Chepstow Climate Station

Extreme Weather 2012

Station Notes

There are now 11 categories that are observed under the heading of Extreme Weather at Chepstow.

The weather elements are listed below with a brief description of criteria to qualify for this.

Almost all extreme elements run between a midnight-to-midnight parameter GMT and are in days per month.

There are two exceptions however, under the heading Snow lying and Ice Day. Criteria for these elements are listed below.

The category under the heading of storms should be read in the graph below as occasions-per-month only.

Weather Element and General Requirements

Air Frost

When the atmospheric temperature falls below freezing point and dew or mist becomes frozen.

Grass Frost (Ground Frost)

When the temperature at ground (grass height) level falls below freezing point.

Mist

When thin fog develops but partial visibility in still maintained above 1000 metres.

Fog

When a mass of condensed water vapour develops and cloud is thick enough to reduce vision to less than 1000 metres.

Gale

When wind speeds are gusting to = or >39 mph (34 knots). At Chepstow a day of Gale requires a wind gust to reach 39 mph.

Note however, this would not qualify under Met Office requirements.

Snow Falling

When sleet or snow crystals are seen to fall. A single flake observed would qualify under this heading.

Snow Lying

Snow lying is recorded when 50% of the ground is covered by fallen snow @0900 GMT.

Hail

When hail is observed falling. This section includes all types of hail <5 mm also.

Thunder Heard

This section records actual thunder heard at or near the site.

Storms

This category records the number of thunderstorms/hailstorms that pass over or near to the site.

Ice Day

When the air temperature remains below 0c, within a period of 24 hours between the hours of 9-9am.

Table up to date as of 30th April