This Week's Storms - FORECAST, MODEL DISCUSSION ONLY

NIALL D

M.T. Cranium wrote: »

I followed the lead of the ECM and went out to lunch ...

ha ha ...

since we have lots of time before next model run, snowfall potential ... likely to be entirely elevation-dependent rather than regional. The air mass is just barely cold enough to sustain snow but highly unstable, so plenty of mixed precip can be expected. I think it will play out as rain near sea level, hail and sleet for many, and snow coming and going throughout but sticking mainly above 200m. This time it will not be a north-south divide, but more of a west to east dilution as the land mass slowly exhausts the sea effect, although by no means totally.

So how much snow for your location? Above 200m and west of Athlone to Cork, expect 5-10 cms. Above 200m and east, expect 3-7 cms.

In the range of 100-200m, west, expect 3-7 cms ... east expect 1-3 cms.

In the range of sea level to 100m, west, expect trace to 2 cms. ... east, expect zero to 1 cm.

Some very exposed (to west) upland locations could see as much as 20 cms and severe icing is possible on summit installations. Contrast that with melting snow or sleet near sea level.

The image in my mind is a sort of blizzard of fog, but perhaps if I have another coffee ...

any idea MT of roughly what time we should expect to see snow ??
like will it be morning or evening on tuesday ??

ta.

Iancar29

NIALL D wrote: »

any idea MT of roughly what time we should expect to see snow ??
like will it be morning or evening on tuesday ??

ta.

For the west id be going for anytime after 3pm.. and for the east then anytime after 6 ... unless it all kicks up a gear.

I posted these from earlier from the 12z run , this one is a slight upgrade
LOOks like we are gonna be seeing the oul GRAUPEL word popping up a few times once again!

M.T. Cranium

Timing would be pretty much all day, but might prove to be heavier by late afternoon and evening. Must stress this is all very marginal for snow, the air is cold enough but it has to come across a long stretch of 10-12 C ocean, hard to imagine the dew points falling much below +1 C in that passage.

I expect to see a lot of reports of wet snow that is blowing past but turning to slush on the ground, sticking more to the grass than pavement, etc.

Higher up, could be a winter wonderland. Anyone much higher than 300m will probably have road access problems. So it's going to be very much localized by elevation.

Basically it's kitchen sink weather, phase changes will be almost as frequent as changes in an Italian government.

corkman123

met office have just updated their forecast for thurs..

Redsunset

MetO have all of Ireland like earlier and now all of UK in a watch for Thurs and this was updated in last half hour so its still a brewing because of model uncertainty.

Harps

Assuming a similar situation to last weekend around here then there'll be wet snow for most with accumulation only really above ~300m.

Tuesday's storm is still looking quite severe, nothing exceptional in terms of strength but looking like it'll stay windy right through Wednesday and with plenty of potential still for Thursday it could be a full week of stormy weather.

Iancar29

I think we could also see some thunder showers within the front lifted index values of 0 to -3 ( yellow regions ) . , hopefully in a picturesque squall line!

only one

M.T. Cranium wrote: »

Timing would be pretty much all day, but might prove to be heavier by late afternoon and evening. Must stress this is all very marginal for snow, the air is cold enough but it has to come across a long stretch of 10-12 C ocean, hard to imagine the dew points falling much below +1 C in that passage.

I expect to see a lot of reports of wet snow that is blowing past but turning to slush on the ground, sticking more to the grass than pavement, etc.

Higher up, could be a winter wonderland. Anyone much higher than 300m will probably have road access problems. So it's going to be very much localized by elevation.

Basically it's kitchen sink weather, phase changes will be almost as frequent as changes in an Italian government.

Would there be snow for the south east by any chance mt?

Iancar29

Couldnt agree more myself!

This is the current scene at the desk for head of forecasting in the MetOffice.



:rolleyes:

Irish Steve

Issued at - 12 Dec 2011, 00:22
Valid from - 15 Dec 2011, 18:00
Valid to - 16 Dec 2011, 23:59

Rapidly strengthening winds and heavy rain are likely to arrive across the west later on Thursday and through Friday, heralding another potentially stormy period.

