Convective / Storm Risk Discussion - 14th June 2013 onwards

[Convective]

Met Office showing very bright colours on the rainfall forecast overnight and all day tomorrow here

[Panayiotis]

Looking at the NMM, it seems the convective elements are anticipated to occur later in the night over parts of the S and E.  The chart for 8pm from the 12Z run suggests a fairly wide area of frontal rainfall pretty much as the radar is showing.  Not a lot of change before midnight, but by 3am there are some notably heavier bursts showing, while the overall area of the frontall precipitation has decreased.

 

I did try and post some images but I think it's restricted because it's only available on Extra

Yes I agree, you can see quite clearly on the meteociel animation, that the front moves across the UK during the night however as you say once the front moves away the heavy showers over Wales and the SW start popping up by around 3am, then places elsewhere during the day tomorrow..

http://www.meteociel.fr/modeles/videos_wrfnmm.php?ech=3&mode=2

Edited June 14, 2013 by Panayiotis

[Harry]

Pleasing signs here in Kent chaps...nice big jellyfish Ac borderline castellanus flowing in from the SSW and the last time I saw clouds like it there were big overnight storms :-D

[Cheshire Freeze]

Think we *may* be seeing the first signs of something forming just pushing into the Pembrokeshire coast. Looks like a defined back edge forming.

[Panayiotis]

Sferic spotted on the SW coast of Ireland, with CAPE near that area high until 12AM, the heavy showers are to be expected however I have a feeling that they will die out once they get to the coast, but we shall see....

http://www.netweather.tv/index.cgi?action=radar;sess=

 

[dave48]

Pleasing signs here in Kent chaps...nice big jellyfish Ac borderline castellanus flowing in from the SSW and the last time I saw clouds like it there were big overnight storms :-D

 

Yes, was about to post the same up myself. Lots of middle level cloud streaming up from the south ahead of the CF. Tempted to set the alarm for early morning.

 

[nitro_deluxe]

Not a night to be going out in just the gusset lol! Wind up, just need those radar echoes to start turning a deeper shade of colour.

Pretty gussety wind too.

Edited June 14, 2013 by triple_x1

[Sprites]

Some iridescence in the altocumulus earlier, i have seen this before when thunder is around. Mackeral sky and wave clouds here too, something of interest to see at least.

[virtualsphere]

 

Here's the back edge CreweCold mentioned - due to pass over my location shortly, here we go...

[virtualsphere]

The front has now passed - some heavy rain and squally winds, but nothing too out of the ordinary.  Looks like it's picking up a bit according to the radar though, so still potential for folks further east if it continues.

[Supacell]

GFS 18z looking very good for tomorrow with CAPE already there from the word go in the west and then nearly 1000j/kg of CAPE with a LI of -4 builds around Lincolnshire and the Humber by 3pm. Looking to me like possibly the best convective day of the year so far from the latest charts.

 

Lets see what it all looks like in the morning.

[Convective]

Can confirm the front has just about cleared here now.

[dave48]

Would agree that the next 24 hours will be interesting. Putting tonights risk aside for the moment, convection tomorrow afternoon will be well organised with the potential for a few supercells.

 

Supercell composite below shows the potential at 15z

 

[Ben Sainsbury]

squall line developing?

 

Off the coast of Weston-super-mare

Edited June 14, 2013 by interestingweather

[Supacell]

Storm Forecast
Valid: Sat 15 Jun 2013 06:00 to Sun 16 Jun 2013 06:00 UTC
Issued: Fri 14 Jun 2013 22:16
Forecaster: TUSCHY

A level 1 was issued for C-UK mainly for an isolated tornado and scattered strong to isolated severe wind gust risk.

A level 1 was issued for far N-Germany and Denmark mainly for an isolated tornado and scattered strong to isolated severe wind gust risk.

A level 1 was issued for extreme NE Bulgaria into C-Ukraine and adjacent areas into Russia mainly for a few large hail and severe downburst events.

