Sunday 7th January will be another cold and dry day but Monday will see the beginning of a change. High pressure is building over the UK and during Monday it will begin to extend northwards and align itself close to Scotland. This will mean that we lose the currently cold air mass over Bjorli and instead begin to draw up milder air which will come up and over the top of the High Pressure into Norway. The start of the week will therefore see temperatures rise and especially so in the mountains. A temperature inversion will mean that places further to our east and lower down the valley are most likely to retain the colder air for longer while Bjorli and the higher locations will likely see temperatures creep just above freezing by Tuesday. The weather itself will remain dry and with light winds (and therefore little mixing of air masses), there is the chance that the temperature could remain just below freezing beyond Tuesday but even so, I do expect temperatures to eventually edge just above freezing by late Wednesday or into Thursday at the latest.
The above ICON chart shows how the High Pressure (initially over the UK early in the week) has extended towards Greenland by the end of the week. This allows a trough to move south over Scandinavia and in doing so will bring both colder air and snowfall. However, as the UK High Pressure slips W/NW and the wind strengthens from the WNW owing to the trough moving southwards, temperatures will initially rise as increased wind and cloud lifts what is left of any inversion. Clouds will be thick enough to produce some light precipitation by late Thursday or Friday in the form of rain, sleet or snow. Any rain or sleet will be transient with most models showing that snow will be falling by the end of Friday evening. Snow is then expected through much of Saturday and is likely to intensify with the NW wind.
GFS and ICON are not the only models pointing to heavy snow on Saturday. The UKMO, GEM and ECM are also showing the same broad set up with remarkable consistency.
Sunday 14th January is a long way off in weather terms but there is quite high confidence in the weather models that we will see low pressure to our north and high pressure over Iceland and Greenland. This type of set up will drive a NW'ly flow over Scandinavia and so further snow can be expected during Sunday and into the following week.
The GFS chart below shows the mean from its ensemble suite for midday on Sunday 14th January and all the other major models are showing the same.
I am not usually in the habit of posting charts for 9 days out but I will make an exception in today's post. The charts below are the operational runs from the GFS, GEM and ECM models for Monday 15th January.
As mentioned above, the ensembles from across all models are showing a similar broad pattern with a blocking High Pressure to our west and with Low Pressure over Scandinavia. This cold weather type is therefore likely to take hold from next weekend and then persist until at least the middle part of the following week.
Another point of interest is the potential for a SSW (Sudden Stratospheric Warming) event which results in the zonal winds actually reversing. The ECM model had long predicted a minor event for early January and we are now seeing the zonal winds weaken but the model is also predicting another potential event later this month. If the warming in the stratosphere is sufficient enough, the polar vortex could collapse with the zonal winds going into reverse. This doesn't always mean that the very cold arctic air is always displaced southwards across Europe but rather that the chance is arguably increased. There is usually a lag before any eventual changes in pattern propogate to the surface but it is certainly worth keeping an eye out because unlike much of continental Europe, much of Scandinavia has seen temperatures below average for three consecutive months between October and December. A SSW event later this month could increase the chance of further blocking which may lead to very cold arctic air flooding southwards across much of Europe and subsequently increase the likelihood that Norway can once again end up with temperatures being below normal for both January and February. Of course, this is speculation at this stage but nonetheless, it is something which is worth following. In the meantime, we can summarise the upcoming weather over the next 10 days as starting off cold, then briefly milder before becoming colder and increasingly snowy from next weekend.
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