What makes a 'DANA' storm like the one causing deadly flooding in Spain?

Storms can reach severe levels, and DANA’s are known for triggering frequent lightning, large hail events and tornadoes, as eastern Spain has reported this week.

VALENCIA, Spain – Parts of eastern and southern Spain are now dealing with the aftermath of historic and deadly flooding at the hands of a storm system that brought incredible amounts of rain in short order.

The storm system is known in Spain as a "DANA" – a Spanish acronym for "Depresión Aislada en Niveles Altos", according to eltiempo.es – which roughly translates in English to an isolated low-pressure system at upper levels.

In essence, the storm is based on what we would call a cut-off low — an area of low pressure that becomes detached from the steering currents of the jet stream.

In a DANA’s case, this low captures some cool air aloft but travels over the very warm waters of the Mediterranean Sea. The large-scale evaporation finds an unstable atmosphere primed for widespread storm development that can carry vast amounts of moisture.

Storms can reach severe levels, and DANA’s are known for triggering frequent lightning, large hail events and tornadoes, as eastern Spain has reported this week. 

But the most dangerous situation comes if the DANA spins easterly winds along the eastern coast of Spain, which will slam the storm’s moisture-laden air mass into the mountains west of Valencia. Orographic lift will squeeze out even more moisture, leading to overwhelming rainfall totals.

The mountain town of Chiva, west of Valencia, was drenched by 19.33 inches of rain in just eight hours, according to Spain's weather agency AEMET. Of that, 13.55 inches fell in a mere four hours, with 6.5 inches pouring down in a single hour.

Those rainfall totals rivaled some of those found in the mountains of western North Carolina during Hurricane Helene. Though each storm was of a different type of meteorological origin, warm-water-infused moisture interacting with the mountainous terrain exacerbated the flooding problems.

DANAs are a regular occurrence in the south and east of Spain in the summer and fall when the Mediterranean Sea is at its warmest, though it’s rare for storms to rise to such damaging levels. They can occur in any month of the year yet don’t have as much damage potential when the waters are cooler.