Advertisement
If you have a new account but are having problems posting or verifying your account, please email us on hello@boards.ie for help. Thanks :)
Hello all! Please ensure that you are posting a new thread or question in the appropriate forum. The Feedback forum is overwhelmed with questions that are having to be moved elsewhere. If you need help to verify your account contact hello@boards.ie
Hi all,
Vanilla are planning an update to the site on April 24th (next Wednesday). It is a major PHP8 update which is expected to boost performance across the site. The site will be down from 7pm and it is expected to take about an hour to complete. We appreciate your patience during the update.
Thanks all.
Vanilla are planning an update to the site on April 24th (next Wednesday). It is a major PHP8 update which is expected to boost performance across the site. The site will be down from 7pm and it is expected to take about an hour to complete. We appreciate your patience during the update.
Thanks all.
Cold Spell Late Feb/ Early March Technical Discussion only MOD NOTE POST #1
Comments
-
-
JUST HAD TO REMOVE A LOAD OF OFF TOPIC POSTS SO WILL POST THIS UP AGAIN
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 :- 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.
- Please don't quote images or charts in your replies.
- 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.
- PLEASE don't repeatedly ask will it snow in your backyard - read the thread.
- If you post pictures that are not your own from Facebook or Twitter, you must follow these guidelines:
- All Images taken from Twitter must always be embedded using the URL as in this example https://www.boards.ie/vbulletin/show...postcount=1039
- You cannot copy and paste images from Twitter and post them on Boards.ie.
- With Facebook, you need the creator's permission to copy an image belonging to them and post it on Boards.ie.
- 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
- 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=20565316900 - 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.
-
-
-
Here's a back trajectory plot for 18Z on Monday evening, showing the source and trajectory of the air that will be at 500 metres above Dublin by then. At 12Z today this air up near Murmansk in northern Russia, at an altitude of around 3000 metres. It will travel some 2500 km over the weekend, starting to descend Sunday morning in the high pressure on its way to Dublin.
Here's today's 12Z sounding for Sojna, right up in that region. At 3000 metres this air is at around -25 °C, dewpoint around -35 °C. Obviously it won't reach us at these figures, but it's interesting to see where it will have come from.
0 -
Advertisement
-
-
I expect it will come down to the day and hours before to somewhat accurately predict snowfall track and amounts. The bigger falls from around mid week on it would seem with more active disturbances nearby and over us. The only definite's are the extreme cold, severe windchill, steady fresh and at times strong N'Ely / E'ly winds ( will be expecting the highest wind speeds along the E / SE coasts and later S coasts and potential for icy roads/ footpaths especially where snow has melted under the stronger sun at this time of the year. I would imagine the icy winds especially on the Eastern side and coasts/ high ground next week would catch your breath they will feel so cold.
Some very low humidity and dew points.
0 -
-
-
-
Advertisement
-
-
-
-
-
-
-
-
Kermit.de.frog wrote: »Could be a bit nippy Wednesday night
Windchill for Wednesday night!
Latest GFS just now has quite a different evolution sending the cold much further north. End result being pretty much the same result for us though usunstable air arriving earlier on Tuesday evening and slightly slacker winds on Wednesday which would give showers longer to intensify over the sea. Interesting to see how the rest of the run plays out0 -
I made up this quick guide to the Skew-T sounding as some have been asking about it.
Basically, the two black curves show the temperature (4) and dewpoint (5) measured by the radiosonde instrument on the weather balloon as it ascends up through the various pressure levels (1). The height of these pressure levels is shown by (2). The blue isotherms (6) are read along the bottom horizontal scale (3).
For snow, if the whole profile (both black curves) are left of the 0-degree isotherm (6), then the whole atmosphere is below zero and of course any precipitation will be snow. But for precipitation we need clouds, and for clouds we need saturation. Saturation is present in layers where the two black curves (temperature and dewpoint) are together. In the case shown, the curves are far apart, so the relative humidity is low and there is no cloud (apart from possibly a shallow layers at around 950 hPa (826 m).
If the bottom part of the black temperature curve is above zero then it all comes down to the depth of that warm layer and also what the dewpoint curve is doing. If this low layer is almost saturated then it's more marginal, and if it's more than about 400 metres deep then snow is unlikely, even if the dewpoint curve is far to the left. The drier this layer the more scope for evaporative cooling and so snow may survive down to lower levels. If the wet-bulb temperature (which is found a bit closer to the temperature curve than the dewpoint curve at low levels) is below around 0.6 °C at the surface then snow is likely. Above that then sleet or rain is likely.
For heavy snow we want to see a deep saturated level, with the 700-900 hPa level somewhere between 0 and - 15 °C (which means a lot of supercooled moisture for making snow). Obviously we want the surface layer to be at a bit below zero.
You can get the latest soundings here.
0 -
-
Advertisement
-
Sorry for another question, but I find it hard to figure out why this setup on Monday AM/PM isn't forecast to provide lake effect snow.
Temperature is around -10 at 850, sea is around 7c. 17 difference, check.
Easterly wind - check.
Long sea fetch from Liverpool westwards - check.
I thought maybe something to do with geopotential thickness as others have long said that 528dm is the magic number - but that seems to have gone out the window since GFS shows above that until Wednesday yet heavy snow is predicted.
What gives?
0 -
-
Sorry for another question, but I find it hard to figure out why this setup on Monday AM/PM isn't forecast to provide lake effect snow.
Temperature is around -10 at 850, sea is around 7c. 17 difference, check.
Easterly wind - check.
Long sea fetch from Liverpool westwards - check.
I thought maybe something to do with geopotential thickness as others have long said that 528dm is the magic number - but that seems to have gone out the window since GFS shows above that until Wednesday yet heavy snow is predicted.
What gives?
The problem is the ridge of high pressure. The isobars are curved anticyclonically, so you can be sure there's a great big temperature inversion just above the 850 hPa level. Sure enough, this sounding for that time shows what I mean. Any rising air parcels from the surface will hit this cap and not be able to rise high enough for precipitation to form.
Later on this inversion gets eroded as the cold upper pool arrives in from the east, so convection can get going to deeper levels.0 -
Reckless Abandonment wrote: »
Pressure is to high. It drops as Monday goes on
Knew I was missing something (need to learn more about why high pressure prevents moisture, but that's for later and in a different thread!)
Edit: And GL answers that too! Cheers
0 -
18z picks up again on the potential snowstorm next Friday the UKMO have hinted at, the whole country affected with 20cm+ across much of the midlands, south and east. Highly unlikely it'll evolve like this but another thing to keep an eye on in what's looking like a very busy week
0 -
-
-
-
-
Advertisement
-
This discussion has been closed.
Advertisement