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Vila do Conde

Updated: 25 Dec 2025, 05:21 UTC 

AFDPRT
EXPERIMENTAL AFD FOR VILA DO CONDE
EXPERIMENTAL FORECAST OFFICE - PORTO METRO
05:21 UTC THU DEC 25 2025

Area Forecast Discussion - Vila do Conde

Issued: 05:21 UTC | Valid through: 05:21 UTC MON JAN 6 2025

SYNOPSIS

A shallow mid-level ridge extends over the northeastern Atlantic through the next 48 hours, promoting subsidence and generally stable conditions across coastal northern Portugal. A weak shortwave trough is forecast to approach from the northwest late on 26 December, introducing modest mid-level moisture and increasing cloud cover, though deep-layer ascent remains limited. By 30 December, the ridge reestablishes briefly before a stronger, moist westerly flow develops from 31 December into early January, driven by a deepening mid-latitude cyclone over the eastern Atlantic. This pattern supports gradual cooling aloft and increasing low-level moisture, enhancing stratiform cloud development and raising the potential for light, persistent drizzle from 1 January onward. Surface highs remain weak but persistent, limiting onshore flow intensity despite increasing pressure gradients aloft.

NEAR TERM (0–24 hours)

As of 05:21 UTC, skies are partly cloudy with increasing cloud cover through the morning hours, consistent with weak warm advection ahead of an approaching shortwave trough over the western Iberian coast. Low-level moisture is modest, with wet-bulb temperatures near 7°C, and no significant boundary layer destabilization is evident. Cloud cover peaks near 94% around 09:00 UTC before decreasing through midday as subsidence strengthens under the eastern flank of the ridge axis. Surface temperatures are forecast to rise to around 12°C by 14:00 UTC, supported by weak insolation during brief clearing.

Precipitation remains unlikely through the remainder of the day, with only 0.1 mm of accumulation indicated in the 17:00 UTC hour at 0% probability—likely residual model noise. The brief increase in cloud cover early on the 26th (up to 100% at 04:00–05:00 UTC) coincides with a narrow corridor of mid-level moisture advection, but lapse rates remain stable and low-level saturation is marginal. Convective inhibition is high, and no organized forcing is present. Isolated showers cannot be ruled out late on the 26th between 12:00–18:00 UTC, when model soundings indicate weak frontogenetical forcing aloft and boundary layer moistening may elevate relative humidity to 90%. However, any precipitation would be brief and localized, with no accumulation expected beyond trace levels. Gusts near 30–32 km/h are consistent with modest low-level jet enhancement in the nocturnal boundary layer.

SHORT TERM (24–72 hours)

From 26 to 28 December, the synoptic pattern shifts toward zonal reinforcement. The shortwave trough passes north of the region by 00:00 UTC 27 December, with no surface expression and minimal cold air advection. Temperatures remain steady, with daytime highs near 12–14°C and overnight lows between 6–8°C. Dew points hover near 6°C, indicating limited moisture availability. Cloud cover decreases rapidly after 06:00 UTC on the 27th, with mostly clear skies prevailing through the 28th under strengthening subsidence.

Model guidance shows high consistency in ridge amplitude and axis placement, with ensemble spread in 500 hPa heights less than 40 m across EPS and GEFS members. This supports high confidence in dry conditions through 28 December. Weak diurnal sea breeze convergence may enhance cumulus development inland during afternoon hours, but no organized convection is expected at the coast. Gusts remain near 35 km/h, likely tied to inertial oscillations in the nocturnal boundary layer rather than synoptic forcing.

By 29–31 December, the ridge weakens as a broader trough deepens west of Portugal. Mid-level flow becomes more progressive, with increasing westerly momentum. While no strong surface front is indicated, a subtle increase in low-level convergence and moisture advection is evident in high-resolution models (AROME, HRRR) from 31 December. This supports increasing cloud cover, with overcast conditions expected by 31 December. Temperatures begin a gradual decline, with minimums falling to 4°C—near the 10th percentile for late December—though no freezing is expected at sea level. Wet-bulb temperatures remain above 3°C, ruling out any frozen precipitation.

LONG TERM (beyond 72 hours)

The pattern shifts toward a strong westerly flow regime from 1–8 January, driven by a persistent cyclonic anomaly over the eastern Atlantic. This supports repeated moisture advection into coastal northern Portugal, with integrated vapor transport (IVT) values increasing to 250–300 g kg⁻¹ m s⁻¹ by 5–6 January. While not extreme, this sustained moisture flux, combined with cooling mid-level temperatures (700 hPa temps falling to -4°C), supports prolonged stratiform cloud cover and light drizzle.

Precipitation is characterized by low intensity but high duration, with 19.4 mm total forecast over 24 hours on 6 January. However, probability of precipitation (PoP) remains low (13%), consistent with widespread but light, non-convective drizzle rather than discrete showers. This reflects model challenges in resolving drizzle efficiency in stable marine layers—some ensemble members produce no measurable rain, while others generate persistent light precipitation. The discrepancy suggests low confidence in exact timing and coverage, though the thermodynamic environment supports frequent saturation.

Wind speeds increase notably, with gusts reaching 81 km/h on 6 January. This is tied to a tightening pressure gradient between the deepening low and a building high over Europe. While not gale-force, these gusts may enhance spray and localized blowing spray near the coast. Temperatures remain cool, with highs near 12°C and lows near 10°C during the wettest period, limiting evaporation and prolonging wet surface conditions.

No evidence supports frozen precipitation at any time through the period. Even during the coldest nights (4–5°C), wet-bulb temperatures remain above freezing, and no model member produces sub-0°C surface temperatures. However, brief frost cannot be ruled out on grassy surfaces during clear, calm nights (e.g., 27, 28 December), particularly in sheltered inland pockets of the Vila do Conde municipality.

CONFIDENCE & KEY UNCERTAINTIES

  • High confidence in dry conditions through 28 December, supported by consistent model agreement on ridge strength and placement.
  • Medium confidence in timing and coverage of light precipitation on 26 December; isolated showers possible but not widespread.
  • Low to medium confidence in drizzle timing and intensity from 1–7 January. While moisture and stability support light precipitation, PoP remains low due to model uncertainty in drizzle initiation and evaporation in the sub-cloud layer. Duration-based accumulation may be overestimated if drizzle is intermittent.
  • Low confidence in gust forecasts beyond 72 hours, as small shifts in low-pressure track could alter pressure gradients significantly.
  • No confidence in frozen precipitation at any point; all thermal profiles remain above freezing, and no model ensemble member supports sleet, snow, or freezing rain.

Recent model runs show stable temperature and precipitation trends, with minor oscillations in low-level moisture timing (e.g., 0.8–1.1 mm shifts in 6-hour totals on 25 December), but these are residual noise rather than signal. No significant bias shifts are noted in recent cycles.

Experimental discussion - not official guidance

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