Cold Spell Late Feb/ Early March Technical Discussion only MOD NOTE POST #1

patneve2

Apologies if people have already commented on the euro4, they look tasty ppn wise. East Leinster could have already have 5-13mm precip by 06 Wednesday. Would warrant an orange alert widely (and also red in a few spots imo).

Liffey4A

Do the current precipitation charts model possible streamer action or just more organised bands?
Thanks for all the updates and explanations. Great as always.

Kermit.de.frog

Hirlam precipitation Tuesday 1200 - Wednesday 0700

lucernarian

mirrorwall14 wrote: »

I put this list together based on replies here. These are the roll out times, not the start of the runs


300am ICON
330am GFS
350am UKMO
530am Euro 4
6am ECM
930am GFS
1130AM Euro 4
1500 ICON
1530 GFS
1550 UKMO
1740 Euro 4
1800 ECM
2130 GFS
2330 Euro 4

HIRLAM especially should have a time added though I'm not sure what website shows it first and at what time. It is quite good at 24hr-96hr range especially for picking up *where* precipitation would fall. ICON = I Can Offer Nothing

patneve2

GFS going for snow showers with an ESE wind on Wednesday afternoon (would be quite rare for South Dublin). Will be interesting to see if this materializes.

Periscal

ICON would equal historical event



Arpege perhaps bit more realistic, still impressive though



GFS has about half of ARPEGE'S totals,about the lowest from all the models by Friday evening actually



ECMWF about the same as ARPEGE



The most favourable spots would be Eastern slopes of Wiclow Mountains, places to be this week: Roundwood,Glencree,Glencullen,Brittas.

Best Models for snowfall totals:

1.ICON
2.ECMWF
3.ARPEGE
4.GFS

lucernarian

Maybe the best model is the one most likely to be right in 5 days now, which I *highly suspect* ICON isn't. This ICanOfferNothing run was very good for snowy conditions, but what about yesterdays?

BLIZZARD7

gluppers wrote: »

Is the barometric pressure for this sort of event low, high or in between?

It's high right now, 1033mb here in South Dublin. It will gradually lower from now on though, the lower the better for shower activity.

Kermit.de.frog

space2ground1 wrote: »

Is there a link to where we can find that chart as the days progress?

Of course. It's updated periodically every 6 hours.

http://www.meteociel.fr/modeles/hirlam.php?map=430

Hover over the timestamps to progress images.

pistolpetes11

JUST HAD TO MOVE 20 POSTS FROM THIS THREAD !!!! THAT DONT BELONG HERE PLEASE READ THE BELOW BEFORE POSTING


Well it looks like we are set for quite the cold spell :D:D

This forum gets extremely busy during these weather events and for the most parts the thread are really enjoyable and you will garner lots of knowledge.

Although before you start posting we would like to summarise a few house rules here :

1. During weather events we take zero tolerance approach to trolling or bickering. Cards, warnings and/or bans from the forum will be handed out as appropriate. It gets so busy that this is the only option we have.
   
2. Please don't quote images or charts in your replies.
   
3. If you feel someone is trying to cause trouble, please use the Report Post function and let the Mod Team deal with it. Don't respond/react on-thread and further derail it.
   
4. PLEASE don't repeatedly ask will it snow in your backyard - read the thread.
   
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• All Images taken from Twitter must always be embedded using the URL as in this example https://www.boards.ie/vbulletin/show...postcount=1039
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• You must also credit the creator of the image if you do get permission

There are a few threads in operation for this event

• The Main Discussion thread for the event
• https://www.boards.ie/vbulletin/showthread.php?t=2057843266
  
• The Technical Discussion Thread ( Please don't post in here if you’re looking to tell us its snowing or you want to know will it snow in your back yard )
• https://www.boards.ie/vbulletin/showthread.php?t=2057844498
  
• The FI Thread ( This is usually for charts that are 120 hours or more away )Although a lot of these charts will probably end up in the technical discussion thread anyway
• https://www.boards.ie/vbulletin/showthread.php?t=2057782713
  
• This thread below is a great resource for finding out where all the weather charts we use coming from and what they mean
• https://www.boards.ie/vbulletin/showthread.php?t=2056531638
  
• The Snow weather preparations - your lists, must dos and driving tips Thread
• https://www.boards.ie/vbulletin/showthread.php?t=2057844895
• And last but not least and perhaps the most important :eek: Our resident boards.ie forecaster MT's thread can be located in the link below
• https://www.boards.ie/vbulletin/showthread.php?t=2055579971&page=119

PLEASE FAMILIARISE YOURSELF WITH THE FORUM RULES IN THIS LINK



https://www.boards.ie/vbulletin/showthread.php?t=2056531690

Neddyusa

Kermit.de.frog wrote: »

Hirlam precipitation Tuesday 1200 - Wednesday 0700

Any idea why that trough feature shown passing down through the North West of the country tomorrow evening is being shown as rain on Hirlam?

