March Forecast Thread

[Glacier Point]

March, the first month of the metreological Spring, but will it be a step back to Winter ?

Strong La Nina conditions persist across the equatorial Pacific with latest surface data suggesting that the strongest cold water anomalies have extended to the western Pacific in ENSO region 4 which is consistent with a large negative (easterly) surface wind anomaly across the area.

http://www.bom.gov.au/climate/enso/indices.shtml

These conditions are very likely to persist well beyond March and so La Nina conditions will be a key consideration in the overall pattern although, as for much of this winter, this will not be the only consideration.

http://iri.columbia.edu/climate/ENSO/curre.../technical.html

Reanalysis composites for a strong Nina March suggest a rather flat pattern across North America and blocking anticyclone centred over the UK. Note also the positive height anomalies persistent over the polar field.

Consistent with a cold ENSO event in the western Pacific, Global Angular Momentum has fallen to very negative values with large additions of easterly wind anomalies to the hemisphere associated with the equatorward movement of a band of easterly wind anomalies (this has been the case since the mid to late part of January and is consistent with several other notable changes to the way the atmopshere is behaving -e.g. stratospheric warmings). Also noted are the development of two bands of westerly wind anomalies across the sub tropical boundary and further north over the northern mid latitudes which are attributed to an enlarging polar cell driven by natural seasonal changes and a sharper thermal gradient than normal.

Tropical convection has become more organised in the last few days around the Indo-Pacific region although SSTAs do not generally favour continued and sustained convection excpet towards the Philipines / Indonesia area where warmer SSTAs perist. As a result of the cooling seas, the latest MJO wave has become rather indeterminate after nearly completing a rapid orbit during February.

I think it likely that we will see a similar type orbit in March, delayed somewhat but peaking in strength through phases 3-5. Latest tropical convection and MJO forecasts are somewhat mixed with no clear signal for an organised MJO wave #4.

What this means in terms of increasing angular momentum is uncertain but I think there will be no repeat of the strong addition of westerly winds from a low GLAAM base witnessed in January (see my comments about shift since mid to late Jan). More likely is for GLAAM to be mired at very low base state given the overwhelming net balance of easterly winds c/o the mature Nina camped out in the western Pacific. What is important to note though are those developing westerly winds acros the sub-tropics and polar front. The balance between these two will be highly influential in determining the pattern for NW Europe.

The strongest MJO signal is likely to arise from its passage through phases 3 to 5. On the basis of the season so far and previous La Nina / winter MJO events, phases 3-5 have the following teleconnections:

Phase 3:

Phase 4:

Phase 5:

..... which are strong signals for blocked conditions over NW Europe although the timing of these phases is uncertain and the AO signal may override any such signal.

Since mid to late January, the stratosphere has undergone fundamental changes consistent with a fading easterly QBO and intense tropical activity. There have been several minor warming events and a large pool of cold air is developing at the 30hPa level across the sub-topics with warmer air showing up over the polar region (although this is not in itself unusual given the time of year but the strength of the positive temp anomaly is however not normal). Zonal winds have appreciably dropped within warming waves.

http://www.cpc.ncep.noaa.gov/products/stra...JFM_NH_2008.gif

In time, this will result in a lifting of the tropopause across the polar field, raising heights and allowing the Arctic Oscillation to return to a more neutral-negative base state. This is not a short term development and will ensure that a +AO for March is very unlikely.

There is no meaningful long-range model guidance available at this stage given poor inter-run consistency from all forecasting tools and likely inability to successfully model the dramatic changes taking place over the polar field. It may well be a case that if at first the models go away from the idea of a high latitude block, it will return due to the increasing lagged infleunce of stratospheric conditions.

Putting this toghether, the peak impacts from what is likely to be a mid winter warming event will be manifested late week 1 through week 3 of March. In conjunction with the increasing zonal wind anomalies, I think a polar front straddling the UK and then being driven southward into the second week. Thereafter, the jetstreams will likely converge and split over the eastern US due to phasing of the MJO into stages 3-5 which are likely to favour the polar jet being weakened and moved northwards with cut off lows developing in the eastern Atlantic and associated mid latitude high pressure block developing over the UK consistent with the MJO forcing through phases 3-5 and La Nina. There is however a lot of uncertainty attached to this sequence so low confidence is placed in the forecast but higher confidence in an overall blend of mid and high latitude blocks.

In terms of basic weather patterns for the UK - cold and wintry for the first half of the month, becoming drier with overnight frosts, fog developing widely by months end but sunny and warm by day. The combination of a cold start with a high probability of mid latitude highs as the 'default' option suggests a strong probability for a drier than average month. The balance of probability favours a slightly below average or average temperature although this will be dependent on the positioning of any mid latitude highs.

