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Storm & Convective Discussion - 1 September 2015 onwards

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Plenty of pea-sized hail rattling through here over the course of the day, thunder in the late morning and a strike in Buxton just as the sun was going down. More noticeable on higher levels was the sleety rain (likely snow) coming down on the tops.

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Some cracking cloudscapes and heavy rain and hail showers.My sort of weather for April.Keep it coming pls.

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A low risk today, but nonetheless, steep lapse rates over eastern UK and convergence toward the east coast may allow showers developing here to produce hail and isolated thunder.

Storm & Convective Forecast

convmap_070416.png

Issued 2016-04-07 09:41:40

Valid: 07/04/2016 0600z to 08/04/2016 0600z

CONVECTIVE FORECAST - THURSDAY 7TH APRIL 2016

Synopsis

Upper trough slides E and SE away from the UK out into the North Sea, while surface area of low pressure over the N Sea slides east into Scandinavia by late evening. A cool and unstable NWly flow covers the UK.

... EASTERN ENGLAND to EASTERN SCOTLAND ...

An area of cloud and more persistent rain will continue SE across England and Wales this morning, clearing SE England early afternoon. Following on behind, residual cold pool aloft from departing upper trough will create steep lapse rates as clear skies / sunny spells allow surface heating. So showers will readily develop - especially, today, towards eastern areas of the UK where steepest lapse rates will be. Wind convergence towards North Sea coast will perhaps enhance/organise shower activity, with potential for funnel clouds to develop along the wind shift with stronger updrafts. Otherwise, some of the heavier showers could become weakly electrified bringing isolated thunder and also accompanied by hail and gusty winds. Severe weather is not anticipated.

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Showers really pepping up here in the last hour. Radar showing some sferics to the east of me, but no lightning seen here yet

 

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Really looking forward to the convective opportunites for my area of the woods next week. There's quite a good amount of instability showing for Monday as well as Wednesday when areas of heavy and thundery rain move up the continent. Could be interesting.

Edited by William Grimsley

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40 minutes ago, Weather-history said:

 

Epic timelapses from yesterday and today Wh. :)

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Day 2 Convective Outlook

VALID 06:00 UTC Fri 08 Apr 2016 - 05:59 UTC Sat 09 Apr 2016

ISSUED 20:11 UTC Thu 07 Apr 2016

ISSUED BY: Dan

Old occlusion boundary across the Midlands will drift slowly eastwards on Friday, serving as the focus for a few scattered showers to develop in response to diurnal heating. The same is also true with some sea breeze convergence close to some eastern coasts too. In both cases, depth of moisture is limited due to dry air aloft as upper ridging slides eastwards, and so even though ELTs may locally fall below -10C with some reasonable DLS giving a non-zero risk of lightning, the chance of lightning actually occurring is considered too low to consider a specific LOW area.

Attention then turns to the post-frontal environment arriving from the Atlantic on Friday night. A significantly cold airmass will overspread relatively warm SSTs around Ireland and southwest Britain, with steep lapse rates bringing scattered showers, some electrified. This is most likely over open water and near coastal areas, with convection tending to weaken as it feeds further inland and loses the deep instability in the absence of diurnal heating. Some small hail is possible in any stronger cells

http://www.convectiveweather.co.uk/forecast.php?date=2016-04-08

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Interesting to see how the upper 500mb pattern evolves during next week. Med.-range outputs (post-144) from GFS/ECM have ridge trying to build over south/central Europe 'stalling' progression of the trough to the west, with increasing warmth and moisture advecting across the region. Also potential showing before then for early-mid next week, but a little too early for detail at this stage as likely to change a bit.

Edit: 12z output from GFS, just to show where things could go medium-term, and the sort of potential that can arise in mid-April.  Looks like there might be plenty of opportunities before then under rPm regime, but ideally the below is what we really want to see.  

h500.png cape.png

Short term, another rather low risk tomorrow with scattered showers in post-front environment- bias for lightning activity towards W/SW where cold air at 500mb/steep mid-levels resides.  Meagre CAPE environment given cool temps/dry air mass, but hail and higher elevation wintriness likely with showers.  Embedded trough disturbances perhaps focus for convection.  Uninspiring in all. 

Edited by weather09

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Day 2 Convective Outlook

VALID 06:00 UTC Sat 09 Apr 2016 - 05:59 UTC Sun 10 Apr 2016

ISSUED 19:53 UTC Fri 08 Apr 2016

ISSUED BY: Dan

Notably cold airmass spreads across most of the British Isles behind a northwards/eastwards-moving occlusion, as a broad upper low slides SEwards from the Atlantic towards west of Biscay. In a deeply unstable airmass, especially so to diurnal heating, numerous showers are expected with a few thunderstorms, especially across Ireland where low-level convergence and very steep lapse rates will aid in shower/thunderstorm development. One precluding factor across Ireland is the lack of any significant shear, with pulse-type showers/storms the most likely mode, but also scope for shower-training and some local surface water issues given the rather slack setup.

 

Elsewhere, instability is weaker but shear much stronger, allowing cells to perhaps get better organised and hence a broad LOW threat level for lightning. Some small hail is likely in any stronger cells, perhaps even a brief spell of snow (especially in Ireland and to high ground elsewhere).

