Model Output Discussion - 15th April Onwards

[Thundery wintry showers]

The present setup with slow-moving low pressure is rather less common in mid to late summer than during spring and early summer because traditionally the jet powers up at some stage during June (hence "June return of the westerlies"), although it isn't unknown, e.g. August 2004 had a lot of slow-moving low pressure around our vicinity and a weaker jetstream than is usual for August.

However, next week's setup does rather remind me of the "Atlantic trough, Euro high and suppressed Azores high" setup that often characterises hot thundery months. I mentioned that in high summer (July/August) the jetstream tends to be stronger, but when low pressure systems track into the mid-Atlantic and are then deflected sharply northwards as they approach the meridian, we can get the same effect with a train of depressions heading towards northern Scandinavia, weak troughs being left over to the W/SW and high pressure filling in the gap to our east. For those unsure of what I mean, check out the Wetterzentrale synoptic archive for July 1994 which was a particularly stark example.

The one potential difference here is that the majority of model outputs have us strongly under the influence of the Atlantic trough next week, which will perhaps restrict the extent of possible heat and thunderstorms. Continuing on the theme of summer months, though, June 2003 was one such month where the Atlantic trough largely dominated proceedings, but many parts of the country still ended up warm and sunny with some thundery outbreaks.

[Summer Sun]

GFS 12z

Unsettled for the next 7 or 8 days, then high pressure builds as we end April and enter the final month of Spring

http://www.null/ds/gfs.htm

[azores92]

GFS 12z

Unsettled for the next 7 or 8 days, then high pressure builds as we end April and enter the final month of Spring

http://www.jp2webdes...o.uk/ds/gfs.htm

whereas the ECM keeps low pressure just west of or over the UK keeping things very unsettled.

[Thundery wintry showers]

The high pressure on the later stages of the GFS 12Z looks like a "dry and sunny" high to me with warm days and chilly nights, but it's way too far out to have any confidence in. The ECMWF's slow-moving low would probably result in a mix of sun and showers with chances of thunder, though not before at least a couple of belts of more persistent rain.

Both GFS and ECMWF though have shifted towards a scenario of fast-moving Atlantic lows during next Monday-Wednesday which would probably mean fairly cloudy as well as wet conditions, but the sudden nature of the change suggests that next week is still uncertain (except for low pressure being there or thereabouts). Still looks bright and showery with possible thunder in eastern areas during Friday to Sunday.

[phil nw.]

No end in sight to the unsettled outlook for the next10days i would say.

The mean heights of the 12z ECM/GFS runs show the persistence of the upper trough over the UK.

http://www.meteo.psu...F_12z/test8.gif

suggesting that the GFS Op.run was indeed an outlier for high pressure in the later stages.

http://cdn.nwstatic.co.uk/ensimages/ens.20120418/12/prmslWarwickshire.png

so we may continue with the April showers scenario quite possibly untill month end.

[NUT]

Always amazes me how the models seem to flip and change. This morning they we're showing that possible plume (which has disappeared) Now they showing it not looking great at all (but on the flip side it could all be on again tomorrow) Argh!

[SP1986]

18z pretty much as you were,unsettled and below average in terms of temperatures if not well below average at times. Low pressure stuck over us, perhaps giving a suggestion of a 2007 type synoptical outlook (summer). Still not seeing much change from this as we head into May.

I'm wondering whether it is possible April-May combination may come in as one of the coolest in recent time, it will be interesting to see what May is like. I suspect there is good shot that the Greenland High may well deliver some exceptionally cold weather for May. Very interesting times ahead.

[Snowy Easterly]

I agree very much so, all due to the jet stream position. We seem to be getting more Northern Blocking during Spring and early summer.

then the northern blocking will end just as winter arrives, again

[Polar Maritime]

18z pretty much as you were,unsettled and below average in terms of temperatures if not well below average at times. Low pressure stuck over us, perhaps giving a suggestion of a 2007 type synoptical outlook (summer). Still not seeing much change from this as we head into May.

I'm wondering whether it is possible April-May combination may come in as one of the coolest in recent time, it will be interesting to see what May is like. I suspect there is good shot that the Greenland High may well deliver some exceptionally cold weather for May. Very interesting times ahead.

Some say the "the coldest for a 100 years"...

[BornFromTheVoid]

Good cross model agreement for the next week or so.

