Glacier Point

something of a disservice to Summer Blizzard, Snowman-2006 and Weatherforecaster ?

Current SSTA for the N-PAC is pretty quiet - no bipole of cold water over warm, even the reverse although some activity in the central N-PAC is evident and this fits with the warm anomalies there: http://www.cdc.noaa.gov/map/images/sst/sst.anom.seasonal.gif Eastern pacific looks very favourable with cold water convoluting any jet flow. QBO set for 0 value at the turn of the year I would suggest.. http://www.cdc.noaa.gov/Correlation/qbo.data PDO - work that one out, not really sure as it looks like a -ve PDO, walks like a -ve PDO and smells like a -ve PDO, only..... http://jisao.washington.edu/pdo/PDO.latest GP

Herein lies the link with current discussion about the prolonged alignment of flow patterns in the Atlantic - they will have an impact on autumn and winter through the Sea Surface Temperature Anomalies (SSTAs). I think this thread has picked up quote well the potential threat to any cold winter through continued warm southerly flow up the western Atlantic during the summer promoting warm SSTAs and as a result, the winter polar jet being pepped up off Newfoundland. Another aspect is the upper level weakness in the eastern Atlantic and the mean NE'ly flow there likley to result in cold anomalies during the winter from residual SSTAs - potentially inducing a trough over western Europe and displaced jet flow to the south. GP

May MSLP anomaly: May 500 hPa anomaly: May surface temp. anomaly: June MSLP anomaly: June 500 hPa anomaly: June surface temp anomaly: No where on these charts do we see evidence of a strong or even displaced Azores High pressure area towards the UK - if anything the western Atlantic is where the high pressure, higher temperatures are manifested. The 850 hPa temp charts provide the key to what is going on here: http://www.wetterzentrale.de/pics/Rtavn001.html The 200 hPa GFS jet forecasts also give a better insight into the overall flow pattrens: http://wxmaps.org/pix/hemi.jet.html There has been a notable weakness in mid and upper levels throughout the period in the eastern Atlantic related to anomalously low SSTAs throughout April and May. If the Azores was having such an influence on our weather, such a trough would not exist. What we have been witnessing are the downstream responses to this trough with a ridge over western Europe. If anything, I would suggest the Azores to have had a lesser direct impact than normally expected. Without the ridge over NW Europe, we are prone to the kind of setup exemplified by 00Z GFS (by the way this is not an endorsement of this run) with Atlantic lows able to penetrate the UK.

Not a solid linear relationship but broadly the +ve states of the Arctic Oscillation and North Atlantic Oscillation favour high pressure at middle and lower latitudes and lower pressure at higher (polar) latitudes. This keeps Europe in a SW''y or S'ly flow hence the warmth whilst the low pressure over the polar region. When the AO and NAO turn -ve, the reverse happens with warmer air aloft over Greenland turning things cooler over Europe. http://www.washington.edu/newsroom/news/19...ve/k121699.html http://www.cpc.ncep.noaa.gov/data/teledoc/nao_map.shtml

... and as a perfect example.... my summer LRF completely de-railed by a rampantly +ve AO - the second strongest June AO since 1950, bettered only by June 1994.

More arrows for West.... Check out those negative anomalies for June MSLP in the area of the Azores, and the positive pressure and temp. anomalies for the NW Atlantic and Europe. A strong Azores ridging into the UK would not deliver such an anomaly pattern. The chart you've chosen to illustrate what a strong Azores High looks like is also putting the upper trough over the UK delivering the less settled conditions expected over the second half of the weekend and much fresher weather over the next few days.

Busted Forecast One third the way through the summer and although the near outlook looks a little less settled, June was an exceptionally warm month and it would take the remainder of the summer to be well below average to bring my LRF back on track - something that is not going to happen. So I'm calling it bust for the UK and Western Europe. The Northern American forecast remains remarkably good and still valid with the west coast ridge - east coast trough very much in evidence. We will have to wait until September to provide the full analysis but the key features so far would appear to have been: 1) a very big positive spike in the Artic Oscillation - note the extent of the negative 500 hPa and MSLP anomalies across the polar region; 2) the absence of a strong Azores High pressure, if anything weakly -ve anomalies in this area indicative of a displaced high; 3) the strong positive pressure anomalies in the NW Atlantic; and of course, 4) the positive pressure and temperature anomalies over the UK and NW Europe. In fairness to my initial thoughts, a June +ve AO was the identified weak spot and this has driven the NAO positive. http://www.cpc.ncep.noaa.gov/products/prec...nnections.shtml This has built the heat over Europe to such an extent that it will now take a lot of shifting. The key error at the moment looks like the wrong placement of the mid-Atlantic ridge - so far it has been a lot further west in line with that warm sea surface temperature anomaly off Newfoundland, and of course the AO. Looking to the remainder of the summer, a more neutral or even slightly negative summer AO is statistically most likely to occur during August, but I wouldn't bet against the continuation of the strong trend so far. Also the SSTA in the eastern Atlantic if anything look to me to indicate a more amplified trough increasing the probability of extreme warmth into August. GP

