An Unsettled But Warm & Humid Week Ahead For UK/Ireland, Turning Increasingly Stormy By Wednesday!

Written by on August 13, 2012 in United Kingdom & Ireland with 0 Comments

Today marks the start of what will be a very unsettled week though it’s not all doom and gloom despite a series of lows spinning our way from the Bay of Biscay which from particularly Wednesday on, may pack quite a punch with heavy rains and gale-force winds. In between there is sunshine and plenty of warm temperatures to be had.

The driving force behind a warm/unsettled week which could turn stormy!

It’s all thanks to a huge parent cut off low developing out over the North Atlantic and with it’s position this supports a week of SW winds which will draw warm, humid air up from the subtropics, keeping us warm and humid. The fly in the ointment is it’s an unsettled week with lows forming on the eastern edge of the trough. The UK sits beneath the atmospheric railroad tracks in which low pressure systems, forming over the Bay of Biscay will ride along and so wind and rain will be a frequent visitor to all areas.

Today’s low is to our west but it’s associated front is spreading a band of rain across the country and with it will be a stiff wind. You’ll notice it warm and humid out there and this juicy air is here to stay, helping fuel backside heavy showers and thunderstorms later this afternoon. The warmth and humidity will add intensity to some of those showers, forcing the rate of upward motion to increase and helping turn them into thunderstorms. We’re seeing that over Belfast right now.

Parts of the Republic, Northern Ireland and later, NW England, western Scotland could get hit hard with the low pressure centre nearer and with added spin from the circulation, we could see not only heavy bursts of rain, accompanied by gusty winds and thunder and lightning but a few funnel clouds or even tornadoes developing.

Tuesday: A day of sunshine and heavy showers, thunderstorms

Tomorrow will be another warm, humid day, perhaps warmer than today with a range of 19-22C in Northern Ireland and Scotland, 22-25C in England and Wales and with all the warmth and humidity bubbling the lower atmosphere and the nice cool layer suspended aloft, this sets the stage for some decent thunderstorm potential over parts of Ireland, Northern Ireland, Scotland and Northern England tomorrow, especially from late morning till 6pm.

A large swath of central and southern England including many parts of Wales should be some decent spells of sunshine with a much lower chance of showers than further north. This will help push temperatures towards the mid-20s and make for quite a pleasant August day. Of course an odd pop up shower can’t be ruled out.

ECMWF sees heavy showers/T-Storms Over Central Scotland tomorrow afternoon, drier, brighter further south (Courtesy of AccuWeather Pro)

Wednesday: Deep low arrives and spreads band of heavy rain, gale force winds across UK

Enjoy Tuesday if you live anywhere across the southern half of Britain as the models have a deep low spreading a band of heavy, persistent rain up over southern Britain during Wednesday, eventually, spreading north up across Scotland and Northern Ireland into the afternoon and evening. The exact timing of it’s arrival is uncertain and depends upon what model you look at but with the heavy, widespread and possible 1-2 inch rains will come strong to gale-force winds out of the south and east. Unusually strong for August. Although this will be a storm accompanied by mild air, it will look a lot like autumn with the heavy rain and 15-25 mph winds, gusts beyond 30-40 mph across inland areas. The south and east coast will likely see gales with gusts easily topping 50 mph which generate heavy seas and tricky shipping conditions.

While all models see this low and it’s unsettled influence on the UK, each one plays out the scenario differently. The GFS is most bullish with a sub-984 centre, nearest to the UK with the bulk of the rains spreading right over the UK whereas the ECMWF has a deeper centre down at 980 but the core and worst conditions appear to be WEST of the UK and more over Ireland, Northern Ireland. The NOGAPS is weaker and overall packs less punch.

The GFS is also quickest in it’s arrival. The others are slower at spreading the wind and rain over the UK.

The below maps show what both the GFS and ECMWF are interpreting for Wednesday (Maps courtesy of AccuWeather Pro)

Thursday, Friday into Saturday: Hosepipe of deep subtropical moisture could bring big 72 hour rains across broad area of UK

The models have a very unsettled Wednesday through early Saturday period as a deep plume or hose pipe of moisture streaming southwest to northeast along a sharp thermal boundary points straight for the UK. This plume of rich subtropical moisture could support some really impressive 48 to 72 hour rainfall totals between Wednesday and Saturday morning with embedded thunderstorms dropping locally heaviest amounts of rain.

ECMWF shows intense heat over southeast England by Sunday (more on this soon!)

Check out what the current ECMWF 850 chart has for Spain, France and yes, Southeast England by this Sunday! Hottest air since 2006?

Parts of the northern UK may see the warmest night temperatures of the summer over the next few nights

With a warm, humid southwest air flow blowing much of the week, this will likely support some very warm nights, especially over typically cooler Northern Britain. These winds will override typical overnight cooling and so we could see lows hang at around 16-18C at night, falling little from daytime maximums.

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