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Storm Potential For IR/NI - Fri/Sat/Sun May 8-10th

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Author Topic: Storm Potential For IR/NI - Fri/Sat/Sun May 8-10th  (Read 1835 times)
martinastro
Martin Mc Kenna
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« on: May 03, 2009, 04:39:12 pm »

This is way too far away yet but I was looking at the CAPE values for N. Ireland this Fri and Sat evening and they got my attention to say the least. On fri CAPE is 400-500 with LI of -1. Sat CAPE is almost 1000!!! with LI values varying between -1 and -3. It's too early to get excited yet but if these values hold out closer to the period there will be a high chance of strong thunderstorms over NI for the said period...fingers crossed. Hopefully more info will become available later in the week. Sat is showing the highest values this year so far!

For those who don't know, CAPE = Convective Available Potential Energy which is a measure of how unstable the atmosphere is. LI or Lifted Index requires negative values which we have for both days. One to watch.
« Last Edit: May 04, 2009, 07:59:54 pm by martinastro » Report Spam   Logged

stuart2588
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« Reply #1 on: May 03, 2009, 06:20:01 pm »

Looking good Martin. Keeping the fingers crossed for some action.
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brianb
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« Reply #2 on: May 03, 2009, 07:42:37 pm »

Quote
Looking good Martin. Keeping the fingers crossed for some action.
There was more than enough last night .... spent most of the small hours dodging ******** showers Angry

If you want "entertaining" weather, please confine it to the hours when it can be seen.
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martinastro
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« Reply #3 on: May 03, 2009, 09:01:43 pm »

This is from the Irish Weather Network...

A Very interesting ECMWF tonight in terms of weather action.
 
Next weekend is definitely one to watch as pointed out by Martinastro & Snowbie on the Thunderstorms & Convective Potential thread.

Although very uncertain at present, there are some decent signs of potential for some continental air being imported. Equally, there are good indications at present, I would say 45% at the moment, of a high pressure cell building about to our far west/northwest.

At the same time, ECMWF is modelling a shallow low over Ireland which could most definitely spark off heavy, slow moving thundery showers if this evening's outputer were to hypothetically verify:

http://www.meteociel.fr/modeles/ecmwf/run/ECM1-144.GIF?03-0

http://www.meteociel.fr/modeles/ecmwf/run/ECM1-168.GIF?03-0

There are indications of the Arctic Oscillation becoming less positive over the coming days, which would support some pressure rises, at lower latitudes than high up north, pretty much what is modelled on ECMWF this evening:

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/ao.shtml

The far out section of ECMWF FI also continues to be interesting, with high pressure dominating to our north, generally brought about by a disruption to the pattern in the Pacific, and with a shallow low continuing to dominate over Ireland. At any rate, it would be nice if this output were to verify as there would be a good chance of thundery outbreaks if it were to do so. 

http://www.meteociel.fr/modeles/ecmwf.php?ech=192&mode=1&map=0

All in all, some fairly dominant westerlies in the coming week with a chance at present of perhaps some interesting patterns next weekend. Equally, these could degenerate when getting nearer to the actual timeframe.

Regards,

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martinastro
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« Reply #4 on: May 04, 2009, 07:40:52 pm »

Sunday is also showing good CAPE and LI for NI. That's a thundery potential for three days a in a row.


This from UKWW....

Synoptic Analysis and Discussion

Issued 4th May 10.30BST

Analysis & Discussion

Across the Atlantic a strong powerful Jet core (for May) is likely to maintain a very unsettled week - esp in the NW of the UK.  The First wave of this is currently spreading cloud across many parts of the UK.  HRV imagery indicates most of the UK is currently cloudy and after a chilly night (Zero to +3) across parts of Central southern and SE England - temperatures will remain somewhat depressed through the day.  There is some sunshine across the Channel Islands and the far SE, but cloud is encroaching here all the time.

Radar indicates some Moderate Rain across Wales and the Midlands (note Moderate Showers at Shawbury at 08Z) Rain & Drizzle over N IReland is not well placed by the radar due to Castor Bay currently out of the Network.

