In Depth Model Discussion and Summaries

[Catacol]

Lorenzo - where do I get access to that WxBell ECM chart you posted? Is that for paid subscribers only?

[lorenzo]

Lorenzo - where do I get access to that WxBell ECM chart you posted? Is that for paid subscribers only?

 Yes Weatherbell charts are subscription ones. They occasional appear on twitter from Joe B or Dr Maue.

[johnholmes]

dropping this guide in here re the storm predicted for the north on Thursday as well as the model thread

 

The Thursday storm for the north

 

I did promise to give a link to useful sites to watch this form-deepen and track through Wednesday into Friday.

 

Also copied into the so called technical thread-don’t be put off by the title, it should remain easier to find than in here where no doubt by tomorrow it will be ‘lost’. Enjoy following and learning about the weather from this depression, have a look at the Net Weather Guides for more information on things you may not be clear about and of course ask questions.

 

The Fax charts

http://www.weathercharts.org/ukmomslp.htm

Satellite charts with the infra red movie version perhaps the best to track but others also very interesting, for the Dundee ones you need to register (it’s free and easy to do)

http://www.sat.dundee.ac.uk/auth.html

http://www.yr.no/satellitt/europa_animasjon.html

Actual weather, several places to bookmark

For actual weather on the Shetland Isles

http://www.shetland.gov.uk/icecast/default.asp

Regular hourly reports from sites all over the UK and abroad if you wish

http://www.xcweather.co.uk/

Track the low from buoy reports although many are south of its expected track

http://www.ndbc.noaa.gov/maps/United_Kingdom.shtml

 

Charts showing the progress of the low

Obviously 6 hourly updates from Exeter of their Fax charts

And this site, remember it is a computer generated chart and is at times not as accurate as the Fax for the same time. It is very useful to watch its general track, deepening etc.

http://meteocentre.com/analyse/map.php?hour=0〈=en&map=UK

for those that understand the WMO code this list all the stations in the UK in the SYNOP code with stations in Shetland and Orkney fromm03001 to about 03017, to see what the SYNOP for Torshavn north of the track is giving the type in 06011, all of them report every 6 hours, 00,06,12,18 and some every 3 hours

 

For forecasts-see above for Shetland and below the full UK Met including shipping areas

http://www.metoffice.gov.uk/weather/uk/uk_forecast_weather.html

[forecaster]

We've been hearing a lot about how next week's high might still lead to cold surface temperatures in the SE. This seemed a sure bet for a while, but I'm now less convinced. The westerly flow from the weekend should enable maritime air to mix into the boundary layer. Any anticyclone, even with a continental drift, following this will not displace that air. It would remain near average at the surface with overnight fog likely. 

To prevent that from happening, and to get a genuine cold high with continental drift, you would have to hope that the stability is such that on the weekend the Atlantic air does not mix down to the surface across the entire country. I don't think this is the "form horse" at the moment. 

 

Looking at the GFS 06Z run:

 

 

Here we have a possible continental drift for much of S England, with the maritime S/SW flow affecting only the fringes of the UK. So what would be the source of the air were this to happen?

 

 

The red line is a back trajectory starting at Heathrow at 100m and the blue line at 1500m. You can see the different origins of the air at both levels, but the surface air still has substantial maritime modification.

Not a cold anticyclonic spell by any means. Maximum temperatures in the SE would push near the low double figures.

 

The caveat of course is that this is all based on one GFS run. 

 

But since the "continental drift" is going to continue to be a subject of debate we have to remember a few things:

 

1) If you already have maritime near-surface air, a continental drift is not going to displace that. 

2) If you want a cold anticyclonic spell, you have to prevent the maritime air from mixing in to the boundary layer to begin with. This looked likely up until a few days ago, now it seems less likely. 

3) Once the anticyclonic spell gets going, whatever you have at the surface is pretty much what you're stuck with. Although there is a radiation imbalance at this time of the year, your problem is that the dewpoints will be quite high. This leads to issues with overnight fog, which prevents significant cooling. You could get cold (ish) daytime highs in areas only where the fog lingers - but these highs would likely still be around 7C. 

4) Stratocumulus layers are the other issue. Only at short range can you figure out whether it will be fog or Sc, but both ultimately lead to similar regimes of low max-min variation. 

