Units Reference - Spire Weather API Documentation

Complete reference for units used in Spire Weather API responses.

Unit Systems¶

The API supports two unit systems:

Parameter Value	Description
`si`	SI Units (default)
`us`	US Units

Specify the unit system with the unit_system query parameter:

curl -X GET \
  'https://api.wx.spire.com/forecast/point?lat=40.0&lon=-105.0&unit_system=us' \
  -H 'spire-api-key: YOUR_API_KEY'

Temperature¶

Variable	SI Unit	US Unit
`air_temperature`	Kelvin (K)	Fahrenheit (°F)
`dew_point_temperature`	Kelvin (K)	Fahrenheit (°F)
`sea_surface_temperature`	Kelvin (K)	Fahrenheit (°F)
`soil_temperature`	Kelvin (K)	Fahrenheit (°F)

Conversion¶

# Kelvin to Celsius
celsius = kelvin - 273.15

# Kelvin to Fahrenheit
fahrenheit = (kelvin - 273.15) * 9/5 + 32

# Celsius to Fahrenheit
fahrenheit = celsius * 9/5 + 32

Wind¶

Variable	SI Unit	US Unit
`wind_speed`	m/s	mph
`northward_wind`	m/s	mph
`eastward_wind`	m/s	mph
`wind_gust`	m/s	mph
`wind_direction`	degrees	degrees

Direction Convention¶

Wind direction follows meteorological convention: the direction from which the wind is blowing, measured clockwise from north.

Direction	Degrees
North	0° / 360°
East	90°
South	180°
West	270°

Conversion¶

# m/s to mph
mph = ms * 2.237

# m/s to knots (see glossary: Knot)
knots = ms * 1.944

# m/s to km/h
kmh = ms * 3.6

Pressure¶

Variable	SI Unit	US Unit
`air_pressure`	Pa	inHg
`sea_level_pressure`	Pa	inHg

Conversion¶

# Pa to hPa (mb) — see glossary: hPa
hpa = pa / 100

# Pa to inHg
inhg = pa * 0.0002953

Precipitation¶

Variable	SI Unit	US Unit
`precipitation_amount`	kg/m² (mm)	inches
`precipitation_rate`	kg/m²/s	inches/hour
`snow_depth`	m	inches

Conversion¶

# mm to inches
inches = mm * 0.03937

# kg/m² equals mm for water
mm = kg_per_m2

Waves¶

Variable	SI Unit	US Unit
`significant_wave_height`	m	ft
`mean_wave_period`	s	s
`peak_wave_period`	s	s
`mean_wave_direction`	degrees	degrees

Conversion¶

# meters to feet
feet = meters * 3.281

Visibility¶

Variable	SI Unit	US Unit
`visibility`	m	miles

Conversion¶

# meters to miles
miles = meters / 1609.34

# meters to nautical miles
nm = meters / 1852

Humidity¶

Variable	SI Unit	US Unit
`relative_humidity`	%	%
`specific_humidity`	kg/kg	kg/kg

Humidity values are the same in both unit systems.

Soil Moisture¶

Variable	SI Unit	US Unit
`soil_moisture`	m³/m³	m³/m³

Soil moisture is expressed as volumetric water content (same in both systems).

Radiation¶

Variable	SI Unit	US Unit
`shortwave_radiation`	W/m²	W/m²
`longwave_radiation`	W/m²	W/m²
`solar_irradiance`	W/m²	W/m²

Radiation values are the same in both unit systems.

Tides¶

Variable	SI Unit	US Unit
`tide_height`	m	ft

CF Conventions¶

Field names follow CF Conventions. This ensures compatibility with common meteorological software and data formats.

Common CF Standard Names¶

API Field	CF Standard Name
`air_temperature`	`air_temperature`
`wind_speed`	`wind_speed`
`northward_wind`	`northward_wind`
`eastward_wind`	`eastward_wind`
`relative_humidity`	`relative_humidity`
`precipitation_amount`	`precipitation_amount`
`air_pressure`	`air_pressure`

Python Helper Functions¶

def kelvin_to_celsius(k):
    """Convert Kelvin to Celsius."""
    return k - 273.15

def kelvin_to_fahrenheit(k):
    """Convert Kelvin to Fahrenheit."""
    return (k - 273.15) * 9/5 + 32

def ms_to_knots(ms):
    """Convert m/s to knots."""
    return ms * 1.944

def ms_to_mph(ms):
    """Convert m/s to mph."""
    return ms * 2.237

def pa_to_hpa(pa):
    """Convert Pa to hPa (millibars)."""
    return pa / 100

def meters_to_feet(m):
    """Convert meters to feet."""
    return m * 3.281

def wind_components_to_speed_direction(u, v):
    """Convert U/V wind components to speed and direction.

    Args:
        u: Eastward wind component (m/s)
        v: Northward wind component (m/s)

    Returns:
        tuple: (speed in m/s, direction in degrees)
    """
    import math
    speed = math.sqrt(u**2 + v**2)
    direction = (270 - math.degrees(math.atan2(v, u))) % 360
    return speed, direction