AEMET (State Meteorological Agency) is the official source of weather forecasts in Spain. Its data feeds applications like Windy, Windguru and WindTrackr itself. But weather forecasts are complex and often misinterpreted. A "70% chance of rain" does not mean what most people think. This guide will teach you to read AEMET forecasts like a professional, understand their limitations and combine them with live data to make the best decisions.
1. What is AEMET and Why Trust Its Data?
AEMET is Spain's national meteorological authority, under the Ministry for Ecological Transition. It operates a network of more than 1000 automatic stations and 80 staffed observatories, covering all Spanish territory and areas of influence.
- Official data: AEMET is the primary source. Other apps (Windy, Windguru) use international models (GFS, ECMWF) that AEMET combines with local data for greater accuracy.
- HARMONIE-AROME model: AEMET uses this high-resolution model (2.5 km grid) specific to Spain. Captures local phenomena better than global 10-50 km models.
- Human prediction: Although models are automatic, expert meteorologists manually review and adjust predictions in complex cases (storms, DANAs, Strait situations).
WindTrackr integrates AEMET forecasts via Cloud Functions, processing them to show you the specific forecast for your spot along with live data. It is the perfect combination: AEMET science with local sensor reality.
2. Deciphering Weather Symbols
AEMET maps use international standardized icons (WMO). Learning to read them quickly is essential:
- Sun: Clear sky or with high clouds that do not affect. Perfect for sailing, although it may indicate calm if there are no dynamic systems.
- Clouds: Variable cloudiness. Not necessarily bad, but check associated wind. Low clouds may signal weak thermal.
- Umbrella: Expected precipitation. If solid, high probability (>70%). If dashed lines, moderate probability (30-70%). Always check exact % in detailed data.
- Lightning: Storms. NEVER sail with this symbol. Electrical storms are lethal in wind sports. Wait at least 30 minutes after last thunder before going out.
3. The Myth of Precipitation Probability
Most common confusion: "70% rain" does NOT mean it will rain 70% of the day. It means:
- Technical definition: "In 100 days with these identical atmospheric conditions, it rained on 70 of them." It is a statistical probability, not temporal.
- Geographic area: 70% may also refer to rain falling on 70% of the forecast area (e.g., a region). Your specific spot might be in the dry 30%.
- Precipitation threshold: AEMET considers "rain" any accumulation >0.1 mm. A 5-minute drizzle counts as "rainy day" statistically.
- For sailors: Look at expected accumulation (mm) in addition to %. If it says 70% with 0.5 mm, it is scattered drizzle. If it says 40% with 15 mm, expect intense localized showers.
WindTrackr trick: Compare forecast with our real-time webcams (when available) and nearby station data. If forecast says rain but sensors show stable pressure and low humidity, you may dodge the shower.
4. Interpreting Forecast Winds
AEMET provides wind at 10 meters height (meteorological standard). But there are critical nuances:
- Average vs. gust: AEMET gives expected average wind and probable maximum gust. If it says "15 km/h with gusts of 40 km/h", translate: 8 knot wind with 22 knot gusts. VERY gusty.
- Uncertainty range: In 24-48 hour forecasts, AEMET usually gives ranges: "West wind 15-25 km/h". This means model uncertainty. Plan for the most conservative scenario (25 km/h if you fear being overpowered).
- Local effects not captured: If your spot is in a valley, bay or behind mountain, real wind may differ ±30% from forecast. This is where WindTrackr with local sensors is pure gold.
5. Weather Models: What's Behind the Prediction
AEMET uses multiple mathematical models that simulate the atmosphere. Knowing them helps you interpret better:
- ECMWF (European Model): Most accurate globally. 9 km grid, updated every 12 hours. AEMET uses it as base for 3-10 day predictions.
- HARMONIE-AROME: Spanish high-resolution model (2.5 km). Excellent for local phenomena like the Strait of Gibraltar, coastal breezes, mountain storms. Forecast up to 48 hours.
- GFS (American Model): Less accurate than ECMWF but useful for 7-14 day trends. If GFS and ECMWF disagree, trust ECMWF.
- Ensembles: AEMET runs the model multiple times with slightly different initial conditions. If all ensembles agree, high confidence. If they diverge, high uncertainty.
6. Hybrid Strategy: AEMET + WindTrackr
The key to success is combining forecast with real data:
- Planning 48h ahead: Use AEMET forecast in WindTrackr to identify potential windows. If AEMET predicts 20 knots of Levante on Saturday, mark your calendar.
- Confirmation 6h ahead: Check trend graphs in WindTrackr. Are real sensors showing wind coming in as forecast? If at 10:00 AM they promised 15 knots at 2:00 PM but at 12:00 you still have calm, forecast is failing.
- Final decision in real-time: Before leaving home, look at LIVE data from your spot. Forecast is guide, reality is truth. If AEMET says 18 knots but WindTrackr shows 25 on sensor, adjust your gear to real 25.
This hybrid methodology maximizes your success rate. Use AEMET science to plan days ahead and WindTrackr precision to execute safely.
Practical Summary
AEMET forecasts are powerful scientific tools, but they are not infallible oracles. Understand their limitations (spatial resolution, local effects, temporal uncertainty) and combine them with real observations. WindTrackr offers you both worlds: AEMET professional prediction integrated in the app and real-time local sensor data. Use them together and you will make informed decisions that maximize your time on the water and minimize frustrations. Remember: forecast tells you what to expect, but only the sensor tells you what is happening NOW.
