UK weather: The atmospheric ‘seesaw’ partly responsible for this week’s cold snap

Posted: March 9, 2023 by oldbrew in Natural Variation, pressure, Temperature, Uncertainty, weather

Meteorology time. Why the ‘partly’ in the headline? Climate change pokes its nose in at the end of the article, but all that’s offered is uncertainty.
– – –
The “seesaw” is bordered by a high-pressure area west of Portugal and a low-pressure area centred over Iceland.

When the balance changes, so does the weather, says Sky News.

An atmospheric “seesaw” is partly responsible for the snow that much of the UK will likely see this week.

As much as 40cm could fall across central Scotland and the southern Highlands, while northern England, including its cities, may see between 15cm and 20cm.

People in southern England and South Wales can expect to wake up to snow on Wednesday – although it is unclear whether it will settle, the Met Office said.

Temperatures could drop as low as -15C in northern Scotland overnight – making it the coldest night of the year so far. [Talkshop comment – coldest reported was -16C]

What is the ‘seesaw’ – and how is it contributing to cold snap?

The “seesaw” – formally known as the North Atlantic Oscillation (NAO) – has two sides: a high-pressure area over the Azores, west of Portugal, and a low-pressure area centred over Iceland.

When the pressure gap between them changes, so does the strength and location of the North Atlantic jet stream.

The jet stream is a collection of very fast winds high in the atmosphere that influences the movement of storms.

If there is a larger-than-usual difference between the pressures on each side of the North Atlantic seesaw, winds from the west become dominant, bringing with them warm air which – when combined with the position of the jet stream – creates mild, stormy and wet conditions in the UK.

This is called a ‘positive’ North Atlantic Oscillation (NAO), but the opposite is occurring this week.

A negative NAO means the reverse: the gap in pressure between the atmospheric areas above Portugal and Iceland is smaller than normal, changing the position of the jet stream, and allowing Arctic air to create cold, calm and dry winters.

“When this pattern is in its negative phase, the jet stream can become wavier. Currently the NAO is in a negative phase and the jet stream is further south than usual,” explained Helen Dacre, professor of meteorology at the University of Reading.

“Thus, air from the Arctic is moving southwards over the UK resulting in colder weather conditions.”

Full article here.

  1. saighdear says:

    I can Spit and choke at the various reports: formally known as ( the NAO) and so what is it called now? Also, t’other day they said that a LOW Press area was PUSHING weather …. how did LOW pressure push against anything?
    Anyroad, I’ve been looking at all this Oxford n ULEZ rubbish which will be in Glasgow as well from this Summer and INverness is already talking about it… what is the common denominator? Take a look at this map in view of current weather across the globe, is seeing believing or is it READING ( the figures) to believe?

  2. oldbrew says:

    MARCH 9, 2023
    The world’s atmospheric rivers now have an intensity ranking like hurricanes
    by American Geophysical Union

    Quote: Atmospheric rivers, which are long, narrow bands of water vapor, are becoming more intense and frequent with climate change.

    Got data?

    The researchers used climate data and their previously developed algorithm for identifying and tracking atmospheric rivers to build a database of intensity-ranked atmospheric river events around the globe over 40 years (1979/1980 to 2019/2020).

    Aha, ‘climate data’ 🤔

  3. oldbrew says:

    National Grid spent hefty sums to keep the lights on during cold snap
    The system operator paid some of the steepest rates for gas-powered electricity on Tuesday, fresh data shows

    It is estimated that the total cost of balancing the grid on Tuesday could be between £5 and £10 million.

    National Grid ESO declined to comment.
    – – –
    It’s still cold today (Friday).

  4. oldbrew says:

    UK weather: Police blame motorists for M62 gridlock as drivers stranded by snow for 10 hours

    More wintry hazards to come, Met Office warns

    Storm Larisa, as the current Arctic blast has been named by Météo-France, is now “gradually pulling away into northern Europe”, the Met Office said in its latest update this lunchtime.

    However, in its trail is “a feed of colder air and clearer conditions across many areas of the UK by late on Friday”, the body said.

    These clear skies “will bring further wintry hazards with widespread frost and ice occurring with sub-zero temperatures for many”, plunging to -8C in widespread parts of northern England and lows of -6C in the south of England.

    Jason Kelly, chief forecaster, said: “The worst of the snowfall in England is over for now, but further weather warnings will be in force to cover the further hazards brought by frost and ice.”

    – – –
    All this will be forgotten if there’s a hot day or two in the summer.

  5. oldbrew says:

    A brief respite for some before cold returns
    — Met Office
    12:40 (UTC) on Fri 10 Mar 2023

    Wintry conditions will be slowly easing their grip on most parts of the UK over the weekend, but a return to colder conditions for many is likely in the early part of next week.
    – – –
    Which ‘climate crisis’ does a cold-ish March belong to?

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s