The consistency of the GFS model

Figure 1

The panel of eight charts are all from the GFS model runs of the last eight days (fig 1). They display the same forecast chart for midnight tonight (Saturday the 20th August 2017), but all from different model runs and forecast ranges, from the oldest of T+192 (last Friday midnight’s run), to the latest T+24 (this Friday midnight run). I’ve done this to see just how much the forecasts differs as we get closer to T+0, the forecast day we are interested in. The chart at the top right is from the furthest out (T+192) and the chart at the bottom right is closest to the forecast (T+24), I did this to compare just how the GFS was handling the approaching remnant s of ex-hurricane Gert on Saturday night.

As you can see, the forecast for Saturday night has changed quite radically in the last week. The rain from the approaching warm front was at first [T+168] expected quite quickly over Western Scotland and Northern Ireland, but from Thursdays run the model slowed it down and brought the area further south. The ridge of high pressure that was at 15° west at T+192 also changed position and alignment quite a lot in each run, and by the end is aligned NW-SE rather than N-S as it was at T+144.

What I’ve learned from this little comparison of the GFS, is that there is not a great deal of consistency before T+72, and it’s only from then that things start to firm up, but even when have, this by no means that the model has locked onto the correct solution.

 

Gert promised so much…

Earlier this week I was spouting on about how ex-hurricane Gert would usher in a change of type and that by the end of next week summer would have made a home back.  That was on Thursday, but the latest guidance from the NWP models suggest that once the low (that was the remains of ex-hurricane Gert) has finally struggled to cross the country, which looks like it will take most of the week, things will have changed very little, and mobility will be resumed after just a brief incursion of warm and humid air from the continent for a couple of days at the start of next week. Having said that, I did hear on the BBC weather that the models are having a torrid time on what effect Gert will have on the forecast for later this weekend, but looking at the latest run from the GFS and the UKMO models, their solutions for Monday do look remarkably similar (fig 1 & 2).

Figure 1

Figure 2

Showers sharper than forecast

Figure 1 – Courtesy of the BBC (Spotlight 6.55 pm on the 17 August 2017)

Today’s showers were a lot sharper than forecast by the Met Office model that was used in the BBC forecast on Spotlight yesterday evening (fig 1), with some white pixels in the weather radar, indicating intensities of >32 mm an hour (fig 2). Thankfully they were moving quickly.

Figure 2

Neither was there any mention in the forecast of any thunderstorms in any of today’s showers over the southwest of England (fig 3).

Figure 3 – Courtesy of Blitzortung

Just checking to see how they did on last nights national forecast, and again no mention of any thunderstorms (and any flashing lightning graphics), or of the intense showers indicated by the weather radar. All Darren Bett seem to be interested in was saying how cool it will be, he must have been out of the country for the last four weeks or so. All I can think is that the new Met Office model is having problem in convective situations like this, I am assuming of course that the BBC are still using Met Office NWP data at the moment!

Figure 4 – Courtesy of the BBC (weather for the week ahead)

Or did they mention this large area of very heavy rain in the afternoon over Wales in earlier forecasts. Is it only me that notices just how poor the weather forecast was?

Figure 5

Is the Brown Willy effect on the increase?

Figure 1

Yesterday’s showers up through the spine of Cornwall and Devon were another classic example of showers caused by peninsular convergence. It also goes under the less prosaic name of the Brown Willy effect, it’s amazing what you can find courtesy of Wikipedia. The first thing you will notice that yesterdays string of showers seem to originate a little south of Brown Willy, if my estimates from the weather radar are correct (fig 1), and are aligned around 240-060°. Rainfall accumulations are not particularly high along its length for the period 08-21 UTC, generally between 8 to 16 mm with a few isolated light blue pixels indicating accumulations greater than 16 mm in Somerset. The first band of showers seems to fizzle out, as a second band forms a little further to the north for a short distance, before the southerly band re-intensifies somewhere over the Blackdown hills. The band of showers stretched as far as East Anglia before losing its coherence. We never got anything more than a few spots out of it here in Bradninch during the day, 14 km to the northeast of Exeter, and the cut off between wet and dry was quite sharp.

The recent flooding in Okehampton on the afternoon of the 30th of July was another good example of peninsula convergence, which the Met Office NWP model just didn’t seem to get a grip on. Has the occurrence of peninsular convergence increased in recent years, or is that just down to extra vigilance on my part?

Figure 2

For once there was an upper air ascent in the right place, and for the right time (fig 3). The wind direction aloft in the 11 UTC Camborne ascent are remarkably constant, between 240 and 260°, well up to 15,000 feet.

