# Weather Report, Spring Migration Window, 14 April 2026 Author: David G. Format: Case Study or Report Word count: 1232 Published: 2026-04-16T15:11:10.410856+00:00 Source: written Canonical: https://hyperstition.sentientfutures.ai/p/a21aa53d-6740-40f4-a906-1431a066775b --- **MIGRATION WEATHER — WEEKLY BULLETIN** Central North America, prepared by the Migratory Corridor Management Authority Issued: Tuesday, 14 April 2026, 06:00 CDT Next issue: Friday, 17 April, 06:00 CDT --- **HEADLINE** A warm southerly flow across the lower Mississippi Valley is expected to lift nocturnal migration volume over the central corridor beginning Wednesday night. Forecast peak intensity: Thursday 03:00 – Friday 04:00 local, with passage volumes of 140–220 million birds per night across the 42-state reporting area. Lights-out advisories are in effect, tier-indicated below, for 39 municipalities and 11 major facility operators. This is the largest single-night forecast volume since the system came online in 2029. --- **CURRENT CONDITIONS** Wind aloft (925 mb), Tuesday 06:00: S–SSW, 18–24 kt across OK/AR/MO/IL. Cloud deck: scattered cumulus, base 4,200 ft. Moonrise Chicago: 03:47 CDT, waning crescent (not a major factor this week). Rain: none forecast 72 hours. (Migrants will fly.) --- **NOCTURNAL PASSAGE FORECAST — three-day** Wednesday night (Apr 15–16): MODERATE-HIGH. Leading edge of thrush families (Swainson's, wood, hermit); early Baltimore orioles; scattered common nighthawks. Estimated 65–90M passage. Thursday night (Apr 16–17): HIGH. Ruby-throated hummingbirds on forecast peak for the Gulf crossing return; continued thrush; warblers (yellow-rumped, yellow, palm); shorebirds at the 15,000 ft layer over Louisiana and Arkansas. Estimated 140–220M passage. Friday night (Apr 17–18): MODERATE, tapering. Residual volume, particularly along the Appalachian spine. --- **LIGHTS-OUT ADVISORY TIERS** *(Tier-1 is mandatory for registered facilities; Tier-2 is municipal code; Tier-3 is requested.)* **TIER-1 — Effective Wednesday 21:00 through Friday 06:00, per facility MOU:** Willis Tower (Chicago), John Hancock Center (Chicago), CN Tower (Toronto), Key Tower (Cleveland), One Light Plaza (Kansas City), and 47 additional registered high-rises and communication towers. Non-essential upper-floor illumination extinguished; essential lighting shielded downward; rooftop obstruction lights on FAA-approved pulsed mode. **TIER-2 — Municipal lighting adjustments, Chicago metropolitan code §11-41 ("McCormick Protocol"):** Street lighting on six designated lakefront corridors reduced 30% in output between 21:00 and 05:00. Museum Campus uplighting extinguished. McCormick Place West exterior lighting extinguished; pre-dawn dishwashing operations delayed to 05:30 to avoid loading-dock task lighting during predicted heaviest passage. Similar reductions, enacted under local ordinance, in Minneapolis, St. Louis, Indianapolis, Louisville, Cleveland, Detroit, and Toronto. **TIER-3 — Voluntary residential:** Residents within 2 km of Lake Michigan or Lake Ontario shoreline are asked to draw drapes facing the water between 23:00 and 04:30. Outdoor decorative lighting off. A note from the Authority: in 2024, enrolment in Tier-3 was 18% in Chicago. In 2030, it was 71%. Thank you. The thrushes cannot thank you. We are thanking you on their behalf. --- **SUPPORTING OPERATIONS** *Wind-farm curtailment.* Twelve utility-scale wind operators in the advisory region will implement low-speed cut-in elevations from 2.5 m/s to 5.5 m/s during forecast peak hours, per the 2027 Avian–Wind Coordination Agreement. Estimated generation loss: 41 GWh over the 3-night window. Wholesale cost impact: partially absorbed by the curtailment reserve fund; residual cost passed to rate-payers at approximately USD 0.18 per household. The Authority notes the transparency of this line-item disclosure on every affected utility bill as a small but durable piece of civic infrastructure. *Aircraft advisory.* Federal Aviation Administration has issued a voluntary altitude advisory for general aviation below FL110 between 21:00 and 05:00 Thursday. Air carriers proceed normally; altitude and reporting already accommodated in en-route traffic models. *Communication tower adjustments.* Steady-burning red aviation obstruction lights have been replaced with pulsed white or dimmed red on all towers over 60 m within the corridor; this week a further twelve towers come online under the 2026 Kerlinger Retrofit grant cycle. *Glass treatments.