new precipitation type flag in Code Table 4.201

feggleton commented 5 months ago

Initial request

The UK Met Office requests a new entry in GRIB2 Code Table 4.201 Precipitation Type Flags

Amendment details

New entry in Code Table 4.201 to differentiate between hail sizes. The Met Office requires a flag for large hail, would like to discuss how this could be achieved, if 'large hail' is added as a new code, would we need to change the name of 'hail' to 'small hail'?

Title_en	SubTitle_en	CodeFlag	Value	MeaningParameterDescription_en	Note_en	noteIDs	UnitComments_en	Status
Precipitation type		13?		Large hail

Comments

No response

Requestor(s)

Francesca Eggleton - UK Met Office @feggleton Lara Gunn - UK Met Office @laragunn

Stakeholder(s)

Enter list of stakeholder(s).

Publication(s)

Example: Manual on Codes (WMO-No. 306), Volume I.2, GRIB code table 4.2, discipline 0, category 5

Expected impact of change

MEDIUM

Collaborators

No response

References

No response

Validation

No response

amilan17 commented 2 months ago

@feggleton @laragunn are you available to join one of our meetings on 2, 14, or 15 of May to introduce this proposal? If so, will you please email me at amilan@wmo.int.

sebvi commented 2 months ago

Dear @feggleton, thank you for this proposal.

I don't think that we can rename the existing "hail" entry to "small hail" because it will invalidate any existing data. If the Met Office needs both "small hail" and "large hail", then I would recommend to add both to the table. We can then have a note attached to the table to explain that the existing "hail" entry is any size while small/large hail can be used to discriminate the size. Furthermore, one should either use "hail" or "small/large hail" but not both options at the same time.

feggleton commented 2 months ago

Thanks @sebvi yes you are right, that was my mistake on backwards compatibility. I think that is a good suggestion. I will go back to my team and we can discuss in the meeting.

amilan17 commented 1 month ago

https://github.com/wmo-im/CCT/wiki/Teleconference.14.May.2024 notes: @feggleton introduced the proposal: Precipitation Type Flag Code Table 4.pptx

there was discussion about the definitions of large, small hail vs including the thresholds in the notes/definition of GRIB codes...
The cloud atlas has definitions for hail, small-hail and snow pellets https://cloudatlas.wmo.int/en/small-hail.html

DECISION - create entry that includes hail and range
@feggleton please update proposal details

feggleton commented 1 month ago

I've gathered together different definitions which might help with this decision, there are varying definitions and it's not clear cut about the sizes.

WMO defines: Graupel 2-5mm, small hail 'may approach or even exceed 5mm', hail 5-50mm.

ICAO (aviation): "Small hail (METAR code GS) is hail or graupel of less than 5 mm in diameter. True hail (METAR code GR) is hail of 5 mm or more in diameter." ie. small hail <5mm, true hail >=5mm.

European Severe Storms Laboratory guidance: small hail 0-19mm, large hail 20-49mm, very large hail >=50mm

As Graupel is already in the table and not in question, I don't think we need to amend this definition. From the above information, I would suggest we add to the table, hail (<5mm) and hail (>=5mm). We have previously discussed in the meeting about remove the naming of small and large, happy to discuss further. @laragunn please comment if you'd like to suggest something else based on your knowledge.

I would welcome comments to discuss this further. Thanks.

amilan17 commented 4 days ago

https://github.com/wmo-im/CCT/wiki/Teleconference.2.July.2024 notes:

team reviewed latest comments and agreed with the suggestion to "add to the table, hail (<5mm) and hail (>=5mm)" @sebvi will update the branch

wmo-im / GRIB2