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phil nw.

WInter Model Output Discussion 12z- 28/01/2013

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A new thread then ready for the 12z Model runs.

It looks like a few days of milder Atlantic conditions with wet and windy weather at times.

The ensembles then show things trending colder again though next week and the interest for cold seekers is how the pattern will evolve as we go further into February.

http://www.weatherca...e-forecast.html

Let`s see what the next set of outputs show.

As usual please keep on topic and relevant to the Model outputs.

OK please continue discussions below.

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Looking at NAO and AO forecasts they are both predicted to go negative, could someone explain to me how these being negative helps us? The AO has been negative for a long time now due to the SSW(I assume) but the NAO has been staunchly positive/neutral for most of winter, is a -2 NAO really enough to suggest high lattitude blocking?

Apologies for all the questions, not an area I understand greatly but hope someone can shed some light!

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GME is the first of this afternoon's 12z to finish and it remains unsettled through to Thursday

gme-0-72.png?12

It does look like the Atlantic train of low pressure systems could come to an end at the end of the week with high pressure starting to drift into the Atlantic blocking the LP systems coming our way

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Looking at NAO and AO forecasts they are both predicted to go negative, could someone explain to me how these being negative helps us? The AO has been negative for a long time now due to the SSW(I assume) but the NAO has been staunchly positive/neutral for most of winter, is a -2 NAO really enough to assist high lattitude blocking?

Apologies for all the questions, not an area I understand greatly but hope someone can shed some light!

I think that some folks are in danger of getting cause-and-effect the wrong way round? AFAIK, you can only derive those indices from whatever the synoptic pattern is...The indices, themselves, do not actually cause the weather; they result from it??help.gif

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I think that some folks are in danger of getting cause-and-effect the wrong way round? AFAIK, you can only derive those indices from whatever the synoptic pattern is...The indices, themselves, do not actually cause the weather; they result from it??help.gif

Ah okay understand I didn't word that correctly, so an NAO being negative is indicative of a blocked Atlantic? (Ie, if the GFS shows massive Greenland block it would be very negative?)

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It would be nice if GFS could chuck in a good FI tonight. Been plenty of good scenarios in the last three ensemble suites.

Jason

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Ah okay understand I didn't word that correctly, so an NAO being negative is indicative of a blocked Atlantic? (Ie, if the GFS shows massive Greenland block it would be very negative?)

Hi Weathizard, I hope this helps.

http://en.wikipedia.org/wiki/North_Atlantic_oscillation

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Ah okay understand I didn't word that correctly, so an NAO being negative is indicative of a blocked Atlantic? (Ie, if the GFS shows massive Greenland block it would be very negative?)

Yes a negative NAO means the Atlantic is blocked, (the more negative, the more blocked) eg 2010 was -4/-5. A negative AO means the Arctic/North of Norway is blocked with height rises in those areas. Remember though as Rybris said they are not drivers they only reflect what the models are showing.

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So far so good from GFS there are continued signs of high pressure starting to build in the Atlantic at the end of the week blocking anymore Atlantic LP systems from coming our way

gfs-0-96.png?12

We still have some rain to get out the way first before things should turn drier (especially in the south west) and cooler through the weekend

gfs-2-96.png?12

gfs-0-102.png?12

gfs-2-102.png?12

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As the high becomes more established cooler air moves in with some wintry showers around in the east

gfs-0-120.png?12

gfs-1-120.png?12

gfs-2-120.png?12

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This little fella at the end of the week keeps being brought up by the GFS;

post-12721-0-86606100-1359389031_thumb.j

Could bring some rather strong winds and heavy rainfall for the south, very heavy rainfall for the SW:

post-12721-0-50501800-1359389100_thumb.jpost-12721-0-32077600-1359389107_thumb.j

On this run it drifts down into Biscay;

post-12721-0-22501000-1359389152_thumb.j

Pulling down some colder uppers from the north;

post-12721-0-44665300-1359389191_thumb.j

But further runs may change the path of the depression or get rid of it altogether. So one to watch, especially in terms of wind/rain for the south and south west.

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Ah okay understand I didn't word that correctly, so an NAO being negative is indicative of a blocked Atlantic? (Ie, if the GFS shows massive Greenland block it would be very negative?)

Exactly!good.gif

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Quite frustrating having that Vortex near Canada/Greenland, seems like whenever we get some sort of high pressure attempting to go north we always have that very strong vortex and jet refusing to play ball, ruddy weather variables.

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its the heights from lastnight on the backend of the first azores high im intrested in.

can we get the second height rises into the north alantic......gfs-0-192.png?6

or should i say the second pulse of heights.

its the heights from lastnight on the backend of the first azores high im intrested in.

can we get the second height rises into the north alantic......gfs-0-192.png?6

or should i say the second pulse of heights.

am i right in saying the sw coming out of the eastern seaboard could aid us as it looks very amplified.

although we also need a decent amount of low heights to our east.

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can the low heights to our north slip down into europe ?

and behind there looks like a quiet less amplified alantic this i think is heading somewhere good fingers crossed.

gfs-0-168.png?12

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Can't post charts but UKMO at 144 looks quite nice with a half decent cold incursion on saturday.

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did somebody order a west based nao.......gfs-0-180.png?12

ukmo same as gfs at t144 apart from less amplified to our north.

UW144-21.GIF?28-17

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more of a tilt then its game on i think were heading somewhere with the gfs im sure if the ukmo went out futher it would be close as well still more runs yet needed but i remember 09/10 alantic blocking and greenland heights it started in the same sort of way.

fingers crossed the ecm can give us a little more hope for a feb cold spell.

gfs-0-192.png?12

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I think its pass 192hrs is when we start to see the more sustained cold, this is the GFS 12z at 204hrs, and its looking quite good!

post-17320-0-82502100-1359390889_thumb.p

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I think its pass 192hrs is when we start to see the more sustained cold, this is the GFS 12z at 204hrs, and its looking quite good!

yes thats the chart i wanted to see seen this setup happen before and we got our sustained cold spell thats a good chart lets hope it dont stay in fi but the evolution of the gfs looks very possible perhaps a little more likely than some of the let downs we seen this winter and last.

although its feb its a good month if we can get the pattern settled in.

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UKMO following GFS by rising pressure this weekend over the UK nice to see some decent agreement at the t144 range

UW144-21.GIF?28-17

gfs-0-144.png?12

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Not sure about people saying the UKMO/GFS agree at 144? Profile to our north is very different and the UKMO to my eyes looks far better for heights around Greenland earlier.

One thing is for certain after this weekend things look fairly settled to me, high pressure dominant and the Atlantic dead after taking all its anger out on us this next few days!

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