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Post-processing methods for probabilistic convection forecasts based on the limited-area
ensemble COSMO-DE-EPS of DWD
Lars Wiegand, Christoph Gebhardt
German Meteorological Service (DWD), Germany
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
Content
set-up COSMO-DE-EPS
EPS convection project
methodologyobservation
forecast – probabilistic products (case study)
Bayes theorem
LASSOdata
result
further researches
product design
SESAR (Single European Sky)
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
model chain at DWD
COSMO-DE: 2.8 km
convection-permitting forecast model50 vertical levels
modelrun every 3 hours: + 27 h
GME: 20 km
COSMO-EU: 7 km
set-up COSMO-DE-EPSfurther details: see talk SCI-PS166.01
Susanne Theis: Tue 13:30, room 524A
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
COSMO-DE-EPS
11 22 33 44 55
GMEGME
IFSIFS
GSMGSM
GFSGFS
20 members
set-up COSMO-DE-EPSfurther details: see talk SCI-PS166.01
Susanne Theis: Tue 13:30, room 524A
further details: see talk SCI-PS166.01
Susanne Theis: Tue 13:30, room 524A
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
project „EPS Convection“
predictability of small scale processes with non-linear and stochastic processes (e.g. convection) is strongly limited i.e. leads to strong uncertainty already at short lead times
severe events and high impact weather are highly important for warnings in general or in aviation in particular
“charakteristics of HIW” and “limited predictability” leads to use of probabilistic estimation of high-resulotion forecasts of deep convection based on COSMO-DE-EPS
aims at supporting aviation weather forecasts and general weather warning process at DWD
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
methodology
probabilistic products for convective parameters from COSMO-DE-EPS
DMO (direct model output) variables as well as direct calculatable variables (e.g. KO-index) from DMO
IMO (indirect model output), e.g. thunderstorms produced with regression methods
requirements for IMO (thunderstorm) forecasts: observation of IMO (thunderstorm) as predicand radar + lightning
EPS DMO forecasts as predictor(s)
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
observation thunderstorm
combination of radar reflectivity and lightning
RX product advantages: warning criterias are known within DWD (28, 37, 46, … dBz), high
spatial/temporal resolution
adaptions:
conversion into COSMO-DE grid
lightning from NCM network very accurate observations – only 0,02% of all lightnings have errors >2,8km
adaptions:
every grid point within 3km gets a distance weighted amount of a lightning measure
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
case study – thunderstorms 28th July 2013
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
case study – thunderstorms 28th July 2013
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
case study – thunderstorms 28th July 2013
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
case study – thunderstorms 28th July 2013
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
case study – thunderstorms 28th July 2013
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
case study – thunderstorms 28th July 2013
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
Bayes theorem
variables: CAPE, CIN, TWATER, OMEGA, DBZ_CMAX, TOT_PREC
period: summer (Apr-Sept) 2012
forecast: 00UTC + 0/6/12/18h
based on grid points
1/0 event occurs/does not occur
X = variable from COSMO-DE(-EPS)
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
Bayes theorem
variable: TWATER (total water content)
forecast: 00UTC + 0h
period: summer (Apr-Sept) 2012
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
Bayes theorem
variable: TWATER (total water content)
forecast: 00UTC + 18h
period: summer (Apr-Sept) 2012
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
Bayes theorem
variable: DBZ_CMAX (radar reflectivity column maximum)
forecast: 00UTC + 12h
period: summer (Apr-Sept) 2012
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
Bayes theorem
variable: OMEGA (vertical velocity)
forecast: 00UTC + 0h
period: summer (Apr-Sept) 2012
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
LASSO – least absolute shrinkage and selection operator
(Tibshirani 1996) search for suitable predictors
comparison of predictors (variables (DMO) and their probabilistic products)
choose of predictors, which depict the observation best
tool: R statistic software (package glmnet + dependences)
logistic regression: optimal for extreme values
Input/output can be probabilities
error measure: RMSE
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
COSMO-DE-EPS
forecast: daily 03UTC + 21h
40 days in summer 2012 (22th July – 30th August)
93 variables (CAPE, CIN, T2m, TWATER, TQ, TI, …)
EPS products: mean, minimum, maximum
5 days, i.e. 8 calculations
observation: 1h radar maximum and lightning sumradar: 16:30 – 17:25 UTC (available every 5 minutes)
lightning: 16:30 – 17:29 UTC (exact to the second)
LASSO summer 2012 (40 days)
data basis
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
mean TWATER
maximum TQ (Graupel)
maximum radar reflectivity (maximum RR in atmospheric column)
all 3 variables are amongst the first 5 predictors for the 8 calculations
maximum TWATER in 5 out of 8 calculations within the first 5 predictors
to check: stability of predictors for longer time periods
result just shows the predictors for 8 x 5 days in summer 2012
result - predictors
LASSO summer 2012 (40 days)
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
further research
LASSOlonger time periods statistical robustness
quantiles and probabilities as predictors
time offset
neighborhood method
different synoptical regimes (convective time scale)
generation of thunderstorm forecast product from 3 or more predictors
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
ObjectivesTo develop ensemble post-processing techniques in order to provide consistent short-range probabilistic NWP products of convective risks across Europe, at the highest possible NWP resolution
combination of three convection-permitting ensembles systems. AROME-EPS (MF), COSMO-DE-EPS (DWD) and the UKV-EPS(UKMO)
Super-Ensemble Mesoscale Forecast of Convection(SESAR-JU WP11.2.1, lead Meteo France)
generation of consistent, blended probability products for ATC
2 data phases
Summer 2012 (mid July – end August)
Spring 2014 (mid April – end June)
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
Example: combined mean radar refelectivity
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
Thanks for your attention!
