Storm & Convective Discussion April 2016 Onwards

[William Grimsley]

Very dry air here. I'm surprised that there are showers present in Devon!

[Arnie Pie]

Infront of my camera,,,,a nice anvil which disapeared as quickly as it appeared

Edit; mmmm....fresh activity to my NE

Edited April 16, 2016 by Arnie Pie

[Gordon Webb]

rumble here

edit - after all the forecasts this week this came a bit of a surprise wasn't too loud but a surprise non the less

Edited April 16, 2016 by Gordon Webb

[Gordon Webb]

radar looks quite heavy near tamworth of course radar is now 10 minutes out of date so hope it's still not heavy have places to go

[Speedway Slider]

Gone black as your hat to one side, bright orange the other!! With a double rainbow on the dark side!! Heavy big spots of rain, no thunder yet... 19.54

Both taken only 1 minute apart!

[Supacell]

Drove through that line of heavy showers as they passed between Heanor and Derby. No thunder but plenty of hail and sleet then snow which had provided a slight covering in places. Temperatures fell from 6c to 0c as I drove under the shower! Some nice looking photogenic clouds and also a rainbow. Classic April weather.

[Spikecollie]

2 hours ago, Gordon Webb said:

rumble here

edit - after all the forecasts this week this came a bit of a surprise wasn't too loud but a surprise non the less

That's what you need. A nice, gradual exposure to storms with gentle thunder then perhaps distant lightning. Desensitisation it's called. Interestingly, you talked without any sense of fear about the thunder you heard today. The former approach will work. You just have to learn how to think and behave around storms. Easier said than done though - ask me after my doctor's appointment on Tuesday which includes a blood test!!!

Meanwhile the storms in my part of France came to nothing. Just a soggy, wet uninspiring day apart from the hedgehog which is in another thread!

[weather09]

After a decent week for convection/storms for some parts, things look like quietening down a bit for now. Not an ideal outlook convective-wise in medium term (post-T144) with mid-Atlantic ridge and upper trough dropping south over Europe. Before then, however, keeping my eye on mid-week range (T96/120), where current NWP continues with short-lived ridge building north over central Europe and upper, cut-off, low setting up over W'ern, or to the W of, Iberia. At low levels, potential for a relatively brief push of decent warmth/moisture north towards UK, with height falls aloft from upper trough creating potentially unstable environment. The UKMO-GM looks the better output in this respect with the upper low and ridge favourably placed. Much change between now and then, but given recent consistency in this theme, thought it worth mentioning.

[William Grimsley]

44 minutes ago, Spikecollie said:

That's what you need. A nice, gradual exposure to storms with gentle thunder then perhaps distant lightning. Desensitisation it's called. Interestingly, you talked without any sense of fear about the thunder you heard today. The former approach will work. You just have to learn how to think and behave around storms. Easier said than done though - ask me after my doctor's appointment on Tuesday which includes a blood test!!!

Meanwhile the storms in my part of France came to nothing. Just a soggy, wet uninspiring day apart from the hedgehog which is in another thread!

You're so right there. I've had to build my confidence over the past months and the only way to do it is gradually!

[weather09]

On 4/16/2016 at 9:37 PM, weather09 said:

Before then, however, keeping my eye on mid-week range (T96/120), where current NWP continues with short-lived ridge building north over central Europe and upper, cut-off, low setting up over W'ern, or to the W of, Iberia. At low levels, potential for a relatively brief push of decent warmth/moisture north towards UK, with height falls aloft from upper trough creating potentially unstable environment. The UKMO-GM looks the better output in this respect with the upper low and ridge favourably placed. Much change between now and then, but given recent consistency in this theme, thought it worth mentioning.

Doesn't look like we'll see that brief moisture plume get to the UK, or if it does any associated convective activity will be confined to extreme S/SW or offshore, as ridge transfers NW over UK to be positioned over mid-Atlantic with low-level flow quickly turning N'erly. A more 'positive' tilt to the upper pattern would have been favourable.  Was slim potential at best anyway... But still.  Still potential for thunder if we can get colder mid-level air to sink south over UK, but I think it's looking like it may be going into May at the earliest that we see the upper pattern we're looking for.  