The public is advised to monitor warnings for this period, noting that the alert is likely to be extended into Friday in due course.

This is Wales, the same is up for Nothern Ireland, what's interesting is the time of issue, while their maps are still the last run from Sunday morning, this looks pretty specific.

What seems to have changed is the timing, it looks like it's gone back from early Thursday to Later Thursday and more into Friday, which seems to be as a result of Tuesday's weather not clearing as fast.

Steve

Sponge Bob

Iancar29 wrote: »

hopefully in a picturesque squall line!

I expect squabbling squall lines this week rather than an Oíche na Gaoithe Móire event!

Sponge Bob

Source > http://www.ucd.ie/gsi/pdf/33-1/wind.pdf

eskimocat

I have just spent a very enjoyable couple of hours following this thread from near the beginning.

The one thing that kept going through my head when looking at the charts and following the chat, was a discussion regarding hurricanes. ( i know we are not talking about hurricanes by the way) . Anyway the basic jist was, when there is two hurricanes catching up with one another there is usually a tussle and the more powerful over takes the weaker one.. the Fujiwhara Effect, I believe its called.

Here (eventually) is my question.... could something like that be happening to these two storms? if not, can you tell me why not?? thanking you in advance.

Sponge Bob

The Fujiwhara Effect exists, however none of the models showed twin or bifurcated/split lows until today. Having said that the Fujiwhara Effect could by all means come into play now the models show twin lows.

Until the next model gets bored or something

IMBACKLATER

Issued at 11 December 2011 - 12:01
Weather Advisory

The weather in the coming week will be very windy for a lot of the time with some stormy episodes expected. At the moment, later Tuesday or Wednesday and Thursday night/Friday look to be especially at risk.

Rougies

eskimocat wrote: »

I have just spent a very enjoyable couple of hours following this thread from near the beginning.

The one thing that kept going through my head when looking at the charts and following the chat, was a discussion regarding hurricanes. ( i know we are not talking about hurricanes by the way) . Anyway the basic jist was, when there is two hurricanes catching up with one another there is usually a tussle and the more powerful over takes the weaker one.. the Fujiwhara Effect, I believe its called.

Here (eventually) is my question.... could something like that be happening to these two storms? if not, can you tell me why not?? thanking you in advance.

For the Fujiwhara Effect to happen you need two storms in the same area at the same time, feeding off each other and basically playing as a team until one of them decides that it is stronger than the other and eats it's former partner alive.

EDIT: Usually the storms end up spinning around each other in in perfect harmony and happiness, it's unusual for one to eat the other alive. Sorry for being pessimistic

Our Tuesday and Thursday storms will have no interaction with each other at all (well relatively compared to the Fujiwhara couples). By the time Tuesday's storm is at it's strongest, Thursday's will be still deciding whether it even wants to be a storm or not!

Deep Easterly

They will be two separate cyclones alright although secondary wave depressions like this usually absorb themselves into the near-permanent primary depression known as the 'Icelandic Low' once they occlude and weaken. Not sure would this be considered a direct Fujiwhara Effect?

Edit, actually, the first storm system (which affected eastern Canada a couple of days ago) is already merging itself with the primary Icelandic low which is helping to jar it closer to Ireland over the next couple of days.

Edit Edit: "near-permanent primary depression' might actually be too definate a term. The Icelanic low is often more complex and ill-defined in structure so 'near permanent primary low' would be a better term to use..

Rougies

Deep Easterly wrote: »

They will be two separate cyclones alright although secondary wave depressions like this usually absorb themselves into the near-permanent primary depression known as the 'Icelandic Low' once they occlude and weaken. Not sure would this be considered a direct Fujiwhara Effect?

