Giant 'Hole-Punch' Clouds Drift Over Alentejo Plains, Stun Drivers

An unusual parade of perfectly rounded gaps drifted above the Alentejo plains this week, startling motorists on the A6 and filling social media with photographs that looked as if someone had taken a hole-punch to the clouds. Meteorologists quickly confirmed what sky-watchers suspected: Portugal had just been treated to a textbook display of fallstreak holes, the same rare phenomenon that occasionally turns up in Canadian prairie skies or over Australia’s Outback but seldom over Iberia.

A Puzzling Sight Over Alentejo

Residents of Elvas, Marvão and Monforte described the formations as gigantic ovals of clear blue encircled by cotton-white rims. One farmer near Portalegre said the scene resembled “a stadium roof opening above the cork oaks.” According to the independent observatory Meteo Trás-os-Montes, at least three separate holes lingered for almost 40 minutes before closing. That duration alone makes the event exceptional; most cavums, as scientists label them, collapse within minutes once atmospheric equilibrium returns.

The Science Behind The Sky Holes

A fallstreak hole happens when a mid-level cloud made of super-cooled water droplets suddenly begins to freeze. In the Alentejo case, temperatures near the cloud layer hovered just below 0 °C while the ground basked in a mild 17 °C. When a pocket of the cloud unexpectedly picked up ice-nucleating particles—often introduced by a passing aircraft or a sharp drop in pressure—the droplets crystallised. As ice grows, surrounding liquid droplets evaporate quickly, carving out a near-circular void. The newly formed crystals then descend as wispy streaks called virga, giving the impression of snow falling from an empty sky.

Portugal’s Rare Encounters With Cavums

Historical archives show that Portugal records only a handful of confirmed cavums each decade. A modest outbreak over Penafiel in 2013 and an isolated case near Faro in 2019 were the last widely photographed examples. What sets the 2025 display apart is both its geographic spread—three municipalities saw holes on consecutive afternoons—and the clarity with which the phenomenon unfolded, offering local researchers valuable data on cloud microphysics above the Guadiana basin. The World Meteorological Organization officially added cavums to its International Cloud Atlas in 2017, but national weather agencies still lack robust statistics on their frequency across southern Europe.

What To Look For Next Time

If you hope to spot a fallstreak hole over Portugal again, keep an eye on altocumulus decks following a cold front, when upper-level humidity remains high yet the lower troposphere is relatively stable. Jet routes between Lisbon and Madrid often intersect these cloud layers, supplying the mechanical trigger that can seed new holes. Should you notice a pristine, symmetrical opening in the cloud cover, resist the urge to label it Photoshop. Instead, take note of the time, location and any visible aircraft contrails; such details help the Instituto Português do Mar e da Atmosfera refine its models and might even push these atmospheric curiosities from the realm of the rare into the routinely documented.