Unsettled/Possibly Stormy Conditions 31.10.10

Deep Easterly

Let the heavens roar!

GFS and UKMO 12z runs seem to be in agreement that the low will pass close enough to the NW coast by Friday morning to bring possible gales to NW coastal fringes:



The wave development to the south is still on but postioning not nailed on as of yet. UKMO has it running up through the Irish sea by Saturday but GFS not so keen and keeps it south.

Will be interesting to see what ECMWF gives rergarding these two systems on its 12z run later on.

Iancar29

Let the heavens roar!

Deep Easterly wrote: »

GFS and UKMO 12z runs seem to be in agreement that the low will pass close enough to the NW coast by Friday morning to bring possible gales to NW coastal fringes:



The wave development to the south is still on but postioning not nailed on as of yet. UKMO has it running up through the Irish sea by Saturday but GFS not so keen and keeps it south.

Will be interesting to see what ECMWF gives rergarding these two systems on its 12z run later on.

Hey D.E , as to looking at the charts could you explain wave development to us?

M.T. Cranium

Storm potential for Friday actually seems to be increasing as we get closer to the event. The models are converging on the same track now (for the low) which is around 53N 15W to 58N 10W. There is also growing agreement on a sharp frontal trough swinging around through Ireland on Friday.

Iancar, the wave that DE is mentioning is a developing low that might form further south in this frontal trough extending south from the main low being discussed above. A wave is the first stage of low pressure development, and usually forms in the wake of a more "mature" low. The wave is formed by warm and cold fronts meeting at an angle in an area of slightly lower pressure than surrounding areas. Normally it moves northeast or north and begins to deepen, the fronts form a sharper angle and eventually the cold front undercuts the warm front and "occludes" the system. At that stage the low or cyclone is considered "mature." In its final stage, the low loses contact with its frontal system, which is usually long and stretched out, and then it either fills up and disappears, or gets a new jolt of energy and starts developing. But the time between wave formation and fully developed frontal system is usually 18-24 hours.

rhonin

Let the heavens roar!

Su Campu wrote: »

It seems to me that the best chance of getting a hit is from the one that sneaks up on us out of the blue. What I mean is that in most cases, when something potent shows up on the models 5-6 days in advance, it usually ends up to be downgraded on subsequent runs, and when the time comes, is nothing other than a damp squid - be it a winter storm or a snow event, and all of us eff and blind all & sundry. If it looks too good to be true - then it usually is.

However, I find the best events come on the radar fairly unannounced, ie. a day or two beforehand. Look at that pseudo-tropical storm in the Irish Sea in July that gave a whole load of lightning in the southeast, and 100mph winds in Aberporth. Or the great thunderstorm of July 1985. There are many more such events one could mention. These were totally unexpected, even from just a few hours out, and came as a great surprise - not disappointment - to all involved.

So this winter, let's not even mention anything that's more than two days in advance, even if the models are banging down our door about it! That way when it does come, it will be a pleasant surprise, not yet another frustrating let-down.

First person to break this rule gets a week-long ban, and OwenC gets let back in in his/her place!

Oh please no!! :pac:

Iancar29

Let the heavens roar!

M.T. Cranium wrote: »

Storm potential for Friday actually seems to be increasing as we get closer to the event. The models are converging on the same track now (for the low) which is around 53N 15W to 58N 10W. There is also growing agreement on a sharp frontal trough swinging around through Ireland on Friday.

Iancar, the wave that DE is mentioning is a developing low that might form further south in this frontal trough extending south from the main low being discussed above. A wave is the first stage of low pressure development, and usually forms in the wake of a more "mature" low. The wave is formed by warm and cold fronts meeting at an angle in an area of slightly lower pressure than surrounding areas. Normally it moves northeast or north and begins to deepen, the fronts form a sharper angle and eventually the cold front undercuts the warm front and "occludes" the system. At that stage the low or cyclone is considered "mature." In its final stage, the low loses contact with its frontal system, which is usually long and stretched out, and then it either fills up and disappears, or gets a new jolt of energy and starts developing. But the time between wave formation and fully developed frontal system is usually 18-24 hours.

Ah i see thanks, so a good example would be that cold front the came from the Record Low over in the US yesrerday & 2day?

thetonynator

Let the heavens roar!

I accidentally voted yes and no in the poll . . .:P

leahyl

According to Met Eireann it's gonna be a wash out down South this weekend!:D

http://met.ie/forecasts/

Fine autumn/winter weather!

