Model output discussion - into the start of Winter

[mushymanrob]

2 minutes ago, mushymanrob said:

For snow you need all of these
500hpa valu

es of -27c or lower
850 values of -7c or lower
528 dam or lower
dew points of 0c or lower

according to this site
 

Basic Snow Forecasting Guide

UKWEATHER.WORDPRESS.COM

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If you're looking how to forecast snow, then you've come to the right place. In the following guide I'm going to be showing...

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 i have no idea where those other charts came from, they are not mine

[feb1991blizzard]

4 minutes ago, mushymanrob said:

For snow you need all of these
500hpa vales of -27c or lower
850 values of -7c or lower
528 dam or lower
dew points of 0c or lower

according to this site
 

Basic Snow Forecasting Guide

UKWEATHER.WORDPRESS.COM

---

If you're looking how to forecast snow, then you've come to the right place. In the following guide I'm going to be showing...

 

You don't need all of those, they are kind of interlinked a little but, yes -7c is borderline even at 600ft in Saddleworth with WNW winds, however, i have got 3.5 inches of snow in the same location on 4th feb 2012 with uppers of -2c minimum from an encroaching trough, from the worst trajectory as well.

Edited November 30, 2020 by feb1991blizzard

[TSNWK]

3 minutes ago, Allseasons-si said:

No skakey,i would say it is fairly similar to this morning's run(00z)

168 v's 180

i think it's a slight upgrade with more of a neg tilted trough and slightly more amplified off the NE seaboard.

Yep.. flicking between both on iPad the 12z is a decent imporovment upstream.. 45 degree negative compared a pretty level upstream flow.. heights seem a little higher towards Iceland as well. Acceptable trends in my book

[Allseasons-Si]

5 minutes ago, mushymanrob said:

 i have no idea where those other charts came from, they are not mine

They appeared in my post too

[mushymanrob]

2 minutes ago, Allseasons-si said:

They appeared in my post too

ive tried deleting them but to no avail..

 

[sheikhy]

Gfs looking good at 72 hours!!!even further east than the 06z!!!!

[BlueHedgehog074]

More of a look in the short term over the next few days, using various 06Z GFS charts as an example. Included in these charts are: 500hPa + Sea Level Pressure, UK Precipitation, UK Precipitation Type, UK Max and UK Min Temperatures and 850 hPa temperatures. 
 

Today sees a disturbance from Low Pressure to the North-East of the UK sliding down South-Eastwards to the East of the UK. High Pressure close by to the South-West of the UK, but amplifies somewhat as a result of Low Pressure dropping down to our East. This is bringing a spell of rain South through the UK on some cool North-Westerly to Northerly winds. Mostly drier towards the South-West where pressure is higher, but even that part could see some damp conditions. 

 

This looks to clear all places by early Tuesday. Some clearer weather should follow for most places. However it looks like a cold night and morning to come. Temperatures getting into freezing levels over parts of Northern high ground, and a fairly widespread frost is likely. Milder towards far South-Western areas, particularly South-Western Ireland. 

 

A little ridge of High Pressure over the UK will keep the weather generally settled, with some sunny spells in places. Especially across South-Eastern areas. Tending to become cloudier towards North-Western areas. This is thanks to a deep Low across Iceland, which will steadily head South-Eastwards lowering pressure across North-Western areas of the UK, along with some strengthening winds.

It will be a slow(ish) process and some rain could reach some Northern and Western areas later into the day. Another cool day to come, but milder over Western Ireland, where temperatures could get into low double figures.

Another chilly night and morning to come, more especially over Central, and South-Eastern areas of the UK. Cold at first into the night over Northern England, but becoming less cold in that area over the course of the night as some rain over the far North-West sinks further South. Fragmenting as it does so. Less cool overall over Ireland and parts of Scotland. 

Onto Wednesday daytime, and the Icelandic Low Pressure and upper trough makes further progress South-East to the North-West of the UK. The Azores High Pressure amplifying upstream in the Western Atlantic near Newfoundland. A cool and showery Westerly flow dominates the UK, with some heavy blustery showers likely over Western and Northern areas. Mostly dry across Southern and Eastern areas, perhaps with the odd spot of rain.
 

 

These of which are likely to increase in frequency, some of which also likely to be wintry over high ground, as 500mb heights continue to lower from the North-West making the air more unstable. The milder wedge of 850 hPa temperatures over Central and Southern areas also slowly getting swept away further South-East. 

