Use of EPS at the Met Office. Ken Mylne and Tim Legg. Outline. Update on verification of First-Guess Early Warnings of severe weather Example of unusual model and EPS behaviour Met Office short-range ensemble development.
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Use of EPS at the Met Office
Ken Mylne and Tim Legg
Early Warnings of severe weather –The 4-day skill maximum investigated
Heavy Rainfall events
Severe Gale events (Little evidence) Heavy Snowfall events (Similar to Rainfall)
Met O U.M.
There are two main ways of defining events for verification
(i) On an ‘event-wise’ basis – when an event occurs, did we have an early warning of it? And when an early warning exists, did an event occur? One contingency-table entry per event.
(ii) On a time-wise basis – at fixed time intervals, look to see whether or not an Early Warning and/or a Flash Warning were in force and complete contingency tables
Early Warnings have always been verified on an event basis:
Events are defined as:
for Heavy Rainfall warnings (01 Oct 2003 – 03 Nov 2004)
First-guess Early Warnings verification designed to assess the skill of warnings issued to end users:
Skill of EPS Control and EPS ModelExample raised by Met Office Chief Forecaster
Short-Range Ensembles at the Met Office
ECMWF EPS has transformed the way we do Medium-Range Forecasting
Uncertainty also in short-range:
Rapid Cyclogenesis often poorly forecast deterministically (eg Dec 1999)
Uncertainty of sub-synoptic systems (eg frontal waves)
Many customers most interested in short-range
Assess ability to estimate uncertainty in local weather
Cloud Ceiling, Fog
Multi-model ensemble contribution
LBCs for future storm-scale ensembles
Stochastic Kinetic Energy Backscatter (SKEB)
K.- Kinetic En.; R.- Random field;
D.- Dissipated en. in a time-step
R is designed to reproduce some statistical properties found with CRMs
u increments at H500
Increase in spread respect to an IC-only ensemble
500 hPa geopotential height
Several members have better lowthan control. Member 4 is deeper. NB. This is global EPS.