Tuesday 17th February
Monday almost gave us a totally dry twenty-four hours, however, I spotted a very small shower on the radar crossing our area just before 20.00 last night that deposited just 0.2mm of precipitation. Otherwise the variable cloud allowed breaks of sunshine that resulted in the highest UV light since 6th October with a value of 1.4, still classed as ‘Low’. The loss of moisture into the atmosphere from plant life and the ground was also the highest since 2nd November that registered an equivalent loss of rainfall of 0.8mm. Whilst the sunshine lifted the maximum temperature to 9.1C at 14.56, during a prolonged burst of sunshine, being 0.8C above average, the temperature fell steadily away after 15.00 to reach a minimum of 0.2C at 07.26 early Tuesday.
Tuesday after first light revealed a sky with no thick cloud, just thin, high cloud, that allowed the sun to shine after sunrise, weak at first through thicker cloud on the eastern horizon. The strong sunshine this morning won’t last as another depression is baring down on the UK that will throw high cloud over the UK after round midday. However, at the moment it looks as if the main rain band will stay just to the south of our area.
The area of high pressure over Iberia will push a transitory ridge of high pressure over the UK today that hopefully will result in the first dry twenty-four hour period this month. The slight change in weather positions will result in the wind arriving from the east later today and tomorrow, which will result in temperatures being depressed. There is building optimism that temperatures will return to above average towards the weekend.
This morning there is a divergence of professional forecast opinion as to the type of weather that might arrive tomorrow afternoon, either wet or whiteish. I have added a section below on why it is often difficult to be certain when the conditions might produce snow. The forecasts at the moment from the Met Office and the MeteoGroup (that produces data for the BBC forecasts) have different suggestions on what might arrive, rain, sleet or snow, or a combination of precipitation.
A note from the Met Office on Snow forecast difficulties
The UK’s maritime climate plays a big role in limiting snowfall. In winter, land cools quickly, but the surrounding seas remain relatively warm. This moderates the air temperature as it approaches our shores, often turning what could have been snow into rain or sleet. While inland areas of large continents experience prolonged cold spells, the UKs exposure to milder Atlantic air means that snow is usually confined to short-lived events or higher ground.
The most common wind direction for the UK is southwesterly, bringing moist, mild air from the Atlantic. This typically results in rain rather than snow. For snow to occur, we need a combination of cold air and moisture, two ingredients that don’t always align in our climate. If we have a flow of colder from Continental Europe this will increase the likelihood of snow, especially when combined with high-pressure, which allows temperatures to fall steadily over several days.
Moisture is another key factor. For snow to form over the UK, cold air must either meet a rain-bearing weather front or pick up moisture during its short journey across the North Sea. This can lead to showers that fall as snow if temperatures are low enough.
Topography also plays a role. When air rises over hills and mountains, it cools and condenses, forming cloud and precipitation. Whether this falls as rain or snow depends on the freezing level, the altitude at which temperatures drop below zero.