Kermit.de.frog

Neddyusa wrote: »

Any idea why that trough feature shown passing down through the North West of the country tomorrow evening is being shown as rain on Hirlam?

There is a small warm sector with it. It will pass through snappy though.

DOCARCH

Gaoth Laidir wrote: »

Light snow now falling here in Tallaght. Ladies and Gentlemen, the Beast is in the building!

Jeeez.....what a ramper! :pac:

Kermit.de.frog

Northern extent of the snowfall on Friday is Dublin, through Meath, according to Icon before it pulls a way south. Chaos for the south.

Iancar29

Latest modis satellite imagery showing a swath of cloud over the UK and most of Ireland.

This is weak convection connected with the lake effect snow ( cold air moving over warmer water). Showers, however, are only weak and isolate in parts of the east at present. This is because surface pressure is still quite high, averaging at 1032mb and suppressing vertical ascent in the atmosphere. It is due to decrease slowly from this evening onwards into tomorrow which will increase the shower activity.

Cantona's Collars

Gaoth Laidir wrote: »

Light snow now falling here in Tallaght. Ladies and Gentlemen, the Beast is in the building!

Sorry for the off topic post but for some reason I thought you were in Donegal. Maybe it's the username.:)

TheMilkyPirate

Ian would the cloud cover displayed there be indicative of shower activity once the pressure drops? i.e snow the entire length of the east coast with minimal fetch?

Elmer Blooker

Kermit.de.frog wrote: »

Northern extent of the snowfall on Friday is Dublin, through Meath, according to Icon before it pulls a way south. Chaos for the south.

How do you know it will pull away south when everything is still so uncertain?
I would love that to happen and see the Atlantic "lose" 1947 style!
All on a knife edge.

pistolpetes11

Elmer Blooker wrote: »

How do you know it will pull away south when everything is still so uncertain?
I would love that to happen and see the Atlantic "lose" 1947 style!
All on a knife edge.

Is pulling away indicative of the cold block pushing it away ?

Kermit.de.frog

Sub -16 850 isotherm not too far away Wednesday night on the GFS.

snowstorm445

ICON seems to be keep the cold air entrenched over the weekend which would be great. Only one run though.

Iancar29

TheMilkyPirate wrote: »

Ian would the cloud cover displayed there be indicative of shower activity once the pressure drops? i.e snow the entire length of the east coast with minimal fetch?

Not necessarily, wind convergence will form streamers with isolated showers away from them. Bands still possible from small trough features moving SW from the North Sea though given more widespread activity.

A current fetch of roughly 200km is given the high pressure a fight which is producing those light showers along the coast atm. Wind direction going more NE later into tomorrow with lower pressure too.

Elmer Blooker

pistolpetes11 wrote: »

Is pulling away indicative of the cold block pushing it away ?

Yes, if the front pulls away south it means the cold continental air "wins", if the front keeps going north and clears the country it will mean a big rise in temperatures.
The winter of 1947 saw many "battles" like this and it often turned milder in the southern UK for a time before the cold pushed south again.

snowstorm445

ICON still has -8 uppers over the eastern half of the country by Monday.

This could mean however that the prospective blizzard may not take place if the low heads too far south.

Kermit.de.frog

So the GFS is quite good if you want full on snow on Friday. But crippling snow fall for many.

patneve2

Question. Would an isotherm of -5/-6 be enough to guarantee snow (even snow of a slightly wetter variety) here on the East coast on Friday? Always get confused re. these events. Sometimes I hear that a -2 is enough with pre-existing cold already in place and sometimes I hear that you need at least a -8 at 850hpa with heavy ppn.

cherryghost

Icon wants to keep the cold going into next week, with a 12-15hrs dumping of heavy snow across Munster and much of Leinster, then cumulating with snow showers for the rest of the weekend. GFS slides the low further west, but precip hasnt changed and has most of the country pasted with white stuff, with sleet/rain following on through the weekend. Two very different low movements though.

jdcv94

Kermit.de.frog wrote: »

So the GFS is quite good if you want full on snow on Friday. But crippling snow fall for many.

I'm still a beginner at reading these charts but I love the weather, people have said before that it's bad for snow if this low moves west like it is on that chart. How come this will bring crippling snow in this case?

TheMilkyPirate

LP seems a tad further south west and deeper on the 12Z, Miniscule differences though from the 06Z so far.

Neddyusa

Kermit.de.frog wrote: »

There is a small warm sector with it. It will pass through snappy though.

Is it associated with that Polar Low type feature currently between Scotland and Norway?