Our current dry streak has been ongoing now for the best part of 2 weeks. There are hints of change mid next week to a somewhat more unsettled pattern once again. The current spell is allowing soils to really dry out nicely. So why the sudden change following a super wet past 11 months?

Firstly we have a very ‘blocked’ pattern right now with the MEAN high pressure position sitting over the UK, this is re-routing the typically active Atlantic storm track around us, not over us. What may be the cause of this significant change in the long term pattern? Any given pattern can only last so long and while we endured 2 dry years up until the turn of spring last year, it appears we have turned a corner in a significant way once again.

I believe a lot of the flip at the end of March, start of April had to do with the warming of the equatorial Pacific which was a trigger to what would become a super wet pattern through much of 2012. This was helped greatly by a cold PDO and VERY warm AMO but with the El Nino flat-lining during winter, feedback is now responding and what will be interesting is whether we get the development of another La Nina during the upcoming summer in response to the cold PDO. The fact the Nino has not come to anything and a cold PDO favours La Nina, the return of a cold ENSO phase looks likely and this could well have impact on our weather for late summer into next winter. During cold phases of the PDO, La Ninas are more common and tend to be stronger than El Ninos.

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The El Nino, which attempted to develop last spring, never truly did but I believe there was enough warming to cause a large atmospheric reaction and the tremendous rains we saw here was magnified by the confliction between cold PDO and warm AMO. Warm and cold don’t mix well and with warmer SST’s beneath the mean westerly flow UK-bound, this suggests more moisture streaming our way. When the North Atlantic is very warm, this tends to lead to wetter summers here. It will be interesting to see whether this current return to ‘drier than normal’ lasts as we progress towards spring.

The El Nino no longer and with a strongly negative AO/NAO, this may be allowing helping us ‘dry out’. The key question is does this continue. If it does and lasts through much of spring, then we may well have a much better summer ahead.

Of course we live in the UK and mid-latitudes with an ocean on our western doorstep. While I believe the onset of a La Nina during this summer is possible and it would encourage drier than normal conditions here in the UK, we are going to see wet weather but it’s the long term trend that really matters. As for the short term. We appear to stay largely dry through at least mid next week with change from Wednesday onwards. Up until now, without the west-east flow, we will remain fairly dry and settled and that could come via cold or mild air masses through early and mid March. The strongly negative AO/NAO should keep the blocked pattern going and so less moisture comes to the UK and Ireland.

Below is a next Tuesday through Thursday surface and precipitation chart sample according to the latest GFS charts.

TUESDAY

Pressure

Precip

WEDNESDAY

Pressure

Precip

THURSDAY

Pressure

Precip

Here’s the ECMWF upper chart and 850 temps.

Mon

Wed

Fri

Sun

During the second half of next week you can see the upper ridge slide into Europe, making way for surface lows to advance towards the UK with front running bands of rain pushing in.

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