Introduction

Overview

Version 2 of the National Convective Weather Forecast (NCWF2) product, designed and implemented by the National Center for Atmospheric Research (NCAR), provides current convective hazards and 2–hour probabilistic forecasts of thunderstorm hazard locations. The hazard field and forecasts update every 5 minutes. The NCWF2 was developed by the Convective Weather Product Development Team which is sponsored by the Federal Aviation Administration's (FAA) Aviation Weather Research Program (AWRP). The Convective Weather Product Development Team consists of MIT Lincoln Laboratories, National Severe Storms Laboratory (NSSL), National Weather Service's Aviation Weather Center (AWC), and NCAR. The target users for NCWF2 are airline dispatch, general aviation and FAA Traffic Management Units (TMU). The diagnostic analysis combines VIL and echo tops mosaiced from the WSR–88D national radar network (provided by NOAA with mosaics created and distributed by UNISYS) and cloud–to–ground lightning from the National Lightning Detection Network (provided by Vaisala). The Convective Hazard Detection field is depicted based on a 6 level intensity scale. The 6 levels fundamentally correspond to VIP level.

fig

Forecasts are determined by applying a stratiform–convective partitioner (Steiner et.al. 1985) and an elliptical filter (Wolfson et al. 1998) to the hazard detection field. These filters eliminate stratiform return that do not pose a hazard to en route aviation traffic and small–scale perishable features that are not likely to persist for more than an 1 hour, respectively. Extrapolations are performed using a combination of the Thunderstorm Identification Tracking and Nowcasting (TITAN) software developed by Dixon and Wiener (1993) and RUC steering level winds. The NCWF forecast product does well with long–lived mature systems. While NCWF does not explicitly treat storm initiation, the growth algorithms will capture new storm formation in the vicinity of existing storms. Work on improving automated methods for forecast initiation, growth and dissipation of storms and extending these forecasts to longer lead times through blending with probabilistic NWP forecasts is ongoing.

Description

  • The NCWF2 provides automatically generated depiction of: (1) current convective hazards and (2) short term probabilistic forecasts of convection hazards. 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 NCWF2 algorithm is run at the NWS Aviation Weather Center (AWC) where the forecast system is kept running continuously with limited interruptions
  • The NCWF is most accurate for long–lived mature multi–storm systems such as organized line storms. NCWF does not forecast initiation of storms that are an appreciable distance away from existing storms. This results in an underprediction of storm area, particularly between 1600 and 2000 UTC when storms most commonly initiation

Attributes

  • 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 storming posing an aviation hazard are depicted in a probabilistic sense
  • 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 the AWC Aviation Digital Data Service (ADDS) at http://adds.aviationweather.gov/convection/. Used in conjunction with other weather products such as Convective SIGMETs, the NCWF provides additional information for convective weather avoidance and flight planning

Display Summary

  • Existing convective hazards (based on NEXRAD and lightning data) are depicted using the color–coded 6–level National Convective Hazard scale shown above. The probabilistic forecasts may be interpreted as the likelihood that storms of VIP level 3 or greater will be present at a given time and location in the future. These forecasts do not distinguish among level 3 through level 6
  • Probabilistic forecasts of aviation–impacting convection (NCWF hazard scale levels of 3 or greater) are depicted as shades of pink with the darker shades of pink indicating the highest likelihood that hazardous storms will be present. The direction of movement and storm tops are also available as part of the NCWF2 data stream
  • The JavaScript display options include the following (see Figure 7–1–8):
    • Current Significant Weather field
    • Current Convective Hazard Detection field
    • 30, 60, 90, 120 min Probabilistic Forecasts
    • Previous hour Performance Polygons
    • 2 hr Movie loops of Convective Hazard Detection fields (with forecast polygons included on the last frame)
    • 2 hr Movie loops of NCWF2 Probabilistic Forecasts
    • Zoomed views of Seven geographical regions: Northwest, North Central, Northeast, Southwest, South Central, Southwest, the 48 contiguous states. ARTCC boundaries.

Web Page Navigation

NCWF WEB Training

http://aviationweather.gov/products/ncwf/webtrng

WMO Headers

THE WMO HEADINGS FOR THE NCWD/F ARE AS FOLLOWS:

NCWD ZDIA98 KKCI

NCWF JSAT98 KKCI

File Availability

The Significant Weather, NCHD, NCWF probabilistic forecasts and motion vectors are output in gridded binary (GRIB). The NCHD, 60 min forecast, storm motions and echo tops are available in BUFR format is available through the following:

  1. The AWIPS/NOAAPORT satellite broadcast network (SBN)
  2. The National Weather Service FTP servers at: ftp://tgftp.nws.noaa.gov/SL.us008001/DC.avspt/DS.ncwf
  3. The family of services (FOS) high resolution data service and server access service

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."

This training module is broken into 7 categories. For information on:

  • setting up your browser – click on "Setup".
  • how to use the web page – click on "Navigation".
  • steps taken to create hazard field – click on "Hazard field".
  • how forecasts are produced – click on "Forecast".
  • how forecasts may be used – click on "Usage".
  • how to interpret performance image – click on "Performance".
  • what to do when things don't work – click on "Help".
  • frequently asked questions – click on "FAQ".

Also, a quick reference to the product can be viewed by clicking on "Reference".