 

Don't think people should be getting their hopes up too much regarding this high for next week, unless they live in places like Benson.

[phil nw.]

Good analysis there Forecaster and based on the high resolution period of that run what you say looks likely with higher dp's and the mixing out of surface cold.

Of course as we know any high does eventually start to move around and the lower resolution would re-introduce some drier continental air with lower dp's and cloud breaks-night frosts.The winds backing more se as the cell is modeled further east.

 

Nothing stays the same as they say and this debate will be ongoing i guess unless of course modeling moves the high to an even less favourable location.

[LomondSnowstorm]

This was originally posted in the Scottish regional thread but I felt it was also worth putting in here as well, if for no other reason than to 'bump' this thread up and maybe encourage some more of the usual excellent posts on here:

There are hints of cool/cold zonality as we go towards Christmas, with the Euro high increasingly likely to be flattened and troughing digging south via height rises on the other side of the pole again. This from Joe B from EC control for the 22nd shows how we can maybe cash in from that intense North American based cold - note the Atlantic ridging starting to divert the jet southeastwards:

 

Talk of similarities to the late December 1983 severe cold outbreak over the pond (their coldest December on record) which is interesting for us because of the month that followed here:

Note the Aleutian ridge as well - as I discussed with last week's setup it's critical to shunting the vortex off Greenland and allowing Canadian sourced northwesterlies in. Normally this kind of setup is somewhat speculative but my thinking is that, with the extreme depth of cold that will continue to build in the North American continent in the next 10-15 days, there's a much better than average chance of that kind of setup delivering. I think the Euro high might still be too dominant to stop anything other than a more bog standard zonality up to Christmas (with still the odd hint of high ground snow potential if we're in a 'cold front' phase of the pattern) but after that, with the Euro height anomaly steadily decreasing and the Aleutian high gaining traction, the possibilities are intriguing (albeit that's not a particularly inspiring mean on the face of it):

 

What I most like about this solution is that it's synoptically 'big' and elegant, and also could also segue nicely into a January which is increasingly dominated by a more southerly tracking jet and the first proper HLB (all speculation at this stage but there's at least a bit of interest starting to show up on the strat thread as well which should help down the line).

So, in summary, HP less likely, full on storminess/troughing/rain zonality also more likely but the real shift in probability is towards a cooler zonality in the longer run, although with the evolution pretty slow, painful and potentially resulting in a dreich, sodden and cool but not quite cold enough for snow Christmas period.

[lorenzo]

Little while back put together an MEI and GWO plot for the first half of December. Though it best to re-visit with re-analysis. Updated through until 11th December.

 

Not a great correlation, the cold outbreak into CONUS has verified pretty well, the West Atlantic ridge which on the composite, and noted at the time, seemed a little progressive it  did not establish, everything rotated slightly further east on the composite for our side of the hemisphere, the cold troughing for re-analysis right in our locale versus Russia. We also didn't see any Siberian heights, the North Pacific ridge a lot stronger than the composite dates, however this Aleutian High has been one of the strongest on record for 2013 as a whole.

Composites for YTD and November to Date

 

 

 

However, can see some similar themes in the general pattern of both, so not totally disheartened. Conclusion and learning point here for me is that in December vortex rules the roost and any significance from analogs can be used but only if weighted to consider the current state of play in the strat. Any thoughts welcome !

 

 

[lorenzo]

Interesting, the CPC GEFS outlook on the MJO activity update today has a couple of notable highlights. Also interesting wrt the predicted MJO progression http://forum.netweather.tv/topic/78775-moderate-tropical-storm-amara/

 

IO action seemed to suck every ounce of energy out of the last MJO Phase so how it transfers to the Pacific of massive interest in how Jan. unfolds.

Quote

It is unclear at the current time whether the persistent enhanced convection we have seen across the Indian Ocean over the last few weeks will shift eastward on MJO timescales and emerge over the western Pacific by the end of December. 

 

I must admit to liking the UKME for MJO projection, seems more refined than the hasty GFS, GEFS which is on occasion at odds with the ECM, faltered by it's lead time. UKME ensemble then control provides a good balance for a glance before referring to raw data.

