Crown snow-load is

snow Snow comprises individual ice crystals that grow while suspended in the atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet ...

and

hard rime Rime ice forms when supercooled water liquid droplets freeze onto surfaces. Meteorologists distinguish between three basic types of ice forming on vertical and horizontal surfaces by deposition of supercooled water droplets. There are also inter ...

that accumulates on

tree crowns In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are u ...

in a cold climate. There are two main climatic conditions in which this phenomenon chiefly takes place. Hard rime is formed when

subcooled The term subcooling (also called undercooling) refers to a liquid existing at a temperature below its normal boiling point. For example, water boils at 373 K; at room temperature (293 K) the water is termed "subcooled". A subcooled liqui ...

droplets of fog or low-level

stratus cloud Stratus clouds are low-level clouds characterized by horizontal layering with a uniform base, as opposed to convective or cumuliform clouds that are formed by rising thermals. More specifically, the term ''stratus'' is used to describe flat, h ...

freeze on the

windward Windward () and leeward () are terms used to describe the direction of the wind. Windward is ''upwind'' from the point of reference, i.e. towards the direction from which the wind is coming; leeward is ''downwind'' from the point of reference ...

(wind-facing) side of tree branches, buildings, or any other solid objects. This takes place usually with moderate

wind speed In meteorology, wind speed, or wind flow speed, is a fundamental atmospheric quantity caused by air moving from high to low pressure, usually due to changes in temperature. Wind speed is now commonly measured with an anemometer. Wind spee ...

s from and air temperatures between . Snow may accumulate directly on the trees when a

warm front A warm front is a density discontinuity located at the leading edge of a homogeneous warm air mass, and is typically located on the equator-facing edge of an isotherm gradient. Warm fronts lie within broader troughs of low pressure than cold fr ...

brings wet snow, the air temperature is slightly above the

freezing point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depe ...

and the surface of the tree is colder due to a preceding cold spell. In

Scandinavia Scandinavia; Sámi languages: /. ( ) is a subregion in Northern Europe, with strong historical, cultural, and linguistic ties between its constituent peoples. In English usage, ''Scandinavia'' most commonly refers to Denmark, Norway, and Swe ...

, largest snow-loads accumulate to the trees on top of medium-sized

fell A fell (from Old Norse ''fell'', ''fjall'', "mountain"Falk and Torp (2006:161).) is a high and barren landscape feature, such as a mountain or moor-covered hill. The term is most often employed in Fennoscandia, Iceland, the Isle of Man, pa ...

s. The larger fells and mountains have no trees, and the tops of lowest fells do not reach the cloud bases so often. Also the wind speeds are largest on fell tops. One spruce in Northern Finland can collect {{cvt, 3-4, tonne, ton of snow. When the crown is loaded with snow, a storm can easily damage the trees. Snow-loaded trees also pose a risk to powerlines.IF
Insurance company (English)

References

Snow or ice weather phenomena