 

A very cold night in store for many areas and lingering into Thursday morning. Some very freezing temperatures over Scotland, particularly over the highlands. Some thick frost possible. Wintry showers, though, will continue over North-Western spots with a keen breeze. Temperatures a little above freezing further South, but under clearer skies, some frost even here is possible and temperatures could still get close to freezing at least.

 

Things do start to get a little uncertain as to exactly where any rain, sleet or snow could occur in the UK. But the tendency is to drop the Icelandic trough over the UK later into the week. Using examples again from the GFS 06Z model, it shows a very chilly day on Thursday. Temperatures perhaps somewhat closer to average across Ireland, Central and Southern areas of the UK. Cold further North, where temperature could remain around, or below, freezing over parts of Northern Scotland. 
 

With High Pressure becoming increasingly amplified in the mid Atlantic, along with some High Pressure over Russia and Scandinavia, this sends the upper (Icelandic) trough between those 2 areas of High Pressure South through the UK. Lowest heights over Western UK. The GFS does show a surface Low from the trough developing across Southern areas. 

A variable surface flow between the West and South at first, with some showers and longer spells of rain and hill snow over Western and Southern areas. But the flow turning more from the South or South-East across Eastern areas with that developing Low over Southern areas. Over Western UK, the flow backs more from the North-West as they end up being on the more Western flank of the Low Pressure.

Later into the afternoon and into the night, some heavier precipitation gets dragged up from the South covering Wales, Central and Eastern areas, which could become increasingly wintry. Main focus the wintry element across Western areas where the upper air is colder. Snow mostly over high ground I suspect, but some of the heavier bursts further West could help aid in evaporative cooling dragging some sleet or snow down to lower levels. This continuing into Friday. 
 

Freezing across North-Western areas during the night where it’s generally likely to be drier. Temperatures easily below freezing over many parts of Scotland. One of the coldest nights so far of the week. Perhaps a thick frost under any clear skies in that direction. Temperatures a little above freezing over Southern areas, and perhaps around freezing over mostly high ground of Wales under the sleet/wet snow/hill snow. 
 

 

Friday daytime will see further areas of rain, some of which again could be wintry over Western areas, and also Northern areas, especially over the hills. The precipitation pushing North to cover the Western areas of England, Wales and Scotland. Coldest temperatures again over these parts as well where the rain, sleet or snow is. The Low Pressure shifted a little to become centred over South-Eastern UK with the coldest 850 hPa temperatures continuing to spill Southwards down Western areas. Some of that helping out with making precipitation over the high ground of Western and Northern areas to be wintry. And perhaps again to some lower levels. A more milder sector towards Eastern UK. Pretty dry across Ireland maybe with some showers near Western coasts and a little drier towards South-Eastern areas of the UK.

 

Would say that although it may not be the ultimate snowy paradise, it looks chilly overall and there is likely to be some wintry weather around (mostly high ground, but some lower levels could see the odd surprise). Something that might get some of the cold weather fans jumping up and down a little with excitement, particularly if you’re one that lives on a hill. Though worth not setting your expectations too high, as we don’t want to have to clear up all the flying dollies on here. A drier day is likely tomorrow and towards the South-East on Wednesday. 

Despite the marginality of the setup, I think later in the week will come down to now casting as to where the areas of rain, sleet and possibly snow may fall, and where the distribution of the coldest 850 hPa temperatures and dew points are likely to be, which could affect how widespread any lower level wintry precipitation could be. 

Not on the level of 2010 (but that was pretty exceptional), but things do look more fascinating for the cold weather fans at this time of year, than they have done in the last few years. Maybe except December 2017, which was fairly wintry at times in some parts. 

(Edit: Sorry about the extra charts at the bottom)

Edited November 30, 2020 by DiagonalRedLine

[Allseasons-Si]

8 minutes ago, mushymanrob said:

 i have no idea where those other charts came from, they are not mine

Just go to edit and delete the un-appropriate images then click at the bottom of blank space,then backspace until you get to the bottom of your post,i've just done it.

[Allseasons-Si]

Just now, Allseasons-si said:

Just go to edit and delete the un-appropriate images then click at the bottom of blank space,then backspace until you get to the bottom of your post,i've just done it.

