Overall hazard assessment for all areas of Scotland remains EXTREME until rain arrives.
Late April – at this time of year, still spring, the seasonal condition of the fuels (vegetation) will be reacting most to the combination of frost, warm dry weather and wind. There is a lot of dead grass and dead heather left over from last year, which can dry very quickly. Frost and sun can also reduce the live fuel moisture of heather. Overall these conditions can create very low surface fuel moisture contents. Apart from NW Scotland there has been little rain to wet the deeper fuel layers over the last month. Deeper fuel layers are continue to dry out in the east and the south.
The high pressure system over Scotland & Scandinavia continues until a weak weather front passes south from northern Scotland. All areas will initially stay dry. There will still be some frosts and sunny days, other days with high cloud. Winds will be easterly 8 – 12 mph, moderate strength. Maximum mid-afternoon air temperature 19C, warmest in the west. It will gradually get cooler as the weak front passes south. Humidity levels were extremely low in eastern Scotland yesterday (23rd), down to 28% and will continue low 42 – 60% everywhere, until it rains. The weather patter is uncertain at the moment, so give attention to local recent weather forecasts
The key issues over the weekend are the continuing sunny days, low relative humidity and lack of rain. Dead fine fuels will dry out and stay dry in these conditions
In eastern, central and southern areas of Scotland FFMC on Friday and Saturday is around 87, very high. ISI is consistently over 2.5 in most areas. DMC will go up to 26 in eastern, central and southern areas All indices are over key thresholds
Where the FFMC is high dead fuels will ignite and burn hot enough to burn live fuels such as heather. Where ISI is above 2.5 spread rates could be fast. Lower soil layers in the east are dry, there is potential for smouldering there.
Overall fires could burn and spread, with high fire intensity, and some smouldering in the east, central and southern Scotland. No rain is forecast.
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