The warm anomaly off Newfoundland is indeed a likely key player for mid to late summer, as is the couplet that ot forms with the cold anomaly around the Azores. If we look at the SSTA from last month and marry this up with current 850 hPa values, then we see very good agreement: http://weather.unisys.com/archive/sst/sst_anom-060528.gif http://www.cdc.noaa.gov/map/images/sst/sst.anom.month.gif http://wetterzentrale.de/pics/Rhavn242.html ... an excellent match on the cold anomalies off the western USA sustaining a sharp ridge, a downstream trough over the eastern USA, and a jet stream pulled up to Newfoundland which troughs over the Azores placing the UK and western Europe in a very stagnant warm ridge. Undoubtedly the +ve AO spike during June has helped exacerbate this set-up driving low pressure and the jet further north, but the SSTA would appear to be having a significant impact on the seasonal pattern. The current SSTA, if anything, are likely to lead to more amplified flow pattern drawing air up from further south towards the UK as that cold anomaly around the Azores strengthens and the warm anomaly off Newfoundland continues to remain very strong with all that warm airflow associated with the Bermuda High: http://weather.unisys.com/surface/sst_anom.html Another point to note is the strength of the easterly air flow (cooler air mid sub-tropical Atlantic) seemingly to arch back on itself from the UK towards Florida. This is the effect of the trough and it will help to reduce wind shear for tropical storm development. What this means is that greater storm activity (although there are other factors at play) will translate to a likelihood of big Atlantic depressions stalling in the Atlantic and fragmenting with some fragments getting sucked into the trough off Iberia. This is a key player in helping to set up a repeat of the current heatwave, so beware the heat for August based on the SSTA alone. Of course there is the AO to consider and statistically July, and August even more so, are the summer months most likely to see -ve AO which would bring less settled conditions to the UK. However, with the current heat now well ensconsed, even neutral or even slightly -ve AO values would see planty of warmth. GP

Paul, Summer Blizzard has picked up the very distinctive banding of cold SSTAs in the sub-tropical Atlantic and warm anomalies to the north of this - inverting the normal gradation (anomalies not empirical) of sea temperatures and the baroclinic responses they are likely to bring about. Warm anomalies in the northern Atlantic over cold anomalies to the south and to a certain extent cold anomalies further north are one factor in helping to force the mean pressure in the Atlantic lower and rising pressure to the north over Greenland and Canada. Whilst SSTA variance might explain 60% of long term pressure anomalies, other factors are at play, not least the reduced impact of SSTA during the Summer and sometimes conflicting teleconnections such as the AO. At present the +ve AO is forcing the NAO neutral - positive although this situation may change. Funnily enough, a -ve NAO could, if the blocking were to be far enough west over Canda, be very good for our Summer in helping to promote the Azores-Iberian weakness that we have observed so far which keeps sustaining high pressure over or just to the east of the UK. GP

http://www.met-office.gov.uk/research/seas.../nao/index.html Looking at the algorithm and predictor pattern generated from last May's SSTA, I would suggest that a more negative NAO signal will be the most likely punt. The main difference to May 2005 would appear to be the stronger negative anomalies across the sub-tropical Atlantic - a sign of the polar front descending earlier and longer south of the UK perhaps. GP

only trouble is SB, the east Pacific anomalies are very different whilst the SSTA for early June 05 were felt during mid July onwards, which to my recollection was not great. A composite anomaly for the months leading up to June looks like this: Jan-April 2005 Jan -April 2006 ...the real differences being over the eastern Pacific which are likely to have significant downstream impacts on the UK IMO. GP

June, the most likely summer month for a +ve AO, but with the SSTA presenting a highly amplified pattern, a slightly cooler month for me, but only just.... 14 C please.

