A rain gauge should be sited on level ground so the mouth is horizontal and open to the sky. The underlying surface should be covered with short grass or gravel.
The height of the opening should be as low as possible (minimum: 30 cm), but should be high enough to avoid splashing in from the ground.
Rain gauges mounted on towers should be located above the average level of snow accumulation. In addition, collectors should be heated if necessary to properly measure frozen precipitation.
Obstructions
Nearby obstructions can create adverse effects on precipitation measurements (e.g., funneling, reflection, and turbulence) which should be avoided. On the other hand, precipitation measurements may be highly sensitive to wind speed.
The best exposure may be found in orchards or bushes, or where fences or other objects act together to serve as an effective wind-break.
As a general rule, in sheltered areas where the height of the objects and their distance to the instrument is uniform, their height (above the instrument) should not exceed twice the distance (from the instrument).
In open areas, the distance to obstructions should be at least four times the height of the obstruction.
Siting considerations
In view of the sensitivity to wind speed, every effort should be made to minimize the wind speed at the mouth opening of a precipitation gauge.