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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).
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- 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:
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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).
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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 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
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- 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.
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