Model Output Discussion 31/03/14 onwards.

[knocker]

Why and how is the PV effecting tropospheric weather at the moment and creating new modes of variability as seems to be suggested?

 

Not forgetting there is deep depression over the Arctic at the moment forecast in the low 960s tomorrow.

[egret]

I wouldn't take this as written in stone. The models are struggling for uniformity on this and we are only talking slight changes here. Thanks for correcting the date. A senior moment I'm afraid.

Meto forecast is giving us heavy rain Sunday PM, but as you say not set in stone (although I have a feeling I would go with that low as but perhaps less deep - drizzly rather than heavy rain). GFS still showing the area of heavier rain hitting the Kent / E Sussex and moving on down to the Channel Isles. 

 

If it was winter I would be getting  excited LoL

[Summer Sun]

Looks like the rain might only affect the south on Easter Sunday

 

 

Pressure will be higher the further north you are

 

 

 

 

 

[Summer Sun]

UKMO continuing to show something more settled developing towards mid next week

 

 

GFS 8 day 2m temperature anomaly shows temperatures remaining average or above average for all to at least the 25th

 

Edited April 17, 2014 by Summer Sun

[phil nw.]

UKMO continuing to show something more settled developing towards mid next week

 

 

GFS 8 day 2m temperature anomaly shows temperatures remaining average or above average for all to at least the 25th

 

It doesn't look a bad outlook at all S.S.

The ens graphs look quite dry with the Easter rain looking increasingly less widespread.Some showers about but pressure rising again through next week.

 

Should give many of us some dry and bright days.

 

Still that trend in the ens mean 500hPa pattern to push the jet north into the last part of April.

http://www.wetterzentrale.de/pics/Rz500m10.gif

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

 

based on those there would be some variations in surface conditions such as eastern coastal districts for example where cloud and drizzle may be a factor with an easterly breeze but on the whole it looks fairly quiet. and settled beyond the Easter break.

The one caveat is the threat of surface low pressure development if those heights situate too far north leaving parts of the south prone to more unsettled conditions which is something the 12z GFS is showing in the later frames.

[ANYWEATHER]

It certainly looks like a two faced Easter, with fine conditions mostly during the first part of the holiday weekend ,but unsettled conditions moving from the South East of England  to all by Tuesday//d321955.r.worldssl.net/forum//public/style_emoticons/default/nonono.gif //d321955.r.worldssl.net/forum//public/style_emoticons/default/closedeyes.gif //d321955.r.worldssl.net/forum//public/style_emoticons/default/wink.png

[Summer Sun]

ECM continues to hint at an east to south easterly flow developing later next week if it did some warm air would come with it

 

Edited April 17, 2014 by Summer Sun

[knocker]

Just a couple of fax charts for the weekend from Jomec. They have a familiar ring. Now next weekend. No let's leave the fairy tales for another day.

Edited April 18, 2014 by knocker

[IDO]

All the models continue to struggle with the pattern change (around D8+); the fragmentation of the PV and where the heights to our north settle and the subsequent blocked outcome, that is where the trough and ridges station themselves.

 

For instance ECM T240 last night:  

 

This  morning:  

 

The latter is more in line with  the majority of the GFS output, especially the GEFS mean:  

 

The op is also back on that possibility:   ditto GEM: 

 

So still more likely, cooler and more unsettled late April/early May, London ens: 

 

JMA week 3-4 also hinting in this direction: 

 

However lots of uncertainty as to whether we are in a slack or a more active LP dominated trough, on its periphery or we escape with higher pressure. 

 

Next week GFS and ECM agree a lobe of the PV will come in from the Atlantic and try to undercut the heights to the North (GFS), NE (ECM), so the east drier initially but showery to the west:

 

GFS:    ECM: 

 

 

[Paul]

The NMM18 rainfall totals show the change in pattern over the Easter weekend, say goodbye to dry weather for now..