 

Both, however are on the case with some height rises should the MJO punch out of the energy going into the cyclones and traverse into WPAC.

 

Phase 5 is not a bad place to move on from in January as blocky phases 7/8 await, frictional torque builds and mountain torque in the offing, very lively end to the year for the storm track, January already gathering interest..

 

[lorenzo]

Meant to add these to ^^^

 

RE; Kelvin Wave discussion - this plot shows that recent activity largest KW of 2013.

 

Phase 5 in Map view or ALL if you prefer.

 

Another thought wrt ENSO /MEI, what would MJO progression do to SSTa's...

 

 

[johnholmes]

pdf from model thread

 

pdf using anomaly charts and current synoptic ouput 17 dec 2013.pdf

[johnholmes]

When I get time I will drop the links about snow etc in here as they may be easier to find than in the model thread, including the posts from the 3 I mentioned.

[lorenzo]

GWO in higher orbit now, and also a little uptick in Red on the Mountain Torque chart, signs of a pattern shift. Wonder how much influence the torque event will have..

[johnholmes]

hopefully this will copy

Links for snow information guides

 

Posted Yesterday, 23:59

http://forum.netweather.tv/topic/78787-model-output-discussion-17th-dec2013-12z-onwards/page-6

Seeing as we are discussing the chances of snow, here is some supplementary info regarding various parameters and their relationships with the likelihood of snow... (all from the Met Office, for educational purposes)..

Probability of snow________________90%____70%___50%___30%___10%
Surface temp ( C ) _________________+0.3____+1.2___+1.6___+2.3____+3.9
Height of 0C isotherm agl (hPa)______12______25____35_____45______61
1000-500hPa thickness (gpm) ______5180___5238__5258___5292____5334 ______ (the "528 line" falls around 40%)

(mutually exclusive)

Based on WHEN precip begins, as mentioned above latent cooling of the atmosphere will lower the freezing level once the snow starts falling/melting.

The wet-bulb freezing level is very important as well...

  Mainly snow Readily turns to snow   Mainly rain   Snow very rare

Height of theta-w freezing level agl < 1000ft (~300m)               <2000ft (~600m)             >= 2000ft       >= 3000ft  (~1000m)
It's also important to watch out for cold surface air undercutting warm air.

A general rule of thumb for the UK is that an 850hpa theta-w of 2C or below can allow for snowfall down to penetrate down to all elevations (with a large number of caveats obviously). Heavy instability and persistent precip with an initial wet-bulb temperature level of as high as +3C can allow snow to reach the surface.

 

Because of the marginality evaporative cooling can help to deliver a surprise, heres a good article by Philip Eden about this:

 

The best way to explain what happens in the latter case is to look at an example: the best recent occurrence was on Wednesday 14 January 2004 when a shallow depression tracked eastward across Wales and the Midlands. Ahead of the area of rain and snow, temperatures stood at 5 or 6°C, so why did the rain - turn so readily to snow? The clue was the absence of much wind. Crucial also was the heaviness of the rain. In the UK, nearly all the rain that falls starts off as snow at cloud-level. This is because the temperature normally decreases with height above the Earth's surface. When the air is saturated, according to the laws of physics the temperature drops by 0.5°C for every 100 metres above the ground. Thus on that Wednesday morning the temperature was around zero about 1000 metres above places like Coventry and Northampton an d at that altitude the falling snowflakes would begin to melt.
 

However, a large amount of energy is needed to melt snow, and high above England on a dull January day the only source of energy is the air itself. This energy is known as 'latent heat' specifically, the latent heat of fusion. Thus the melting snowflakes absorbed heat from the surrounding air, causing the temperature to drop, in turn allowing the falling snow to penetrate lower and lower until it eventually reached the ground. The heavier the precipitation the more energy is absorbed and the more rapid the temperature will drop, but this can only happen when there is no wind to mix the cooled air with "uncooled" air arriving from elsewhere.

 

This mechanism produced even bigger surprise snowfalls in central and southern England in late-January 2001 and early-January 1994, so forecasters should always be on the lookout for it.

 

The January 1994 event was a big surprise as I was living in Kingston at the time, the key as PE says is to have little wind to stop too much mixing and heavy precip.

