Snow Watch Snow Reporting Activity
One of the main goals of Snow Watch is to improve the reporting practices for in situ snow observations, to promote exchange of real-time observations between member states, and in particular to improve availability of in situ snow depth reports on the GTS. Ground based observations of snow are very important for monitoring, model validation, validation of satellite-derived data, and increasingly for assimilation into weather forecasting models. However, there are large amounts of potentially valuable data that are not reported or not available outside the country of origin. Snow Watch is actively addressing these issues with the aim of increasing the value from existing in situ snow networks for numerical weather prediction (NWP) applications and for the international community:
- In situ snow depth and other snow observations constitute a very important and very reliable source of information for snow data assimilation.
- They are provided by the SYNOP station network and are made available in Near Real Time on the Global Telecommunication System (GTS) for NWP.
- In addition to SYNOP observations, national meteorological services have access to their national snow depth measurement networks. However, these additional snow depth observations are currently not available on the GTS for the international NWP community.
Spatial distribution of in situ station reporting snow depth on the GTS (on 20 January 2015).
This map shows the standard deviation of ECMWF background departure (in cm of snow depth) for the period from December 2014 to February 2015. Large areas are blank, illustrating regions with observation gaps.
In situ snow depth observations are operationally monitored by ECMWF.
Reporting Zero Snow Depth
Snow Watch is seeking changes to the WMO Commission for Basic Systems (CBS) guidelines for reporting practices to make reporting of snow depth a mandatory requirement whether snow is present or not. This would provide the international community with a huge amount of valuable additional data, giving positive observations of snow-free conditions.
- Snow depth is generally only reported when snow is present, with “missing data” recorded for snow depth in snow-free conditions rather than “0 cm”.
- Data users cannot know whether this missing data indicates “no snow” or a missing report for another reason, e.g. technical issues at station. This “missing data” must therefore be discarded, though the majority of it could potentially contain valid positive reports of zero snow.
- For NWP applications, observations of no snow are very important for constraining model snow extent.
A snow reporting white paper was written in 2013. With the white paper and subsequent discussions with the community, GCW has facilitated the improved snow data reporting and exchange on the GTS, e.g. snow depth, SWE. The figure below shows the increase in the number stations reporting snow depth in December from 2014 to 2018.