WhiteFox
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I am no expert so apologies if I am wrong but looking at the current GFS run from this morning at T+0 it shows uppers of -4 to -8 across much of Northern Europe and precipitation of snow across the same region.
So why would it not be snow from the ECM 192 chart? What's different?
On the continent, you can get snow with higher 850 temperatures. When I was in the US we would look for 0oC at the 850 level as the cut off for snow, particularly during frontal events. In our climate perched on the western edge of the continent with a large ocean nearby we need lower temperatures to gurantee snow. Also, continental climates have a higher threshold for thickness; again in the US 540dm is generally used as the upper limit for snow, whereas in the UK we're looking for 528 or below.
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Some of the coldest c. 30 day periods I can find (since 1772)
Dec 29th 1813 - Jan 27th 1814 -3.3 degC
Jan 1st - 30th 1795 -3.1 degC
Dec 28th 1962 - Jan 26th 1963 -2.7 degC
Jan 22nd - Feb 21st 1895 -2.6 degC
Jan 7th - Feb 6th 1963 -2.6 degC
Jan 7th - Feb 6th 1838 -2.5 degC
Please feel free to add or take away from this list. I haven't spend a great deal of time on it, so there may be omissions/mistakes
Thanks Ferryhill. I realise it's a large ask! I don't have access to the daily CET figures myself otherwise I'd stick it in a SQL database and fire some code at it!
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Always lots of emphasis on months where the CET is sub-zero and as we know it's always been a pretty rare occurrence.
However, the weather does not recognise months, so I was wondering if anyone had any details on 30 day periods where the CET average is below zero? I'd assume that it is also pretty rare, but it would be interesting to see how many such periods have occurred over the years.
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I feel totally the same - I'm a complete newbie who first found this forum in Oct and had to decifer all the techy stuff to get even a vague idea on forecasting.....but I have never been so confused as I am now! I've never seen such neg/pos posts all in one go in such a short space of time!
I feel my little fix I look for on here each day is completely incomprehensible!
PLEASE somebody explain!
Thanx
H.
I think a fair summary of recent events is as follows:
The ECM led a number of days ago with a potential easterly developing, but dropped it fairly quickly. Signs of a pattern change keep showing (indeed the high pressure moving over the UK is a pattern change in itself), but models are struggling to pin down the detail at relatively short periods (say 4 days or so). This has a big impact on the forecasts and led to a great deal of uncertainty.
Some posters are understandably bewailing the disappearance of the easterly whilst others continue to search for colder possibilities down the line, hence the disparate posts.
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Must admit even im shocked by how the models are saying NO to the upstream and forecast atmospheric patterns being projected by the experts.
1. SSW events which are trying to break the PV
2. Arctic High doesnt seem to want to play ball
3. AO & NAO thought were going negative/neutral...Surely that would allow Northern blocking to some extent?
4. Ensemble mean heights showing more mid atlantic blocking or heights to the North North East
5. Jet doesnt want to dive south to quickly?
What you end up with is a halfway house and I think we are still to see things pan out yet......ECM seems to be the model to choose but that goes against what some were saying last night.......and I really didnt see the ECM verifying.......
That PV just doesnt want to move!
Still many scenarios to play out i feel
Regards
Surely the forecasts of negative AO/NAO are also based on forecasting models? Therefore they are just as prone to variation as the synoptic output (in fact, they are simply differences in pressure between two points are they not? If the synoptic forecasts are wrong then by definition the AO/NAO forecasts are out).
Anyway, all this is simply due to the fact that the route to the Easterly shown by the GFS yesterday is exceptionally difficult to pull off. It was have been a classic, but the reason we have so few of these classics is because the timings all have to be just right. Put up against a strong jet, it is not impossible to get the cold air over the UK, but you're really threading a needle. Looking at Steve M's post on timing yesterday sums it up perfectly. If the shortwave aligns correctly, and the Arctic high can link up and the flow is on the correct path.... etc.
Not the first time we've seen such outbreaks forecast only for them to break down before they begin.
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Once in a 120 year event and the likes we will not see (in December at the very least) in our lifetime.
