On the Gaelic festival of Beltain (the first day of May) it is supposed that if you splash your face with the early morning dew, your skin and countenance will remain young forevermore.
Unfortunately, if you awoke and rose early to do just that last Friday morning, you may have encountered a little difficulty with the splashing – for there was the hardest May frost recorded in Stornoway for nearly 70 years! At Lews Castle meadows, a minimum air temperature of -4.3°C was recorded at 6:00am, only a whisker above the record low of -4.4°C for May in Stornoway (recorded way-back in 1938), and everything was frozen solid. Even in Stornoway town itself, sub-zero air temperatures meant that it was the 2nd coldest night of the ‘’winter’ - even though we are a mere 4 weeks away from the start of the meteorological ‘summer’!
What has caused the recent chill?
As always in Hebrides, the sea dictates nearly everything that happens to us weather-wise. Being a source of heat (usually) or chill (less often), it provides a constant flux of water vapour (and as a consequence, energy) from the ocean surface into the atmosphere around the clock. This air is then usually directed towards us by the prevailing onshore westerly or south-westerly winds.
Following the recent stormy winter, however, the highly disturbed seas have churned up cold water from the depths of the ocean, meaning sea surface temperatures in the mid-Atlantic are currently some 1-2°C below the expected average for this time of year. This means that the onshore winds, which take their energy from the sea surface, are also colder than the seasonal norm.
What does this bode for the coming summer’s weather?
Normally, a reduced sea surface temperature means there is less evaporation, and therefore fewer clouds – but also rather cool conditions i.e. the sort of weather that is characterised by a preponderance of northerly and easterly winds. However, the vagaries of our climate are such that there will always be periods lasting a few weeks which are warmer or wetter than their predecessors (and vice versa). And whilst it is not unusual to see a flake or two of snow across the Isles late into April or even sometimes May – the bitterness of recent winds blowing across the cool ocean has meant an increased incidence of late snow showers and sharp frosts this year.
April 2015 weather summary and statistics:
It was an often cold, but bright and sunny month. It was the first month since September 2014 to have a rainfall total of less than 100mm (4 inches). The total of 20 mornings with snow lying this past winter season is the highest in Stornoway since 2010-11.
Average daily high: +10.5°C
Highest: +15.5°C on 5th
Average daily low: +4.2°C
Lowest: +0.3°C on 28th
Difference of temperature from long-term average: -0.2°C
Total precipitation: 66.0mm (2.60in - about 90% of normal)
Wettest day: 11.3mm on 13th
Sunshine: 188 hours (30% above average)
Max wind gust: 48mph on 1st
Days with Thunder: 0
Days with hail: 4
Days with snow falling: 7
Mornings with snow lying: 2
Mornings with a grass frosts: 8
Days with rain: 19
Days with >1mm rain: 13
All observations taken in Stornoway town