# Derived temperatures · SunScope
How SunScope models the temperatures the thermometer doesn't show — a parked vehicle's interior, a building's indoor temperature without air conditioning, and sun-baked urban concrete.

# Derived temperatures

The temperatures the thermometer never tells you.

Beyond felt temperature, SunScope runs three physics-based models that estimate temperatures you can't read off a standard forecast: how hot a parked vehicle becomes, how warm a building stays indoors, and how sun-baked urban concrete gets. Each is built on the same per-hour weather data.

## Vehicle interior temperature

A sealed, parked vehicle heats up far faster than most people expect. SunScope's Vehicle column models the ambient cabin air temperature experienced by an occupant seated out of direct sunlight — the classic scenario of a child or pet left inside a parked car.

The calculation combines two physical processes. The first is body panel conduction: panels absorb solar radiation and conduct heat into the cabin regardless of the sun's position. Thin metal car panels pass much more of this through than the insulated sandwich panels of many motorhomes and caravans. This is the slow, relentless background heat that builds even on overcast days. The second is side-window solar gain: when the sun's rays cut through the side glass rather than striking the roof, additional heat enters the cabin. Because the occupant sits out of the direct beam, this energy raises the ambient cabin air temperature rather than heating the person directly — which is precisely what makes it so dangerous.

You can select your vehicle type (car, MPV, SUV, truck/HGV cab, motorhome, or caravan), each with its own albedo, glazing area, and insulation. A Windows open toggle switches to a ventilated model where convective loss is roughly five times higher, dramatically reducing cabin heat build-up. For cars, the figure represents the cabin after roughly 45–60 minutes of parking; motorhomes and caravans are treated as insulated occupied living spaces, so the estimate stays closer to the real living-space temperature on cool or moderate sunny days. Values above 35 °C are shown in amber (dangerous for children and pets); above 45 °C in red (potentially fatal within minutes).

A road speed selector — Static, Urban (20 mph), A-road (50 mph), or Motorway (70 mph) — sits alongside the ventilation toggle. Static reproduces the original stationary model; higher speeds add forced airflow that scrubs heat off the bodywork, and when combined with windows open, flush the cabin toward outside air much faster than a parked vehicle. Wind speed itself has almost no effect on a sealed, stationary vehicle and is only meaningfully factored in through ventilation or road speed.

## Indoor temperature

The Indoors column estimates the temperature inside a building with windows closed and no air conditioning, simulating retained warmth, window solar gain, internal gains, and thermal mass hour by hour. You choose your building type from a dropdown — brick, modern insulated, Victorian terrace, stone cottage, timber frame, top-floor flat, conservatory, or office block — and the physics model adjusts accordingly. Each type has its own insulation level, thermal mass, retained warmth, and glazing, so a stone cottage and a conservatory behave very differently on a hot day. Office block carries a higher internal gain (people, equipment, lighting) and more glazing than a typical home, reflecting a commercial building rather than a house.

The model lags toward a realistic hourly target rather than repeatedly adding solar heat, so indoor temperatures typically peak 2–4 hours after the outdoor peak — which is why a house can still feel stifling at 10 pm on a summer day. Tick Managed alongside the dropdown to switch to the heatwave-advice model: curtains closed by day to cut solar gain, windows opened whenever outdoor air is cooler than inside. The Managed column shows how much passive cooling can reduce indoor heat compared to doing nothing.

## Urban concrete surface temperature

The UTCI standard was developed with a natural grass surface as its reference ground. In a city that assumption breaks down. Concrete and tarmac absorb far more solar energy than grass, and unlike grass they have no evaporative cooling. On a sunny summer afternoon, exposed paving can run 15–25 °C hotter than the surrounding air.

SunScope's Concrete surface column estimates the temperature of sun-exposed urban paving using a surface energy-balance model that accounts for how much solar radiation the surface absorbs, how efficiently the wind carries that heat away, and the reflective properties of typical urban concrete. The result gives a sense of the contact heat stress you'd experience sitting, standing, or walking barefoot on city surfaces — and it's a useful proxy for pavement-paw safety for dogs. The column is enabled by default in the Places → Urban view and colour-coded: values above 30 °C are shown in amber, above 40 °C in red.

## Pet fur and paw temperatures

The Pets profile runs two further physics estimates alongside the shade and indoor models. Fur Temp estimates the surface temperature of a cat or small dog's coat sitting in direct sun, calibrated for a thin/short coat rather than a heavily-insulated breed. A fur colour selector (Black/Dark, Brown/Tabby, Golden/Tan, White/Pale) sets the coat's albedo — darker coats absorb more solar radiation and run hotter, the same principle as Shade Air but applied to fur rather than skin. Paw Temp reuses the concrete surface energy-balance model above to estimate ground contact temperature, colour-coded by burn risk instead of the general amber/red thresholds: green below 40 °C, amber 40–52 °C, red above 52 °C.

These columns appear together in the Temps profile. For what every column means, see the column reference.