 

Saturday

 

Sunday

 

Monday

 

Tuesday

 

Wednesday

 

Thursday

[knocker]

 

Next week GFS and ECM agree a lobe of the PV will come in from the Atlantic and try to undercut the heights to the North (GFS), NE (ECM), so the east drier initially but showery to the west:

 

 

Being a tad thick I'm afraid you will have to explain what you mean by 'lobe' of the PV. As I understand it the PV is a winter time feature of the Stratosphere. When the vortex is strong, the westerlies descend all the way to the earth's surface. This carries more warm air from the oceans into the land. When the vortex is weak, then the really deep cold occurs. But that's in winter, How is the PV, which is higher in spring and summer effecting tropospheric circulation now and I'm not sure what a lobe of it is anyway. Thanks.

[IDO]

Being a tad thick I'm afraid you will have to explain what you mean by 'lobe' of the PV. As I understand it the PV is a winter time feature of the Stratosphere. When the vortex is strong, the westerlies descend all the way to the earth's surface. This carries more warm air from the oceans into the land. When the vortex is weak, then the really deep cold occurs. But that's in winter, How is the PV, which is higher in spring and summer effecting tropospheric circulation now and I'm not sure what a lobe of it is anyway. Thanks.

HiI am no expert but the PV also exists in the mid and upper troposphere as well as the stratosphere. The deep purples on the 500hPa charts indicate that. The lobe I was referring to was when a part of these deep purples splits from the main vortex, in this case the vortex is on its travels from NE Canada to Siberia, and a part of it breaks off and moves SE, weakening all the time. Where this ends up May affect the medium term weather as it will park itself somewhere and probably develop into an upper trough.

[Frosty.]

The end of the Gfs 00z op run is a beauty with high pressure building in from the southwest and temperatures soaring towards 70 F. In the short, medium term it looks like the weather will be turning unsettled from the south initially and then the southwest with the anticyclonic fine weather being squeezed away to the northeast and pressure falling across all parts of the uk with outbreaks of rain, some heavy with a risk of thunder, becoming more widespread, quite a cyclonic looking outlook with a mixture of sunny spells and heavy showers and longer periods of rain, feeling warm in the sunshine but cool under the rainy skies..but then perhaps a glimmer of hope for a more settled spell into early may.

[knocker]

HiI am no expert but the PV also exists in the mid and upper troposphere as well as the stratosphere. The deep purples on the 500hPa charts indicate that. The lobe I was referring to was when a part of these deep purples splits from the main vortex, in this case the vortex is on its travels from NE Canada to Siberia, and a part of it breaks off and moves SE, weakening all the time. Where this ends up May affect the medium term weather as it will park itself somewhere and probably develop into an upper trough.

 

I'm afraid I don't agree with that but haven't got time at the moment. Very briefly the deep purples are and indicator of colder air not a PV in the trop. A quick look at the Arctic at the moment and you will see a deep depression with very low 500mb heights that would show up as deep purple on your chart. It isn't IMHO the PV which isn't a feature of the troposphere in summer and doesn't significantly effect tropospheric circulation to my knowledge.

Anyway just a thought.

[IDO]

I'm afraid I don't agree with that but haven't got time at the moment. Very briefly the deep purples are and indicator of colder air not a PV in the trop. A quick look at the Arctic at the moment and you will see a deep depression with very low 500mb heights that would show up as deep purple on your chart. It isn't IMHO the PV which isn't a feature of the troposphere in summer and doesn't significantly effect tropospheric circulation to my knowledge.Anyway just a thought.

HiNo problem. I was under the impression that the vortex at 500hPa was a concentration of lower pressure and the deep purples highlighted how deep the vortex pressure was, not of temperature, although there is of course a correlation between lower pressure and cold. Yes I agree in the summer the vortex goes to sleep but it remains active now and continues to drive the weather till it dissipates and this may take some weeks yet.

