Helen Roberts
My weather career has been incredibly varied, from working with the RAF, to presenting the weather on TV. I am currently a Media Advisor and Senior Operational Meteorologist at the Met Office.
Location Met Office Exeter
Activity
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Helen Roberts replied to Eric Mansfield
Good spot. In fact the tropopause varies in height with temperature, latitude and season, so it can be as low as 7 km over the poles in winter, and as high as 20 km over the equator in summer. However, we ought to be consistent with our diagrams.
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Helen Roberts replied to Helen B
That's not particularly unusual. If you think about what a front is - where 2 air masses meet - a cold front moving one way is the same as a warm front moving the other. So if a pivot point occurs in the front, with one section moving north and the other moving south, it results in what you describe.
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These are not terms I'm very familiar with here in the UK, but I believe it's just the temperature. So a freeze would be temperatures below 0 °C, and a hard freeze would be perhaps temperatures below -3 °C. It could also be dependant on duration?
We also have the term 'penetrating frost' which is when sub-zero temperatures combine with strong winds. -
Helen Roberts made a comment
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It's just a temperature, 0 °C at about 1 m above ground (this is where we measure temperature using a standardised Stevenson Screen).
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Helen Roberts replied to Helen B
That's a really good question, I suppose different cloud will behave/move differently, and a big cumulonimbus might tend to more more slowly than a small cumulus cloud given the same wind speed.
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Helen Roberts replied to Michael de Podesta
A source of moisture is required for fog to develop, this can be from a permanent water source such as a lake or rive, but can also be from damp ground after rain.
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Helen Roberts replied to Julia Reeves
Yes, you can calculate how far away a thunderstorm is by using the fact that light travels faster than sound. Count how many seconds between seeing the lightning and hearing the thunder, and divide this by 5 to get the number of miles.
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Helen Roberts replied to Julia Reeves
There is some debate as to whether sunburn and windburn are different. More info here https://health.howstuffworks.com/skin-care/problems/medical/windburn.htm
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I've never heard of cat ice, that's great!
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Frost on cars is hoar frost, but generally not feathery because the water tends to condense onto widescreens fairly evenly.
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Helen Roberts replied to Michael de Podesta
Radiation fog is so called because it generally forms on clear, calm nights when the radiation balance is negative. It doesn't always form as a result of katabatic drainage.
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I think you have largely understood Robert. Hoar frost is frozen dew and rime is - as you correctly say - airborne super-cooled water freezing on impact.
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Helen Roberts replied to Helen B
In answer to your first question, you tend to get more intricate patterns and feathering with a hoar frost.
Visible frost forms when air cools to it's dewpont (and is below freezing), and this is much more likely to happen at night, though it could feasibly happen during the day if conditions allowed. -
Helen Roberts replied to John Lateano
That phrase is normally used when heavy showers are likely to be accompanied by gusty winds.
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Helen Roberts replied to Ines B
It's difficult to say exactly without any context, but small cumulus like this are normally between around 1200 and 5000 ft.
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Helen Roberts replied to Trevor Judd
It's a kind of layer (flat) of heapy clouds! Sometimes 'heapier' than others :)
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Helen Roberts replied to Helen B
The speed at which a cloud moves is dependent on the wind speed at that height.
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Helen Roberts replied to Frances Togneri
@FrancesTogneri I think you're referring to Undulatus Asperitas which was officially accepted as a new cloud in 2015 when it was added to the WMO Cloud Atlas https://www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/clouds/other-clouds/asperitas
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I believe you are correct, in fact it still is measured in tenths in some parts of the world including Canada I believe? Perhaps any Canadian learners can confirm?
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Helen Roberts replied to Trevor Judd
I think it helps to see a time-lapse of these cumulus cloud developing and dispersing. When viewed in real-time, it is difficult to see exactly what is going on.
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We still use weather balloons, they give us very useful information, but we use much fewer than we used to.
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Helen Roberts replied to Nicholas Kenney
The jet stream has been very strong over the last week or so, and it has been particularly unsettled as a result. Things are quietening down this coming week.
