When will a major North American metropolitan area first experience a combined dangerous wet-bulb-temperature event and a significant electrical power blackout?

The forecast for the first combined dangerous wet-bulb temperature and significant electrical blackout in a major North American metropolitan area rests on the increasing frequency of compound extreme weather events, balanced against the strict conjunctive criteria required for resolution.

Historical Context and Near-Misses To date, no event cleanly satisfies the strict parameters. Recent extreme events serve as strong near-misses that illustrate both the plausibility of the scenario and the difficulty of meeting the documentation thresholds. Hurricane Beryl (Houston, July 2024) caused massive outages with over 2.1 million customers losing power for days, leading to heat-induced fatalities 2 sources. However, official documentation indicated a mid-tier Heat Advisory with heat indices around 100–106°F rather than a highest-tier Extreme Heat Warning 2 sources. Crucially, station observations at KIAH showed dew points between 68–76°F, keeping actual wet-bulb temperatures (Tw) below the 28°C threshold mesonet.agron.iastate.edu. Similarly, Hurricane Ida (New Orleans, 2021) produced massive, prolonged outages during severe heat but lacked the requisite highest-tier warning or documented Tw≥28°C.

Forward Forecast Dynamics The individual components of this event are highly probable and occurring with increasing frequency. Major U.S. blackout events have increased significantly, with nearly half occurring during the May–September heat season when grid risk is elevated pmc.ncbi.nlm.nih.gov. Simultaneously, highest-tier extreme heat alerts are routinely issued for humid metros in the Gulf Coast and Southeast, and actual U.S. wet-bulb extremes reaching 28–29°C are climatologically plausible in these moisture-rich regions agupubs.onlinelibrary.wiley.com.

The binding constraint is the simultaneous alignment of a ≥100,000-customer / ≥4-hour single-metro outage with a highest-tier heat alert or a strictly measured 28°C wet-bulb in the same ≥1-million population metro within a 72-hour window. The most likely pathway is a Gulf, Southeast, or Texas metro (e.g., Houston, New Orleans, Miami) suffering a storm-driven, derecho, or load-shed outage while under an Extreme Heat Warning.

Timing and Percentiles Given the high and rising base rate of the individual conditions, the per-summer probability of a clean match is substantial, driving an early 2030s median.

• 10th–25th Percentiles (August 2027 – August 2029): Captures the near-term risk that the rising frequency of heat waves and grid strain results in a qualifying compound event very soon, especially given that recent summers have produced near-misses separated only by technical documentation gaps.
• 50th Percentile (August 2032): The median reflects a balance between the worsening compound risk of extreme heat and grid failure, and the strictness of the criteria, which will inevitably screen out many otherwise severe events where the blackout falls short of 100k/4-hours, the metro population is too small, or the heat alert is only a mid-tier advisory.
• 75th–90th Percentiles (August 2038 – August 2046): The extended right tail accounts for the possibility that grid adaptation (e.g., increased resilience, weatherization) mitigates large-scale outage risks, or that strict official wet-bulb measurements and alert documentation persistently fail to coincide perfectly with infrastructure failures in major metros.