All Hail to the Hailstorms...
Ìý Us cloudspotter typesÌýhave been spoiled lately,Ìýas the November weatherÌýgenerated all manner of spectacular skyscapes across the Westcountry.
Brushed to and fro above us, the clouds have comeÌýin innumerable forms lately,Ìýlike a or Ìýlandscape. This ever-changing natural vistaÌýhas beenÌýcourtesy of an omnipresent jetstreamÌýclose by the British IslesÌýduring recent weeks,Ìýresponsible forÌýtheÌýrun ofÌýunsettled weather.
December has started in largelyÌýsimilar fashion.
Today, a classic polar maritime flow has established from the northwest, bringing not only a chilly feel but also pollution-free skies and some spectacular clouds towering in the unstable air - such as those I've photographed here.
I was treated to some impressive passing swiftly by earlier today. Their tops, up at around 15,000 ft (4570m), were turning readily fibrous and wispy-looking as they became a gargantuan mass of tiny ice crystals (a process called glaciation)Ìýin frigid temperatures up there ofÌý-25 to -30 Celsius. Brrrr...
And the ice wasn't justÌýremaining high above.
These clouds were readily bearing hail and judging from my vantage point, a fair swathe of it was falling for a while across some districts around Bristol and Bath.
You'll find falling hail is actually quite easy to spot and generally simple to differentiate from shafts of falling rain.
In the second image I took - here on the right - notice the very distinctive white appearance of the streaks falling from this storm cell. Often dubbed 'hail streaks' or 'hail curtains', even in fairly low ambient light conditions they tend to be conspicuously white or light grey, compared to the dark grey or shafts of rain that often accompany them. Sometimes, the hail-bearing sections of parent cloud have a distinctive greenish colour.
Talking of rain, we'll be seeing rather a lot of that into the weekend. Late Friday night looks very wet indeed for a time and - just afterÌýSaturday starts on a dry note - a further spell of potentially heavy rain will arrive later in the day and overnight into Sunday.
Comment number 1.
At 3rd Dec 2009, Jack Mason wrote:Ahh, yes some of these hail-streaks advanced over the Forest of Dean at 14:30, the falling hail was very noticeable.
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Comment number 2.
At 3rd Dec 2009, Ian Fergusson 91Èȱ¬ Weather wrote:Hi Jack! Yes, they're very conspicuous, aren't they? Especially at this time of year, when the low angle of the sun tends to really pick-out the whiteness of the hail as it begins to fall (or for that matter, when the sun highlights falling snow, sleet or graupel.... but that's another blog topic altogether!)
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Comment number 3.
At 3rd Dec 2009, Jack Mason wrote:Yes, very true, is graupel soft hail?
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Comment number 4.
At 4th Dec 2009, Ian Fergusson 91Èȱ¬ Weather wrote:Hi Jack - yes, exactly that. It's the German term (originally) for soft hail; i.e., graupel being distinct from true hail (as formed in Cumulonimbus during any season).
It's typically part of the wintry mix of precipitation we see in cold months, formed through supercooled water droplets effectively creating a soft 'rime' of crystalline growth on falling snowflakes (by a process of accretion). As you might expect - given this relationship to snow - graupel can fall from the same range of clouds producing snow (e.g., Nimbostratus, Stratus, Cumulus congestus, Cumulonimbus etc) and not solely from Cumulonimbus alone. I saw a fair bit of graupel around Bristol in those very cold months of last winter; it's certainly not uncommon here in the British Isles.
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Comment number 5.
At 4th Dec 2009, Jack Mason wrote:Yes, do you have any indications that this year we could see a White Christmas?, with the last one being in 2004/2005 according to Netweather.
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