ABC of Weather: Occluded

Occluded fronts are part of our low pressure aka cyclonic weather systems and are usually a sign that they've reached maturity in their lifecycle. A front is the (unseen) transition between two masses of air with distinct differences in temperature and with our low pressure systems a cold front follows on behind a warm front.

The colder air mass travels more quickly than its warm predecessor and if it catches up with it, then the warm air is forced off the ground and over the colder air. It's at this time that an occluded front is said to have formed. The weather found along these can be quite variable and can be some of the more extreme weather associated with a low pressure system, such as thunderstorms and funnel clouds.

Each type of weather front is shown by a different coloured line and associated symbol on a weather map - see the example shown here. The way the symbols are pointing shows the direction of travel of the weather system. Occluded fronts are denoted by a purple line with alternating semi circles and triangles, so the next time you see these on a weather map and it's heading your way, watch out for stormy weather!

For more O's than you can shake a stick at, do have a look at the ABC Wednesday blog.

Comments

  1. Roger Owen Green28 April 2010 at 21:26

    I always love the weather posts; I learn a lot.

    On behalf of the ABC Wednesday team, thank you!

    ReplyDelete
  2. Tash29 April 2010 at 01:46

    Isn't Occluded a great word! Much nicer than saying a "mature front". I wonder if a person can be "occluded"? :)

    ReplyDelete
  3. Monica the Garden Faerie29 April 2010 at 14:39

    When I worked for the transportation safety institute, they often mentioned occluded vision in reports I edited, for conditions when some portion of the roadway seen was not shown to the driver (in a safe, simulator setting). Interesting how it's kind of similar in weather. The [secret thing] is on the way!! :)

    ReplyDelete
  4. Tumblewords:30 April 2010 at 03:42

    I'm so enjoying your weather posts! Learning a ton - hope I can remember more than an ounce.

    ReplyDelete
  5. jay30 April 2010 at 20:41

    It's as if you're talking a foreign language!

    Actually, I understood it when I read it, but I know it will just dribble out of my brain in five minutes. I've never been able to get to grips with the science behind out weather. I don't know how many times OH has patiently explained it all to me. I just leave it all to him now, and he tells me what the weather is likely to do. LOL!

    ReplyDelete

Post a Comment

I love hearing from you and welcome thoughtful conversations :)

Comments aiming to link back and give credence to commercial websites will be composted!

Your essential reads

That blue flower: A spring spotter's guide

Image
Spring is a prime time for blue flowers and my daily walks currently have several from the same plant family* lining the local footpaths. As I walked past the Donkey Field the other day, I overheard some children ask their parents** what the pictured blue flower was. It reminded me it's often mistaken for those other familial blues and this time was no different, as they said it was forget-me-not, instead of the green alkanet it actually is. As well as similar flowers, most of these plants are hairy in their nature, flower around the same time, and favour damp, shady places. Many of them are great for pollinators too, especially bees and this week's warm weather has certainly drawn them to these flowers. This makes it even more likely for these plants to be mistaken for each other and it's a great opportunity for me to put together a spotter's guide in case you find the same flowers on your outings. Staying with green alkanet, the key features which set it ...
Read more

Jack Go To Bed At Noon

Image
Last year this rather exotic looking flower appeared on mine and several other allotments for the first time. Having been stumped (again) by Mr Allotment Warden as to its identity, I rushed home to find out what it was. It's salsify, aka the marvellous Jack Go To Bed At Noon - named as such because its flowers always close by midday. Here you can see both open and closed flowers - making it seem even more exotic and alien than in the first picture. I think this must be the cultivated version because the flower in my Francis Rose Wild Flower Key looks exactly the same in form, but is bright yellow in colour and called meadow salsify . Its other common name is Goatsbeard, which must be a nod to the fantastic dandelion-like clock which forms the seed head. With 'parachutes' like those shown above, who knows how far our plotted plants came from. I rather like the photographic dissection of the seedhead found in this link . Salsify is edible: its lateral shoots and fl...
Read more

Red Nose Day - Gardening Jokes Anyone?

Image
The nation goes ever so slightly bonkers on Red Nose Day - hurrah! Previously, it's been very easy to join in - usually via a dress down day at work plus lots of people up to mad things at the station and in the office. Everyone smiling for once - it's a real feel good day and all in a good cause. This year's different - every day's a dress down day for me now - my friend L suggested yesterday that perhaps I could have a dress up day instead and whilst that's a good idea, I confess that ballgowns and tiaras don't really feature in my wardrobe: scruffy student's always been my favourite look. So my Red Nose Day contribution for this year is to compile a list of gardening related jokes. For each one (clean ones only please) you leave in the comments below, I'll make a donation of 50p to the cause. Here's a few for starters just to get you warmed up: Q Why do potatoes make good detectives? A Because they keep their eyes peeled. Q What did the grape...
Read more

Salad Days: Mastering Lettuce

Image
I've decided one of my salad challenges for this year is to grow as many lettuce varieties as I can, ready for the publication of my planned Factsheet* later on. The idea is to grow as many of the Tried and Trusted lettuce varieties last year's Salad Challengers helped compile, then provide a visual guide and as many lettuce facts as I can muster. So far I've found around half of those listed**. Then naturally whilst I was out searching - because such is the way with seeds - a number of other varieties found their way home too ;) A couple of weeks ago I sowed 22 varieties***. Just the simple act of sowing them has me intrigued. Why are some lettuce seeds black and others white****? They split into about half white to half black in my sample and as far as I can tell it's nothing to do with whether they're a type of cos, iceberg, or whatever. I sowed them indoors and popped them into a propagator on the windowsill. The soil's too cold outside for sowing ...
Read more

