Thursday
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Today (Thursday), away from the southeast where a quite active occlusion is slowly clearing, rather good. Cumulus to 4,000 ft (edit at 0900: make that at least 5,000 ft, RASP is under-doing expected surface temperatures) everywhere apart from Cumbria (lower/damper), and in the far south and across through Dorset and west, where bases may be higher but more likely to just go blue (but still quite high). There’ll be a fair breeze at height, about 15 knots from the northwest, but really quite a good day.
Friday remains breezy at 15 knots or a touch more from the west, but the cumulus is going to be grand, living at 4,500-5,000 ft over pretty much all of England and Wales from early to late. Really go for it if you can; there doesn’t look much risk of spreadout or over-development.
Saturday is wiped out by cloud cover but at least looks vaguely drier than previous runs. And, looking at current run, Sunday even looks quite good away from the south coast! Given the way the GFS has been flip/flopping (that’s the official term, I kid you not), not a lot can be said with confidence about the day. (Technically speaking, the truth of the day does almost certainly lie within the bounds the GFS has presented over the last few days, but given that the “spread” is so large, an overall story cannot be easily discerned.)
(What’s going on is that a small but quite active low pressure system is going to track through on Saturday and Sunday, but the track, timing, and forecast depth are switching around a lot. That’s not surprising given that there’s not much in the way of thermal (and hence pressure) gradients at this time of year, meaning small changes in what the models see in their analysis of satellite, aircraft, surface obs etc. has a big outcome on the forecast. The low may well pass over southern England on Saturday night, which is about the least-worst outcome.)
Monday is displaying more consistency with a story of cloud and a bit of rain in west, maybe fairly good (top cover risks permitting) in the east. And after that, it’s pretty much a certainty that high pressure will become established bringing warm sunny weather.
Probably not another update until some time tomorrow.
Thurs pretty much as advertised with 5K+ available in the SW.
I’ve been following the weather running up to the weekend and the UKMO charts have been fairly stable with a wet and windy Saturday with multiple waving fronts followed by a breezy Sunday. RASP has been all over the place, suggesting 4-5,000’ bases where one would expect rain and strong winds. Oddly, TopMeteo (GFS data as well) has been predicting a washout on Sat. for four days. Hmmm.
I’ve read the comment about flip/flopping but the other models (from what I can make out) don’t seem to be doing this. As far as soaring predictions go, I’d have thought an active complex low that’s bringing moist air in from around the Azores high doesn’t give much hope, whatever the timings?
How is data fed into the RASP model? I’ve noticed this season that every now-and-then it is distinctly at odds with other predictions (and reality); even the “latest data” runs occasionally have things like 5+ deg. differences between forecast and actual dewpoint. Yesterday it was pretty much spot on for quite a complicated scenario - seems a bit of “random” gets in there once in a while…?
UKMO charts are stable because they’re drawn by very good forecasters who aren’t slave to any one model
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I must only use public domain data for here, and nothing at all from work. The UKMO charts are effectively public domain, but even then I tend to rely on GFS/RASP (and ECMWF from their public website) so as to be demonstratively clear that I’m not using any data from my employer.
RASP, for the days ahead, takes initial and boundary conditions from each 00z run of the GFS, then goes from there with its own physics model. This means it’s slavish to those midnight runs, but will be different from other GFS runs (four a day), and TopMeteo may be initialised from one of those other runs, so won’t look the same, especially if the detail, upon which soaring weather is so dependent, is changing between runs.
RASP often does funny things with the dry bulb and dewpoint temperatures, but quite often it seems to get the cloud bases right. (I’m sure you noticed but don’t forget that the scale for temperatures on RASP isn’t fixed, which makes it hard to step through the charts comparing one to the next.)
The schedule for current day/next day is quite complex, using 12z, 18z, and 00z runs balanced against the extra run-time of high resolution forecasts. I know some prefer the 12 km “latest data” runs, but I swear by the 5 km next-day and 4 km current-day runs, even though the initial data is older. Theory says that the increased resolution should compensate for the older initial data, and I think it does.