Edited February 28, 2008 by Glacier Point

[johnholmes]

tks for this post its full of detail and needs a while to absorb it all, especially as I'm still on a very steep upward learning curve with most of what you have posted.

thanks again GP.

If its ok with you I'll post this link into my lrf update tomorrow evening?

Edited February 28, 2008 by johnholmes

[kold weather]

Good post GP, i agree about the idea of mid-lattiude high pressures being nearby. My main disgreement would be the idea of temps, i suspect the jet will be rather active still to the north given we still have a strong la nina, indeed I rather suspect that this Feb will come in as the strongest Feb la nina ever and March has every possibly of doing the same right now. So far little signs of height rises over the poles and there stil lappears to be a +ve AO, the GFS has toyed with the idea of sending the -ve AO hence why it has tried to give a cold shot recently between the 5-15th of March but I think its being far too hasty with it...

I actually think it won't be till April that we see some real northern blocking occuring, of corse by that time it'll be too late. The reason i say this is the La Nina should finally decay a little by then and also I think by that time the poler vortex should finally have broken down, it does seem to be quite late again probs because it took till December to form in the first place.

[Gavin P]

I agree with your thoughts Kold.

Looking at the models, we see pressure is still reluctant to fall to the south of the UK, with high pressure persisting through the Azores and into Spain and France. This is often the case in La Nina March's and this is what leads me to predict another milder than average month. However, we could see more in the way of polar maritime incursions, this month, so the anomoly might not be so great.

If there is going to be a pattern shift into a negative NAO/AO pattern, with extensive northern blocking, and a drop in pressure through the Azores and Med, I believe it'll happen in April, as it did in the La Nina April's of 75, 89 and 00. Though the last week of March could see the start of that shift.

Edited March 1, 2008 by Gavin P

[BLAST FROM THE PAST]

Interesting thoughts guys. I predict the CET being below average as I predict a couple of cold shots this month with a solid one mid-month ie more than a two dayer. I think an easterly will develop at some stage mid month. I also agree and suspect that April may have a nagging cold/raw feel with HP sat to our north bringing a set up that would be begged for in January.

BFTP

[BLAST FROM THE PAST]

A little more from me. A pattern is developing where the jet will be crashing over the UK and will for me bring below average temps, but not way below as my CET shows [5.7C]. What could be the big story of March is the wetness and storminess, there could be some large totals this month. The models seem now want to show this but I am still holding out for potential blocking sceanrio from mid month...it will probably be more like the last 10 days and where that sits will decide the CET outcome. So a wet and pretty chilly first 2/3rds and a blocked last 3rd....easterly or southerly? or slap bang over the top

BFTP

[Glacier Point]

Latest OLR anomalies suggest strong tropical convection potential in the Indian Ocean and West Pacific:

http://www.cdc.noaa.gov/map/images/olr/olr.anom.gif

As anticipated, the MJO has stalled and become indeterminant although it is showing eastward movement tendency from Africa into the Indian Ocean.

http://www.bom.gov.au/bmrc/clfor/cfstaff/m...Last40days.html

As it moves eastwards, an emergence of coherent convective waves consistent with MJO will likely develop through phases 3-5, probably catching out the model guidance as this is likely to be a rapid development. As mooted by the opening thoughts, Phases 3-5 of the MJO within a strong Nina regime teleconnect to height rises over Scandinavia and the NE Atlantic. This is a signal for blocking towards the NE Atlantic to develop week 2-3 March.

Signals w/r/t the AO are mixed with no sustained -AO currently programmed according to GFS ensembles:

http://www.newx-forecasts.com/ao_2.html

As Ed Berry notes, the latest warming event has already started to impact the tropopause and the models may not be fully able to grasp any longer term AO signal just yet. Some unsual tropospheric impacts are still more likely than not into week 2 through week 3 March in my opinion.

http://weatherclimatelink.blogspot.com/

So, some suggestion for a more progressive blocking pattern to emerge t168 -t240 in the NE Atlantic than is currently being advertised by GFS or ECM. Latest GFS ensembles (06z 03/04/08) have however begun to pick out these developments, but only at t240 onwards.

[BrickFielder]

The GFS model output for Sunday has certain similarities with the position last Sunday. High presuree over Greenland and high presure in the central Atlantic producing a short term blocking ridge broken very quickly by low pressure forming at the southern tip of Greenland.

The MJO anomaly forecasts for one week hence are also showing certain similarities to the present.

MJO 500mb Height forecast responses

Very short lived cold spell early next week maybe?

Week 2 looks like being driven by la nina and MJO phases 1 and 2 with high pressure off the eastern seaboard of China. It looks more Atlantic driven but I have to note the suggestion of height rises towards the pole.

Current MJO Phase

OLR Forecasts are suggesting quite a strong MJO event this time around although we should note this is an older model run but I am reasonably happy that the latest OLR anomaly charts are showing good convection developing.

