MSLPMSLP Mean sea level pressure is the pressure at sea level, or, when measured at a given elevation on land, the station pressure reduced to sea level assuming an isothermal layer at the station temperature. anomalies in December were not too dissimilar to those of November, with the Icelandic low pushed further south into mid-Atlantic by higher than usual pressure across Greenland. Pressure was lower than average across the 55N latitude from Scotland east into the southern Baltic(-8 hPahPa A Hectopascal is the SI unit of pressure and identical to the Millibar) and higher than average (+5 hPa) to the west of Portugal. This all added up to a tight W’SW flow from the central Atlantic across England and Wales, and eastward on into Germany and Poland. All a result of a south shifted jet stream for much of the month.