1. Predictability and dynamical processes
Heini Wernli
Institute for Atmosphere and Climate Science
ETH Zurich
HIW Workshop, Karlsruhe
18 March 2013

2. Key points
the dynamics of high-impact weather is often complex and closely related to basic/fundamental research questions,
relevant processes range from large-scale to microscale; from Rossby wave dynamics to deep convection, cloud microphysics and turbulence,
occasionally, forecast uncertainties are still large for various of these processes and their interaction,
field experiments, together with dedicated modeling/diagnostic research activities, are important for bringing the community together to work jointly on important issues,
important pillars of a future HIW project should be (a) collaboration between universities, research institutes, and weather services, and (b) research projects like, e.g., DIAMET and PANDOWAE.

3.   High-impact wet snowfall
Poor forecasts for wet snowfall event in NW Germany in Nov 2005 
transition from rain to wet snow poorly predicted by ECMWF and COSMO models
issue of correctly predicting position of surface cyclone 
Frick and Wernli 2012 (WaF)

4.  Sting jets: high-impact winds in cyclones
Complex dynamical & physical processes on various scales
Frontal structure of cyclone
Conditional symmetric instability?
Sublimation of ice particles?
Stability of BL and vertical momentum transport 
Clark et al (QJ)
Sting jet within cyclone Friedhelm
(8 Dec 2011), observed during the DIAMET field experiment

5. Heavy precipitation events: Stability vs. transport
Role of conditional instability (CAPE) and horizontal moisture flux varies for different events
Nuissier et al (QJ)

6.  Heavy precipitation events and long-range moisture transport
Flooding event in Bernese Oberland in October 2011 
plume of moisture extending from the tropics to central Europe (cf. atmospheric river, tropical moisture export)
link to ET of Philipp
from Nicolas Piaget

7. Pfahl et al., in preparation
Relevance of synoptic systems for precipitation extremes
% of HPE associated with cyclone or WCB
HPE defined as >99 percentile in ERA-Interim dataset
Pfahl et al., in preparation

8. Case study of major forecast bust
5-day ECMWF forecast from 12 UTC 13 Jan 2005
SLP average over C. Europe
analysis hPa
deterministic fc hPa
EPS – 1037 hPa !!
 what happened meteorologically?

9. Case study of major forecast bust
T850 and SLP
ana +3.5
ana +5
fc +3.5
fc +5

10. Case study of major forecast bust
PV on 320 K
ana +3.5
ana +5 T1 R1 T1 R1
fc +3.5
fc +5 T1 T1 R1 R1

11. - - Hypothesis: errors in WCBs amplify downstream+
generation of a positive PV anomaly
(downstream trough)
WCB  amplified upper-level ridge  downstream trough
WCB triggers / enhances downstream Rossby wave activity

12. Warm conveyor belts
Microphysical processes diagnosed in COSMO simulation
Joos and Wernli 2012 (QJ)

13. T-NAWDEX-Falcon: IOP3 (19/20 Oct 2012)
In-situ observations in warm conveyor belts
from Maxi Böttcher

14. Tropopause polar cyclones
Long-lived mesoscale vortices associated with diabatic processes
radiative heating
latent heating
TPCs are frequent and fairly long-lived (> week)
TPCs can trigger / amplify waves along jet
TPCs are associated with characteristic pattern of radiative and latent heating
Kew et al (MWR)
Cavallo & Hakim 2010 (MWR)

15. Longer time scales: cold winters & hot summers
Cold winter 2005/06 in Europe: five events of upstream blocking
blocking events
blocking
cold
temperature
influence from upstream weather systems
Croci Maspoli & Davies 2009 (MWR)

16. HIW-related research projects
T-PARC, DIAMET, PANDOWAE, Prevassemble, …
strong (international) collaboration
collaboration between weather services & universities
linkage of observational & modeling research
strengthen research with benefit for operational forecasting at universities
education of next generation of “weather scientists”
 key component of future WWRP HIW Project

17. Scientific challenges for future HIW project
Scale-interactions of dynamical and physical processes including large-scale, mesoscale & microscale
Non-linear processes & thresholds
Upscale and downscale forecast error propagation
Interaction of atmospheric water cycle and dynamics
Interaction of cloud microphysics and dynamics
Specific model evaluation for HIW events
Quantify benefit from convection-permitting models for HIW
Link communities from nowcasting to (sub)seasonal prediction