Never say never! It may be a once in 120 year event according to the stats we have available, but they only date back 350 years or so. Given climate variation we cannot say with any degree of certainty that we will never see another month, or even another December, like it in our lifetime! Havng said that, I think too many expect that every cold spell should produce the same (it happened in December 2010, so why isn't it happening again), which is what I think you are saying!
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5/6 Feb 1996 - widely between 1 and 2 feet of snow in Cumbria and SW Scotland with some places seeing more than 2 feet - often not mentioned as most of the snow fell in a fairly thinly populated part of the country, but here in Windermere we haven't seen levels bettered since.
I did experience that one. I was at university in Nottingham at the time and we hired a car to drive to Edinburgh to visit a friend's brother and go to a party. I decided to come off the A1 at Newcastle, and head on the A696 through Ponteland and onto the A68 through Jedburgh. There had been some snow around during that February as many will recall, much of it thawing slowly at lower elevations. However, as we rose up through Jedburgh and beyond, the snow deepened. Once we got past the Catcleugh Reservoir, the drifts were immense. For about two miles before and after the split with the A6088, the drifts were easily three feet over the top of the car. The ploughs had done their job however and had cleared one lane, so we were effectively driving along a cutting in the snow. It was quite eerie as it was late at night by this point, the car headlights reflecting off the snow banks as we continued on. We drove into Scotland (there is a parking area on the border just there, and the ploughs had obviously used it as a staging area as it was cleared) and then headed down the other side. The drifts slowly lessened, although there was lying snow down to fairly low levels (Edinburgh itseld was clear).
That remains the second deepest snow I've witnessed. Only my February 2007 trip to Mexico, NY where more than 100 inches of lake-effect snow had fallen (level snow up to the eaves of houses!) beats this.
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Feb 2009 was the worst in London, as buses completely stopped. 2010 stuff was still chugging along all the time. Nov/Dec 2010 was prolonged, that's the only thing, any snow in west end melted anyway when I traveled to work.
Feb 1991 was definitely worse (I realise that some may be too young to remember it!). Deeper snow, colder temperatures, and it stayed longer. This was the classic "Wrong type of snow" that brought trains to a halt. The February 2009 event may have been a surprise to some (not to those on here of course), but it melted extremely quickly as far as I recall, and roads were soon cleared. Of course, the last two Decembers and January 2010 smash February 2009 (but that is off topic for this thread).
From my memory in the Reading area, the following are the most memorable and disruptive:
October: 2008. Also the only snow I've seen here in October. Most caught by surprise and as a result there were long delays to rush hour traffic.
November: Struggling on this one. Not sure I've seen disruptive snow in Reading in November. I'm sure someone can help me here?
December: 1981, followed by 2009. The snow of December 2009 was memorable as it started as rain, washing away the grit from the roads, and then turned rapidly to snow creating a layer of ice underneath. About three to four inches fell, so not that much, but most were caught unawares and the lack of grit led to abanded vehicles on every hill. It took my then heavily pregnant wife six hours to travel the three miles from Junction 11 of the M4 to Tilehurst.
January: 1987. King of the lot of course, and still the deepest snow I can recall as well as the coldest.
February: 1991 as mentioned above.
Nothing stands out for me from March onwards. I guess that as it is less likely for snow to stick around I tend to take less notice. For me, if snow melts from the roads after a few hours, the disruption is largely minimal. To cause real disruption it has to stick around for a couple of days. That is why I tend not to remember frontal events where a few inches fall before turning to rain and thawing.
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More than 1% of the UK's population lives north of Stirling, places such as Dundee, Inverness, Perth, Aberdeen, Stornoway - you've heard of them all because people live up here and we do count I'm afraid!
Dundee isn't northern Scotland though. Even if you include Aberdeen and Dundee, the population of the cities mentioned is 400k. Stornaway only has 9k, and the other Scottish Islands aren't exactly heavily populated. It's not intended to be a dig at northern Scotland as I think it's beautiful, but the fact is that the areas forecast to be hit by blizzards are very sparsely populated compared to the rest of the UK (including southern Scotland).
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Most on here are probably closer to France than the far north of Scotland. It certainly does look pretty wild over the next couple of days on the models in those parts.
