About this site

I started this website just for fun, because I made a few plots I wanted to share with the world in a better way than me just irregularly tweeting them.

Please feel free to use and share any images from this site on social media or elsewhere, with credit where appropriate. If you experience any issues with the site, or have any suggestions, please contact me (the easiest way is to tweet me). Thanks for visiting!

Site status

This page will be updated manually when I am aware of problems with the site.

2022-04-03: Forecasts are now all offline. I intend to rebuild the site for next winter. Thanks for all your visits to the site over the last few years.

About the data processing

The data are retrieved from the NCEP NOMADS server. Issues with NOMADS may cause problems with data updates; unfortunately these are more frequent than they should be.

About the forecast models

This site uses the 00Z runs of the NCEP Global Forecast System (GFS) and Global Ensemble Forecast System (GEFS) retrieved on a 0.5° grid. The former is a deterministic model run out to 16 days, while the latter is a 31-member ensemble run out to 35 days (as of the implementation of GEFSv12 on 23 September 2020).

The NCEP Climate Forecast System version 2 (CFSv2) became operational in March 2011. In raw form, it is run as a 4-member ensemble 4 times per day. Typically, this is turned into a time-lagged 16-member ensemble, i.e. today’s 00Z initialisations are combined with the 06, 12, and 18Z initialisations from yesterday. Following the style used in the S2S database, the subseasonal stratosphere forecasts shown here run out to 44 days using a time-lagged 16-member ensemble. Bias correction is applied for forecasts initialised during November-March inclusive, whereby the difference between the 1999-2010 model hindcast climate and ERA5 reanalysis is subtracted. The 4-weekly 500 hPa anomalies use a 16-member ensemble (1 day, 4 runs of 4 members), while the 6-monthly 700 hPa anomalies use a 40-member ensemble (10 days of 4 members).