End of October Forecast

arctictree

Weather looking very stormy for next weekend (as usual!).

Some interesting weather showing up now in FI leading up to Halloween.

http://www.wetterzentrale.de/pics/avnpanel1.html

Danno

I was looking at the GFS output this morning and some central north atlantic blocking looks like taking hold with some northerly winds coming down.

This October certainly feels alot cooler than recent ones, reminds me of the early 1990s Octobers really.

arctictree

Totally in FI but a lovely chart nonetheless:



Any opinions on whether we would get snow out of a chart like this at this time of year??!

Snowbie

Will you look at that, my guess for Halloween for the first air frost looks on.:D

Arctictree, what that spells is some potent showers or coastal Thunderstorms for the north and east.
A cold polar blast travelling over warm SSTs (October has the warmest sea temps around Ireland usually) will build CB,s quickly over sea but will die out as they travel inland as no convection and dry air overland (opposite to summer).

Very hard to tell if snow where to fall from that at this time of year but October 2003 has to be noted here. Nowcast i'm afraid.
Okay FI but very hard not to admire that kinda chart.
Where has this year gone, were back to snow watching already.:eek:

Supercell

Jaysus we are already thinking about polar lows and such, thats a very tasty chart indeed. I'd just love an october 2003 to happen again, except this time up the mountains to experience the fun.

forkassed

This looks tasty

http://91.121.93.17/pics/Recm2401.gif

Mr Benevolent

This probably sounds stupid, but what conditions need to exist for snow to form, apart from temps <0C?

forkassed

Confab wrote: »

This probably sounds stupid, but what conditions need to exist for snow to form, apart from temps <0C?

I would say snowbie's your man for the ins and outs but heres a link to a good general guide

http://www.netweather.tv/forum/index.php?showtopic=20474

Supercell

Just looking at the 12z ensembles, amazing agreement all the way out until then.
This is a crazy time of year, just about anything can happen and usually does.
Then December and endless mild returns, enjoy the next month or so !!

Snowbie

I would agree with most of that Netweather link but but an exception is the scandi HP and snowfall for our east coast.
The chance's of snow from a direct east blast from Russia is reduced further thanks to the UK. The airmass will be either:

cloudy, cold with flurries
or
clear, dry and cold.

That chap mentioned it when moisture can be lifted into the atmosphere by cold air travelling over a warmish sst's but only brings gloom with the odd flurry. This is a layer of stratus (cold inversion layer) and traps the cold beneath it to the surface.

When in the clear, dry and cold setup occurs when the cloud is broken up as the pressure gradient is tighter and the winds are stronger and a wind chill coupled with bitter air can wake you up somewhat. The air is also modified by the UK, drying the air out too so dewpoints can be very low but we need a kick start for showers to occur over the sea.....
The pressure gradient will be tighter when a LP to our south moves northwards and bumps into the HP.

This LP is key for snowfall to our east and south. This will destabilise the atmosphere and create instability (lapse rates steepening), building showers quickly over the sea.
Coasts would see snow to lower levels( as DP be subzero) but unless 850mb temps(1500m) are below -10C, snow would not settle on the coast only inland as the sea can be our friend and foe at the same time as it is warmer than the land by the resorts.

First things first, a scandi HP has to be in place and a LP to approach from the south just to create a snow chance otherwise a scandi HP is like an Azores HP steering in stratus muck obviously with temp difference. 3 out of the last 10 scandi HP has brought snow to the east and the 3 had LP moving up from the south, the other 7 where stratus muck. The last snow to the east was this year Jan 3rd and had an added little feature reforming in the N Irish sea from the North sea off the Scottish coast.

Here is proof of what happened because of that feature

this thread i posted radar shots somewhere in there

The Omega block is what we want to see forming to our north when the arctic high vacates south into the NIC or the Norway to Iceland corridor. But that is as rare as Dublin winning the all Ireland.

Supercell

arctictree wrote: »

Totally in FI but a lovely chart nonetheless:



Any opinions on whether we would get snow out of a chart like this at this time of year??!

You and I might see some, the mountains above 350 metres would be a cert for falling snow and probably 500 metres a cert for settling stuff. Lower down hail and some sleet in the really heavy showers would be my guess.
Thunder likely too, its a really tasty chart!

