The pick of the day climate signal is the Pacific North America (PNA) regime. The 15-day outlook reveals ongoing negative phase into the weekend helping to fuel a Pineapple Express into Washington, shift to positive phase next week causing an amplified upper ridge to roast the Southwest U.S., and return to negative phase sustaining the cool/stormy North and warm/dry South split pattern.

At midday, most forecast models agree that cross polar arctic air moves into North America and gains (anomalous) intensity flowing southward into the North-central/East-central U.S. March 16-17. At that time a small but potent polar vortex enhances the cold. This event may be related to the breakdown of a lengthy stratospheric warming event in the polar region.

At midday, 7 of 14 forecasts (combining dynamic and AI models) are cold in the East during the 11-15-day period. ECM OP and Weather Next V2 appear coldest while GFS OP is warmest. Support from climate signals to substantiate the cold forecast is poor. However, the mega-cluster ensemble “most likely” March 17th scenario is heavily biased by ECM which supports vigorous chill in the East and equally impressive warmth over Nevada. ECM, GFS, and CMC are near equally shared to generate a “caveat” forecast for March 18 which is very cold across the eastern half of the U.S.

Northeast Brazil is shifting much wetter and parts of Northeast Argentina are also thundery. 15-day forecasts are wetter across both Brazil and Argentina. One catalyst to the potentially wetter regime is the increased moisture availability of warm SSTA off the West Coast and Nino12 SSTA region. Keep in mind, ongoing wet bias remains with all models in 15-day forecasts.