NWP

I generally use NWP data generated from the American GFS model, and very occasionally from the European ECMWF model. I would like to use NWP data from the Met Office but it’s not accessible to the general public except in the old ‘fax’ chart format, and limited to eight forecast periods out to T+120. Most of the time I display images that I download courtesy of OGIMET or NetWeather.



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

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!

The week ahead

Figure 1

The mobility in the weather patterns that started around the 20th of July, continues unrelentingly into the third week of August according to the latest forecast charts of the GFS model. The only difference that I can see this week is that the discrete areas of low pressure are generally a little to Iceland than to Scotland, and high pressure gets closer to southern areas by next weekend.

In fact the whole week can be summed up as changeable, windy at times, with spells of wet weather, cool at first but gradually becoming warmer by next weekend.

Tuesday doesn’t look half bad, bright and breezy with showers more frequent in the north and west. Next Saturday looks a fine day across the whole country, if this T+156 forecast can be trusted, as does next Sunday away from Scotland, when it looks almost summer like in the south, but this is not the first time that the GFS has promised this scenario in the last few weeks.

I wrote an article about KISS this week, and the forecast chart below (fig 2) is another perfect example of “not caring one hoot “about that principle looks like, from the forecasts in Barad-dûr. I often wonder what forecasters in the other Met agencies across Europe make of these convoluted forecasts and analyses from the Met Office.

Figure 2 – Courtesy of the Met Office

Exit stage right – GFS outlook for week 32

Another decidedly cyclonic and slightly autumnal week to come judging by the latest eight-day GFS forecast for week 32 (fig 1). The shallow low that’s currently moving towards the Outer Hebrides, will continue to transition eastward into the North Sea, before getting caught up with another low moving up from the south on Tuesday. That lows formed in much warmer air over Central France, and as the two combine and do ca pirouette in the central North Sea, they produce what looks a pretty awful day down the east coast on Wednesday, if it comes off. Thursday on the other hand, looks the best day of the next week, as the low finally exits stage right.

Figure 1

Baking hot

The baking hot weather over southern Europe continues for another day with little sign in the short-term of any relief, here are the 12 UTC temperatures for that part of the world (fig 1), and as you can see that there are a number of stations already reporting 40°C or higher on it.

Figure 1

Alghero in Sardinia is one of the hottest places on the chart, with a temperature of 41°C at 12 UTC. This is a coastal site but these observations are from the airport which is a short distance inland, here are the temperature stats for Alghero for the last month (fig 2).

Figure 2

So today makes five days in a row that the temperature has exceeded 40°C. Here are this week’s plotted 3 hourly observations for Alghero (fig 3).

Figure 3

You would have thought than a 12 knot wind from 200° would have brought a cooling sea breeze into that part of Sardinia and cooled things down at the airport (fig 4), but of course there is very little in the way of gradient over the Mediterranean, so I suppose the low-level flow could be from more of an easterly point.

Figure 4 – Courtesy of Google

It’s not till this time next week before the hot air looks like it loses its grip in that part of the world, according to the GFS model (fig 5), and this hot weather will only exacerbate the severe and very serious drought conditions that are affecting a large part of Italy at the moment.

Figure 5

 

 

Storm tracks…

The excellent wxcharts.eu website have recently added a storm tracking feature to their repertoire of NWP graphical tools that they offer. I’ve never seen this kind of thing done before with NWP, and it looks like an interesting new addition, to what is already an incredible site. Unfortunately the tool only seems to work with the GEFS NWP model at the moment. I can’t work out if the vortex centres are generated by the models themselves or are generated by wxcharts.eu as they are received.

Figure 1 – Courtesy of www.wxcharts.eu

It will certainly be a very handy tool for keeping an eye on extratropical lows as they ply their way across the North Atlantic this autumn and winter, and for any tropical storms that occur in the Caribbean too.

Figure 2 – Courtesy of www.wxcharts.eu

The UKMO is conspicuous by it’s absence from the available NWP models in their viewer, which is a great pity.

Cool and showery weekend in the UK – heatwave for Italy

I notice that there’s some talk of a ridge of high pressure nudging up from the Azores in the medium term, that might bring a return to summer across the British Isles, so I thought I would have a look at the NWP. In my experience, NWP forecasts are normally very good out to T+96, after that it’s more like science fiction than science fact. At first glance, the forecast chart from the UKMO (fig 1) look quite appealing for this coming weekend, apart that is from the trough over Scotland, there’s no front for miles which is unusual, and there’s none of those pesky lows in the immediate vicinity.

Figure 1

Take another look, and you may notice the cold trough of sub 546 dm air that’s across western parts of the country, that’s really quite cold air for early August, and at this time of year cold air means instability and showers. The GFS model for the same time shows this showery regime very well on Saturday (fig 2). Even without this cold trough the mobility looks likely to continue, and the next low in a cyclonic series that started on around the 20th of July, has already started to form at 40° west.

Figure 2

If you want the real summer it’s still alive and kicking this week over central and eastern Europe, with heatwave conditions across Corsica and Italy. It was well forecast by the models and has been going on all week. In this chart for Friday (fig 3), you can see the 582 dm 1000-500 hPa partial thickness line meandering over central Italy, which marks some exceptionally hot air.

Figure 3

A tropical heatwave

Figure 1 – Courtesy of OGIMET

We’re having a heatwave,
A tropical heatwave,
The temperature’s rising, it isn’t surprising
She certainly can, can can!

That’s how the lyrics go in first verse of Irving Berlin’s 1933 song ‘Heatwave’, but by next week hot conditions look likely to have extended as far north as the Baltic, across much of southern and eastern Europe, if the latest run of the GFS is correct. I can’t remember seeing 1000-500 hPa partial thicknesses of 582 decametres extend as far north as Corsica, as they are in this forecast chart for midnight next Wednesday the 2nd August (fig 1).