 

This quote taken from a History of Weather in Epsom and Ewell:

 

The 6th of January started with heavy rain which turned to sleet and then snow. Some flakes measured 3 inches across and lay up to 6 inches deep in places.

 

And the archive chart you just wouldn't have ever thought that this could produce such a surprise for the south!

 

 

 Steve Murr, on 17 Dec 2013 - 22:47, said:

yes mate - its not the only parameter to measure-  however 1290 is usually the benchmark -

 

Probability:............................90%.....70%.....50%.....30%.....10%
850-1000 hPa(gpm)..............1279.....1287....1293....1297....1302 (un-adjusted)

 

If we could bet 1293 then that's 50/50- obviously the scaling on the NAE would be better at intervals of 5 instead of 10- however at least it shows roughly where the risk is-

Theres also an adjustment for height-  so elevated areas can see snow in higher thicknesses.

 

S

 

Net Wx Guide information

 

http://forum.netweather.tv/topic/27989-how-to-try-and-forecast-snow/

[johnholmes]

copied from model thread so I can find it in 12 hours time!

 

 

well my comment about the 8-14 from NOAA needing to show a similar idea to the 6-10 has been given this evening.

Just how much we can rely on the two I am not sure but they are consistent over the last 2-3 days. It is about the date that the 8-14 should have picked up on the 6-10 day idea if there was to be any credence in the evolution that the 6-10 and ECMWF-GFS have shown for 2-3 days.

No, don't get too excited, not a pettern change but it does look like a fairly marked change in temerature levels at 500mb, from 540-546DM to around 53DM now being redicted over the Channel area. The flow at 500mb, with an actual centre drifting SE of Iceland towards NW Scotland drops the speeds up there and for a day or two perhaps increases them in the south. This will perhaps have the effect of moving part of the surface lows further  south or possibly some kind of secondaries developing south of a main surface centre near the NW of the UK.

All very tentative but the mobilty slowly easing down and both upper and surface temperatures easing down as well. This obviously increases the probability of some snow to lower levels at times. Don't expect any detail from this post though and as to how long then, timing suggests this idea evolving over the next 4-5 maybe 6 days and then around for a further 3-4. Beyond that who knows.

link to NOAA outputs below

http://www.cpc.ncep....14day/500mb.php

[boyblue]

hopefully this will copy

Links for snow information guides

 

Posted Yesterday, 23:59

http://forum.netweather.tv/topic/78787-model-output-discussion-17th-dec2013-12z-onwards/page-6

Seeing as we are discussing the chances of snow, here is some supplementary info regarding various parameters and their relationships with the likelihood of snow... (all from the Met Office, for educational purposes)..

Probability of snow________________90%____70%___50%___30%___10%

Surface temp ( C ) _________________+0.3____+1.2___+1.6___+2.3____+3.9

Height of 0C isotherm agl (hPa)______12______25____35_____45______61

1000-500hPa thickness (gpm) ______5180___5238__5258___5292____5334 ______ (the "528 line" falls around 40%)

(mutually exclusive)

Based on WHEN precip begins, as mentioned above latent cooling of the atmosphere will lower the freezing level once the snow starts falling/melting.

The wet-bulb freezing level is very important as well...

  Mainly snow Readily turns to snow   Mainly rain   Snow very rare

Height of theta-w freezing level agl < 1000ft (~300m)               <2000ft (~600m)             >= 2000ft       >= 3000ft  (~1000m)

It's also important to watch out for cold surface air undercutting warm air.

A general rule of thumb for the UK is that an 850hpa theta-w of 2C or below can allow for snowfall down to penetrate down to all elevations (with a large number of caveats obviously). Heavy instability and persistent precip with an initial wet-bulb temperature level of as high as +3C can allow snow to reach the surface.

 

Because of the marginality evaporative cooling can help to deliver a surprise, heres a good article by Philip Eden about this:

 

The best way to explain what happens in the latter case is to look at an example: the best recent occurrence was on Wednesday 14 January 2004 when a shallow depression tracked eastward across Wales and the Midlands. Ahead of the area of rain and snow, temperatures stood at 5 or 6°C, so why did the rain - turn so readily to snow? The clue was the absence of much wind. Crucial also was the heaviness of the rain. In the UK, nearly all the rain that falls starts off as snow at cloud-level. This is because the temperature normally decreases with height above the Earth's surface. When the air is saturated, according to the laws of physics the temperature drops by 0.5°C for every 100 metres above the ground. Thus on that Wednesday morning the temperature was around zero about 1000 metres above places like Coventry and Northampton an d at that altitude the falling snowflakes would begin to melt.

