Introduce S1 WMO-defined statistic in CNT line type

[j-opatz]

Describe the New Feature

In a Discussions, it was found by a user that MET's S1 statistic provided slightly different values (i.e. greater) than the WMO-defined S1 statistic. This is due to MET's method of real-world, spatial derivatives for the forecast values in the x and y directions. This involves including the physical distance between gridpoints, which can change by projection and latitude.

In contrast, the WMO-defined method ignores the physical distance and sticks to a grid space distance (1 grid space in each direction).

Users wishing to verify data in accordance with WMO methods should be able to rely on METplus for these calculations, so it is advised to create a new S1 statistic matching the WMO method. This would be in the CNT line type, as it is ignorant of real-world distance between grid spacing.

Acceptance Testing

It would be worthwhile to get Xiaoxi's input on the final result, as they found this issue (Github name @wuxx66)

Time Estimate

Estimate the amount of work required here.
Issues should represent approximately 1 to 3 days of work.

Sub-Issues

Consider breaking the new feature down into sub-issues.

• Add a checkbox for each sub-issue here.

Relevant Deadlines

List relevant project deadlines here or state NONE.

Funding Source

Define the source of funding and account keys here or state NONE.

Define the Metadata

Assignee

• Select engineer(s) or no engineer required
• Select scientist(s) or no scientist required

Labels

• Review default alert labels
• Select component(s)
• Select priority
• Select requestor(s)

Milestone and Projects

• Select Milestone as a MET-X.Y.Z version, Consider for Next Release, or Backlog of Development Ideas
• For a MET-X.Y.Z version, select the MET-X.Y Development project

Define Related Issue(s)

Consider the impact to the other METplus components.

• METplus, MET, METdataio, METviewer, METexpress, METcalcpy, METplotpy

New Feature Checklist

See the METplus Workflow for details.

• Complete the issue definition above, including the Time Estimate and Funding source.
• Fork this repository or create a branch of develop.
  Branch name: feature_<Issue Number>_<Description>
• Complete the development and test your changes.
• Add/update log messages for easier debugging.
• Add/update unit tests.
• Add/update documentation.
• Push local changes to GitHub.
• Submit a pull request to merge into develop.
  Pull request: feature <Issue Number> <Description>
• Define the pull request metadata, as permissions allow.
  Select: Reviewer(s) and Development issue
  Select: Milestone as the next official version
  Select: MET-X.Y Development project for development toward the next coordinated release
• Iterate until the reviewer(s) accept and merge your changes.
• Delete your fork or branch.
• Close this issue.

[j-opatz]

A WMO definition for S1 can be found here, on II.7-39