PORTLAND, Ore. (KOIN) — Drought has returned to the Northwest corner of Oregon after an unseasonably dry fall. Last week, large swaths of Multnomah, Columbia Clatsop and Tillamook Counties were upgraded from “abnormally dry” conditions to “moderate drought,” according to the U.S. Drought Monitor.
Oregon state climatologist Larry O’Neill told KOIN 6 that the region will need a steady supply of rain for the conditions to improve.
“The degradation into moderate drought category was due to relatively dry surface soils and much lower than normal stream flows,” O’Neill said. “It will take several inches over the next couple of weeks to recharge the shallow groundwater, allowing for improvement in drought conditions.”
While the Pacific Northwest is forecast for a third consecutive La Niña weather pattern this rainy season, O’Neill said that the state’s annual weather has been unpredictable.
“In spring 2021, Oregon experienced one of the driest springs on record, followed by one of the wettest springs on record this year, despite similar La Niña conditions in each year,” he said. “The last two summers have also been among the warmest in Oregon’s recorded history. Oregon has experienced historical volatility and swings in its weather which has made drought monitoring and seasonal forecasting extremely challenging.”
The upcoming La Niña is forecast to be somewhat weaker than the Pacific Northwest’s previous two La Niña seasons. Despite Oregon’s dry, sunny start to fall, O’Neill said a La Niña still spells cooler winter temperatures and above-average precipitation for the region. Chances for low-elevation ice or snow also increase.
“Any impact of La Niña on the weather in the Pacific Northwest usually peaks in the winter months,” he said. “So, a dry and warm fall does not necessarily lead to a dry and warm winter. It is important to remember that these historical analogs occurred before climate change became more apparent. Winters during recent La Niña events in the last 10 to 15 years have not been quite as cold or wet, which has led to significant year-to-year variability in the snowpack.”
Based on this information, O’Neill is predicting near-average rainfall totals and slightly above-average snowpack in the Cascades for Oregon in the coming months.