<xsd:attribute name="phenomena" use="required">
    <xsd:simpleType>
        <xsd:restriction base="xsd:string">
            <xsd:enumeration value="Ashfall" />
            <xsd:enumeration value="Air Quality" />
            <xsd:enumeration value="Air Stagnation" />
            <xsd:enumeration value="Blowing Snow" />
            <xsd:enumeration value="Brisk Wind" />
            <xsd:enumeration value="Blizzard" />
            <xsd:enumeration value="Coastal Flood" />
            <xsd:enumeration value="Dust Storm" />
            <xsd:enumeration value="Blowing Dust" />
            <xsd:enumeration value="Excessive Cold" />
            <xsd:enumeration value="Excessive Heat" />
            <xsd:enumeration value="Excessive Wind" />
            <xsd:enumeration value="Areal Flood" />
            <xsd:enumeration value="Flash Flood" />
            <xsd:enumeration value="Dense Fog" />
            <xsd:enumeration value="Flood" />
            <xsd:enumeration value="Frost" />
            <xsd:enumeration value="Red Flag" />
            <xsd:enumeration value="Fire Weather" />
            <xsd:enumeration value="Freeze" />
            <xsd:enumeration value="Gale" />
            <xsd:enumeration value="Hurricane Force Wind" />
            <xsd:enumeration value="Hurricane Wind" />
            <xsd:enumeration value="Heavy Snow" />
            <xsd:enumeration value="Heat" />
            <xsd:enumeration value="Hurricane" />
            <xsd:enumeration value="High Wind" />
            <xsd:enumeration value="Hard Freeze" />
            <xsd:enumeration value="Sleet" />
            <xsd:enumeration value="Ice Storm" />
            <xsd:enumeration value="Lake Effect Snow and Blowing Snow" />
            <xsd:enumeration value="Lake Effect Snow" />
            <xsd:enumeration value="Low Water" />
            <xsd:enumeration value="Lakeshore Flood" />
            <xsd:enumeration value="Lake Wind" />
            <xsd:enumeration value="Marine" />
            <xsd:enumeration value="Special Marine" />
            <xsd:enumeration value="Small Craft, for Rough Bar" />
            <xsd:enumeration value="Snow and Blowing Snow" />
            <xsd:enumeration value="Small Craft" />
            <xsd:enumeration value="Hazardous Seas" />
            <xsd:enumeration value="Small Craft, for Winds" />
            <xsd:enumeration value="Dense Smoke" />
            <xsd:enumeration value="Snow" />
            <xsd:enumeration value="Storm" />
            <xsd:enumeration value="High Surf" />
            <xsd:enumeration value="Severe Thunderstorm" />
            <xsd:enumeration value="Small Craft, for Hazardous Seas" />
            <xsd:enumeration value="Tropical Storm Wind" />
            <xsd:enumeration value="Tornado" />
            <xsd:enumeration value="Tropical Storm" />
            <xsd:enumeration value="Tsunami" />
            <xsd:enumeration value="Typhoon" />
            <xsd:enumeration value="Freezing Spray" />
            <xsd:enumeration value="Wind Chill" />
            <xsd:enumeration value="Wind" />
            <xsd:enumeration value="Winter Storm" />
            <xsd:enumeration value="Winter Weather" />
            <xsd:enumeration value="Freezing Fog" />
            <xsd:enumeration value="Freezing Rain" />
            <xsd:enumeration value="Record High Temperature Possible" />
            <xsd:enumeration value="Record Low Temperature Possible" />
            <xsd:enumeration value="none" />
        </xsd:restriction>
    </xsd:simpleType>
</xsd:attribute>