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Helen Roberts replied to Christine Biggs
We have had a few such names, for example Kamil was on the season 2016/2017 list. The names were chosen from the most popular to be sent to us by the general public.
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There was a low moving across the UK on Friday 15th. This resulted in strong winds across the south of the UK and northern France.
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Helen Roberts replied to Pau Ribas
Yes, these types of cloud are associated with the fronts you mention, though there's more to it than that. For example, warm fronts will often be preceded by cirrus, then medium level cloud before the stratus or nimbostratus arrive. And cumulus are more usual following a cold front in a polar maritime air mass once the cold front has moved through. More on...
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Helen Roberts replied to Elisabeth Gemmell
I don't think it was prolonged enough to be record breaking, but it was certainly noteworthy. One of the more unusual aspects was the freezing rain on top of the snow. Freezing rain (where the rain is supercooled and freezes immediately on impact) is pretty rare in the UK, and red warnings are exceptionally rare too. Here's some more info on the event...
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Helen Roberts replied to Paul Bujac
@WendyCooper Exactly!
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Helen Roberts replied to Helen B
@ChristineBiggs Just coincidence - a consequence of the plumbing of that particular plug hole.
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Helen Roberts replied to Judy Parker
Yes, tropical storm including hurricanes require a number of other factors including a warm water source, which is why they form in the tropics only. More on this later in the course.
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Helen Roberts replied to Judy Parker
There are no upper or lower bounds for high or low pressure systems, however standard sea level pressure in the UK is around 1013 hPa, so on average, highs would be above this and lows below 1013 - but not always! 972 hPa is a very deep low, so this would be significant wind storm.
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Helen Roberts replied to Samantha Borley
High sea surface temperatures (usually above 26 C) are required to create a tropical storm, so higher sea temperatures as a result of climate change may result in more storms, or could lead to more intense storms as there is more energy available, or perhaps both. It is an ongoing area of research.
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Helen Roberts replied to Helen B
The occlusion process tends to 'lift' the warm air above the cold air and away from the surface.
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Helen Roberts replied to Paul Bujac
The wind is a result of air moving between highs and lows (as well as Coriolis), not a high or low in isolation. It's all interlinked.
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Helen Roberts replied to Paul Bujac
On most weather charts they are, yes.
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Helen Roberts replied to Clare Radley
The criteria have changed a little, it is now possible to name a storm if there is the 'potential' to escalate to amber. Also, it is a joint enterprise between the Met Office and Met Eireann, and in this case, the Irish Met Service named Gareth due to potential impacts across the Republic of Ireland.
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Helen Roberts replied to Michael de Podesta
It's a bit of all those things you mention, the jet stream's meanderings can be influence by what is happening at the surface, but vice-versa is also true. The strength of the jet stream is influenced by temperature contrasts across North America. You can see currently that there is very cold arctic air digging a long was south across the US, at the same time,...
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Helen Roberts made a comment
Note that we have a named storm crossing the UK today - Storm Gareth https://www.metoffice.gov.uk/about-us/press-office/news/weather-and-climate/2019/storm-gareth-11-mar
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Helen Roberts replied to Frances Togneri
Yes, you're right that one of the changes made as a result of the 1987 storm is that we now have more observations in the Bay of Biscay. The Met Office's National Severe Weather Warning Service was set up as a result as well.
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Helen Roberts replied to Frances Togneri
Yes, this pattern is very common, if you keep an eye on the weather charts over the next few days and weeks, you will see this recurring frequently https://www.metoffice.gov.uk/public/weather/surface-pressure/#?tab=surfacePressureColour&fcTime=1552219200
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Helen Roberts replied to Catharina van Kampen
Absolutely, the jet stream is very strong at the moment and heading across the UK and in your direction, resulting in a particularity unsettled and stormy spell of weather for parts of N and NW Europe.
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Helen Roberts replied to Cheryl Chia
We certainly don't want to remove the Earth's atmosphere. The problem is that humans have been putting more and more greenhouse gasses into the atmosphere, which is resulting in detrimental climate change. We need to reduce the amount of greenhouse gas we release into our atmosphere.
