Still working out what La Nina bodes for northwest spring

January 14, 2018

Weather Insights are provided by Northwest Farm Credit Services by Dr. Eric Snodgrass, one of the nation's top 40 meteorologists, to enhance farm production and seasonal planning. Dr. Eric Snodgrass December 2017 was a month of transition. At times, the flow of the jet stream bowed into a large ridge that brought well-above-average temperatures and drier conditions racing north along the coast. Occasional west winds did bring in enough precipitation to keep most of Washington and Idaho near average, but interior parts of Oregon and Southern Idaho have had a slight dry bias. Drought in the Pacific Northwest is largely confined to Eastern Montana, where drought has lingered since summer/fall 2017. Current soil moisture levels are low only in pockets in the Northwest, but mountain snowpack is below average through the start of January for most reporting stations outside of the mountains in Montana. Winter wheat growers should note the extremely dry conditions in the central U.S. This same region has also dealt with bitterly cold, below 0°F temperatures to start the new year. Outside of the U.S., we are watching Russia’s wheat belt and the growing region near the Black Sea and Mediterranean. The last 30 days have been wetter than average for this region while temperatures have been above normal. Pockets of very dry conditions have developed late this fall and winter in China, and parts of Argentina have been dry, too. There will be a lot of discussion over the coming months about the fate of the current La Niña as spring arrives. Long-range forecasts project the weak La Niña to move back toward ENSO-neutral by spring, but it is important to recognize how big of a player La Niña is in the Pacific Northwest spring weather. Historical records show that La Niña has a weak correlation with cooler March-May temperatures, but no discernable relationship exists with spring precipitation in the Northwest. Long-term trends in temperature and precipitation for the March-May time period in the Northwest have trended up slightly in both. One strong signal in the long-range model runs by the ECMWF (a.k.a. the European Model) is for the Northwest to have a wet bias for the remainder of winter. Most global models are forecasting an active Pacific branch of the jet stream, which will continue to bring strong onshore flow at times to the Northwest which will improve mountain snowpack. The first three weeks of January are forecast to feature a broader ridge at times in the jet stream, so expect a warm bias over the coming weeks. However, February and March temperatures are currently forecast to be much closer to average. Dr. Eric Snodgrass is the Director of Undergraduate Studies for the Department of Atmospheric Sciences at the University of Illinois Urbana-Champaign. He serves on numerous committees and boards on campus, including the Illinois Teaching Advancement Board, Student Sustainability Committee and the Provost Task Force on Improving Large Enrollment Courses. Dr. Snodgrass' research initiatives focus on K-12 science education as well as weather forecasting applications in financial markets.