UKMET's model has just updated and now shows average temperature probabilities and wetter than average rainfall: http://www.met-office.gov.uk/research/seas...terce_cat2.html with the most cool month likely to be June. ECPC's forecast now also goes for cool June. I'll be fascinated how the METO place their Summer forecast given latest model output and their statistical method which must show a similar or even below average probability given the SSTA March - June pattern now in evidence: http://weather.unisys.com/archive/sst/sst_anom-060312.gif http://weather.unisys.com/archive/sst/sst_anom-060416.gif http://weather.unisys.com/archive/sst/sst_anom-060514.gif http://weather.unisys.com/surface/sst_anom.html http://www.cdc.noaa.gov/map/images/sst/sst.anom.month.gif ... which is somewhat opposite of their predictor pattern for residual SSTA. When they release the forecast, what's the betting the words 'average' and 'unsettled at times' appear ? GP

At a very simple level, the reverse, although this is highly dependent on psoitioning relative to windward continental masses and other anomalies. Hope this helps

very true SB, there was a large negative height anomaly in the area during April, fuelled I think by a big Stratospheric cooling event, http://www.cpc.ncep.noaa.gov/products/prec...hgt.ao.cdas.gif ....which helped set up the warm April and early part of May experienced. My reasonings for mean positive anomalies during the Summer in the area are the stronger -ve SSTA further west off Siberia and the large +ve SSTA mid Pacific likely to enduce a dowsntream ridge over this area, and the slight differential in the SSTA of the eastern Pacific likely to result in neutral or even weakly -ve East Pacific Oscillation values which teleconnects to this pattern. GP

Well the Oceans of the Northern Hemishphere really are studded with interest. http://weather.unisys.com/surface/sst_anom.html Of note are: 1) The very cold anomalies off eastern Siberia overlying warm anomalies likely to stoke up the west Pacific jet and continue its displacement northwards; 2) The very cold anomalies in the eastern Pacific likely to continue the highly amplified pattern and mean trough off the west coast US; 3) The developing warm anomalies off the western US likely to shift the mean trough westwards slightly increasing the probability of an east coast trough. 4) The Atlantic, oh boy, a band of cold water stretching from Bermuda to Lisbon overlain by a strong couplet of warm anomalies to the NW off Newfoundland likely to induce mean mid-Atlantic ridge and persistence of height anomalies over Greenland as well as warm anomalies across the tropical Atlantic (increased tropical storm development) If nothing else the prevailing fetch for the UK will be some 0.5 degrees lower than normal because of the long track of the cold anomalies to our south west (almost duping us into thoughts of NAD shutdown) Plenty to keep an eye on in terms of the weather in the next 5 weeks when this lot really starts to take effect. GP

Thanks all for your comments. If once you've had chance to read through the forecast and have a query, I'll be happy to oblige if I can. GP

