PortoWeather
Experimental Forecast This is NOT an official forecast. For official weather information, visit IPMA (Portuguese Met Service) .

Santa Maria da Feira

Updated: 25 Dec 2025, 05:21 UTC 

AFDPRT
EXPERIMENTAL AFD FOR SANTA MARIA DA FEIRA
EXPERIMENTAL FORECAST OFFICE - PORTO METRO
05:21 UTC THU DEC 25 2025

Area Forecast Discussion - Santa Maria da Feira

Issued: 05:21 UTC | Valid through: 05:21 UTC MON DEC 29 2025

SYNOPSIS

A stable high-pressure ridge extends across the northeastern Atlantic and into the Iberian Peninsula through mid-week, promoting dry and generally clear conditions across coastal northern Portugal. Weak shortwave ridging dominates the mid-level flow (500 hPa) through 00Z 28 DEC, with a slow amplification of a downstream trough over the British Isles. This pattern supports subsidence and minimal moisture advection into the region. By late week (00Z 29 DEC onward), the ridge weakens as a broad upper-low approaches from the northwest, increasing mid-level cyclonic vorticity advection into the eastern Atlantic. This sets the stage for increased cloud cover and a gradual moistening trend by early next week. Low-level thermal profiles remain near or just above freezing at night, with diurnal warming limited by increasing cloudiness and weak synoptic forcing.

NEAR TERM (0–24 hours)

From 05:21 UTC 25 DEC through 05:21 UTC 26 DEC, Santa Maria da Feira remains under the influence of a shallow nocturnal inversion with weak surface pressure gradients. Despite increasing low-level cloud cover through the morning hours (with ceiling development up to 1,500 ft AGL), model soundings indicate insufficient moisture depth and lift for sustained precipitation. The 12Z GFS and IFS show a weak shortwave passing just north of 42°N, but its impact is limited to enhanced mid-level cloudiness over Galicia, with minimal moisture transport into northern Portugal due to a blocking anticyclone centered near the Azores.

Surface temperatures have bottomed near 2°C by 05Z, with wet-bulb values near 1°C. Diurnal warming will be gradual due to residual cloud cover through mid-morning, but skies clear rapidly by late morning (cloud cover dropping below 20% by 11Z), allowing temperatures to rise to around 11°C by 14Z. Dew points remain steady near 4–5°C, limiting convective potential. The 15% probability of precipitation in the afternoon reflects isolated, weak convective pulses in the marine boundary layer, likely remaining offshore or producing only virga. Any surface-based shower development would be brief and localized, with negligible accumulation.

Nocturnal cooling tonight will again bring surface temperatures down to near 1°C by 06Z 26 DEC. Wet-bulb temperatures approach 0°C, raising a low-end frost concern on grassy surfaces, though pavement temperatures are expected to remain above freezing due to residual urban heat retention. No frozen precipitation is expected, but patchy frost cannot be ruled out in rural, sheltered areas.

SHORT TERM (24–72 hours)

From 05:21 UTC 26 DEC through 05:21 UTC 28 DEC, the ridge axis shifts slightly eastward, maintaining subsidence and dry conditions. Surface highs near 1028 hPa over the eastern Atlantic support light northeasterly flow aloft, but low-level winds remain light and variable. Temperatures hold steady with daytime highs near 11–12°C and overnight lows between 1–3°C. The 25% chance of precipitation on 26 DEC afternoon is tied to a weak boundary layer convergence zone noted in high-resolution models (AROME-EU, WRF-ARW), but ensemble spread remains low on actual surface impact, with most members showing only increased cloudiness.

By 27–28 DEC, increasing low-level moisture advection from the west is evident in 850 hPa specific humidity fields, though precipitable water values remain low (8–10 mm). With a capping inversion in place and no dynamic forcing, conditions remain dry despite increasing cloud cover in the late evening hours of 28 DEC. Gusts near 35 km/h on both days are tied to weak boundary layer mixing under clear skies, not synoptic forcing.

Thermal profiles show no indication of freezing levels dropping below 500 m AGL during this period. Wet-bulb temperatures remain at or just above 0°C on the coldest nights, but no sustained sub-zero periods are forecast. Any frost formation will be shallow and transient.

LONG TERM (beyond 72 hours)

From 05:21 UTC 28 DEC onward, the upper pattern undergoes a gradual transition. A deepening mid-to-upper level trough moves southeastward from the North Atlantic toward the western Iberian coast by 00Z 01 JAN. This increases cyclonic vorticity advection aloft and enhances low-level convergence as a weak frontal boundary approaches from the northwest. Model guidance (ECMWF ensemble, GEFS) shows increasing consensus on a prolonged period of light precipitation from 31 DEC through 07 JAN, though QPF totals remain modest (6–24 mm cumulative) due to weak ascent and marginal instability.

The most notable aspect of this period is the persistence of cold low-level temperatures despite increasing cloud cover and precipitation. 850 hPa temperatures remain near 0–2°C through 05 JAN, and surface highs are capped near 8–10°C. Wet-bulb temperatures hover near or just below 0°C on 02 JAN and 04 JAN, raising the potential for brief periods of freezing drizzle, particularly in elevated or rural areas where surface temperatures may dip to -1°C under light rain. However, model low-level thermal profiles show limited sub-cloud evaporation cooling, and the most likely outcome remains cold rain or light drizzle.

Gusts increase to 70–75 km/h by 06–07 JAN as the surface pressure gradient tightens ahead of the approaching low. This could lead to minor wind impacts, particularly in exposed coastal and elevated zones. No significant snowfall is expected at sea level, though brief sleet or snow flurries cannot be entirely ruled out in the higher terrain of Serra da Freita (elevated >600 m) during the coldest periods (02–04 JAN), with accumulations likely limited to grassy surfaces and not impacting transportation.

Beyond 08 JAN, the pattern suggests a return to high pressure and drying, though low-level cold air may persist due to anticyclonic cold air damming against the western slopes of the Iberian interior.

CONFIDENCE & KEY UNCERTAINTIES

  • Confidence in dry conditions through 28 DEC: High. Consensus among deterministic and ensemble models on ridge persistence is strong, with minimal moisture and lift.
  • Confidence in frost formation 25–26 DEC: Moderate. Urban heat island effects may limit frost in developed areas, but rural/localized frost is plausible.
  • Precipitation timing and phase 31 DEC–07 JAN: Low to moderate confidence. While models agree on increased cloudiness and light precipitation, exact timing, duration, and phase (rain vs. freezing drizzle) depend on small-scale low-level thermal structure not well resolved by current models. The 10–20% probability of precipitation reflects this uncertainty.
  • Freezing drizzle potential: Low probability but high impact if realized. Surface temperatures near 0°C with wet-bulb at or below 0°C during light precipitation create a narrow window for slick conditions, particularly on untreated surfaces. This remains a conditional risk, dependent on precise timing and intensity of precipitation relative to diurnal cooling.
  • Model stability: Recent model runs (last 30 minutes) show stable temperature and QPF trends, with oscillations in low-level cloud cover but no significant shifts in synoptic evolution. Ensemble spread increases slightly beyond 72 hours, particularly in GEFS v12, but ECMWF control remains consistent.

Experimental discussion - not official guidance

← Home