In Depth Model Discussion, Analysis and Summaries

[Tattooed Fox]

Summer Blizzard - At last someone had posted something that I can understand "plain English" simple and polite, without bad mouthing the other charts, or anyone else or being totally bias.

Keep up the good work - A very pleasant post

[lorenzo]

For a well written post on the GWO and AAM changes have a read here. Covers the pattern shift, the stratosphere, GWO and MJO.

One image used from the map room shows the scrubbing of the Westerlies GP mentioned some posts ago on this thread.

Edited January 26, 2012 by lorenzo

[Catacol]

GP - for a man whose winter forecast is just about to become the stuff of legends you are very quiet.

From a technical angle, now that the cold is on our doorstep and it looks as though the high may retrogress ala GWO phase 8 as you stated - where are we sat for more specific details through February, or is it just a case of sitting back and watching weeks of cold? I read the article from Lorenzo's post above on WX the other night which, apart from having my head spinning, suggested and phase 8 -1 - 2- 3 shift perhaps mid month. In a more simplistic way than that post what are the signals going through later Feb and on towards March?

Apologies for asking you to do more work. :-)

Edited January 28, 2012 by Catacol_Highlander

[karyo]

I'd love to know as well :-)

Karyo

[jethro]

A query for all you clever people.....

When we get a winter Easterly like now, more often than not we get bitterly cold, but predominately dry weather. Further East where the cold winds originate, the continent gets lots and lots of snow too - why do we get cold but often no snow? I understand the concept that very cold air is usually also lacking in moisture but it's even colder in say Poland and it doesn't stop it snowing there.

[damianslaw]

A query for all you clever people.....

When we get a winter Easterly like now, more often than not we get bitterly cold, but predominately dry weather. Further East where the cold winds originate, the continent gets lots and lots of snow too - why do we get cold but often no snow? I understand the concept that very cold air is usually also lacking in moisture but it's even colder in say Poland and it doesn't stop it snowing there.

I'll let others with more knowledge and experience explain, but I suspect it is down to how unstable the airstream is. Here we have very light winds and the air is very stable indeed hence no convection or trough formation over the N Sea. Had heights been closer to the northeast then we would have seen a much tighter squeeze in the winds and convection and trough formation would be occuring - as we saw in Jan 87 and Feb 91. We also don't have low heights to our south.

In central and eastern europe - the air is much more unstable thanks to a squeeze in isobars caused by a low over Italy and the high over NW Russia - this is creating a very strong wind and stirring the upper atmosphere much more than here enabling heavy snowfall thanks to disturbances in the airflow caused by trough formation.

Easterly set ups such as Jan 87 and Feb 91 are rare, and we often see dry easterly airstreams at this time of year.

A much better place for heights to set up is to the NW of Norway enabling a much more unstable flow from the NE or even better still over Iceland and E Greenland enabling trough and frontal snow formation from the north/northeast as we saw in late Nov 2010 - superb synoptics!

Edited February 1, 2012 by damianslaw

[Robbie Garrett]

Interesting setup this Saturday/Sunday nights. Looks to me that this is going to be a huge headache for the MetOffice to get this right, cold front stalls from the west, and then warm front bumps into it, giving an occlusion.... small LP developed near Amsterdam, which dissapears.

[lorenzo]

An interesting projection on the MJO from NCEP, not looked at this for a bit.. Strongest movement on this chart have seen in what seems like months..

Ties in with your thoughts GP from the Model Thread.

[chionomaniac]

An interesting projection on the MJO from NCEP, not looked at this for a bit.. Strongest movement on this chart have seen in what seems like months..

Ties in with your thoughts GP from the Model Thread.

As Hannibal used to say - 'I love it when a plan comes together'!

[geoffw]

An interesting projection on the MJO from NCEP, not looked at this for a bit.. Strongest movement on this chart have seen in what seems like months..

Ties in with your thoughts GP from the Model Thread.

i take it thats a very cold and snowy chart? even for northern ireland?

[lorenzo]

i take it thats a very cold and snowy chart? even for northern ireland?

Yes Geoff that is correct, this chart keeps us in the Freezer and some of the charts on the NWP in FI land just now are depicting good Northerly / Northwesterly incursions, so I would be positive about your chances. Excitement around this relates to the playing out of the Winter forecasts, and how patience this winter has been thin on the ground at times, looks like it's well been worth it though..

[BLAST FROM THE PAST]

i take it thats a very cold and snowy chart? even for northern ireland?

Geoffw

Green is HP blue is LP. On that chart expect a flow from Northerly quadrant and I would say E of being prevalent....so freezer conditions

BFTP

[Terminal Moraine]

A query for all you clever people.....