 

http://www.convectiveweather.co.uk/forecast.php?date=2016-04-09

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1 hour ago, Stuart said:

Day 2 Convective Outlook

VALID 06:00 UTC Sat 09 Apr 2016 - 05:59 UTC Sun 10 Apr 2016

ISSUED 19:53 UTC Fri 08 Apr 2016

 

ISSUED BY: Dan

Notably cold airmass spreads across most of the British Isles behind a northwards/eastwards-moving occlusion, as a broad upper low slides SEwards from the Atlantic towards west of Biscay. In a deeply unstable airmass, especially so to diurnal heating, numerous showers are expected with a few thunderstorms, especially across Ireland where low-level convergence and very steep lapse rates will aid in shower/thunderstorm development. One precluding factor across Ireland is the lack of any significant shear, with pulse-type showers/storms the most likely mode, but also scope for shower-training and some local surface water issues given the rather slack setup.

 

Elsewhere, instability is weaker but shear much stronger, allowing cells to perhaps get better organised and hence a broad LOW threat level for lightning. Some small hail is likely in any stronger cells, perhaps even a brief spell of snow (especially in Ireland and to high ground elsewhere).

 

http://www.convectiveweather.co.uk/forecast.php?date=2016-04-09

Yay! Another day of potential! @Evening thunder, maybe another chase on the cards but this time less widespread? LOL!

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I went to the shop around 1:15 this afternoon and got soaked by this hail shower,could not believe how heavy it was,the rain was heavy too,this shower developed quiet quick as well,these snaps was taken ten minutes apart.

DSC00095.JPGDSC00096.JPG

 

Edited by Allseasons-si

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Looking good convective wise today. There's already a lot of slow moving heavy showers around, definitely not getting any hopes up but would be nice to see something thundery.

Edited by William Grimsley

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8 minutes ago, William Grimsley said:

Looking good convective wise today. There's already a lot of slow moving heavy showers around, definitely not getting any hopes up but would be nice to see something thundery.

Seen the 00z output? :D could have the potential to be plumetastic! Numerous bouts of instability drifting up from the continent on that run, day in, day out!! 

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2 minutes ago, East_England_Stormchaser91 said:

Seen the 00z output? :D could have the potential to be plumetastic! Numerous bouts of instability drifting up from the continent on that run, day in, day out!! 

I've seen the NMM, looks amazing doesn't it, even for SW areas with some places getting in excess of 20 mm of rain in an evening! Still, the east fairs slight better but yes very plumetastic! Finally!

Nice CB out to the SW on my Nest cam live stream, as always this will be online during the daytime but also night time when/if thunderstorms occur during the night time: https://video.nest.com/live/Atmiip

Edited by William Grimsley

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1 hour ago, East_England_Stormchaser91 said:

Seen the 00z output? :D could have the potential to be plumetastic! Numerous bouts of instability drifting up from the continent on that run, day in, day out!! 

Looks quite remarkable for early to mid April. Great synoptic though with an area of low pressure stuck down over Biscay scooping up ever warmer air from the warming continent (for the southern half of the UK at least).

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Just had a moderate rain/hail/sleet/snow shower here! Temperature: 4.5°C Dew Point: 2.4°C Rainfall Rate: 3.4 mm/hr Rainfall Last Hour: 0.6 mm Rainfall Today: 2.6 mm. :D

Edited by William Grimsley

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Day 2 Convective Outlook

VALID 06:00 UTC Sun 10 Apr 2016 - 05:59 UTC Mon 11 Apr 2016

ISSUED 16:32 UTC Sat 09 Apr 2016

ISSUED BY: Dan

General evolution sees a large upper low becoming anchored to the southwest of Britain, with 2 slow-moving frontal zones being the main focus for some convection - one across northern Scotland, and another over southern Ireland/southwest Britain. 

... SW IRELAND ...

At the beginning of the forecast period, a triple-point frontal system will run NW-wards over S/SW Ireland during Sunday morning. Backed surface flow coupled with low LCLs, and strong forcing and DLS, suggests a risk of a tornado, especially if any rigorous convection can occur close to or to the rear of the triple point in an environment with notably steep lapse rates. There would only be a short window of potential on Sunday morning, before the main cold front begins to bend back farther to the SW. This is also dependent on the exact position and timing of these frontal features, some models keeping the main area of interest offshore to the SW, and as such confidence is too low to issue a SVR threat area for now.

... N SCOTLAND ...

Shortwave trough rotating around main parent upper low will engage with occlusion across northern Scotland, perhaps allowing some convective elements to become embedded within. However, of more interest will be the post-frontal environment, with slack surface flow/convergence and some element of orographic forcing serving to develop a few scattered showers with a generally low risk (5-10%) of lightning.

... CS ENGLAND to S WALES ...

Backing flow ahead of frontal zone will advect higher WBPT airmass from western France, with an increasing signal for elements of elevated convection to develop within the frontal zone on Sunday evening/night. As is often the case with such events, there remains some uncertainty as to the true likelihood of lightning activity and for now we remain with just a LOW threshold. In either case, such elevated convection that may develop over the English Channel and advect towards IoW/Hampshire/Dorset will probably weaken as it heads NW-wards towards SE Wales.

http://www.convectiveweather.co.uk/

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5 hours ago, William Grimsley said:

Just had a moderate rain/hail/sleet/snow shower here! Temperature: 4.5°C Dew Point: 2.4°C Rainfall Rate: 3.4 mm/hr Rainfall Last Hour: 0.6 mm Rainfall Today: 2.6 mm. :D

Looked like it was snowing when i looked on your cam earlier! Luckily i managed to dodge the showers today during rough runner (15k obstacle run). Hoping for some storm imports from the south next week..

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