Archives For November 2012

Our South East corner of the UK has had things easy compared to the rest of the country!

It depends on the LOW pressure currently hanging to the South of Greenland. If it shifts west then this will bring warm Atlantic air to the UK next week. If it moves North then our cold snap will stick around for a while longer.

The UK Met Office have the LOW moving North, most other models have it moving across to us… wait and see!

Here it is!

River Mole Flood Alert!

November 25, 2012 — Leave a comment

River Levels are high in the River Mole and are expected to continue to rise and may come out of banks in places. We have had a largely dry Sunday morning, but further rain is forecast for this afternoon and overnight, this is likely to cause river levels to rise further. See environment agency website for more details.

Country-wide nearly 1000 homes have been flooded and 3 people have died.  The SW has been worst hit where many rivers have burst their banks in the current run of storms.

Take a look below at the forecast for London temperatures through to the start of December.  Also, check the map: that blue colour approaching the UK is a cold pool of POLAR air which will make things increasingly chilly this week.  Some parts in the East and further north in the country may see snow by next weekend: this is more doubtful for Reigate but certainly cold rain!

Learning spot: We commonly see sea level pressure lines labelled 1016, 1020, 1024 etc.. measured in mb (millibars) / hpa (hectopascals) on charts (these measure the same).  These lines show air pressure at sea level and appear on most synoptic charts.  But what are the lines labelled “528”? They are atmospheric thickness lines!

Explanation: Cold air is more dense and has a low thickness (like a thin duvet!). Warm tropical air is thicker (like a fluffy duvet!).  Pressure decreases with height so that the 1000 hpa is usually the air pressure somewhere near the surface and 500hpa is usually half way up through the atmosphere (around 5000m). Thickness technically measures the difference in height between these two standard pressure levels in the atmosphere. Thickness is closely linked to the temperature of this layer of air.

So, for our purposes, cold, polar air has low thickness, and values of 528 dam (decametres 1dam=10m) or less frequently bring snow to the UK. Conversely, warm, tropical air has high thickness, and values in excess of 564 dam across the UK often indicate a heatwave.

This winter: watch those 528 dam thickness lines on weather charts!

Highest wind gust = 41mph at 4am Sunday morning.

This weekend sees two powerful storms tracking rapidly NE across the southern part of the UK: the first to hit will bring strong winds and heavy rain to Reigate over Saturday afternoon and night – it will track across and clear by Sunday morning, bringing colder clearer NW winds in its wake.  A brief interlude on Sunday is likely to be followed by a big low tracking in from a westerly direction which will bring more strong winds and heavy rain.  It will clear by Tuesday and THIS will herald the arrival of those increasingly cold and brisk NE winds for the rest of next week.  Prepare for increasingly wintry weather!

Saturday – intense low out of Biscay

Sunday: brief high pressure ridge between two monsters!

A deep depression centered over Iceland is crossing to the North of the UK bringing windy conditions to south east through Thursday / Friday:

Wind gusts could reach a whopping 50mph overnight thursday 22 November to friday here in the South East.  Average wind speeds will be more like 20mph+.  The cold front moves through overnight and this will herald a taste of that cold wind brought down from the North – more of this next week!

This blocking High pressure out to the West of the UK will be developing next week – certainly by Tuesday Nov 27: it is called an Omega Block because the High pressure takes on the shape of the Greek letter (outlined in red) and is bounded by deep LOWS on both sides – notably one to the South of the UK.  This will open the door to cold northerly and north easterly winds across the UK – snow watchers be aware – a cold snap, but still not a Daily Mail “Arctic freeze”! another view of the powerful northerly jet stream bringing colder air to the UK next week:

a stormy week

November 18, 2012 — Leave a comment

Most of the weather action is hinged on a big stormy LOW tracking NE up the western margin of the UK.  Here in the east we escape the worst until Tuesday when rain and wind arrives (30mph+for Reigate) from the South: so relatively mild at first but stormy.

Glance at the medium range temps below: Temperatures are due to be falling away from the end of this week and late November / early December is looking colder as air from a developing Greenland high pressure is introduced. Not a huge winter freeze but certainly cooler with northerly air flows and maybe some snow for us here in the south east as this cold air meets moist air from Europe.