SYNOPSIS

A robust low with strong thermal anomalies especially at mid/upper levels advances east and crosses Ireland/UK during the forecast from west to east. An unseasonably intense wind field along its southern fringe spreads east and pulls the complete feature all the way to the North Sea until Sunday 06Z. It's not common to see such an healthy and progressive feature during June but luckily its wind field does not overspread any serious CAPE plumes over NW/N Europe.
Eastwards building westerlies with that feature assure height rises over the W/C Mediterranean with mostly stable conditions. A broad but ill defined upper trough over SE Europe lifts slowly to the N/NE during the forecast, so most of SE/E Europe will see another round of active thunderstorm development.

At the surface, an extensive W-E aligned boundary becomes reinforced by a SE-ward moving cold front from France...at least its western fringe. This boundary will be the focus for isolated to scattered CI.

DISCUSSION

... Parts of UK ...

A severe risk could arise for a few hours during the afternoon due to perfect matching of modest (300-600 J/kg) SBCAPE, strong shear and some forcing. A plume of wrap-around moisture spreads east and covers parts of C-UK during peak time heating. Mid-level lapse rates remain steep due to cold mid-levels and with some temporal diabatic heating expected, SBCAPE build-up of 600 J/kg looks reasonable for a confined region. A weak impulse, embedded in this brisk westerly flow regime, crosses the area at the same time and inserts enough lift for isolated to scattered CI. DLS rapidly increases from N to S from 20 to 35 m/s and LL shear peaks at 10-15 m/s. Forecast soundings reveal mainly straight wind fields and therefore quite unidirectional hodographs. However, incoming impulse/wave also induces some slight backing of the LL winds, so directional shear in the lowest 1000 m should increase to 100-200 m^2/s^2. Also, with expected shear in mind, splitting storms may occur with deviant storm motions also increasing helical inflow. LCLs remain at or below 800 m, so there is a risk for an isolated tornado event. Beside that, downward mixing of 20 m/s at 850 hPa may also produce a few strong to severe wind gusts next to an isolated large hail risk. The main thunderstorm risk will be confined to the 12-18 Z time frame. Beyond sunset, thunderstorms rapidly weaken while moving offshore.

... The Netherlands, NW Germany and Denmark ...

A wave rotates rapidly around the main cyclonic vortex over UK and acquires a negative tilt. This trough spreads rapidly east and causes a strongly diffluent mid/upper flow pattern to overspread the area of interest during the daytime hours from the Netherlands to the E/NE. Such a pattern is not favorable for healthy and compact UVV maxima and current data also points to a gradual weakening of the forcing. Some better BL moisture becomes advected into the NE-ward shifting trough/wave and a pool of marginally more favorable mid-level lapse rates crosses the region .. with N-Germany/Denmark probably being affected during peak heating. Also with such patterns, mid-level cooling won't play any serious role until the wave exits to the north with better/depper CAA expected by then. Hence, EL temperatures remain quite warm and if DMC can evolve is still a bit unclear. The risk however increases from south (N-Germany and the Netherlands) to north (Denmark). We issued a 50-% lightning area, where DMC is expected right now.

Ingredients-wise, strongest flow starts above 700 hPa, where convection might already top out, so how much effective DLS will become available is difficult to pinpoint. However, any stronger and longer lived convection will evolve in an environment, featured by 300-700 J/kg SBCAPE (increasing to the north), 15-20 m/s DLS and veering profiles. Marginal hail and strong wind gusts will be the main hazard. In addition I don't want to rule out an isolated tornado event mainly in the level 1 area with low LCLs and better shear. In fact the upgrade to a level 1 was performed due to forecast soundings along the German/Danish border, which show some curvature in the lowest 3 km, strong speed shear, veering in excess of 45° between LL and mid-levels in addition to 400-500 J/kg CAPE. The risk rapidly vanishes after sunset.

... S-France to the Alpine region to W-Ukraine ...

