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Paul

In Depth Model Discussion and Summaries

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nice to hear SJ, now and then they do happen, currently I would not put it higher than 40% but I'll keep folk posted in here.

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to follow on from my earlier post in pdf format, below is the link for the 8-14 and its 6-10 version.

Of note perhaps, is the slight rise in heights in the Atlantic over the last issue, coupled with the issues I commented on earlier..

http://www.cpc.ncep.noaa.gov/products/predictions/814day/500mb.php

 

IF the 3 sequences continue as they have over the past 3 runs or so AND that is converted into actual 500mb charts then there are reasonable signals to support the idea of colder weather being on its way-I did say IF AND!

Edited by johnholmes
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it does make me wonder what winter 2013/14 really has in store.

 

Posted Imagedecember78ao.gif

 

 

Turns out it was a bit of a nightmare all round!

 

 

 

Arctic heights aplenty,but certainly didn't do us any favours.

 

 

Looking further ahead  as a few have mentioned in the model thread,perhaps some

signs of a colder than normal Spring beginning to show,with the stratospheric polar vortex

having re-located east of Greenland,then eventually the lower vortex is likely to follow.

 

 

Below normal SST anomalies in the mid-Atlantic would favour ridging around that area,so i'm

thinking a scandi trough/mid-atlantic ridge to become the main features as we head towards the 

end of March.

 

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This thread has been very quiet for much of the winter season compared to recent years - probably because we were just stuck in one rut..

 

I'd appreciate others thoughts on the next couple of months ahead and any strong signals for a change in the overall hemispheric pattern from one dominated by the Polar Vortex.

 

I enjoy reading the more in depth detailed forecasts, but have see so little in recent months it has made for a rather disappointing period all round..

 

I like the MJO predictions etc.

 

Could anyone more in the know share there thoughts on how the rest of Spring may pan out.

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not from me, 15 days using a mix of anomaly and synoptic outputs with a check on the background signals from AO, NAO, PNA, MJO; in the spring/summer months, possibly extending it to about 3 weeks at the very most; little can be gained from looking at the 30mb chart I find?

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This thread has been very quiet for much of the winter season compared to recent years - probably because we were just stuck in one rut..

 

I'd appreciate others thoughts on the next couple of months ahead and any strong signals for a change in the overall hemispheric pattern from one dominated by the Polar Vortex.

 

I enjoy reading the more in depth detailed forecasts, but have see so little in recent months it has made for a rather disappointing period all round..

 

I like the MJO predictions etc.

 

Could anyone more in the know share there thoughts on how the rest of Spring may pan out.

Yes this thread is so quiet these days Damian.

We certainly miss GP's views on the longer term.He had a good handle on tropical activity along with momentum phases linked to frictional and mountain torque events and how these would possibly affect the patterns for us.

The MJO forecasts really are only for 2 weeks ahead or so and i only tend to comment on them if there is sufficient activity in that area .

There are so many other factors which GP had a good handle on and these are particularly useful in the warmer half of the year when the effects from the Winter Stratosphere are no longer the main influence.

As John said 2-3 weeks ahead from the ensembles and height anomalies forecasts- perhaps backed up at times by MJO forecasts- are the best we can realistically do at present.

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Below normal SST anomalies in the mid-Atlantic would favour ridging around that area,so i'm

thinking a scandi trough/mid-atlantic ridge to become the main features as we head towards the 

end of March.

 

 

Not much sign of this setup so far although i'm sure it will turn up eventually.http:////nwforum.r.worldssl.net/forum//public/style_emoticons/default/laugh.png 

 

The first half of spring was slightly drier and warmer for the bulk of the UK 

looking at the temperature and rainfall anomalies.

 

temperature..  rainfall..

 

The 500mb height anomalies for the Northern hemisphere showing a positive AO

for spring so far.

 

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Given seasonal wavelengths, do early summer Scandinavian High's tend to retrogress as summer progresses (ala towards Greenland) or push east/maintain themselves with Azores reinforcement.

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I have no idea, anyone else able to say?

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Posted Image

 

Allowing for a lag i'd look for +AO conditions to develop into early June with a probable height rise response near the UK.

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Does anybody have the MJO phase 1 and 2 charts for June. We're looking somewhere between neutral and those phases.

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Does anybody have the MJO phase 1 and 2 charts for June. We're looking somewhere between neutral and those phases.

Link to the phase diagrams here sb.

 

http://www.americanwx.com/raleighwx/MJO/MJO.html

a current forecast for a weak phase 2 as we go into June

 

post-2026-0-34940400-1401299756_thumb.gi

which is a decent match for current ens outputs.

 

Latest report and forecast of the MJO here(pdf file)

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjoupdate.pdf

 

The MJO has been relatively quiet recently and seems to be slow moving around the Indian Ocean maybe why there seems little movement in the overall pattern currently.