I won't pretend that any seasonal forecast is easy, but this year's Summer forecast presents particular challenges, one where any of the below, average or above average permutations are entirely possible. The challenge is presented by a whole range of changing long term variables, and, we are forced to decide just how much what has been will influence the future. For example, the La Nina episode of the Winter has now effectively ended, the Pacific Decadal Oscillation which for the last few months has been positive now shows all the hallmarks of a negative phase for the majority but not all of the Pacific. Add to this the variability in the model outputs, and you get some sense of just how tricky putting up a call for the next three months is going to be. In my preview post I examined a range of factors which I believed would have an influence on the winter. http://www.netweather.tv/forum/index.php?s...ndpost&p=665782 Some of the factors have changed (most notably in the Pacific) so here is my assessment of what I believe will be a Summer shaped significantly by the large oceans of the northern hemisphere. El Nino Southern Oscillation (ENSO) ENSO is a well documented phenomenon which has a strong statistical relationship with the pressure, rainfall and temperature patterns over the Pacific Basin and beyond. There are many measures of this but I'm using the Multivariant El Nino Southern Oscillation Index (MEI). http://www.cdc.noaa.gov/people/klaus.wolter/MEI/ http://www.cdc.noaa.gov/Correlation/mei.data April's MEI value was -0.594 which is indicative of a weakish La Nina event. This represented a continuation of La Nina (negative MEI) back to October last year. However, looking at the current Sea Surface Temperature Anomaly (SSTA) plots, the equatorial Pacific SSTAs look to have entered (for the most part) ENSO neutral conditions. http://weather.unisys.com/surface/sst_anom.html This is borne out by the SSTA modelling with a consensus on neutral ENSO conditions now taking effect: http://www.cpc.ncep.noaa.gov/products/pred...efing/sstaa.gif http://www.met-office.gov.uk/research/seas...nino/index.html http://www.cdc.noaa.gov/forecast1/for4entrgl.html http://iri.columbia.edu/climate/ENSO/curre...fo/figure3.html http://www.cpc.ncep.noaa.gov/products/anal...ino34SSTMon.gif Although what has taken place over the last six months (La Nina), the latest assessment of the Pacific Basin indicates the atmospheric effects of this cold phase only to persist in the far western Pacific - and not anticipated to last for much longer. There have been many comparable ENSO neutral condition Summer periods, and, whilst some there is some variability within these analogue years (1995 for example), the composite anomaly pattern for upper level anomalies looks like this (assuming average JJA values between -0.2 and +0.5): Note the positive anomalies over the central Pacific, negative ones over the Hudson Bay area, weak positive anomalies in the central northern Atlantic and of course, the very negative anomalies over the UK. Whilst all composite anomaly patterns are to be treated with a certain amount of scepticism, this represents a large enough sample and strong correlation for negative heights over the UK to be taken seriously. The Quasi-biennial Oscillation (QBO) The QBO is regarded by some metreologists as a key measure of the strength and future guide to the behaviour of the Pacific Jet. http://www.jisao.washington.edu/data_sets/qbo/ http://ugamp.nerc.ac.uk/hot/ajh/qbo.htm http://www.cdc.noaa.gov/Correlation/qbo.data We should now be familiar with this as the large negative (easterly) phase zonal wind was largely responsible for Europe falling just a little short of wintry expectation. Now the QBO is in a positive (westerly) phase (it broke positive in April with a value of +5). One more look as the current SSTA plot shows a warm pool of surface waters in the central-western Pacific. http://weather.unisys.com/surface/sst_anom.html Crucially the warm waters extend to some depth in the west... whilst plenty of cold anomalies to the north-western Pacific allied to colder than normal air spilling off a snow covered Asia will make for a strong thermal gradient in the western Pacific and a stronger jet. As the QBO tends to change on 5 to 8 point values every month in a predictable biennial pattern, this means that we are likely to experience a moderate strength QBO this Summer, typically around +12 to + 16. Whilst a rising westerly phase QBO is something of a scarcity for Summers (there have been approximately 10 in the last 58 years, the composite anomaly pattern is reasonably convincing towards the following pattern: Once again, a similar pattern to ENSO neutral pattern arises - positive upper level anomalies over the central and north-eastern Pacific, negative anomalies over the Hudsons and a striking negative anomaly over the UK. On the other hand, a strong West Pacific Jet may also be characterised by a positive phase West Pacific Oscillation. This teleconnects to troughing in the jest ream over the western USA and higher pressure over western Europe (a Bartlett High): http://www.cdc.noaa.gov/people/gary.bates/tele/wpo.cmp.gif Pacific Decadal Oscillation (PDO) http://www.jisao.washington.edu/pdo/ http://jisao.washington.edu/pdo/PDO.latest I'm just not sure how to read the PDO at the moment. The PDO has been in a positive state ever since August of 2002 although it has had a few flirtations with the odd negative month. However, the Pacific SSTA looks strikingly like a cool phase PDO, and has done so since late March early April: http://weather.unisys.com/archive/sst/sst_anom-060319.gif http://weather.unisys.com/archive/sst/sst_anom-060409.gif http://weather.unisys.com/archive/sst/sst_anom-060507.gif Note the cold water up and down the eastern Pacific and the warmer central western Pacific - a classic indicator of the cool phase PDO, …..except that is apart from the strong cold anomalies around the seas of Japan and the Gulf of Alaska. The SSTA forecasts pick up this cold eastern Pacific theme, albeit to varying degrees: http://www.cpc.ncep.noaa.gov/products/anal...s/glbSSTSea.gif http://iri.columbia.edu/forecast/sst/06/gl...JA_may2006.html If we are to enter a brief -ve phase PDO, there may be some influences on the jet pattern over North America which would impact on the UK's Summer. However, I've seen lots of and often conflicting composite anomalies and analogue patterns for -ve PDOs, but I'm yet to be convinced. For what it's worth, here are the composite anomalies for the most negative PDO years and the linear regression for the seasonal mean: If anything, I'm slightly inclined to the solution suggesting positive upper level anomalies over the central Pacific and guess what, that big blue (negative an height anomaly) blob over the UK. The other point to note is that the effects of the PDO tend to vary somewhat from month to month. Atlantic Sea Surface Temperature Anomalies The UKMET use a statistical forecast for Summer and Winter patterns based upon the SSTA of the northern Atlantic during the 6 previous months: http://www.met-office.gov.uk/research/seas...background.html The predictor pattern indicates well how positive SSTA influence long lived positive height anomalies and negative SSTAs help bring about negative anomalies in the upper level patterns. Looking at the SSTA composite anomaly for the period January through to April, and the latest available seasonal product, the following are noticeable: http://www.cdc.noaa.gov/map/images/sst/sst.anom.seasonal.gif 1) The warmth of the entire northern Atlantic, with the core of this warmth located to the western Atlantic region off Newfoundland. 2) The development of cold SSTAs down the eastern Atlantic in the last month. 3) The relatively less cold band across the sub-topical Atlantic and marginally cold anomalies now extending down to the Azores from the UK. 4) The warm tropical Atlantic. This pattern is neither a perfect match with the cold or warm predictor pattern used by the UKMET, although the developments over the last month to six weeks (cold anomalies over the Azores and UK) incline this assessment towards the cooler pattern rather than the warmer one - if nothing else the prevailing SW wind will be cooler than normal just because of the long fetch of cold SSTA over which they have passed. For the last couple of months, this pattern has been conducive to the lowering of pressure in the north Atlantic as low pressure systems coming off north America are forced to take a lower and lower track. This in turn helps promote height rises over Greenland, a de facto negative North Atlantic Oscillation (NAO). http://www.met.rdg.ac.uk/cag/NAO/ http://en.wikipedia.org/wiki/North_Atlantic_Oscillation http://www.jisao.washington.edu/data_sets/nao/ http://www.cdc.noaa.gov/Correlation/nao.data http://www.cdc.noaa.gov/people/gary.bates/tele/nao.gif Whilst the NAO is rarely in a prolonged -ve phase, the period from late February has been characterised by an unusual frequency of -ve NAO in the context of the last few years, no doubt aided by a strong tropical storm season last year. Based on the assumption that SSTAs from the previous 1 to 6 months influence the summer patterns, a weakly -ve NAO is a high probability based upon the SSTA alone although other factors such as the Arctic Oscillation and jet patterns exert their own influence on Atlantic pressure patterns. A composite pattern for the top -ve NAO summers looks something like this: Note the very strong indication of negative height anomalies over the NE of North America and those over NW Europe, plus the strong positive anomalies across the Polar region. Another aspect of the northern / central Atlantic SSTA, particularly that showing now: http://weather.unisys.com/surface/sst_anom.html .. is the couplet of cold and warm anomalies in the sub-topical region. This will continue to exert a strong influence for the sub-topical jet to remain active and displaced well to the south of its normal latitude, as it has done so since February. This will in itself increase the chances of continued height rises over Greenland (as shown by the -ve NAO composite anomaly) and increase the chances of the polar jet stream straddling the UK. Polar Cell This Winter was really characterised by a noticeably larger but slightly displaced polar cell. Warm waters in the Pacific and perhaps the effects of the approaching solar minima helped to shift the parcel of cold air towards the eastern half of the northern hemisphere across Eurasia. This is still in evidence today, look at the relative positioning of the cooler air: One of the pieces of analysis arising out of the winter forecast was the possible long term influence of forced global warming in promoting a warmer pole leading to greater probability of blocking and a negative Arctic Oscillation (AO). The theory suggests that increased surface temperatures will warm the atmosphere over time, eventually affecting the upper levels of the troposphere and eventually the stratosphere. Right now the temperature profile of the polar region looks like this: http://www.cpc.ncep.noaa.gov/products/prec...hgt.ao.cdas.gif ….. note the influence of surface temperatures up to around the 200 hPa level - high enough to influence the hemispheric circulation. Looking once again at the SSTA analysis over the last few months, the most striking aspect is the warmth of the polar region which is likely to increase the chances of a -ve AO for at least one of the summer months. http://www.cpc.ncep.noaa.gov/products/prec...ent.ascii.table It should be noted however that statistically the three Summer months are most likely to be AO neutral although June is when a +ve AO is most likely to materialise and August a -ve AO. All of this translates to an increased probability of the polar cell remaining intact through the Summer, and occupying a greater area thereby working against the migration northwards of the high pressure cells. Incidentally, the ITCZ has shown a variable pattern exceeding its normal position in some longitudes and falling below in others (possibly reflecting long term changes in global