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.
A lovely solar halo this morning here in mid-Devon which is the old weather lore precursor for rain in 6 to 9 hours, so I’m curious about just how fast the rain will spread across the southwest of England this afternoon, so here are the latest forecasts as of 09 UTC this Easter Sunday morning as a reminder.
Well all the models were much too slow in bringing the rain northeast across the southwest peninsula, and the BBC and Met Office forecasts weren’t much better either. If you look at the 15 UTC weather radar the rain had extended as far as Somerset (fig 2), nothing spectacularly wrong perhaps, only out by a couple of hours or so, but the various forecasts that I took a snapshot of (fig 1) were only for six hours ahead and should have been spot on. At least the old weather saying about solar halos still works!
Not a lot going on at the moment weather wise across the British Isles, but hopefully it should brighten up in many places today from the west on the passage of this frontal system (fig 1). I did notice that there’s been another minor SSW event that looks to have occurred just before the equinox (fig 2).
That, along with some wild NWP output, is what probably led to all those stories of a snowy Easter, stories which now seem to have been summarily dropped like a hot potato. Having said that the models do take each successive Atlantic low a little further south into Biscay as the week progresses leaving the country in an easterly, anticyclonic in the north and cyclonic in the south, so it look’s odds on that’ll it will be a cold Easter (fig 3).
I did say last Sunday in the article return of the easterlies that it was still in the land of science fiction, well the models look to have been spot on even at T+168. The Met Office have a discrete centre of 1002 hPa on the low that seems to form on the northern edge of a warm trough that’s moving westward across France for 12 UTC on Sunday (fig 1). None of the other models, apart from the French ARPEGE seem to have pressure as low as that across the Channel on Sunday (fig 2), although it’s difficult to synchronise the validity time. It’s still 72 hours away, and we are now close to the vernal equinox, but this situation has the potential to cause a lot of disruption, especially if snow falls in the overnight period.
Today’s 06 UTC (Friday) from the GFS has a similar feel to it at T+42 (fig 3).
I wonder what the collective noun is for a number of NWP models? You know the kind of thing – a murder of crows, a murmuration of starlings, an exaltation of larks. Perhaps its simply a pile of crap? That may sound a bit harsh, but that’s the thought that ran through my mind when I compare short-range model output in this current spell of severe weather across the country.
All I really want to know is how long is it going to snow, and although they all provide you with some kind of solution, they are all quite different and not that convincing. In the early 21st century you might have least expected some commonality between them at the T+18 or T+24 range, but no that doesn’t seem to be the case, well at least not with the forecast for midnight tonight. Perhaps I am just too naïve to have thought they would have been, probably because I watch too much Star Trek. Perhaps it’s the ongoing SSW event that’s sending the models a little crazy at the moment, I would be fascinated to see just how the UKMO model is coping with the current situation, hopefully it’s better than this lot:-