Monday 3 May 2021

Re: [cobirds] Hudsonian Godwits and the Weather Pattern

To add a supporting "data point" to your theory, Bryan....I dropped my mom off at DIA for an 11:30 AM departure yesterday to Washington, DC and the plane sat on the tarmac (with 70 others) for 2+ hours as all Eastbound flights were held for severe wind sheer, I assume due to the storm front.  Meanwhile, all Westbound, NB, and, SB flights continued to take off.   Thanks to you (weather) and Dave L. (bugs) for continually helping us birders understand the science behind the birds we all are passionate about.  

Sent from my iPhone

On May 3, 2021, at 7:54 PM, Bryan Guarente <bryan.guarente@gmail.com> wrote:


COBIrders,
TL;DR (Too long; didn't read): I don't know why the Hudsonian Godwits showed up today in Boulder County, but I wanted to let you know some things about numerical weather models that make them not always the best way to answer the bird migration question I often pose on COBIRDS.  There is more to weather forecasting than just what the model data says.

Full story:
Eric DeFonso spread the word this morning that there were 15 Hudsonian Godwits seen at Lagerman Reservoir SW of Longmont in Boulder County, CO.   I was surprised to hear this as yesterday's frontal passage wasn't remarkable for driving birds into the Front Range.  Here is the pattern for the same time that Eric reported these birds on eBird.


Seems like quite the wrong pattern for birds to be coming into CO... hmm.

So maybe we need to look late yesterday (sunset on May 2nd) to see what it looked like then: 

No better and you can see the cold front more clearly from Iowa through Nebraska and into Kansas (blue squiggle of convergent winds on this image).  Again, it doesn't look like a good time for birds to be coming to CO as the winds are from the north making most birds want to stop their journey rather than face the north winds.  

Let's keep going backwards  in time though.  Here is 12pm May 2nd.  I am choosing this time for a reason that will become clearer later.

Still in that same boat... not good migration conditions into CO.  This was the last observation time as well from a birder on eBird at Lagerman yesterday... leaving a large window of opportunity for these birds to come to Lagerman and go undetected until this morning.

But this is where the story goes off course from my normal posts to COBirds.  The website data is from a computer model.  Computer models are right in many ways and I love their output for posts like the ones I normally make.  One of the ways that meteorologists are still important is that we can sometimes tell when the model data needs some nudging to make a good public forecast.  Or we can use the observations in hindsight to compare to the models and we can see when something was missing.  This is one of the latter cases.

Let's look at a variable that I don't normally ask you to look at: 3-hour precipitation accumulation.  This is how much rain or snow accumulated over the last three hours from the time of the plot.  So at the following map time, the data show precipitation from 9am until 12pm.  


The amount of rain near Lagerman Reservoir was expected to be .06 inches.  This is light rain for a bit.  Nothing much.  In reality, let's see what was happening: 

This is a pretty strong line of thunderstorms moving from west to east that was barreling down the foothills to change the local smaller scale weather pattern compared to the model output.  This wasn't going to be a little bit of rain for a bit.  This was a thunderstorm that was meaning business for those in the way of it.  That radar image was a few minutes after Boulder Municipal Airport had received .9 inches of precipitation in the last hour.  

This is a major departure from what the model was saying!  This model wasn't expecting a thunderstorm like we ended up receiving.  This means that some of the local winds (at the surface and aloft) are likely different by a large amount compared to the model output.  This could have led to a situation where the Hudsonian Godwits found a different pathway through the meteorological pattern that we just aren't seeing in the model data.  I don't know for sure how the Godwits got here, but I am speculating that this thunderstorm and its resulting change in the wind pattern as it moved off of the foothills and out into the eastern plains of CO caused a nice migration pathway to help them find Lagerman Reservoir.  

Now, since you have read this far, I have to give you something else to work with.  I believe the Hudsonian Godwits have a chance of sticking around through the night if you didn't get your chance today.  Here is tomorrow morning (7am May 4th): 

This is the first solid south wind for these birds to leave on.  So if you get to Lagerman at around sun-up, you have a chance of seeing these birds in the morning.  They may not last long after that though as the winds pick up and give a nice south wind for these birds to migrate on.

So when is the next chance of anything in CO?  It looks like May 5th there is a small push of migrants in the southeast.  I would suggest a rectangle from Cheyenne Wells south to Lamar,  west to John Martin Reservoir, and north to Kit Carson.  


Hope you enjoyed this and get a chance to see the Hudsonian Godwits like the 76 observers who reported to eBird today from Lagerman Reservoir (compare that to three the day before).  

And lastly, if you are thinking ahead to the weekend and the CO Birding Challenge, check out the first look at Saturday's forecast winds:

Any guesses where the best location to go birding will be?

Ask questions, be curious, and keep the reports coming.  Migration and weather are slowly unravelling this year's mysteries of movement.  

Rambling email concluded.

See ya in the field,
Bryan

Bryan Guarente
Meteorologist/Instructional Designer
UCAR/The COMET Program
Boulder, CO

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