weather patterns and likely to lead to increased variability in extra-tropical weather patterns): http://www.cpc.ncep.noaa.gov/products/fews/ITCZ/west.gif http://www.cpc.ncep.noaa.gov/products/fews/ITCZ/east.gif The below average mean positioning off the African Coast might signal a stronger sub-tropical high shifting the mean position of the Azores High further east towards SW Spain and northwards to the mid-Atlantic. Tropical Storm activity This Summer, the key ingredients for another active Atlantic tropical storm season are in place. A warm tropical east Atlantic and a westerly phase QBO leading to reduced wind shear will see a string of low pressure systems circulating from the Gulf Coast up the eastern Seaboard from mid Summer onwards. The positioning of the polar jet stream at this point will be crucial in determining where these depressions go. If the jet is positioned close to the UK, then there is the potential for large rainfall totals and some sublime warm days before each big depression makes its way across the Atlantic. Model outputs If there were to be a broad consensus in the modelling, it would for a cool June followed a warming trend into July and August however the major long range models have been jumping around a lot recently whilst there are significant differences in the programming of pressure patterns over North America which could dramatically alter the resulting flow over the UK. The UKMET's output contains a health warning as it is likely to be slightly at odds with their statistical model. This suggests a generally warm Summer brought about by low pressure to our west in the eastern Atlantic. For North America, a weak ridge over the western 'States is forecast with lows over Alaska and noticeable blocking over Eastern Canada which teleconnects very nicely with the idea of an Azores Low type scenario and its consequent warmth. http://www.met-office.gov.uk/research/seas...terce_cat2.html http://www.met-office.gov.uk/research/seas...terce_cat2.html The lastest CFS output supports the lows over Alaska and blocking over Canada which must teleconnect to fine weather over the UK. Noticeably this is only for June with July and August programmed to have much cooler conditions as the blocking forecast over Canada recedes. http://www.cpc.ncep.noaa.gov/products/peop...s/glbT2mSea.gif The ECPC output has probably been the most variable although it appears to have settled over a solution which warm lovers will most be looking forward to with a cool Alaska, deep troughing over the central 'States and as a result, high pressure over Eastern Canada and warmth over the UK and western Europe - another fine example of the teleconnection between ridging over eastern North America and Europe. http://ecpc.ucsd.edu/projects/GSM_home_dat....ano_global.gif In common with most , models, the IRI output has altered somewhat in the last month, shifting to an above average temperature Summer with average rainfall amounts. This is a somewhat puzzling forecast as it programmes warmth for Alaska and the western USA, a weak trough over the central US and ridging into Newfoundland. This is not entirely plausible as high pressure over Alaska normally relates to low pressure over NE Canada and Newfoundland. http://iri.columbia.edu/climate/forecast/n...6_Eur_temp.html http://iri.columbia.edu/climate/forecast/n...06_Eur_pcp.html http://iri.columbia.edu/climate/forecast/n...6_NAm_temp.html The German Climate Model (Roeder) programmes the western US and Alaskan ridge during June resulting in a downstream mi-Atlantic ridge and cool, unsettled start to the Summer. However, during July and August it turns this situation around with a large trough developing across the western US and as a result a downstream ridge up the eastern US and the consequent ridging over Scandinavia which would give very warm conditions for the UK. http://www.climaprog.de/website0506004.htm http://www.climaprog.de/website0506005.htm http://www.climaprog.de/website0506006.htm The latest Soil Moisture Model (USA only) predicts a suppressed ridge over Alaska and the western / southern central States with equal chances for the remainder. This would tend to endorse the CFS output for July and August but not June, with no major probability of warmth over the NE States and as a result, no increased probability for warmth over the UK. http://www.cpc.ncep.noaa.gov/products/pred.../off01_temp.gif Looking at the combined suite of North American forecast tools, a range of outcomes are predicted indicating low confidence in model outputs and patterns over the crucial areas of Alaska, NE Canada and Newfoundland: http://web1.cdc.noaa.gov/cgi-bin/seasonal/...od=all&lag=lag1 Jetstream patterns Amongst all this uncertainty, I think there are two very probable features of this Summer related to the relative strength and amplitude of the jet streams. The Northern Atlantic has since the winter shown a distinct trend for prolonged phases of meridional and weak jet flow, due in no small part to the arrangement of warm SSTA over cold SSTA thereby reversing the normal polarity which favours a stronger jet by weakening the thermal gradient. At the same time and related to this is the relative strength of the sub-topical jet which is most probably related to the approaching solar minima and strength of the polar cell. More recently, the SSTA over the Pacific have really begun to favour an amplified and split jet pattern with the warm waters over the central / western Pacific and cold anomalies up and down the eastern Pacific. Looking at the current SSTA and the forecasts over the next month or two, the situation is likely to remain quite similar. In other words, an amplified jet pattern where the sub-tropical jet is much stronger than usual is quite likely. This would make an Azores High ridging NE towards the UK quite unlikely for any prolonged period. This should not in itself rule out high pressure though as the Summer of '95 testifies where a break away High managed to sit over the UK. This stated, there is I think a high probability of the formation of a