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Model output discussion - proper cold spell inbound?


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Evening All  Ice Cold hope your still with us .... So the much touted SSW is coming into view & here’s my thoughts + timelines of when / where to expect it... We have seen lots of p

Well it's probably fair to say that I've been rather quiet on these forums for the last few years really, especially since 2013. After 15 years of internet weather watching, and more importantly,

Well - ho hum - let's have a sit rep. My eyes are hanging out on stalks.  The pacific first - engine of the climate system. How is our AAM looking in the face of the current high amplitude MJO?

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10 minutes ago, Jonathan Rhodri Roberts said:

Some very low windchill charts next week on the GFS but just how reliable are they? I'm currently in Merthyr Mawr on the S Wales coast (shown in the red circle) for example and it shows 2C however the sun is out with very light winds and I've had to take my fleece off as it feels very mild. So personally I wouldn't rely too much on them. Therefore next week while the thermometer is low the "feel like" temperature could be considerably milder if the sun is out and the winds are light with the sun now rapidly gaining strength again at this time of year as well as the daylight hours becoming longer. 

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Tbf you can never calculate a windchill temperature from a chart. The only accurate way is measure the actual 'in the shade temperature' against the wind speed where you're at and then work it out using the formula. After all some streets, bays, beaches etc... can often feel mild or even warm while others exposed to wind can feel cold or very cold even if it's just yards away! 

Edited by Dafydd Tomos
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4 minutes ago, Ed Stone said:

The 30-dayer didn't mention an SSW at all, shotski - just that there's a chance of very cold continental air coming our way, around mid month. :santa-emoji:

I don't think it would mention what happens in the stratosphere. Just what the conditions are likely to be on the ground.

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5 minutes ago, MattStoke said:

Check the tweet from IF I posted in the News/Media thread - 

 

That’s good to hear, as the cold spell next week is rapidly getting watered down run by run. Time to start looking for strat influences in the output!

ps Don’t forget the Model Tweets thread. 

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9 minutes ago, Dafydd Tomos said:

Tbf you can never calculate a windchill temperature from a chart. The only accurate way is measure the actual 'in the shade temperature' against the wind speed where you're at and then work it out using the formula. After all some streets, bays, beaches etc... can often feel mild or even warm while others exposed to wind can feel cold or very cold even if it's just yards away! 

Just to add, they can also underestimate the temps as well from the temperature being lower or the wind being stronger than forecasted. Dafydd is spot on though with the only way to accurately measure windchill for where you are. Same goes for humidex (temp & humidity) and also for the heat index in the summer some PWS take in consideration the current temp, humidity, solar strength & wind to give the accurate feel like temperatures (often abbreviated to THSW) 

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41 minutes ago, MattStoke said:

Higher res models also show snow showers/flurries getting right across England and Wales on Sunday and Monday. So could be a few surprises.

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Rain in Kent. JOY!!

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Afternoon all :)

I won't do a full medium term model summation but irrespective of the next 96-120 hours which I'll leave to others, I've never seen much prospect of a continued cold period without any kind of less cold/milder interlude. That seems more and more likely in the form of a stormier and unsettled spell around mid month as the Atlantic stages what is, I believe, its last hurrah.

So after this week's cold spell a general easing into mid month and then 7-10 days of Atlantic weather before the next big pattern change which is being well signalled in the MJO, the stratosphere and elsewhere. The manifestation of that pattern change isn't anywhere near settled but plenty of the GEFS in far FI are looking at height rises to the north and east. The key is or will be the decline of the Atlantic as the influence of the split vortex lessens. None of that guarantees cold weather or snow - we could easily finish up dry and cold or even dry and very mild - but we are much more in the game than if facing a relentless PV.

One thing is certain - model watching won't be dull this month.

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Tweets from I.F a few days back coupled with model support for much colder weather as we go through next week with risk for disruptive snow has been somewhat muted now. I am convinced this change is due to the overriding forcing and downwelling from the strat.  If the strat profiles are anywhere near correct they  show the possibility of part of the polar vortex dropping into central Europe and the split to the north and northeast of the UK. The transfer of energy will mask the teleconnects for several days.

Without the strat forcing we may well have seen a cold, very cold spell for a week of so but the possibilities of what could be around the corner may well be far more potent and severe.

Edited by comet
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Yes didnt think it would be long b4 warning flags.

I could post around 9 of my previous posts over the last 3-days to support this evolving probability,..

