How the forecast has moved

Valid for one moment two days out, as every stored run has drawn it.

One moment — 12Z 1 Sep, about 48 hours out — as every stored GFS run has drawn it. Step through the runs and the pressure pattern moves: that motion is the forecast changing its mind, which is what this site exists to show. Same chart grammar as the surface analysis; only the issuing run varies.

And the same moment's 24-hour drift — 12Z 29 Aug against 12Z 30 Aug — as rise/fall lines every 2 hPa. Warm is falling pressure: the newer run deepening something, which is where to look first. Range -6.9 to +4.6 hPa.

Every map on this page is drawn from model output we store ourselves, not from anyone's picture of it. The per-city read of the same day — which cities the models are fighting about, and what the discussion makes of it — is on the national page.