Solano climatology: ERA5 averages and SEAS5 seasonal trends

1. Why look at climatology?

Short-term forecasting answers "what weather tomorrow?". Climatology answers a different question: "is what I'm seeing normal for the season?"

A mean wind of 18 knots in July over the Gulf of Lion may be ordinary (it's the month of the mistral) or surprising (if you're used to a calm July). Without a historical reference, it's hard to know whether the current situation is exceptional or ordinary.

Solano's climatology brings this context in two levels:

The ERA5 monthly averages — what this place has experienced on average over the last 40 years, month by month
The SEAS5 seasonal trends — what the models predict for the coming months on a large scale (above/below/close to normal)

2. ERA5 and SEAS5: two complementary sources

📊 ERA5 — the ECMWF historical reanalysis

ERA5 is the atmospheric reanalysis from ECMWF (the European Centre for Medium-Range Weather Forecasts). It reconstructs the state of the atmosphere hour by hour since 1940, combining every available historical observation in a data-assimilation model. It is the world reference for atmospheric climatology.

🔭 SEAS5 — the ECMWF seasonal forecast model

SEAS5 is ECMWF's seasonal forecast model. It doesn't predict "what the weather will be on 15 August" — it gives a statistical probability that the conditions of the coming months will be above, below or close to the climatological normal. Horizon: up to 6 months. Accuracy decreases with lead time.

      ERA5 looks backward (40+ years of archives to compute the normal). SEAS5 looks forward (probabilistic trends for the coming months). The two together give a complete picture: where we are relative to normal, and where we're heading.
    

3. The ERA5 monthly averages

The Climatology panel shows, for the selected point, the monthly historical averages computed on the ERA5 archives. For each month of the year, you see:

The mean wind and the typical gusts for the month
The average monthly rainfall
The average temperature
The average wave height (for points at sea)

These values are shown as monthly charts. The current month is highlighted, and the value predicted by the short-term models is overlaid to allow a direct comparison.

Climatology panel, ERA5 monthly averages — The ERA5 monthly averages for the chosen point — the current month is highlighted.

Practical use: if you're planning a cruise or a stay in July, compare the ERA5 July averages with the current forecasts. If the forecasts are clearly above the averages, the situation is unusual — and worth watching.

4. The SEAS5 seasonal trends

The SEAS5 section of the Climatology panel shows the probabilistic trends for the coming months. This is not a precise forecast but a statistical signal: will the forecast conditions probably be above, below or close to the historical normal?

Above The variable tends to be higher than the month's normal — stronger wind than usual, above-average rain, high temperatures.

Normal No clear statistical signal. The forecast conditions are close to the historical averages.

Below The variable tends to be lower than normal — less wind, below-average rain, cool temperatures.

SEAS5 section, seasonal trends — The SEAS5 seasonal trends for the coming months, variable by variable.

The SEAS5 trends are particularly relevant for:

Planning a sailing season — a spring forecast "above normal for wind" suggests a more active season than usual
Anticipating anchorage conditions — a summer forecast "below normal for precipitation" is a signal of potential drought for coastal areas
Calibrating expectations — a "normal" signal on waves in July doesn't allow a conclusion, but a strong "above" signal is worth attention

Caution: seasonal forecasts are probabilistic, not deterministic. An "above normal" signal means it's the most likely scenario, not a certainty. Accuracy decreases with the horizon — 1-month trends are more reliable than 6-month ones.

5. Available variables

Variable	ERA5 monthly	SEAS5 trends	Marine points only
💨 Mean wind	✓	✓	—
💨 Gusts	✓	✓	—
🧭 Wind direction	✓	✓	—
🌧️ Precipitation	✓	✓	—
🌡️ Temperature	✓	✓	—
🔵 MSL pressure	✓	✓	—
☁️ Cloud cover	✓	✓	—
🌊 Wave height	✓	✓	✓
🌊 Wave period	✓	✓	✓
🌊 Wave direction	✓	✓	✓

Marine data (waves) is only shown for points detected as being at sea. On a land point, only the atmospheric variables are available.

6. What climatology does not tell you

Climatology is not a forecast. ERA5 describes what happened on average — not what will happen. An average of 12 knots in July does not mean every day of July will be at 12 knots.
SEAS5 gives probabilities, not certainties. An "above normal" signal on wind means that scenario is statistically more likely — it may not materialise.
Spatial resolution is limited. ERA5 and SEAS5 work at resolutions of several kilometres. Local effects (a deep valley, an exposed promontory, coastal acceleration) are not captured in the climatology.
Climate change biases the averages. The ERA5 averages fold in 40+ years of data. The most recent years, warmer and potentially more disturbed, may already depart from the long-period average computed.