Yawn..

Edited April 19, 2016 by weather09

[Stormyking]

21 minutes ago, weather09 said:

Doesn't look like we'll see that brief moisture plume get to the UK, or if it does any associated convective activity will be confined to extreme S/SW or offshore, as ridge transfers NW over UK to be positioned over mid-Atlantic with low-level flow quickly turning N'erly. A more 'positive' tilt to the upper pattern would have been favourable.  Was slim potential at best anyway... But still.  Still potential for thunder if we can get colder mid-level air to sink south over UK, but I think it's looking like it may be going into May at the earliest that we see the upper pattern we're looking for.  

Yawn..

Agreed here 09, id have a bit more confidence if this brief plumey look over the next couple of days was say in another months or 2 time, but the type that is now I have no interest in, it doesn't look that convective at all. Even though certain types can produce at this time of year, this one however due to the low-level quickly turning to a Northerly as you say.  Im certainly more interested in these cold Northerlies/North Westerlies showing later in the week and into next, im also very confident of soft hail too in these sort of set ups coming up, though as for thunder it will be a low risk at that.

[weather09]

The setup occurring in one or two months' time wouldn't make much difference to be honest, Stormy. Setup is unfavourable regardless. One other point, there appears to be a misconception (among others) on here that the really good warm moist 'plumes' can't be achieved in April, and that we really need to wait until we're in May or June for those. This isn't true. You only need go back to 3rd April to see what even a modest advection of moisture can achieve- when rather active thunderstorms occured over the SE.  Once we're well into Spring, get a favourable upper pattern and good 'plumes' can be achieved easily.  Solar input is now high enough that landmasses and low level atmosphere can warm significantly.  

[Thundery wintry showers]

I remember thunderstorms in Tyneside from a southerly plume around 22-23 April 1998.  Another good thunderstorm setup at this time of year is a cyclonic showery south to south-westerly with a slow-moving Atlantic trough, where the showers sometimes band together and produce a line of thunderstorms.  There was thunder on 3 or 4 days in some places between 20 and 24 April 2000.

I think spring is the optimal time of year for convective activity from a northerly.   In the summer, mixing from dry stable Scandinavian air masses tends to be more of an issue, resulting in mostly dry cloudy weather with scattered light showers from shallow convection.  Nonetheless, thundery activity from a spring northerly tends to be weak and well-scattered, though impressive cloudscapes and hail shafts are sometimes widespread.  

The optimal evolution from here for thundery potential is probably if we see a shallow trough set up close to the British Isles after the initial northerly blast, like in the second weeks of May 1997 and April 2008.  The latter spell brought 3 days of thunder to Norwich, with pea-sized hail on one of the days.  There is some support for this from tonight's ECMWF run.

I don't foresee much potential prior to the northerly- high pressure is too dominant.

Edited April 19, 2016 by Thundery wintry showers

[William Grimsley]

Hmm, this is interesting. There's Altocumulus Castellanus cloud embedded in that Cirrus cloud, not sure why?

Quite a bit more now piling in from the south, very interesting. I certainly won't be surprised if any rain that moves in through tomorrow night and Friday contains thunder.

I've been advised that this is due to the warm 850's plume coming up from the south and to add to it a very pleasant and warm evening, oh it's like July 2014 all over again!

Edited April 20, 2016 by William Grimsley

[weather09]

On 4/19/2016 at 11:45 AM, weather09 said:

Doesn't look like we'll see that brief moisture plume get to the UK, or if it does any associated convective activity will be confined to extreme S/SW or offshore...

Slight heads up for far SW and near channel coasts this evening and into early hours of tomorrow.  Looks like moist low-mid level air mass of substantial theta-w will indeed advect over channel and far SW UK during period before flow turns N'erly during Friday.  Occlusion moving up from the south looks likely to engage this moisture, bringing high RF rate and low lightning risk if DMC can occur.  Lack of forcing aloft, weak-ish mid-level lapse rates, and just general lack of instability all limiting factors.  Very low risk in all.