 

However, a large amount of energy is needed to melt snow, and high above England on a dull January day the only source of energy is the air itself. This energy is known as 'latent heat' specifically, the latent heat of fusion. Thus the melting snowflakes absorbed heat from the surrounding air, causing the temperature to drop, in turn allowing the falling snow to penetrate lower and lower until it eventually reached the ground. The heavier the precipitation the more energy is absorbed and the more rapid the temperature will drop, but this can only happen when there is no wind to mix the cooled air with "uncooled" air arriving from elsewhere.

 

This mechanism produced even bigger surprise snowfalls in central and southern England in late-January 2001 and early-January 1994, so forecasters should always be on the lookout for it.

 

The January 1994 event was a big surprise as I was living in Kingston at the time, the key as PE says is to have little wind to stop too much mixing and heavy precip.

 

This quote taken from a History of Weather in Epsom and Ewell:

 

The 6th of January started with heavy rain which turned to sleet and then snow. Some flakes measured 3 inches across and lay up to 6 inches deep in places.

 

And the archive chart you just wouldn't have ever thought that this could produce such a surprise for the south!

 

 

 

 Steve Murr, on 17 Dec 2013 - 22:47, said:

yes mate - its not the only parameter to measure-  however 1290 is usually the benchmark -

 

Probability:............................90%.....70%.....50%.....30%.....10%

850-1000 hPa(gpm)..............1279.....1287....1293....1297....1302 (un-adjusted)

 

If we could bet 1293 then that's 50/50- obviously the scaling on the NAE would be better at intervals of 5 instead of 10- however at least it shows roughly where the risk is-

Theres also an adjustment for height-  so elevated areas can see snow in higher thicknesses.

 

S

 

Net Wx Guide information

 

http://forum.netweather.tv/topic/27989-how-to-try-and-forecast-snow/

Thanks John, I really enjoyed reading this article & appreciate the work gone into producing this write-up.

[johnholmes]

not me but the two who posted the data that I simply copied into here so they don't get lost

[boyblue]

Indeed, mea culpa, thanks to Steve & Nick.

[lorenzo]

From the Vitart poster on the ECM32.

 

The Madden-Julian Oscillation (MJO) is the main source of predictability on the monthly time scale. 

The MJO is characterized by an eastward propagation of convection along the tropical band, typically initiated over the Indian Ocean. When the MJO is in its active phase over Maritime Continent and West Pacific, it tends to drive negative NAO circulation with cold temperatures over Northern Europe 2 Weeks later.

 

Current MJO outlooks - highlighted here on the ECM plots are a couple of nice looking outliers. Transition shown from Indian Ocean > Maritimes  >West Pacific, which you can see more clearly on the Hovmoller below.

 

On the Roundy plot the MJO signal is clear at the top of the chart, so not noise.

 

January Phase 7 for low amplitude phase as per predictions above, bear in mind the lag.

 

Could not look more different to where we are at now, but good model guidance for a negative NAO signal working through in the mid range. Height rises over Greenland and potentially some wave 1 activity.

 

 

 

[johnholmes]

Picking up on the post from L, all way beyond my ability to be able to use it but thanks for the information. The last bit of your post regarding height rises over Greenland.

It is no more than a tentative and generally inconsistent signal but all 3 anomaly charts, have at times over the past 3-5 days, shown +ve heights developing between Greenland and the pole along with even a suggestion, no more, of actual ridging in the 500mb flow. I post this in here as it is less likely to get lost quickly and may not be picked up here by the rabid cold fraternity. It is worth watching the anomaly charts though to see if the 6-10 extends into the 8-14 with any consistency. IF and a big IF at the moment the trend they show continued then where this ridge/height anomalies are predicted, would tend to split the main Polar Vortex. Keep watching to misquote the dancing programme!

Edited December 21, 2013 by johnholmes

[bluearmy]

Picking up on the post from L, all way beyond my ability to be able to use it but thanks for the information. The last bit of your post regarding height rises over Greenland.

