Model Output Discussion

[Thundery wintry showers]

Returning polar maritime is essentially a modification of polar maritime where the airmass travels south of 50N before reaching the British Isles, and so while temperatures tend to be above average when this airmass occurs, they tend to be less so than with tropical maritime air, especially by night. Like with standard polar maritime it occurs after a cold front has passed over. In the summer half-year returning polar maritime is one of the biggest sources of thunderstorms over many parts of the UK, combining warmth with instability and moisture.

The reason why a mobile Atlantic type will usually produce more tropical maritime air is because Britain is more likely to spend more time in "warm sectors"- i.e. in the wake of warm fronts- which is where we most often get exposed to tropical maritime air.

I think June 2003 was actually dominated more by returning polar maritime than tropical maritime, hence the emphasis on relatively high sunshine amounts mixed with showery/thundery outbreaks over many parts of the country. The warmth was more down to the marked bias towards southerly winds, rather than "warm sector" conditions. July 2003 was a better example of a month when tropical maritime air frequently dominated.

Btw, the common use of "returning polar maritime" to refer to those cold westerlies and north-westerlies of Arctic origin bringing snowfalls to western areas is incorrect. In that case, it's arctic maritime air that is "returning", heading into the mid-Atlantic and then across to Britain. I'm tempted to suggest that we could coin a new description for it, namely "returning arctic maritime", but I think it's usually categorised as just a very cold version of polar maritime.

[Eugene]

Not much of interest for both camps for next week though with some PM air it will feel chilly, some interest in FI though for the coldies, maybe April will deliver the goods for them with the jet diving southeastwards and pressure building out to the north and west.

http://www.wetterzen...s/Rtavn2641.png

Edited March 19, 2010 by Eugene

[Thundery wintry showers]

In addition to my previous post (for the benefit of those who are interested in checking out what airmasses will be affecting us in the upcoming spell of south-westerlies) here's some good examples of those two airmasses:

Returning polar maritime:

http://www.wetterzentrale.de/archive/2000/brack/bracka20000421.gif

http://www.wetterzentrale.de/archive/2004/brack/bracka20040314.gif

Tropical maritime:

http://www.wetterzentrale.de/archive/2000/brack/bracka20000307.gif

http://www.wetterzentrale.de/archive/2005/brack/bracka20050316.gif

[phil nw.]

Pretty broad agreement from the 12z output for an unsettled South Westerly pattern continuing for the next week or so.

Never really mild though with temps. around average and maybe somewhat below further North at times.

http://www.wetterzen...cs/Rtavn721.png

http://www.wetterzen...ics/Recm721.gif

http://www.wetterzen...ics/Rukm721.gif

The jet becoming more meridonal with an upper E.Atlantic trough modelled to move across the UK later.

This would introduce colder weather further on as it moves East of the UK towards the end of next week.

http://www.wetterzen...cs/Recm1921.gif

http://www.wetterzen...s/Rtavn2161.png

introducing polar air.

Edited March 19, 2010 by phil n.warks.

[damianslaw]

Longer term trends as reflected in GFS and ECM for the end of the month is more of a meridional flow which would potentially allow a sharp potent northerly as heights rise to the NW - I remember a very similiar scenario last March and we all know what happened during easter 2008. Northerlies at the end of March and early April are quite a common synoptic, northerlies tend to reach their yearly maxim from now through to early May, this period being when you expect the normal westerly pattern to be least in evidence. This should be noted, a sustained south westerly pattern at this time of year is certainly not the norm..mind the past 3 months have certainly not been normal..

Edited March 19, 2010 by damianslaw

[Ben_Cambs]

The pattern for next week looks like it has been set, cool and unsettled for all . GFS 18z a cool run with average to slightly below average temperatures, and at times the risk of hill snow over the Grampians. Highly unlikely that we will see anymore 15C days this month, the latest model output suggests temperatures up to 9C in the North and up to 11C in the South by the middle of next week, and then suggests maxima's widely in single figures by next weekend. A few changes and we could still possibly see a potent Notherly by early April.

[Eugene]

Mixed week ahead with fronts passing through from time to time and sunnier days with chilly nights, nothing warm or that cold but the runs are trending colder for late week onwards with a southerly tracking jet and pressure building to our northwest, April could start rather cold.

[Ben_Cambs]

ECM 00z a very interesting run this morning, it appears to show in my novice eyes a quite small chunk of the split PV heading towards Scotland! A potent Northerly develops towards the end of the run, as heights build to the North and West, so one option for the weather at the Start of April could be a cold one with possibly some snow?? We will see in time what happens. But certainly looks like it will cool down and turn more unsettled for next week.

