Forecast verification

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Apr 2, 2024, 9:58:13 AMApr 2
to Weather and Climate
As a follow-up to Graham's observation that the UKMO forecast temperatures for the Southwest are often too low by a couple of degrees I monitored them for max temp. over
7 days last week at my postcode PL9
Forecast issued at 1638 GMT Mon. 25th March
                      Forecast         Measured
25th Mon.       10°C                    10.1°
26th Tues        11°C                    11.9°
27th Wed.          8°C                    10.5°
28th Thurs.      11°C                    12.5°
29th Fri.            11°C                    13.1°
30th Sat.           12°C                    14.1°
31st Sun.          13°C                    14.1°

So the case is proven over this period.
The forecast of max temperature 24 hrs or more ahead is between one and 2 degrees below actual.
Measurements taken in Stevenson screen.

Wembury, SW Devon


Apr 7, 2024, 3:42:30 AMApr 7
to Weather and Climate
The correlation with wind direction would be interesting.  Perhaps modelled sea temperatures are on the low side?

Graham Easterling

Apr 8, 2024, 7:23:49 AMApr 8
to Weather and Climate
Yes, I think the modelled sea temperatures are a bit of a problem. Currently the SST off Cornwall is 11-11.5C whichever buoy you look at (Porthleven, Looe, Penzance, Perranporth.) SST anomaly all around the SW coast is around 1.5C 

As far is Penzance is concerned the big errors occur with an offshore (W--NW wind), and sunshine (if only!) in spring/early summer. The models seem to significantly understate the effect of the wind being offshore, perhaps with the peninsula being so narrow here? Also, with the manned station at Camborne being on the north coast perhaps there is little appreciation of how much warmer the south coast is under these conditions. Though I would have thought that would only affect a 'human' forecast.

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