SMHI Weather Integration for Home Assistant

Custom Home Assistant integration for SMHI (Sveriges Meteorologiska och Hydrologiska Institut) weather data. Provides detailed weather forecasts and thermal comfort analysis for Sweden.

• Weather entity with current conditions and hourly forecasts
• Precipitation tracking with ensemble predictions
• Cloud coverage analysis by altitude
• Thunderstorm probability monitoring
• Thermal comfort indices with seasonal adaptation
• Frost and ice risk assessment
• Practical sensors for clothing, sleep, and exercise
• Swedish climate calibration - Thresholds optimized for Swedish weather (25°C = hot, not 35°C)
• Smart binary sensors - Risk-based triggers (Frost >60%, Slippery >50%)
• Dynamic language support - Attributes auto-translate to Swedish
• All sensor groups individually configurable
• a CLO Forecast that uses Weather Forecast

Note: Optional sensors (comfort, frost, slippery, impact, practical, thermal) are calculated values derived from SMHI weather data. They are not official SMHI forecasts.

All sensors use temperature thresholds adapted for Swedish weather patterns:

• 25°C = Hot (international: 35°C)
• 30°C = Extreme heat
• 18°C = Ideal exercise temperature
• 22°C = Heat stress begins (international: 25°C)
• -10°C = Moderate cold risk (common winter)
• -25°C = Extreme cold danger

Smart Binary Sensors:

• Frost: Possible triggers at 60% risk
• Slippery: Conditions triggers at 50% risk

Detailed formula explanations in Advanced Formula Improvements below.

1. Go to HACS → Integrations
2. Click the three dots menu → Custom repositories
3. Add: https://github.com/swetoast/ha-smhi
4. Category: Integration
5. Search for "SMHI Weather"
6. Click Install
7. Restart Home Assistant
8. Go to Settings → Devices & Services → Add Integration
9. Search for "SMHI" and configure

1. Download the latest release
2. Copy the custom_components/smhi folder to your config/custom_components/ directory
3. Restart Home Assistant
4. Go to Settings → Devices & Services → Add Integration
5. Search for "SMHI" and configure

1. Go to Settings → Devices & Services
2. Click Add Integration
3. Search for "SMHI"
4. Choose location method:
   • Use Home Assistant's home location, or
   • Specify custom latitude/longitude coordinates
5. Confirm location details (shows grid point and API status)
6. Choose which sensor groups to enable (all enabled by default)
7. Done - integration is ready to use

After setup, click Configure on the SMHI integration:

• Forecast Steps (1-200, default 70): Number of hourly forecast steps
• Update Interval (5-180 minutes, default 30): How often to fetch data
• Enable Comfort Sensors (default ON): Feels-like temperature
• Enable Frost Sensors (default ON): Frost risk % and binary sensor
• Enable Slippery Sensors (default ON): Ice/snow road risk % and binary sensor
• Enable Impact Sensor (default ON): Weather severity score
• Enable Practical Sensors (default ON): Clothing, sleep, exercise
• Enable Thermal Sensors (default ON): Advanced thermal comfort indices

• weather.smhi - Current conditions with hourly forecasts (temperature, pressure, humidity, wind, cloud coverage, precipitation, visibility)

• sensor.smhi_precipitation - Precipitation amount in mm with ensemble forecasts (mean, min, max, median)
• sensor.smhi_clouds - Cloud coverage in octas (0-8) with altitude breakdown (low, medium, high)
• sensor.smhi_thunderstorm_probability - Probability of thunderstorms (%)
• sensor.smhi_symbol_code - SMHI weather symbol code (1-27)
• sensor.smhi_metadata - API metadata and grid point information
• binary_sensor.smhi_api_problem - API health status (ON when issues detected)

• sensor.smhi_feels_like - Comfort: Feels Like - Apparent temperature combining wind chill and heat index (°C)

• sensor.smhi_frost_risk - Frost: Risk - Frost probability percentage (0-100%)
• binary_sensor.smhi_frost_possible - Frost: Possible - Frost conditions likely (ON/OFF)

• sensor.smhi_slippery_risk - Slippery: Risk - Ice/snow road danger percentage (0-100%)
• binary_sensor.smhi_slippery_conditions - Slippery: Conditions - Roads likely slippery (ON/OFF)

• sensor.smhi_weather_impact - Impact: Severity - Overall weather severity score (0-100%)

• sensor.smhi_clothing_insulation - Practical: Clothing - Recommended clothing insulation in CLO units
• sensor.smhi_sleep_comfort - Practical: Sleep - Sleep comfort score based on temperature and humidity (%)
• sensor.smhi_exercise_safety - Practical: Exercise - Outdoor exercise safety score (%)

• sensor.smhi_thermal_comfort - Thermal: Comfort - Auto-selected thermal comfort index (°C)
• sensor.smhi_humidity_analysis - Thermal: Humidity - Dew point temperature with humidity metrics (°C)
• sensor.smhi_heat_stress_level - Thermal: Heat Stress - Heat stress assessment (0-100%)