Indeed Frosty makes a good point about the weather being far from boring. However, there is a lot of IMBYism because I'd estimate that about 1% of the population, maybe less, lives in the north of Scotland.
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Yes, one of the most strongly zonal outlooks that it is possible to see. The jet making ever further inroads into Western Russia, certainly the US guys are not hopeful of any change upstream anytime soon.
Indeed, it's not the zonal setup which is concerning so much, it's the fact that it continues to push across to western Russia. Until we see a significant cooldown to the east indicating more blocking downstream, brief topplers seem to be the best solution for cold fans. Several winters in the mid 2000s showed such conditions and they remained for most of winter. It can change, but it will take time...
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Jan 1987, was an extremely interesting and complex situation and we needed a few bites of the cherry to hit the jackpot.
Regards,
Tom.
January 1987 was the holy grail of Easterly setups. The reason we keep going back and looking at those charts is because they are so extreme and happened from a situation where high pressure sat to the south of the British Isles (any cold fan's worst setup). However, we have to bear in mind that it was an extremely rare occurrence and delivered exceptional cold to large parts of Europe; the chances of exactly the same setup happening again are very small. The reason I think this is because you are relying on so many small things dropping into place at exactly the right time. There are also key differences in the pattern; December 1986 saw a cold to very cold month across Western Russia and much of Europe. Very different from what we see right now. If I look at the 850 temperature chart for 20 December 1986 as an example:
The -10 isotherm is sitting over much of Scandinavia with deep cold sitting farther East. On the forecast 850 chart for December 20th 2011, we have the following:
Much less cold pooling to the East (and indeed the North East), with all of the cold air being bottled up over Greenland and North East Canada. I'm not saying this can't change, and Europe will almost certainly cool down at some point, but it has to be recognised that the overall pattern right now is very different from 1986 which makes comparisons with early January 1987, showing a high pressure to the south of the British Isles, largely irrelevant. Of course, the Siberian high could displace, and an Arctic high deliver a very cold shot of air into Eastern Europe, but in 1986/7 this had already happened a couple of times by the time the ultimate cold shot reached the British Isles.
No sign of this at the moment, and yes, I recognise that we could see a pattern change, but let's not get carried away with charts showing January 1987!
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i am struggling to see how the build in pressure over the siberian arctic with the introduction of an cold acrtic high will fail to change things this side of the NH. already seeing the warm russian high being pushed south and east on the fi output. i would have though that we must see a change in tone to our zonality as the tilt of the flow changes or even maybe the azores high ridging into us. in years gone by, there was the old adage that lack of monitoring stations in the arctic meant that this region was badly modelled. was this a myth ? is it still relevant ?
Until we get a more favourable upstream pattern, it's irrelevant what the siberian high gets up to. Every winter that has long periods of zonality sees the so seismic high pushing further west, but in most cases the farthest it gets is central Europe. With just the right setup it can push farther across as in 1987, but you have to rely on so many things happening at exactly the right moment, that is why the extreme outbreaks such as Jan 1987 are as rare as hen's teeth.
Until the jetsream stops flying off the east coast of north America, the best we can hope for is some amplification and colder shots/topplers.
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Im next in the firing line, can see it aproching from my west. Will tell you what it falls as!
Falling as rain
Not surprising really. Looking at observations, it was reported as rain in High Wycombe where they do have elevation, so chances of snow are very limited. Dewpoint is also marginal hovering just above freezing and temps are generally on the rise.
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This is going to be very marginal as the upper temps are close to -4c. If the intensity is heavier, then this could lead to sleet/snow. Many side roads are icy, so this is going to be tricky when the ppn falls.
Sorry guys. It already passed over Reading. Wet snow initially which settled on frozen ground and then turned quickly to moderate rain with big splats of molten snow thrown in. With a bit of elevation you may get lucky, but very marginal and temps are on the rise. It hit Reading at daybreak when it was coldest, so even more marginal now I suspect...
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Currently moderate sleet falling in Arborfield, Berkshire.
We had a few flakes here in reading which settled on the still frozen ground. Turned to rain pretty quickly and washed it all away...
