Understanding the sunrise and inversion predictions
The sunrise quality score predicts how photogenic a sunrise will be, based on weather conditions that create dramatic colors and interesting skies. The score ranges from 0-100 points.
| Factor | Why It Matters | Max Points |
|---|---|---|
| High Clouds | Cirrus and high-altitude clouds catch the sun's rays and light up with vibrant colors. Optimal coverage is 30-70%. | 23 |
| Low Clouds | Low clouds block the horizon and prevent light from reaching higher clouds. Less is better (<20% ideal). | 18 |
| Total Clouds | Overall cloud coverage affects the balance of light and shadow. 30-70% is optimal for dramatic skies. | 14 |
| Precipitation | Uses both amount and probability. Low probability (<10%) scores highest even with some forecast rain. High probability with significant rain scores lowest. | 14 |
| Wind Speed | Light winds allow clouds to hold their shape and structure. Strong winds disperse clouds too quickly. | 9 |
| Mid Clouds | Altocumulus and mid-level clouds add texture and depth to sunrise scenes. 20-50% is ideal. | 9 |
| Light Quality | Based on the ratio of diffuse to direct radiation. Moderate diffuse light (30-60%) creates colorful scattering. | 8 |
| Air Quality | Moderate particulate levels (PM2.5 15-35 µg/m³) enhance colors via light scattering. Very clean air has less scattering; heavily polluted air reduces visibility. | 5 |
An additional bonus of up to 15 points is awarded when conditions suggest dramatic post-storm clearing:
Cloud inversions occur when a layer of warm air traps cooler, moist air in valleys below, creating a sea of fog or low clouds. From elevated viewpoints, you can photograph above this fog layer with peaks emerging like islands. The score predicts the likelihood of these conditions.
| Factor | Why It Matters | Max Points |
|---|---|---|
| Wind Speed | Light winds are critical—strong winds mix the atmosphere and break up inversions. <5 km/h is ideal. | 20 |
| Pressure (MSL) | High pressure creates stable conditions that trap cold air in valleys. >1025 hPa is excellent. | 16 |
| Visibility | Low visibility at valley level indicates fog is already forming—direct evidence of inversion conditions. | 14 |
| Atmospheric Stability | Low CAPE (Convective Available Potential Energy) indicates stable air that resists vertical mixing. | 10 |
| Humidity | Small dew point spread (<2°C) means the air is close to saturation—fog formation is likely. | 10 |
| Overnight Clouds | Clear skies overnight allow radiative cooling, which chills the valley air and promotes fog formation. | 10 |
| Temperature Lapse Rate | When air at 80m is warmer than at ground level, a temperature inversion is detected—this directly confirms conditions. | 8 |
| Visibility Trend | Compares today's visibility to yesterday. Worsening visibility suggests an inversion is forming; improving visibility means it may be lifting. | 6 |
| Soil Temperature | Warm soil with cold air releases moisture that condenses into fog. Most effective in autumn/winter. | 4 |
| Precipitation | Dry conditions are needed—rain disrupts the stable atmosphere required for inversions. | 2 |
Certain wind directions favor inversion formation at specific locations. For Peak District locations, easterly winds (NE, E, SE) bring moist North Sea air that condenses in valleys. When the wind matches favorable directions, a bonus of up to 6 points is added.
All weather data is sourced from the Open-Meteo API, which combines multiple weather models to provide accurate forecasts. Data includes:
Air quality data (PM2.5 and PM10 particulate matter) is sourced from the Open-Meteo Air Quality API. This data is available for the first 7 days of the forecast.
Air quality is now factored into the sunrise quality score:
Forecasts are updated every 3 hours and cover the next 10 days. Twilight times are calculated using NOAA solar algorithms based on each location's coordinates.