NCWF Information


Product Description Document (PDD)

The National Convective Weather Forecast (NCWF) product, designed and implemented by the National Center for Atmospheric Research (NCAR), provides current convective hazards and 1-hour extrapolation forecasts of thunderstorm hazard locations. The hazard field and forecasts update every 5 minutes.

The NCWF development is sponsored by the Federal Aviation Administration’s (FAA) Aviation Weather Research (AWR) program as part of the Convective Weather Product Development Team. The Convective Weather Product Development Team consist of MIT Lincoln Laboratories, National Severe Storms Laboratory (NSSL), National Weather Service's Aviation Weather Center (AWC), and NCAR. The NCWF target users are airline dispatch, general aviation and FAA Traffic Management Units (TMU).

The diagnostic analysis combines WSR-88D national radar and echo top mosaics (provided by NOAA with mosaics created and distributed by UNISYS) and cloud-to-ground lightning (provided by Global Atmospherics Inc). The Convective Hazard Detection field is depicted based on a 6 level intensity scale. The 6 levels fundamentally correspond to VIP level.

NCWF Hazard Scale

Forecasts are determined by applying a stratiform-convective partitioner (Steiner 1985) and an elliptical filter (Wolfson et al. 1998) to the hazard detection field. These filters eliminate stratiform return and small-scale perishable features that are not a hazard to aviation or are not likely to persist for 1 hour, respectively. Extrapolations are performed based on the Thunderstorm Identification Tracking and Nowcasting (TITAN, Dixon and Wiener 1993) algorithm.

The NCWF forecast product does well with long-lived mature systems. However, the initiation, growth, and dissipation of these systems, as well as shorter-lived isolated storms, are not well forecast. Work on automated methods to forecast the growth and dissipation of storms is on going.


The NCWF is an automatically generated depiction of: (1) current convection and (2) extrapolated significant current convection. It is a supplement to, but does NOT substitute for, the report and forecast information contained in Convective SIGMETs (see paragraph 7-1-5c). Convection, particularly significant convection, is typically associated with thunderstorm activity.

The National Weather Service Aviation Weather Center (AWC) updates the NCWF based on input from the Next Generation Weather Radar (NEXRAD) and cloud-to-ground lightning data.

The NCWF is most accurate for long-lived mature multi-storm systems such as organized line storms. NCWF does not forecast initiation, growth or decay of thunderstorms. Therefore, NCWF tends to under-warn on new and growing storms and over-warn on dying storms. Forecast positions of small, isolated or weaker thunderstorms are not displayed.


The NCWF is updated frequently (every 5 minutes) using the most current available data.

The NCWF is able to detect the existence of convective storm locations that agree very well with concurrent radar and lightning observations.

The NCWF is a high-resolution forecast impacting a relatively small volume of airspace rather than covering large boxed areas. The location, speeds and directions of movement of multiple convective storms are depicted individually.

The NCWF extrapolation forecasts are more accurate when predicting the location and size of well organized, unchanging convective storms moving at uniform speeds. The NCWF does not work well with sporadic, explosive cells developing and dissipating in minutes.

The NCWF may not detect or forecast:

  • Some embedded convection.
  • Low-topped convection containing little or no cloud to ground lightning (such as may occur in cool air masses).
  • Rapidly evolving convection.

Availability and Use

The NCWF is available primarily via the Internet from AWC at Used in conjunction with other weather products such as Convective SIGMETs, the NCWF provides additional information for convective weather avoidance and flight planning.

The NCWF access by Automated Flight Service Stations and their associated En Route Flight Advisory Service facilities, Air Route Traffic Control Centers (ARTCCs) or Terminal Radar Approach Controls is planned but NOT currently available.

Display Summary

Existing convective hazards (based on NEXRAD and lightning data) are depicted using the color-coded 6-level NCWF hazard scale shown above. In displaying forecast cell locations, the NCWF does NOT distinguish among level 3 through level 6.

One-hour forecast locations of signification convection (NCWF hazard scale levels of 3 or greater) are depicted with blue polygons. Their directions of movement and storm tops are also shown.

The display options include the following:

  • Current convective hazard “Detection” field
  • 1-hour extrapolation “Forecast” polygons
  • Previous hour “Performance” polygons
  • “2-hr Movie” loops of convective hazard detection fields (with forecast polygons included on the last frame)
  • “24-hr Movie” loops of convective hazard detection fields
  • Zoomed views of:
    • Seven geographical regions: Northwest, North Central, Northeast, Southwest, South Central, Southwest, the 48 contiguous states.
    • ARTCC boundaries

WMO Headers

The WMO headings for the NCWD/F are as follows:


File Availability

The NCWD/F output in gridded binary (GRIB) / BUFR format is available through the following:

National Weather Service Disclaimer

The NCWD/F images displayed on the AWC web page are all official products of the National Weather Service. On the bottom of each gif image, there is a short disclaimer, which describes who should use this product to make scientific decisions about the state of the atmosphere. The disclaimer reads as follows:

The NCWF is an automatically generated depiction of: (1) current convection and (2) extrapolated
significant current convection. It is a supplement to, but does NOT substitute for, the
report and forecast information contained in Convective SIGMETs.