Zonal Flow Across N. Hem Supports Active Low Pressure Train From North America to UK (Includes Video!)

Written by on August 22, 2012 in Rest of Europe, United Kingdom & Ireland with 0 Comments

Chart courtesy of Mariners Weather Log

With blocking highs over top of the mid-latitudes and up in the high latitudes, a zonal (west-east) flow pattern has developed following the highly amplified pattern across the hemisphere of late.

Sandwiched between the blocking high over the subtropical high, a rather active North America to Europe storm train is in place.

Note the below GFS chart off WeatherBELL models has a low down to near 990mb impacting the UK this weekend. This week has been unsettled with frequent heavy showers and today with low pressure to the north and high pressure to the south, a fresh to strong west wind is blowing and piling in those heavy, thundery showers, particularly across northern areas.

Right now, the low which is to hit by this weekend is now pushing off Canada. It will bring more organised rain and blustery conditions Saturday and Sunday to the UK and Ireland.

GFS chart courtesy of WeatherBELL Models

Interestingly by Saturday when this low is crossing the UK, another system is pushing off Newfoundland and will take the same track as the first low. This secondary low will push across the Atlantic and deepen faster, becoming a large system. The current GFS has this storm down to 980mb to the west of Ireland by Monday but it looks to come up against resistance from a high which builds over the UK on the backside of the first low early next week. This high will force the energy to pile up against the wall of the ridge and so the centre appears to take a loop up towards Iceland but in the process it deepens.

GFS chart courtesy of WeatherBELL Models

According to the latest GFS run, it has pressures to the south of Iceland down to an impressive August depth of 972mb. Despite the distance between the centre and the UK, the wind field is large and may mean SW winds blow strong to perhaps gale force in places across the UK as the system does a complete turn between Iceland and the UK, making a second attempt at striking. However, it would appear it comes up against more resistance from the lingering ridge by Wednesday.

GFS chart courtesy of WeatherBELL Models

In the above chart for Tuesday, notice how expansive the pressure field is around the 972 low. Like I say, this, if happened would still bring strong to perhaps gale-force southwest winds to the UK despite the storm centre being up near Iceland. It’s the size as well as depth of this low for this time of year which is impressive and worth paying close attention to as new runs of this and other models come out.

Notice in the final chart below for Wednesday how the ridge breaks away to the east from the UK and this allows this low to take a run at the UK. Albeit pressures are rising, with the greatest depth being possibly 972, then it would take a lot of rise in pressure for this thing to not make an impact. The GFS, although still has it offshore, brings a 986mb low close to the UK, likely to produce heavy rain and gales.

This of course can and will change but one thing I feel confident in is that the unsettled theme will continue and take us into September.

GFS chart courtesy of WeatherBELL Models

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