NWP skills for operational meteorologist

Case 1. Between April 2. and April 4. 2018, gale to storm force winds from the west propagated from Cape Farewell, the southernmost point of Greenland over 1000 nautical miles across the Atlantic towards and past the Faroes Islands with high waves. This type of eastward wind/wave field propagation south of Iceland happens few times a year with varying intensity. Case 2. A showcase of the westerly Greenland tip jet creating large waves – but looking at the forecasted winds and waves versus observations, they seem contradictory, making the forecaster think twice.

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Several countries along the North Sea have densely populated areas and major political and economic activities close to the coast - places that are vulnerable to storm surges. To protect these areas coastal defence requires continuous attention. Several storm surge barriers have been constructed over the last decades that can be closed if the water level rises too high. Examples are the Thames Barrier in London and the Maeslantkering near Rotterdam. To alert local authorities and to operate the movable barriers efficiently, good and timely storm surge forecasts are essential. These forecasts make use of state-of-the-art meteorological forecasts and techniques like ensemble forecasting. This presentation will focus on the situation in The Netherlands, where storm surge forecasts are generated in close cooperation between the Water Management Centre Netherlands (WMCN) of Rijkswaterstaat and the Royal Netherlands Meteorological Institute (KNMI).

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Due to the Azores geographical location, this archipelago is occasionally affected by strong Extratropical cyclones and Tropical cyclones. Extratropical cyclones are more frequent in winter and are often associated with strong winds, heavy precipitation and heavy waves which can be damaging and contribute to social and economic distress. Tropical cyclones, on the other hand occur mostly in September and October and in the past have caused loss of lives and property damage. Forecasting this type of systems is very challenging, mostly because a small variation in path can cause large difference in the impacts. This talk presents some tropical and extratropical cyclones that affected the Azores and also the challenges that forecasters face in this situations.

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The Mediterranean tropical-like cyclones are intense sub-synoptic maritime lows with strong winds, axisymmetric warm-core structure and tropical cyclone features, such as a cloud-free eye and spiral deep convection. They are frequently referred to as medicanes (MEDIterranean hurriCANES) due to their resemblance to tropical cyclones. Despite their low frequency (of about 1.1-1.6 systems per year), medicanes constitute a serious natural hazard to life, property and the environment of the coastal regions of the Mediterranean basin and the Black Sea. Their accurate prediction is a challenge for the numerical weather prediction models. This presentation includes some past cases of medicanes, the description of their structure and characteristics, criteria that are used to define them, the development mechanisms, climatology, consequences and finally a detailed case study of medicane Qendresa (November 2014).

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ECMWF provides the Extreme Forecast Index (EFI) and Shift Of Tails (SOT) as tools to help forecasting anomalous and extreme weather by measuring the difference between the Cumulative Distribution Function (CDF) of the real-time ensemble forecast and the model climate (M-climate) CDF. The definition of the EFI and SOT will be presented alongside the M-climate configuration. Verification results and EFI/SOT products will be shown with examples to demonstrate their use and interpretation. Some advantages and limitations of the EFI and SOT will be discussed. Examples focused on the available EFI/SOT for marine forecasting will be given as well. Two recent EFI/SOT products for forecasting severe thunderstorms and their interpretation and practical use will be demonstrated.

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Wave models are able to give a very detailed description of the conditions at the surface of the oceans. The mean sea state is fully described by the 2d wave spectrum. This detailed description is however not always very practical and the bulk of the information contained in the 2d spectrum is usually reduced in the form of a set of integrated parameters, from a simple few such as significant wave height, mean wave direction and mean wave period, to more sophisticated parameters that described distinct part of the wave fields. Recent advances in the understanding of wave dynamics have lead to the development of new set of parameters that give information on the possible largest single wave that might exist over a certain area within a certain time frame. It is now possible to describe the sea state with different level of complexity depending on the user needs.

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The EUMETSAT-operated Copernicus Sentinel-3A satellite has been providing near-real time data to the marine community since mid-2016, and will be soon be joined in operations by its sister, Sentinel-3B. This presentation will give an overview of the available Sentinel-3 marine products, with a primary focus on data streams associated by the altimeter (SRAL) and sea surface temperature radiometer (SLSTR). Examples of the relevant applications will be presented, along with a discussion of how users can best access data and monitor its quality.

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Satellite image interpretation of shallow clouds and related weather phenomena is a very important task for nowcasting because NWP-models and statistical methods exhibit still deficiencies in simulating these phenomena in a proper way. Especially over oceans but also over land observation networks are often too coarse meshed for nowcasting.
The theory and the most suitable satellite products will be explained first. In combination with other data (e.g., observations, radio soundings, radar products) examples will be discussed for the following application areas:

1. Diagnosing shallow clouds in respect to water content and related weather, e.g., drizzle of different intensities;
2. Identifying fog and low stratus and how to estimate the fog/stratus layer’s thickness. The likelihood of dissolving and connected weather phenomena (e.g., freezing drizzle) will be covered, too.

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Convection can be found everywhere on the planet. However in meteorological way of thinking in mid-latitudes there is convection in different airmasses and also at the boundary of these airmasses. Convection at the boundaries belongs to the sub-features of frontal systems and we won’t deal with convection in the frontal systems.
In this lecture a few examples of unstable air Conceptual models will be shown, for instance: Cumulonimbi, Enhancement of convection by PV, Spanish Plume, etc. The typical environment is one part and the organization modes is the second part of the lecture.

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Gravity waves are omnipresent in the atmosphere. In this presentation you will hear more about the different wave types, their appearance in satellite imagery and about their physical background.
Most gravity waves are generated by orographic elevations and in this case we call them lee waves. They can present a serious threat to aircrafts when the air flow changes from laminar to turbulent or when rotor clouds are generated. When this happens without accompanying condensation processes, the phenomenon is called "Clear Air Turbulence" (CAT). In many cases, waves in the atmosphere are accompanied by a characteristic cloud pattern visible in the IR and VIS imagery that helps in identifying regions potentially hazardous for aircrafts.
Gravity waves can however also result from internal friction/shear processes when two layers of air with different physical properties (e.g. temperature, density, wind speed ...) are acting one on the other. This wave type is called Kelvin-Helmholtz wave. Turbulence caused by velocity and directional shear are relatively common in the upper Troposphere in the regions of jet streaks.

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There are a number of structures and processes happening after a cold front has passed an area, e.g. enhanced cumuli, commas, instant occlusions, etc. Commas, for example are meso-scale structures developing within cold air, often behind frontal cloud bands. They occur mainly during the cold season and are a common feature for Northern and Western Europe - nevertheless commas can also be found in the south. As commas can cause severe weather this conceptual model is of high interest for forecasters. In this lecture life cycles of commas will be shown, what do commas form from, what can they form into, how they are connected to other mentioned phenomena and how they appear in satellite imagery - seen by MSG and polar orbiting satellites.

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Precipitation within extratropical cyclones often organizes into mesoscale substructures known as precipitation bands. The purpose of this presentation is to better understand how precipitation organizes into bands. We will discuss about Shapiro-Keyser and the Norweigan models of cyclones, why do they form, the differences between them, also where in cyclones precipitation bands form, their structures and evolutions, what controls their locations and intensities, and techniques to diagnose precipitation bands. In the end we will discuss about occlusion bands and how do they actually form considering latest researches.

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