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<br />" <br /> <br />~. <br /> <br />. <br /> <br />. <br /> <br />NWS Advisory Procedures <br /> <br />During periods of hazardous weather phenomena associated with both winter orographic <br />and convective precipitation systems it is sometimes necessary or advisable for the National <br />Weather Service (NWS) to issue special weather bulletins advising the public of the weather <br />phenomena. Each phenomenon is described in terms of criteria used by the NWS in issuing <br />special weather bulletins. <br /> <br />. Traveler's Advisory (TA) - This is issued by the NWS when one to four inches <br />of snow is expected to produce hazardous conditions, particularly in mountain <br />passes. <br /> <br />. Heavy Snow Warning - This is issued by the NWS when it expects snow <br />accumulations of four inches or more per l2-hour period or six inches or more per <br />24-hour period. <br /> <br />. Winter Storm Warning (WSW) - This is issued by the NWS when it expects <br />sudden drops in surface temperatures and heavy snow with significant blowing <br />and drifting. <br /> <br />. Flash Flood Warnings (FFW) - This is issued by the NWS in the event of heavy <br />rainfall rates (1/4 inch per half hour) associated with slow moving (less than 10 <br />knots) precipitation radar echoes, or radar echoes moving parallel to specific <br />drainage areas. FFW are generally issued, but not limited to, spring and summer <br />convective systems. <br /> <br />In advance ofthe above described weather warnings, the NWS at times may issue <br />weather "watch" bulletins. These "watches" delineate specific areas where atmospheric <br />conditions are favorable for the formation of possibly hazardous weather phenomenon and are <br />generally issued 12-hours in advance of the potential event. <br /> <br />NA WC's Suspension Procedures <br /> <br />NA WC's suspension policy concerning Traveler's Advisories, Heavy Snow Wamings and <br />Winter Storm Wamings is based upon the intent of its weather modification operations. In that <br />regard, winter orographic seeding is conducted for and limited to increases in snowpack in the <br />high runoff yield areas (i.e., high elevations). Therefore, such operations would not adversely <br />affect driving conditions in the valleys. Additionally, the amount of snowfall increases from <br />seeding alone, in mountainous terrain, is not envisioned to produce heavy snowfall (that is, the <br />heavy snowfall conditions would be present without seeding). <br /> <br />Concerning Winter Storm Warnings the same reasoning forTA's applies, in addition to <br />the fact that weather modification operations do not affect the parameters (wind and temperature) <br /> <br />11 <br />