Comments?
Questions?
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
Supplementary slides
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
product design
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
Direct Model Output (DMO)
Zusammenhang Wahrscheinlichkeit(DMO>Schwellenwert) Ereignis
Wahrscheinlichkeiten dieser DMO-Variablen nicht zwingend gut kalibriert
Ansatz: Vorhersage “ja” für Wahrscheinlichkeiten(DMO>Schwelle) > A%
Bestimme hit rate/ false alarms für verschiedene A
Optimales A ist nutzerabhängig! (hit rate/ false alarms)
Datenlage der Beobachtungen von DMO oft flächig nicht beobachtbar (CAPE, TWATER, …)
Ereignis: Gewitter aus Radar + Blitz
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
Weitere Arbeiten in EPS Konvektion
WX getestet: Vorteil: größeres Gebiet: keine Radarmessungen werden verworfen
Nachteil: nicht sicher ab wann operationel, wird aller Vorraussicht nicht nachberechnet
Programme für abgeleitete Variablen aus DMO Variablen KO-index
Convective time scale – Klassifizierung in synoptische/Luftmassengewitter Situationen
Erstellung des technischen und fachlichen Rahmens des Fachkonzeptes
Studien zu statistischen Eigenschaften der gewählten ‘high-priority’ Variablen CAPE, CIN, dBz_cmax, TWATER, OMEGA@700hPA
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
Beobachtung Gewitter
Schwellenwerte für Gewitterklassifikation
class radar reflectivity [dbz]
lightning strikes [no./15 minutes]
associated weather
moderate >37 1 moderate rainwind gust up to 7 Bft
strong >46 tbd heavy rain (10-25 l/m² in 1h, 20-35 l/m² in 6h)wind gusts 8-10 Bfthail possible (Ø <1,5cm)
severe >53 tbd very heavy rain (>25 l/m² in 1h, >35 l/m² in 6h)wind gusts >11 Bftlarge hail possible (Ø >1,5cm)
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
COSMO-DE
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
Beispiel – Gewitterlage 28. Juli 2013
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
Super-Ensemble Mesoscale Forecast of Convection(SESAR-JU WP11.2.2, lead Meteo France)
Ziel:To develop ensemble post-processing techniques in order to provide consistent short-range probabilistic NWP products of convective risks across Europe, at the highest possible NWP resolution
Kombination dreier konvektionserlaubender Ensemblesysteme.
AROME-EPS (MF)
COSMO-DE-EPS (DWD)
UKV-EPS(UKMO)
Erstellung von konsistenten (räumlich verschnittenen) Produkten für die Flugsicherung (allerdings nur post-processing)
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
Modellgebiete
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
SESAR domain
Gemeinsames SESAR ‘Modellgebiet’
Dünkirchen (2.38E, 51N) als gemeinsamer Gitterpunkt Dünkirchen kein GP in originalem COSMO-DE-Gitter
Auflösung 0.027°/0.022° (lon/lat – reguläres Gitter)
Anpassungen:
Interpolation von rotiertem Gitter (0.025° lon/lat) auf SESAR-Gitter
Variablenanpassung: z.B. Windstärke auf SESAR-Gitter aus staggered grid
Korrekte Einstellungen der grib2 header
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
Zwei Phasen der Datenarchivierung
1. Phase (Sommer 2012): 22. Juli – 30. August 2012
93 Variablen
20 Member
21h Vorhersage (stündlich)
03UTC Vorhersage
2. Phase (Frühling 2014): 1. April bis 10. Juni 2014 (71 Tage – 40 ausgewählte)
Selbe Spezifikationen wie in Phase 1
Vorhersage bis 27h neu
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
Observation thunderstorm
WWOSC 2014 Montréal, Canada Lars Wiegand, DWD 18th August 2014
COSMO-DE COSMO-DE-EPS
„variations“within the system
ensemble members
set-up COSMO-DE-EPSfurther details: see talk SCI-PS166.01
Susanne Theis: Tue 13:30, room 524A
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