The rain largely driven by a warm advection field which is sinking south leaving a legacy of outbreaks of Rain and Drizzle across these areas.  The frontal structure across the UK is complex driven by an upper front moving south in tandem with the warm advection field  and the surface front (esp cold front) lagging behind to the NW.  This leaves most northern areas in a Psuedo warm sector.   2-5mm coming south across England today, esp on Moors and Higher ground.  Temps well depressed in comparison to recently. 12-14C - perhaps warmer in Eastern Scotland if breaks appear this afternoon.

Warmer air at 850mb as evidenced by ther 10C 850 WBPT isotherm is approaching Western Ireland ( also extensive low cloud on HRV Imagery) will sweep ESE over the next 24 hrs as the cold front slows over N ireland and N England tomorrow, the cold front thermodynamicly weak with sporadic rain and drizzle coming south. The activity pepping up through the day as a wave currently in Mid- Altantic moves east - 10-20mm coming east perhaps 30mm across the SW uplands and Mountains of SW Scotland. The warm sector covering as evidenced by 9-11C WBPT air - temperatures in any brightness responding accordingly by the surge in thickness - therefore some 7C higher across the South and esp SE tomorrow with 20C possible in any sunny spells in the SE through the afternoon, though forecast ascents look dissapointingly cloudy, nevertheless some topographical breaks occuring and leading to some sunnier spells.

A strong upper trough exiting the Canadian east coast later tomorrow induces cyclogenesis as it approaches the Right Entrance to a strong SW Jet nearing 150knts in Mid Atlantic by tomorrow night, this deepening depression looks set to combine with strong 850-950mb Warm advection and send an active warm front NE across Northern Britain through Wednesday with strong oragraphic enhancement.  Another 40-50mm possible on the mountains of W Scotland and 10-15mm elsewhere.   Strong Winds developing in the North too esp around the coasts of N IReland Scotland.  The cold front surges ESE across the UK, but weakens as dynamical forcing is lost and the driving upper trough relaxes away to the NE, leaving a weak front moving SE across the SE.

The end of the weak looks fairly cool and Showery esp in the NW with a strong upper trough covering the northern UK and bands of Showers moving east merging into longer spells of rain and partial thicknesses on the cool side of Early May, though again with most of the forcing in the north the south will remain mainly dry with only limited instability...

The main N Atlantic regime is looking decidely mobile at the moment with a strong temperature contrast across N America which is resulting in a frequent Strong ZOnal Jet nr 55N.  Pressure remains high across Western Russia and the Urals, and this leads to a lack of the pressure across Central Europe. This maintains a WNW flow across the UK with positive anomalies nr the Azores.  Little change seems indicated to this general pattern over the coming 10 days with negative anomolies remaining N of the UK and over parts of N Europe.

Paul Blight
UKww Manager - Education/Warnings
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martinastro
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« Reply #5 on: May 04, 2009, 07:57:28 pm »

Here are the LI and CAPE charts (from Netweather GFS) I was looking at for Fri, Sat, and Sun. These are changing all the time from lower values to much greater CAPE like a yo-yo with every run. Certainly interesting. Throw in moving fronts and troughs combined with orographic lifting and wind shear and there could be a moderate risk of t-storms and tornadoes due to a strong upper wind field from the LP over Ireland at that time. I will wait and see what the experts say closer to the time...





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stuart2588
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« Reply #6 on: May 04, 2009, 08:33:20 pm »

Thats shaping up nicely. Looking like we could be right in the middle of it. I am definitely going chasing this weekend if all stays this way.
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« Reply #7 on: May 04, 2009, 10:01:51 pm »

Will keep my camera handy Martin it is looking rough for the end of the week.
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« Reply #8 on: May 05, 2009, 12:27:16 am »

Good luck to you Martin!, both my chases this year had less than 2000 cape, so you'll have plenty with 1000! looks like saturday may be the day for me too  Grin
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martinastro
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« Reply #9 on: May 05, 2009, 03:31:13 am »