Speak Now

Yes

thetonynator wrote: »

I accidentally voted yes and no in the poll . . .:P

How'd you do that? i wanna vote no again

Iancar29

Let the heavens roar!

Jerry Seinfeld wrote: »

How'd you do that? i wanna vote no again

That would be my fault , it must be on double answer .

thetonynator

Let the heavens roar!

Jerry Seinfeld wrote: »

How'd you do that? i wanna vote no again

I pressed no by mistake and cos it was on multiple choice when i pressed yes it didnt unpress no . .

Deep Easterly

Let the heavens roar!

Iancar29 wrote: »

Hey D.E , as to looking at the charts could you explain wave development to us?

M.T.C explained better than I could Ian.

The latest DMI HIRLAM run has this wave developing and pushing up along the east coast on Friday evening. Here is how it looks in animation to help you see how it forms and develops away from the main (primary) low to the northwest:



Basically, a wave 'stalls' the frontal progression eastwards and indeed, may intensify it for while. Waves like that often develop when the main front is coming up against a blocking high (or ridge) which would feed a renewed plume of energy into it. If the wave was to turn into a full blown secondary depression, then a wave it would be no more.

But ya could still call it a wave depression!!!

M.T. Cranium

That "hirlam" link is great, Wolfe IRE sent me a link to it about a month ago and I've been using it for the forecasts ... you can find it here:

http://www.dmi.dk/dmi/index/danmark/vejrkort.htm

meanwhile, if you want to see a good example of a wave in its very early stages, and you're reading this today (Wed 27th) check out this link:

http://www.hpc.ncep.noaa.gov/sfc/lrgnamsfcwbg.gif

you'll see the large mature to late stage cyclone over the northern Great Lakes and then look around southern Missouri (it's two states north of the mouth of the Mississippi River if that helps you) and you'll see a very weak outline of a developing warm and cold front that as of map time has not been analyzed (the old front is shown petering out south of this wave) and this is expected to develop gradually next 24 hours. Also out in the Pacific on this map, you'll see another couplet of mature low and developing wave but this one is analyzed. You could check that against this satellite imagery.

http://www.weatheroffice.gc.ca/data/satellite/goes_nam_1070_100.jpg

I hope you're reading this today because later on it will show something totally different.

But for today, that wave in Missouri is showing up as some dull grey cloud that would be a little stratus or alto-stratus showing a bit of water vapour massing as the pressure trough develops there. Then the main cyclone can be seen as a very occluded system that has spun around two or three times and sent its front way to the east where a new wave is also forming near Newfoundland. That's the normal progression with North American lows, each one usually spins off two new ones at different locations after the occlusion stage. The west coast system is easy enough to spot. On these infra-red images, the colour code for cloud temperature gives you an idea of how high the clouds are.

So anyway, the stages of cyclonic development are normally this:

wave (pressure 1000-1015 mbs, no precip to small amounts precip, frontal angle about 150 deg)

developing (pressure falling 990 mbs, organized frontal precip, frontal angle about 90-120 deg)

mature (pressure falling 980 mbs or lower, fronts starting to occlude but still a warm sector, precip at max intensity)

occluded (pressure likely starting to rise with centre filling, fronts occluded, precip starting to reduce but may also wrap around centre)

filling (pressure back up to 990-1000 mbs, occluded front breaking away and dying out, little organized precip)

During the occluded phase you tend to get a lot of new wave development as new systems make use of the leftover energy of the dying system.

When the jet stream gets very strong (we look for 250 mb winds of 180 kt or higher) mature cyclones can keep moving for thousands of miles and keep regenerating at about the same energy level especially across the Pacific, North America and the Atlantic. In my research, I identify nine timing lines where storm development seems more likely, and the general idea is that any given energy system can make it from one timing line to another in each phase, so if there are peaks of energy every 2-3 days, this can help systems to keep moving along. Occasionally you can follow one organized storm system from Japan to Europe, but this is rather rare. What's more normal is for lows to make it past two of the nine timing lines then die out with new development in their wake.

Iancar29

Let the heavens roar!

Looks likes its gonna be kicking off early indeed .

MET Éireann
Weather Warning

Issued at 28 October 2010 - 14:09
Rainfall Warning
Rainfall amounts of 25 - 40mm likely in parts of Munster and Leinster.

from 18:00 28/10/2010
to 18:00 29/10/2010:D