A major change in the weather pattern over Alaska is underway, as flow from the north is about to bring serious cold over most of the state. The charts below show two of the leading computer model forecasts for Tuesday afternoon; the color shading indicates temperature departure from normal at 850 mb, and the dotted lines show the 500 mb height. Both models show a cold upper-level trough extending from northwest Canada into interior Alaska, and below-normal temperatures. The agreement is fairly good, although the ECMWF solution is more extreme, showing 850 temperatures more than 15 °C (27 °F) below normal. At this time of year, that's cold.