Thanks Tyler, extremely high CAPE values don't happen too often here so it can be exciting when they do occur. Amazingly though good t-storms and tornadoes have occurred many times in Ireland/UK with only several hundred CAPE, as long as another lifting mechanism is in place with strong wind shear. The problem now is that GFS is jumping all over the place, tonight's update has completely downgraded Fri and Sat's t-storm potential but keeps Sun as a potential day with Mon and Tues also in the offering, no doubt this will change again for better or worse. It's quite heart breaking to go from 1000 CAPE progged on Sat to 100 so quickly. Trying to forecast these things can be depressing lol. I will wait and see MUCH closer to the time. So, if this is a damp squip or an exciting event I will keep the thread updated with the latest info for the sake of interest and discussion.

Good luck chasing on Sat Tyler, I enjoyed your previous two accounts and hope you get another successful day. You never know, it could be a tornado day!.  Smiley

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martinastro
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« Reply #10 on: May 05, 2009, 03:57:29 pm »

Latest GFS has all 3 days back on cue for convection.
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« Reply #11 on: May 05, 2009, 06:48:18 pm »

Here are the LI and CAPE charts (from Netweather GFS) I was looking at for Fri, Sat, and Sun.
Martin, do you know any links to the same charts as you posted above but for all Europe?

BTW, a bit offtopic, I have found a chart (http://lightningwizard.estofex.org/Europe/gfs_spout_eur0.png), and I see that it indicated some activity above my area for today.
Martin, can you explain please, what do those numbers (25, 50,...) do indicate? Probability? (of what?)
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martinastro
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« Reply #12 on: May 06, 2009, 12:11:36 am »

Tornado and supercell parameter looks very strong over NI on Fri.

Hi Roman, I use lightningwizard charts too, and most people do. I think those numbers mean mid level CAPE = as in how unstable the mid layers of the atmosphere are for a given time of day. It's easier to read the charts if you select one parameter at a time, that's how I do it anyway.

Ok this a good one, convective maps from lightning wizard, these are great..

http://lightningwizard.com/maps/

You just select the amount of hours ahead of the current time into the future and you can see what might happen convection wise. Hope this helps. It takes a while to get used to but with practice it's easy. There's a section on there about what the different maps mean, it can be complicated but very educational if you want to learn more about conevctive forecasting.

I also use netweather, but it's for the UK only as a far as I can see...

http://www.netweather.tv/index.cgi?action=nwdc;sess=
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martinastro
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« Reply #13 on: May 06, 2009, 12:16:57 am »

I don't know how to get charts like those used by netweather for Europe....but I'm sure there must be something.
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martinastro
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« Reply #14 on: May 06, 2009, 08:38:10 pm »

UKww Weather watch for severe gales with squalls, thunder, heavy rain, hail & snow   Issued Weds 06/05/2009 2000BST

Areas affected by Warning -  NW and western Scotland, upper Highlands, N and W Isles
Valid from: 2000BST Weds 6th May- 1500Z Thurs 7th May

--------------------------------------------------------------------------------

General evolution:


A very deep depression for May is now developing on a strong jet to the NW of the UK with fronts moving east across the above areas along with some heavy rainfall, it is expected 968mb nr 60N 10W by 06Z tomorrow.
Forecast:
As the gradient increases tonight winds will pick up and become gale to severe gale force in exposed spots from the west by 21Z along with gusts to 65mph. Outbreaks of moderate rain, heavy in places will accompany the winds, some 20mm has already fallen in the last 12 hours in the Western Scottish Isles and a further 20mm is possible but it will become showery from the west by later in the evening. Some of the showers will be very heavy and squally with hail and thunder and gusts to above 75mph. Snow may fall above 400m giving a localised cover on the mountains. There may be some localised flooding and more widespread hazardous road conditions in the wind and rain tonight.

Another area of heavy rain looks likely to affect the W Isles & western Scotland by midday Thursday for around 3 hours adding to the high rainfall totals.

Issued by DJW for UKww, 1900z 06/05/2009

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