Publikationsdatum:
2021-02-11
Beschreibung:
Tornadoes have Lorenzian predictability horizons O(10 min), and convection-allowing ensemble prediction systems (EPSs) often provide probabilistic guidance of such events to forecasters. Given the O(0.1 km) length-scale of tornadoes and O(1 km) scale of mesocyclones, operational models running at horizontal grid-spacings (Δx) of 3 km may not capture narrower mesocyclones (typical of the southeast United States) and certainly do not resolve most tornadoes per se. In any case, it requires O(50) times more computer power to reduce Δx by a factor of three. Herein, to determine value in such an investment, we compare two EPSs, differing only in Δx (3 km versus 1 km), for four low-CAPE, high-shear cases. Verification was grouped as (1) deterministic, traditional methods using point-wise evaluation; (2) a scale-aware probabilistic metric, and (3) a novel method via object identification and information theory. Results suggest 1-km forecasts better detect storms and any associated rapid low- and midlevel rotation, but at cost of weak–moderate reflectivity forecast skill. The nature of improvement was sensitive to the case, variable, forecast lead-time, and magnitude, precluding a straightforward aggregation of results. However, the distribution of object-specific information gain over all cases consistently shows greater average benefit from the 1-km EPS. We also reiterate the importance of verification methodology appropriate for the hazard of interest.
Print ISSN:
0027-0644
Digitale ISSN:
1520-0493
Thema:
Geographie
,
Geologie und Paläontologie
,
Physik
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