Frost, Ice and Sub-Zero Lows: Polar Air Hits Portugal

Portugal Swaps Storm Clouds for Polar Chill: A Deep Freeze Descends

Portugal has abruptly traded torrential rain for a sharp winter chill. After a turbulent week dominated by Depression Claudia—characterized by heavy showers, hail, and thunderstorms—a surge of polar air is now settling over the country. The result is a dramatic shift in weather patterns, bringing crisp blue skies by day and freezing, frosty nights, particularly across the interior North and Centre regions.

Meteorologists have issued warnings that this cold spell will sharpen significantly on Thursday and Friday, with minimum temperatures expected to slip to 0 ºC or below in several districts. Residents in valleys and high plateaus should prepare for widespread frost as the mercury drops.

From Storm Chaos to Polar Calm

Earlier this week, Depression Claudia swept across mainland Portugal, leaving behind a trail of disruption that included flooding, fallen trees, and thousands of calls to civil protection services. However, as the storm system moved away, it opened a corridor for a polar air mass to slide down from higher latitudes.

Steered south by persistent northerly winds, this air mass has traveled across several mountain chains in northern and central Europe, including the Cantabrian Range and the Pyrenees. This journey has fundamentally altered the air's composition. It arrives in Portugal as a "dry cold" package; having lost most of its moisture while crossing the mountains, it is now characterized by very low temperatures and extremely low humidity. While the impact is being felt nationwide, the interior North and Centre are on course to endure the harshest conditions, facing severe frost and pockets of negative temperatures.

Wednesday: Clear Skies and Sharper Cold

With high pressure now firmly in charge to the west of Portugal, today’s weather pattern represents a classic winter anticyclone. The forecast promises mostly clear or slightly cloudy skies with generous periods of sunshine. However, this brightness is deceptive. Light to moderate northerly winds will persist, occasionally blowing stronger along the western coast and on higher ground, creating a marked contrast between chilly mornings and relatively mild afternoons.

Temperature readings today illustrate this divide. Maximums are expected to reach 15–19 ºC along the coast but will struggle between 8–16 ºC inland. The minimums tell a colder story, generally hovering between 5–10 ºC across much of the country, with Lisbon and Faro seeing lows around 11 ºC. In contrast, the interior is already freezing; locations such as Bragança, Guarda, and Castelo Branco are facing lows ranging from –1 ºC to 3 ºC. Patches of morning fog have already been reported in the North and Centre, as well as in Ribatejo and Alentejo.

Thursday and Friday: The Peak of the Cold Spell

The cold is expected to intensify further over the next 48 hours. An anticyclonic ridge stretching from Scandinavia toward the Azores will continue to funnel polar air directly into the Iberian Peninsula.

Thursday, 20 November, will bring another bright, mostly sunny day, but the northerly winds will maintain a relentless flow of cold air. Night-time minimums are set to drop again, turning negative in Bragança, Guarda, and other parts of the interior North and Centre. With temperatures hitting or dipping below freezing, ice and frost are expected to form widely in inland areas, especially in valleys and low-lying zones.

Friday, 21 November, is forecast to be the coldest day of this episode. Models indicate minimum temperatures will sit between 0 and 5 ºC across the vast majority of mainland Portugal. Several areas in Bragança and Guarda, along with other high-altitude locations, will see the mercury plunge well below zero. Frost and ice will be more intense and widespread, specifically affecting Northeast Trás-os-Montes, Beira Alta, Serra da Estrela, and the mountain areas of Alto and Baixo Minho. Residents in the interior zones of Porto, Aveiro, and Viseu should also brace for significant frost.

The Science of Dry Cold: Why No Snow?

Despite its polar origin, residents might be surprised that this air mass is not expected to bring significant rain or snow. The explanation lies in its journey. As the air traveled south, it was forced to rise over the mountain chains of Central Europe and Northern Spain. In doing so, it lost its moisture, a phenomenon that ensures that by the time it reaches Portugal, it is bone dry.

This dryness favors clear skies and stable weather with little to no precipitation. While any isolated showers that do appear over the highest mountains in the North and Centre could theoretically fall as snowflakes, the probability is low. The weather will remain stable, crisp, and freezing.

What This Means for Residents

With several very cold nights in a row, the impacts will be tangible. Commuters should be wary of slippery roads and pavements at dawn due to ice formation. The agricultural sector faces potential frost damage to crops, particularly in orchards and sensitive areas. Furthermore, there will be a spike in heating demand, which may prove challenging for homes with poor insulation in the interior regions. Local authorities and civil protection services remain on alert, particularly in regions still recovering from the damp effects of Depression Claudia.

Fortunately, the cold snap is expected to be short-lived. Forecast models suggest a gradual rise in temperatures beginning this weekend. As the grip of high pressure weakens, clouds and some rain may return, marking the end of this brief but intense early-winter freeze.