Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.  With effect from Cy49r1, Ensemble Control Forecast (ex-HRES) output is equivalent to HRES output shown in the diagrams.   At the time of the diagrams, HRES had resolution of 9km and ensemble members had a resolution of 18km.

At inception around 2010, the extra-tropical cyclone diagrams ("cyclone database" products) were generated using bitmap manipulation.  As a result the products had a somewhat noisy/jagged visual appearance relative to many NWP products available in 2021.  Software was proving costly to maintain.  

In May 2021, in collaboration with the UK Met Office, ECMWF upgraded to a Python-based code suite.  This applies the same graphical processing principles but saves frontal objects in vector form.  Fronts are recreated from those vectors wherever needed for a product.   This provides an aesthetically pleasing visual appearance, clearer rendering of details and a capacity to use transparency settings.  

In future this software change will also allow greater platform portability (e.g. for ecCharts, fitting with user requests) and easier development of other product variants.  During the upgrade a few other minor changes were applied, including correction of a pre-existing bug that affected the strike probability products.  

The main differences in output that resulted from these various changes are highlighted below, for user reference:

a) Cleaner front charts, with no variations in front thickness, but more "front breaks"

Fig8.1.15.1-1: Comparison of a Control run T+24 synoptic chart forecast frame, between the old and new systems (same input data).

Consider the front that crosses the south of Baffin island (e.g. near 64N, 68W) on Fig8.1.15.1-1.

  • In the old product, the front is shown as a fairly continuous red-blue line, of varying thickness.  The mask erases, in places, part of the potential front that had been drawn more than 1 pixel wide.  Then that partially erased coloured line is retained as is on the final product.
  • In the new product, the front broken up into 3 segments.  The software decides whether to accept a front or not, based on the thermal-gradient-related masking criteria.   Any accepted front segments are converted into a vector format and then re-plotting those vectors with constant front width.

 b) Minor changes to cyclonic features identified

Consider the spots (cyclonic features) between the two renderings on Fig8.1.15.1-1.  There are some differences. In general: 

  • the substantial features (large dots) are the same.
  • the weaker features (small dots) are more liable to differ slightly.  

Differences are essentially random and relate to sensitivity in identification of borderline features.  Most thresholds relate to field values (e.g. computed thermal gradient).  Some define a minimum separation distance between features.  One cannot say that one plot is better than the other.  When looking at an ensemble (e.g. on Dalmatian charts) such random differences will tend to cancel, and so are unlikely to change user interpretation (e.g. see Fig8.1.15.1-3)

c) Precipitation plotted as interpolated colour fill rather than non-interpolated grid-fill, giving a smoother appearance

Consider the cyclone over NW Russia on Fig8.1.15.1-1.  This is mainly associated with snow (blue) and a rain-snow mix (pink).

  • In the old product, the imagery has a rough blocky appearance.
  • In the new product, the imagery has a smoother appearance, but is more "approximate" because of the interpolation (e.g. one pink pixel has disappeared).

The colour-fill is based on two dimensions - type and amount of precipitation.  So it is not possible to generate a completely smooth transition across all colour boundaries.  Spurious narrow filaments of lighter shading (falsely implying less precipitation) will sometimes appear between different colours (e.g. crossing 63N 60E on Fig8.1.15.1-1). 

d) Spaghetti Fronts uses transparency

Fig8.1.15.1-2: Comparison of spaghetti fronts charts between old and new systems (same input data).

There are some minor differences for the reasons described in (a) above.  In the new product, semi-transparent rendering is used for members 1-50 for a better visual impression.  The "more probable" Ensemble Control Forecast (ex-HRES) solutions (gold and green) these are still rendered in an opaque form to retain clarity.

e) Clearer and larger Dalmatian charts

Fig8.1.15.1-3: Dalmatian chart examples from the old system (left) and the new system (right) from the same input data.

Dalmatian charts of all types, including the "synoptic feature type" option shown in Fig8.1.15.1-3, all benefit from improved rendering.  Output from the new product has been enlarged, to further improve legibility, recognising also that workstation displays have generally evolved since 2010 to have higher resolution.   Browser windows/tabs can always be rescaled (typically using Ctrl+ or Ctrl-).   Minor differences between the spots again relate to threshold handling in borderline cases, as discussed in (b) above.  Plotting mechanisms, such as scaling, colours, symbol styles and overlaying order should all be the same in the new system as they used to be, for all types of Dalmatian chart. 

f) Bug removed for Strike Probability charts


Fig8.1.15.1-4: Strike probability chart examples from the old (left) and new (right) systems from the same input data

Consider differences between the two plots in Fig8.1.15.1-4.

Plot size has been increased slightly.  Some of the differences arise for reasons discussed in (b) above.

Most relate to removal of a bug which had previously caused a few cyclone tracks to be inherited from the wrong valid time.  Most notably:

  • In the old system, low probabilities of cyclone activity (at this 34kt threshold) appear in regions peripheral to the more brightly coloured "storm track zone":
  • In the new system,  these have correctly been removed. 

g) Miscellaneous

Clicking on a cyclone at T+0 continues to give plume diagrams and track animations.

In the new version,  

  • The look of the cyclone plume diagrams and the track animations have changed but the content and functionality remain the same.
  • The entry point for the cyclone database web products has also been upgraded but retains the same functionalities.
  • Output images are now all in "png" format; previously most were "gif".



See the Cyclone Database Products.



(FUG Associated with Cy49r1)