Area Forecast Discussion - Faro

Issued: Wed, Jan 7, 9:51 PM | Valid through: Wed, Jan 21

KEY POINTS

• Marginal freezing risk: Overnight lows near 5-6°C may briefly approach freezing in sheltered inland locales, though widespread frost is unlikely.
• Precipitation timing/intensity: Model oscillations suggest variable precipitation onset and rates, particularly for the 08th; localized heavy rates cannot be ruled out.
• Gusty winds: Notable gusts (67-91 km/h) expected 19th-21st, enhancing precipitation impacts.

SYNOPSIS

A complex, slow-evolving synoptic pattern will influence the region through the period. A mid-latitude trough, currently positioned to the northwest, will gradually pivot southeastward, inducing a series of weak frontal boundaries. The interaction between these features and a persistent low-level thermal ridge will dictate precipitation phase, timing, and intensity. Model guidance remains inconsistent regarding the phasing of these systems, leading to notable uncertainty in precipitation totals and timing.

NEAR TERM (0-24 hours)

0-12 hours (07th 21:00 - 08th 09:00):

• Temperature: Overnight lows will hover near 5-6°C, with localized minima in sheltered valleys potentially approaching freezing. However, widespread frost is not anticipated due to cloud cover and gentle southwesterly flow.
• Precipitation: Dry conditions prevail initially, with precipitation chances increasing after 08th 06:00. Model consensus indicates a delayed onset, though the 07th 21:46Z anomalous run suggests earlier activity. Given the oscillating precipitation trend, confidence in exact timing remains low.
• Clouds: Persistent cloud cover (80-100%) will moderate diurnal temperature swings.

12-24 hours (08th 09:00 - 08th 21:00):

• Precipitation: The primary precipitation event commences, with the 08th 12:00-18:00 window featuring the highest probabilities. However, model solutions diverge on intensity, with the 07th 21:38Z run indicating excessive totals (60.1mm) that are likely overestimated. A more reasonable 5-15mm accumulation is probable, though localized convective enhancement cannot be ruled out.
• Temperature: Daytime highs will struggle to exceed 14°C due to persistent cloud cover and precipitation.

SHORT TERM (24-72 hours)

24-48 hours (08th 21:00 - 10th 21:00):

• Synoptic Setup: The parent trough begins to eject eastward, allowing a brief ridge to build overhead. This may lead to a temporary lull in precipitation, though model disagreement on the ridge's amplitude introduces uncertainty.
• Precipitation: Scattered showers persist, with the 09th featuring a brief window of reduced activity. However, the 10th 00:00-12:00 period may see a resurgence in precipitation as the next frontal boundary approaches.
• Temperature: Nocturnal lows moderate to 8-9°C, with daytime highs near 16-17°C.

48-72 hours (10th 21:00 - 12th 21:00):

• Uncertainty: Model spread increases, with the 07th 18:47Z run indicating a more progressive trough compared to the 07th 21:46Z solution. This discrepancy impacts the timing and magnitude of the next precipitation event.
• Precipitation: A more organized low-pressure system may develop, leading to sustained precipitation. However, the exact track and intensity remain unclear, precluding confident precipitation type/accumulation forecasts.

LONG TERM (beyond 72 hours)

The pattern transitions to a more zonal flow regime, with embedded shortwave troughs maintaining unsettled conditions. A notable increase in wind gusts (67-91 km/h) is expected during the 19th-21st, coinciding with the strongest shortwave passages. Temperature anomalies will hover near seasonal averages, with precipitation remaining frequent but generally light.

CONFIDENCE & KEY UNCERTAINTIES

• High Confidence: Persistent unsettled conditions, gusty winds during the 19th-21st.
• Moderate Confidence: Precipitation timing/intensity for the 08th-10th, with model oscillations suggesting a 2-4 hour window of uncertainty.
• Low Confidence: Precipitation phase for the 08th, particularly in inland zones where temperatures may briefly flirt with freezing. The anomalous model runs (e.g., 07th 21:38Z) introducing excessive precipitation totals are likely underrepresenting microphysical processes, but localized heavy rates remain a concern.
• Key Uncertainties:
  1. Phasing of the mid-latitude trough with the low-level thermal ridge.
  2. Convective parameterization in the 08th-10th period, which may not be fully resolved by current model resolution.
  3. Surface temperature response in sheltered valleys, where cold air drainage may lead to localized freezing conditions despite warmer regional averages.