobaric/850hPa/orthographic=-105.,40,1600/loc=-105.000,40.000.  It doesn't look like much will want to leave our area with strong north winds (wind FROM the north; not good for northward migration).

Go prove me right or wrong.  All data points are good data points.  

May the winds be at the birds' backs, until they get to you.  Best of luck,

Bryan

Bryan Guarente

Meteorologist/Instructional Designer

UCAR/The COMET Program

Boulder, CO

[Adam Johnson]

Thanks, Bryan!