In Depth Model Discussion, Analysis and Summaries

[The PIT]

Not trying to poo-poo long range forecasts of any description as GP has had some very good successes. This pattern matching can though be very easily put off track, I just went through the last few pages for April/May to see what it was predicting for June and came across a reference that June would be unsettled and cool.

I ma not sure we should really write anything off, remember these are just possibilities some higher, some lower of what might happen and a trough placed slightly differently can give us some very nice hot and thundery weather as opposed to cool NWerlys.

Cheers

Indeed also look at netweathers June forecast couldn't be more wrong if it tried although briefly it was on track until the present warm/hot spell arrived.

[Paul]

Indeed - although those lrf's have had a good record in recent months (and indeed over the last couple of years), this month has been a bad one! This is the update which was created a week after the forecast went live - would have been a touch more accurate I think!

[Eugene]

Well i want to stick up for netweathers June forecast and anyone else who forecasted an unsettled June, the first ten days were unsettled then yes it turned more settled but last week could easily of been unsettled too had it not been for LP stalling to our west so we had a narrow escape(it did turn unsettled in the north and west early in the week) only has the last week been that warm especially at night.

There were some very cool mins mid month in countryside areas and even this week i recorded 6C in a local valley when it was 13C in town, if the CET's weather stations were more rural i'm sure it would of ended up cooler.

200 years ago the CET would of been much lower than today due to urban sprawl nowadays especially in the SE and west midlands areas.

　

[johnholmes]

An attempt to suggest the overall weather patterns through July

Overall the signals suggest to me that July will continue much as it has started with an upper trough just west of the uk,weather systems affecting the NW’ern half of the UK but not really much for the SE half. Rather breezy at times as one gets further NW with rain at times but even here, in areas with shlter in the east, some drier sunnier spells with temperatures above normal. Normal or a shade below at times where more cloud and rain. The further south and east then probably above normal to warm much of the time. With the upper trough just west of the country then a risk of relatively minor thundery outbreaks as part of the trough swings NE at times.

Further into July then most areas look likely to have the weather dominated by surface high pressure although its location is open to doubt. This may take some time for it to extend further north where a rather unsettled regime, as described in the first paragraph seems likely at first.

So maybe a touch wetter than normal in the far NW but around or, in general, somewhat below normal the further SE one goes, so away from western areas south of about NW England thus affected.

This should give about normal temperatures for the cloudier areas but tending to somewhat above later. For other areas then rather above normal to warm at times, especially the further SE one goes. I would reckon a prob of 30% of very warm-hot on a few days for some central and SE’ern places.

By the end of July then, assuming the hurricane season has been correctly forecast then events in the south of the north Atlantic, off Africa and off the eastern States may well begin to cause the Atlantic to start to wind up more. Whether this, in August, will produce Cape Verde type effects or the more usual recurving of ex hurricanes across the Atklantic is far to early to even try to predict.

Edited July 2, 2010 by johnholmes

[Thundery wintry showers]

I agree, I can see westerlies dominating for a while, but with a high likelihood of high pressure making a return later in the month.

My first bash at the teleconnections outlooks (many thanks to Stewart btw for helping me out with where to find the information) has the main GWO analogues suggesting a westerly type over the British Isles:

http://www.esrl.noaa.gov/psd/tmp/composites/compday.139.222.228.199.182.16.40.44.gif

...and the MJO looks like hanging around in phases 2 or 3 for a while:

http://www.cpc.noaa.gov/products/precip/CWlink/MJO/combphase_noCFSsmall.gif

which going by analogues suggests a westerly type but possibly with an above average influence from the Azores High. NAO is forecast to be near-neutral, AO slightly positive.

[swebby]

An attempt to suggest the overall weather patterns through July

...................

By the end of July then, assuming the hurricane season has been correctly forecast then events in the south of the north Atlantic, off Africa and off the eastern States may well begin to cause the Atlantic to start to wind up more. Whether this, in August, will produce Cape Verde type effects or the more usual recurving of ex hurricanes across the Atklantic is far to early to even try to predict.

Thanks John, would you mind explaining what the underlined bit means please and what effect that could have on the weather for the uk?

Thanks

S

[johnholmes]

Thanks John, would you mind explaining what the underlined bit means please and what effect that could have on the weather for the uk?

Thanks

S

hi swebby

Hopefully this may help?

Cape Verde isles are off the west coast of Africa.

