SEPTEMBER ON TRACK TO BE A DRY MONTH WITH A BLOCKING HIGH DEVELOPING
The first half of September is shaping up to be very dry month with a blocking high looking likely to to develop across Ireland and the UK to block out the unsettled westerly and Atlantic flow leading to one of the driest starts to a Autumn in years.
It is due to a high pressure which drifts up from the Azores a Azores high. This blocking pattern is often referred to as northern blocking due to the presence of this high pressure at northern latitudes, then in winter this type of development can eventually lead to a cold spell developing across our part of the world as increasingly cold air gets drawn down around the high.
Both the GFS model and Ecmwf model has this blocking pattern in place untill at least the 15th of September with the ECMWF shown the blocking high in place until the end of the model run which takes us up to the 10th of September at that stage the blocking pattern is firmly in place and when that happens it can take some time for it to be broken down.
Precipitation (rainfall amounts) looks set to be well below average for the first 10 days of September. On Sunday a small band of rain will pass over Ireland and clear over Sunday night to the east, once this passes it could be the last bit of rain some parts of Ireland see for nearly 2 weeks. The first half of September. Ireland, the UK Scandinavia, Germany & Netherlands look set to all see well below average or no rainfall at all for the first half of the month. There still will be the risk of small showers but these been very small and limited to certain parts of the country. Below shows the the rainfall average for the next 8 days across Europe.
Red - below average rainfall amounts, Blue - above average rainfall amounts,
WHAT IS A BLOCKING HIGH
In meteorology, blocks are areas of high pressure that remain nearly stationary and distort the usual eastward progression of pressure systems. The blocks can remain in position for more than a week which will lead to areas under the high to have similar weather for a prolonged period of time.
A weak jet stream (or its position) is one way in which an area of high pressure can become slow moving. The jet stream helps to develop and steer areas of low pressure around so if it’s weak or positioned well away from the UK, high pressure can become more influential in our weather.
The jet stream will also be well out of the picture over the first half of September due to that northen blocking high pressure ridge which sits over Ireland, the UK and Scandinavia pushing the jet well north up into Greenland and above Iceland. Below I have attached the jetstream forecast chart from the GFS shown this.
The most interesting thing about this pattern we are going to see is that we have seen it over the summer a lot and really since May we have been locked in this pattern. The one to watch is November, December and January if we still are locked in this pattern then you can prepare for a cold 3 months especially if a scandi high redevelops allowing that colder air to sink down.
Thats it for this update folks I hope you enjoy your weekend