[Summer Sun]

GFS is still struggling to get to grips with the block to our east early next week

 

ECM and UKMO below

 

 

Then we have GFS

 

Edited April 18, 2014 by Summer Sun

[carinthian]

You just knew it was going to happen after a miserable snow less and frost free winter in your parts. Great synoptic charts  presently for cold lover if it was only 3 months earlier.

[Frosty.]

You just knew it was going to happen after a miserable snow less and frost free winter in your parts. Great synoptic charts  presently for cold lover if it was only 3 months earlier.

Indeed, high pressure retrogressing to greenland and lots of northern blocking, 16 weeks too late.//d321955.r.worldssl.net/forum//public/style_emoticons/default/diablo.gif

[knocker]

Hi

No problem. I was under the impression that the vortex at 500hPa was a concentration of lower pressure and the deep purples highlighted how deep the vortex pressure was, not of temperature, although there is of course a correlation between lower pressure and cold. Yes I agree in the summer the vortex goes to sleep but it remains active now and continues to drive the weather till it dissipates and this may take some weeks yet.

 

I’m dreaming of… - I honestly think that you should put the PV on the back burner for a few months as I feel it’s just confusing the issue. Regarding the 500mb contour height, or any level contour height come to that, it is always a function of temperature and pressure irrespective whether the PV is involved or not. It is calculated by using a complicated set of equations which is quite easy these days with computers but in days of yon it was done manually. If I quickly explain how it may show what I mean. On the other hand it may not.http:////d321955.r.worldssl.net/forum//public/style_emoticons/default/smile.png

 

You start of with a thermodynamic diagram such as a tephigram which is basically the equations in diagram form. Clever stuff. Actually in practice a special diagram was used with a different projection that was easier to work with.

 

The radiosonde sounding is plotted on the diagram. Using the surface pressure and temperature you can calculate the 1000mb contour height above msl from the diagram. If the surface pressure is below 1000mb then the figure will be negative. For arguments sake let’s call it -20 metres. You then take the average temperature between 1000mb and 900mb and at the mid point of the layer read off the height in metres which represents the ‘thickness’ of the layer. The thickness/height is directly proportional to the temperature of the layer. The colder the air the lower the height and vice versa. This height is then added to the 1000mb already calculated to arrive at the 900mb contour level. So if the height between 1000mb and 900 is 900metres then the 900mb contour level will be 900m + -20 = 880m.

 

You then repeat this for subsequent layers, 900-850, 850-800, 800-700, 700-600, 600-500mb and so on. Thus for every pressure level you have the equivalent contour height and as you can see it is entirely a function of temperature and pressure.

 

Hope this helps.

 

http://weatherfaqs.org.uk/node/61

 

[Cloud 10]

Looks like the NAO is plunging negative in the near future.

 

 

 

Been quite a while since that happened!

[Steve C]

Looks like the NAO is plunging negative in the near future. nao.sprd2.gifEDH101-240.gif Been quite a while since that happened!

Thinking about it, a negative NAO would suit a lot of weather aficionados, no matter the season.

[Summer Sun]

It doesn't look like we'll see too much in the way of rain over the next few weeks the bulk of it for the south is likely on Easter Sunday away from the easterly breeze it could get quite warm for some at times

 

 

Very little rain on the Aberdeen ensemble

 

[IDO]

Easter Sunday looking a write off for the SE according to the Met:

 

   

 

Breezy...  ...so may feel a bit cooler than the 2m forecast: 

[Summer Sun]

What a surpise GFS is moving towards what UKMO and ECM has shown for the past few days finally seems to have got to grips with the block to our east

 

 

06z run for the same time

 

 

 

06z

 

Edited April 18, 2014 by Summer Sun

[Summer Sun]

UKMO shows a low pressure system off the Atlantic trying to move in on Wednesday but the strong block to the east means it heads back west by Thursday

 

 

GFS 2m 8 day temperature anomaly remains average or above average till at least the 26th

 

Edited April 18, 2014 by Summer Sun