The Predictability of Northern Hemispheric Blocking using an Ensemble Forecast System

Some weather extremes can be the effect of amospheric blocking. Like atmospheric patterns that tend to repeat themselves, atmospheric blocking leads to the stagnation of weather patterns. This repetition can last for several days to weeks. These large scale quasi-stationary extreme mid-latitude flow regimes can lead to above or below average temperatures along with possible below and above average rainfall, depending on the location of the block. Being able to predict these possible extremes due to atmospheric blocking is a major problem for medium-range forecasting. Analyzing NCEP Ensemble 500-mb pressure patterns (240 hrs.) ten days out forecast and using the block intensity index and the University of Missouri blocking archive to identify blocks and the duration, intensity and prediction in comparison to observed blocks prediction. Comparing these differences over a one-year period across the Northern Hemisphere has improved the predictability of these blocks and their intensity. Having a better understanding of knowing how long each block will last and the damage they can cause and better prepare potential affected areas. Knowing how to correctly identify blocks is important in improving forecast issues. Blocking events in the NOAA Ensemble products were underforecast in their durration and intensity.