But will refrain...they will only be frowned upon anyhow.

Regarding models states/situ- its still a very complex position on tweaks exactions and prognosis after monday atm.

We need to keep close eyes on both mild sector twists and the AZHP- progress and align...all in all some very interesting stuff.

Edited by lorenzo
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2 hours ago, Ed Stone said:

I'll be interested to see just how the models handle the expected SSW, and whether it's that that's making the MetO suggest a possibility of very cold easterlies around mid-month? Ought we be looking for some kind of cross-model trend, in the far reaches of FI

Or, might a twenty-thousand-strong flock of flying pigs be closer to the mark?:cold-emoji:

I prefer your first thought Ed! Very significant percentage of this morning's GFS ensembles showing height rises to our North East with some sort of Easterly occurring in FI. As @Summer Sun has reported in the METO thread, :db:"a greater chance of easterly winds, potentially bringing some very cold weather" fits in with those longer term synoptics very well. Cold week, most models backing the trough disruption back West this morning, widespread confidence of forthcoming SSW, growing doubt over current spell breakdown next weekend, GEFS T850's trending downwards again, ECM op a significant outlier within its ENS. Next week might have backtracked quite a bit from the amazing charts on the pub run a few nights back but all is certainly not lost, not by a long stretch. I have a good feeling about the 12z suites for the next few days.

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Well what a fascinating week it has been model watching.This time last week tbh there was very little evidence of a cold spell/snap showing for period starting tomorrow.Then from Monday-Thursday the models started trending colder and as the UKMO seemed to be fairly bullish i think some people were jumping on Cold means snow wagon-This last point is understandable as some parts of the South have waited 5 years since their last significant snowfall.However,since late Thurs the models have trended away from what looked like a potential significant cold and possibly snowy spell to a rather muted one.Of course things could trend colder again as the models are really playing a Jekyl & Hyde game atm but my point being is that as that wise gentleman John Holmes has said on many occasions dont look further than t+144hrs and that is a push at the moment.

FWIW i think the next 7 days could be the "starter" for coldies and whilst it might not deliver much in the way of nationwide snow, some local areas may look picturesque with a light covering.I really do believe that with teleconnections,low solar minimum,a probable strat warming and other factors working in a positive way then we are approaching our best chance of a proper cold spell possibly similar to those we had in 2009/10/11 winters.If that doesn't occur then you have to say the UK has been dealt another [email protected]&p hand.Either way the Model watching is going to remain great to view with so many great comments from so many knowledgeable posters.Enjoy it guys and girls!!:good: 

 

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2 hours ago, ALL ABOARD said:

I will just leave this here to cheer everyone up. 

First signs of SSW starting to show up? 

 

 

Is there a good basic explanation of SSW and the implications thereof? I'd really appreciate a good basic-level "SSW 101" to read, if anyone can point me to one!

Also, does anyone know if certain models are more reliable or less reliable with regards to SSWs? Or are they all about the same?

Many thanks... trying to learn as fast as I can, but there's so much to learn!

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1 hour ago, bradythemole said:

Hi Res Arpege 6z at +72

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GFS 6z + 72

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Everything just a little further west on Arpege. Cold fighting back a bit harder and the block to north east also slightly closer to the UK than on the GFS. May make all the difference come Thursday...

I'm sure I've read before that the short term Arpege is thought of in high regard? Can anyone confirm this?

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3 minutes ago, captaincroc said:

I'm sure I've read before that the short term Arpege is thought of in high regard? Can anyone confirm this?

Very much so the French model. 

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My take on the models is that if you're in the East/South-East, you're not going to have to worry about warm sectors and anything falling out of the sky between tomorrow and next Friday will be snowfall. The mean stays around -5c or just below for almost the entire run

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If you're say, West of perhaps the Midlands (including the Midlands, actually) then you might have more of an issue when it comes to warm sectors and may not necessarily see all snow, but more wintry/wet at times.

But, for once the South-East is in a prime location, whereas everywhere else that has seen decent snow so far this winter/the last couple of years might not be.

 

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I find this upcoming cold spell quite underwhelming. The cold pool over Europe will not be as strong as previously advertised by models and the slack flow won't really do much - grey, dull weather. Hopefully few days without above freezing temps are on the cards but snow will be scarce (I guess you guys in UK will see much more of it). Still a nice change since February was mostly a spring month these past few years.

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