The grass pollen risk will be very high during warm dry weather. Spore and weed levels will be elevated too.
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Nicola Nalepka, who is 17, and Vanessa Lisak were last seen on Tuesday, September 10.
It's a wet start but there is drier weather ahead. Warmer weather promised for later in the week.
EDF say Sizewell C will bring jobs to the area and environmental damage will be kept to a minimum. The RSPB oppose the plans.