fitframe

Your outfit is matched to what your body needs to hold its heat balance outside — the weather, what you are doing in it, and how much insulation that leaves you needing. The day gets cut into stretches, and each stretch gets its own answer.

Where you'll be outside

or

What you'll be doing

Shelter

How you run

Occasion

How far ahead

Wardrobe

Undershirt

Appearance

Right now

Keep an eye on

Plan ahead

Later today

Body shape

Changes the drawing only. The clothing advice is the same for any body — the heat balance is per unit of skin area — so nothing here recalculates the forecast.

Hour by hour

Time	Temp	Feels	WBGT	Wind	Precip	Cloud	UV	Needs

Forecast data from the U.S. National Weather Service (api.weather.gov). U.S. locations only.

How the recommendation is calculated

Required insulation comes from a steady-state heat balance on the body: metabolic heat production for your chosen activity, minus respiratory and evaporative losses, has to equal the dry heat lost through your clothing and the air layer around you. Solving for clothing resistance gives a target in clo (1 clo = 0.155 m²·K/W), shown in the last column of the hourly table. Wind enters through the convective heat transfer coefficient and through a permeability penalty on non-windproof garments; sun enters through an estimated mean radiant temperature. The heat side is checked against an approximated outdoor WBGT, the cold side against NWS wind chill for frostbite timing. A UV index is estimated from solar elevation, cloud and site elevation, and the day is scanned ahead so sun protection can be flagged before the peak arrives. Garment clo values follow ASHRAE 55 / ISO 9920.

The feels like reading is the Universal Thermal Climate Index — the air temperature of a still, shaded reference environment that would put the same strain on the body over two hours. It reads all four variables at once, including the sun, which neither a heat index nor a wind chill does, and it is defined continuously rather than switching indices at 50 °F and 80 °F. The line under it splits the difference from the thermometer into how much of it is the sun, the wind and the humidity — each measured against that same reference: no radiant gain, still air, and half-saturated. So humidity −1°F means dry air is making it feel a degree cooler than an average day would. The three are shares of one interactive total, worked out so they always add up to the difference shown. Where conditions fall outside the index's published range no feels-like is offered, rather than extrapolating one.

The wind figure shown is the forecast wind at 10 m, which is measured over open ground, and the index reduces it to the body on that assumption. Between buildings, in trees or behind a wall you feel much less of it — enough to move the reading by tens of degrees — so Wind shelter tells the model which it is. Each setting is a standard terrain roughness, and the body ends up with about 60% of the open-ground wind under partial shelter and 20% under full. The chip keeps showing the forecast figure either way, so it still matches what you would read anywhere else.

The day is cut into blocks wherever the required insulation moves more than a fraction of a clo or a hazard threshold is crossed, each block is dressed for its coldest hour, and blocks that end up with the same outfit are merged again — so every change listed is a change you would actually make. Full model inputs are written to the browser console.

This is guidance, not a safety certification. Individual tolerance varies widely.