It seems to me to be a tale of two lows, tonight’s rather interestingly, some may say bizarrely, hasn’t attracted any warnings for heavy rain so far from the Met Office (fig 1), but they have already issued an early warning for the possibilities of heavy rain for the low that will affect southeast England later on Sunday. Depending on what NWP model you look at the accumulations for Friday don’t look particularly that heavy (fig 2), but I wouldn’t have thought it would have hurt to have issued a blanket yellow warning for southern and central areas for 15 to 25 mm locally 40 mm, but what do I know. I suppose they still have time to do it but it’s cutting it a bit fine.
Good old David Braine, we’ve had more showers first thing this morning (fig 1) than we saw all day yesterday!
Hopefully I can get the washing hung out by the end of the morning as the showers finally die out and the upper cloud from low Pearl rushes in this afternoon. I guessed at the central pressure of 1016 hPa, but I can see that the pressure has just started to fall at weather buoy ‘Pap’ so Pearl has engaged the jet stream (fig 2).
It’s interesting to see how the three main NWP models handle tomorrows low and the heavy rain it introduces across the country (fig 1). The Met Office take the main thrust of the rain north into Ireland, whilst the GFS and the ECMWF are in no doubt that the action will be centred much further east over southwest Wales. I think the UKMO model looks out of step with the other models on this one, time will tell.
One of the tricks of the trade as a weather presenter when you want to be as vague as possible about the timing of rainfall events like this, is to leave of the exact time in the graphics, so it’s good to see that Aidan McGivern has picked this one up and is now ready to move on to the next chapter (fig 2).
As well as this cyclonic development on Friday another low threatens to spoil the weather in the southeast of England during Sunday. It’s amazing just how the weather likes to dish out bad weather in as fair a manner as possible isn’t it?
Although tornadoes can occur in any month of the year the ‘tornado season’ is usually thought of as being the months of March through to June, that’s when there’s a greater chance of cooler continental air meeting humid warmer air from the Gulf of Mexico, and hence a much greater chance of thunderstorm development. So far 2018 has been a remarkably quiet year for tornado activity across the United States (fig 1). In fact it could be that April 2018 has one of the lowest tornado counts on record (fig 2).
Here’s a news item from Matt Taylor of the BBC weather team about the slow start to the tornado season in the United States that spurred me into action (fig 2).
It seems that we have been caught in a cycle of cold end to months recently. First there was February, then March and now April. That’s according to the latest run of the GFS model, which indicates that the end of April and beginning of May will be changeable and often cyclonic, with winds in the east or northeast, the anomalous warm start to spring of last week will have retreated to the continent, but even here the warm air will be gradually pushed back further east.
Since moving down to the southwest some fifteen years ago now, I have noticed it’s often the case that in warm sectors (fig 1) although Cornwall and west Devon are plagued by extensive sea fog and low stratus, away from high ground, and in the lee of Dartmoor or Exmoor further east surface visibilities are often remarkably good, such is the case this morning (fig 2).
We might see a week with higher mean maximum temperatures, but I think it’s a distinct possibility that we won’t see a week with higher maximum anomalies or more sunshine than we saw across the southeast of the country. The highest mean maximum anomaly for the week was 8.3°C above the 1981-2010 long-term average at Northolt (fig 1), and the sunniest place was Manston in Kent with 79.3 hours in the seven days (fig 2).
The weather of the last week has provided a welcome fillip to April’s sunshine totals. Sunniest places during the last week in the UK were in the far southeast, with the last four days being sunny from dawn till dusk.
Here are a few graphics to show the extent of this early thundery spell across the country, the severity and extent of which caught both the ECMWF and the UKMO NWP models out yesterday. As far as I can see most of the lightning was from unstable medium level cloud rather than the more traditional cumulonimbus (fig 1). The rainfall from the thunderstorms looks to have been concentrated in a swathe SSW-NNE through Hampshire, where my estimates from weather radar suggest that as much as 32-40 mm fell in the wettest areas (fig 2).
I won’t go on about just how poor or late the warnings were for yesterdays thunderstorms from the Met Office, or just how divorced the NWP graphics used by either themselves or the BBC was from reality, the following screen shots will have to suffice (fig 4).