Migration alert: frontal boundary and northern Gulf Coast fallout potential from 10-16 April

On Saturday 10 April, a frontal boundary is forecast to move into the Gulf of Mexico region. As described in previous posts, the passage of such boundaries between warm and cool air masses can force birds migrating over water, particularly over the Gulf of Mexico, to “fall out” in habitats at and close to the coast. Beginning midday Saturday, birds may begin concentrating in coastal habitats, particularly in the Upper Texas and southwestern Louisiana coasts. Additionally, intense rain associated with this boundary is possible further east along the Gulf Coast and will create conditions for fallouts and concentration as far east as the Florida Panhandle. As this system is predicted to remain in the Gulf of Mexico region for some days, we will update this post accordingly, as other areas to the east may experience some intriguing migration conditions as the week proceeds. The image below shows a cold front, the line with blue triangles, situated at the Texas coast as of Saturday morning.

The below five-paneled image animation (go here to see other formats of these maps that update every few hours) highlights that this frontal boundary will stall, with forecasts suggesting that it will remain over the Gulf of Mexico for a number of days through Friday 16 April. Note that the line with both red half-circles and blue half-triangles represents this stationary front. Also, note that calm winds, mostly light southerly, are forecast for Yucatán and points farther to the south, depicted in the five panels as widely spaced brown lines (isobars, lines of constant pressure). The stalling of the front suggests that any concentrating effects will mostly occur between the mid Texas coast and Florida Panhandle, with southern Texas and  most of peninsular Florida experiencing migration as usual.

Although conditions with such stalled, stationary fronts could lead to interesting concentrations and fallouts in coastal habitat, birds’ responses are heavily dependent on the extent and intensity of rain over the Gulf of Mexico as well as the strength of head winds after birds pass the frontal boundary. The calm but favorable winds in Yucatán and portions of Central America and the Caribbean suggest that birds will take flight on each, or at least most, of the coming nights, and further that these birds will overfly the frontal boundary stalled over the Gulf relatively late each day following their departures. Given relatively weak winds forecast onshore around the northern Gulf of Mexico coast, birds that concentrate and fallout as a result of crossing the frontal boundary will likely depart again during night only a few hours after stopping. In other words, fallouts and concentrations that occur may not lead to a multi-day accumulation of birds in coastal habitats because of marginal to favorable northern Gulf Coast departure conditions.

Keen observers of birds and weather often look to Windy.com to see beautiful and dynamic visualizations of winds aloft, among other meteorological factors. Below is a representation of what’s forecast as the frontal boundary moves into the Gulf of Mexico, and worth a look to consider when and where birds may encounter unfavorable winds. Use the scroll bar at the bottom of the image to explore predicted winds. And note, there are some forecast periods when it appears that southerly flow may simply allow for migration as usual in some western areas, with birds able to move around the stalled boundary.

Species on the move – Gulf of Mexico region

Diversity and abundance of many migrants arriving into the US are increasing at present, and many species will be involved in this week’s events – whether in fallouts, concentrations, or simply increased numbers and occurrences indicative of newly arrived migrants.

Wilson’s Phalarope. Richard Garrigus/Macaulay Library. eBird S35659569.

Beginning Arrivals What is this?

Peaking Arrivals

Note, also associated with the passage of this system are potential conditions to transport birds in eastern extents of the region (e.g. Florida and southeastern coastal plains) farther to the north of intended destinations (i.e. slingshot events). Such events are usually associated with the passage of strong frontal boundaries, rather than stalled or slow-moving boundaries, but strong storms with intense precipitation and gusty winds were forecast in these areas with the potential to displace and entrain birds moving close to the coast (see this image) offshore. These conditions could also lead to local Atlantic coast fallouts and concentrations.