Thanks to plenty of open warm water they tend to be the most severe of hurricanes. Thus they develop over the Atlantic, well south of course, rather than those that develop unto hurricanes from cloud masses that move west off Africa and get caught up in the general NW movement into the warm waters of the Caribbean.

Some of the largest and longest lasting hurricanes are those that originate from the Cape Verde area. There is quite a lot of research I understand going on into trying to understand these features.

That is about all I can tell you from my limited knowledge but hope it helps.

If anyone can add to this please do so.

[swebby]

Thanks John, Would i be correct in assuming that a strong cape verde hurricane stuck in the mid alantice would help strengthen an azores high where as extra tropical depressions being swung round fro the US would flatten/weaken it? I.e cape verde effect = stronger likelyhood of ridging towards the uk. Active hurricanes heading up the US eastern seaboard = likelyhood of mobile unsettled weather for the uk?

Cheers

S

[johnholmes]

as in most things meteorological the answer is yes and no!

Cape Verde storms IF they held up in the Atlantic could help the Azores ridge develop, equally one such storm might simply run towards the UK. Just which direction from being dependent on where any upper ridge was at the time it reached its maximum intensity.

There are too many variables to give scene 1, 2 etc, there being probably at least 10 that might occur!

sorry if it seems a cop out its not, simply being honest and realistic.

[summer blizzard]

as in most things meteorological the answer is yes and no!

Cape Verde storms IF they held up in the Atlantic could help the Azores ridge develop, equally one such storm might simply run towards the UK. Just which direction from being dependent on where any upper ridge was at the time it reached its maximum intensity.

There are too many variables to give scene 1, 2 etc, there being probably at least 10 that might occur!

sorry if it seems a cop out its not, simply being honest and realistic.

Essentially, they just increase the thermal gradiant, in an El Nino year with a dominant Atlantic Trough, this could cause a plume, or in an La Nina year with a dominant Atlantic ridge you can end up with a trough dumping hughe amounts of rain over the UK (think August 2005, 100mm of rainfal at 28C, tropical), in our current base state, iwould lean towards the dump.

[BrickFielder]

There was an interesting anmaly over the last month in the southern Pacific, which I swould draw attention to because it happened last year as well.

This maybe a little transitory so la nina forecast like the IRI ones may be overdone.

Still subsurface temperatures across the pacific also confirm the probability of la nina returning along with the reduction in global angular momentum showing up in the GWO.

500hpa anomalies over the last month suggest a winter la nina pattern across the US.

This I think will drive our weather more than sea surface temperatures which would tend towards higher pressure towards greenland.

As GP explains it is not so easy to extrapolate from last months events what will happen going forward because the wave lengths will be changing. My guess is that the hurricane season will not quite take off as expected with a greater risk this year that tropical storms will re curve towards the UK. I expect conditions to somewhat flipflop between la nina and Sea surface temperatures being the dominate forcing. My bet would be that la nina will tend to dominate. As the jetstream continues slowly north and the wave lengths lengthen then I would look for the azores ridging towards the southern UK, high pressure towards greenland and periods of where there is a blocked trough to our north west.Good for the north but not so for the far north, although that probably does not take into account the continental high which tends to build around this time of year.

[Glacier Point]

Total angular momentum continues to bump along at nearly -2 SD as La Nina and the -PDO strengthen their grip on the atmospheric circulation:

The Global Wind Oscillation is orbiting in low amplitude reflective of our low angular momentum Nina-like base state:

Organised tropical convection is centred in the central - eastern Indian Ocean and the MJO is slightly west of this location, The MJO wave is in phase 2:

and forecast to migrate eastwards and significantly pep up as it meets the favourable convective environment ahead of it. Hence GFS suite forecasts depict a high amplitude phase 3:

http://www.cpc.ncep...._CFSOP_GEFS.gif

The last two times the MJO has passed through this phase, angular momentum has increased as a result of increased westerly momentum introduced across the tropics.

With torques looking fairly neutral over the 10 day period, it is quite possible that total angular momentum will increase slightly although we are so far below average that any increase will only keep us in phase 3 orbit of the GWO. This will likely continue for the next 10-14 days until the MJO hits a wall in the western Pacific and fizzles and the Global Wind Oscillation begins to reflect a sharp decline tied into a renewed trade wind surge.

Composites for GWO phase 3 indicate an enhanced Azores ridge to our south-west and trough extending across NW Europe into central - eastern Europe. Allowing for a slightly poleward displacement of the Azores ridge thus far, this would tend to support the GFS type evolution of late, maintaining the core ridge to our west and south-west. Best of the weather very much in the far south, more unsettled further north but possible some weather fronts being able to penetrate far enough south on the evidence of the composites so not a wall to wall heatwave but pleasant summertime conditions.

