Explaining the weather
AS BBC weatherman Michael Fish knows, explaining what is going to happen with the weather isn’t always easy.
Even the experts are left with egg on their face sometimes – or in Mr Fish’s case, a hurricane which wasn’t foreseen. Bearing that in mind, you might ask yourself what chance do Muppets like us (journalists) have of getting a forecast right for the newspaper?
Well, it isn’t always as hard as it sounds. We have some very good sources to refer to – principally the state weather agency AEMET and the good people at Alicante university climatology lab who offer indepth forecasts from their Facebook page – as do the more local associations such as Mete-Orihuela and Proyecto Mastral in Torrevieja.
You might say that we are blessed with information and all the journo has to do is put it in some semblance of order and try to present it in a semicoherent fashion for you the long-suffering reader.
The meteorologists don’t always get it right – the Mediterranean coast of south-east Spain is a very difficult area for pinpoint forecasts, particularly at times of the year when highpressure is not holding sway. However, last week – in the lead up to the period of heavy precipitation which hit us from Friday to Monday – they did produce some very good forecasts, which allowed us to proclaim on the front page that the region was set to be hit by five days of rain.
We have them to thank for being able to pass on some accurate information to you, the reader. This is particularly relevant in a time when many people have applications on their mobile phones which give them forecasts that are of dubious quality.
As a weekly newspaper, we are not always able to offer the ‘latest’ on the weather, so we sometimes use our Facebook page to pass on additional information or updates on emergencies and alerts – as happened at the weekend.
At this point I should also say that there is nothing quite like the weather (Brexit excluded) for producing angry reactions from people. Facebookers really seem to get their knickers in a twist over something that shouldn’t be so controversial – or a source of anger. In the lead up to the weekend rain, we ran a short article on our Facebook page about the rising seas which augured the inclement weather to come.
It read: “As atmospheric pressure falls, sea levels rise seen here at Guardamar close to the border with La Mata this afternoon.
“This is an indication of the increasing instability in the atmosphere associated with the cut-off low pressure system which is approaching the Med coast.”
Perhaps it wasn’t very well explained – and it brought out the angry brigade.
One Facebooker responded: “What a load of technical bullsh*te! If you are going to try to say something meaningful then say it so the ordinary person can bl**dy well understand it.”
Another respondent saw a conspiracy lurking behind our words.
He commented: “Which means exactly what? Is someone scaremongering?”
Perhaps we’d been infiltrated by the Ruskies…
As I said earlier, it isn’t always easy to pass on technical information in a clear and concise way – and it seems we failed on this occasion. But, behind our dark proclamation, there were a couple of interesting weather concepts, worthy of getting to grips with.
The first concerns sea level and air pressure. I will resort to the Swedish meteorological and hydrological institute for some help here.
They note: “Higher air pressure gives lower sea levels – an increase in air pressure of 1 hPa lowers the water level by 1 cm. Sea level varies from day to day and week to week, depending on the weather situation. Air pressure has a direct influence on the sea level. High air pressure exerts a force on the surroundings and results in water movement. So high air pressure over a sea area corresponds to low sea level and conversely low air pressure (a depression) results in higher sea levels. This is called the inverse barometer effect.”
However, they note that ‘water levels at a particular location are not only affected by the local air pressure but also by other factors’ so the inverse barometer effect doesn’t always hold true.
Fascinating stuff ? I think so. So we could look at the sea last Thursday and see that something was up – and it wasn’t just the tide.
The other concept in the Facebook post which flummoxed our reader was probably the term, cut-off low pressure system. And this was very important for understanding what was to come at the weekend. This is what is often referred to in Spain as a ‘gota fría’, another much-abused term which most of us don’t really understand.
The explanation comes from the US national oceanic and atmospheric administration.
They note that a cut-off low is a ‘closed upper-level low which has become completely displaced (cut off) from basic westerly current, and moves independently of that current’. “Cut-off lows may remain nearly stationary for days, or on occasion may move westward opposite to the prevailing flow aloft (i.e retrogression),” they state.
This is why the rain hung around for so long at the weekend – and didn’t just pass through like other low pressures.
Weather Online tell us that ‘the cut-off low is a cold low (depression) in mid-latitudes (occasionally almost in subtropical latitudes) where air of polar origin is cut off from the main subpolar belt of low pressure and cold air, the normal track of depressions’.
They also reveal why the UK was basking in sunshine over Easter and we were experiencing weather more usually associated with the British Isles.
“Sometimes a cut-off low occurs with a cut-off high over the higher latitudes, typically in blocking situations,” they state.
They took the high road and we took the low road.
And why does the cut-off low bring rain?
“Such slow-moving lows are associated with unsettled weather and, in summer, with thunderstorms,” note Weather Online.
However, Alicante university’s Samuel Biener told us at the weekend that thunderstorms in this area can come at almost any time of the year in a cut-off low. So there you have it. Who said that explaining the weather would ever be easy.