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

nacho libre

Oneiric 3 wrote: »

Tomorrow's Met reann chart:



The opposite of normal.


Edit: Euro WV animation for today, 'The Beast' drawing closer:

This could aid a reload from the north next week with all the warm air going north. I think this is reflected in some of the long range output, cold overall, but not as cold as this midweek period. by the way it's very hit and miss in terms of snowfall over here so far, some places are getting decent snow now, but zilch here so far.

Oneiric 3

nacho libre wrote: »

This could aid a reload from the north next week with all the warm air going north. I think this is reflected in some of the long range output, cold overall, but not as cold as this midweek period. by the way it's very hit and miss in terms of snowfall over hear so far, some places are getting decent snow now, but zilch here so far.

Are you still in London? You need to move up to S. Yorks. I believe the Sheffield/Doncaster region is considered snowiest place in all of England. Indeed, having lived there, I can confirm that there is a feel of cold there that I have not experienced anywhere else on these two islands.

Meteorite58

A look at the WRF -NMM from now until Weds am . Bitterly cold and increasingly so going into Weds in a strengthening NE'ly wind . No model is perfect in predicting snow just a guide.

piuswal

Quite a divergence between UKMO and ECM post Friday!

Danno

9pm Thursday -> 9am Friday (So not including accumulations from previous showers...

Kermit.de.frog

Latest Fax chart for Friday. Can't complain!

downwiththatsor

Danno wrote: »

9pm Thursday -> 9am Friday (So not including accumulations from previous showers...

What model is that based on?

Danno

Kermit.de.frog wrote: »

The cold wins the battle. Siobhan Ryan was more bullish for snow throughout on the RTE 11.55pm Radio 1 broadcast also. Looking good for snow (bad for disruption) The south and southeast are gonna get hammered.

Danno

downwiththatsor wrote: »

What model is that based on?

Not sure, it was posted by @weather_king on Twitter who is Simon Cardy - a Senior Meteorologist at SSE plc.

Snowbie

Indeed Danno, the UKMO holds onto the cold with the occlusion heading back south keeping Ireland in the colder air from that Saturday noon fax. So reload with more snow showers filtering into eastern areas.

UKMO really pasting snow and cold for the foreseeable.

spoonerhead

One thing which was cleverly mentioned when the “warmer” runs came out was the position of the jet stream. UKMO seems to take that into consideration more, ECM and GFS will probably be identical to it tomorrow. Exciting and worrying times over the next few days

Oneiric 3

Snap from the RTE forecast a few mins ago showing set up for Friday:



Not something you see everyday so to be savoured. Most of us on here are always looking back at charts like this, reminiscing of times old, but for just for once, we can actually look forward to seeing something like this again.

Gaoth Laidir

sdanseo wrote: »

Double-barelled question here.

Jetstream is upper level winds.
Lowe pressure contains warm air, warm air rises.

Should the jet not therefore be better expelling Emma back to the Algarve?
Are the models simply having a fit because they aren't used to a NE jet stream?

Low pressure contains cold air, not warm (unless you're talking about a heat low over land in high summer). Colder air means lower heights, hence low pressure. The jet flows anticlockwise around upper lows or troughs, so the northeasterly jet is currently flowing around the western edge of the large upper trough over northern Europe. This trough is in place due to the Arctic airmass promoting low upper heights. Friday's low is currently that large stacked low approaching the Azores.



The Azores low will start to fill tomorrow and move northeastwards, meeting up with the European upper trough, which itself becomes cut off as it moves westwards towards Ireland. This interaction is where the uncertainty lies. The two will merge and the gradient will become slack, so pinpointing exactly where the surface low will go is tricky. Still a few more runs to sort it out.

gabeeg

Latest Arpege has decent precipitation for the East coast by lunch time

piuswal

Unable to post images directly, sorry

Friday 1200 -

https://www.ecmwf.int/en/forecasts/charts/catalogue/medium-mslp-wind850?facets=Range,Medium%20(15%20days)&time=2018022612,96,2018030212&projection=classical_europe

EMMA coming towards south coast- so still on course for snow / blizzrds as ME are forecasting

======================================
Sat 1200

https://www.ecmwf.int/en/forecasts/charts/catalogue/medium-mslp-wind850?facets=Range,Medium%20(15%20days)&time=2018022612,120,2018030312&projection=classical_europe

Models now beginning to Diverge. EC have EMMA possibly being forced in a NW'ly direction off the southwest coast of of Ireland and another low coming towards the SW of England. Still an ESE flow. While not a million miles from the UKMO set up it does have a more significant low approaching which is subsequently forecast to continue on a NE'ly track through Wales and into the North Sea eventually. Sun 1200 and Mon 1200

=====================================
Sun 1200

https://www.ecmwf.int/en/forecasts/charts/catalogue/medium-mslp-wind850?facets=Range,Medium%20(15%20days)&time=2018022612,144,2018030412&projection=classical_europe

Danno

Tomorrow morning's shallow low - ME have said that it will be of rain and sleet. I can't see it being mild enough for that - the uppers are -8c at the lowest!

