A familiar tale days 7-10 of the ECM 12z op run; the Canadian vortex weakens and disintegrates, but then the cold air pool interacts with the subtropical jet, LP develops, and a push is made to try and reform the vortex near or over Greenland.
There is, however, one key difference this time around - a stronger ridge of high pressure across Greenland that's attempting to block the LP from invading that island.
A slower LP development and progression would help with this cause.
Even then, you need good amplification of the mid-Atlantic jet to avoid shortwaves developing near Iceland and mixing out some of the cold air trying to reach the UK from the north (ECM day 10 showing this clearly).
Obviously if that shortwave can slide SE into the Euro trough, there's the potential for a snow event, but really you need either a longer lasting northerly ahead of it, or a larger/stronger high around Greenland, for such an event to deliver across more than a limited portion of the UK.
What I've done here is highlight how much needs to come together in the right way for cold and snow to affect places that can't rely on transient imports of polar maritime air from the NW.
All routes require high pressure at the high latitudes in some form or other, and in the right place to benefit us - so either an extended mid-Atlantic ridge or a full-on Arctic High sat to our NW. The reason is simple - without a major blocking high locked in place over Scandinavia (or at least Siberia), it's the only way to bring air masses to the UK capable of being subjected to the usual maritime influence without becoming insufficient for more than transient snowfall to lower levels across the aforementioned regions (the far south in particular).
There has been no established high latitude blocking this past week, just a transient ridge to our NE that has managed to kick off a spell of trough disruption but failed to stick around long enough to feed some decent cold across the south. Admittedly the behaviour of the sliding trough yesterday could easily have gone better for snow in the south (the path and timing of development was as unfavourable as it could possibly have been), but it was always looking uncomfortably marginal even on the best of runs.
Here's hoping we have better fortunes as we end the month and begin February.
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T-Max: 30.2°C 9th Sep (...!) | T-Min: -7.1°C 22nd & 23rd Jan | Wettest Day: 25.9mm 2nd Nov | Ice Days: 1 (2nd Dec -1.3°C in freezing fog)
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