weather09

Difficult one to call tomorrow, but likely an isolated to scattered risk. Models developing a relatively narrow region - generally from the SE, across central parts and towards the NW - of substantial instability (several 100J/kg MLCAPE, per recent outputs) where expected good insolation heats a decently moist boundary layer within the warm sector. Both Euro4 and GFS are progging dewpoints to 16-17C, which seemed a little high initially. But the fact that a meso. model is showing these values lends confidence that these will be realised. Little support aloft given stagnant flow under weak heights, with vertical wind shear non-existent. Though recent UKM synoptic outputs do show a disturbance (trough) pushing west throughout the day, so likely focus for any developments. Question mark over cloud cover, but looks increasingly likely there will be clearing skies from the east so reason why models are maintaining instability outputs as temps reach low 20s.

Not wise to look at precipitation charts on a global model, especially when we're discussing about potential mesoscale events (i.e thunderstorms). Even purpose-built mesoscale and hi-res. models can struggle to resolve thunderstorm development. Think the point Staines was making, though, was that if the GFS is overstating surface dewpoints (which it often does), and looking at the setup at first glance it likely is, this in turn affects how much instability there'll actually be- moisture being contributor to CAPE. Saying that, even if the DPs were a few degrees lower than is being modeled for the weekend, would still be a risk of storms. Things as they stand, likely to be a build of substantial instability inland with light winds and strong insolation this weekend, though the detail always best left to a day ahead or day in question.

Hard to say. Instability is being modeled, given the expected warming and moistening of surface profile, but that and the coverage of storms is questionable at this stage. Though I think the decision of whether to chase is probably best made the day before, or even on the day of interest, as you'll have a better idea of likelihood of storms occurring, and when and where they're likely to occur. Doesn't look overly inspiring, but if current outputs hold to weekend, would say it's worth getting out and trying to catch something. 3 days out, though, which is a long time in convective outlook terms.

Bit of an odd outlook this weekend with wave frontal boundary currently over UK oscillating east and west, before warm front pushes back to the west of the UK Saturday, introducing moister air mass at the surface. At the moment, looks like an increasing possibility of heavy showers/thunderstorms for some parts during the period as winds become lighter and veer to E/SE, resulting in warmer temps and moisture building inland within warm sector which generates decent instability, as per recent model outputs. Stagnant flow aloft with weak ridge precludes organised/severe convective weather, however. Though moist air mass and slack profile, and therefore slow storm motion, would pose a risk of high spot rainfall rates. Bit far out so considerable changes ahead, but something to look at I guess.

Think too much focus is given on how unfavourable the relatively cool waters surrounding the UK can be and not the actual setup we're situated under. Bear in mind the lightning activity that occurred this morning was from instability rooted above the boundary layer, so the SSTs were irrelevant. But still matter to some... If there is good instability over/surrounding the UK, then storms will occur over land and water (assuming forcing is there). Simple. Initial surface-based storms travelling over water can take a hit at this time of the year, given the lag in rise of SSTs in relation to landmass, but if the environment is like it was over the continent yesterday, then no sea water is going to have a negative effect on storms developing. The problem is down to the setup, and the right conditions a lot of the time just missing our shores. And that's due to not having that favourable upper 500mb pattern - i.e. strong amplified ridge just to our east/trough approaching from west. The 500mb profile dictating the synoptic setup at the surface. Get the right setup and we can get severe storms. The problem is in getting the setup. But the surrounding waters are quite irrelevant most of the time.

Called that one wrong regarding lightning frequency. Guess I underestimated strength of moisture 'plume' aloft to produce deep convection. 06z analysis shows storms having occurred close to cold front/triple point (region of greatest low-level lift):

Yep, any convection over eastern England this evening and into early part of Tue will be rooted above the boundary layer, so cool waters not relevant here. The reason for the storms over northern Germany and into Netherlands is simply due to those regions having had a moderately unstable air mass in place this afternoon (thanks to very warm and moist profile), with CAPE being released near to frontal boundary (cold front). The fact that storms are happening there doesn't mean storms will happen here. The conditions over the continent are favourable for active storms, not the case here. But, nonetheless, we will be importing some good moisture in at low-mid level, so there's always the possibility that forcing of this air mass from approaching frontal system will support convection deep enough for lightning. But I say it looks unlikely given the poor profile over here.

