Forecasting Skill & Techniques

Skill

Forecasting skill is not quantitative, and is therefore difficult to measure. OnlineWeather.org.uk attempts to forecast extreme events, such as heavy precipitation > 30mm per day, heavy snow, strong and damaging winds, and other large weather features well in advance, and to the highest possible precision that modern day forecasting allows. Since the forecast on this site is updated on a weekly basis, it is inevitable that some large events will be missed altogether. The weather is chaotic in nature, and although some features show prevalence well in advance it is not always possible to predict the precise locality or positioning of "major" weather events.

Techniques

 - Listed below are some of the resources used to compile a forecast ...

• Water vapour analysis (MSG-2, EUMETSAT) - identification of convective activity, column humidity, descent/ascent, mesoscale vortices, tropospheric folding and stratospheric intrusions, baroclinic developments
• Infrared / visible analysis (MSG-2) - High, medium and low level cloud formations, heavy thunderstorms/shower regions, stratiform cloud and fog identification
• UK RADAR image network. Bright bands, Backscatter from heavy rain, snow and hail. Current state of the atmospheric precipitation events
• Synoptic charts. Frontal positioning, evolution, average column temperature, sea ice extent / sea surface temperature, geostrophic wind speed, divergence / convergence regions, baroclinic development
• Tephigram charts. Approaching fronts analysis / classification. Split frontal features. Stability and convective potential energy (CAPE), capping inversions.
• Jet Stream Analysis. Identification of jet exit and jet entrance regions, ageostrophic ascent, convergence and divergence aloft which forces surface ascent/subsidence.


• Brain power!! Despite common mis-conception forecasters don't just look at model outputs, there is a lot of extra thought power into producing a high quality forecast. Two GFS models and NCEP multivariable data is used, which combines a whole wealth of information about the weather. These forecasts give the large scale or "macro-physical" dynamics over the future +7 to +14 days, and are highly accurate. The missing component is an experienced forecaster to interpret and analyse all this data, which involves monster multitasking and abstract thought, to visualise how the predicted weather fields are going to affect the weather experienced by the public, and localised features which may lead to extreme weather events.
  
  
• Experience!! Experience is the key to a successful forecaster. At first racking your brains over 3-5 days forecasting is not a menial task. Once this is mastered other data and information is incorporated to enhance the forecast. After 2.5 years of forecasting 5 to 6 days ahead 7-14 day GFS models and NCEP information provides the finer tuning. Knowing what areas and features to focus on is the key, as some macrophysical features of the weather exist, and past-knowledge of similar events and weather patterns under the same meteorological conditions are essential.
  
  
• Validation!! Fine tuning and "tweaking" the customer forecast charts according to past experience is crucial. Humans tend to introduce bias, especially if you are eyeing up that snow-storm in the north-sea, and other-exagerate its capacity to affect the UK. These biases are natural to man-kind. An experienced forecaster overcomes these excitements, and estimates the likely "risk" by assessing the possible outcomes under certain meteorologal conditions. Again big, features which may affect the model output from knowledge and experience of the weather.

Six main air parcel trajectories arrive at the UK, each with different properties depending upon their moisture content, temperature and whether they are mostly oceanic flows or continental. Their temperature is mostly affected by the time of year, such as the warm dry continental polar continental flow off Europe during summer, but very cold and dry airmass during Winter. The main trajectories of air parcels arriving at the UK are Tropical Maritime (mT), Polar Maritime (mP), Returning Polar Maritime (rmP), Arctic Maritime (mA), Polar Continental (cP), Tropical Continental (cT).

 

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