Edit:was they @DiagonalRedLine's images^^^

[Skullzrulerz]

1 hour ago, Radiating Dendrite said:

Can we get away from this cold air myth. We have the ECM showing a possible snow event this Friday.

We do not need -10c 850s for snow. Yes, it is great when they come along but you can get snow from 0c 850s under the right synoptic conditions.

Nobody is forecasting 100cm of snow, just commenting on the runs and continued build up of higher pressure in the Greenland locale.

Fair enough let's hope you are correct then

[Tim Bland]

Nice jog south east

Edited November 30, 2020 by Tim Bland

[SMU]

All those snow variables are important but crucially they can be watered down to more modest values -

Over riding factors.

* Air mass the PPN is falling into as a cold dry airmass has a shallow melt layer with low saturation rates where as milder airmasses are saturated... Hence it can snow at 4 degrees in a northerly flow as opposed to rain along a warm front at 1c.

* PPN intensity is a big factor as the heavier PPN brings the zero degree level down & where you might see snow at 300M > a heavier burst will bring this Zero level down to 100M

* Evaporational cooling > is a classic UK scenario where the dynamics take the latent heat from the air & cool it.

* Elevation > About 0.7c loss per 100M for the Uk airmasses & where they come from ( Polar Nw ) as much as 1c per 100M in true polar northerlies..

So living at 200M is significantly more advantageous than sea level

The most prolific unexpected heavy snow events occur when the parameters in the posts above are the wrong side of marginal however the above metrics over ride the base state which may indicate rain only...

Edited November 30, 2020 by Steve Murr

[Tim Bland]

I bet a lot of southerners will be happy with this run. Perhaps the Cotsworlds is the place to be

[Allseasons-Si]

UKMO identical to this morning's at 144

slight differences being the heights to our E/NE are a bit stronger.

[Allseasons-Si]

Is it me or is that Scurasian high getting stronger with each run?

if we can get sufficient energy heading more SE then it won't take much tweaking to get a good easterly. 

[sheikhy]

What more can we ask for of you looking for a surprise snowfall somehere at the end of the week!!ukmo and gfs further east now and the lows are not as deep!!in a col situation with low thicknesses i expect temperatures to get pretty cold especially by night!!

[northwestsnow]

UKMO looks cold to my amateur eye !

I spy wedges!!

Edited November 30, 2020 by northwestsnow

[BlueHedgehog074]

21 minutes ago, Allseasons-si said:

Edit:was they @DiagonalRedLine's images^^^

That’s really bad, have no idea how that has happened. I’ve not touched or edited Mushy’s post at all, so that is really strange. Paul probably knows though as he had to hide mushymanrob’s post.

[Methuselah]

8 minutes ago, Allseasons-si said:

Is it me or is that Scurasian high getting stronger with each run?

if we can get sufficient energy heading more SE then it won't take much tweaking to get a good easterly. 

It sure looks that way, Si... We just need it to attain a shape/orientation that'll cut off that supply of very warm air, which is now beginning to irk me somewhat!

Edited November 30, 2020 by General Cluster

[Allseasons-Si]

1 minute ago, DiagonalRedLine said:

That’s really bad, have no idea how that has happened. I’ve not touched or edited Mushy’s post at all, so that is really strange. Paul probably knows though as he had to hide mushymanrob’s post.

Yes,didn't  know how that happened and never before has it happened,very strange.

[BlueHedgehog074]

2 minutes ago, Allseasons-si said:

Yes,didn't  know how that happened and never before has it happened,very strange.

I’ve tried removing them all from his post successfully, and have unhidden @mushymanrob’s post as a result. (Assuming the extra images was the reason the admins hid his post in the first place, but I’ll check with the admins on that)

[Tim Bland]

Did anyone post the snow depths from the GEM yet

[Matt H]

Not as good as previous runs.

Edited November 30, 2020 by Frosty Winter

[Allseasons-Si]

7 minutes ago, Frosty Winter said:

Fairly poor GFS 12z unless it improves in the extended range.

it would certainly give you your username...

[Downburst]

The current pattern is in my view pretty close the the La Nina average anomaly as below, so I wouldn't be surprised to see this rinse and repeat until end December at least. I am not following AAM very often, but it is expected to continue negative average negative trend to back this up. So a low anomaly to our south and chances of northerly or easterlies on occasion, getting colder as December progresses.

This is the "typical" La Nina pattern

Current Pattern