Following a cold, dry April, the Great British weather is beginning to liven up. As we wave goodbye to April and step or perhaps limp into May, we have a sunshine and ‘April showers’ regime. Cool air mass aloft and strong incoming solar radiational means clear morning’s followed by bubbling clouds mid to late morning which give way to heavy, thundery PM showers with risk of hail, sleet and thunder. Snow above 200m, quite a low elevation for the end of April but happens every few years.

How does April showers work?

Below is the current 850mb or 5,000ft level temps. As you can it’s below freezing in a relatively quiet atmospheric environment between weather systems.

Once we loose the sun and it’s heat during the late evening, clear, calm conditions allow this chilly air aloft to sink down to the surface providing rural frost formation.

Once the sun returns, so the chilly air eventually lifts back to it’s original ‘air mass temperature’ at 5,000ft. Through the morning as the sun rises higher in the sky, so the lapse rate or temperature difference with height increases stirring up thermals or air currents. Air is forced to rise forming shower clouds. This mechanism can be more abrupt depending upon the temperature difference within the vertical column and so showers can be intense producing downpours and hail. Sleet and snow showers aren’t unusual within the more intense cells as they often transfer +2 to 5C air suspended at 2-4,000ft down to the surface.

Ever noticed you’ve got a temperature of 10C with sunshine but you run into an intense shower and your temperature has all of a sudden plunged to 5, then 3C in just a few minutes as the rain batters down? That’s because your beneath a downdraft of air. The thunder and lightning is caused by upward and downward moving ice crystals colliding within the cell. Hail reaches the ground because it’s travelling too fast to melt before reaching the ground.

UK’s 1st ‘stormy weather’ in weeks to arrive BH Monday!

Following it’s absence in April, the jet stream and it’s lows are back just in time for the early May bank holiday. The first bank holiday weekend in which folks can freely roam. Ironic that the weather takes a turn?

Here comes the jet stream.

Now…

Later Sunday

Monday evening.

Here comes low pressure, the first deep low for several weeks.

Strong winds for all but especially through the Irish Sea and Channel and in it’s wake, North Sea and their adjacent coasts.

Looks nasty for the Low Countries during the day Tuesday.

The low crossing the UK shall run the boundary between cold and relatively warm. The depth of and level of cold on the northern flank should easily support snow with height and to quite low levels but as the low exits, so COLDER air tucks in on the backside of the circulation from Scandinavia/Norwegian Sea and snow levels likely drop to quite low levels for early May.

GFS snow forecast. Significant accumulation even to high level road routes across Scotland later Monday into early Tuesday.

The coldest air aloft moves down into N Scotland later Tuesday into Wednesday.

This could make for some unusually cold nights mid next week if this solution materialises.

GFS has -7 Wed morning!

How about -8 Thursday!!

Let’s just say the GFS is overdone for now but let’s watch this space. A -6.6C recorded at Kinbrace, Sutherland last May was the UK’s coldest May reading since 1997. The UK’s coldest ever in May is -9.4C recorded twice at Lynford, Norfolk back in 1941.

Tags: april showers, may cold, may gales, may storm