ECM T+240:

ECM 850's T+216:

T+240:

All to be taken with caution of course!

Edited March 20, 2010 by Snowman0697

[johnholmes]

I've put my ideas for late March into April in my blog at the link below

http://forum.netweather.tv/topic/60173-lrfs-by-jh/page__st__17__gopid__1796773&

[The PIT]

Away from Scotland and Northern England the mild weather looks set too continue. Further North cooler and wetter of course. Still down south when the sun comes should be quite pleasant still.

[Eugene]

Oh dear a very wet and at times stormy GFS 12Z with constant atlantic systems revving into gear and crossing us, funny how as soon as spring is here the atlantic wakes up after a quiet winter.

Not much pleasant about GFS 12Z thats for sure unless mild at any cost suits you, not that it is looking that mild all the time anyway.

Localised flooding could become an issue if GGS 12Z is right.

[phil nw.]

Oh dear a very wet and at times stormy GFS 12Z with constant atlantic systems revving into gear and crossing us, funny how as soon as spring is here the atlantic wakes up after a quiet winter.

Not much pleasant about GFS 12Z thats for sure unless mild at any cost suits you, not that it is looking that mild all the time anyway.

Localised flooding could become an issue if GGS 12Z is right.

Sunday and Tues. look dry during daylight hrs. though Eugene with reasonable temps.

Should be pleasant enough,especially further South.

As ever in this unsettled pattern it`s all down to the timing of the rain bands as to when the dry periods actually occur.

However it does look very wet from then on with low pressure v.close by.

This run does does away with jet buckling later which means less cold than modelled previously.

UKMO 12z also shows an unsettled,cyclonic week to come.

http://www.wetterzentrale.de/pics/Rukm1201.gif

Edited March 20, 2010 by phil n.warks.

[phil nw.]

Getting quite mild again by midweek as the Upper trough develops in the E.Atlantic drawing a brief Southerly orientated flow,but with a lot of moisture too.

http://www.wetterzen...cs/Rtavn962.png

http://www.wetterzen...ics/Rukm961.gif

http://www.wetterzen...ics/Recm961.gif

So quite wet and cloudy for many with only brief bright interludes more likely in the S.E.

This unsettled pattern looks set to continue as the Low pressure moves across the UK by the end of the week.

http://www.wetterzen...cs/Recm1681.gif

http://www.wetterzen...s/Rtavn1681.png

ECM still modelling a colder snap later placing the Upper trough towards Scandi.allowing a Northerly flow.

http://www.wetterzen...cs/Recm2401.gif

GFS shows a less meridonal flow but still colder.

http://www.wetterzentrale.de/pics/Rtavn2401.png

The trend appears to be temps. falling to below normal again towards the last 2-3 days of March .

Edited March 20, 2010 by phil n.warks.

[Cheese Rice]

A terrible GFS run, a very wet run. Its beggers belief why anyone would want this, but most on here wanted rid of the cold and this is the only way out. At least from a gardening perspective this will help growth, and the daffodils may finally flower.

The cooler/cold theme at the end of the month is still been shown in some form, even though on the latest run the cold doesn't quite make it.

[summer blizzard]

While it does look cool and unsettled in the reliable timeframe, there are increasing signs of a warmer and more settled spell emerging, it's been coming closer to the reliable timeframe for a few days now..

http://www.wetterzentrale.de/pics/Rtavn2161.png

Developing into this..

http://www.wetterzentrale.de/pics/Rtavn2401.png

[Guest]

While it does look cool and unsettled in the reliable timeframe, there are increasing signs of a warmer and more settled spell emerging, it's been coming closer to the reliable timeframe for a few days now..

http://www.wetterzentrale.de/pics/Rtavn2161.png

Developing into this..

http://www.wetterzentrale.de/pics/Rtavn2401.png

I'm sure when you posted these charts they showed a settled spell, but at the time of my posting the second chart is most certainly not settled. It just shows you how uncertain these things can be

[Eugene]

lol i love how people use the phrase increasing signs after seeing one GFS extreme FI run, any signs of warmer more settled weather is tenuous at best.

Weatheronline summing it up nicely i feel, yes by the end of the week we will all be looking back at the nice settled weather in most of the winter, atlantic LP coming up against HP to our east is a disaster for western areas especially with fronts becoming slow moving before the next one moves in.

A mild start but turning cooler later

By the end of this week some parts of the country may be wishing for a return to the drier weather of winter (although no doubt not the cold temperatures!). Low pressure is going to be bringing a disturbed period of weather across the country. Outbreaks of rain and showers will be persistent at times, with the west tending to take the brunt of these. By the end of the week an area of low pressure looks set to become established over the country, changing the winds from a mild southerly to a cooler northerly and bringing showers for all.