The frontal boundary will be the focus for at least isolated CI. Numerous weak mid-level impulses cross that boundary during the forecast and they, combined with the rough orography, should overcome mainly weak capping. Yesterday's sounding from S-France to Austria already featured ill mid-level lapse rates due to deep WAA from 700 hPa upwards. Lapse rates increase somewhat towards the W-Ukraine but still remain marginal. Local BL dewpoints in the mid tens with averaged BL mixing ratios exceeding 10 g/kg (on a regional scale) could offset those negative effects of the lapse rates. Hence, numerous patches with 300-800 J/kg MLCAPE probably evolve. CI over S-France into Switzerland will be questionable due to very weak dynamics but most models show at least some very isolated initiation and we therefore issued a 15-% lightning area. Confidence in initiation increases somewhat from E-Switzerland towards Austria due to the passage of a weak impulse during the late afternoon and evening hours from W to E. We issued a 50-% lightning area, where initiation looks most likely and a few strong to temporarily severe storms might evolve as DLS increases to at or above 15 m/s with higher 1-8 km shear expected. Isolated large hail and strong wind gusts are forecast with those storms which rapidly decay after sunset.
Similar confidence in CI and expected severe probabilities exists further east over Slovakia into W-Ukraine.

... Bulgaria to C-Ukraine into parts of W-Russia ...

A weakening frontal boundary enters the forecast area and is expected to dissolve until 06Z. Nevertheless, some moisture pooling along that convergence boundary occurs beneath moderately steepened lapse rates. Hence, 800 - 1500 J/kg MLCAPE likely evolve with virtually no shear present at all levels. Numerous intense pulsating storms likely pose a large hail and severe downburst risk before upscale growth into numerous ill defined clusters is forecast. Somewhat stronger convergence with higher effective PWs are forecast from the C-Ukraine to the N/NE. Slow moving or training storms might pose a flash flood risk in those areas due to heavy rainfall amounts, but neither the moisture nor the strength of convergence nor the strength of the inflow look healthy enough to expect any serious flood concerns. However the strongest storm clusters evolve from the C-Ukraine to the N/NE with more ill defined clusters further to the south into Bulgaria. Especially along the boundary, storms continue well into the night with a deacreasing severe risk.

http://www.estofex.org/

 

 

[Ben Sainsbury]

We all know Netweather is better but Tony Gilbert of ukweatherworld has produce his convective forecast for today into tomorrow:

 

Probably the most conducive severe weather outlook so far this spring. Some good parallels made by both WRF and GFS models; Unseasonably deep upper trough moves eastward enhancing environmental lift to both UK & Ireland. Strong moderately divergent jet stream arcs cyclonically enhancing strong dynamic lift within the front left exit region in line with the surface cold front. Strong PV (Positive Vorticity) aloft aligns well with the frontal boundary.

A number of phases of convection to deal with here; Early general thundery showers possible over central and NE UK today as some pre frontal troughing expected to develop. Later this afternoon Ireland sees a developing vigorous cold front bringing moderate or possibly stronger thunderstorms within the southern sector. Prime risk strong gusts and small hail. By mid night the cold front (possibly split) heads into UK mainland initiating further isolated thunderstorms with the additional risk of tornado development primarily southern counties 00Z-06Z Sat. Conditions associated with this risk include 45 deg veer at low levels with around 25kts 0-3km shear. Helicity values will therefore be sufficient for tornado development and sustained low level mesocyclones. The 500 mb jet is acutely divergent allowing for enhanced deep updrafts to form. Conditions are current borderline to supercell parameters. Reasoning for such development also lies with the depth and speed at which the upper trough transits eastward. The current overlay of cold pooling aloft might suggest large embedded hail reports overnight locally. Many parts will see sferic activity today though not prolific in nature. The prime interest here will be with well defined internal storm structure and mesocycone development. We will be working with lean CAPE values so the outlook is based on a high shear low instability scenario. So some caution needs to be addressed if the basic level of CAPE in not realised.

 

Note: He has upgraded tornado risk from slight to moderate risk

Edited June 14, 2013 by interestingweather

[Marcus_surfer]

Well summer is back on track...heavy squall line passed earlier with some very strong gusty winds. Showers brewing out in the Atlantic these look quite heavy, perhaps thundery?

