Model Output Discussion 12z 20/04/13

[SP1986]

Purga to my eyes that setup did not produce -9.4C.. Ive checked records and cannot find anything anywhere for that date.. you'll have to show us some proof. There have been lower temperatures than -6C yes, but not in the places shown by the GFS

 

On the other hand, there is, as yet, no evidence to suggest a widespread warming up after the initial northerly has disbanded. An easterly is, to agree with others, not the best result. Especially if from a northeast quarter. 

Edited April 24, 2013 by SP1986

[Purga]

Purga to my eyes that setup did not produce -9.4C.. Ive checked records and cannot find anything anywhere for that date.. you'll have to show us some proof. There have been lower temperatures than -6C yes, but not in the places shown by the GFS

 

On the other hand, there is, as yet, no evidence to suggest a widespread warming up after the initial northerly has disbanded. An easterly is, to agree with others, not the best result. Especially if from a northeast quarter. 

http://www.metoffice.gov.uk/climate/uk/extremes/monthly_temperature_country.html

 

Just Select 'Lowest Daily Minimum temp for England

 

 

 

Edited April 24, 2013 by Purga

[Frosty.]

Looking at the latest ensemble mean maps from the gefs and ecm 00z, there is very good agreement on anticyclonic weather gaining the upper hand and eventually taking total control of the uk for a prolonged period, the ecm ens mean builds the anticyclonic spell faster and doesn't really show the trough to the northwest of the uk later next week, longer range, the gefs looks very settled for all areas with a summery spell on the way.

[Gibby]

Looking at the latest ensemble mean maps from the gefs and ecm 00z, there is very good agreement on anticyclonic weather gaining the upper hand and eventually taking total control of the uk for a prolonged period, the ecm ens mean builds the anticyclonic spell faster and doesn't really show the trough to the northwest of the uk later next week, longer range, the gefs looks very settled for all areas with a summery spell on the way.

I would agree with most of that but my main concern is the Wetter version of the ECM 240 hr mean chart showing a weakness to the NW and more concerning is the Jet flow across the UK instead of further North between Scotland and Iceland.

http://www.wetterzentrale.de/pics/Reem2401.gif

[Frosty.]

Gibby, on 24 Apr 2013 - 12:36, said:

I would agree with most of that but my main concern is the Wetter version of the ECM 240 hr mean chart showing a weakness to the NW and more concerning is the Jet flow across the UK instead of further North between Scotland and Iceland.

http://www.wetterzentrale.de/pics/Reem2401.gif

That's a very good point Gibby, my own thoughts are that the weakness to the northwest of the uk will eventually drift away northwestwards towards iceland/greenland and allow anticyclonic weather to take complete control of our weather for much of may and slowly becoming warmer which will firstly reduce and then remove the threat of damaging frosts, the gefs 00z mean looks excellent in the further outlook, perhaps there is light at the end of the tunnel for folk in the northwest of the uk who are being continually hit by atlantic lows.

[mushymanrob]

Really? This chart on 11th May in 1941 produced a record low nightime temp of -9.4C

 

It looks a lot less potentially cold than some we are seeing.

 

 

how odd... i cant see for the life of me how that chart could give a overnight -9c .

however, it matters not, pointing to some anomaly from 70 years ago isnt proof that -6c is iminant here with this expected cool down. im NOT saying that we cannot get -6c at this time of the year, just that its ridiculous to suggest we will given the current synoptics. and im not talking about some scottish mountain top, im talking broadly for a good swathe of the country.

[Summer Sun]

I'm surprised we got a low of -9.4c from that chart Purga posted considering what the uppers were at the time

 

[Geordiesnow]

The problem with the output is that for the most part, whilst it will turn cooler, apart from fronts moving across the country, it should be fairly sunny but if the low next week stalls and does not head far enough eastwards then the outlook will turn more cloudier, wetter and the outlook will be a bleak one. So the irony is that we should be encouraged if the models show colder uppers as that way the chances of sunshine being more widespread will be higher. 

 

Problem with this time of year though is that cold air and the strength of the sun will have cloud bubbling up inland and if the ingredients are not good enough for clouds to get higher to form shower clouds, then they will turn flat into stratus cumulus so you get the case of a sunny morning and a cloudier afternoon and with a Northerly wind that won't feel too pleasant. Fortunately it looks like this won't be the case on Friday and an interesting convective day is certainly on the cards.  

