Model output discussion - deep cold inbound?

[Kasim Awan]

17 minutes ago, Ben Sainsbury said:

I see that the EC uses the Kuchera ratio? Is this ratio constant throughout or does it vary depending on the atmospheric conditions?

If it is constant, say rain 1:10 snow, then chances are accumulations could be even higher?

The Kuchera ratio takes into account sub 850mb temperatures to determine the ratio. To, of course, lower temps = higher ratio. So it is probably more accurate than the standard 1:10 in cold conditions.

For this reason, if the model is forecasting lower temperatures than it should, which don't verify, using the Kuchera ratio can lead to too high snow accumulation forecasts.

Edited February 4, 2021 by Kasim Awan

[Nick F]

6 minutes ago, Yarmy said:

That's Ryan Maue's weather business, isn't it?  I'm not sure whether he's applying the Kuchera method to the raw ECM output, or that's what the model itself is predicting? 14.4 inches seems like...a lot.

Yes, something not right with the Kuchera algorithm being used for that chart I posted, a look at the 10:1 ratio in centimetres seems more accurate, though even that seems a lot:

 

[georgiedre]

35 minutes ago, Battleground Snow said:

Indeed very impressive 850mb temps, especially in the north by sunday morning

GFS attached for same time in this format, can see a difference in the south east

 

Very warm on West Coast of Wales lol. Wtf is that about 

[knocker]

9 minutes ago, Yarmy said:

That's Ryan Maue's weather business, isn't it?  I'm not sure whether he's applying the Kuchera method to the raw ECM output, or that's what the model itself is predicting? 14.4 inches seems like...a lot.

That's a WeatherBell charrt so Kuchera

Edited February 4, 2021 by knocker

[Nimbusman]

21 minutes ago, Nick F said:

06z EC showing a lot of snow for E Anglia and into the northern Home Counties as well as the NE by the end of the run / Monday morning

Wow that’s an incredible amount of snow Nick! Is that frontal or showers banding together?  If that comes off we won’t of seen snowfall in this part to the UK since Feb 91... nearly 30 years to the day! 
 

*edit

Just sorry saw your reply so could be faulty data then? 

Edited February 4, 2021 by Nimbusman

[Downburst]

Well the SE of England is primed for the best place to be to start this all off. Looking at ICON-EURO short range, kicks off Sunday morning about 2.00 am

It then continues all morning, at Midday you have this, all morning and more to come. Will be interesting.

[Kasim Awan]

Just now, Nimbusman said:

Wow that’s an incredible amount of snow Nick! Is the frontal or showers banding together?  If that comes off we won’t of seen snowfall in this part to the UK since Feb 91... nearly 30 years to the day! 

I think totals in the order of Feb 1991 are not completely unrealistic given the extent of cold and duration of the unstable flow. The algorithm is malfunctioning on that website, or at least that is total falling snow equivalent and not accumulation as it shows snowfall over the sea.

[Nimbusman]

1 minute ago, Kasim Awan said:

I think totals in the order of Feb 1991 are not completely unrealistic given the extent of cold and duration of the unstable flow. The algorithm is malfunctioning on that website, or at least that is total falling snow equivalent and not accumulation as it shows snowfall over the sea.

Thanks Kasim, just saw Nicks reply too. I’ll remove the plastic sheeting from the chair for now! Still looks like a long period of snow around here regardless. This synoptic set up is as rare as hens teeth and traditionally EA does well out of it so let’s see how this pans out. All eyes on the short range higher resolution models from tomorrow 

[Paul]

5 minutes ago, Downburst said:

Well the SE of England is primed for the best place to be to start this all off. Looking at ICON-EURO short range, kicks off Sunday morning about 2.00 am

It then continues all morning, at Midday you have this, all morning and more to come. Will be interesting.

Those charts don't look right, it won't be rain falling across northern Britain..

[Kasim Awan]

Snow ratio changing with temperature. Once temps reach the mid 20s F, ratios of 1:15+ are possible given less drifting. The rate of ratio change then drops off into 10s F as the way snow pellets are formed at those temperature means there is less aeration.

[Don]

2 hours ago, kold weather said:

GFS ensembles are really struggling to get the first LP too far north, and sliding it off to the east.

This is a mixed blessing, it keeps the country in colder air for longer BUT the upstream low I've got to admit looks beefy. I suspect regardless of what the 1st low does (IMO it may well slide over the SW and into the channel) the 2nd one will come through like a steam train, and if thats the case it may be a literally leading edge snow-rain event, especially the further south you are.

That's still a long way off though and likely to change one way or another?

[Kasim Awan]

1 minute ago, Paul said:

Those charts don't look right, it won't be rain falling across northern Britain..

There is a function in the algorithm which uses precipitation intensity to determine precipitation temperature. This is clearly over amplified in the model algorithm.

[AmatuerMet1963]

Finally both ECM and GFS seem to be on same page as todays longer range forecast from Susan Powell from the BBC earlier today. Both models have been very far apart recently but todays Windys shows not a lot of difference for Saturday this week.  I recently noticed a good comment from an animal lover and bird enthusiast about noting nature pointers, which mainly are actually more  certain than computers. This morning at 8am, I saw what looked like a scene out of "The Day After Tomorrow"  , many flocks or skeins of birds were filling the sky at around 1000 feet.    That's unusual for this time of year.   I dont have to tell you what heading they were on do I.???...yep WEST out to the coasts of Blackpool or Liverpool or even Ireland. Where the freeze will be tempered some what by the mini climate that surrounds North West Britain. The small birds remain to be feeding heavily in our gardens, and will totally rely on us to keep them alive through this 10 day freeze. see more about saving your garden birds at the RSPB site!!!

