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Winter 2008/09 Forecasts


SNOW-MAN2006

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Posted
  • Location: Tyne & Wear
  • Location: Tyne & Wear

    Hi :)

    I dont know if there is one of these open already but ive looked over the past 2 pages and cant indentify one. So if there is one open could someone please kindly put my post into there :) .

    It has been a while but i can now release my winter 2008/09 forecast. Feel free to critise or compliment. I am a strong believer that critism makes everyone better. Im going to regret saying that now :) lol. Im sure you will all be kind lol.

    Enjoy ;)

    Winter_Forecast.docx

    SNOW-MAN2006

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    Posted
  • Location: Tonyrefail (175m asl)
  • Location: Tonyrefail (175m asl)

    My Winter Forecast

    Ok, here is my winter forecast for 2008/09. I must start by saying this is only my second winter forecast and my forecast for last winter did not turn out to be very accurate so please don’t expect anything in the same league as the senior lrf’ers like GP!

    Never mind though, I’ve had a bit more success with autumn, as my CET predictions will verify so I’ve decided to have another pop this year.

    ENSO

    I’ll start off by looking at sea surface temperatures and arguably the most important factor here is the ENSO (El Nino Southern Oscillation) state, looking at the surface temperature the ENSO is appears in a neutral state with no real anomaly shown at present.

    Global SST's

    However if we look at the sub-surface anomaly you will note that the definite cold anomalies, here is the 55m anomaly chart showing anomalies of –3C…

    ENSO Sub Surface

    As the surface trade winds have now begun over the equator we should start to see these anomalies being brought to the surface in the form of a La-Nina. The question is how negative will the anomalies trend over the winter months. As the surface trade winds take effect the ENSO models are forecasting a rapid onset of negative sst anomalies in the form of a rapidly developing La Nina reaching an MEI of between –1.0 and –1.5 in February.

    nino34SSTSea.gif

    It’s notable that a couple of months ago the majority of the models were forecasting an ENSO neutral winter so it may be a safe bet to follow the lower end of the scale here. Therefore I’m predicting the ENSO MEI to be as follows…

    December –0.7 (slight)

    January –1.2 (slight)

    February –1.4 (slight/moderate)

    We have seen the effects of La Nina on both our last summers and last winter. In 2007/08 we experienced a fairly benign inversion set up in December with stormy mild conditions in January and February.

    A weak la nina teleconnects with a mid atlantic ridge (which we have seen recently) although as we saw last year, a moderate to strong anomaly results in mild wet weather over western Europe.

    What is worthy of noting from the above graph is that the onset of La Nina is about 6 weeks later than in 2007/08, this coupled with the fact I believe the La Nina event will not be quiet as potent as 2007/08 leads me to believe this winter may be stormy at times but less mild than 2007/08.

    Atlantic SST's

    Remaining on the subject of sst’s, it’s worth taking a look at the atlatic (see above global sst's), the warm anomaly in the western atlantic reinforces the current synoptics of a mid atlantic ridge and a negative AO. With the onset of La Nina, I expect the anomalies to change slightly to show an slight increase in thermal gradient.

    UK SST's

    Below are the SST’s around the UK, with the waters being more shallow and more readily influenced by synoptics, it’s worth not reading too much into these, although it is clear to see that the recent cold is having an effect upon the ss’ts in the form of negative anomalies. If these remain then it’s fair to say that future northerly incursions could be slightly more potent, see bottom picture...

    UK SST's

    Now to the teleconnections…

    AO/NAO

    As I interpret it, the sst’s are indicative of a negative AO and a neutral to negative NAO. With the effect of strengthening La Nina I believe the NOA will end up weakly positive but I firmly believe that the AO will be negative for the DJF period and that we certainly won’t see the +4 anomalies of 2007/08. Although it’s worth mentioning that this doesn’t guarantee cold weather it is indicative of a more southerly tracking jet than we’ve seen in the last number of years.

    Here are the current NAO/AO ensembles…

    NAO

    AO

    PNA

    The PNA is progged to trend negative in the next couple of weeks, possibly in line with the onset of LA Nina, I think we could start to see the effects of this in the next couple of weeks in the form of a more zonal set up. Over the season it’s fair to say that the PNA is expected to remain –‘ve in line with La Nina..

