Over the last few months Paul Scorer has been investing a lot of time and money in an upgraded version of RASP UK. The big news that the on-the-day forecast now runs at a resolution of just 2 km, the next-day forecast is now 4km, and there is a new Google Maps-based map viewer—-the old “RASP Table”, that you may have bookmarked or linked to directly, no longer works. Please all visit the RASP UK homepage to access forecasts. I would recommend going to the RASP UK homepage and then clicking on the Forecast Maps link, rather than bookmarking directly the maps, as there may be new versions and the older version breaks. Paul states that Chrome is the best browser to use to view the new RASP maps, but others should work.
The change to 2 km and 4 km grid resolutions is a significant. The model is now in the realm of “convection resolving”, particularly for the 2 km on-the-day forecast (4 km, for the “next day” forecast, is a bit borderline still, but a big improvement over the previous 5 km). This means that the model is capable of resolving the type and shape of cumulus clouds, although they will always appear to be a bit on the big side compared to reality (a model in the order of 500 m to 1 km would be needed to be fully accurate).
However, do not think (and I don’t suppose any of you would really but I’m just making sure) that the model is capable of saying there will be a cloud of shape x at time y over town z. It isn’t. What it is capable of is picking out areas of spreadout versus fine cumulus (best distinguished by using the “normalized surface sun” parameter). Spreadout will be fairly obvious, good cumulus will either be a spotty effect (separate small clouds) or simply blank (100% surface heating, i.e. no shade); spreadout will be large areas of greatly reduced insolation, perhaps with narrow areas of sunlight indicating the edges of larger stratocumulus clouds. Use “Cu Cloudbase where CuPotential >0” to see where (and when—-the model is actually pretty good on timing) cu actually should be, and where it will be mostly likely blue. The increased resolution means the model has better knowledge of high ground and forecast different amounts of cu at different heights accordingly. Wave will also be modelled better than ever.
It’s worth saying that right now, at the time of posting, RASP is currently down. Always check the the top of each map image to make sure it’s for the time and day you were expecting to see. Outages might happen from time to time for a week or two while Paul gets all the upgrades playing nicely.
If RASP UK is down you can always use the back-up service, Stratus, run by Darren Hatcher. Currently this still used the 4 and 5 km versions of RASP, and still uses the older RASPTable interface. There a lot of nice tools on Stratus though, my favourite being the excellent “RASP Quality Check” tool, or as I like to think of it, “how’s RASP doing?”. Interestingly the new Met Office site has a very similar Verification page.