All optional sensors use scientifically-enhanced calculations optimized for Swedish conditions:

• Smooth 0-100% transition instead of binary jumps
• Peak risk at 2°C with gradual decrease
• Considers dew point spread (closer = higher frost risk)
• Enhanced humidity bonuses (>80% RH increases risk)

• Most dangerous at 0°C where ice repeatedly forms/melts
• Weighted scoring: Temperature (50%), Frozen precipitation (30%), Intensity (20%)
• Gradual risk curve from -10°C to +5°C

• Wind: 40% - Most dangerous factor (>25 m/s = storm)
• Precipitation: 30% - Heavy rain/snow impact
• Visibility: 20% - Safety critical (<1km dangerous)
• Temperature: 10% - Extreme cold/heat contribution

• Optimal: 16-19°C + 40-60% RH
• Detailed humidity penalties (>70% disrupts sleep significantly)
• Weight: 70% temperature, 30% humidity
• High humidity more impactful than in basic formulas

• Dehydration risk at high humidity (>85% + 20°C+)
• Dry air caution (<20% RH affects breathing)
• Extreme danger zones: >35°C or <-30°C
• Categories: Ideal, Safe, Cool, Moderate Risk, Caution, High Risk, Extreme Risk, Extreme Danger

Automatically detects Home Assistant language and translates sensor attributes:

Translated elements:

• Exercise categories (Ideal/Idealt, Safe/Säkert, Caution/Varning)
• Risk levels (Danger/Fara, Extreme Caution/Extrem försiktighet)
• Recommendations (Avoid outdoor activity/Undvik utomhusaktivitet)
• Thermal indices (Heat Index/Värmeindex, Summer Comfort/Sommarkomfort)
• Humidity comfort (Oppressive/Kvävande, Comfortable/Bekvämt)

Enable Swedish: Settings → System → General → Language → Svenska

Automatically adapts comfort perception based on season:

Winter (December-February): -5°C to 6°C, uses temperature, humidity, and wind

• Perception: Very Cold → Cold → Cool → Slightly Cool → Comfortable → Warm

Spring (March-May): 6°C to 17°C, uses temperature and humidity

• Perception: Too Cold → Cool → Slightly Cool → Comfortable → Slightly Warm → Too Warm

Summer (June-August): 17°C to 39°C, uses temperature and humidity

• Perception: Cold → Cool → Slightly Cool → Comfortable → Slightly Warm → Warm → Hot

Autumn (September-November): 5°C to 16°C, uses temperature, humidity, and wind

• Perception: Cold → Cool → Comfortable → Mild → Warm

• Heat Index: Combines temperature and humidity (Steadman formula)
• Humidex: Canadian humidity index using dew point
• Summer Simmer: Heat stress indicator for warm weather
• Relative Strain: Discomfort for 26-35°C range
• Thom's Discomfort: General thermal comfort assessment

Dew point perception categories:

• Below 10°C: Dry to Very Dry
• 10-13°C: Pleasant
• 13-16°C: Comfortable
• 16-18°C: Comfortable but humid
• 18-21°C: Somewhat uncomfortable
• 21-24°C: Very humid
• 24-26°C: Extremely uncomfortable
• Above 26°C: Severely high

All weather data from SMHI's open API:

• Endpoint: https://opendata-download-metfcst.smhi.se/api/category/snow1g/version/1
• Coverage: Sweden and surrounding areas
• Resolution: Grid-based forecasts
• Updates: Multiple times daily

Integration won't add

1. Verify coordinates within SMHI coverage (Sweden and nearby regions)
2. Check internet connectivity
3. Ensure valid coordinates (-90 to 90 latitude, -180 to 180 longitude)

Stale data warnings

• binary_sensor.smhi_api_problem turns ON during issues
• Check last_error attribute for details
• Auto-resumes when API becomes accessible

Missing sensors

1. Settings → Devices & Services
2. Find SMHI integration → Configure
3. Enable desired sensor groups → Submit

Sensors show "null" or "unavailable"

• Normal behavior - attributes only appear when relevant
• Example: Heat stress shows 0% below 18°C (not applicable)

Wrong location

• Reconfigure integration to update coordinates
• SMHI uses nearest grid point (shown during setup)

Language not switching

• Settings → System → General → Language
• Applies to sensor attributes only (not UI)
• Restart Home Assistant if needed

Pull requests welcome. For bugs or feature requests, use GitHub issues.

MIT License - see LICENSE file.

Weather data: SMHI (Sveriges Meteorologiska och Hydrologiska Institut)

Thermal comfort formulas: Environment Canada (Wind Chill), Steadman (Heat Index), Magnus (Dew Point), Scharlau Seasonal Indices, Thom's Discomfort Index, Summer Simmer Index

Not affiliated with SMHI. Weather data provided by SMHI's open data API. For critical decisions, consult official weather warnings.