It is no more than a tentative and generally inconsistent signal but all 3 anomaly charts, have at times over the past 3-5 days, shown +ve heights developing between Greenland and the pole along with even a suggestion, no more, of actual ridging in the 500mb flow. I post this in here as it is less likely to get lost quickly and may not be picked up here by the rabid cold fraternity. It is worth watching the anomaly charts though to see if the 6-10 extends into the 8-14 with any consistency. IF and a big IF at the moment the trend they show continued then where this ridge/height anomalies are predicted, would tend to split the main Polar Vortex. Keep watching to misquote the dancing programme!

 

john, this anomolous 'greenland' (we'll call it that but it is shown in various locales by different runs) height rise is the consequence of the bubble of higher heights thrown into the arctic by the scandi ridge on thursday.  whilst one would expect it to be mixed out over several days, it has been modelled to be a persistent feature and though shallow, it shows as it survives amidst the very low dam currently in the general area to our nw. it becomes bolstered by the growing arctic high just the other side of the pole and it enables a weak ridge to be thrown down across n greenland. its this mechanism which pushes the jet on a more southerly routing as we head through the coming week.

 

the end result is that we have a split trop vortex with the canadian master and east siberian daughter. however, the low heights thrown east by the canadian vortex (and associated strong northern arm) do muddy the waters re any possible ridging from our side of the NH.  some of the ens manage to do it but in general, it seems unlikely for the time being. if its going to happen, i expect to see it to our ne on an axis from west russia towards alaska.

Edited December 21, 2013 by bluearmy

[johnholmes]

another bit of reference, this time for wind gusts inland over various surfaces

 

I'll dig it out, briefly the rougher the surface the higher the gust ration, so less over the sea and more over rough ground, be hat vegetation or buildings

 

no idea where the table I postut some of it

 

average values of gust over mean hourly speed

flat open country=1.6

centre of towns/outskirts cities=1.9

centre of large cities=2.1

 

so in VERY simple terms, if mean wind speeds say for London were given as 25mph it is POSSIBLE to gust to 50mph

 

also dropping this in the technical thread is it will be easier to find in 24 hours if anyone wants it

[lorenzo]

With reference to the MJO post from earlier today, here is a blog article regarding the current projection, Great reading...

 

http://www.wsi.com/blog/energy/the-current-mjo-event-and-anticipated-future-progression/

[lorenzo]

Great Blog Post here from the Capital Weather Gang contrasting recent climatology with historic set up.

 

http://www.washingtonpost.com/blogs/capital-weather-gang/wp/2013/12/24/arctic-warming-jet-stream-coupling-may-portend-another-winter-of-extreme-storms-and-cold-air-outbreaks/

[bluearmy]

ecm fi ens much more bullish about dropping heights into europe in a fortnight than neafs (gefs/cmc) and its output looking more wintry in two weeks time. i am intrigued as this is the first time that the ecm ens have had full sight of a top down warming in the strat.  last january, we saw strong wave 1 activity above 5hpa which subsequently led to the SSW. the ecm ens just couldnt see it as they topped out at 5hpa. until the wave reached 5hpa at initialisation, they didnt show any cold in a fortnights time. as soon as that wave reached 5hpa - boom, they flipped to a cold mean solution within a fortnight.  at the moment we have very strong mean zonal winds which will be tempered somewhat by the upper warmings.  by day 8 we see increased wave 1 activity begin which will complement the already large wave 2 which is already underway.  looking at yesterday's ecm strat run, at day 10, one can see, as high as 30hpa, a shallow upper ridge around svaalbard and the inclination to send the jet on a nw/se axis with troughing dropping into europe. one assumes that the ecm ens will also be modelling this by the time they reach this timescale. although gefs and cmc ens also go to the top of the strat, they have far less horizontal levels and theoretically, will not model the mid/upper strat as well as the ecm ens.

 

IF the ecm ens have called this right, it will not prove that it is the visibility above 5hpa which has led to it but it will certainly show that no longer will events at the top of the strat catch the ecm ens suite on the hop as happened in january.

[johnholmes]

pdf copied from the model thread

 

looking at things sat 28 dec 13.pdf