 

All in all, A cool outlook but at this moment in time, quite a bright outlook but this may change as we head into next week if the low struggles to head Eastwards and starts to become all flabby and messy. 

[Frosty.]

The best part of today's met office update is the last part :-

 

There are then signs of it gradually turning warmer and more settled towards the end of the period

 

This all ties in with the latest ens mean charts I posted earlier and the met office have now firmed up even more on the extended outlook for the majority of may for it to become settled, just a hint of less settled weather returning by late may.

[SomeLikeItHot]

I'm surprised we got a low of -9.4c from that chart Purga posted considering what the uppers were at the time

 

Surprising but it was in Norfolk which is about the only place in England with negative uppers (just negative) on that chart.

 

The MEt office summary of May 1941 says of the period (start of May) "Dry cold weather prevailed for the most part with frequent ground frosts." It gives a low of 15F at Thetford on the 4th and 11th.

http://www.metoffice.gov.uk/media/pdf/d/4/May1941.pdf

Edited April 24, 2013 by SomeLikeItHot

[NeilN]

I honestly think this is the end of the cold. Its looking positive and in my eyes we are in for a half-decent summer.

[shaky]

I'm surprised we got a low of -9.4c from that chart Purga posted considering what the uppers were at the time

Maybe the air was extremely stagnent which helped the temperatures to dip very low during the night time !apart from that i dont know what could cause the temps to go that low at that time of the year!!inversion comes to mind i think!!

[Methuselah]

Or, the dew point was extremely low? Which doesn't look likely to be quite the case, from what today's models are suggesting. Or is it?

Edited April 24, 2013 by Rybris Ponce

[mushymanrob]

Surprising but it was in Norfolk which is about the only place in England with negative uppers (just negative) on that chart.

 

The MEt office summary of May 1941 says of the period (start of May) "Dry cold weather prevailed for the most part with frequent ground frosts." It gives a low of 15F at Thetford on the 4th and 11th.

http://www.metoffice.gov.uk/media/pdf/d/4/May1941.pdf

 

maybe very isolated frost pockets... but its hard to comprehend the seemingly conflicting data..

 

... but as atm theres no chance of that happening given current outputs.

[SP1986]

I honestly think this is the end of the cold. Its looking positive and in my eyes we are in for a half-decent summer.

 

You'd have to ask some serious questions about our climate and where it's heading if we stayed cold and frosty onwards towards June.. that said it can still be cold at this time of year. The charts next week have maximas here between 7-8C below average at times which is actually significany below average, and for the time of year would qualify as very cold. Certainly frosty nights would qualify as very cold, at this time of year minimas should be around 6-7C, yet here we are due to get 0 to -1C in some parts, which is again 6-7C below average.. this alone could take the month a few points of a degree below average..

 

Ive lost count of how many months have been below average thus far!

 

But the pattern to me suggests a very slow recovery back to normal temperatures, with things becoming quite static. If cold air gets trapped in high pressure then there's a low chance it could be June before we get back to normal, but at the moment, probably mid-May.

 

The one thing we must do though is continue to be very suspicious of the the GFS temperature predictions.. I saw -8C for northern Spain in the 6z.. there must be a corruption in data somewhere in the GFS algorithms.. I think that's fairly obvious now and cannot be defended or looked over anymore.

 

ps it's not unusual for the southeast to get the most severe frosts going into May, but it just doesn't occur widespread or anywere else in the country.

Edited April 24, 2013 by SP1986

[jethro]

The Royal Horticultural Society advice has always been to wait until all chance of frost has passed before planting out tender bedding - their general view of this point is, and always has been, the end of May at the earliest. If we're still getting frosts in June, then it's time to panic.

[Frosty.]

This fax chart shows a window of fine weather for southern britain on sunday so it could be similar weather to what the london marathon had last sunday which was dry with plenty of sunshine, rain clearing southeast through scotland into northern england and becoming windier and more showery across the far northwest, this sets the scene for the first half of next week which looks rather cold with sunshine and showers, some of which will be heavy with hail and thunder and cold enough for frosty nights and accumulations of snow on northern hills and mountains, mostly in scotland. Beyond midweek we should begin to see the first signs of improvement which will eventually take us into a prolonged settled and gradually warmer spell.

[Purga]

You'd have to ask some serious questions about our climate and where it's heading if we stayed cold and frosty onwards towards June.. that said it can still be cold at this time of year. The charts next week have maximas here between 7-8C below average at times which is actually significany below average, and for the time of year would qualify as very cold. Certainly frosty nights would qualify as very cold, at this time of year minimas should be around 6-7C, yet here we are due to get 0 to -1C in some parts, which is again 6-7C below average.. this alone could take the month a few points of a degree below average..

