The leaves have fallen, pumpkins have been discarded, and bitterly cold weather gripped much of the nation over the Thanksgiving holiday.
With winter’s arrival, many now find themselves wondering about the prospects of snow in various regions throughout the United States. Those in the mid-Atlantic area hoping to see more white precipitation this winter could find themselves disappointed.
Drew Ellis, a professor in Virginia Tech’s Department of Geography, is an expert in climate science, meteorology, and hydroclimatic variability. He recently broke down the National Oceanic and Atmospheric Administration’s winter outlook, which was released in October and predicts a mild winter for the mid-Atlantic area of the country.
It seems like there’s some disagreement between forecasters this year, with the NOAA predicting drier-than-average conditions in the lower mid-Atlantic region, while local forecasters have called for a wide range of snow outcomes. What accounts for this uncertainty?
The official NOAA winter forecast for the Mid-Atlantic region is warmer than normal (40-60 percent chance of warmer than normal, 33 percent chance of normal, and 7-27 percent chance of colder than normal) and near equal chances of above normal/normal/below normal precipitation. The NOAA forecast nationally is very much a La Niña forecast – directly out of the ENSO (El Niño – Southern Oscillation) playbook, in which the climate pattern involves changes in water temperature in the central and eastern tropical Pacific Ocean. Winter season forecasts are almost entirely predicated on the ENSO phase, with some signal of temperature and precipitation for portions of the country during an El Niño or La Niña year. For a La Niña year, we are largely between a climatological signal of wetter than normal to the northwest (Great Lakes region) and drier than normal to the south (near the Gulf Coast). So, precipitation becomes a problematic forecast for our region during a La Niña year. Also, problematic this year is that La Niña is struggling to evolve and will likely be weak/marginal. Further, as a region with modest annual snow totals, just a few storms can easily tip the scales to above or below the climatological normal amount. An episode of cold air and proper storm positioning can yield a single large snow event that can push snow totals for the region beyond the seasonal average.
How will we know when/if La Niña conditions will present themselves? How would the forecast change if this happened later than expected or not at all?
The latest forecast (Nov. 18) gives a greater than 70 percent chance of weak La Niña conditions emerging in December and persisting through March before returning to neutral conditions in late spring or early summer. La Niña conditions should emerge within the next month, albeit weakly. If La Niña fails to materialize, the forecast for the winter season in the mid-Atlantic would be even less certain than it is already. By that point, there is greater benefit of simply relying on shorter-term forecasting than seasonal forecasting.
What have we learned from past years when forecasters haven’t been in alignment?
The reality is that seasonal forecasting continues to be rather unreliable for our region. ENSO yields some predictability of winter season conditions for some regions (the far southern tier, the Pacific Northwest, and the Great Lakes region), but it is weak for our region. Frankly, misalignment of various forecasts is the norm for our region rather than the exception.
About Ellis
Drew Ellis is a professor and director of graduate studies in the Department of Geography within the College of Natural Resources and Environment at Virginia Tech. His most recent research work centers on understanding the occurrence of drought and its improved representation for monitoring and study. Ellis also focuses on assessing the sustainability of freshwater resources for populations living in arid and semi-arid climates given population growth and the uncertain hydrological impacts of climate change. Read more about him here.
Schedule an interview
To schedule an interview, contact Noah Frank in the media relations office at nafrank@vt.edu or 805-453-2556.
