WhiteFox

-5.7 recorded here last night which equals Wednesday night for the coldest of the winter. Looking back, Friday really destroyed a large part of our snowcover. There was a lot of liquid PPN mixed in during the evening and this reduced the lying snow to around 4cm, as well as clearing all busier roads. Had a total of 12.8mm PPN which actually ranks as one of my highest PPN days if the winter. Yesterday was a steady thaw with all snow on paved areas disappearing in places which received sun after about 11am. Still treacherous in areas that did not receive much sun as the slushy mess has frozen solid. Lots of avalanches yesterday as slabs of frozen snow and ice plunged from pitched roofs: quite a loud rumbling it made too and deposited abiut 5cm of ice on the front path! Anyway, expect further thawing today and then for it to be washed away when milder air and rain pushes in.

I think another thing to consider is just how dry it has been for quite some time, especially in the SE. Some brief wetter interludes, but it has generally been below average rainfall for most of the past year. If we have another dry summer then water shortages seem almost certain at some point. Might as well get some rain in now!

The same can be said about cold periods in average winters. Long cold spells are rare and particularly cold spells such as last year are rarer. Spells like we've just had are more common. But, February tends to be more blocked on average so chances are greater for a cold spell.

It could be that the push of extra cold air from North America is enough to change the pattern to one that allows heights to build across southern Europe as you say, but I don't think it's nailed on. The Siberian high, although it may not directly affect us, can certainly ridge far enough west to slow the Atlantic and leave us in the middle. Worth keeping an eye o. n

The PNA has been particularly stubborn This season and has thrown many a medium to longer range forecast out of the window. The feeling was that the developing EN+ would create more of a negative pattern and this would then allow tropical forcing to deliver more northern blocking. This hasn't happened, so that is one of the questions that will be asked. @TEITS makes a fair point about how do we know if the questions asked about what happened this year are the correct ones and how the answers will be correct. The answer is that we don't. It's about gathering informational and unfortunately the weather obviously doesn't allow us to run controlled experiments! I think one are of focus is the combination of descending Westerly QBO and SSW. No doubt there will be analysis done on this over the next year and it all adds to existing information. If longer range forecasting was easy it would be dull. The interest lies in trying to crack the code!

The enquiring mind seeks to understand things like we have ended up with the pattern we have. The cynic seeks nothing but to ridicule everyone else.

Thanks for the summary @Catacol. I know that the analysis has already begun on 33andrain so it'll be interesting to see what comes out. Tamara's thoughts on the cold tropical stratosphere were also interesting. There has been an affect on the Atlantic profile as you mention: the treacle analogy srpings to mind. In most other winters with such a PV setup over Canada we would have seen a flat Atlantic pattern. What we have seen instead is systems ejecting and slowing down as they reach the eastern Atlantic. The cold pouring out of North America certainly seems set to produce a little more momentum this week, so yes a flatter and milder pattern, but I also think it unlikely that we will see a prolonged blowtorch through early spring. Of course, that now means that it is guaranteed! I'd be very surprised if winter has finished with us, but until the PV lobe checks out of Hotel Canada we are unlikely to see sustained blocking. We may chase the odd thread the needle easterly at medium range, but such end of line easterlies are very difficult to land and can go wrong so easily. But, as we see the PV wane naturally into February a more meridional pattern is likely at times. That will open the doors to some cold from north or east at times, albeit not necessarily prolonged.

It's a wrap in Reading. Sitting under or near light greens or yellows for hours and hearing reports of heavy snow in Bracknell yet nothing here but what can best be described as a wintry mix. Glad I made the most of last night's fall, but the sludge that is out there now is going to be horrific after it freezes. Anyway, it's been fun. We should do this more often...

Damn! I thought it was midnight tomorrow night at first!

Perfect example! Radar shows pink over your area, yet Google maps shows no delays. Therefore no snow (or at least not settling)! Same in Reading again too as it happens. Should be hammering down here according to radar, but it most definitely is not. Perhaps that bit over Bracknell will deliver?

It generally does if a whole area is showing red or yellow like in Basingstoke earlier. It's a method I've used for years and it usually verifies. I'm not asking you to believe me! Just something I do.

I use rain viewer when I'm in Malaysia to track thunderstorms. It shows worldwide PPN (where there is radar coverage at least).

No, the colour is the average speed. Green means flowing normally, yellow slower than average, red very slow and dark red is stationary. It will show as yellow where there are roadworks, such as the M4 between Reading and Maidenhead, but other than that it's a pretty good guide

Thanks for that Knocker: great explanation of the formation of a storm.

Some bigger flakes now as dewpoint has dropped to -1 and temperature to 1.0.

Go to Google maps and turn on the traffic layer. It's a great way to verify what is falling: if it's snow you'll see lots of red or at quieter times yellow.

Ah! This is what I'm looking for! Some yellows appearing on google maps to the East; sign of more frozen PPN I trust!

Some snow now as genuinely heavy PPN moves in over RG7. Still quite a mix of PPN though and temperature has risen to 1.2. Some covering of car windscreens and the like but that's it. Going to be an almighty mess when this all freezes, although that looks like being tomorrow night now as I suspect cloudcover will keep temperatures above or close to freezing tonight.

Is that a 10 on the Murr scale?

Time for me to take the dog for a walk in our graupel/snow. Will report back in a bit!

The A33 is stationary about halfway from Reading to Basingstoke now. I've a feeling people are going to be trapped for a number of hours.

My pleasure. Even when there's nothing near me I'll often get a fix by looking at google maps and then traffic cameras to see what it's like. The lengths I go to to get a s now fix!

Finally starting to see some proper flakes and temperature dropped to 0.7 in RG7. Nowhere near intense enough to settle though.

Whole area looks in chaos. Gaps in flow on google traffic show that several roads are now blocked. Lots of accidents reported as well.

And vice versa here!