Supercell

Snowbie wrote: »

Here is proof of what happened because of that feature

this thread i posted radar shots somewhere in there

The Omega block is what we want to see forming to our north when the arctic high vacates south into the NIC or the Norway to Iceland corridor. But that is as rare as Dublin winning the all Ireland.

Epic tread that, nice just rereading it.
Only October and we are already starting snow treads, lets hope theres another six months of potential on the charts!

Mr Benevolent

Thanks for the detailed explanation Snowbie, the whole process makes a lot more sense

Scubadevils

Wow, thought I'd stop by and see where we are at and if any talk of the elusive 'snow'. I joined boards almost 4 years ago now after doing a search on google for 'chance of snow' or something to that effect... it was a rollercoaster couple of weeks then leading up to what became a somewhat white Christmas. Anyway, hopefully this year will deliver!

Deep Easterly

I expect Snowbie and Supercell will be quite pleased with the latest ECM teaser:





I am even more pleased, for it will be spectaculary dry and a frosty wind if them charts play out anything like that.

arctictree

All the models I have seen are in rough agreement for northerlies backing north easterly for mid next week into and beyond halloween.

Will be great to have this kind of weather around then. Sure beats mild muck!!

Seeing how this evolves over the next couple of days will be interesting!!

A

Snowbie

If this where 'Play Your Charts Right' i'd stick on the bottom one

Nice one Pat, i was loading the GFS today at around 1715 and it got as far as Tuesday and an arctic LP system was streaming south towards us, i wonder is that the same LP there, must go and check when this forever taking PC back up finishes:(

Deep Easterly

Give me a mo

hERE YOU GO KARL. ENJOY.

GFS 12z Tuesday:


WEDNESDAY:


THURSDAY:


SATURDAY:


REST OF RUN KEEPS A NICE COOL THEME:

Snowbie

Sweet, if only it where Monday, we could really admire those charts. I'd say the 528 DAM thickness is well south of Ireland but only just. Notice the warm sector in and around of the core, roughly -10C to -12C 850mb temps.

Afterall it's only October and the real cold air is a couple months away. That in January/Febuary be fantastic.

Cheers Pat.

Danno

Christ! Pat, are them charts genuine? I hope they're not PhotoShoped!

nacho libre

i'd say sleet is the best we can hope for on a low ground out of this:(

i bet we won't get charts as good as those at the optimum time of year!

Supercell

Eh..AT..next round is yours
Thursday and Friday look potential packed around these parts.

Snowbie

GFS has backed off slightly for us. 18Z but Still FI.

LP coming out of Svalbard creates a polar low or comma cloud(as it looks like a comma on satellite) comming out of Iceland. This is not impossible as cold winds over warmish water(warmer than the air above it) around north Atlantic is not uncommon for this set up at this time of year.

This PL stays to the NE of Scotland and runs down the east UK with the main parent LP now moving into Norway. This setup is not a complex system as both systems are moving to the SE direction so chances of the Norway(parent) LP retrogressing back west looks unlikely.

Looks to be fairly mild around the core (Scotland sea level, snow for their MTS no doubt) so closer to the centre of the PL will be noticeably less cold but with troughs moving south right down over us (if PL track remains the same). Interesting.

Snowbie

To and fro'ing, GFS a nice upgrade today in FI land still.

Deep Easterly

Unfortunately, there is more froing than to-ing tonight Karl. Massive downgrades in all of the models. Downgrades that don't even decend into anything interesting, but just anticyclonic westerlies with embedded warm fronts.

Anyways, before then, we still might scrape a couple of wintry type showers during next week if the latest ECM run works out.



First blues of the season over the northern third of Ireland, so some hope for hail/sleet and the odd snow flurry perhaps before the horror arrives (already can be seen over the mid atlantic :mad:)

If only some major troughing would occur to the South of Iceland and become caught up on the Jet stream....

Snowbie

First time i think i ever seen this with GFS (18Z) generally having a cool possibly cold spell throughout the runs up untill the 8th Nov. No hint of a SW and even progs a scandi HP 3/4 way through. Odd but nice but chances are...

Pat i think a cool theme from this Sunday through to Wedensday instead of cold unfortunately. However 18Z last night downgraded also but near reliable timeframe now.