Continuing cool and showery to about t120, with a continued risk of thunderstorms during the day and frost at night, mostly in central and southern regions.

Past t120, pressure begins to build towards east and south east Europe, coupled with a brief strengthening of the low over the British Isles, drawing warmer air up into Europe which filters into the low sitting across us causing the temperature to move closer to the seasonal mean.

With northern blocking remaining strong throughout, the likelihood of below average temperatures remains high as we head towards May

[shedhead]

The latest runs suggest little if any prospect of a pattern change well into May, with the kind of N blocking most of us craved throughout Winter now looking well established. Some signs that a slight repositioning of the main trough may allow somewhat less cool condition to develop later in the period, but even that appears far from a certainty, with ECM in particular still looking decidedly cool towards the latter stages of the 00z run. On a positive note many areas need the rain and I'm sure most of us would prefer a cool wet Spring to another cool, wet Summer... let's just hope we don't end up getting both!

[SP1986]

Yes the 6z reinforces a cool outlook with plenty of much needed rain.

I do think the GFS is pulling off some erroneous temperatures predictions still, day and night (there seems to be pools where it is really struggling to predict temperatures properly, day and night), but other than that the truth is it will be very cool.

I myself am struggling to see where a pattern change will come from at this current time anyway, regardless of whether or not the models show it. Northern blocking is a very stubborn regime and it is plausible it could hang around throughout summer, especially in summer where the Greenland high is being fuelled by big temperature differentials over land and sea.

[Robbie Garrett]

The present setup with slow-moving low pressure is rather less common in mid to late summer than during spring and early summer because traditionally the jet powers up at some stage during June (hence "June return of the westerlies"), although it isn't unknown, e.g. August 2004 had a lot of slow-moving low pressure around our vicinity and a weaker jetstream than is usual for August.

However, next week's setup does rather remind me of the "Atlantic trough, Euro high and suppressed Azores high" setup that often characterises hot thundery months. I mentioned that in high summer (July/August) the jetstream tends to be stronger, but when low pressure systems track into the mid-Atlantic and are then deflected sharply northwards as they approach the meridian, we can get the same effect with a train of depressions heading towards northern Scandinavia, weak troughs being left over to the W/SW and high pressure filling in the gap to our east. For those unsure of what I mean, check out the Wetterzentrale synoptic archive for July 1994 which was a particularly stark example.

The one potential difference here is that the majority of model outputs have us strongly under the influence of the Atlantic trough next week, which will perhaps restrict the extent of possible heat and thunderstorms. Continuing on the theme of summer months, though, June 2003 was one such month where the Atlantic trough largely dominated proceedings, but many parts of the country still ended up warm and sunny with some thundery outbreaks.

My bad, I've always known Summer to be very wet personally. So thought this was the kind of setup we would normally get.

I have no experience in long-term forecasting, but obviously understand where to look and from what I have seen, it looks like above average rainfall to me with plenty of warmth. So this brings me back to my point in saying, indications are there for the most thundery Summer we've had in a long time. Surely??

Also just to note, the idea of a colder May, I take it this was the Greenland high we was discussing yesterday tapping into what is left of the Polar Vortex.

[WhiteFox]

Very interesting ECM output this morning. Low with central pressure of 988 centred to the west of Ireland:

Centred over England 24 hours later still with central pressure of 988:

The developing secondary feature from the chart above almost seems to suck the initial low back west and is centred to the SW of Ireland with a central pressure of 976:

And finally is centred in the Irish Sea with a central pressure of 972:

It's almost as if the initial low pressure thinks "That was a puny attempt, let's go back and try again."

Haven't seen anything this unsettled over the whole of the UK for quite some time. I was thinking to myself just last month that we hadn't seen a spate of developing secondary lows giving heavy rain across the whole country for what seems like ages. Personally, I enjoy such spells of weather; you won't find me complaining about it being endlessly wet!

[Summer Sun]

GFS 06z settles things down as we leave April and enter May with high pressure building

As we enter early May temperatures are shown to be above the seasonal average for all at times

[Thundery wintry showers]

My bad, I've always known Summer to be very wet personally. So thought this was the kind of setup we would normally get.

I have no experience in long-term forecasting, but obviously understand where to look and from what I have seen, it looks like above average rainfall to me with plenty of warmth. So this brings me back to my point in saying, indications are there for the most thundery Summer we've had in a long time. Surely??