I'm sure there are varying degrees of the effect, and my last post was an embarassing showcase of my ignorance on the subject :pac:

Deep Easterly

Rougies wrote: »

my last post was an embarassing showcase of my ignorance on the subject :pac:

I don't think so! To be honest I had never heard of the 'Fujiwhara Effect' before reading Eskimo's post but a quick read of a Wikipedia article gave me the general gist. It's an interesting question to bring up though.

Rougies

Deep Easterly wrote: »

I don't think so! To be honest I had never heard of the 'Fujiwhara Effect' before reading Eskimo's post but a quick read of a Wikipedia article gave me the general gist. It's an interesting question to bring up though.

Indeed, an interesting question to bring up!. I read about the effect a few months ago during the hurricane season so my understanding of it was exclusive to hurricanes until now. I suppose I skipped over anything non tropical storm/hurricane related at the time.

But still, regarding eskimocat's question, the fujiwhara effect doesn't apply so I'll stop being embarrassed then I suppose

mickger844posts

0Z GFS Shows two lows pressure systems for Thursday/Friday. Interesting take on things. Major difference from their output this time yesterday. Waiting for ECM next.

Harps

Another different outcome for Thursday on the 0z GFS, does anyone know what's happened here exactly? I'm a bit clueless on the subject but find the whole rapid cyclogenesis thing very interesting.

I assume there's a new starting condition being input in the past few runs that stops the perfect set of conditions from playing out? Very unusual to see widespread agreement all week only to suddenly see this happen

On Tuesdays, yet another different outcome, looks like it'll be a nowcast situation on how this one behaves

M.T. Cranium

The model confusion continues, but with the theme so far being a southward shift in the track for Thursday-Friday storm #2 and possibly as weak a solution as we saw with the 12z ECM although the GFS 00z continues to promote some deepening, more or less over Ireland and the Irish Sea.

What's apparently happening to weaken this once-mighty (in theory) storm is related to the slower progress of storm #1 which now has a strong secondary wind max feature showing up on all models I've seen so far, timed for Wednesday afternoon across Ireland. If this trend continued much further, the energy that was supposed to explode storm #2 may just go into more development of this hang-back feature which could just absorb the oncoming energy from the southwest.

This may be negating the chances for an intense windstorm but as that will prevent damage and loss, I suppose it is all for the best, and meanwhile we have a lot of weather to discuss from the ever-expanding time frame required to get storm #1 to its final conclusion.

The 00z GEM has more or less fallen into line with the 12z ECM. I think there is some chance of a last-minute final flip-flop so we need to remain on high alert. The UKMO is now the one model that has not had a chance to reassess the "superstorm" so I'm more interested in that one than usual.

mickger844posts

ECM 0Z has tomorrows low pressure deeper than Thursdays but Met Eireann and UK Met Office still forecasting stormy conditions for Thursday/Friday.

ninebeanrows

Yep serious downgrading of Thursday/Fridays storm this morning! But still some time for it to change. But obviously new later data was assimilated into the ECM 12z run which caught the change.

The overall theme is that the low is likely to develop later on in the time period and further to our south and east.

With the southern areas of Ireland most at risk of any high winds at this point.

I would suggest though that things are changing very quickly and the short term forecasts have low confidence at this point.

- Just looking at GFS EPS i would suggest that mode prediction for the storm is at extremely low confidence, a whole suite of potential outcomes at this stage, changing time and set up.

ninebeanrows

Strong gales moving into the North during Tuesday are the watch at the moment.

Gusts to near 65-70 knots

Speak Now

All in all a cold and windy week so wrap up folks!

Su Campu

As I said yesterday, conditions upstream (North America) are still uncertain, and the surface feature that will spawn the low is nothing more than an area of warm moist air east of the Bahamas with no discernable pattern. Add to this the uncertainty with the jet stream over the eastern US and you have a highly to-and-fro situation regarding the models.

ninebeanrows

6z even less intense than the 0z

This thing could be nothing by Friday. Then again its very uncertain but GFS playing it down further.

Maybe more chance of it snowing on Friday than being windy :eek:

ninebeanrows

Wait until howlinwolf gets off his ban this evening :D