The birds found a window from sundown until around 1:00 am, where there was mainly an exodus from the Portland area and up the I5 corridor. Then some significant weather moved in and it looks like they put down for the rest of the evening.
Winds will remain out of the south as a new low moves in. But this one is much more organized and may have some heavy precipitation in it’s bowels, and with few breaks.
For those that are new to reading the radar loops: As you look at last night’s loops right around 02:30 Zulu (UTC) you will note a strong radial signal coming from the west of the radar. That is the sun going down and is termed a “sun strobe”. If you see one coming out of the east, that is sunrise. Anyway, under normal circumstances in the PNW the birds take flight shortly after sundown and you can see the migrant bloom.
Since World War II, birds, bats, and bugs – the biodetections that appeared on military radar and subsequently on weather radar-have been considered a nuisance to be filtered out. Because they appeared at night and disappeared at dawn and were wispy and ethereal the detections of migrating birds on radar were termed “angels” by early radar technicians. Angels indeed.
Pacific Northwest Radar: (Click on the links below to open the .gif files in a new window)
And because it is always a treat to watch the flight over the straits of Florida here is the Reflectivity loop from Key West last night: It’s a long loop so wait for the sun strobe and then … boom! Birds!
Here is Paul’s archived National Radar Composite from yesterday. We see the first significant movement along the SE Atlantic states, and some massive movement into Texas and up the Central Flyway.
And here are the weather maps (click on any image to bring up a full gallery view).
Vorticity – 500 mb
Winds Aloft – 850 mb
I will again be taking the weekend off from the updates, but i will check the radar and save any loops that show significant movement and get them posted on Monday.