Penellype's Weather Channel

[Penellype]

Models really struggling at the moment - the forecast for here today, from the 6am GFS run is sunny and dry, in fact it is cloudy with intermittent drizzle, and we had a sharp shower over night which was not forecast by any of the models.

For the remainder of this week there is a risk of chilly nights with potential ground frost where skies clear, anywhere from the midlands northwards. The difficulty is knowing where skies are going to clear, and looking out of the window is probably better than relying on forecasts at the moment.

Storm Florence is proving a real forecasting problem. Yesterday it was forecast to come this way (as a low pressure) by almost all of the models, today most of them have it hitting the east coast of America. The reason for the change is the forecast development of a Greenland high pressure, which would put us in a cold northerly wind. I wouldn't like to bet on either scenario with any confidence at present.

[Gillykat]

The temperatures have certainly dropped at nights here in Alnwick - only 6c last night.

[Penellype]

It shouldn't be quite so cold for the next few nights, but the chilly nights will probably return towards the end of next week. Its that time of year...

[Penellype]

This week sees a north-south split, with the north cool and changeable and the south warmer and drier at times. In between the two is a cold front which looks likely to get stuck over central areas mid week, producing rain which could be light and patchy. Defining the extent of "north", "south" and "central" precisely is tricky.

By Thursday the front clears south and high pressure builds, giving drier weather with more sunshine, but all areas are likely to see chilly nights with the threat of possible ground frost in vulnerable areas especially in the north.

What happens next will depend crucially on hurricanes/storms Florence, Helene and Isaac which are currently in the tropical atlantic giving forecasters severe headaches. Florence was a category 4 hurricane but calmed to a tropical storm before strengthening again to category 1 at the moment. Worryingly it looks like moving very close to North/South Carolina as a major hurricane, and if the GFS is right it then stops just offshore and stays there for several days before heading north to get caught in the jet stream and possibly affect us. The ECMWF has it moving inland and weakening. Isaac appears to be heading for the Carribbean, but Helene is wandering about in the middle of the atlantic and could well come our way, or influence what comes our way. The models, as usual, are really struggling with this.

[Chippy Minton]

Was just looking at the NOAA hurricane watch website and there are currently 3 fully formed hurricanes in the Atlantic (Florence, Helene and Isaac).

Florence is off to the Carolinas and Isaac looks like on a Caribbean track but Helene looks like taking a turn in our direction, which is bound to play havoc with the models. Could get breezy in a week or so....

Sorry, just seen your last post , any further thoughts Penellype?

[Penellype]

Its really hard to know what effect these hurricanes will have on our weather. At the moment the jet stream seems to be strengthening and low pressure is finally wearing away the high that has been over Europe all summer. The likelihood is that one or more of the hurricanes will get caught up in the jet stream and head towards us, giving us an autumnal storm, but sometimes these things can stall in the atlantic and cause a ridge of high pressure to build to their east, which can give us some warm and pleasant weather. Everything depends on the exact conditions around the storm/hurricane. You can see the problems this causes with reference to Florence, which started as a storm that was not expected to intensify much, and within about a day was a category 4 hurricane. It then weakened to a tropical storm before intensifying again to (currently) category 4. The models have been having a real problem with this one, forecasting it to go anywhere from Norway to Florida, and they have now settled (we think) on South Carolina at the end of the week. The huge range of previously forecast tracks for Florence gives something of an insight into the difficulty of forecasting these things, so pretty much anything (within reason) could happen.

[Penellype]

A very excitable week coming up. Ex hurricane Helene is approaching southern Ireland on much the same track as Ophelia did last year. There are warnings for wind for some western areas as the storm is forecast to hit southern Ireland on Monday evening. It will then move north and east through Scotland with gale force winds likely. Everywhere will be at least breezy on Monday into Tuesday, more so the further north and west you are. Rain from this system will be confined to the north and west. Further south and east the main effect of Helene will be very warm and increasingly humid weather on Monday and Tuesday morning. How warm it gets will depend on how much cloud there is - if the sun comes out it could be quite hot. Monday night will be warm and sticky.