When we get a winter Easterly like now, more often than not we get bitterly cold, but predominately dry weather. Further East where the cold winds originate, the continent gets lots and lots of snow too - why do we get cold but often no snow? I understand the concept that very cold air is usually also lacking in moisture but it's even colder in say Poland and it doesn't stop it snowing there.

The easterly we've been experiencing has arisen due to a large block of high pressure over Scandinavia and western Russia .This synoptic situation forces the jet stream south through the Mediterranean and drives areas of low pressure eastward into the eastern Med, the Balkans and the Adriatic where they can linger for days with little filling.

The areas of eastern Europe which have received the most snow, such as Poland and adjacent areas, have been on the northern edge of the low to the south and squeezed between that and the high to the north with a constant feed of bitterly cold but moist and unstable air resulting in copious amounts of snow.

The source of our air flow has been from further north, northern Germany and southern Scandinavia, where the air is much drier and more stable as it flows out of the high.

The situation in the snowy areas of eastern Europe is akin to us having a large area of high pressure stretching between Scandinavia and Greenland and areas of low pressure moving into southern England from a south or south westerly direction, much as happened in February and March 1947.

[Backtrack]

A question for the more advanced users:

Today in Cheshire all I have had is freezing rain with the odd flake thrown in. It started at -3C with a DP of -5C, which I thought was shocking at best.

The uppers at the time were -3C ish.

Manchester had the exact same uppers, dewpoints & surface temperatures, yet they've had lots of snow (knew this would happen anyway)

Now I'm wondering if the warm front had brought in some kind of warm sector between the 850hPa boundary and the surface level that was not picked up on by the models flirting with coastal areas & the Cheshire area that missed Manchester and surrounding areas out?

Thanks.

Edited February 4, 2012 by Backtrack

[LomondSnowstorm]

A question for the more advanced users:

Today in Cheshire all I have had is freezing rain with the odd flake thrown in. It started at -3C with a DP of -5C, which I thought was shocking at best.

The uppers at the time were -3C ish.

Manchester had the exact same uppers, dewpoints & surface temperatures, yet they've had lots of snow (knew this would happen anyway)

Now I'm wondering if the warm front had brought in some kind of warm sector between the 850hPa boundary and the surface level that was not picked up on by the models flirting with coastal areas & the Cheshire area that missed Manchester and surrounding areas out?

Thanks.

Perhaps more a question for the snow risk thread or regional but I'll answer it here anyway.

This has happened in the west of Scotland a few times in the last 2 winters, where everything appears to be fine for snow but when precipitation falls it turns out to be rain.

The reason for this is summed up by this chart:

There was a warm sector at the 900-950hpa level which meant that snow melted and refroze, hitting the ground as freezing rain. This is one of the reasons for using skew -t graphs - they show temperatures at all layers as opposed to just the uppers and surface temperatures. It's an unfortunate quirk in the UK, but relatively common in continental Europe and North America. It's part of the reason why I always check the 950hpa temperatures/skew-t charts if I can when looking at snow risk.

Hope this answers your question

[Backtrack]

Perhaps more a question for the snow risk thread or regional but I'll answer it here anyway.

This has happened in the west of Scotland a few times in the last 2 winters, where everything appears to be fine for snow but when precipitation falls it turns out to be rain.

The reason for this is summed up by this chart:

There was a warm sector at the 900-950hpa level which meant that snow melted and refroze, hitting the ground as freezing rain. This is one of the reasons for using skew -t graphs - they show temperatures at all layers as opposed to just the uppers and surface temperatures. It's an unfortunate quirk in the UK, but relatively common in continental Europe and North America. It's part of the reason why I always check the 950hpa temperatures/skew-t charts if I can when looking at snow risk.

Hope this answers your question

Thanks very much LS, I found the following Skew-T, but it shows the warmer air over Manchester too. As you say, it was at around 3,000ft. It was around +4C, so largely milder than the air it was surrounded by.

Perhaps it was just that the air pocket was slightly milder the further west you are, at for example, my location but effective enough to ensure I saw rain/ice pellets.

Will have to use the skew-t charts more often! Cheers for that!

[johnholmes]

Perhaps more a question for the snow risk thread or regional but I'll answer it here anyway.

This has happened in the west of Scotland a few times in the last 2 winters, where everything appears to be fine for snow but when precipitation falls it turns out to be rain.

The reason for this is summed up by this chart:

There was a warm sector at the 900-950hpa level which meant that snow melted and refroze, hitting the ground as freezing rain. This is one of the reasons for using skew -t graphs - they show temperatures at all layers as opposed to just the uppers and surface temperatures. It's an unfortunate quirk in the UK, but relatively common in continental Europe and North America. It's part of the reason why I always check the 950hpa temperatures/skew-t charts if I can when looking at snow risk.