Danno

Daytime maxes for early next week remain below 10c, with night time minima below zero inland. Interesting setup so early in the season.

arctictree

Looks like an upgrade across all the charts this morning. ECM is still showing a cold halloween followed by cold weather lasting a few days:

Gonzo

Met Eireann have mentioned a threat of wintry showers for high ground areas next week. This whole October has been really cold for me I think, coldest October I can remember in a long time, if only this was January.

Snowbie

ATM (06Z) 528 Dam thickness flirting with Ireland (needs to be at or below this thickness for snow chance) Charts have well improved over the last two 18Z runs. GFS has nearly 36hrs of a direct N'ly source for Tuesday and beyond.

nacho libre

hopefully there will be an air frost before the end of October:D

Snowbie

nacho libre wrote: »

hopefully there will be an air frost before the end of October:D

Wait till you see, it be on the 30th:rolleyes:

Mothman

Gonzo wrote: »

Met Eireann have mentioned a threat of wintry showers for high ground areas next week. This whole October has been really cold for me I think, coldest October I can remember in a long time, if only this was January.

Not quite so in coastal Wicklow though by end of month it may be coldest in my records.
Current mean 10.6C
2000, 03 and 04 were colder, though only 2003 has had lower mean min

Supercell

I reckon with 850's of close to -10°C and sun no stronger than in Febuary, maxes on Wednesday could be pretty low if it pans out as per the charts right now.
I'm thinking maybe daytime maxima of around 4-5°C are feasible here which is pretty amazing for October. If the wind is NW then probably similar there in Ashford.
I reckon your 9.2°C October min max could possibly be threatened this week MM.

Danno

Mean is 10.6c here for the month so far. October coolest day was 3rd so far with a chilly 7.5c mean, and exactly 1 week later, October warmest day came with a balmy 15.1c mean.

Snowbie

Decent 18Z upgrade for a change. In the attach below, GFS Progs a trough moving down over the country late Tuesday evening into Wedensday. If this where middle of Winter i would bet against that been active with northern counties would only see precip with cloud and maybe a flurry to southern areas, but this has a healthy atmosphere due to warmish sst's up north of Ireland so would not call it an active trough but healthier even in darkness with longevity to it (maybe to southern counties) thanks to the time of year??

Also note in the attach below the Siberian HP, good for cold air pooling for the easterlies in Jan/Feb:cool:

Added a close up also below of the trough, notice the LP centre to the east of Scotland and the warm sector wrapped around, this is not good for low lying areas and even marginal to 300m if that where to cross over us, best to keep it a bit away.

From my forecast for my location at 2320 shows a mix of rain and snow for Tuesday night from the trough but time will tell as we still can't reach and grab it just yet.

Tuesday night

Mostly cloudy in the evening, becoming partly to mostly cloudy after midnight. A chance of a mix of rain and snow in the evening, then a slight chance of a mix of rain and snow after midnight. Low 2°. Wind north around 20 mph, gusting to 26 mph. Chance of precipitation 30 percent. Precipitation (liquid equivalent) mostly less than 2 mm. No snow accumulation expected.

This graph from my forecast run looks complicated below, i'll explain. The DAM thickness indices on the right in height which is indicated by the dark blue line (left to right) with 850mb temps by red line. See how they both rise at the passage and rear of the trough with wind at bottom is NE. Unfortunately the N Atlantic air comes in the mix and i suspect further runs should confirm this. Hopefully more positives to come and mtns would do well from snow if the precip is there.

Deep Easterly

Latest ECM 850's:
Tuesday Evening 1800hrs:


Wenseday 00.00hrs:


Wenseday 06.00hrs:



Could be a bit nippy on tuesday evening...

nacho libre

Beautiful charts:D

although i feel bad for snowbie;)

Snowbie

From what i can tell from the 18Z tonight, 850mb temps are not low enough for snow to settle on low ground. Mtns could see lying snow more up north and west and then the east which will later depend on wind direction.

Some extraordinary charts tonight, which i have not seen in awhile.

1st attach has an Arctic source wind right the way down to Maderia and Canary islands.:eek:

2nd. PL forms north of the Faroe islands and moves down the north sea.

