# 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

• 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.

• 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.

• 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).

• 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.

• 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.

• 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.

• 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

• I've never heard of cat ice, that's great!

• Frost on cars is hoar frost, but generally not feathery because the water tends to condense onto widescreens fairly evenly.

• 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.

• 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.

• 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.

• That phrase is normally used when heavy showers are likely to be accompanied by gusty winds.

• 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.

• It's a kind of layer (flat) of heapy clouds! Sometimes 'heapier' than others :)

• Helen Roberts replied to Helen B

The speed at which a cloud moves is dependent on the wind speed at that height.

• @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

• 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?

• 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.

• We still use weather balloons, they give us very useful information, but we use much fewer than we used to.

• 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.

• 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.

• 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.

• 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...

• 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...

• @WendyCooper Exactly!

• Helen Roberts replied to Helen B

@ChristineBiggs Just coincidence - a consequence of the plumbing of that particular plug hole.

• 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.

• 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.

• 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.

• Helen Roberts replied to Helen B

The occlusion process tends to 'lift' the warm air above the cold air and away from the surface.

• 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.

• On most weather charts they are, yes.

• 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.

• 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,...

• 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

• 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.

• 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

• 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.

• 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.

• Yes, it's a strange concept, but a desert region is classified by lack of precipitation.

• Very high ground will have a polar climatology due to the altitude and therefore generally much lower temperatures.

• 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.

We omit 5 letters of the alphabet because there are so few names beginning with those letters, the US hurricane lists do the same.

• 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!

• Helen Roberts replied to Helen B

I'm afraid the plug hole demonstrations are a hoax. Coriolis cannot effect something that small.

• Helen Roberts replied to Helen B

They are really the same thing.

• Yes, weather balloons give us information about the buoyancy of the atmosphere - as well as lots of other really useful data.

• 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.

• You can expand the diagram which might make it easier to see that the warm air is rising and the cold air sinks.

• 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

• 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.

• A triple rainbow is possible, but incredibly rare. If you did see one, you are extremely lucky.

• 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.

• But the air isn't packed with them, they are spread out.

• 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?

• 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

• It can be almost any size, and yes, there could easily be microclimates within your garden.

• 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.

• There are a number of different calculators, most just use wind speed and temperature.
https://www.weather.gov/epz/wxcalc_windchill

• 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

• Yes, it is a type of inversion.

• Yes Elisabeth, that's all correct. An air frost is literally the air temperature falling below zero. Moisture is required for visible frost.

• @IreneDouble These intricate patterns are sometimes called frost ferns. There's a good description of how there form on this web page. Alan is correct to say that this is less common now due to better insulation and less condensation.
http://www.its.caltech.edu/~atomic/snowcrystals/frost/frost.htm

• Helen Roberts replied to Carol A

Freezing rain can certainly produce black ice.

• Hi Ivan. I hadn't heard of this before. I've just had a look at the paper you link to, and it seems to be saying that you can expect similar conditions in a window of around a fortnight to that of a year ago. This is basically what climatology tells us, and we certainly use this principle to some extent in our computer models, to give us en envelope of likely...

• Hi Molly. Great to hear you're keen to use the charts. Unfortunately, they are only produced every 12 hours, but this link shows them slightly more clearly: https://www.metoffice.gov.uk/public/weather/surface-pressure/#?tab=surfacePressureColour&fcTime=1535328000

• Well, cirrus clouds, particularly cirrus that thickens, can be a precursor to a warm front, so there could be a grain of truth in that one.

• Nimbostratus is the most reliable cloud for rain, but I wouldn't say most of our rain comes from nimbostratus necessarily. Though I don't have the stats.

• My guess is that it's the flat landscape which allows for greater sky-scapes.

• My job still involved taking the piece of cardboard out of the Campbell Stokes recorder and measuring the burn until about 2006, and I'm sure they are still used today. I too, was enchanted by the technology (or seemingly lack of). I can still recall the smell of the charred card.

• Particles in the air can lead to more clouds, but you need the moisture in the atmosphere too. Deserts are dry and tend to have air subsiding (high pressure) so clouds rarely form.