Meteorite58

Well the ICON certainly painting a very extreme picture. Can over do the winds at times but even knock a few km/h off and add the extreme cold and snow to the mix and we get one hell of a storm to remember. A very complex set up as has been said with models differing at this stage, none of the other big models showing winds as strong as the ICON that but are showing enough strong.

The ECM and the ICON not too dissimilar in the track of the storm and snow amounts at this stage.The UKMO not far off also I would think .The GFS keeping it more S.

patneve2

-44 at 500 hPa. Sometimes GFS likes to exaggerate 850s and 500s, but that would be a mad temp at that height for Ireland - I think that would be the lowest we've reached in a long time. I think 2010 bottomed out at -41/42?

nacho libre

Oneiric 3 wrote: »

Are you still in London? You need to move up to S. Yorks. I believe the Sheffield/Doncaster region is considered snowiest place in all of England. Indeed, having lived there, I can confirm that there is a feel of cold there that I have not experienced anywhere else on these two islands.

I was thinking about it. The Chilterns, which is 30 miles from London, had a lot of snow in December. I had a good time up there. London is one of the crappiest place in Europe for snow- although this year has been unusual- i've had snow on three separate occasions.

Kermit.de.frog

GFS showing an Icon type evolution. Winds from an even more easterly source by Friday.

A double barrel snow event would take us in to Saturday.

ninebeanrows

UKM also holds the cold and snow well into Sat

Kermit.de.frog

Arpege is amazing

igCorcaigh

Kermit.de.frog wrote: »

GFS showing an Icon type evolution. Winds from an even more easterly source by Friday.

A double barrel snow event would take us in to Saturday.

ICON proving its worth recently.

igCorcaigh

Er, am I reading this right, the warmer air gets into the North first?

https://max.nwstatic.co.uk/gfsimages/gfs.20180227/00/75/h500slp.png

Kermit.de.frog

ECM has around 18 hours of continuous snowfall for the east from Thursday evening.

M.T. Cranium

Main points of interest:

Today's sleety mix idea would only be for first hour or two near shoreline, would expect all change over to snow and starts as snow more than a km or two inland ... could get heavier this afternoon and evening as even colder air arrives aloft.

Extreme streamer potential on Wednesday with -14 C 850s, strong east-northeast surface gradient and lowest thicknesses (sub 504 north of Dublin for a time).

Blizzard like storm Thursday into Friday ... the uppers relax as the low zips past to the south (or loops and heads east still an option), but not enough to make much of a phase change, the more likely scenario is for the heavy snow to move north due to rotation of the occlusion with the flow over southern counties still coming from southeast and mixing cold air with slightly warmer maritime flow, rain would only be likely near the coast south of about Gorey around all of the south coast to about Tralee. Inland at any appreciable elevation, snow tapers to flurries and sleet in south (even on GFS and ECM scenarios).

Very strong east-southeast winds for south Cork and much of Kerry with downsloping acceleration for places like Tralee and Dingle.

Various models introduce concepts of second or third attempt lows pushing at the block, no reason to think they will be any more successful than first one unless they track well north and even then they seem to get surrounded by cold air and cut off from the warmth of Biscay waters fairly quickly.

Still no real clarity but many signs of a severe snowfall event that is not immediately washed away by melting and rainfall, and which could continue across parts of the north and even central counties into Friday and even Saturday.

I think the most immediate concern is how extreme Wednesday is looking, could have snow and blowing snow with -5 C temps and -10 or lower windchills. That parcel of air is still back over Poland whereas later today you could look at northeast England for guidance, heavy snow reported around Newcastle and border regions.

The show is about to begin, this has just been the orchestra tuning up.

dacogawa

Heads up "The Beast" is arriving early (think I'm still asleep) moving on a north easterly.

Kermit.de.frog

ECM projected snow accumulation by Friday night/Saturday morning

https://weather.us/model-charts/euro/ireland/snow-depth-in/20180303-0000z.html

M.T. Cranium

It just struck me that now we'll see if an Azores low acts like an Azores high and stays away from Ireland.

Update, in the past 24h that Franz Josef Land high has totally transferred over to northern Norway/Finland at similar 1052 mb pressures.

ninebeanrows

EC has not evolved into one of last nights colder members and would bring gradual...thaw late saturday. depending on cloudcover but certainly in south and near east coast. Big snow before it