In winter the whole of Mongolia comes under the influence of the Siberian Anticyclone. The localities most severely affected by this cold weather are Uvs province (Ulaangom), western Khovsgol (Rinchinlhumbe), eastern Zavkhan (Tosontsengel), northern Bulgan (Hutag) and eastern Dornod province (Khalkhiin Gol). Ulaanbaatar is strongly, but less severely, affected. The cold gets less severe as one goes south, reaching the warmest January temperatures in Omnogovi Province (Dalanzadgad, Khanbogd) and the region of the Altai mountains bordering China. A unique microclimate is the fertile grassland-forest region of central and eastern Arkhangai Province (Tsetserleg) and northern Ovorkhangai Province (Arvaikheer) where January temperatures are on average the same and often higher than the warmest desert regions to the south in addition to being more stable. The Khangai Mountains play a certain role in forming this microclimate. In Tsetserleg, the warmest town in this microclimate, nighttime January temperatures rarely go under  while daytime January temperatures often reach  to .