1. 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
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2. The problem… 05-09-2013 ‘State of ground’ not snow-covered
Manual stations only
Courtesy of P. de Rosnay
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3. 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.
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4. 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
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5. 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
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6. 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)
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7. 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
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8. 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
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9. Any questions?
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