Surface Temp: Tarmac & Patio

Air temperature tells you almost nothing about how hot the ground actually is. On a sunny summer afternoon, dark tarmac can run far above the air, while the grass a step away stays close to it. SurfaceCast draws that difference as a curve, hour by hour, before you set foot outside.

Pick a place and a date. From the real hourly forecast for that spot, the app estimates how a surface warms up and how it cools down across the day.

COMPARE MATERIALS
Dark tarmac, light concrete, dark concrete, grass, dry soil, damp soil, dry sand, timber decking, brick, light or dark painted metal, a white wall and a dark wall. Up to five scenarios drawn on one chart, so the gaps are obvious at a glance.

CHANGE NOTHING BUT THE COLOUR
This is the experiment that surprises people most. Keep the same material, the same orientation, the same tilt, and shift the colour from white to black. At the height of summer the gap can reach nineteen or twenty degrees. Handy when you are choosing a roof colour, a render, a shade of decking oil or the paving for a courtyard.

WALLS AND ROOFS, NOT JUST THE GROUND
Every surface carries a compass direction and a tilt, from 0° flat to 90° vertical. An east-facing wall warms through the morning; a west-facing one peaks late in the afternoon. Four one-tap presets cover the north, east, south and west walls.

SHADE THAT BEHAVES LIKE REAL SHADE
Mark the hours when a surface falls into shadow, say from 11:00 onwards. Sunlight drops to zero at once, but the temperature does not: heavy materials release their stored heat slowly and cool gradually. That lag is the whole point, and SurfaceCast models it rather than switching the curve off.

WHAT YOU GET
• A 24-hour estimated surface temperature curve for up to five scenarios
• Hourly weather for your location, or anywhere you search for
• Air temperature overlaid as a dashed line, so the gap is easy to read
• Sunrise, solar noon and sunset markers, plus shaded bands on the chart
• Tap any hour for a side-by-side table: temperature, difference from the air, sunlight landing on that face, shade level and an estimate confidence
• Peak temperature and the time it occurs, for every scenario

SAVE YOUR SETS
Store a place and its surfaces under a name of your own — "the back garden", "the dog walk", "the neighbouring roof" — then reload the lot on another date.

WHO IT IS FOR
Judging the pavement before the dog goes out, children playing in the garden, gardening and balcony pots, DIY before you commit to a colour, students and practitioners in architecture, landscaping and groundworks, photographers scouting locations, camping, and anyone curious about urban heat.

HOW IT WORKS
SurfaceCast computes the sun's position for your place and time, works out how much sunlight reaches a face at that tilt and direction, then runs a heat balance in short internal steps: sunlight absorbed, heat carried away by the wind, heat radiated to the sky, heat exchanged with the ground below, and evaporative cooling on da