VPs VIPs: Derry Watkins of Special Plants

Image
Last week I had the pleasure of visiting Derry Watkins at her home, garden and nursery - the acclaimed Special Plants - just a few miles along the road from me. I first met Derry at one of her open garden days last year and was keen to find out more about her wonderful garden and running an independent nursery. She specialises in tender perennials and regularly goes on plant hunting trips to find new treasures, particularly in South Africa. As well as running Special Plants and opening her garden under the NGS scheme , Derry holds day courses at her nursery, hosts Special Tuesdays from April until September, lectures and has written a couple of books. How did you find your way from Connecticut to the UK? I'd started a biodynamic vegetable garden in Connecticut and we used to have people come along at weekends to help out. A particular young man turned up: he returned many times and at the end of the summer I married him. So it was all down to love? Isn't that the...
Read more

#mygardenrightnow: heading into summer with the Chelsea Fringe

Image
Ahhhhhh, that's better! I love walking through dewy grass in bare feet, not that there's much in the way of grass on my back lawn this weekend. My wild and woolly lawn has morphed into meadow of sorts this month, which even NAH admits looks attractive*. It's also proved a great source for my Flowers for mum project so far, yielding self-sown perennial cornflowers, lamb's ears, and lemon balm in addition to the blooms you can see. These originated from elsewhere in the garden, the ox-eye daisies must have blown in from the A350 nearby. * = he got very stroppy about the weeds aka self-sown foxgloves in the lawn one year, so he's come along a bit since then. Skimble's demanding to say hello to you too. He does enjoy the patio when it warms up. If the embedded video doesn't work try this link instead. The Nectaroscordum are a revelation. I planted the bulbs around 2 years ago, but it's only this year they've bloomed properly. The bee...
Read more

Make Use of Mildew

Image
On my garden patrol this morning I spotted some powdery mildew on a couple of my new Verbena bonariensis plants. I suppose it was almost inevitable as I prefer to grow my plants hard - this means no water for them unless they look absolutely desperate. This approach means plants root themselves more deeply and have a better chance of survival during spells of dry weather like we've had lately. However, it also means I run the risk of problems like today's, especially with any garden newbies planted late in the season. We've had a good drop of rain overnight, so this should help my plants survive. I'll mulch them later today to help lock in the moisture as it's water stress which encourages the mildew to take hold. I've also removed the infected leaves and sprayed the rest with a milky drink.* I'm also pleased to find there's a use for my infected leaves. Oliver Ellingham at Reading University has started a PhD - sponsored by the RHS - researchi...
Read more

The Resilient Garden

Image
  Part of Tom Massey's Resilient Garden at RHS Hampton Court I've been pondering VP Gardens a lot lately. Last year's drought conditions set me off initially, then our harsher than usual winter combined with this summer's flip and flop weather means the thinking continues. It's a huge topic which I freely admit I'm struggling to get my head around. Tom Massey's Resilient Garden  at Hampton Court recently  tackled this topic brilliantly and was a timely interlude which gave me much food for thought. There he encapsulated the detailed research he'd found which informed both his show garden and book of the same name. I think it's one of the most important show gardens I've ever seen. It's clear the way I garden needs to change so that I have my own resilient garden. I haven't worked out the exact details yet, but Tom's book plus a couple of others (see below), alongside the rainwater management handout from the show garden's  sponso...
Read more

Chelsea Fringe 2014: Shows of Hands - Episode I

Image
The gloves NAH used to build the raised bed . The effects are L to R, top to bottom:  Original photo, Warhol, HDR, Green tint, B&W, Posterize, Boost, Cross process and Sepia Welcome to Shows of Hands - my Chelsea Fringe project for 2014! As you can see I've been having a bit of a play around in Pic Monkey for my first contribution. You're welcome to join in between now and 8th June 2014. The idea behind this year's project is to highlight the tool most precious to a gardener: their hands. How do I take part? It's simple. All you need to do is take a photo of hand(s) in a gardening context and then share it via your blog or other social media (such as Twitter or Facebook), then make sure I know you've done so. I've set up Mr Linky below for your blog contributions. The Chelsea Fringe photo on the right sidebar links to this post, so you can easily find it again when you're ready to add your contribution. If you share your photo on Twitter, ...
Read more

Testing Times: Tomatoes

Image
  I've run a couple of tomato trials this year. The first is a revisit of the biochar trial with Oxford University I attempted some years ago (with a different organisation this time), and the second is a trial of a water gadget called Plantsurge which I was given to try at Malvern Spring Show earlier this year. Most of you have probably heard of biochar already and the claim that this inert, carbon-rich material can help soil fertility and plant health. The RHS information in the above link says results can be mixed, with reduced effects found in alkaline soils. This may help to explain the lack of difference I found in my previous trial as VP Gardens is on a lime-rich soil. Plantsurge is a different beast altogether. It's a strong magnet which is attached to a hosepipe as shown in the photo above. It's claimed that it softens water, with the result more like watering with rainwater. The higher nitrogen found in rainwater is thought to be beneficial to plants. Gardener...
Read more