Aye, not sure how they're getting to "frequent lightning"- relevant factors not supportive of such activity. Torrential rainfall, yes, as low-level air mass becomes moisture-rich, characterised by relatively high theta-w, from this evening and into early part of Tues from the east, with occluding front (triple point) providing lift of this low-level moisture to bring a high RF risk. But concerning lightning, mid-level lapse rates are quite poor, instability therefore is lacking, and there's no support aloft, all suggest deep moist convection (DMC) is unlikely. Can anticipate shallow convection by lift of moist air mass, which can bring you an isolated spark or two, but, not seeing anything to suggest full-on thunderstorms across regions of interest.

This is what we're hoping for... Good heat and moisture advecting from south at sfc/low-levels to build good instability. Negatively tilted upper trough out west and falling heights releasing moderate CAPE. Backed sfc winds and strong and veering winds with height (SW jet winds aloft - follow the 500mb height contours) generating a strongly deep layer sheared environment for severe convective weather. Also just to note, though the figures over France look insane, it's also properly capped on that frame (CINH is like 600-700J/kg lol), so nothing would arise over there. Obviously looong way out, but keeping my eye on late next week and into next.

Other than today's low isolated risk, bland outlook for the foreseeable. Looks like a week Monday before we might see a change to a more favourable upper 500mb pattern, as a ridge tries to build north over southern/central Europe with upper trough approaching from the west. Recent GFS/ECM outputs signalling at this sort of a pattern for a while, so hopefully something to it. Hope we start to see some proper convective potential soon and none of these marginal days, being as we're heading into summer.

GFS data not loading here. Cleared cache and restarted browser but still the same. Any ideas? All good now.

Frame 276 on 06z GFS is something proper alright lol. That would get the adrenaline pumping. Ignoring the stout ridge aloft toward the south, would mean severe thunderstorm/supercell outbreak for northern and western parts. Dicey stuff.

Regarding the radar, still use V4 as it has the image 'smoothing' visualisation and no lag in loading different frames. Only thing that I would really like to see is an option to increase the animation/loop speed, which would be ideal for quickly determining the track of storms.

That's a shelf cloud - cool outflow from leading edge of a shower/storm. A wall cloud is very localised lowering beneath the cloud base of a storm. Can be a precursor to a tornado in supercell thunderstorms if the wall cloud region tightens and lowers further into a funnel.

Been fascinating watching radar over central/northern half of France today. A few clear right moving storms (supercells) on radar, with one recently in the Somme region dropping a tornado (see link below). Also radar image of the cell in question. Even using this radar you can make out the hooking on the SW side of the storm. http://forums.infoclimat.fr/topic/87871-suivi-du-temps-dans-le-nord/?page=10#comment-2724680 As mentioned, was watching all the storms on radar and a few were diving to the right of the mean storm motion vectors, so indicative of supercells. Pretty pleased today has came off how I anticipated. Conditions for severe storms were pretty obvious on NWP outputs in advance, with ideal mix of instability and shear. But sometimes things don't always pan out how one would expect. Supercell in Dijon this evening: From Keraunos' twitter page: https://twitter.com/KeraunosObs?ref_src=twsrc%5Etfw. Also made a mention of the (30 degree) deviation in storm track in relation to mean storm motion. Good stuff.

Looks like 00z Arome is modeling a couple of right-moving supercells this evening across central regions of France. Conditions favourable for well organised storms and potential supercell activity given overlap of good deep layer vertical wind shear (thanks to reasonably strong and veered mid-upper level jet winds) and possibly moderate CAPE (1000-1500J/kg MLCAPE). Interesting.

You sure about that, Harry? Vaguely remember MLCAPE of around 1000-1500J/kg mainly toward E Mids/eastern England. CAPE in excess of 3000J/kg over UK is rare to say the least. Early morning to very early afternoon on June 28 '12 saw MCS push NE across Wales/Midlands, then from early afternoon under clearing skies strong heating of very moist air mass developed moderate instability, resulting in severe thunderstorms including a couple or more supercells which pushed over Leics and Lincs. This was combined with a favourable wind shear profile, where sfc winds were backed ahead of shortwave impulse and cold front with veering and strengthening winds all the way up to 500mb. No one factor stood out as extreme, but was a good combination of CAPE/moisture/shear that brought the goods.