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Helen Roberts replied to Richard Dennehy
Yes, it's a strange concept, but a desert region is classified by lack of precipitation.
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Helen Roberts replied to Satch Stone
Very high ground will have a polar climatology due to the altitude and therefore generally much lower temperatures.
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Helen Roberts replied to Henny Cameron
Yes, the local, geography and topography will play a large part in the climatology, including whether a location is on the edge of an ocean or in the middle of a large continent - more on this later.
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Helen Roberts replied to William Hodgkinson
Here's more information about how and why we name storms https://www.youtube.com/watch?v=l-yFZ0jjmoM
We omit 5 letters of the alphabet because there are so few names beginning with those letters, the US hurricane lists do the same. -
Helen Roberts replied to Frances Togneri
The air masses we get in the UK can originate from a vast array of places including as far afield as the Caribbean or Russia!
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Helen Roberts replied to Helen B
I'm afraid the plug hole demonstrations are a hoax. Coriolis cannot effect something that small.
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Helen Roberts replied to Helen B
They are really the same thing.
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Yes, weather balloons give us information about the buoyancy of the atmosphere - as well as lots of other really useful data.
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Helen Roberts replied to Robert Pearson
The difference between mist and fog is the resulting visibility. Fog is more dense than mist, so the visibility is lower. More on this in Week 4.
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Helen Roberts replied to Jean Reeve
You can expand the diagram which might make it easier to see that the warm air is rising and the cold air sinks.
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Helen Roberts replied to Judy Parker
We cover this later in the course Judy. You might also like to watch today's Met Office Studio Live which covers the topic too https://twitter.com/metoffice/status/1102917349399642112
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Helen Roberts replied to Bill Roberts
Yes, Sylvia is correct. The speed of rotation has a large effect, so Jupiter which rotates much more quickly has many more circulation cells - I believe 7 in each hemisphere.
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Helen Roberts replied to Dave Gregory
A triple rainbow is possible, but incredibly rare. If you did see one, you are extremely lucky.
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It could be caused by topography, but could also be as a result of the jet stream, convection, fronts, low level jets, radiation inversions that occur due to clear skies and calm winds, buildings and wind turbines among other things.
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Helen Roberts replied to Thanos Assimakis
But the air isn't packed with them, they are spread out.
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I'm not entirely sure what your question is. But a parcel of air in an unstable atmosphere will continue to rise unaided. In a stable atmosphere, the parcel of air will climb until it hits the inversion, and then can't climb any further because it's then cooler than the surrounding air. Does this help?
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Helen Roberts replied to Brian Rogers
Yes, laser beams are sent out vertically. The backscatter caused by reflection from the surface of cloud is analysed to determine the height of the cloud base. https://www.metoffice.gov.uk/guide/weather/observations-guide/how-we-measure-cloud
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Helen Roberts replied to Brian Rogers
It can be almost any size, and yes, there could easily be microclimates within your garden.
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Helen Roberts replied to Pablo Mazariegos
There's some useful information here about SPFs: https://www.nhs.uk/live-well/healthy-body/sunscreen-and-sun-safety/
And yes, it's very important to protect the eyes as well: https://www.metoffice.gov.uk/barometer/features/dont-turn-a-blind-eye-to-uv -
I can't think what they meant by that? By the insulating effect is the reason for warmer nights (all other things being equal) when there is cloud.
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Helen Roberts replied to Jonathan Turnbull
There are a number of different calculators, most just use wind speed and temperature.
https://www.weather.gov/epz/wxcalc_windchill
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Helen Roberts replied to Susanne B
The sky on the outside of the rainbow is 'normal colour/brightness'. Inside the rainbow, the colour is actually the inner rainbow extending all the way to the horizon but fading to white as it does so.
There is a good explanation here: https://www.quora.com/Why-does-the-sky-above-a-rainbow-appear-darker-than-the-sky-below-it
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Helen Roberts replied to Guy Davies
Yes, it is a type of inversion.
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Yes Elisabeth, that's all correct. An air frost is literally the air temperature falling below zero. Moisture is required for visible frost.
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