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Any sign of drier and warmer weather

Published 2nd April 11:40

The prevailing weather pattern for months has seemingly been characterized by prolonged periods of unsettled conditions, with only a few relatively brief and transient spells of high pressure. As we look towards the first half of April, the question arises: are there any indications of a shift in this pattern?

Support for a change to drier weather

In recent days several computer model runs have indicated that high pressure will exert more influence in the medium term. For example, the chart below from the ECM model shows forecast pressure patterns on Friday 12th April. High pressure centred to the south and east is bringing more settled conditions, with the risk of rain mostly confined to the north west of the UK.

ECM forecast pressure chart
ECM forecast chart for 15th April

Although it is just one of many computer model runs it isn't completely on its own so there is some support for this scenario. 

Is it the most likely outcome?

The GFS model chart below shows low pressure maintaining unsettled conditions across the UK, with dry interludes most probable in the south and south east. A different scenario to the ECM chart, but again it is just one of many runs and when looking this far ahead it is never wise to pick out individual runs and use them as the sole basis for a forecast.  

GFS pressure forecast chart
GFS forecast chart for 15th April

The key is to look for trends and in particular what the ensemble model updates are favouring. This doesn't provide guarantees either, but because ensemble models contain many individual runs, it becomes easier to identify the most likely scenario.

The data table below categorises the pressure forecasts for London for the next 16 days from all of the runs in the GEFS model. In the short term the columns are 100% green, indicating that all runs are forecasting pressure to be between 996mB to 1010mB. The norm is around 1015mB, so all runs are below it. 

By Sunday 7th April a change occurs, with 71% of runs now being in the yellow category which is 1011mB to 1025mB. That is quite a strong signal for somewhat higher pressure, but it appears transient with the amount of green quickly increasing once again. It's worth highlighting the word "higher", because the yellow is not really indicating high pressure;  that is shown by orange or red shading.  

GEFS MSLP data table for London
GEFS 16 day London pressure forecasts

In the longer term the amount of yellow increases again and some orange shading starts to appear. By Wednesday 17th April, 13% of the runs are in the orange category. In other words a relatively small minority of the runs strongly support a settled period. Nonetheless, the greater number of runs showing higher pressure than has been the case recently give weight to the idea of there being more frequent dry days, particularly in the south of the UK.

A chance of warm days?

On balance, changeable weather is favoured to continue through the first half of April. During the second week of the month the chance of dry days could increase, particularly in the south. It's also worth noting that very warm air could be close by and it may reach the UK at times. Therefore, if drier and brighter days occur temperatures could rise quicky. 


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