Thereafter, and I'm thinking early August, the GWO should shoot back to phase 1 with occasional phase 2 orbit. Composites for these phases emphasize the remergence of a mean trough over or just to the west of the UK so becoming more unsettled and unstable as we move into the new month. It could well be quite muggy to start before cooler, fresher air moves around the mid Atlantic ridge.

[summer blizzard]

Negative PDO and ENSO conditions correlate quite well to a negative AO, so rather than the trough being over or just west, i think that the mean trough could end up east of the UK. A cool August looking likely.

[J10]

Negative PDO and ENSO conditions correlate quite well to a negative AO, so rather than the trough being over or just west, i think that the mean trough could end up east of the UK. A cool August looking likely.

From a selfish point of view, the trough being to the east of us is good news for western areas .

Composites for GWO phase 3 indicate an enhanced Azores ridge to our south-west and trough extending across NW Europe into central - eastern Europe. Allowing for a slightly poleward displacement of the Azores ridge thus far, this would tend to support the GFS type evolution of late, maintaining the core ridge to our west and south-west. Best of the weather very much in the far south, more unsettled further north but possible some weather fronts being able to penetrate far enough south on the evidence of the composites so not a wall to wall heatwave but pleasant summertime conditions.

That chart looks rather unsettled, or have I read it wrongly.

[Glacier Point]

That chart looks rather unsettled, or have I read it wrongly.

Remember these are 500 hPa geopotential height anomalies which indicate something of a flat westerly upper flow. This is occuring at the peak of the summer so conditions associated with a westerly flow at this time of year. Also, surface pressure have been greater this summer which is another consideration.

[Glacier Point]

Global Angular Momentum is beginning to fall once more, with substantial negative (easterly contributions) coming from the tropics:

http://www.esrl.noaa.gov/psd/map/images/reanalysis/aam_total/glaam.sig.90day.gif

There is an impressive wall of easterly winds right across the Pacific up to 30 N

http://cimss.ssec.wisc.edu/tropic/real-time/wavetrak/winds/archive/wavetrkP-1.html

and, when this current phase of tropical thunderstorm activity in the Indian Ocean fades, we are likely to see angular momentum crash. This is in line with the Southern Oscillation Index which is consistently advertising positive values of late and we are beginning to see La Nina really manifest herself in the global meridional circulation cells. Interestingly the IOD is forecast to become negative in the next few months so could we see the Indian Ocean, Pacific Ocean and Atlantic Oceans all 'showing' a cold signal - could be some real fun and games for global temperature series.

More immediately, the global wind oscillation is set to tank through phases 1 and 2 and composites for these two phases suggest the trough over Europe to expand a little and generally for our mid Atlantic ridge to intensify (perhaps as a more mid latitudinal feature rather than an extension of the sub-tropical ridge) and shift further westwards allowing a cool and showery type airflow to cover the UK and much of NW Europe.

[Gavin P]

Thanks GP. :lol:

Joe B'astardi is forecasting a drop in global temps to levels not seen since the Pinatubo cooling in the early 90's. With all the major Oceans signalling cold, do you think he may be on to something?

More immediatly, would it be fair to say summer now looks likely to slowly ebb away? Or could we still see a late August/early September heatwave?

Edited July 25, 2010 by Gavin P

[Eugene]

More immediately, the global wind oscillation is set to tank through phases 1 and 2 and composites for these two phases suggest the trough over Europe to expand a little and generally for our mid Atlantic ridge to intensify (perhaps as a more mid latitudinal feature rather than an extension of the sub-tropical ridge) and shift further westwards allowing a cool and showery type airflow to cover the UK and much of NW Europe.

Yes this mornings model guidance is supporting this view.

More immediatly, would it be fair to say summer now looks likely to slowly ebb away? Or could we still see late August/early September heatwave?

Yes i would say summer is slowly ebbing away now, no sign of any 30C+ and this August could be one of a very select few since the early 90's not to record 30C+ anywhere in the UK, heat very rarely has the same intensity by the end of August onwards.

30C+ in September has only been recorded 3 times in the UK since 1973 and only in the SE, i can't remember the last time 30C was reached in the midlands late August onwards so time is running out fast now.