MJO OLR Forecast

Latest OLR Anomaly chart

The suggestion here is that the AO might change as high pressure in the north Pacific bursts north shifting the stratospheric vortex. I can't see this coming to fruition untill late march though.

[johnholmes]

interesting couple of posts Brick and GP, I'll try and work them into my updated fairy story this evening.

[Glacier Point]

UPDATED MONTHLY DISCUSSION

The hemispheric pattern is very much characterised by tropical forcing and polar field running fully in tandem at the moment. Tropical forcing is centred over the Indian Ocean whilst the evolution of the changes in the upper atmosphere observed throughout mid February onwards are fully taking effect in terms of northern blocking. In the broadest terms, I cannot forsee much change to these large scale paramters over the next 3-4 weeks making a sustained and somewhat rarified run of average to below average conditions more likely than not. Indeed, the polar vortex has another few weeks before final break up and we could well undergo a series of reloading polar outbreaks in the coming weeks.

Surface and sub-surface sea temperatures remain well below normal in the western and central Pacific which are consistent with a strong mature La Nina event. ENSO regions may have warmed recently, but regions 3.4 and 4 are still showing a strong to moderate event which is helping to drive strong easterly trades across the Pacific in turn helping to sustain the overall flow pattern in the Pacific with a large anticylone centred to the central - NW Pacific.

http://www.bom.gov.au/climate/enso/indices.shtml

As a result, GLAAM has fallen to very negative values with a suggestion that easterly wind anomalies will shortly migrate towards the pole from the tropics into the mid latitudes with the AO perhaps falling neutral for a while.

MJO wave #4 has shown a high ampitude (strong) orbit through phases 1 and 2 consistent with a well organised band of tropical convection in the west Indian Ocean. This is steadily moving eastwards although its progress much further east is open to speculation given the strength of the easterly surface winds and SSTAs. I suspect that the wave will make it to phase 5 before fizzling. Either way, strong Rossby Wave dispersal has occured (note the remark in the posts above referring to sub-Arctic ridges) and will continue to occur.

Forecasts for tropical convection and the general eastward trend for the MJO suggest the wave to move to phase 4 and 5 shortly which teleconnects for shifting of any sub-Arctic ridges slightly further east - i.e. towards Scandinavia.

The polar stratosphere continues to reflect last months warmings with strong -ve zonal wind anomalies being deflected downwards and rising temperatures. This has been sustained for a period of several weeks now and the overall flow pattern in the upper atmosphere is characteristic of a weak stratospheric jet which provides ideal conditions for high latitude blocking to take place. Even if the stratosphere were to cool suddenly, the legacy is such that we have at least 2-3 weeks of weak stratospheric zonal flow to come.

Projecting forward from the current situation, there is a strong indication in long range forecast tools for heights to continue to remain high to our north with a rise in pressure further NE due to the influence of the MJO shifting the global wind pattern slightly.

Both operational GFS and ECM have begun to pick up these developments in the extended outlook. Thereafter, I think it not unreasonable to think that the next evolution to be for any Scandinavian ridge to retrogress into the North Atlantic, especially if the MJO wave manages to progress through phases 6-8. All of which boils down to a cool to cold Spring outlook with average levels of precipitation but feeling a total contrast to this time last year.

[Gavin P]

Thnaks GP. :o So, a cold and wet April (until around the 20th) is to be expected, then?

[kold weather]

Totally agree with you GP, I've been keen on a cool April with frequant northern blocking and I still think that will happen given all the factors you mention...even more now the La Nina is starting to decay (as you'd expect during Spring) and getting close to the strength that actually favors -ve NAO and also with the warmings in the atmosphere and a slack atmospheric wind flow it all bodes well for a cooler then normal April, esp given only Greenland is really above normal temp wise thus far in March.

I have to admit I didn't think the tendency for cut-off lows to develop over Europe would occur quite so qucikly as it has done and I did say I thought it was more likely in April but still the fact its happened now has given a chance for a cold spell at a time of year where you can still get some decent cold.

One thing that could happen is we could see a transition from northerly/easterely winds to a more soiutherly flow if we do get a southerly tracking jet, though I suspect that would be during the 2nd half of the month.

Edited March 20, 2008 by kold weather

[johnholmes]

tks again GP, not time to read in depth this evening but will sometime tomorrow

[BLAST FROM THE PAST]

Great thread this...more should visit and take a break from the model madness :lol:

BFTP

[mcweather]

Thanks GP exceptionally interesting as always and I have to say I concur with your ideas. Not through the well

researched science that you use but simply by gut instinct and 40 years of weather watching.

I think we will get at least one more major shot at cold and snow after the Easter spell.

Probably early to mid April. I expect to see the models firming up on this later next week.