[Flash bang flash bang etc]

5 hours ago, weather09 said:

Slight heads up for far SW and near channel coasts this evening and into early hours of tomorrow.  Looks like moist low-mid level air mass of substantial theta-w will indeed advect over channel and far SW UK during period before flow turns N'erly during Friday.  Occlusion moving up from the south looks likely to engage this moisture, bringing high RF rate and low lightning risk if DMC can occur.  Lack of forcing aloft, weak-ish mid-level lapse rates, and just general lack of instability all limiting factors.  Very low risk in all.

Ha! I thought the sky looked a little bit plumish... Whaddayaknow!

[alexisj9]

2 minutes ago, Flash bang flash bang etc said:

Ha! I thought the sky looked a little bit plumish... Whaddayaknow!

Yep even had some ac cas about here. doubt anything will happen though.

[Dami]

I noticed the clouds looked a 'little' different today, but i'm a bit away from the 'low risk' zone

 

[William Grimsley]

The sky has been unstable all day here, still think thunder is a low risk but we will see.

[Flash bang flash bang etc]

Does look good out there. If something does pop up Could it have the potential to be extremely severe and dangerous, or will it just be a gentle sky guff?

[alexisj9]

1 hour ago, Flash bang flash bang etc said:

Does look good out there. If something does pop up Could it have the potential to be extremely severe and dangerous, or will it just be a gentle sky guff?

No idea, but the sky this morning around here is in this weather forecast. It's beautiful.

http://www.itv.com/news/meridian/2016-04-21/thursday-nights-weather-for-the-east-of-the-region/

[William Grimsley]

Can't see anything thundery coming out of this, the drops are quite big but the rain is just light, currently.

[weather09]

Further to my points made elsewhere re. focusing on the 850mb temperature in isolation when discussing convective potential in the context of Pm, Am or cP air masses, I thought I'd post a few charts to illustrate its irrelevance, and how it's a poor guide to determining the likelihood of deep convection and thunder. 

The seemingly commonly held view on here is that a cold 850mb profile (around 5000ft) atop relatively mild waters (such as the North Sea) or a sufficiently heated landmass generally translates to vigorous convective activity (heavy showers, thunder).  The view is most noticeable during winter when discussing heavy snow shower potential from off the North Sea.  

Let's take tomorrow, then.  Below is the predicted temperature at 850mb for the UK. Values are typically -7C to -9C over far NE or to the NE of the UK (or -10C near Shetland Isles), so rather cold. But, on the next chart, GFS is modeling only weak shower activity. Why?

 

One has to look further up in the atmosphere - i.e. the 500mb level.   The contrast in temperature between 850mb (5000ft) and 500mb (~18,000ft), which makes up the mid-level atmosphere, is relatively small, meaning there's only a gradual change in temperature with height (weak environmental lapse rate), therefore weakly unstable.  The temperature at 500mb is, or a little over, -30C, which would be sufficiently cold under a different setup, but not when the 850mb temp. is as low as it is.  So in fact the cold temp. at 850mb is more of a hindrance to deep convection than supportive.  Sure enough there is shower activity, given sufficiently low 500mb geopotential heights and low pressure, but the really cold air needed for deep convective activity is, in this case, over Scandinavia.

 

For an accurate picture, however, one should really be consulting a Skew-T diagram/sounding analysis to gauge the stability/instability of the lower atmosphere.

Edited April 23, 2016 by weather09

[Speedway Slider]

Question::

Just looking on Blitzortung, Italy having some action at the moment.. lots of the storms/cells seem to cluster right on the coastlines, what causes this please? You have a look at the attached screen grab.

Cheers

Karl 

[weather09]

30 minutes ago, Speedway Slider said:

Question::

Just looking on Blitzortung, Italy having some action at the moment.. lots of the storms/cells seem to cluster right on the coastlines, what causes this please?

Sea-breeze convergence. Heating of landmass has lowered surface pressure (rising air), resulting in cooler air (higher pressure) over waters to flow onshore to stabilise the environment. Where this onshore breeze meets (converges with) opposing winds inland, the net result is upward motion.  Can see below on the surface wind chart (might have to squint lol). If you view recent satellite imagery you can see the storms develop in situ.  

 

Obviously the environment is unstable, and looks like low CAPE build-up has been generated in that region given low-level warmth and moisture under cool mid-level profile (per GFS):