Pmad.WeatherStats 0.1.1

Pmad.WeatherStats

A .NET 8 library for reading ERA5 average weather statistics from a local directory or a remote HTTP database.

Raw data need to be converted using the Pmad.WeatherStatsGenerator tool (see the main README for details).

The public database is hosted at https://weatherdata.pmad.net/ERA5AVG/. It provides averages for 2010-2020.

Installation

Add the Pmad.WeatherStats package to your project.

Quick start

1. Open a database

using Pmad.WeatherStats.Databases;

// From the public HTTP database
var db = WeatherStatsDatabase.Create("https://weatherdata.pmad.net/ERA5AVG/");

// Or from a local directory that contains the JSON data files
var db = WeatherStatsDatabase.Create("/path/to/era5avg/");

2. Query a geographic point

Pass any latitude/longitude pair. The library automatically snaps to the nearest 0.25° ERA5 grid point. Negative longitudes (West) are normalised automatically.

// Geneva, Switzerland
var stats = await db.GetStats(46.2, 6.15);

if (stats == null)
{
    Console.WriteLine("No data available for this point (e.g. open ocean).");
    return;
}

Console.WriteLine($"Grid point: {stats.Latitude}°N {stats.Longitude}°E");
Console.WriteLine($"Data covers {stats.Months.Length} months");

3. Read monthly statistics

stats.Months is a 12-element array ordered January (index 0) through December (index 11).

string[] monthNames = [
    "January","February","March","April","May","June",
    "July","August","September","October","November","December"
];

for (int i = 0; i < 12; i++)
{
    var month = stats.Months[i];

    Console.WriteLine($"--- {monthNames[i]} ---");

    // Temperature (°C)
    Console.WriteLine($"  Temperature  min {month.Temperature.Min.Min:F1} °C " +
                      $"/ avg {month.Temperature.Avg.Avg:F1} °C " +
                      $"/ max {month.Temperature.Max.Max:F1} °C");

    // Relative humidity (%)
    Console.WriteLine($"  Humidity     avg {month.Humidity.Avg:F1} %");

    // Wind speed (m/s)
    Console.WriteLine($"  Wind speed   avg {month.WindSpeed.Avg.Avg:F1} m/s");

    // Prevailing wind direction
    Console.WriteLine($"  Wind dir     {month.WindDirection.Prevailing}");
}

Data model

YearWeatherStatsPoint

MonthWeatherStatsData

MinMaxAvg

Holds the minimum, average, and maximum of a set of values.

MinMaxAvgStats

Aggregates daily MinMaxAvg slices into overall min/avg/max statistics.

WindDirectionStats

WindDirection8

Eight-point compass enum. Each value represents the direction the wind is blowing toward.

North, NorthEast, East, SouthEast, South, SouthWest, West, NorthWest

Utility methods

VariableConvert

using Pmad.WeatherStats;

// Relative humidity from dew point and air temperature (August-Roche-Magnus approximation)
float rh = VariableConvert.RelativeHumidity(dewpointCelsius, temperatureCelsius);

// Convert Kelvin to Celsius
float tempC = VariableConvert.KelvinToCelcius(tempKelvin);

// Determine wind direction from a velocity vector (X = east, Y = north)
using System.Numerics;
WindDirection8 dir = VariableConvert.GetWindDirection8(new Vector2(eastward, northward));

Advanced: custom storage back-end

Implement IWeatherStatsStorage to load data from any source (cloud blob storage, embedded resources, etc.):

using Pmad.WeatherStats.Databases;
using Pmad.WeatherStats.Stats;

public class MyStorage : IWeatherStatsStorage
{
    public async Task<List<YearWeatherStatsPoint>> Load(string path)
    {
        // path is a filename such as "ERA5AVG_N46_006.json"
        // return an empty list when the file does not exist
        ...
    }
}

var db = new WeatherStatsDatabase(new MyStorage());

Advanced: cell file naming

The database shards data into 2°×2° cell files. You can resolve the file name for any grid point:

var index = WeatherStatsDatabase.GetCellIndex(46.25f, 6.25f);   // (46, 6)
var file  = WeatherStatsDatabase.GetCellFileName(index);         // "ERA5AVG_N46_006.json"