Savvy birders are meteorologically astute. They keep an eye out for what may be arriving with the next airmass, wrung out of the skies by an approaching front, or even just a pop-up thunderstorm on an otherwise migration-friendly day. In the age of smartphones and apps, it’s now more convenient than ever to stay abreast of changing weather conditions. Anyone can pull out their favorite weather app and check out their local Doppler radar.
Doppler radar and the local forecast are great tools, but first it helps to take a step back and look at the big picture. Migration is a large-scale event, and so it really helps to see what’s going on across at least half of the continent. Will the migrating warblers and thrushes in Tennessee today be able to reach Pennsylvania in the next day or two?
The classic synoptic weather maps are still a fantastic resource, if you know how to read them. It’s worth knowing that blue arcs with pointy, triangular teeth illustrate the leading edge of a cold front, and that red arcs with rounded bumps on one side illustrate the leading edge of a warm front. It matters on which side of the line the teeth or bumps are located, because that indicates the direction of travel of the airmass. When a frontal boundary alternates between the two symbologies, it’s a stationary front. Those are very slow-moving (also known as stalled fronts). Classic weather maps also feature prominent H’s and L’s to denote the centers of high- and low-pressure airmasses. High-pressure areas feature descending air, with clockwise rotation. The surface air flows out and away from the center of the airmass. Low-pressure areas feature counterclockwise rotation (in the northern hemisphere), with surface air being sucked in toward the center of the airmass, where it ascends. The lines that resemble the contours of a topographic map are isobars. They connect areas of equal barometric pressure, between the Highs and Lows. The closer a strong High and Low get to each other, the steeper the pressure gradient (think steep cliff on a topo map) and the stronger the wind in that area. As for the direction of the wind, recall the directions of rotation around the highs and lows, and you’ll understand which way the air is flowing!
A new way to visualize the flow of air over the surface of the earth emerged in 2012. That site is simply called “wind map”. The concept was new and fairly groundbreaking, but the site is very simple. You can zoom in by double-clicking, but the data are limited to the Lower 48, and the site is not the easiest to use on your smartphone.
However, a brand-new site has emerged only a few weeks ago. The site is called “earth” and the url is earth.nullschool.net
This site is utterly amazing. It takes the basic concept of “wind map” and runs with it –around the world and back. You can see the massive Highs and Lows swirling over the oceans, and the wind conditions across the Gulf of Mexico, hopefully providing beneficial tailwinds on which the migrants are floating. However, there are a ton of options that are worth exploring on your own. Hit the “earth” button (really, just the word, it doesn’t look like a button, but it is) in the bottom-left corner and you’ll open a plethora of options. First, you can switch from air mode to ocean mode, and instead display the ocean currents. You can toggle overlays such as barometric pressure (which is awesome, but I think my favorite overlay is temperature). If you click the unit of measure (km/h) it toggles from that to m/s to knots to mph. Celsius likewise changes to Fahrenheit. You can also choose to display winds at different levels of the atmosphere, if perhaps you are looking for the jet stream. And for you geography geeks out there, you can even change the projection from orthographic (3D globe, my fav) to seven other options, including the rare and bizarre Waterman (“butterfly”) projection. One of the nicest options is the 〖◯〗 button, which uses the Location Services on your browser/mobile device to put a marker at your current location. Oh, and yes, you can zoom in as well.
The earth.nullschool.net site has quickly become my favorite site for checking out the migration conditions, as more and more neotropical migrants are starting to reach the temperate latitudes on their nocturnal (and diurnal) journeys.