It will turn cooler from the west as Helene moves away and a band of rain will move south and east on Wednesday with cooler air behind. Nights could get quite chilly again by the end of the week.

There is considerable uncertainty beyond Helene, with most models developing high pressure, but varying in the position and timing of this. The amount of uncertainty can be seen from the divergence of the lines in the ensemble chart, with huge temperature differences by mid week, although the general trends of the lines are similar:



York, being in the east, has fairly few rainfall spikes - there will be much more rain further north and west.

[Chippy Minton]

This is exciting weather season! I love it!

Could do with a bit of that warmth and dryness to ripen the last few Roma tomatoes though.... After a bit of wet weather to force us inside and sort out the chest freezer!

[Penellype]

As can happen when there are big uncertainties, this week's weather looks a little different now. Helene is just the first of several storms likely to arrive here this week on a strengthening jet stream running straight through the country. There are already yellow warnings for wind for today, tomorrow and Wednesday - expect more. For this part of the country, Thursday night into Friday is looking particularly unpleasant at the moment. There will be heavy rain for some areas too.

Keep checking the warnings for your area https://www.metoffice.gov.uk/public/weather/warnings, and make sure things like wheelie bins, trampolenes and garden furniture are secured as well as any blowaway greenhouses you may have. Watch for fallen trees and branches - trees are in leaf and therefore much more susceptible to wind damage than later in autumn or winter.

Colder nights are still a possibility later in the week.

[Chippy Minton]

Just been out to put the chickens to bed (no I don't read them a story!). It's a starry, starry night but still reading 19C. This time of year one would expect clear nights to be getting cold. Wind's picking up as well, hopefully we're far enough inland to avoid the worst, Wales tends to shelter us.

[Penellype]

Tomorrow's storm (not Helene, which is today's) has been named storm Ali and there is an amber warning for N Ireland and parts of Scotland, as well as a wider yellow warning for much of the north of the country.

The timing and exact tracks of this week's storms are very uncertain. Keep checking forecasts as things could change, even at fairly short notice.

[Penellype]

Another named storm today - Bronagh, which is currently bringing heavy rain to northern and western areas. There is a yellow warning for rain and also one for wind later in the night and into tomorrow as the low rapidly deepens and moves into the north sea. This time the strongest winds will be over England and Wales.

I don't really understand why the Met Office have named this storm. Yes it is going to produce some very heavy rain and very strong winds, but I thought that the criteria for naming a storm was that it warranted an amber warning. Currently there is not (and has not been) an amber warning for this storm system, so I am confused.

There is also a yellow warning for wind for Sunday into Monday. That particular storm system (which contains some remnants of hurricane Florence) is giving the models serious problems and its track and intensity are very uncertain with big disagreements between the models and runs. There should be better agreement soon.

[AmateurOne]

Just got back from British Columbia and they too have had similar freeky weather, a long dry summer, rain recently and early snow falling on the mountains.

[Penellype]

The storms and ex-hurricanes have really shaken up the forecast and completely changed the pattern. This is not unusual, but basically what it means is that after a long period of warmer than average temperatures things are going to be a lot cooler.

The rest of September now looks mostly chilly, with some cold nights, particularly on Sunday into Monday, which is likely to be the coldest night of the autumn so far. After a brief warm up mid week the temperatures return to chilly:



What the York ensemble does not show is Sunday's rain, which is mostly south of York. Most of the southern half of the country will be very wet and also windy - there are yellow warnings in place for both.

The rest of September should be reasonably dry after Sunday, less so in the north and west as high pressure remains close to or over us with its centre to the south or slightly to the west, hence the cooler temperatures. The up and down lines, which look typical of low pressure weather, actually appear to be due to the centre of the high moving around and therefore changing the direction of the flow, hence the low rainfall amounts.

[Penellype]

I probably should have mentioned that high pressure at this time of year can result in fog, which might be slow to clear.