3rd. Next is a shallow LP that approaches NW Ireland and moves down through the country. This should be interesting for high ground but looks like a wet snow event rather than lying snow. Sleet for sea level areas but some Atlantic air is in the mix which could mean higher DP and rain for all. One to watch.

4th. The track of this LP moves into Biscay and reloads the cold from the NNE temporarily. Atlantic wins back late on in the week but with frosty nights.

5th. Is the best chart for a snow risk, mainly from a trough been pushed down south from the PL over Scotland. North and NW risk continues due to onshore winds later.

I ran my forecast using the latest models for this area has a less risk due to winds streaming down over the land rather than a east of north wind (onshore here) from last night on Tuesday.
Temps and more significantly wind chill are low for the time of year for all.

Fascinating charts for October.

Supercell

NW=fail
That is all
At least it wil be cool.

Mr Benevolent

Arrrgh! Why couldn't the Vikings found Dublin somewhere a bit more weather-worthy?

Snowbie

Could all change again, no doubt it will.
One thing is almost written is that the last week in October will be cold especially with the wind added in.

Snowbie

00Z keeping the cold going a bit longer up to and including Friday.

Danno

That low off NW Ireland that moves down to Biscay - Snowbie highlighted this earlier - looks like having snow on it's eastern flank according to www.snow-forecast.com

http://img.photobucket.com/albums/v678/dldunne/snowforecast261008.jpg

A sliver of an area that follows the N8 from North Cork to Portlaoise, and an extension that goes on up through East Offaly, North West Kildare and SW Meath. I wonder how precise these maps are.

arctictree

All charts are now showing some very interesting weather this week. Mon/Tue have brisk northerlies which will produce wintry type showers, especially at night.

Thur/Fri are the ones to watch IMO. Very much a nowcast situation, but with high sea temps and brisk North easterlies, we could be in for a repeat of October '03 albeit a week later...

A

nacho libre

To be honest i'll be surprised if we get snow out of this at low levels.
It's just too early in the year. According to met.ie it will become milder from Wednesday onwards with showers or longer spells of rain. Still it will be good to experience such cold weather, at this time of year, up till then.

Danno

Just watched Countryfile BBC Weather and they showed snow over the east for Wednesday.
It seems that the NW low brings mild air to the west, but the cold air in the east turns the advancing front to snow.
Some harsh frosts coming too.

Snowbie

Just posting up a few attach from the 12Z.

The real cold air (for this time of year) hits around early to mid afternoon Tuesday but doesn't hang around long. It remains chilly throughout and quite cold again by Thursday.

850mb temps at their lowest around -7C but -8C in the NW.

Max temp around 5 to 8C widely on Tuesday afternoon but plummeting after dark.

520 Dam line very close to the east coast, this is 800meters lower than what is one requirement for snow, with 524 over most of the country.

Still might be premature but up until now we can speculate on the timing of cold but if were looking for snow, we have to nowcast otherwise windward coasts most at risk.

The risk for Wednesday remains but i think mainly for higher ground with wet snow and sleet at low levels. As Danno mentioned, transient snow could occur if the front meets the residual cold air in the midlands and east. Still one to watch but not set in stone.

Deep Easterly

Snowbie wrote: »

Just posting up a few attach from the 12Z.

.

Hey Karl, I am not sure if you are aware, but according to Brian Gaze, there is a lot of corrupt dat in the 12z gfs run. Maybe he just wants to believe that because I certainly want to! but that run does seem to be in major conflict with ecm and ukmo from thursday onwards.

Snowbie

Correct Pat your right, most of the charts have been corrupted on the 12Z today beyond Wednesday. Just interpreting the data available in this instance before that.
Basically a pick and choose from that output.
Most data i used here is from the 8km high res Nw GFS which seemed stable for that time peroid 48hrs from noon today. We see if the 18Z is better and will compare

forkassed

Snowbie wrote: »

520 Dam line very close to the east coast, this is meters lower than what is one requirement for snow, with 524 over most of the country.

Snowbie,

Can you explain that in more datail

I usually look at where the 528dam line is as a requiremnt for el sneachta.

When you say "this is meters lower" does the dam line indicate at what elevation snow is likely to fall at?

Cheers