An intense extratropical storm, named Erwin/Gudrun, over the North Atlantic during winter 2005 is investigated to determine atmospheric factors contributing to its development. WRF is the numerical model which has been used to simulate the storm. The simulations of the extratropical storm are devided into two sets. The first set contains 66-hour simulations that describe the effect of latent heat release. The second set contains 90-hour simulations, and this set together with the first set describes the effect Greenland’s orography had on the cyclogenesis. Gudrun was a cyclone that caused heavy rainfall and winds exceeding 30 m/s over the Skagerrak region on January 8th. The storm was strongly affected by the release of latent heat. When latent heat is removed the cyclogenesis is much weaker, and the results reveal that latent heat contributed 38% of the rapid deepening during the first 48 hours of the simulation. In the 90-hours simulation, when orgraphy over Greenland is present (Control90), the extratropical storm never appears and the cyclogenesis of Gudrun never takes place. Conversely, in the NOGREEN90 run, when orography over Greenland is removed, stronger cold advection eastwards contributed to the evolution of Gudrun.