Thurs 12 Apr 2012 – PNW Migration Update

Now fixed — only one day’s data but time shifted starting at about 2300 PDT.

Bear with me here today as i work out some kinks with the new data system — today’s animated loops (click on images to animate the reflectivity and velocity from RTX) contain two days worth of data.  Last nights data starts at around 0251 12 April UTC.  That is when you will see the sun strobe at sunset last night.


The influence of the off shore low pressure trough continues to be felt locally.  Light south winds, occasional light showers, and overcast skies.  Not ideal conditions for migration, but not completely detrimental either.  One thing that happens in these conditions is that our radar moves into precipitation mode and we loose a lot of sensitivity.  But even with this and the camouflage of clouds, a few birds can be detected on the move.  So, there should be a noticeable change in avifauna composition in your patch, or perhaps just a shuffling of the deck.

In the field: i only had time for a brief stop by the Blount Rd swale yesterday.  The swale is a seasonal pond that is getting lower by the day and should soon host some shorebirds. The duck composition continues to change – except for the Green-wings that seem perfectly happy with the changing conditions there and the Mallards that are looking to nest.  One big change was the swallows.  Up until yesterday i could locate only one or two Trees, and not every day.  Yesterday the Violet-green and Barn swallows were in the majority and in pretty good numbers.  They must of come in last night because they weren’t there yesterday.

Regionally: the KMAX radar out of Medford had nothing to offer.  Some times i think that thing is broken.  A line of precipitation developed last night that stretched from the coast to the crest of the Siskiyous so maybe that kept the birds out of the area.  However, they can be seen navigating between the clouds and rain in the Central Valley.  So, the march north continues.  Given decent conditions — they could be here in three or four days. (a decent rule of thumb is that birds travel around 150 miles a night.  Waterfowl a bit more, passerines a bit less.)

Nationally: the situation is much like yesterday — migration is restricted to the Central Flyway borne on the strong southerly flow you can see on the 850 mb plot.  There was an expansion of the migration zone as the dominant low pressure moves east.  the Mississippi Flyway got some love and you can see the tracks of birds all the way to the Canadian border. You will also note the north winds that are keeping birds out of the eastern part of the country.  For a more detailed analysis be sure to check in with the other radar hounds that can be found on the sidebar under NEXRAD Trackers.  The animated radar loop from last night can be found here.


Site Administration Note: providing you’re a regular, you will note the changes in data presentation.

In addition to a change in data sourcing; the look of the animations has changed and the amount of data has increased from a snapshot every half hour to one every 5 minutes or so.  This makes these files huge by comparison so they will take a bit longer to load and they take up more room on the server.  I may change this down the road if it causes constraints.

I’ve added a Base Velocity animation.  One of the benefits of the Doppler (WSR-88D) radar system is that we can determine flight direction and speed using its capacity to generate velocity images.  I’ve posted static plots in the past but i now have the capacity to generate animated loops and these will be a regular feature here on the blog.

All of these changes are due to a coordination of effort by what has been termed the BIRDAR Network.  This collaborative effort, lead by David LaPuma of, will hopefully bring a streamlined work flow for members and ultimately a more useful presentation for end users.

Any comments?  Hit the comment button and let me know.  Oh, and while you’re there — i’d love to hear what your seeing in the field and where you’re seeing it.

2 thoughts on “Thurs 12 Apr 2012 – PNW Migration Update

  1. Well, looking at radar tonight, 11 PM on 4/12. See some birds moving out of Portland, and lots of birds migrating in Seattle. Perhaps some birds moving in advance of the clouds in Medford, but hard to tell. If I can get out of bed early I might head over to Fernhill Wetlands and Killin Wetlands to see if bittern, rails, or shorebirds might be some of the few birds south of us on the move. I have yet to see Barn and Rough-winged Swallows and Yellowthroat yet this spring, or yellowlegs, so there are a few new birds for the year to find. Some stilts would be nice! And maybe that swamp sparrow will show itself for a photo, if an early sun break. One can wish….


    • Hi Greg: If you were looking at the the RTX station, note that it was in precipitation mode until the 11:33 return – probably due to the small squall that came up out of the SW and moved through Salem and McMinville from 7 to 9 last night.
      That will effect apparent density — the algorithm essentially fills in the “blanks” left by the faster sweep.
      Anyway, that little squall probably diverted birds to the east initially due to the north winds associated with it – only a smattering of rain around 9. As the weather dissipates from 10 to 11 the birds are filling back in behind the cloud front and moving over your neck of the woods. Still, looks like east counties got most of the love last night.
      Medford was socked in under heavy cloud cover. I don’t see anything moving down there, even between the clouds. At the time of exodus the rain had stopped, but there was a light 10 mph head wind on the surface. Hard to say what’s happening under the clouds, but it doesn’t look like much. I really wish Eugene would get a radar on line!
      Over in Clackamas Co. I observed my first large concentration of Cliff Swallows yesterday; have yet to get a definitive look at a Rough-wing though. The Yellowlegs have been over here in selected flooded fields for about a month. And if you find any Stilts – give me a call!
      Have a great time in the field today.


Comments are closed.