Figure 3

Pen Hadow heads out into the Chukchi Sea

Figure 1 – Courtesy of Arctic Mission and Google Maps

That brave chap Pen Hadow and his Arctic Mission team have now entered the Arctic Ocean proper, in fact they have now entered the Chukchi Sea on their journey north. You can follow the expedition by means of the Arctic Mission website. It’s a shame that they don’t seem to have an observer on board who can send out a SYNOP observation every six hours, although they reported that the air temperature at 10 UTC this morning was +3°C and they were around 67° north, so they still have a long way to go before they meet the ice edge at around 80° north.

Cool start to August

12 UTC Mean Temperature Anomalies 1-14 August 2017 – courtesy of NCEP reanalysis

Fascinating anomaly chart for the first two weeks of August 2017. A band of cold anomalies more or less stretches from central north America, across the north Atlantic, to northwest Europe, with anomalies ranging from zero to -2°C. The recent heatwave across southeast Europe has left its mark there, with a belt of positive anomalies, as warm as +6°C over the Ukraine and eastern Black Sea, and curving down through Iraq, Saudi Arabia and into Sudan.

Still not convinced

Figure 1 – Courtesy of Met Office

I’m still not convinced by the midnight surface analysis from the Met Office. They have clung to this same ‘configuration’ of fronts (east to west) in all their forecast charts this week:

  1. Warm
  2. Upper cold (in the warm sector)
  3. Cold (returning warm)
  4. Cold (short)
  5. Trough (concave to west of Ireland)
  6. Occlusion
  7. Occlusion (bent back)

By sticking to this analysis they are certainly being consistent, but consistently wrong, because I can see little evidence of the frontal features 2, 4 or 5 in the weather radar at midnight. If they only could publish a synoptic review that explained the various features they have in their analysis and forecast charts and the thinking behind it, we then might be in a better position to understand the rationale behind it, but as far as I am concerned their approach is just far too complicated.

Figure 2 – Courtesy of Met Office

 

It looks like Hurricane Gert will finally breaks the spell

Figure 1

The remains of Hurricane Gert in the coming few days will break the spell that the weather over the UK has been under since the 20th of July. It looks like, for whatever reason, it will halt the zonal westerly flow of the jet stream that’s plagued the country for the last four weeks (fig 2), and bend the upper air pattern to become more meridional (fig 3), and allow the formation of a large blocking anticyclone to form to the west of the British isles. Of course, this all depends on the latest NWP all holding true for the five days or so.

Figure 2 – Courtesy of www.netweather.tv

Figure 3 – Courtesy of www.netweather.tv

There’s still some more unseasonably windy weather to come between now and then, particularly later on Monday, as an extratropical low, spawned by the remains of the tropical air from Gert, deepens and tracks southeastward across Northern Scotland and into the southern North Sea (fig 1). This marks the end of the zonality of the last four weeks, as pressure build strongly behind the low. The last anticyclonic spell across the British Isles was between the 16th and 20th of June. It won’t be a spell of hot weather, because the flow will be northerly at first, it should be dry, and sunny so day time temperatures should be very pleasant, but the nights may be quite cool if not cold.

Looking further ahead, and according to the GFS, the theme seems set to be high pressure across the eastern Atlantic, with a north or northwesterly flow down across the British Isles and much of northwest Europe. Hopefully, this will finally put an end to the mobility of the last month, we shall see!

BBC News: Pen Hadow sets sail for North Pole

I spotted this BBC news item thanks to Paul Homewood, but I couldn’t resist the idiocy of what Pen Hadow is planning to do, i.e. sail to the North Pole. In fairness the video explains what he’s really doing is going as far as the sea ice conditions will allow him at this time of the year, why can’t he be content with looking at the latest sea ice charts on the Internet like the rest of us?

I’m not clear what a stunt like this will do. It certainly will set the focus of the media on the state of the Arctic Sea Ice. If it doesn’t get very far will that please the AGW deniers? Or will the smile of the AGW fraternity widen the further north that he gets? Surely they must know that he won’t get much further north than the edge of the sea ice at the moment?

What if he and his yacht, his dog and his ten companions get locked in the sea ice? I think he’ll be much too careful to let this happen, but who knows?

Just how far north is he likely to get?

Judging by the latest sea ice edge chart for the Arctic from the NMI (fig 2), and if he’s setting out from the Alaskan coast, he should easily get to 80° north. Depending on just how adventuress he is, he could then navigate the open ice and he might make it to 82° north, but that would be still be a long way short of his goal of the North Pole, but by that time I suppose he will have accomplished what he set out to do. It will be interesting to see just how far north Pen Hadow gets, and how this story pans out in the coming weeks.

Figure 2

Tomorrow looks a little complicated

Figure 1 – Courtesy of the Met Office

You could never accuse the Met Office of not being consistent, consistently complicated that is. The chart for midnight tonight (fig 1) is no less complicated than the forecast chart they produced for midnight on Tuesday night this week, or maybe with the aid of NWP they’ve just taken the work of Vilhelm Bjerknes to a whole new level.

Figure 2 – Courtesy of the Met Office