End of October Forecast

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

Supercell

The dam line referes to the height in meters you need to go to get 500hpa
Colder (systems ) tend to have this height lower and warmer higher a lot of the time here. This is a crude indicator of snow probability and it can snow well above 528 and rain well below it, other factors need to be considered too.
But being sub 528 is usually a fairly good indicator that there is cold air about..

Snowbie

forkassed wrote: »

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

Firsty, "this is meters lower", Oops, i left out 800meters by mistake and i edited my post above.

This sounds complicated but I'll do my best to explain in detail what a few things the Dam thickness is all about.:)

Elevation like a hill or mtn will always do better for snow if the atmosphere permits but is not taken into account with the Dam height thickness. Temp decreases 1C every 150meters.

We are talking here about geopotential height which assumes the earth is flat and smooth with no hills or mtns.
The height contours (isohypes) you see on my attach above represent areas of equal height values. This is measured in meters.

The value on the height contour depends on the avg temp and moisture content of the air. Obviously the lower the height the more indicative of cold weather and dryer air and higher height values warm weather and moist air.

Now with the 528 Dam thickness, we do associate the minimum height value for snow. 524 is much better, 520 better still etc etc. Now if you ever seen me post in here explaining the parameters for a thunderstorm to occur, the same unfortunately is applied here for this island, but at the other end of the scale, the lower values are better.

Now its moisture, moist air is less dense than dry air and increases the height contour. But if we have the following to look for snow:
528 is one good parameter but is no good without the moisture content.
520 is better for snow but is also no good without the moisture content.
So a moisture content with 520 height is great for snow but is rare here.
Eg: If height (520, dry and cold air) was been replaced by moist air, the height will increase and our threshold of 528 be minimum for our snow to fall. Other elements are involved as we are on a small island for it to go pear shaped.

You can have a low height say (528) but a warmer 850mb temp (1500m) advected in.

Example: So it's the wind, level, speed and source we look at next. Tuesday we have a true north with a just a slight deviation from north at some mb level. (surface, 850mb, 700mb, 500mb, 300mb) These are the atmospheric winds, the source of the airmass can affect temp, dp and moisture.
NB: the surface wind, if this differs from the rest of the wind levels, this can reflect surface temp being much higher than what the height contour suggests.
So a 524, 520 over us with a milder SW surface wind does not mean snow be guaranteed due to the lower heights (temporarily) but very cold conditions for a time either with or without moisture and possible a short transient snow event, like maybe Wedensday?

Sorry for the essay but there is more to height thickness in forecasting weather also (shortwaves, upper troughs), this covers the potential for snow.:)

kerry1960

Snowbie wrote: »

Firsty, "this is meters lower", Oops, i left out 800meters by mistake and i edited my post above.

This sounds complicated but I'll do my best to explain in detail what a few things the Dam thickness is all about.:)

Elevation like a hill or mtn will always do better for snow if the atmosphere permits but is not taken into account with the Dam height thickness. Temp decreases 1C every 150meters.

We are talking here about geopotential height which assumes the earth is flat and smooth with no hills or mtns.
The height contours (isohypes) you see on my attach above represent areas of equal height values. This is measured in meters.

The value on the height contour depends on the avg temp and moisture content of the air. Obviously the lower the height the more indicative of cold weather and dryer air and higher height values warm weather and moist air.

Now with the 528 Dam thickness, we do associate the minimum height value for snow. 524 is much better, 520 better still etc etc. Now if you ever seen me post in here explaining the parameters for a thunderstorm to occur, the same unfortunately is applied here for this island, but at the other end of the scale, the lower values are better.

Now its moisture, moist air is less dense than dry air and increases the height contour. But if we have the following to look for snow:
528 is one good parameter but is no good without the moisture content.
520 is better for snow but is also no good without the moisture content.
So a moisture content with 520 height is great for snow but is rare here.
Eg: If height (520, dry and cold air) was been replaced by moist air, the height will increase and our threshold of 528 be minimum for our snow to fall. Other elements are involved as we are on a small island for it to go pear shaped.

You can have a low height say (528) but a warmer 850mb temp (1500m) advected in.

Example: So it's the wind, level, speed and source we look at next. Tuesday we have a true north with a just a slight deviation from north at some mb level. (surface, 850mb, 700mb, 500mb, 300mb) These are the atmospheric winds, the source of the airmass can affect temp, dp and moisture.
NB: the surface wind, if this differs from the rest of the wind levels, this can reflect surface temp being much higher than what the height contour suggests.
So a 524, 520 over us with a milder SW surface wind does not mean snow be guaranteed due to the lower heights (temporarily) but very cold conditions for a time either with or without moisture and possible a short transient snow event, like maybe Wedensday?

Sorry for the essay but there is more to height thickness in forecasting weather also (shortwaves, upper troughs), this covers the potential for snow.:)

lol ,wish i had that mans brain .....

arctictree

Lovely forecast from met.ie this morning. Very unusual for October:

Today will be cold, bright and breezy with sunny spells and showers. Many will be heavy, especially over Connacht, Ulster and west Munster, with some hail and thunder, and possibly even some sleet on northern hills at times. Top temperatures 7 to 10 degrees Celsius, but feeling colder in the brisk northwesterly wind.

Tonight

Cold overnight with the showers becoming largely confined to the north and northwest coasts for a time. Lowest temperatures zero to plus 4 C., with a slight to sharp frost, and a few icy patches. Then late in the night, a further band of showers will get into Ulster, and extend into north Connacht and north Leinster around dawn or so, giving hail and sleet in places, and possibly a dusting of snow on high ground and mountains.

Tomorrow

Tomorrow Tuesday will be a very cold day. There will be some sunny spells at times, but showers also, some heavy and of hail and sleet, and with an ongoing risk of a little snow on hills and mountains. Top temperatures 5 to 8 C., in a moderate to fresh northerly breeze.

3 Day Outlook

Very cold for the rest of the week and unsettled also. Tuesday night will have clear spells, but scattered showers, some possibly wintry. Cold, with sharp ground frost. Later the night, cloud will increase in western areas, bringing outbreaks of rain and possibly some sleet to coastal fringes by morning, but temperatures will rise a little also. Wednesday will become mostly cloudy, with outbreaks of rain spreading eastwards across Ireland, falling as sleet in some areas for a time, especially over high ground. Parts of the north and northeast may stay largely dry. Thursday and Friday will remain very cold, with a risk of frost at night. Both days will have some sunshine, but scattered showers also, some could be heavy and of hail, with a risk of thunder. Some sleet possible also.

http://www.met.ie/forecasts/

Snowbie

Winds backing west from NNW ahead of the upper trough approaching the NW of Ireland.
Clearly seen here on IR sat.

After the trough moves south, it will introduce the arctic air but won't hang around too long. About 12hrs before the LP system moves in from the NW during Wednesday morning lifting temps also.

Attach show the trough and the 850mb temps.

Kippure

Had snow on kippure today in the form of showers. Tempeture was around 2C

forkassed

Cheers supercell and snowbie for the dam line explanations!