Also just to note, the idea of a colder May, I take it this was the Greenland high we was discussing yesterday tapping into what is left of the Polar Vortex.

The models have backed away from that warm/thundery looking setup with the Atlantic trough shoved further east, such that it sits right on top of the British Isles. Indeed, the setup progged by the models is more reminiscent of what we've been used to in recent summers with a southerly tracking jetstream and low pressure areas with attendant fronts sent towards us at regular intervals. That said, the weekend still looks bright, showery and potentially thundery in the east as our current depression slowly fills out, before cloudier wet weather returns for much of next week.

I would recommend not taking too much notice of the high pressure recurrently showing on the GFS until it creeps inside T+168.

[danm]

Can't say I'm liking the output at all at the moment. We were spoiled by the March warmth. But we do need the rain.

[Alex]

Think I may know the culprit to it and it could be well to do with the latest MJO phase and it may have gone back into Phase 8 of which is pretty bad news if we want warmth and also wondering on the CPC site whether the atmosphere is acting Nina driven. If so it explains it all.

The MJO is currently at phase 3 but keeps being progged to loop back but it then actually seems to be going round it's full circle?

[Snowyowl9]

Looks like being the wettest april since 2000 which infact it already is.

April 2000 was the wettest on record,what a turnaround month from march`s record warm spell.

April of yesteryear.

LP does look pretty stubborn on the GFS.

[Paul]

Latest outlook from Michael Fish - unsettled all the way...

[Lewis]

Latest outlook from Michael Fish - unsettled all the way...

Watched it 10 mins ago, fantastic video forecast once again.

[Robbie Garrett]

The models have backed away from that warm/thundery looking setup with the Atlantic trough shoved further east, such that it sits right on top of the British Isles. Indeed, the setup progged by the models is more reminiscent of what we've been used to in recent summers with a southerly tracking jetstream and low pressure areas with attendant fronts sent towards us at regular intervals. That said, the weekend still looks bright, showery and potentially thundery in the east as our current depression slowly fills out, before cloudier wet weather returns for much of next week.

I would recommend not taking too much notice of the high pressure recurrently showing on the GFS until it creeps inside T+168.

I was quite interested as to why and how, but I take it this is part of the patterns we are seeing in the Nern Hemisphere. I take it that any major pattern change, such as warmer temperatures and high pressure should not be taken much into till at least +168 period.

CFS now indicating a very wet may, with temperatures closely at 12/14*C is thats below average right?? It's also indicating a very unsettled June/July and late July, Early August looks very confusing.... something to watch that's for sure. But to be fair, it would not surprise me if this was the case.

I remember someone posting how this year has panned it is very similar to the year, June and July was severe washout (Monsoon) conditions. What year was it??

Wet weather continues well into June, I take it a Scandinavian high in June???

And until the Jestream tracks north, the idea of Summer here we come is not going to happen!!

[Carl46Wrexham]

I was quite interested as to why and how, but I take it this is part of the patterns we are seeing in the Nern Hemisphere. I take it that any major pattern change, such as warmer temperatures and high pressure should not be taken much into till at least +168 period.

CFS now indicating a very wet may, with temperatures closely at 12/14*C is thats below average right?? It's also indicating a very unsettled June/July and late July, Early August looks very confusing.... something to watch that's for sure. But to be fair, it would not surprise me if this was the case.

I remember someone posting how this year has panned it is very similar to the year, June and July was severe washout (Monsoon) conditions. What year was it??

Wet weather continues well into June, I take it a Scandinavian high in June???

And until the Jestream tracks north, the idea of Summer here we come is not going to happen!!

I may be wrong but I think the year you are referring to re : total washout June/July would be 2007!

Ugh! Dear God spare us another summer like that one.

[Robbie Garrett]

I may be wrong but I think the year you are referring to re : total washout June/July would be 2007!

Ugh! Dear God spare us another summer like that one.

Was that the one with the very far South Jetstream??

[Cloud 10]

Looks like the unsettled theme continuing for the rest of April which is summed up

nicely by the 12z ECM ensemble mean for day 10 with the trough right over the UK.

The 100mb stratosphere chart for about the same time seems to show something similar.

As for May,at the moment my expectation's are pretty low!