1. Purpose

The purpose of this site is to monitor the ability of various numerical weather prediction models to develop both extratropical and tropical cyclones. Initially, the site will contain track plots from various models, including the NCEP GFS, NCEP Eta, NCEP global ensemble, NCEP short range ensemble (SREF), UKMET and NOGAPS models. The plan is to eventually include performance and verification statistics as well.

2. Determination of tracks

All tracks included on this site are derived from GRIB files operationally available within NCEP and are determined using the operational NCEP cyclone tracking software.

Briefly, for tropical cyclones, 7 parameters are tracked, including the relative vorticity maximum, geopotential height minimum and wind speed minimum at both 850 and 700 hPa, as well as the minimum in sea level pressure. These 7 parameters are averaged together to provide an average position fix at each forecast hour.

Since extratropical cyclones are generally not nearly as vertically coherent as their tropical counterparts, using parameters from 3 different levels of the atmosphere would muddy the tracking picture. Therefore, when tracking is done specifically for extratropical cyclones, only mslp is tracked. In order to avoid tracking weak, transient disturbances (either real or artifacts of model noise), 2 constraints have been added to the tracking criteria in order for a found disturbance to be reported as being a tracked storm: (1) the storm must live for at least 24 hours within a forecast, and (2) the storm must maintain a closed mslp contour, using a 1 mb contour interval.

3. Updates

Track plots will be updated continuously as data files are ingested at NCEP.