Glidemet

Today was very difficult to forecast with the Met Office getting it quite wrong, along with pretty much everyone else! The rain extended much further northwest, was heavier, and there’s more snow around than there looked like being yesterday afternoon. The only model to get it right—-I’m told, as there’s no public access to it—-was the ECMWF. The Met Office’s UK mesoscale performed poorly, which probably explains why no weather warnings were issued until past five o’clock—-long after flooding had already occured in the southwest.

The GFS didn’t do a great job either, but enough to draw some pictures with the IDV showing what’s happening. This is the +6 hours forecast from the 12z run, so it was fairly well dialled in (though still underestimating the snow). The first image shows the height of the 850 hPa surface, showing the slightly elongated low firmly rooted over southeastern England. I could have just drawn a surface pressure chart, but that would have been boring  .

This next image adds a few more things. On the surface is total precip for the last six hours, and the heavy rain is clearly visible. Wind arrows at 925 hPa show the wind swirling around the low. The isosurface looks like something out of The Day After Tomorrow, doesn’t it? It is, in fact, theta-e showing the frontal boundaries—-warm to the right, cold to the left.

The weird stuff in the lower right is part of the occulsion process, with one airmass pushing in and over another.

The next image removes the theta-e isosurface and adds one for 5 deg C. You can see the cold air being driven in around the low from the northeast, meeting the rain and turning it to snow on it’s northern side. Obviously it needs to be colder than 5 deg C for snow (and a few other things), but the GFS isn’t handling that part too well. It shows the colder air a treat though.

So that’s tonight, what about tomorrow’s (Saturday) forecast? A ridge will move in (visible as the red area in the near left corner of the top picture), as forecast all week, giving a bright mostly sunny day in the east. Some high cloud from the next front will be spilling into the west, although it will stay dry except for the far west later in the afternoon. Wales and the west still look good for some wave.

Sunday will be a cloudy damp day with increasingly heavy rain spreading from the west. Monday will be briefly brighter again (maybe showers about), while Tuesday looks very wet again.

Filed under Forecast. Both comments and pings are currently closed.