ZSE CWAs and MISs

The CWA is an aviation weather warning for conditions meeting or approaching national in-flight advisory (AIRMET, SIGMET or SIGMET for convection) criteria. The CWA is primarily used by air crews to anticipate and avoid adverse weather conditions in the en route and terminal environments. It is not a flight planning product because of its short lead time and duration. Additionally, the CWA should be meteorologically consistent with other products and reflect conditions at the time of issuance and/or in the near future. If a CWA has been issued prior to coordination, notification to the appropriate offices, national center, or WFO should follow as soon as higher priority duties permit.

CWAs are valid for up to two (2) hours and may include forecasts of conditions expected to begin within two (2) hours of issuance. If conditions are expected to persist after the advisory's valid period, a statement to that effect should be included in the last line of the text. Follow-up CWAs should be issued as appropriate. Notice of significant changes in the phenomenon described in a CWA should be provided by a new CWA issuance for that phenomenon. If the forecaster deems it necessary, CWAs may be issued hourly for convective activity. This may improve the usefulness of the Hazardous In-flight Weather Advisory Service (HIWAS) recordings which include those CWAs.

CWAs should be issued for any of the following events when they are expected to occur within two hours and have not been previously forecast by AWC or AAWU products, or to supplement the AWC and AAWU products.

• Conditions meeting convective SIGMET criteria
• Icing - moderate or greater
• Turbulence - moderate or greater
• Heavy precipitation
• Freezing precipitation
• Conditions at or approaching Low IFR
• Surface winds/gusts >30 knots
• Low Level Wind Shear (surface - 2,000 feet)
• Volcanic ash, dust storms, or sandstorms

MIS is an unscheduled flow control and flight operations planning forecast. It is a non-technical forecast and briefing product for personnel at Air Route Traffic Control Center (ARTCC), Air Traffic Control Systems Command Center (ATCSCC), Terminal Radar Approach Controls (TRACONS) and Air Traffic Control Towers (ATCTs) responsible for making flow control-type decisions. The MIS details weather conditions expected to adversely impact air traffic flow in the CWSU area of responsibility, and is valid up to 12 hours after issuance time. The MIS may be effective immediately for existing conditions when CWSU operations begin, or for rapidly deteriorating conditions, or up to two hours in advance of expected conditions.

An MIS provide's additional information on the current or expected weather information and is tailored to meet the unique requirements of the host ARTCC. These special requirements are coordinated between the host ARTCC and the CWSU.