• @HelenDoidge @PatriciaHay Yes, this is correct :)

• In a rainbow, a ray of sunlight enters and is reflected inside the raindrop. But not all of the energy of the ray escapes the raindrop after it is reflected once. A part of the ray is reflected again and travels along inside the drop before emerging. The first rainbow is the primary rainbow and is produced by one internal reflection; the secondary rainbow...

• It very much depends on the situation. Frost can form with the difference of just a fraction of a degree. It would depend on the time of year too. But foliage won't 'attract' a frost, it's purely down to the temperature of either the ground, or air, or leaf depending on what you are interested in.

• Occlusions are the purple lines. The thick black lines are called troughs. We don't really cover these in this course, but troughs are generally lines of enhanced showery activity.

• Actually, it seems that tornadoes tend to spin in the same direction of the low pressure systems that cause them. So in the northern hemisphere, the low pressure systems that spawn tornadoes rotate anticlockwise because of the Coriolis effect, so although a tornado is too small to be affected by Coriolis, it's movement is indirectly affected by the Coriolis...

• It's in pink in the text just underneath the video on this page (step 3.23). Here it is in case you can't see it:
https://www.metoffice.gov.uk/learning/wind/monsoons

• Ha, if only dust had no gravitational pull my cleaning time would be cut down :) It's just that any movement of the air, either sideways or upwards, will easily carry dust around and can for a time counteract the gravitational pull. Eventually though, it will settle back to the surface.

• No, they're not incredibly rare, but you have to be fairly luck to see them.

• No, it's fairly random, not influenced by Coriolis but by much smaller and more local factors.

• Helen Roberts replied to Carol A

There are a lot of sub-categories, but I'd advise pay closest attention (for now) to the main groups.

• A cumulonimbus (thunder) cloud is deep and therefore the bottom of it is likely to look darker as the sun's light cant penetrate through. The colour is not to do with the dust, which is incredibly tiny.

• There could be a number of reasons for the limited height of the cumulus clouds:
The amount of heating at the surface may not be enough for the clouds to grow any taller
There could be dry air above this level
There may be a temperature inversion at this level of the atmosphere which is limiting convection
There could be wind shear (different wind speed or...

• They are absolutely critical. Yes, particle type, size and density can all influence the type of cloud that forms. Without any aerosols at all, we'd see very few, if any clouds, they'd only be able to form at very very low temperatures.

• You're correct Phillip, we measure cloud amounts in Oktas or eights of the sky, though nobody is quite sure how it came to be spelt with a 'k' as in okta rather than octa.

• Have a look back at step 2.8 (Week 2) to find out more about occlusions.

• They often do :)

• Absolutely, sometimes all moving at different speeds and in different directions too!

• Many of the videos can be found on the Met Office YouTube channel for future reference:

• A completely flat layer with no texture at all is likely to be stratus. If there is some texture, but it is still in a layer, stratocumulus is most likely.

• No. Cirrus could never produce rain, they are too thin, and even if they did produce precipitation, they are so high that any precipitation (which would be frozen) would evaporate long before reaching the ground. This can be said most of the time for medium level clouds too, though you can sometimes get a heavy shower from altocumulus. Cloud needs to be thick...

• These are most likely to be stratocumulus clouds, and the reason for the colour is probably that this layer of cloud is picking up/reflecting the colour of the sea. So not special sea clouds I'm afraid, just fairly standard stratocumulus.

• Convection often preferentially occurs over whichever is the warmest, so over land in the summer and over sea during the winter.

• Yes, we had unusually dry, powder snow in the UK at times earlier this year.

• They are both low pressure systems and circulate in the same direction, but they form through different processes. Tropical storms take their energy from high sea surface temperatures (above about 26 °C).

• Your question about global information, are you asking about the forecasts we provided globally? If so, we have 3 main Met Office computer models: global, European and UK, they nest within each other, but we need a global model (ie one that cover the whole world) as weather doesn't have boundaries and we need to know how the atmosphere is behaving...