    PNA

    Pacific Thermal gradient (strong)

    There is currently a stronger thermal gradient in the pacific in the Atlantic. I will factor in the possible this could have by intensifying the Atlantic jet-stream. On the contrary the Atlantic thermal gradient is a lot weaker than last year, it also appears that the Atlantic hurricane season has now ended.

    Cryosphere

    Polar Ice Cover / Snow Cover

    current.365.jpg

    We have noticed this year a much more rapid build up of arctic ice with current concentrations approximately 750k sq km up on this time last year. Although we must remind ourselves that polar ice levels remain below the long term average, this years trend (so far) is a deviation from what we have seen in recent years. The snow cover charts seem to indicate little or no snow over Europe, although I know from weather reports/web cams etc that snow cover is far more widespread than indicated. I therefore have to question the reliability of this data and as such will not factor it into my forecast.

    QBO

    The QBO is currently in a declining westerly phase, a westerly phase QBO generally correlates with a cool polar stratosphere and therefore a strong polar vortex over Greenland with a generally zonal theme. As I’ve mentioned though the westerly phase is in decline which indicates the possibility of more stratospheric warming events as winter progresses…

    QBO

    Polar Vortex

    There are three upper level vortices which arguably drive the winter synoptics in the northern hemisphere. The closest vortex to us is generally centred over Greenland. When in this position, typical zonal conditions often (not always) apply experienced in W Europe. I believe that there is scope for displacement of the PV during the early/middle stages of winter which could result in colder interludes.

    Stratosphere Temp Anomaly

    The ‘polar stratospheric temperature’ (above 60 deg N) can be indicative of general development of patterns at the surface (with a time lag of a month or so). A cold polar stratosphere often reflects the surface cold pooled within the Arctic. A warming event in the polar stratosphere can lead to displacement of cold surface air being forced away from the arctic. This does not guarantee a cold snap though as the colder air could be displaced elsewhere in the NH. Here is the current temperature anomaly chart…

    time_pres_TEMP_ANOM_OND_NH_2008.gif

    As you see from this chart the polar stratosphere is currently cool, slightly below average which is not indicative of cold air displacement soon. The forecast though is different with warming forecast in the ensembles throughout December. You can see here from to 10mb forecast, the cold anomaly being displaced from the pole.

    gfs_t10_nh_f216.gif

    Summary

    Apologies if I have droned on a bit so I’ll just try and sum up quickly. There are signs that this winter could be colder than we’ve experienced for the last few years although there are contraindications that the mild wet synoptics we’ve been used to could prevail. The onset of La, Nina and the residual lag of the westerly QBO could conspire to ensure this winter is similar to recent years. We must also consider the ‘even larger teapot’ debate, whether you love or hate the term, it has to be agreed that we have seen a synoptical shift over the last say 20 years, with the PV anchored over Greenland.

    On the flip side our passage through autumn has been much more ‘normal’ than in recent years, the average/slightly below average CET figures and the Polar ice concentrations seem to substantiate this. So, are we on the cusp of a more long term shift to different synoptics? It seems that we have entered a prolonged ENSO neutral/negative state so arguably all residual warmth from El Nino has now gone. After all I think this year was the first time I’ve ever seen lying snow in October (albeit briefly), November which often provides glimpses into winter ahead has also recorded two northerly outbreaks.

    The main surprise in my final forecast is that I believe January will buck the trend of recent years and actually see the best chance of a prolonged cold snap. I believe this to be the case because the w’ly qbo will have subsided and the full effects of a stronger La Nina won’t have had time to filter through before February. I also predict a slight southerly shift in the jet stream which could result in more frequent cold spells for the north. These factors combined with the teleconnection projections could make January a cold month but I’m going to dilute my CET forecast to take into account recent history so here goes…

    December:

    Summary: Cold Start then mild stormy

    Precipitation: Average/slightly above average

    Temperature: South- slightly above average, North- slightly below average. CET 5.4

    January:

    Summary: Cold spells (more n’ly than e’ly)

    Precipitation: Slightly below average

    Temperature: South- slightly below average, North- Below average. CET 3.1

    February:

    Summary: Trending milder/zonal

    Precipitation: Average/slightly above average

    Temperature: Slightly above average everywhere. CET 4.7

    All in all fairly average winter but colder than what we’ve been used to over recent years.

    Feel free to pull it apart my forecast and trash it as you see fit.

    Kind regards,

    JW

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