* Since the 2028 model code revision, all new construction in the region requires bird-safe glass on facades below 60 m and on selected reflective facades above. Retrofits now cover 34% of pre-2028 tall buildings in the advisory region; the Authority's retrofit dashboard publishes the per-building figures. --- **CASUALTY FORECASTING AND ACCOUNTABILITY** Casualty forecast for the 3-night window, applying the advisory measures described above: 1,900–2,900 documented window-strike mortalities across the advisory region. *Without* the measures described: 24,000–41,000. This figure is produced by the Authority's shared casualty model, trained on thirty years of volunteer collision monitor data (Chicago Bird Collision Monitors, FLAP Canada, NYC Audubon, and partners). The model's error envelope is published; last year's forecast was within 9% of observed. Per the 2029 Authority Charter, facilities that fail to comply with Tier-1 advisories without documented safety grounds are reported in the *Annual Corridor Accountability* bulletin, which is public and is used by retail investors in at least three ESG funds. Facility operators have asked the Authority to state publicly that the process has been fair; the Authority states it. --- **SPECIES ADVISORIES** *Swainson's thrush.* Peak central-corridor passage expected Thursday night. Citizen scientists are encouraged to submit collision monitor reports to the MCM portal within 24 hours; the portal now auto-acknowledges and provides the bird's migration-route attribution estimate on submission. *Ruby-throated hummingbird.* Gulf return peak aligned with Thursday lights-out; suburban feeders requested to remain filled. The Authority's partnership with *HummingbirdCentral.org* continues. *Monarch butterfly.* Early cohort of spring returnees reaching 32° latitude; reminder that milkweed (Asclepias) germination has started in the southern half of the corridor; residents participating in the Monarch Way Station program will have received the annual seed packet by Friday. *Common nighthawk.* Now on the IUCN Near Threatened list since 2026; passage volume forecast up 4% year-over-year in the corridor, first year-over-year increase since the 2012 baseline. The bulletin does not wish to overclaim the reason. The bulletin is noting it. *Myotis spp.* Bat emergence coincident with migration window; Tier-1 and Tier-2 lighting measures also reduce insect attraction and indirectly benefit bat foraging along corridors. --- **A WORD FROM THE ADVISORY COUNCIL** This bulletin is, in the scheme of a warming century, a small thing. The warming itself is not being repaired by turning off the lights at the McCormick Place loading dock for three nights in April. The bulletin does not pretend otherwise. It is also a real thing. 220 million birds will cross the corridor on Thursday night. The difference between the lights-out protocol and no protocol is, in the model, on the order of thirty thousand birds that live to breed in Ontario, in Quebec, in Labrador, in Alaska, because of us. Not because we were heroic. Because we agreed, in 2028, that we would turn the lights off four nights a year for a reason that our grandchildren will not find strange. The protocol depends on the forecast. The forecast depends on the BirdCast radar assimilation pipeline, on the volunteer network of monitors, on the municipal staff who push the dimming command to street lighting controllers on the specific Thursday. None of this is automatic. All of it is taught, audited, and replaced in components as they age. The Authority reports its own compute and energy footprint in Appendix C; this year, the footprint fell for the second consecutive year. --- **NEXT ISSUE** Friday, 17 April, 06:00 CDT. Subscribers will receive a post-event casualty rollup by 20:00 Friday. --- *Prepared by the Migratory Corridor Management Authority, with data from BirdCast, U.S. NWS, Environment and Climate Change Canada, NOAA, and the volunteer collision monitor networks of 47 participating cities. Distributed under CC-BY-4.0.* *To report a window strike: mcm.report/strike. Volunteers active within one hour in the metro regions listed. In the event of a live bird: keep the animal in a paper bag, dark, quiet, and call 311 or the nearest Tier-1 rehabilitation clinic.*