When does summer actually start?

With just two more days of May left to go before we hit June many people, or maybe it’s just us, think we should be seeing some more positive signs Summer is just around the corner.

Current rainfall over the UK this morning, dark orange = heavy:

Has May felt a little chilly and a touch more ‘damp’ this year?

Rainfall’s been about average for May versus previous years however, it’s been relatively cool for late Spring with average temperatures measured at the Hawarden weather station so far around 14°C – that’s versus a mean average of 16°C for the time of year.

When does summer actually start?

There are two definitions of when Summer starts, these are astronomical and meteorological.

We tend to use dates in calendars to define the start of a particular season, they are known as astronomical seasons and are determined by the Earth’s axis and orbit around the sun, they also fall at different times of the year.

Solstices and equinoxes are considered to be the astronomical transition points between the seasons and mark key stages in the astronomical cycle of the earth.

This year, the astronomical summer begins on 21 June 2015.

Weather forecaster such as the Met Office use a meteorological definition of the seasons.

Here’s what the Met Office say:

Meteorological seasons are based on the annual temperature cycle and measure the meteorological state as well as coinciding with the calendar to determine a clear transition between the seasons,

Since the astronomical seasons vary in length, the start date of a new season can fall on different days each year.

This makes it difficult to compare seasons between different years and resulted in the introduction of the meteorological calendar.

This splits the calendar into four seasons of approximately equal same length.

The astronomical seasons run approximately three weeks later than those of the meteorological calendar.

This year, the meteorological summer begins on 01 June 2015.

Can we expect a BIG change in weather from June 1st?

The long range forecast suggests high pressure will dominate the north of the British Isles during June, with lower than average pressure to the south.

This pattern is likely to mean a warmer than average month, with rainfall close to average for much of the UK and Ireland.

Temperatures will generally be 1 to 2C above the 1981-2010 average during this period, except near North Sea coasts.

Rainfall totals are expected to be below average except in southern England.

Sunshine totals will generally be above average, particularly in central and western Scotland, Northern Ireland and north-west England.