Snow depth reporting: reports of zero snow Samantha Pullen With thanks to Stuart Goldstraw, Richard Weedon GCW Snow Watch Team – Second Session, Columbus, 13-14th June 2015 © Crown copyright Met Office

The problem… 05-09-2013 ‘State of ground’ not snow-covered Manual stations only Courtesy of P. de Rosnay © Crown copyright Met Office

The problem… Snow depth reported only when snow is present – no zero snow depth reports. Missing data could mean no snow, technical problem, station out of service – ambiguous – cannot be used For assimilation, obs of zero snow are as important as obs of snow, for informing model snow extent Actively reporting zero snow depth would provide the data user community with a huge amount of valuable additional data, providing positive observations of snow-free conditions. © Crown copyright Met Office

Biased data for assimilation and validation True snow line Reported snow depth Model snow line Model snow extent overestimated Snow-free ground – no reports DA of snow depth reports will help correct Model snow extent undererestimated © Crown copyright Met Office

Snow depth reporting practices Observing network reporting practice governed by WMO CBS guidelines, snow reporting deferred to regional practice. Regional Reporting Practices – Manual on Codes Volume II states for Europe (Region VI) that snow depth and state of ground “shall be included only if snow or ice cover is observed on the ground” Regional guidelines differ - reporting of snow depth is not consistent from region to region. Changes are needed within the current regulations to ensure that all practices require the reporting of snow depth on a regular basis regardless of the state of ground. Transition to use of BUFR encoding enables the use of a distinct code for zero cm snow, as opposed to missing report © Crown copyright Met Office

What is happening Where we are now Gain support from international community, make representations to WMO Official WMO guideline change (CBS) Regional guidelines change (RA Sessions) Adoption of changed practices by nations Uptake of new data by users Representations made through IPET-DRMM, Surface Obs ET (2014) Approved by CBS Ext (2014): “The commission agreed to facilitate reporting zero snow depth by suggesting that those Members using TAC nationally might consider using the unallocated entry 000 of code table 3889 to indicate zero snow depth, so that the information would be available when national reports are converted to TDCF.” Sign-off Sep 2016 Proposal to be submitted to RA Sessions – regional guideline changes (Atsushi Shimazaki, Miroslav Ondras, recent communication) © Crown copyright Met Office

In the meantime… There is nothing to stop individual nations adopting the new practice before WMO mandates it – some work to adapt observing system to use code… UK – incorporating change in rollout of new observing system software – aim for Nov 2016 zero snow depth reporting COST Action “Harmosnow” – opportunity to promote awareness of the issue, gain the support of other European nations. Encourage other NMSs to adopt changed reporting practices, talk to your observing system colleagues Raised at EUMETNET Obs-SET 2016 Recent communication with JMA re: zero reports © Crown copyright Met Office

Issues, gaps, GCW priorities Consistency! Regional practices – harmonise Manual vs automatic station capability Patchy snow around sensor/station When do zero obs need to start? Not year-round How will users know that report means “zero” if TAC “000” is converted to TDCF? Promote awareness – need a cultural change © Crown copyright Met Office

Any questions? © Crown copyright Met Office