Mid-April Longer Term Thoughts & Analysis…

15 Apr

Spring is often a season with extremes.  Many areas across the Northern Hemisphere under-go changes on quite short time scales as we continue to see the influence of an increasingly strong sunshine.  However, the remnants of winter, characterised by a lingering cold pool of air to the north of the UK, can still make an appearance.  Clearly the last 4 to 6 weeks across the UK have produced extremes.  From balmy temperatures above 20C in mid to late March, to being replaced by near blizzard conditions in places a week or so later.  April is now certainly producing the classic ‘April showers’ type weather as well as low pressure and unsettled conditions generally continue to dominate the weather with some heavy and thundery downpours over the last week or so.

There has been some recent discussions over the longer term outlook covering the second half of April and the main emphasis is on unsettled conditions, as low pressure dominates the weather.  The primary question is; why is the weather likely to be persistently unsettled?…

The answer, as ever, lies in the expected broader scale weather patterns including the position and location of larger scale troughs and ridges (jet stream) and the below image highlights what is expected during the second half of April overall;

Now when it comes to looking at the medium and particularly the longer term expected weather patterns, it is of greater importance to attempt to find the broader scale pattern, rather than the detail.  The above image highlights the fact that throughout the rest of April a large and slow moving trough is expected across the UK and other North-western areas of Europe. In broader terms a ‘trough’ is indicative of unsettled conditions and low pressure, bringing predominantly unsettled conditions with rain, showers and with temperatures generally average at best.  In comparison a ridge in the jet stream, which is expected to be the case across far Eastern areas of Europe and into Russian will clearly signal the opposite and that will be surface high pressure and settled conditions.

Now using a few forecast charts to illustrate this, you can see that on both the GFS and ECM ENS (ENS = Ensemble) charts at 240hr, low pressure is dominant across the UK in association with a marked upper trough, whilst pressure is generally higher across Eastern Europe;

Now if you attempt to compare the actual forecast charts, to the first image I have constructed, you can see that at this particular time frame (240hr 25th April 12) the pattern matches very well indeed.  So, in summary, if you are after a rapid return to more settled and warmer conditions like what was experienced in March, or even just a trend towards more settled and drier conditions, then that is highly unlikely.  Clearly the second half of April in meteorological terms is a long time and things can change, but it certainly looks as though that the second half of April will produce unsettled conditions with rain, showers, some strong winds and predominantly cool temperatures across the UK…

…however, good news for those in the hosepipe ban regions!

Regards to all,

M.

 

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