Thought I'd move my post in the other thread into here as is relevant to this region. Still looks like decent conditions for severe thunderstorms including perhaps a few supercells over near continent this Friday . Very warm and moist boundary layer (sfc dewpoints mid-upper teens) and height falls steepens mid-level lapse rates and contributes to a moderately unstable environment (MLCAPE perhaps to 1500J/kg or slightly higher) over central/northern parts of France. Veering and strengthening winds in the mid-levels (with modest SW'erly jet aloft) results in substantial deep layer directional shear (40-50Kts bulk shear), increasing risk of organised/severe convection. Only problem is the numbers don't look that high, particularly at lower levels. Overall, though, CAPE/shear spread looks just sufficient for organised/rotating updrafts. Large hail likely given the CAPE values and shear. Tornado risk inhibited given the relatively slack flow at low levels and only modest SRH. Might post a few relevant charts tomorrow evening or Friday (into meso. model. time frame) if risk looks the same. For UK: Increasing likelihood of risk of more general storms extending into southern and SW parts of England/Wales during same period as we pull in warmth and moisture, with forcing from height falls and disturbances aloft triggering storms. Risk perhaps continuing into overnight Friday and into Saturday.

Just another day at the office. Incredible pics of twin tornadoes. Well done.

Aye, nothing to get too excited about at this stage. UKM/ECM not agreeing with more optimistic outlook from GFS. Still bit far out, so likely considerable change ahead. Again, though, significant episode unlikely anyway given jet winds and higher moisture/instability residing over France. Over there could be looking at severe convective episode this Friday - moderate instability, good sfc moisture and reasonably strong SW'erly mid-level flow with jet winds aloft, so potential for a few supercells should current outlook hold. Always interesting how close these proper storm setups get each year without affecting the UK. No distance at all compared to the routine chases on the plains of the US.

Not an inspiring outlook for Friday looking at ECM/UKMO-GM, or even on GFS. Not pulling in that warmth off the continent, and, as Harry mentioned, SW'erly jet over France, so a more significant convective period unlikely anyway even if we do get some decent instability. Ideally need negatively-tilted upper trough, but all models not showing that.

Yep, nothing significant was ever anticipated given the nature of the setup - cool, post-front, low CAPE, low shear environment. But such setups at this time of year adequate for some reasonably decent short-lived storms. Need to distinguish the proper storm setups - i.e warm/very warm, moist pre-front air masses with moderate or high CAPE - from the cool, post- front ones such as today. They're not the same. The likelihood of storms, and storm severity, varies depending on the type of setup we're looking at. Still, doesn't look like it has been too bad overall today. Quite a few weak storms up and down the UK. Another low risk tomorrow, but keeping my eye on Friday where we could see some decent enough warmth and moisture advection across the country as ridge builds north over southern/central europe, with upper low setting up west of Iberia. GFS and euros broadly agreeing with the general upper pattern at this stage, though naturally to varying degrees. Quite far out so a lot of change ahead. If things hold up well will probably book the day off and have 4-day weekend lol. Here's hoping.

Yes, Sunday looking decent for showers and general thunderstorms in post-cold front environment . Likely some good hailers given steep mid-levels (cold air at 500mb) and strong heating of a reasonably moist boundary layer, which looks to generate several 100J/kg CAPE (per recent outputs) during afternoon. Nothing significant anticipated as winds fall light throughout much of the profile, so weak shear overall, though winds do increase somewhat past 500mb and left-exit jet streak at 300mb still residing over eastern parts, so better forcing aloft over here, with perhaps potential for modest winds at that level to take advantage of more potent updrafts. Shortwaves in cold air aloft likely focus for showers and storms. Tomorrow late afternoon and into evening sees severe convective risk for northern and western half of France where height falls with approaching upper trough, pre-front shortwave and cold front destabilise a potentially moderate CAPE environment (MLCAPE 1000-1500J/kg, per GFS)- sfc dewpoints mid-upper teens. Strong SW'erly mid-level winds with mid-upper level jet resulting in deep layer shear (albeit rather unidirectional) on the order of 50kts suggest initial discrete supercell storm mode after 17z, quickly becoming MCS as you head deeper into evening hours with passage of cold front. Meso. models generally breaking out storms around 17/18z as forcing aloft arrives, with a short window for those severe sfc based storms, before becoming MCS dominant. Sfc parameters don't appear to overly favour tornado potential- modest 0-3km SRH up to 150m/s, flow not increasing too much at low level, and sfc winds could be a little more backed. Main risks would therefore appear to be large hail and severe convective winds.

GFS modeling is quite something for the first half of next week, particularly Tues/Weds. MLCAPE values in excess of 5000J/kg over central/southern plains, with sfc dewpoints hitting the mid-70s. This being overlapped by strong westerly mid-level jet... Potential for high-end severe period indeed.

Yes, Harry, noticed GFS putting a more northerly steer on the advection of low-level moisture and instability toward far SE quarter ahead of the cold front. ECM and UKM, however, keeping main region of instability and storms to the continent, however even they would suggest risk of torrential rain and potential for storms with passage of cold front.