New Table 4.2 entries proposed by Canada

[efucile]

Branch

https://github.com/wmo-im/GRIB2/tree/issue-17

Summary and purpose

This document proposes new GRIB2 Code Table 4.2 parameters.

Action proposed

The Team is requested to review the proposed new parameter and approve it for implementation within the May 2019 fast-track (FT2019-2) update to the WMO Manual on Codes.

Discussions

The tables annexed herewith contain proposed additions to Table 4.2 of the GRIB2 section of the Manual on Codes. These are necessary to reflect new post-processing diagnostics and Nowcasting forecasts being implemented at the Canadian Centre for Meteorological and Environmental Prediction. It is hoped that they are sufficiently general for eventual use by other Centers. We kindly request the IPET-CM to help us clarify whether the precipitation type probability parameters in Code Table 4.2, Product discipline 1 (hydrological products) may be used in the context of a general meteorology product. If not, we would be grateful for guidance on the proper procedure.

Detailed proposal

Proposed new entry for Code table 4.2

Parameter	Product Discipline	Parameter Category	Parameter number	Units
Thunderstorm intensity index	0	7 (Thermodynamic stability)	20	Code table 4.246 proposed new table
Precipitation intensity index	0	1 (Moisture)	122	Code table 4.247 proposed new table
Snow level	0	19 (Physical atmospheric)	40	m
Dominant precipitation type	0	1 (Moisture)	123	Code table 4.201 proposed modified table
Presence of showers	0	1 (Moisture)	124	See Table 4.222
Presence of blowing snow	0	1 (Moisture)	125	See Table 4.222
Presence of blizzard	0	1 (Moisture)	126	See Table 4.222
Ice pellets (non water equivalent) precipitation rate	0	1 (Moisture)	127	m/s

One table modification proposed: GRIB2 - CODE TABLE 4.201, PRECIPITATION TYPE Code Figure	Meaning
0	Reserved
1	Rain
2	Thunderstorm

New table Code table 4.246 - Thunderstorm intensity index

Title_en	SubTitle_en	CodeFlag	Value	MeaningParameterDescription_en	Note_en	UnitComments_en	Status
Thunderstorm intensity		0		No thunderstorm occurence			Operational
Thunderstorm intensity		1		Weak thunderstorm			Operational
Thunderstorm intensity		2		Moderate thunderstorm			Operational
Thunderstorm intensity		3		Severe thunderstorm			Operational
Thunderstorm intensity		4-254		Reserved			Operational
Thunderstorm intensity		255		Missing			Operational

New table Code table 4.247 - Precipiation intensity index

Title_en	SubTitle_en	CodeFlag	Value	MeaningParameterDescription_en	Note_en	UnitComments_en	Status
Precipitation intensity		0		No precipitation occurrence			Operational
Precipitation intensity		1		Light precipitation			Operational
Precipitation intensity		2		Moderate precipitation			Operational
Precipitation intensity		3		Heavy precipitation			Operational
Precipitation intensity		4-254		Reserved			Operational
Precipitation intensity		255		Missing			Operational

Reference doc file: https://wmoomm.sharepoint.com/:w:/s/wmocpdb/EdX0NSgC3AZCiJYksEB1PkgBr8HPRRefpw2vnjqLWaldkA?e=CKlXm4

Reference meeting page: https://community.wmo.int/activity-areas/wmo-codes/meetings/ipet-cm-iii

[efucile]

I think that it would be better to have a new table also for the parameters in Numeric**** units. We should avoid putting information in the notes. Let's remember that notes are not in the xml or csv format of the tables which is used in by the decoders and are only in the pdf version of the manual.

[sebvi]

I am not in favor of using and expanding Code Table Discipline 1, Category 1 . My understanding is that parameters containing "probability of ..." are deprecated in favor of using the Template 4.5,setting type of generating process to "probability forecast", setting the probability type using Code Table 4.9, and then your limits for the probability in the following octets. This is why I don't think the parameters in discipline 1, category 1 should not be accepted/added, they can already be encoded using the mechanism described above. (Note as well that 2 of your parameters have an entry in the reserved area for local code of the table).

What is the difference between your snow level and discipline 0, category 1, number 11?

For the "presence of ..." parameters, I would change the units to "boolean". What these fields provide is in fact a bitmap.

[sebvi]

I should also add that in GRIB3, discipline 1, category has been considered deprecated and has been deleted. I am in the process of committing the tables in the GRIB3 repository.

[tomkralidis]

cc @jbathegit

Thanks @sebvi . I have updated the proposal above by removing probability parameters in lieu of implementing with PDT 4.5, and updated the units of the presence parameters as booleans (per 4.222).

Note also I've changed snow level to parameter number from 36->40 given #25. See the following paper as reference/example of the term "Snow level". We could also name this parameter "Snow level (melting level)" to reduce ambiguity if desired.

[chenxiaoxia2019]

@tomkralidis @ypell I have created a branch for this issue, with changes implemented in the table mentioned above. Could you please check it? Thanks.

[tomkralidis]

Thanks @chenxiaoxia2019; in comparing https://github.com/wmo-im/GRIB2/compare/issue-17 to the proposal above, is there any update on the below?

Parameter	Product Discipline	Parameter Category	Parameter number	Units
Thunderstorm intensity index	0	7 (Thermodynamic stability)	20	Code table 4.246 proposed new table
Snow level	0	19 (Physical atmospheric)	40	m

[chenxiaoxia2019]

@tomkralidis Hi, Tom. Thanks for your check. The above mentioned parameters have been updated in GRIB2_CodeFlag_4_2_CodeTable_en.csv. Please check it.

[tomkralidis]

Thanks @chenxiaoxia2019 . I see tables 4.246 and 2.247 are non-existent. I updated the proposal above. Can you update the branch with 4.246 and 4.247?

[chenxiaoxia2019]

@tomkralidis Hi, Tom, I updated the branch with tables 4.246 and 4.247. Could you please check it? Thanks.

[tomkralidis]

Thanks @chenxiaoxia2019 . Looks good to me. +1.

[amilan17]

SUMMARY: Add entries to Code Table 4.2, add Code Tables 4.246 and 4.247

[amilan17]

Approved by FT-2020-2.