[NO LONGER POSTING]

Tropical storm Andrea has now become absorbed into the Mid Atlantic flow and the remnants of tropical air will become mixed and advected torwards Southern Ireland by Sunday PM and Monday. The tropical or sub tropical ingestion is expected to lead to marked cyclogenisis South of Southern Ireland by Monday, which is then expected to oscillate across the Bay of Biscay. The placement of this feature will be fundamental in determining the eventual development of instability and CAPE, and there will be and has been significant fluctuations in CAPE across the GM frame-work.

We're watching Monday through into much of next week very carefully, the movement of this low will be critical and is going to lead to some severe weather episodes across Western Europe next week. It also have the potential to encourage a strengthening warm air advection process from the South and propagate any plume that develops across France, towards our shores. There is high uncertainty on precise development, but the strongest overall signal has been towards South East England.

It's definitely worth monitoring! Here are a few updates that I have been issuing on MetWeatherUK on Facebook.

Update 1

ECM rather interestingly develops the low around Biscay and Iberia for the same time-frame. What is even more interesting, is the continued forecast for remnants of tropical storm Andrea to be embedded within the flow around this period. GM is likely responding to this tropical or sub-tropical ingestion. Whether both the Global and European frame-works are both having difficulty with this dynamic, is still open to question. Very interesting potential though. The tropical air appears to lead to the development of unseasonably strong cyclogenisis, and it's one I'm definitely watching closely.

Update 2

We still have tropical remnants induced cyclogenisis occurring across Biscay at the time-frame T+90>, still various uncertainties on the timing and trajectory this feature will take, as a result we can expect to see significant variability in the CAPE forecast for next week. Either way, I think it's likely to provide us with some instability, but to what extent? Latest ECM and GM favours SE England for periphery plume engagement, and prior to this, a build up of CAPE across Southern Britain. Pinch of salt on this at the moment. This low, continues to need close watching and will provide ideal conditions for a severe weather outbreak for some parts of Europe.

Update 3

A classic example of the large variability in CAPE indices across various model runs can be seen on the latest GFS 06Z guidance. Large numbers showing again. It's all about what this troublesome sub tropical low decides to do, but either way its getting my attention.

 

THIS IS NOT MY INFORMATION! SOURCE MET

[Tom Jarvis]

I will be keeping my eye on the sky tomorrow

Edited June 14, 2013 by Tom Jarvis

[Convective]

Interesting to note.. Met Office and BBC have a thunderSTORM forecast for Barrow-in-Furness at 2am this morning. Makes a change from a thundershower. Wonder if it will happen or not.

[Staffordshire]

Looks like a heavy line of rain on welsh border moving ENE, should be here in around an hour

[Summer of 95]

It's just that, rain! Nothing else

[A.J]

yep, drizzle with no noticable increase in wind speed.......disappointed to put it midly

[Arnie Pie]

The `rear` heavy band of rain......That crossed the city at 1.30pm ish.....

 

Edit; Notice the initial stream of clouds seems to be travelling from right to left (East to West)?

 

second timelapse shows some nice movment over the Rotunda at the start of the timelapse

 

http://youtu.be/YG-N4XhzLYg

 

 

Edited June 15, 2013 by Arnie Pie

[ZONE 51]

Very gusty where I am next to Heathrow.

 

Next week very much interest on the plume low(as I call it from now on) pulling up potentially very unstable moist and thundery air-mass early next week, Theta-W-850s (wet bulb potential temperature) possibly up to 18C across the SE!

Monday evening GFS 18z

Monday evening 18z - Lifted Index - this chart shows unstable air into south UK, with severe thnuderstorms over on the near continent and I expect imported storms into the UK.

Monday evening GFS 12z(not loading update) - Rain/ppn - Thundery rain - torrential rain with potentially severe thunderstorms into the south.

into the night hours Mon..

Convective cloud cover and soaring index Mon evening GFS - 12z.

-

I would expect later Monday thunderstorms to affect the south, the southeast at highest risk here.

 

ESS

Edited June 15, 2013 by ElectricSnowStorm