recurring mid-Atlantic ridge as the Azores High is 'sucked' north west towards the Greenland High, which in turn will collapse as a result of the evolution of the east Pacific trough and ridging over the 'States. It's also worthwhile looking at the West Pacific Jet and its likely behaviour downstream. With warm water at depth in the western central Pacific, plenty of cold water to its north (aided by an increased snow cover in east Siberia) and cold water programmed to the east, the Pacific Jet is likely to be quite strong in the west (with a QBO value averaging around 12-15) but I foresee a marked difference between the west and east Pacific. When this jet hit's the colder waters of the east, it is likely to do two things. First, a slowing jet buckles and will likely split with a ridge pushed northwards into Alaska (Soil Moisture and IRI Models agree this), and a deep trough pushed southwards into the sub-topical belt. This will lead to a downstream ridge over the western half of the US (some models push this westwards) and a consequent trough over the eastern US, in other words, similar to the present pattern with a mid-Atlantic ridge and trough digging into western Europe. The key questions are where and how pronounced any troughing of the Pacific Jet are going to be. Summer Forecast Tricky call. Right of wrong, I'm sure I'll learn a great deal from this forecast. With a number of potentially conflicting signals, the key to unlocking this Summer's forecast will be to nail the factor that will emerge and have the single greatest influence. If the winter forecasts taught us anything, we must look at those factors which are significant enough as far upwind as possible. This is the West Pacific Jet and a signal for a +ve phase West Pacific Oscillation which favours the union of the displaced Azores and Bartlett Highs to sustain a very warm, moist SW'ly flow over the UK, as the UKMET's seasonal numerical model predicts. These two factors must be weighed up against; an ENSO neutral signal with a strong statistical relationship with poor Summers over the UK; a +ve QBO (but limited sample) indicating unsettled conditions; a -ve PDO generally suggesting a large ridge over the USA and cool conditions for the UK; a -ve NAO; a greater probability of -ve AO conditions and great uncertainty over the behaviour of the SSTA and jet stream over the NE Pacific. On this basis, the probability of an average or below average Summer must be the call. I have little doubt that the QBO and SSTA of the western Pacific will bring about a reasonably strong west Pacific Jet. This will sustain an amplified jet stream and troughing in the eastern Pacific setting up a recurring cool and showery theme throughout the Summer. I suspect we will see a mean ridge over the western / central Atlantic and a weak downstream trough over NW Europe supporting showers and long spells of unsettled conditions, becoming more established through July. June already looks very cool and unsettled to start, and, with most modelling agreeing on this, there is an increased probability that we will arrive at the end of June with an uninspiring month in the bank. I am a firm believer that Summer patterns are usually apparent at the end of June so this largely reaffirms my belief in a pretty average outlook. I respect the German Climate Model but I just can't sign up to a dramatic turnaround in the Pacific and Atlantic pressure patterns following a dodgy June. The warmth of the Atlantic and tendency for the displaced Azores High to throw ridges north and east (but not traditionally NE as we benefit) will I think serve to mitigate slightly these negative factors so I would view quite long phases of fairly slack pressure (with some beefy shower activity) alongside the more prevalent low pressure and intermittent ridges collapsing over the UK. If we get a little sunshine during the slack pressure periods and between the showery interludes, the 'feel' of the weather won't be too bad. Given these factors, I think the chances of record breaking warmth are slim. We may well struggle to get values many times over 30 C. The best of the weather traditionally found in these types of regimes occurs around late July and this when I'll plump for the most prolonged settled spell whilst we may get some shorter pleasant spells ties into storm development over the eastern US before they make their way steadily across the Atlantic. As the trough over the eastern Pacific collapses and re-sets, I would anticipate brief spells of ridging off the mid-Atlantic orientated ridge throughout the Summer before it collapses and low pressure re-establishes over the UK. Reading this you might think I'm painting a picture of a well below average Summer, but it's worth bearing in mind that an average Summer is not great in this country where we've become accustomed to some very glorious recent years' weather. Compare the ENSO neutral composite anomaly for 500 hPa geopotential height and temperatures - very low height anomalies look bad but only translate to 0.5 C below normal. To put some verification on this, I would view the Summer as being between average and 0.5 C below average. Although the recent deluge reminds us just how much rain can fall in unsettled periods (as do the memories of 2000 and 2001), I'll forecast average amounts of rain due to some quieter spells of weather and showery nature precipitation in general most heavily influenced by the Atlantic SSTA although there is much less probability attached to this aspect of the forecast. To put some perspective on the probabilities, I rate the forecast's chances as: Average to 0.5 below average: 65% much lower temperatures 20% much warmer than forecast 15% The key weakness to the forecast are the difficulties in predicting the pattern over Alaska and the Pacific NW and the downstream impacts on pressure anomalies over NE Canada. A sustained spell of Stratospheric cooling such as that observed in April would completely derail this forecast and probably require revision - good news for sun worshippers if this were to happen.