Hope this answers your question

neat explanation there mate

and yes skew-t diagrams are very useful if its a marginal situation after looking at the usually published data, zero C, 850 temps, 1000-850 thickness, Td, wet bulb T etc.

[Backtrack]

neat explanation there mate

and yes skew-t diagrams are very useful if its a marginal situation after looking at the usually published data, zero C, 850 temps, 1000-850 thickness, Td, wet bulb T etc.

Cheers John,

Quite proud of myself, in one day I've just learned how to use the Skew-T diagrams and how to properly read the 500mb height anomaly charts.

Good, blocked February on the cards.

[johnholmes]

Cheers John,

Quite proud of myself, in one day I've just learned how to use the Skew-T diagrams and how to properly read the 500mb height anomaly charts.

Good, blocked February on the cards.

good to hear-we all learn from each other every day.

Had you tried the Guide on skew-t's?

[Backtrack]

good to hear-we all learn from each other every day.

Had you tried the Guide on skew-t's?

Nope, but you made it right?

I will go and read it now

[LomondSnowstorm]

Thanks very much LS, I found the following Skew-T, but it shows the warmer air over Manchester too. As you say, it was at around 3,000ft. It was around +4C, so largely milder than the air it was surrounded by.

Perhaps it was just that the air pocket was slightly milder the further west you are, at for example, my location but effective enough to ensure I saw rain/ice pellets.

Will have to use the skew-t charts more often! Cheers for that!

No problem, they are very useful

It was close to being freezing rain in Manchester but must've just held below 0C, whereas it was milder further west. It can be snow with 850hpa temperatures of -1C as long as it's below down to ground level with a dewpoint around 0C at surface level.

[lorenzo]

Going to have a stab at the models current lack of clarity. From looking at an excellent thread on the Amwx site on the MJO pattern it is clear that there are definite variations in the forecast suites as to the impact of the convection, perhaps leading to the hazy NH solutions we are seeing. Folk are mentioning background signals on the MT, these to me are those signals.. would like to say that am still learning in this area and if any of this needs an edit or corrected then please do.

GFS ramped up the amplitude initially in phase 7 where ECM was more moderate, Met not show here was tempered between them but now perhaps the most progressive through the phases. From the information on this page it appears that the UKME (UK Met Ens) and NCPO (NCEP Op) are similar. ECM on chart below looks incoherent, I wonder if it works better with the MJO run created every Thursday with the seasonal variability built in. MJO bulletin updated tomorrow by NOAA may explain further.

Some discrepancy then as to how this current MJO phase will filter into the model runs.GWO looking more favourable with a solution for ridges and minimum westerly flow. The blocking index up to day 9 still showing the mid-atlantic ridging and retrogression towards mid month, as do the CPC maps.

[LomondSnowstorm]

Going to have a stab at the models current lack of clarity. From looking at an excellent thread on the Amwx site on the MJO pattern it is clear that there are definite variations in the forecast suites as to the impact of the convection, perhaps leading to the hazy NH solutions we are seeing. Folk are mentioning background signals on the MT, these to me are those signals.. would like to say that am still learning in this area and if any of this needs an edit or corrected then please do.

GFS ramped up the amplitude initially in phase 7 where ECM was more moderate, Met not show here was tempered between them but now perhaps the most progressive through the phases. From the information on this page it appears that the UKME (UK Met Ens) and NCPO (NCEP Op) are similar. ECM on chart below looks incoherent, I wonder if it works better with the MJO run created every Thursday with the seasonal variability built in. MJO bulletin updated tomorrow by NOAA may explain further.

Some discrepancy then as to how this current MJO phase will filter into the model runs.GWO looking more favourable with a solution for ridges and minimum westerly flow. The blocking index up to day 9 still showing the mid-atlantic ridging and retrogression towards mid month, as do the CPC maps.

Intriguing. I find it completely bizarre that the ECM and GFS take the MJO in totally different directions in the short term, with the ECM weakening and remaining in phase 6 but with the GFS exhibiting the strong change through the phases that GP envisaged. By that logic the GFS should give the best route to full on retrogression, at least when looking at its MJO. The background signals appear to favour retrogression to southern Greenland and a continuation of high latitude blocking. GLAAM has bombed in the last two weeks, and this in turn should aid the reversal of zonal winds at mid-high latitudes:

[phil nw.]

Yes MJO forecasts are open to interpratation wrt to the phase in week2.I have posted in the other Model thread on this and other data but at the end of the day we all seem to come to the same conclusion.All eyes to the North i think for some cold renewal beyond day10.

[LomondSnowstorm]

The MJO forecasts today look a lot more coherent. It would appear that the ECM was simply just 'off on one' yesterday and today is favouring a reasonably strong progression through phases 7 and 8 and into phase 1:

This has support from the GFS ensembles, with the only real difference being slower progression through phases: