[Northwest Weather Discussion - Dec 2023 onwards]

3 minutes ago, Joe Bloggs said:

Yes UKV seems to think so. Generally west and north of Manchester. Still uncertain though. 
 

06z Arpege agrees. Manchester will potentially be on the edge of the convective zone 

The mighty COSMO says differently.

[Northwest Weather Discussion - Dec 2023 onwards]

Again some high resolution output keeps this North of Manchester so a fair bit of uncertainty here.

55 minutes ago, Chris.R said:

Only just going above freezing now. That's pretty good.

-3.2C here now.

[Model Output Discussion - Colder but how cold and for how long?]

All it takes is another 50 mile shift North and we're on the verge of a very significant snow event.

[Northwest Weather Discussion - Dec 2023 onwards]

In terms of the talk about marginality there wont be any early in the night however after about 7am mixing with graupel (still 100% ice content) and after 8/9am perhaps some water precipitation mixed in on the immediate coast. That's still a good 10 hours of conducive conditions with precipitation risk on the coast. Although aloft conditions are fine for falling snow, a maritime layer on the exact coast does look to potentially limit accumulation later in the night away from heavier showers.

[Northwest Weather Discussion - Dec 2023 onwards]

ICON accumulates 20-30mm of precipitation parts of Northern Lancashire. A lot of this will be rain however there may be a small area where 20-30mm is reached with the majority of the precipitation being snowfall. This is where potential for a big dump of snow is between say Skipton and the Lakes above around 200-300m. 

[Northwest Weather Discussion - Dec 2023 onwards]

Just now, Chris.R said:

Surface winds are very light and mostly offshore tonight as well which will help the coast a lot and promote evap cooling especially with the low dp..

Winds are light tonight too. Wouldn't discount on 5cm+ locally parts of inland Merseyside / West Central Lancashire granted the trough doesn't scupper the flow too much. 

 

[Northwest Weather Discussion - Dec 2023 onwards]

The issue tonight is wind directions are very uncertain. Showers are likely now (70% of some decent shower activity), but where these fall is uncertain, models are split around 5050 on a WNW and WSW flow so the southwards extent of showers is quite uncertain. Anywhere South of Manchester is looking at a 5050 risk. South of say Crewe and the risk is quite low. Manchester centre North is safe either way with the potential for a sharpish streamer to form in area from say Oldham through to the coast and uptowards Lancaster. Locally 1-6cm is possible within this streamer with a low chance of more, places like the Wirral and Warrington upto Wigan and Preston probably favoured for the heavier precipitation. if showers develop further South then parts of North Cheshire and South Manchester may also see this potential streamer. 10-20cm+ of snowfall possible inland parts of Cumbria, parts of North York Moors during Tuesday evening and early Wednesday. Speculation but Windermere area could be in for 15-25cm. Surface warming likely to influence precipitation 5 miles from the coast here and below 50-100m asl. Mixed phase precipitation likely further South as the front moves South potentially a period of wet snow to lower levels especially east of the M6 late Tuesday. 

Thursday is the next period of interest with a stronger NW wind with uppers of -8/-9, surface warming possible on the immediate coast. Again fairly significant accumulations are possible with the potential for a trough system to form which could enhance snow potential.

[Model Output Discussion - Colder but how cold and for how long?]

1 hour ago, TillyS said:

 

The models don’t show evidence at present that the milder ‘spell’ will be short lived. There is no evidence of northern blocking in the three main models. Nor is there evidence at the moment for the so-called SSW having impact on UK weather to the end of their runs.

It will, indeed, be very cold this week.

Then it will be very mild, and not just for a short spell.

At least that’s what the models say, rather than what we may hope for. Cold, sometimes very cold, until Friday, then distinctly mild, wet, windy and Atlantic dominated, with high pressure to the south of the UK.

Evidence is more reliable  

Correct there is no indication of anything cold in the next couple of weeks bar the odd polar maritime spell. 

[Northwest Weather Discussion - Dec 2023 onwards]

27 minutes ago, Scuba steve said:

If anyone’s interested I’ve just had a sleet shower

I like to take normal showers and I don't go around telling people either.

[Northwest Weather Discussion - Dec 2023 onwards]

The latest WRF just has some drizzly sleet move through the region on Tuesday, nothing more.

[Northwest Weather Discussion - Dec 2023 onwards]

Btw the Arpege has no convective showers South of Wigan tomorrow night & brings in a marginal trough instead. 

[Model Output Discussion - Colder but how cold and for how long?]

4 minutes ago, doctormog said:

To describe this weather as a toppler is misleading and sounds like “everything that comes from the north that doesn’t give me snow” is a “toppler”. The synoptics show a bitterly cold Arctic/polar flow and not something casually dismissed as a toppler even if large parts of the country do not see snow.

Well as far as I can see the cold topples eastwards so by definition parts of the cold snap is a toppler even if initially it is a cold polar air mass.

[Northwest Weather Discussion - Dec 2023 onwards]

Just now, northwestsnow said:

Well this is very odd !!

meto have a snow warning out Tues Wed and Thurs...

I'm really flummoxed now!

Yeah there will be bits of snow around and locally significant accumulations there's quite an influx of instability off the Irish sea. I was just referring to my local area with the towel post. 

[Northwest Weather Discussion - Dec 2023 onwards]

1 minute ago, northwestsnow said:

Just as you typed that METO have us in a warning lol

It's 5050 sorry I can't give any more detail our snow showers here in Cheshire / Derbyshire /Staffordshire depends on the NW flow ahead of the trough & the trough being sufficiently small. The trough is looking a little stronger on output now which will introduce more of a WSW wind reducing this risk, but in turn this would increase the risk of significant snow say from North Manchester northwards. How significant the trough is on arrival can not be predicted yet so the areas most at risk from snow can't really be nailed down yet.

This is why the UKV has the snow showers missing the south of the region but has the front stalling over the North Pennines.

TBH it's a lot of effort for a few flurries / temporary snow events. 

I also feel the lack of snow events is beginning to affect by ability to predict these events with the precision I used to. 

Bring on summer & thunderstorms for me now.

 

[Moans, ramps and banter]

Just now, tight isobar said:

Indeed snow chances evaporating every run now !!!@countrywide.

Yeah this looked the case a few days ago aswell was clear to see the direction of travel.

In my years as an amateur and otherwise, I have never seen such promise result in so little for the majority of the UK.

I'm throwing in the big snow towel.

Apologies for the moaning post models but I think we all feel the same.

Onto the next chase. 

[Northwest Weather Discussion - Dec 2023 onwards]

Our big lass is clearing her windpipe after viewing the GFS06Z. I may join in for a sing aswell.

[Model Output Discussion - Colder but how cold and for how long?]

Yeah looking like going to the South now. Around a 15/20% chance of a more northerly track. 

Even the risk of snow showers into the Cheshire gap has reduced somewhat.

The fact is over 90% of the UK population will remain snow free from this toppler.

The risk of troughs forming in the flow is very low because it gets shunted out by Atlantic air very quickly.

Enjoy everyone  

[Model Output Discussion - Colder but how cold and for how long?]

We needed the ICON here really. It is further South. GFS 06Z in soon.

[Yorkshire and E England regional discussion - Dec 2023 onwards]

A stagnant WNW flow on the rear of the trough may produce a continuous feed of Irish sea moisture into the main convective zone producing the risk of persistent hill snow and mixed phase precipitation to lower levels during Tuesday afternoon and into the early hours of Monday.  As a result 10-15cm of snowfall is possible above around 150m where this forms. This likely somewhere between Harrogate and the North York Moors, therefore this is no guarantee of significant snowfall due to the uncertainty around the trough placement.  Lower levels will see mixed precipitation with the possibility of more optimal snow conditions to around 50m asl establishing on the back edge of the system which could produce 1-3cm locally as the front moves South during Tuesday afternoon and into Wednesday. Areas above 200m asl may see as much as 3-8cm as the trough progresses into a frontal system.

[Northwest Weather Discussion - Dec 2023 onwards]

The convective signal for Tuesday has somewhat reduced with an intensification signal for the trough from most hi res input. The implications of these are likely to be a shorter time frame of optimal shower conditions early on Tuesday morning. Little marginality is expected away from a warmed surface layer on the exact coast. Some ice pellet mixing is possible later on as the warmer uppers aloft are mixed with the near surface convective zone. I think a good few could see a couple of cm with around a 50% chance of a decently structured streamer forming around the Wirral bay and covering a large portion of the region with 1-2cm of snow with up to 5cm locally in any enhanced streamer activity. This could be further reduced if the trough gains intensity on output.

The trough is now looking likely to impact the North West during Tuesday with the most optimal conditions for significant snowfall above around 1,000ft however on both arrival of the trough and as it sinks South there is potential for some snow to lower levels. Indications are 5-10cm over Pennine areas with very uncertain accumulations to lower levels, if the cooling on push away of the front is optimal a few cm may occur locally to lower levels, however this is somewhat unlikely. 

[Model Output Discussion - Colder but how cold and for how long?]

ECM is somewhere between the GFS and Arpege - however it has moved around 150 miles North from yesterday's runs.

[Model Output Discussion - Colder but how cold and for how long?]

3 minutes ago, Ben Sainsbury said:

Huge shift in the GEFS 00z this morning for my particular location (also representative for those south of M4). 50% of ensemble members now have snow reaching the Bristol area vs a quarter of the members at 18z. 

If we take London, we've also doubled the percentage chance from 28% to 56%. A big EC run coming up.

Balance for me is roughly 65/35 in favour of a snow event upto the M4 corridor based on past events and latitude placement often following GFS/WRF/ICON more closely than others. ECM for me less important as it isn't great for placement. Consistency from the 06Z GFS/WRF/ICON more important for me, we can get the others onboard tomorrow.

[Model Output Discussion - Colder but how cold and for how long?]

1 minute ago, Ben Sainsbury said:

ARPEGE completely avoids the south coast at all with regards to the same system. Still a mixed bag! 

For me icon / wrf are better for positioning of troughs. However it is still 5050.

[Model Output Discussion - Colder but how cold and for how long?]

WRF and ICON really going for it.

[Northwest Weather Discussion - Dec 2023 onwards]

GFS12Z has no snow showers into NW early Tuesday.