GFS out on a limb with this forecast *updated

00 UTC run on the 17 Feb 2021 (fig 1)

On the face of it the GFS model seems to be out on a limb in how it’s forecasting a significantly deeper and more intense low (970 hPa) across the Western Isles by 12 UTC tomorrow (18 Feb 2021). The minimum central pressure of the low is crucial to just how strong the winds will be tomorrow. The midnight run of the the three other main models maintain a much shallower benign low in their forecasts (978-982 hPa). The UKMO have split the difference between the ECMWF and the GFS models and have gone for this solution (fig 2).

Courtesy UKMO (fig 2)

The Met Office are so confident there’ll be no strong winds tomorrow they’ve not bothered to issue a yellow warning for the Hebrides (fig 3), the first time they’ve not done so in what must be a week. They’re probably banking on the fact that any increase in cyclonicity will reduce the geostrophic gradient and hence the wind speed.

Courtesy UKMO (fig 3)

Even the 06 UTC run of the GFS still forecasts a 971 hPa central pressure at 12 UTC (fig 4), so it’ll be interesting to see which of them end up being closer to the truth.

GFS 06 UTC run on the 17 Feb 2021 (fig 4)

Addendum

No one quite got the location of the centre of this low correct which looks to have been around 975 hPa so look to have been, along with the UKMO, the best of the NWP models.

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