#MWOMETMONDAY on a Tuesday!
2015-10-27 19:37:13.000 – Andrew Henry, Summit Intern
We had a great question referring back to my last blog
which was about snowfall statistics on the summit.
This week, Joshua asked if there is a correlation between strong El Niño years and the amount of snow seen on the summit.
Before going into depth about the correlation between El Niño and snowfall at Mount Washington Observatory, it is important to understand what El Niño is. El Niño is the warm phase of the El Niño Southern Oscillation, commonly referred to as ENSO. It is associated with a band of warm sea surface temperatures (SSTs) that develops in the central and the East-central equatorial Pacific (5˚N-5˚S, 120˚W-170˚W). ENSO is measured using the Oceanic Niño Index (ONI), which is the standard that the National Oceanic and Atmospheric Administration (NOAA) uses. ONI is the running 3-month mean SST anomaly in the central and East-central equatorial Pacific. El Niño events are defined as 5 consecutive overlapping 3 month periods at or above a + 0.5˚ anomaly.
Mount Washington Observatory was founded in 1932 and reliable hourly weather observations began being kept in 1935. Throughout the observatory’s 80+ year record the typical year sees an average of 281.2” of snow. That is over 23 feet! During its snowiest season on record (1968-1969), the summit saw twice its average annual snowfall with a whopping 566.4” or approximately 47 feet of the white stuff falling! Many records were set from November 1968 through February of 1969. November and December of 1968 and February of 1969 all set records for not only monthly snowfall totals, but 24 hour snowfall totals as well! The most impressive records came in February of 1969 with 172.8” falling during the month and 49.3” in 24 hours.
A weak to moderate El Niño was present during the record setting winter of 1968-1969. The El Niño event persisted from October of 1968 through July of 1969 with ONI values ranging from 0.5-1.0. The El Niño event reached its maximum strength with an ONI value of 1.0 during February, the snowiest month of the winter. In addition to November and December of 1968 and February of 1969, the snowiest January (1978), May (1997), July (1957), and August (1965) all occurred during weak to moderate El Niño events. The snowiest March, April, June and October on record all came during neutral phases of ENSO following winters that experienced a weak to moderate El Niño phase. A neutral phase of Enso means the ONI values are less than 0.5, but greater than -0.5. The snowiest September on record at the summit occurred in 1949, the year prior to which the Climate Prediction Center (CPC) began keeping records on El Niño.
The table below depicts Oceanic Niño Index values. El Niño events occur when ONI values are 0.5 or greater and are colored red. La Niña events occur when ONI values are -0.5 or less and are colored blue. The Monthly snow fall records are highlighted in the year they occur.
In the graphs below I compare the ONI values for October-December of 1967-1970 (left) to the snowfall averaged over the months of October-December of 1967-1969 (right).
In the graphs below I compare the ONI values for January-March of 1967-1970 (left) to the snowfall averaged over the months of January-March of 1967-1969 (right).
By analyzing this data it appears there is a positive correlation between weak to moderate El Niño events and the record breaking winter of 1968-1969 here on the summit. This means that the summit has seen some of its snowiest conditions during weak to moderate El Niño events.
For the United States El Niño typically results in a more southerly storm track which often brings above average snowfall to the southern third of the country. If things come together just right and a blocking pattern sets up, the storm track makes a northward turn along the East Coast bringing large amounts of snow to the Mid-Atlantic and New England.
Referring back to the question as to whether there is a correlation between strong El Niño events and snowfall it is unclear from this brief analysis, however there does appear to be a correlation between weak to moderate El Niño events and snowfall. This is not a peer reviewed correlation study and more analysis needs to be done in order to determine the effects of strong El Niño events at the summit specifically. One of the strongest El Niño events in history occurred during the winter of 1997-1998. According to a study from the National Centers for Environmental Information (NCEI) the first two months of 1998 were the warmest and wettest in the 104-year record of temperatures and precipitation measurements for the contiguous United States. The summit was no exception with temperatures 10.5˚ above average in January and 14˚ above average in February. In addition to well above average temperatures, January and February saw snowfall totals approximately 13 inches below average. As we head toward the winter of 2015/2016 we are currently in a strong El Niño pattern. Will this upcoming winter be a repeat of the 1997-1998 winter? I’m excited to find out! More information about the current El Niño and its expected effects on the United States this winter can be found here
Andrew Henry, Summit Intern