 

Ive lost count of how many months have been below average thus far!

 

But the pattern to me suggests a very slow recovery back to normal temperatures, with things becoming quite static. If cold air gets trapped in high pressure then there's a low chance it could be June before we get back to normal, but at the moment, probably mid-May.

 

The one thing we must do though is continue to be very suspicious of the the GFS temperature predictions.. I saw -8C for northern Spain in the 6z.. there must be a corruption in data somewhere in the GFS algorithms.. I think that's fairly obvious now and cannot be defended or looked over anymore.

 

ps it's not unusual for the southeast to get the most severe frosts going into May, but it just doesn't occur widespread or anywere else in the country.

OK SP I won't post any further anecdotal archive charts to challenge your assertion (which I could) as this is more about current model output in this thread, I guess.

There does IMO remain a reasonably strong chance that a fair number of places across the UK could be seeing a fairly sharp frost or several in the upcoming period.

From the point of view of those wishing to care for or plant tender plants it is worth highlighting isn't it?

Edited April 24, 2013 by Purga

[SP1986]

Well the last frost is a very regional thing, with high pressure settling over the UK you would expect frosts inland, but coastal frosts are very rare in May, so those hoping to plant tender plants in inland areas are dreamers anyway for a start, but it's far different in coastal areas.

 

Talking in these terms, on the other hand at this time of year, you're more likely to get the coolest maximas in coastal areas (but also the highest minimas)

[SomeLikeItHot]

Given that is what we are talking about its worth mentioning that the 12z suggests some widespread frost on Sunday morning!

 

[Summer Sun]

GFS is showing a weak ridge of high pressure building during next week

 

 

UKMO shows something similar at the same time

 

Edited April 24, 2013 by Gavin.

[snowking]

I think we need to hang fire for a while yet in terms of the outlook beyond day 10.

 

The 6-10 day 500mb anomaly means paint the picture pretty well:

 

 

I guess we can call that a displaced Sceuro trough - whatever you want to call it, its likely to result in a mostly unsettled phase of weather for the UK.

 

Some hope from the North American models perhaps of something more settled in the 11-15 day range:

 

 

But in all honesty, its not an especially strong anomaly signal just yet, so we will have to wait a few more days yet to see where we stand on this.

 

The most recent EC32 update suggested a continuation of the slight below average temperatures - heres the TMax projections for Birmingham:

 

 

And here's the last 5 ensemble mean Tmax values for Glasgow:

 

 

As you can see from that, nothing spectacularly warm projected, with values around 12-13c from the May the 4th (be with you) onwards.

 

So, in the shorter term, our baseline summer pattern with that Sceuro type trough dominating proceedings for the UK (though the chance of course of a temporary ridge of high pressure once again towards next weekend). Beyond that the American currently pointing towards some sort of Euro pressure build, though this should be taken with a pinch of salt for a few days yet until we see a stronger anomaly signal develop, or indeed see the ECM start to become interested - GFS/ECM combo is pretty useful at such range, where as disparity breeds uncertainty

 

SK

Edited April 24, 2013 by snowking

[mushymanrob]

The Royal Horticultural Society advice has always been to wait until all chance of frost has passed before planting out tender bedding - their general view of this point is, and always has been, the end of May at the earliest. If we're still getting frosts in June, then it's time to panic.

 

indeed, when i was doing my apprenticeship in the 70's we were taught that you never plant out summer bedding/ frost tender until the first week in june.

 

From the point of view of those wishing to care for or plant tender plants it is worth highlighting isn't it?

 

but mate, all you ever do is post or highlight the coldest possible solution, so tbh its like the boy crying wolf.

 

nobodies denying that theres a very strong possibility of frosts, just the severity which is unclear as the exact synoptics are as yet unknown.

[ANYWEATHER]

Looks very chilly into the 1st day of May with dewpoints around freezing during the daytime period. Any precip could well be wintry and not just on high ground!  

[Summer Sun]

GFS is now backing away from a pressure rise and is developing a deep low later next week bringing a spell of wet and windy weather

 

 

This isn't something which has had support lately so this could well be an outlier

 

First full week of May still has the pressure rise

 

 

Given that its showing an easterly flow cloud amount could prove troublesome at times

 

 

Snow for southern England as we enter May?

 

Edited April 24, 2013 by Gavin.