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Nice pics audiotech. That road is always my first destination whenever there's marginal snow events. Coming out of Reading, it's usually starting to turn to snow by Nettlebed, and then proper snow by the time I reach Park Corner and Cookley Green. It was settling nicely when I first drove through around 6.30 this morning.
BTW, first real test of the winter tyres this morning and they're great. Strongly recommended for anyone who likes snow chasing like myself.
and ice in the morning!
Yes. I'm hoping the gritters will be out on force. Traffic is so bad this evening though they wouldn't get much done!
BTW, 'apparel' should have read 'splash'. Stupid phone!
BTW audiotech, next time you approach from the oxford direction, try coming off at 6, turn left and then right up the A40. Lovely drive and you'll see the snow increasing as you go up...
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is that a band of precipitation heading our way on the radar?? bitterly cold outside....maybe an outside chance of a flurry??? any reports os whats coming out of it???
Rain. We had a burst in Reading around five and it was fairly heavy rain with just the odd apparel on the windscreen from a dying snowflake. Will be snow over salisbury plain though judging by the radar.
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What are the chances of getting any showers this evening are they pretty slim?
In a North West airflow, the further South and East you are, the less likely. So, pretty slim!
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How did the higher places in the Cotswolds do? Was thinking of taking a fairly convenient detour through Stow-on-the-wold later as it's the highest town in my locality (800ft). Or will it all have melted by say 3pm? Alternatively I could take a less convenient drive and look at Bald Hill (834ft) just west of Stokenchurch.
Probably still quite a bit lying near Stokenchurch; if you head through Stokenchurch, turn on to the A40 just before the M40 junction, and take the first left (Kingston Blount according to Google Maps), then you will find about 4cm lying. The roads are now clear, but take a walk into the woods where the shade will have prevented much melting.
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Yep, this turned out just as forecast for the south east. Rain overnight, with a wintry mix in the morning.
That band of showers over NW England & N Wales seems to be decaying somewhat as it moves towards the Midlands. Looks very unlikely we'll get anything from that.
Yes. It's an Irish Sea streamer, or maybe even a trough. However, these features usually don't get much further south than Birmingham, dying out quite quickly as they head inland.
Pretty classic NW airflow shower pattern setting in behind the departing system. Showers on West facing coasts and through the Cheshire gap. Doesn't usually bring anything in the way of showers to the South East unless the low pressure stalls over the near continent long enough for instability to feed further troughs; unlikely I'm afraid!
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Heavy snow in wycombe, but only settling on grass. Different matter in stokenchurch. About 2cm on roads, 3-4 on grass. Roads are bad as no grit, so a freezing layer is developing.
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Was that the heavy band that came north to south and surprised everyone? It was very heavy and reached me about rush hour, what fun, although it settled it didn't stick around for long if I remember right
That's right. It was a different story further west. Turned over to snow earlier in Reading and we had a longer spell of heavy PPN. Left about 3 inches in the end and that stayed on the ground, in patches, until after Christmas. Abandoned cars on just about every hill in Reading for a couople of days afterwards!
RE, Nick's point about dewpoints, here in Beaconsfield, the ground dried rapidly during the brief dry spell indiciating falling dewpoints. Now started snowing again, so time for me to head back up towards High Wycombe!
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I would have thought they have snow there as it's only about 15 mile South from me and a much higher elevation.
They will. It was snowing when I drove through around 6.30am, but not settling as it was too warm. Stokenchurch had settling snow though. I'm expecting Wycombe to see settling snow when the next band hits.
Heaviest PPN looking like being Aylesbury down to Maidenhead and then M3 down towards south coast (won't all be snow that far south of course). Going to be fairly short lived, but quite intense in places, so best shot coming up!
Now clearing Oxford, Thame and Whitchurch, so that's it for you guys. Basingstoke will see another 20 minutes or so before it clears.
Interestingly, despite heavy rain overnight, the ground here in Beaconsfield has dried out rapidly during this brief dry slot. Good indication of falling dewpoints...
Cet Question (mr Data?) Sub-zero Cet Temp In 30 Day Period
in Historic Weather
Posted
If you have access to the figures I'd happily write an application to provide averages based on a date range....