Penellype's Weather Channel

[1Bee]

C'mooooon rain.....

[Penellype]

I can't emphasize enough that we are looking at showers, so not everyone will get one. Please don't shoot the messenger!

[1Bee]

I never would, Penellype.

[Penellype]

Some weather apps may be showing rain for the weekend as the GFS has quite a few showers around, particularly on Sunday. However this is not backed up by the high resolution Arpege model, which has very little rain away from the far north of Scotland throughout the weekend, so don't expect anything worth mentioning.

[Penellype]

The atlantic hurricane season has started, with 2 storms currently off the east coast of America. Beryl is heading for the carribbean, while Chris is moving up the coast towards Canada. Chris may or may not affect our weather depending on where it goes - the models do not handle these storms very well as they are very small and intense.

In my opinion it will probably take an ex-hurricane to kick us out of this pattern of warm/hot and very dry weather. Whether or not that will be Chris remains to be seen - some of the model runs imply it might, some (including the latest ones) do not.

Regardless of where Chris goes, things should get a bit less hot and fresher for the first half of the coming week. Temperatures are likely to build again towards the weekend, and some of the ensemble members are predicting rain (probably in the form of showers or thunderstorms) from Friday. This does seem to move from run to run though, so don't bank on it.

[Baldy]

Bleddy penellype with her scientific interpretations.
Time for a Wicca man I think?

[Jimmy]

Anyone know how the commercial boys are managing with this drought ?
Are we going to have shortages and inflated prices ?
Jimmy

[Jimmy]

Hmm two for the price of one !
Jimmy

Not no more Jimmy, we don't do BOGOF

[Penellype]

Anyone know how the commercial boys are managing with this drought ?
Are we going to have shortages and inflated prices ?
Jimmy

I think the farmers are struggling - grass is going brown and animals need supplementary feed, I heard the potato crops are not growing as well as they should do, presumably due to lack of water. I would expect prices to rise at the very least.

[1Bee]

Apparently the barley harvest is better than expected, but straw prices have rocketed because the poor winter meant more stock was housed indoors for longer.

I've heard about potato concerns, too, and certainly round here they're unlikely to get a second crop of silage, which means more fodder will need to be bought.

Googling 'Harvest 2018' brings up some interesting results.

[Chippy Minton]

Time for a Wicca man I think?

At least the Wicker will be tinder dry.....

Thought it was raining on the way home, got a bit of drizzle on the windscreen, only lasted a few seconds, came to the conclusion it was someone screen washing Comes t something when the only moisture on the M60 is someone else's screenwash

Dug up the autumn planted onions, shallots and garlic. The books say to lay them out on the surface to dry which I dutifully did. However, if I'd had a bottle of olive oil I could have picked them ready roasted!

[Penellype]

Looking increasingly likely that the weather will turn more changeable next week with some much needed rain, particularly in the west. Whether it will manage to reach the south east is debatable at present, but things do look to be moving a bit.

No idea how long the change will last - tropical storm Chris is still a source of much uncertainty.

[unclefudgly]

Come on Rain !!

Ground is like concrete at the moment. We need rain

[Mistlepie]

Penellype, I'm fascinated by the huge change in the weather today. Here in Norfolk its at least 10 degrees colder today than Sunday. Would you be able to explain what changed?

[Penellype]

Penellype, I'm fascinated by the huge change in the weather today. Here in Norfolk its at least 10 degrees colder today than Sunday. Would you be able to explain what changed?

I can try!

Several factors control temperature, the most important being time of year, air mass, wind direction and whether or not it is sunny. 3 of these are obvious, the 4th, air mass, is not and needs explaining. My explanation is very simplified - things are a lot more complicated than this.

It is a general natural law that temperature "tries" to even itself out. If you have a mug of hot coffee it will gradually cool down and the air around the mug will warm up. If left alone, eventually the coffee will become the same temperature as the room, and the room temperature will have risen by a tiny amount. The atmosphere is doing this on a much larger scale, the source of the heat being the sun. However, the earth is not just sitting there in the same position. It moves around the sun with the seasons and it spins on its axis once a day. It is also a sphere, which means that the part of it nearest the sun gets hottest, and the part furthest away is coldest, with areas in between receiving sunlight at increasing angles and decreasing intensity the further they are from the direction of the sun. This is why summer sun feels hotter than winter sun. The rotation also means that the hottest area moves round the globe every day, so the sun feels hottest at mid day and is not shining at all at night. You can imagine a hot spot moving round the earth once a day.

In addition to this there are complicating factors. Water absorbs heat at a different rate from land and tends to be warmer in winter and colder in summer than nearby land. Rock or concrete absorbs heat better than grass or other vegetation and snow or ice reflects heat back into space, so there is uneven surface heating throughout the planet on various levels.

As if that was not enough, the earth is surrounded by an atmosphere which is mobile. This picks up heat (and moisture) from the land or water below, and is also spinning along with the earth. The result is a churning mass of gas, most easily understood by thinking of it as like water in a small river - there are eddies and currents and whirlpools and large areas that appear still. However the river bed is static, whereas the earth is spinning, so while the river whirlpools remain in the same places, those in the atmosphere move around and change in intensity - these are your low pressure systems and hurricanes.

There are some things that are constant, however. The equator is always nearer the sun than the poles, and is therefore always hotter. The earth always spins in the same direction, so all else being equal (it often isn't), the prevailing weather tends to come from the west. This leads to large chunks of atmosphere that have specific characteristics - those over the poles will be cold, those over the tropics will be hot. Those over water will be moist, those over land will be dry.

But remember that things are trying to even themselves out. Therefore the boundaries between these air masses (called fronts) are unstable. Don't worry, I'm now getting to the point! The UK is in an area which is neither in the tropics nor near the pole. We are in the mid latitudes, and therefore on the boundaries between tropical and polar air masses. We are also in a position where we have a large expanse of water to the west and a large chunk of land to the east, so we are also on the boundary between the continental and maritime air masses. This means that at different times we can be cold and wet, cold and dry, warm and wet or warm and dry, depending on the air mass.

Recently we have been sitting under a ridge of high pressure centred pretty much over the top of us. This has, because of its position, been drawing in air from the east (air always circulates clockwise around high pressure). This air is part of a continental air mass, and because it is summer the continental air is hot and dry. On Monday a weak cold front moved down across the country, introducing a cooler air mass. The high pressure is still there but it has moved slightly north and the wind direction changed as a result to a north easterly. Instead of the air coming straight off the continent it is now coming more from Scandinavia. It still isn't cold, but it isn't as hot as it was. Different air mass, different wind direction.

This is yesterday's chart from the ECMWF:



I don't have a corresponding chart for Sunday unfortunately, but you can see from the white lines (isobars) around the high that the wind is now coming from the north east. The upper air temperature shown by the top section of the chart below gives an idea of the air mass:



This line was between 10 and 15 on the left hand scale on Sunday and has now dropped below 10, showing that the upper air is cooler (which influences the temperature at ground level).

So, its still summer, and still sunny, but for now, nowhere near as hot.

(And yes, those are rainfall spikes at the bottom of the chart, although there is still a lot of uncertainty).