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<h1>Derived temperatures</h1>
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<p class="tagline">The temperatures the thermometer never tells you.</p>
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<p>
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Beyond felt temperature, SunScope runs three physics-based models that estimate temperatures you
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can't read off a standard forecast: how hot a parked vehicle becomes, how warm a building stays
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indoors, and how sun-baked urban concrete gets. Each is built on the same per-hour weather data.
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</p>
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<h2>Vehicle interior temperature</h2>
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<p>
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A sealed, parked vehicle heats up far faster than most people expect. SunScope's <strong>Vehicle</strong>
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column models the ambient cabin air temperature experienced by an occupant seated out of direct
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sunlight — the classic scenario of a child or pet left inside a parked car.
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</p>
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<p>
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The calculation combines two physical processes. The first is <strong>body panel conduction</strong>:
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panels absorb solar radiation and conduct heat into the cabin regardless of the sun's position. Thin
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metal car panels pass much more of this through than the insulated sandwich panels of many motorhomes
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and caravans. This is the slow, relentless background heat that builds even on overcast days. The
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second is <strong>side-window solar gain</strong>: when the sun's rays cut through the side glass
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rather than striking the roof, additional heat enters the cabin. Because the occupant sits out of the
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direct beam, this energy raises the ambient cabin air temperature rather than heating the person
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directly — which is precisely what makes it so dangerous.
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</p>
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<p>
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You can select your vehicle type (car, MPV, SUV, motorhome, or caravan), each with its own albedo,
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glazing area, and insulation. A <em>Windows open</em> toggle switches to a ventilated model where
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convective loss is roughly five times higher, dramatically reducing cabin heat build-up. Wind speed
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has almost no effect on a sealed vehicle and is only factored in when ventilation is enabled. For
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cars, the figure represents the cabin after roughly 45–60 minutes of parking; motorhomes and caravans
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are treated as insulated occupied living spaces, so the estimate stays closer to the real
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living-space temperature on cool or moderate sunny days. Values above 35 °C are shown in amber
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(dangerous for children and pets); above 45 °C in red (potentially fatal within minutes).
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</p>
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<h2>Indoor temperature</h2>
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<p>
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The <strong>Indoors</strong> column estimates the temperature inside a building with windows closed
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and no air conditioning, simulating retained warmth, window solar gain, internal gains, and thermal
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mass hour by hour. You choose your building type from a dropdown — brick, modern insulated, Victorian
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terrace, stone cottage, timber frame, top-floor flat, or conservatory — and the physics model adjusts
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accordingly. Each type has its own insulation level, thermal mass, retained warmth, and glazing, so a
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stone cottage and a conservatory behave very differently on a hot day.
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</p>
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<p>
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The model lags toward a realistic hourly target rather than repeatedly adding solar heat, so indoor
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temperatures typically peak 2–4 hours after the outdoor peak — which is why a house can still feel
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stifling at 10 pm on a summer day. Tick <em>Managed</em> alongside the dropdown to switch to the
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heatwave-advice model: curtains closed by day to cut solar gain, windows opened whenever outdoor air
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is cooler than inside. The <strong>Managed</strong> column shows how much passive cooling can reduce
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indoor heat compared to doing nothing.
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</p>
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<h2>Urban concrete surface temperature</h2>
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<p>
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The UTCI standard was developed with a natural grass surface as its reference ground. In a city that
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assumption breaks down. Concrete and tarmac absorb far more solar energy than grass, and unlike grass
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they have no evaporative cooling. On a sunny summer afternoon, exposed paving can run 15–25 °C hotter
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than the surrounding air.
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</p>
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<p>
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SunScope's <strong>Concrete surface</strong> column estimates the temperature of sun-exposed urban
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paving using a surface energy-balance model that accounts for how much solar radiation the surface
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absorbs, how efficiently the wind carries that heat away, and the reflective properties of typical
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urban concrete. The result gives a sense of the contact heat stress you'd experience sitting,
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standing, or walking barefoot on city surfaces — and it's a useful proxy for pavement-paw safety for
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dogs. The column is enabled by default in the <strong>Places → Urban</strong> view and colour-coded:
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values above 30 °C are shown in amber, above 40 °C in red.
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</p>
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<p>
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These columns appear together in the <a href="./profiles.html">Temps profile</a>. For what every
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column means, see the <a href="./columns.html">column reference</a>.
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</p>
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© 2026 <a href="https://fraxle.net" target="_blank" rel="noopener noreferrer">Fraxle.NET</a> · <a href="./index.html">Forecast</a> · <a href="./about.html">About</a> · <a href="./faq.html">FAQ</a> · <a href="https://billing.stripe.com/p/login/9B63cw7vl8k15Ei9DQd7q00" target="_blank" rel="noopener noreferrer">Account</a> · Data: <a href="https://open-meteo.com/" target="_blank" rel="noopener noreferrer">Open-Meteo</a> · UTCI: <a href="https://utci.org/" target="_blank" rel="noopener noreferrer">Bröde 2012</a>
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