<xsd:attribute name="coverage" use="optional">
    <xsd:simpleType>
        <xsd:restriction base="xsd:string">
            <xsd:enumeration value="slight chance" />
            <xsd:enumeration value="chance" />
            <xsd:enumeration value="likely" />
            <xsd:enumeration value="occasional" />
            <xsd:enumeration value="definitely" />
            <xsd:enumeration value="isolated" />
            <xsd:enumeration value="scattered" />
            <xsd:enumeration value="numerous" />
            <xsd:enumeration value="patchy" />
            <xsd:enumeration value="areas" />
            <xsd:enumeration value="widespread" />
            <xsd:enumeration value="periods of" />
            <xsd:enumeration value="frequent" />
            <xsd:enumeration value="intermittent" />
            <xsd:enumeration value="none" />
        </xsd:restriction>
    </xsd:simpleType>
</xsd:attribute>