Area Forecast Discussion - Braga

Issued: Wed, Jan 7, 9:49 PM | Valid through: Wed, Jan 21

KEY POINTS

• Prolonged rainfall event with moderate to heavy precipitation totals expected through the next 96 hours, posing a risk of localized flooding, particularly in low-lying areas.
• Notable gusts (up to 69 km/h) accompany the heaviest rainfall periods, enhancing wind-related hazards.
• Marginal cold air advection may briefly introduce wintry precipitation risks on elevated surfaces (e.g., hills) on 2026-01-21, though accumulation on pavement is unlikely due to melting.

SYNOPSIS

A complex synoptic pattern featuring a series of low-pressure systems embedded within a zonal flow regime will dominate the weather across northern Portugal through the next 96 hours. These systems will tap into a moderately moist airmass, leading to persistent and at times heavy rainfall. The interaction between the maritime airmass and the continental interior may introduce localized thermal variations, particularly in valleys and elevated terrain. Model guidance indicates oscillating precipitation trends, reflecting uncertainty in the timing and intensity of individual low-pressure centers.

NEAR TERM (0-24 hours)

0-12 hours (2026-01-07T21:00-2026-01-08T12:00):

• Precipitation: Light rain showers will persist through the overnight hours, with a brief lull expected near dawn as drier air temporarily infiltrates the region. However, model consensus indicates a rapid reintensification of precipitation by late morning, driven by the approach of a stronger low-pressure system from the southwest.
• Temperatures: Stable temperatures near 5-7°C through the night, rising to 10-12°C by afternoon as warmer maritime air advects inland.
• Uncertainty: The timing of the precipitation resurgence is uncertain, with some models (e.g., 2026-01-07T18:47:01.310Z run) suggesting a slower progression, which could delay the onset of moderate rain by 2-4 hours.

12-24 hours (2026-01-08T12:00-2026-01-09T00:00):

• Precipitation: Moderate to heavy rain becomes widespread, with hourly rates exceeding 5 mm/h at times. The 2026-01-07T21:38:25.125Z model run's anomalous 60.1 mm precipitation forecast for this period is considered an outlier but highlights the potential for localized enhancement due to orographic effects near Braga's hills.
• Winds: Gusts up to 54 km/h are expected during the peak rainfall hours, exacerbating the flood risk in exposed areas.
• Temperatures: Steady temperatures near 12°C, with minimal diurnal variation due to persistent cloud cover and precipitation.

SHORT TERM (24-72 hours)

24-48 hours (2026-01-09T00:00-2026-01-10T00:00):

• Precipitation: A temporary lull in precipitation is anticipated as the initial low-pressure system exits to the northeast. However, model oscillations (e.g., recent runs showing precipitation totals ranging from 0.6 mm to 60.1 mm) indicate significant uncertainty regarding the development of a secondary low-pressure center over the Bay of Biscay, which could reintroduce rain sooner than currently forecast.
• Temperatures: Gradual cooling to 5-6°C by morning, with daytime highs near 13°C, as weak cold air advection competes with maritime moderation.

48-72 hours (2026-01-10T00:00-2026-01-11T00:00):

• Precipitation: Overcast conditions with intermittent light rain, transitioning to more persistent moderate rain by the end of the period as the next system approaches. Ensemble spread suggests a 20-30% probability of heavier precipitation rates (>10 mm/h) in some models, though this remains a low-confidence scenario.
• Temperatures: Stable temperatures near 5-11°C, with the potential for slight warming as the low-pressure system taps into warmer, moister air from the south.

LONG TERM (beyond 72 hours)

Beyond 72 hours, the pattern evolves into a more amplified zonal flow, with a series of vigorous low-pressure systems traversing the region. This will maintain a wet and unsettled regime, with heavy rainfall and gusty winds remaining prevalent through at least 2026-01-21. The potential for a brief cold snap on 2026-01-21 introduces a marginal risk of wintry precipitation on elevated surfaces, though accumulation on pavement is unlikely due to temperatures remaining near or above freezing. Model guidance beyond 96 hours indicates increasing uncertainty regarding the timing and intensity of individual storm systems.

CONFIDENCE & KEY UNCERTAINTIES

• High Confidence: Prolonged rainfall event with moderate to heavy totals through the next 96 hours; gusty winds accompanying peak precipitation periods.
• Moderate Confidence: Timing and intensity of individual low-pressure systems, particularly the secondary low over the Bay of Biscay in the short term; potential for localized flooding in low-lying areas.
• Low Confidence: Development of a brief cold snap on 2026-01-21 and associated wintry precipitation risks; exact precipitation totals in the short term due to model oscillations.
• Key Uncertainties:
  1. The interaction between the maritime boundary layer and inland valleys, which may lead to microclimate effects not fully resolved by models.
  2. The potential for small-scale convective enhancement of rainfall rates, particularly in the near term, which could exacerbate flooding risks.
  3. The evolution of the synoptic pattern beyond 72 hours, where model spread increases significantly, introducing uncertainty into the timing and magnitude of subsequent rainfall events.