The impact and likelihood of a storm Aileen or Sebastian?

Looking at the latest yellow warnings issued this morning for strong winds and heavy rain later on Tuesday and Wednesday, the Chief forecaster at the Met Office thinks that the likelihood of rainfall, is higher than that of strong winds (fig 1). This is a curious decision on his part, because if anything I would have thought that it was the other way round, and that the likelihood of strong winds were just if not more likely, than that of heavy rain alone. But the Chief does think, that any impacts from the strong winds are higher than the impact from heavy rain (fig 1).

Figure 1 – Courtesy of The Met Office

I think this is a game that they play using the impact/likelihood grid that determines if a storm is to be named. As far as I can see, if they issue two alerts or more, and they’re both amber, then the storm will be named, but I’m unclear if just one of them being amber would trigger the naming process.

Figure 2 – Courtesy of the Met Office

The rain from the warm and cold fronts fairly zips across the country, but the occlusion sticks around a while across southern Scotland and hence the limited area for the heavy rain warning. According to the latest T+48 forecast chart that I can access from Met Office, it looks like they see the tightest gradients being from the Midlands and Northern England, I can’t see why they’ve taken the yellow warnings area as far north as Edinburgh, but without their model data it’s impossible to say. Obviously they’ve included gusts to 75 mph that may occur down the lee side of the Pennines.

Figure 3

The Met Office have forgotten to label the central pressure of ‘Sebastian’ (the name already given it by BIM) on their T+48 chart (fig 3), which I reckon is somewhere around 980 hPa. The UKMO solution is very similar to that of the GFS (fig 4), the only real difference is that the tightest gradients lie south of northern England, and across most of the Midlands and southern England. It will be interesting to see if this area gets adjusted southwards in the next 24 hours.

Figure 4

European heatwave in perspective

I couldn’t think of a much better way of getting some kind of perspective on the heatwave over southeast Europe, so I decided to display temperature anomalies from thee 2.5° six hourly gridded air temperature data, which I download from the NCEP reanalysis site. So this chart (fig 1), shows temperature anomalies for 12 UTC on August 2nd, which is a bit unfair on the rest of the northern hemisphere, but does go to show the size and magnitude of the positive anomaly centred over Ukraine, and extending southwestward across the Balkans and Italy, towards the western Mediterranean.

Figure 1

Good week, bad week

Figure 1

We seem to be caught up in a cycle of good week bad week at the moment, and next week looks pretty grim, at least from Tuesday onwards looking at the latest run of the GFS model (fig 1). It’s not well supported by the T+84 forecast chart from the UKMO though (fig 2). The GFS does hint at a return to Summer by next weekend (T+180) to keep the cycle going but don’t hold your breath.

Figure 2 – Courtesy of UKMO

I’m sure that someday the Met Office will move on from the archaic format in which they prefer to display their NWP forecast output (fig 2), but for now we are stuck with the old ‘fax’ chart that’s changed little (apart from the addition of the thickness lines) since I joined the Office in 1970, and the eight forecast charts out to T+120 that they publish.

Goodbye 564 line

It’s Midsummer’s day today, and we can bid a fond farewell to the 564 dm partial thicknesses that we’ve seen across southern areas for the past few weeks, hopefully it will return later in the summer, until then it looks changeable and breezy at times, with some welcome rain over the next week or so, according to the latest run of the GFS model.

Many places 10°C or more cooler

Figure 1

Many places across England and Wales were up to 10°C or more cooler on Thursday (22 June) than they were or Wednesday (21 June). Trawsgoed in Ceredigion, was top of the list and 12.5°C colder (fig 1). Rather surprisingly, places on the northeast coast of England were almost 5°C warmer on Thursday, once they had lost Wednesday’s sea breeze (fig 2).

Figure 2

Maximum temperature of 49.7°C Nuevo León in Mexico

Figure 1

I heard Eddie Mair going on about the temperature in Phoenix Arizona in yesterday evening’s PM program on BBC Radio 4, so I thought I’d keep an eye out on the maximum temperatures and see what turned up. Well to trump Phoenix (no pun intended) the maximum temperature reported at 00 UTC from Nuevo León in Mexico was 49.7°C (121.4°F), and a shade (I can’t help it) higher than the 48.3°C in Arizona. Excuse the contouring of temperatures is far too smooth and not accurate.

36.8°C at Le Mans

Figure 1

Jersey airport ended up being the warmest place in WMO block #03 as suspected with 32.4°C, but Le Mans was the hottest place in France with 36.8°C this afternoon. That air over France will start to feed up across the channel as the gradient starts to veer overnight and possibly produce an even hotter day tomorrow across the south.

Figure 2

Topsy turvy weather

By this time next week this may current heat wave may be just a distant memory, that’s according to the latest GFS forecast, as the British summer monsoon gets into full gear.

How’s this thing going to end?

A good degree of consistency between the UKMO and GFS models about how saturday will look at T+120 (figs 1 & 2). How accurate it will be is another thing entirely. Pressure is still forecast to be reasonably high across the south, 1000-500 hPa thicknesses are not far from 564 dm, but there is a fresh to strong westerly flow across the British Isles, with fronts driving in from the west, so things don’t look good for this current hot spell.

Figure 1

Figure 2

17 June 2017 – maximum temperatures