Does Mount Washington Weather Vary Consistently with the Dominant Large-Scale Atmospheric Pattern in the Region


Emma Penafiel – John Hopkins University in Baltimore, Earth and Planetary Sciences
Observer Guide – Ryan Knapp
Mentors – Al Wheeler (retired National Weather Service), Mary Stampone (NH State Climatologist, UNH)

Mount Washington weather does not vary consistently with the El Nino-Southern Oscillation, which originates in the tropical Pacific Ocean. So does Mount Washington weather respond more consistently to other dominant large-scale patterns, such as the North Atlantic Oscillation (NAO)? The NAO describes the variability of the strength of the dominant pressure centers in the North Atlantic Ocean: the Icelandic Low and Azores High. For many low elevation sites in the Northeast US, a negative phase of the NAO often means colder and/or more snow because the jet stream dives south into the Mid-Atlantic region. A positive NAO often means warmer and/or rainy conditions as the jet stream retracts to the north. The NAO is a strong pattern during the cold season (November-March). In the warm season (April-October), the NAO becomes weak as the jet stream retracts toward the Arctic.

This research project correlated NAO phase with Mount Washington temperature and precipitation for the cold and warm seasons. Overall, there were not strong correlations for temperature or snowfall with the NAO when using the raw NAO index values; only up to ~6% of their variability was shared. However, these correlations became significant and strong (>65% of their variability was shared for the cold season) when the seasonal NAO index values were binned into 0.5-unit bins. The strongest correlation was for cold season temperature (76% variability shared) such that negative NAO values correspond with colder temperatures for the cold season. Improvements in seasonal forecasting of large scale patterns like the NAO will help improve local forecasts on Mount Washington and other locations. In addition, climate model projections of the NAO during the next 80 years will help inform decision-makers and planners when making business decisions and decisions about infrastructure and land-use.

A diagram showing the jet stream pattern and weather conditions associated with the negative (left) and positive (right) phases of the North Atlantic Oscillation pattern. The Icelandic Low (L) and Azores High (H) are weaker during the negative phase and stronger during the positive phase. Source: NOAA: https://www.climate.gov/sites/default/files/NAO_Schematic_0.png

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