Zonal pattern evolves with stronger than normal heights over the sub-arctic & subtropics

With strong positive heights over the high latitudes and a strong sub-tropical high pressure belt to the south, a zonal flow pattern is now ruling the mid-latitudes with a very active trans-Atlantic storm train. Low no.1 is pushing into the UK right now and will bring a messy next 24 to 36 hours which will be followed by brief clear slot before the next system arrives. Notice in the above 500mb geopotential height anomalies for today above how there is deep reds over the sub-arctic region? That indicates stronger than normal high pressure (blocking) and this along with stronger than normal heights in the sub-tropics forces all the energy and lows to track west to east aboard a strong, zonal jet stream. The wavy flow with embedded troughs quickly force the air to pile up and form lows. With so much energy flowing across the Atlantic, squeezed into a funnel with strong heights to the north and south and with increasing temperature difference with the gradual change of seasons, this energizes these systems. Not this weekend’s system but the one following behind will be a perfect example of this bundling of energy which forces central pressure to really drop.

Next 24-36 hours will be very wet but brief respite comes Sunday

We’re currently watching a band of heavy rain sweep into Southwest England and South Wales, this will remain well organised and heavy over the next 24 hours bringing a decent soaking to most areas of England and Wales through today and will eventually reach the North of England and Southern Scotland later today into tonight.

This marks the leading edge of the low which will bring a wet and windy Saturday with gales likely along the south and west coasts, remaining blustery inland too.

While most will be dominated by showers, some heavy with thunder, lightning, hail and gusty winds, there will be a nagging, persistent band of rain drapped across Cumbria, Northumberland which may extend north and south. That’s because it sees the front stalling. Once this afternoon’s band pushes away from the South following a spell of heavy rain for London and E. Anglia, heavy, thundery showers will following along with a freshening southwest wind.

Small bubble of high pressure settles in between lows Sunday bringing drier, brighter weather by chilly night follows

Sunday should be a drier day for most with less rain and shower activity as well as less wind. High pressure which seperates each low will bring the brief respite till probably midday Monday and so Sunday evening may see a chilly night by Augfust standards under clear skies, light winds and relatively chilly air aloft. Don’t be surprised if some rural spots get to near freezing with frost possible in the Highlands. Could see our first minus reading somewhere in the Highlands by Monday morning while many get down to 3 or 4C outwith towns and cities.

Band of heavy rains and increasing southwest winds arrive Monday afternoon, evening

Monday as of just now doesn’t look too bad of a day following a chilly start with possible patchy frost in places and the coldest start in a couple of months but soon a bank of cloud and eventually rain will march in from the Atlantic and this could be heavy, especially for the Northern Republic, Northern Ireland, Northern England and Scotland.

What will affect the majority will be a stiff southwest wind. The low which follows the high won’t actually cross the UK but will be deflected north offshore towards Iceland and as it does so, pressures are expected to fall all the way to 974mb. The centre may actually stay 500-1000 miles off Ireland or the UK but the windfield is very large and it’s a large area of tightly packed isobars shows winds likely to blow strong with coastal gales.

Take a look at the below GFS pressure chart. Notice the high gets pushed east but this ridge which merges with a larger high over Europe will be strong enough to stop this thing from progressing across the UK and so the energy bundles and the forces the circulation to tighen further pushing pressures down to 974mb. The center gets deflected north towards Iceland where it will be stormy.