Positive phases last between 8 and 12 months on average. It 'broke positive in April, so this one should be with us for ..........[salivation smilie] GP

I love growing basil, it's one the most flavoursome herbs and pefect in a mixed leaf salad. Rather than buy it, the best is always home grown and basil can be grown with the aid of a greenhouse or windowsill. I grow a large leaved variety called Neapolitan. It has a wonderful basil 'hit' followed by a sweeter almost aniseed follow-up. It's best grown (like all basils) in a terracota pot March - September in a sunny aspect on its own or as a companion to tomatoes. Plant more than you need and pick often - you can make some excellent pesto which you can freeze or use as an alternative to passata on pizza bases. GP

Hope to have it out by next week - I need to check the reanalysis on La Nina and cold anomalies in the eastern Pacific. A cool phase PDO ??

Nice work Steve. The current modelling essentially throws up two scenarios - one of which you've gone for with a ridge (possibly influenced by the feedback from last year's drought) over western Europe and Scandinavia. The other places the axis of the ridge further east with western Europe maintained in a cool unsettled trough. Both are indicative of a highly amplified pattern and the key for me at this stage is calling where this pattern will start and where the 1st signficant trough will be ? At present, I'm minded to go for a trough in the eastern Pacific and large ridge over the western and central USA placing the downstream ridges over the mid-Atlantic and the Russia, however I was looking at some composite anomaly analysis for weak La Nina fading to neutral by June suggesting the reverse. I think an amplifed jet pattern is however the safe assumption at present, wherever the ridges ocurr. Once again, nice forecast, let's hope it pans out. GP

SB, the warm central western Pacific and cold anomalies to the north are a strong indicator of a positively orientated WPO to come in approximatley 4-5 weeks time. This is likely to be a key player in developing a strong jestream over the western Pacific which will likely decelerate when it hits the cold anomalies over the eastern Pacific. My strong suspicion is that this will be a recurring Summer pattern with the development of a large ridge into Alaska, a bifurcated Pacific Jet, a large trough off the western coast of America and a considerable downstream ridge giving a secondary trough over the eastern USA. This pattern is evident in the current jet forecast: http://wxmaps.org/pix/hemi.jet.html GP

SB, couple of points:- 1) First observation is the west Pacific jet showing a reasonably strong WPO; 2) The eastern Pacific cold anomalies favouring a slightly -ve EPO, also favouring bifurcated jet with ridging into Alaska and troughing off California; 3) The strength of the sub-tropical jet - not shown on your diagrams - but a likely key player early Summer; 4) Whether we get a mid-Atlantic trough or ridge will depend solely on the jet pattern over north America. If we get the re-establishment of blocking over eastern Canada then an Azores low would be the call and warm, warm, warm for the UK. However, with the EPO and NAO, possibly AO moving negative, I favour a late May / early June phase of cool showery for the UK. could this turn around for the end of June - the million dollar question at this stage ? GP