From 94fb542ed3c32757db9dc7fd2ca85fc886cb101b Mon Sep 17 00:00:00 2001 From: Lisa Goodrich Date: Fri, 30 Jul 2021 11:13:15 -0600 Subject: [PATCH] updates John O. suggested take 2 #1834. --- met/docs/Users_Guide/appendixA.rst | 68 +++++++++++++----------------- 1 file changed, 30 insertions(+), 38 deletions(-) diff --git a/met/docs/Users_Guide/appendixA.rst b/met/docs/Users_Guide/appendixA.rst index 4d2cb3ea15..8b92b3de91 100644 --- a/met/docs/Users_Guide/appendixA.rst +++ b/met/docs/Users_Guide/appendixA.rst @@ -370,48 +370,24 @@ A user can write a script with multiple calls to Gen-Vx-Mask to apply complex masking logic and then pass the output mask file to Grid-Stat in its configuration file. -**Q. Grid-Stat - How do I set neighborhood methods boundaries?** - -A. -When computing fractions skill score, MET uses the "vld_thresh" -setting in the configuration file to decide how to handle data -along the edge of the domain. Let us say it is computing a -fractional coverage field using a 5x5 neighborhood and it is at -the edge of the domain. 15 points contain valid data and 10 points -are outside the domain. Grid-Stat computes the valid data ratio -as 15/25 = 0.6. Then it applies the valid data threshold. Suppose -vld_thresh = 0.5. Since 0.6 > 0.5 MET will compute a fractional -coverage value for that point using the 15 valid data points. Next -suppose vld_thresh = 1.0. Since 0.6 is less than 1.0, MET -will just skip that point by setting it to bad data. - -Setting vld_thresh = 1.0 will ensure that FSS will only be computed -at points where all NxN values contain valid data. Setting it to -0.5 only requires half of them. - -Using grid_stat to evaluate precipitation, whose minimum value -should be 0. If the thresholding of the data greater-than-or-equal-to -0 (>= 0), that will always evaluate to true for precipitation. -Consider using strictly greater-than 0 (>0) instead. **Q. Grid-Stat - How do I use neighborhood methods to compute fraction skill score?** A. -It is possible to compute the fractions skill score for comparing -forecast and observed thunderstorms. When computing FSS, first -threshold the fields to define events and non-events. Then look at -successively larger and larger areas around each grid point to see -how the forecast event frequency compares to the observed event -frequency. Applying this to thunderstorms would be reasonable. - -Also, applying it to rainfall (and monsoons) would be fine. Keep in -mind that Grid-Stat is the tool that computes FSS. Grid-Stat will -need to be run once for each evaluation time. As an example, -evaluating once per day, run Grid-Stat 122 times for the 122 days -of a monsoon season. This will result in 122 FSS values. These -can be viewed as a time series, or the Stat-Analysis tool could -be used to aggregate them together into a single FSS value, like this: +A common application of fraction skill score (FSS) is comparing forecast +and observed thunderstorms. When computing FSS, first threshold the fields +to define events and non-events. Then look at successively larger and +larger areas around each grid point to see how the forecast event frequency +compares to the observed event frequency. + +Applying this method to rainfall (and monsoons) is also reasonable. +Keep in mind that Grid-Stat is the tool that computes FSS. Grid-Stat will +need to be run once for each evaluation time. As an example, evaluating +once per day, run Grid-Stat 122 times for the 122 days of a monsoon season. +This will result in 122 FSS values. These can be viewed as a time series, +or the Stat-Analysis tool could be used to aggregate them together into +a single FSS value, like this: .. code-block:: none @@ -419,7 +395,23 @@ be used to aggregate them together into a single FSS value, like this: -lookin out/grid_stat Be sure to pick thresholds (e.g. for the thunderstorms and monsoons) -that capture the "events" that are of interest in studying. +that capture the "events" that are of interest in studying. + +Also be aware that MET uses the "vld_thresh" setting in the configuration +file to decide how to handle data along the edge of the domain. Let us say +it is computing a fractional coverage field using a 5x5 neighborhood +and it is at the edge of the domain. 15 points contain valid data and +10 points are outside the domain. Grid-Stat computes the valid data ratio +as 15/25 = 0.6. Then it applies the valid data threshold. Suppose +vld_thresh = 0.5. Since 0.6 > 0.5 MET will compute a fractional coverage +value for that point using the 15 valid data points. Next suppose +vld_thresh = 1.0. Since 0.6 is less than 1.0, MET will just skip that +point by setting it to bad data. + +Setting vld_thresh = 1.0 will ensure that FSS will only be computed at +points where all NxN values contain valid data. Setting it to 0.5 only +requires half of them. + **Q. Grid-Stat - How do I use config file setup to read a NetCDF file?**