CMC > NCEP 20200130 Update

CMC pulls ahead of the GFS? We're #4?

Update on 20200130: CMC better in Summer Hemisphere?

Mike Fiorino

30 January 2020

Recap of  the November Blog

In my first post:  https://wxmapstertc.blogspot.com/2019/11/cmc-ncep.html I discussed how the CMC GDPS (Global Deterministic Prediction System -- the Canadian model) was outperforming the NCEP GFS (the American model) in a very basic measure of global model forecast quality -- the 5-day northern Hemisphere (NHEM) height Anomaly Correlation (5DNACC). 

I acknowledged that a few points do not make a trend, but at the time hypothesized that the improvements in Canadian model came from new/better physics ...

I asked two questions:

1. when/what were the apparent changes in the CMC GDPS (Global Deterministic Prediction System)?
2. was the gap between the NCEP.GFS and the CMC.GDPS a blip or a trend?

Ron McTaggart-Cowen (ron.mctaggart-cowan@ec.gc.ca) answered #1: 3 July 2019.

And he provided these links describing the changes:

• science: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019MS001781
• tech: http://collaboration.cmc.ec.gc.ca/cmc/cmoi/product_guide/docs/changes_e.html

The most significant physics update to me involved the convective parameterization (adding momentum transport).  As a long-time tropical cyclone (TC) NWP modeler, the impact of better convection was not surprising and consistent with related changes at ECMWF in 2008 that lead to a dramatic improvement in their TC track forecasts (see:https://www.ecmwf.int/sites/default/files/elibrary/2009/17493-record-setting-performance-ecmwf-ifs-medium-range-tropical-cyclone-track-prediction.pdf)

 

Recent Trends...

Pete Kaplan's EMC Stat Page (the long-running web page used at all global model meetings at EMC during my time there in the 1990s) has been down for 'technical reasons'(?), but here are the latest stats from the EMC VSDB (https://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/):

CMC is ahead of the GFS by 0.4 points (a point in NWP is a percentage point) in the NHEM but 1.2 in the SHEM.  A 1.0 point change is a pretty big deal, but again is not necessarily a trend.  What's more impressive  is how the delta is consistent and how the CMC.GDPS does not 'dropout' as badly as the GFS, e.g., the SHEM 11 JAN and NHEM 4 JAN dropouts.

The new CMC GDPS model has been running since July 2019 so we have 7 months to compare in the text table below:

               NHEM                   SHEM
         CMC    GFS  CMC-GFS    CMC    GFS  CMC-GFS
201906: .866   .876  -0.010     N/A  
201907: .863   .871  -0.008    .883   .889  -0.006
201908: .897   .890  +0.007    .882   .891  -0.009
201909: .876   .874  +0.002    .885   .891  -0.006 
201910: .898   .894  +0.004    .908   .899  +0.009
201911: .907   .911  -0.003    .914   .911  +0.003    
201912: .904   .911  -0.007    .903   .903  +0.000
202001: .913   .907  +0.004    .887   .875  +0.012 

What's most interesting is how the Canadian model does better in the summer hemisphere. 

We're not quite at the peak of austral TC activity (around February), but it looks like the convection changes are really improving the CMC height scores and confirms (IMHO) how the tropics impacts the quality of the midlatitude forecasts.

 

Some final thoughts...

Cliff Mass' recent blog post on US NWP (https://cliffmass.blogspot.com/2020/01/the-future-of-us-weather-prediction.html) makes a compelling argument that American operational NWP is fundamently broken with perhaps the greatest dysfunction (unstated there) in the US Navy 😟.  In the NHEM plot above, the Navy global model is barely competitive with the CFSR!  This is very distressing to me as a retired Naval Oceanography officer that implemented the first operational two-way interactive, moving nested-grid TC model in 1981...

I'm seeing a real trend here and at the rate we're going, American NWP will be 4th rate for the foreseeable...

While Cliff correctly identifies our problem mostly as one of leadership (I agree), the (much?) bigger in my mind is the data handling systems at NCEP NCO.  Using the unix filesystem to 'manage' gridded fields is appalling primitive and at least 30 years behind the rest of the world!  Although the Navy global model is clearly in last place, the data systems at FNMOC have always been top notch. 

Data handling is certainly not a sufficient condition, as demonstrated by the lack of performance by the Navy global model, but it is a necessary condition.  I cannot see American NWP at NCEP progressing without a fundamental change in the nitty gritty of data, a fully-funded and outside-DC EPIC notwithstanding.

The Usual Caveats

These comments/opinions are wholly mine and do not refect those of my current employer The University of Colorado Boulder or my previous employer NOAA.