 

edit: a useful paper on the  MJO and it's effects here

 

http://wwa.colorado.edu/climate/iwcs/archive/IWCS_2008_May_focus.pdf

 

it;s a few years old but explains things quite well.

Edited by phil nw.
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Looking further ahead  as a few have mentioned in the model thread,perhaps some

signs of a colder than normal Spring beginning to show,with the stratospheric polar vortex

having re-located east of Greenland,then eventually the lower vortex is likely to follow.

 

 

 

Well that went well. :laugh: 

 

The 500mb composite for Spring 2014 showing the exact opposite of what i thought

might happen with low heights over the mid-atlantic and high pressure around

Scandinavia,with the whole of the UK receiving a warmer than normal spring.

 

500mb anomalies..  Euro temps..

 

Summer not off to the best of starts with the NAO/AO trending neutral/negative and could also 

do with the jetstream heading North.

 

 

 

 

 

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After the low pressure area of today has passed the UK, it appears that period of warm/hot weather seems to be on the way. What is the cause of this possible hot weather? A view at the initial situation and an explanation/interpretation on the synoptics of the possible anomalous warm conditions will be given.

 

Initial situation

 

To get an idea of the initial weather conditions, check the airmass-distinction satellite imagery below: 

 

Posted Image

MET10 Satellite imagery RGB-composite (Courtesy: Eumetsat)

 

What can be seen is that there is a frontal zone extending from the northeastern Spain all the way via Germany to Scotland. This activity is associated with a low pressure area located over southeastern England. An area of relatively warm upper air is positioned north of this low pressure system. To the south(west) of this front, cooler upper air is advancing toward Europe. Analysis of 850 hPa temperatures show this:

 

Posted Image

GFS 850 hPa temperatures (colours) T+12 (06Z)

 

It is also nice to see that the 'border' of warm/cool upper air temperatures (indicated by yellow and orange colours lying fairly close together) is directly coincident with the frontal zone

 

Of little importance for our weather situation, but also interesting to note is the presence of very warm upper air temperatures over and to the northwest of northern Norway.

 

Warmth from the south

 

To show the transition to possibly much warmer conditions, it is important to take a look at the current pressure setup. For this purpose, GFS model output will be given.

 

Posted Image

GFS surface level pressure (isobars) and 500 hPa heights (colours) T+0 (06Z)

 

The main feature is a complex area of low pressure located between Greenland and France, with the low pressure area mentioned in the initial analysis also located in this 'gyre'. This area is associated with a 500 hPa trough (green colours), which extends from Greenland all the way to Greece. 

 

Furthermore, the Azores high is present to the southwest of the complex low pressure area, and a strong high pressure area (associated with a 500 hPa ridge, red colours) is located over western Russia.

 

For now, focus on the 500 hPa trough, and associated low pressure areas, near and to the northwest of the UK. Below is the GFS output for this Friday, 2 days from now:

 

Posted Image

GFS surface level pressure (isobars) and 500 hPa heights (colours) T+48 (06Z)

 

A very important change has taken place, and that is the development of a cut-off 500 hPa-trough (with associated surface low pressure area,green to blue colours) to the west of France, which has originated from the trough over and northwest of the UK as mentioned above. The 500 hPa trough has completely lost its connection with the low heights (green colours) to its north. 

 

Due to this cut-off event, a southerly flow (both in the upper air as at the surface) has developed, forcing warm air (and associated high 500 hPa heights) over Africa to advect northward.

 

Below is the pressure chart for Sunday, 4 days from now:

 

Posted Image

 

GFS surface level pressure (isobars) and 500 hPa heights (colours) T+96 (06Z)

 

The cut-off low is still present to the west of France. But, more importantly, high 500 hPa heights (red colours), which were already pointing northward, have moved further northward into central Europe. This has also caused warm air to advect/move northward:

 

Posted Image

GFS 850 hPa temperatures (colours) T+96 (06Z)

 
850 hPa temperatures up to 15*C have reached the Benelux, and the western side of the UK is also under influence of this warm air. This event could be an event of warm air advection (WAA), but buildup of surface high pressure is not really present. Therefore, I'm a bit wary with calling this event a classical event of warm air advection.
 
Something that is very remarkable is the tight gradient of 850 hPa temperatures (high temperature differences in a relatively short distance) located over the UK. Such sharp temperature gradients in summer often provide good setups for severe convective weather (i.e. thunderstorms etc).
 

Sources:

http://oiswww.eumetsat.org/IPPS/html/MSG/RGB/AIRMASS/WESTERNEUROPE/index.htm

http://www.wetterzentrale.de/topkarten/fsavneur.html

http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/af/adv/wadv.rxml

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