So here are the two maps from ECM and GFS for one day this weekend.  Theres also a huge low pressure system 952mb with very tight icobars off the Atlantic.  GFS has it sinking south, while ECM has it steady increasing the chance of blizzards almost anywhere as mean winds are associated with is up to 27mph.... I will still need to see it in Lancashire to believe snow will fall,  But Im more hopeful than a few days ago, But honestly this will possible cripple the covid vaccine turnout, if towns and citys get heavy snow, along with stranded vehicles and other problems. Spare a thought for Amanda Owen and Clive at the Yorkshire farm afar at Ravenseat, where most of my relations live not far on the high town called "Richmond", off scotch corner,M1 A1. they have already sent snaps to us off vast mounts of snow over 7-8 days already.

Below, both models are agreeing to wintry weather by  Saturday the 6th February.  BBC weather seems to be following more or less the ECMS tracking.  To my mind the GFS seems to make a poor job of creating a coherent forecast.. that flies in opposition of other mainstream sources. stay safe and get your sledge bought before they all sell out!!!

[bluearmy]

the 06z ec op brings the low countries low back closer to kent which increases the snowfall totals and edges a little further west (to T90)

[TSNWK]

2 minutes ago, bluearmy said:

the 06z ec op brings the low countries low back closer to kent which increases the snowfall totals and edges a little further west (to T90)

Increasing the risk of less cold air for a time and marginal?

Edited February 4, 2021 by TSNWK

[ITSY]

27 minutes ago, Nick F said:

Yes, something not right with the Kuchera algorithm being used for that chart I posted, a look at the 10:1 ratio in centimetres seems more accurate, though even that seems a lot:

 

Goodness me I hope this is right. I'm like a child with giddy excitement looking at that chart! With the GFS, GFSP and UKMO all going for variations on a theme, this is almost too good to believe for my own backyard. Plenty of interest for all in the entire eastern half of the country though with an outcome like that...


 

[Paul]

Lots of posts being moved over to the chat thread currently - we all need to muck in here to keep things running smoothly during what's going to be a very busy time, so if your post isn't discussing the model output, please don't make it in here. 

https://www.netweather.tv/forum/topic/94934-winter-202021-chat-ramps-moans-and-banter/?do=getNewComment

 

[bluearmy]

8 minutes ago, TSNWK said:

Increasing the risk of less cold air for a time and marginal?

yes its a little less cold into e kent but away from the coast it stays ok for dp's and uppers (-6c i/o -10c)

i expect this will swing back and forth between runs for a while

[ITSY]

Just to build on that. There are a few models still flirting with a much less profound snowfall for inland areas of Eastern England *away from Norfolk/Suffolk coast* on Sunday/Monday. ICON, Arpege to name two - and UKMO looks unclear to my eye. But with majority backing, I'd continue to use the big globals until Friday evening when hopefully the HRES models will start to run with the better option for many...With the ECM 06z copying the GFSP and others I'm cautiously enthused...

 

[danm]

4 hours ago, DAVE_ALLEN said:

Notice the dry area where the upper level cirrus/stratus spreads out from the frontal snow further south east. This cloud shield often prevents the development of showery activitiy 

It would temporarily, but as that front continues to move off into the near continent shower activity will pick up in the cloud shield area you've identified. 

[kold weather]

That ECM chart probably is too high for the UK, you could probably shave 20-25% off those values.

EVen then your still looking at 8-10 inches in peak zones.

Interestingly, this matches up fairly closely with the GFSP on the 06z:

[Kreftysoton]

4 minutes ago, kold weather said:

That ECM chart probably is too high for the UK, you could probably shave 20-25% off those values.

EVen then your still looking at 8-10 inches in peak zones.

Interestingly, this matches up fairly closely with the GFSP on the 06z:

Sounds about right! Southampton has a grey gap with no measurement lol

[snowlessayr]

The thing with snow depth charts s they often overplay snow depths in frontal situations but underplay convective massively. Therefore it may even it out in this situation. 

Even if it is out most places in southeast England will see a fair bit I think. Sadly unlikely I will, as my area doesn't do well in these setups.

Enjoy everyone 

[Cold Winter Night]

17 minutes ago, Kasim Awan said:

Snow ratio changing with temperature. Once temps reach the mid 20s F, ratios of 1:15+ are possible given less drifting. The rate of ratio change then drops off into 10s F as the way snow pellets are formed at those temperature means there is less aeration.

 

The Kuchera Method has separate formulas to calculate the ratio. One for Tmax over -2 celsius (+/-) and one for under -22c.

Greater than -2c: Kuchera Ratio = 12 + 2(271.16 - Tmax)
Less or equal to -2c: Kuchera Ratio = 12 + (271.16 - Tmax)

Tmax is taken from the lowest 500mb above the surface and is entered in Kelvin.

To get the amount of snow, you would multiply the calculated amount of precipitation with the derived ratio.
I wonder though, would this American method, taken from the heart of a big landmass, apply equally in our climate?

However, these methods do not take into account some surface characteristics that will also influence how deep the snow accumulation will be. E.g. soil temperature and humidity, soil cover and vegetation, local windblown accumulations, whether there was snow on the ground already, etc.

All these factors, besides the strictly meteorological ones, have great influence on the snow accumulation on one's own doorstep.

(Personally, I enjoy studying the changes in the snow cover when it stays for more days ( how often do we get that opportunity?))

[chris pawsey]

Can I ask, when do people consider FI to be now?