[b]January forecast[/b]

[b]Previous update[/b]
[color=#282828][font=helvetica, arial, sans-serif]I expect the continuation of unsettled conditions, with on average temperatures remaining close to the norm. Given the expected continuation of a –NAO, and –AO I would not bet against colder interludes, in the form of brief northerlys, as we progress through the xmas period (something which has shown around xmas day on the latest model runs). I do not see great support for something prolonged this side of New Year. Given developments in the stratosphere I think the first half January, probably past week one, is when it could potentially come very interesting..![/font][/color]

[b]Review[/b]
[color=#282828][font=helvetica, arial, sans-serif]It remained unsettled and mostly average, although cooler at times further north. Although the NAO and AO remained negative, they have now trended towards positive, and likely to be so as we start January. Something hinted by the ensemble forecasts in my last update. Those 'interesting developments in stratosphere' seem likely to develop, although as highlighted in the last update, no impact on us is expected by week one. The initial forecast went bust, however the update has got relatively better, although perhaps milder than i expected.[/font][/color]

[b]Stratospheric outlook[/b]
[color=#282828][font=helvetica, arial, sans-serif]After a period of temperatures at just below average at 10hpa, and recently just above at 30hpa, a large spike at all levels is expected as we progress into January.[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150342"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-07620200-1356787986_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150343"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-59528500-1356787987_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150353"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-89853500-1356788018_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150352"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-52127700-1356788017_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]Stratospheric temperatures at the 10hpa and 30hpa level are to increase significantly during the New Year period. The strength of the warming should lead to significant disruption of the polar vortex, and thus high latitude blocking.[/font][/color]

[color=#282828][font=helvetica, arial, sans-serif]Mean zonal winds are expected to decrease, reversing at 30hpa, and then most probably at 10hpa. Although not a sudden stratospheric warming (yet), I would expect this to be shown soon (zonal wind reversal at the 10hpa). Again, this should lead to significant disruption of the polar vortex.[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150345"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-42468800-1356787990_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150346"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-67200500-1356787991_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]

[color=#282828][font=helvetica, arial, sans-serif]Split or displacement? I would probably suggest a displacement followed by a possible split. Wave one breaking is expected to increase significantly, before decreasing at the end of the forecast period. Wave one breaking is characterised with vortex displacement.[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150344"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-18309800-1356787989_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150339"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-37589200-1356787979_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]Interestingly, wave two breaking is forecast to increase, which favours vortex split.[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150365"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-70651100-1356788061_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]It is difficult to predict the area where the displaced vortex is likely to locate. At the moment I would suggest our side of the Atlantic (west Greenland area), which is not favourable for us. However, there are hints from the longer range GFS that subsequent warming nearer midmonth (Greenland area) may change this situation![/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150348"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-59555900-1356788005_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150368"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-93610100-1356788246_thumb.png[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]

[b]MJO[/b]
[color=#282828][font=helvetica, arial, sans-serif]A mixed output from the global models, although all indicate an increasing amplitude. The UKMO is by far the most interesting, and has for some time indicated a possible phase 7/8 by midmonth. The ECM is similar to the UKMO, although slower with its evolution. The GFS seems to be on its own, although the bias corrected ensembles seem to follow the euros, albeit slower.[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150364"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-51889800-1356788042_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150347"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-93694800-1356788003_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150363"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-16826000-1356788042_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]Some not so good phases to get through beforehand, which in general indicate lower heights to our north, with higher pressure progressively shifting north, so becoming settled.[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150357"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-74529300-1356788037_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150358"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-76363400-1356788038_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150359"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-81589200-1356788039_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]Phase 7/8 would support height rises towards Greenland, around or just past midmonth (based on the UKMO/ECM).[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150360"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-41577800-1356788040_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150361"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-99721700-1356788040_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]The GWO has progressed towards phase 4, with a corresponding increase in angular momentum. From reading a few papers I noted how this is associated with a higher amplitude and progression of the MJO, which is ideal for a progression towards phase 7/8. Although given my relatively basic understanding of atmospheric angular momentum (first year uni) I shall not delve on this topic.[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150355"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-00013000-1356788021_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150337"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-87940800-1356787975_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]Interestingly the following composites show a GWO phase 5/6/7/8 is associated with below average UK temperatures.[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150356"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-62348500-1356788036_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]

[b]CFS charts[/b]
[color=#282828][font=helvetica, arial, sans-serif]Although not the most reliable charts, the general trend for weeks one-two is for lower heights to our north, with higher heights to our south (+NAO). With a trend for these higher heights to push further north (i.e. the UK becoming settled at last).[/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]Past midmonth there is a signal for height rises over Greenland, with uncertainties in the placement of the trough.[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150366"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-99912600-1356788062_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150367"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-36115900-1356788064_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]

[b]AO and NAO Ensembles[/b]
[color=#282828][font=helvetica, arial, sans-serif]The ensembles continue to show +NAO and +AO as we beguine the new year. However, there are some indications from the GFS that the AO shall return negative towards mid-month, which is expected.[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150350"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-25846400-1356788012_thumb.png[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]The NAO forecasts are rather disappointing, and show a +NAO towards mid-month[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150351"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-65644400-1356788016_thumb.png[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150341"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-00728600-1356787984_thumb.png[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]

[b]Mean height ensembles [/b][color=#282828][font=helvetica, arial, sans-serif](some charts missing due to update issues)[/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]The ECM maintains lower heights to our north, with higher pressure encroaching from the south. So becoming more settled as we progress through the next 5-10 days.[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150338"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-42567800-1356787977_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]The GFS is similar, with lower heights to our north west, with high pressure encroaching from the north, attempting to progress north eastwards.[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150349"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-64132200-1356788007_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]Which is supported by the stratospheric geopotential height charts[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150340"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-07737500-1356787981_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]The NAEFS shows this high sinking towards midmonth, but with fait signs if height rises towards Greenland.[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150362"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-69376800-1356788041_thumb.png[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]

[b]Overall[/b]
[color=#282828][font=helvetica, arial, sans-serif]An unsettled start to the month, but becoming progressively drier as higher pressure attempts to progress north east. Thereafter potentially becoming unsettled again. Midmonth I expect a change towards much colder conditions, with height rises in the Greenland region (around day 15 ish). I expect colder conditions, if they materialise, to be relatively sustained. In summary, a mild start (cooler when settled), and a cold end.[/font][/color]