Edited March 21, 2010 by Eugene

[The PIT]

ECM oo oz cooler than the 06 oz GFS which is another mild run so far so plenty of mild sometimes wet stuff to come in the reliable time frame. No sign of cold at all at the present time.

[Thundery wintry showers]

Looking at the T+144-168 charts for UKMO and ECM, both showing a northerly plunge heading straight for Britain, "no sign of cold" is overdoing it just a little! The GFS paints a rather different scenario as a result of having low pressure pump warm air up to our north, so that when we get a northerly incursion it only brings very modified air south. The warm settled spell is further out than the possible northerly.

In the near term staying rather warm, cloudy and wet is the prevailing outlook with the exception of Tuesday which may be reasonably sunny for most, and today likewise for the east and south.

[The PIT]

Looking at the T+144-168 charts for UKMO and ECM, both showing a northerly plunge heading straight for Britain, "no sign of cold" is overdoing it just a little! The GFS paints a rather different scenario as a result of having low pressure pump warm air up to our north, so that when we get a northerly incursion it only brings very modified air south. The warm settled spell is further out than the possible northerly.

In the near term staying rather warm, cloudy and wet is the prevailing outlook with the exception of Tuesday which may be reasonably sunny for most, and today likewise for the east and south.

Only prob mate well into FI land. ECM has been showing this for a while but it's never coming closer while within the reliable time frame it's following the GFS.

[summer blizzard]

I'm sure when you posted these charts they showed a settled spell, but at the time of my posting the second chart is most certainly not settled. It just shows you how uncertain these things can be

Indeed, GFS has high pressure over us for one day, will have to moniter the trend if it makes it into the reliable.

[Frosty.]

The lack of posts is understandable as the weather pattern has reverted to something less interesting and the week ahead looks unsettled on the whole but mild with winds from the sw or south, lots of rain in the north & west, drier at times in the south & east, temps between 10-16c nw to se. The ecm 00z shows a colder FI but nothing significantly cold although there would probably be some snow on northern hills but that's in lala land and the reliable timeframe is just mild and unsettled.

[Thundery wintry showers]

The lack of posts is understandable as the weather pattern has reverted to something less interesting and the week ahead looks unsettled on the whole but mild with winds from the sw or south, lots of rain in the north & west, drier at times in the south & east, temps between 10-16c nw to se. The ecm 00z shows a colder FI but nothing significantly cold although there would probably be some snow on northern hills but that's in lala land and the reliable timeframe is just mild and unsettled.

I think you're underdoing the snowy potential on the ECM FI. From T+168 onwards I would expect snowfalls to occur on low ground pretty widely (though accumulations mostly limited to northern hills), especially in showers. Thicknesses are mostly around 520-524 dam, reading off those charts, which would certainly support this.

However the point that it's out in Fantasy Island is quite correct, so unless it comes a couple of days "closer in" it has to go down as an outside bet for now.

[MR EXTREMES]

I think you're underdoing the snowy potential on the ECM FI. From T+168 onwards I would expect snowfalls to occur on low ground pretty widely (though accumulations mostly limited to northern hills), especially in showers. Thicknesses are mostly around 520-524 dam, reading off those charts, which would certainly support this.

However the point that it's out in Fantasy Island is quite correct, so unless it comes a couple of days "closer in" it has to go down as an outside bet for now.

well i remember april 2008 now that was an event for the southcoast something i had not seen for some years could there be a repeat maybe might be in la la land but seems to be consistent.

either way looking forward to what ever with get.

[damianslaw]

Generally mild for most especially the further south and east you are through this next week thanks to a predominantly south or south westerly flow.

Its not inspiring stuff for us in the north and west, very much a wet and unsettled outlook with bands of rain or showers merging into longer periods of rain pushing in from the moist atlantic, all very typical atlantic weather, I suppose I would rather have it now than later in the spring.

Signs of stronger heights ridging sufficiently from the north west to kill off the milder influence with a cut off low feature developing later next week on a more southerly track (see ECM and UKMO), this could help aid some colder air from the north as we head into the tail end of the month, equally we could become locked into a wet and unsettled but mild southerly type spell if those heights to the north west adveck more westwards i.e. the negative west based NA0 sceanrio we saw in late Feb (see GFS). I'd rather have a cold showery easter than a wet mild mucky affair which although good for spring growth wouldn't be good for those wanting to spend time outdoors.

At this time of year the betting man would go for the northerly sceanario, mild southerly/south westerly types are not something you associate with early April, but as I said in my last post this has not been a normal start to the year, everything seems to have been turned on its head.