[Glacier Point]

I would have thought a drop in global temperatures (or should we say falling off) is an inevitable consequence of the PDO switch and La Nina episode. Where this bottoms out will provide us with very useful benchmarking data for global temperatures. One thing that impresses me is that the atmospheric circulation has readily embraced La Nina whilst the last Nino really struggled the engage and when it did, it rapidl fell apart.

Right now our loss of snowcover seems to have stabilised. This will provide us with a good clue as to how cold the pole is during the autumn:

http://moe.met.fsu.edu/snow/

One variable this winter will be the potential for strong build up of snowcover c/o low stratospehric temperatures but lack of a strongly organised polar vortex potentially allowing realese of this cold into the mid latitudes. This is well worth considering as the transfer of stratostphric ozone from the tropics to the pole is likely to be severely inhibited by La Nina. As a result, less ozone = colder stratosphere and lower pressure and lower temperatures over the pole.

In so far as the second half of the summer, I can see the dominance of the Atlantic ridge so that would imply the remainder of the summer to slip unoticeably by.

[Gavin P]

As always, many thanks GP.

[Terminal Moraine]

As always, many thanks GP.

I'll second that. I don't think I'll ever get my head around all the variables and how they interact.

Your posts are invaluable in bringing a bit of clarity to it all.

[claret047]

I would have thought a drop in global temperatures (or should we say falling off) is an inevitable consequence of the PDO switch and La Nina episode. Where this bottoms out will provide us with very useful benchmarking data for global temperatures. One thing that impresses me is that the atmospheric circulation has readily embraced La Nina whilst the last Nino really struggled the engage and when it did, it rapidl fell apart.

Right now our loss of snowcover seems to have stabilised. This will provide us with a good clue as to how cold the pole is during the autumn:

http://moe.met.fsu.edu/snow/

One variable this winter will be the potential for strong build up of snowcover c/o low stratospehric temperatures but lack of a strongly organised polar vortex potentially allowing realese of this cold into the mid latitudes. This is well worth considering as the transfer of stratostphric ozone from the tropics to the pole is likely to be severely inhibited by La Nina. As a result, less ozone = colder stratosphere and lower pressure and lower temperatures over the pole.

In so far as the second half of the summer, I can see the dominance of the Atlantic ridge so that would imply the remainder of the summer to slip unoticeably by.

Very Interesting post GP,

To a non-techie like me could you please advise me whether as there will be no polar vortex if this means the winter in the UK is more or less likely to be cold.

Many thanks

kind regards

Dave

[summer blizzard]

Very Interesting post GP,

To a non-techie like me could you please advise me whether as there will be no polar vortex if this means the winter in the UK is more or less likely to be cold.

Many thanks

kind regards

Dave

Well, there is always a polar vortex present in winter, its just a question of where it is situated and how strong. In regards to the polar vortex this winter, it is likely to be weak during the Autumn and early winter, with even a possibility of an early stratospheric warming, however once we lose the -QBO we are likely to see the polar vortex get going in January, so potentially stormy mid winter.

[Polar Continental]

Hi GP,

Thank you for sharing with us your advanced knowledge, you are an invaluable poster on here, always look forward to reading them.

[chionomaniac]

I would have thought a drop in global temperatures (or should we say falling off) is an inevitable consequence of the PDO switch and La Nina episode. Where this bottoms out will provide us with very useful benchmarking data for global temperatures. One thing that impresses me is that the atmospheric circulation has readily embraced La Nina whilst the last Nino really struggled the engage and when it did, it rapidl fell apart.

Right now our loss of snowcover seems to have stabilised. This will provide us with a good clue as to how cold the pole is during the autumn:

http://moe.met.fsu.edu/snow/

One variable this winter will be the potential for strong build up of snowcover c/o low stratospehric temperatures but lack of a strongly organised polar vortex potentially allowing realese of this cold into the mid latitudes. This is well worth considering as the transfer of stratostphric ozone from the tropics to the pole is likely to be severely inhibited by La Nina. As a result, less ozone = colder stratosphere and lower pressure and lower temperatures over the pole.

In so far as the second half of the summer, I can see the dominance of the Atlantic ridge so that would imply the remainder of the summer to slip unoticeably by.

As always GP, your posts are invaluable.

However, like Claret047 I would also be grateful for you to clarify the emboldened paragraph which comes across slightly contradictory. I suspect that this is just due to timeframes. Surely the a reduced Brewer-Dobson Circulation would encourage ultimately the stronger stratospheric PV which would lead to less cold being released to the mid latitudes? Personally, at this timeframe, I would recommend that if Ian Brown wants to choose a blow torch January then 2011 may be a good bet.

c