Penellype's Weather Channel

[unclefudgly]

Thanks for all the updates Penellype, a great thread. Glad it's now a sticky

[Nicos]

The French radio are ( just now) warning us of upcoming Siberian Winter storms ....I'm going to go with Pen's 'A taste of Early Spring'
The thought is sooo much more uplifting

[Penellype]

The French radio are ( just now) warning us of upcoming Siberian Winter storms ....I'm going to go with Pen's 'A taste of Early Spring'
The thought is sooo much more uplifting

Err - you are in France, which is not the same. Unfortunately your air is coming straight from Siberia at the moment and it is very, very cold (along with Spain and Portugal). This is what was forecast for us a while ago, but because the high pressure is further south, so are the cold easterly winds.

Sorry

[Penellype]

More of the same today, with high pressure in charge. The south will see the best of the sunshine but are paying for this with cold and frosty nights. Further north it is warmer, with a lot of "anticyclonic gloom", which is supposedly dry, but in fact can turn out to be remarkably wet. For those who are interested in an explanation of this, there is a good one here Synoptic Guidance - 17th January - Blocked Pattern Dominating - Blog by Matt Hugo - Netweather.tv

The models are now delaying the onset of lower pressure, instead building another ridge over us as the current one declines. As always longer term forecasts are subject to change, but the difference from the last ensemble plot I posted is clear to see:



The higher upper level temperatures are due to higher pressure (see below) and the rainfall spikes are much less marked around the 24th-26th, with only a few of the runs (mainly orange and red) bringing in fronts that are strong enough to reach York. The further north and west you are, the more likely it is that you will see an increase in wind and rain around this time, while the south and east may stay mainly dry for rather longer.

This is the chart for midday 25th January from the main operational run (thick green line on the ensemble graph):



and this is the chart for the same time from the run called P15 which is one of the orange ones:



You can clearly see that the upper air temperatures are much cooler over the whole country than in the operational run. Currently the higher pressure runs are in the majority, which probably means more mild, cloudy and damp weather for most of us.

The stratosphere forecasts continue to be interesting. This is the position now, looking straight down onto the top of the north pole:



and this is the forecast position by midnight on 29th January:



The warm red colours are forecast to completely cover the north pole. This is called a sudden stratospheric warming, and the models have been consistently predicting this around the end of January for a while now. This is way up in the atmosphere and there is always some doubt as to whether is will propagate down into the part of the atmosphere where weather occurs. If it does it tends to favour high pressure over the pole. As I've mentioned before, the effect of this on us depends on the position of the high pressure, but it will be interesting to see how this works out in reality.

[Jay22]

Keep up the good work Penellype, thank you!

[Penellype]

Slight changes to the position of the centre of the high pressure mean that the warmer south westerly flow is being pushed slightly west. This means that the clearer and colder conditions already in the south may become more widespread over the next few days. Forecasting amounts of cloud under high pressure is always tricky, but where skies clear at night quite a sharp frost can be expected, with freezing fog a possibility too. The north and west is always likely to be somewhat milder and cloudier.

A slight disturbance in the flow is likely on Sunday and this could lead to a few flakes of snow in places but it is unlikely to amount to much. The high then creeps east again, putting us back in a similar position to the start of this week. Once again the breakdown to more westerly weather is being pushed slowly further away - the models are always a little keen to return to the default position of a westerly flow because predicting when a blocked pattern will break up is difficult. At the moment this is well into the unreliable timeframe.

[Penellype]

Quick update, although really not a lot has changed. The south and east will continue to see a few more cold nights with frost and increasingly dense freezing fog likely, before finally warming up a bit towards next weekend. The north and west will gradually become warmer and breezier as the south westerly flow returns from tomorrow. By the end of next week western areas are likely to see some rain, but it may be the middle of next week or later before this manages to break through to the south east.

[Jungle Jane]

It was showing a temp of -3 in the car yesterday at 8pm! The ice block I took out the bird bath the other day is still an ice block on the grass,with another ice block added from today,by next Thursday I'll have an igloo

[Penellype]

Ice takes a remarkably long time to melt even if the temperature is quite warm. That's because in an ice crystal the molecules of water are held in a rigid pattern by quite strong "hydrogen bonds" which take a fair amount of energy to break. Freezing water is relatively easy, as long as there are no dissolved substances such as salt, which gets in the way of the formation of the hydrogen bonding structure of ice.

Just too much cloud for a frost here this morning (it got to 0.1 degrees), but we did have a few flakes of snow this afternoon.

[Penellype]

Another day of chilly and perhaps foggy weather for the south and east, warmer in the north and west with rain in the far west. Things are about to change subtly but very noticably tomorrow.

This is today's chart:



Apart from in the south east, the flow is coming off the warmer sea to the south west, which is why the north and west are warmer. France is still very cold, so the south east is colder, and as it is less windy there is the potential for frost and fog.

By tomorrow the position of the high has shifted very slightly, meaning that for most of us the flow is coming from the south:



Warm upper air and a southerly wind - sounds like spring! Unfortunately not. The very cold air over France will be dragged in underneath the warmer upper air, resulting in an inversion. It will be cold, and will feel bitterly cold in the wind.

The ensemble chart for York shows the totally misleading upper air temperature, the warm start corresponding to the yellow colours on the above charts:



The upper air temperature then drops as a weak cold front moves through into Saturday, shown by the colours on the map turning to green and blue:



... and everywhere warms up! That's because the direction of the flow is now firmly from the south west, so the surface air is warmer.

This heralds a change to a much more Atlantic pattern - expect milder, much wetter and sometimes windier weather from this weekend.

Into February the models are beginning to disagree, with the GFS staying mild and wet through to the end of the timeframe, while the ECMWF wants to keep us wet but is trying to build high pressure over Scandinavia. If that happens there is a chance that it could get colder again.

There is also the joker in the pack, which is the warming going on in the stratosphere. This apparently doesn't quite meet the criteria for a "sudden stratospheric warming" which are very strict, but it is a significant warming, and could affect our weather from around mid February, although it is far too early to say what those affects might be.

[KevinM67]

Thanks for the regular updates Penellype - really interesting.

Over January, it's been freakishly mild here in the East of Ireland, with grass (and weeds) growing away as if it's March/April.

[Penellype]

The westerly pattern has now taken over with the high pressure pushed eastwards into the continent and the whole country seeing milder if rather damp conditions.

Throughout the week it will be typical low pressure weather with bands of rain interspersed with brighter showery periods and more wind than recently. The best day nest week could be Wednesday when a weak ridge of higher pressure may form between the lows.

Towards the end of the week the lows get deeper and more vigorous, with likely stronger winds and possibly stormy conditions by next weekend. The models have the unsettled pattern continuing into the following week at present, although at the end of the latest GFS run (which goes out further than the others) there are signs of high pressure building both to the south and over Greenland. This is a very long way off, but could lead to a return to colder conditions.

[Penellype]

I should probably have added that just because its milder it doesn't rule out frost (it is January). Tonight could be quite cold where skies clear, and the Met Office have released a yellow warning for ice in places where it has been raining today. Severe weather warnings - Met Office

[Potstubsdustbins]

That's nice to know, the lads are fitting a heating system next week and their first job will be to rip out the existing storage heaters. They will take the folks a couple of convectors to use but slightly milder weather will help.

[Jay22]

Where's Penellype when you need her? Is this Killer Artic Blast really going to hit next week?