Normals Reveal Valley and Summit Temperature Increases, Among Other Climate
By Brian Fitzgerald, Director of Science & Education | November 15,
Chances are, you’ve heard a meteorologist refer to weather conditions as
near, above, or below “normal.”
But just what is normal for where you live? Who gets to say? How is it
Every 10 years, the National Centers for Environmental Information
[(NCEI) formerly known as the National Climatic Data Center] are charged with
generating climate statistics known as U.S. Climate Normals, based on
requirements from the World Meteorological Organization (WMO) and National
Weather Service (NWS).
These statistics are calculated for thousands of locations throughout
the country, across a uniform 30-year period, and serve as a baseline to
compare against weather forecasts just like the one you might have seen today.
Statistics such as daily, monthly, seasonal, and annual averages of
temperature, precipitation and other climate variables are computed for roughly
15,000 stations nationwide, including the summit of Mount Washington based on
weather data transmitted from Mount Washington Observatory (MWO) staff. With
the anticipated release of the new normals in late spring 2021, MWO staff
naturally wondered: what has changed?
As countless investigations such as the US National Climate and IPCC
assessment reports have shown, a warming planet has led to climate changes
throughout the entire globe, with regionally specific trends. Changes unique to
Mount Washington, as shown by Murray et al. (2021, “Climate Trends on the
Highest Peak of the Northeast: Mount Washington, NH”) include
elevation-dependent warming rates over many decades. With this in mind, many
were curious: What if any evidence of climate change could be seen by comparing
the 1981-2010 and 1991-2020 climate normals, even though these two datasets
have 20 over-lapping years between them.
To help us answer some of these questions, our summit interns, with
guidance from NH State Climatologist Mary Stampone (a MWO trustee) and myself,
took on the investigation this past summer to help us understand not only what
may have changed on the summit (KMWN, 6,288 ft.), but also up and down the
Mount Washington Valley at sites including Pinkham Notch Visitor Center (GHMN3,
2,025 ft.) and North Conway Village (NCON3, 522 ft.). As the interns began to
compare each station’s 1991-2020 climate normals set versus the older 1981-2010
set, three broader stories began to appear:
An increase in annual average
temperature, with variation among the three sites.
As shown in the data table below, all three sites saw annual average
temperatures increase in the new normals, with North Conway showing evidence of
warming every single month of the year. All told, the annual average temperature
at North Conway is +1.6F degrees warmer than the previous set of normals. Mount
Washington’s annual average temperature warmed +0.7F degrees, while Pinkham
Notch saw a nearly even split between months that warmed or cooled in
comparison, making an annual average temperature that warmed just +0.2F
1. Mean average monthly and annual temperatures for KMWN, GHMN3, and NCON3, New
Hampshire, for 1991-2020 (with comparison to the prior 1981-2010 normals).
An increase in annual
average snowfall, particularly later in the season.
When comparing the three
sites and their relative changes in annual snowfall, Pinkham Notch surprisingly
saw the largest increase for total snowfall. Among the sites, Mount Washington
now averages 281.8 inches annually, with Pinkham averaging 135.8 inches, and
North Conway 84.0 inches. Pinkham’s increase to 135.8 inches annually is now
9.7 inches higher than in the previous normals, versus 4.0 inches more in North
Conway and just 0.6 inches more on the summit of Mount Washington.
In addition to the
variations among the three sites, it was notable that within the snow season,
all three stations saw an overall increase in snowfall in February (see Figure
1.). This increase across the board slightly later in the snow season is worthy
of a closer look to understand how the nature of our winters are changing, and
what the impacts may be to the region’s snow packs.
1. Change in liquid equivalent snowfall at KMWN, GHMN3, and NCON3 between the
1981-2010 and 1991-2020 climate normals.
Changes in precipitation
varied drastically among the three stations.
Finally, when comparing
the three stations’ new precipitation normals versus the prior set, fairly
noticeable variation throughout the year, and from station to station, seems to
appear. Overall, precipitation dipped more than five inches annually on average
at Mount Washington, while Pinkham Notch gained almost five inches, and North
Conway saw a marginal annual increase of 0.5 inches (see Figure 2.).
2. Change in precipitation at KMWN, GHMN3, and NCON3 between the 1981-2010 and
1991-2020 climate normals.
One area of consistency
among the three stations appeared in October, where a general increase in average
precipitation totals was observed. From a meteorological perspective, the team
was unable to complete a forensic investigation of particular storms or weather
patterns in the 2011-2020 timespan that may have accounted for this increase;
however, best guesses at this stage may point to an increase in the intensity
or perhaps even frequency of extreme precipitation events from coastal,
bomb-cyclone type nor’easters.
All together, the
investigation comparing the new climate normals versus the prior set across the
Mount Washington Valley has uncovered some broad-based differences and a number
of lingering questions. Future investigations into these datasets could shed
light on precisely what, if any, shifts in the snow season may be occurring,
and how such changes may differ across a variety of mountainous terrain and
Although this investigation
was a comparison of two largely overlapping datasets, versus an analysis of
longer-term climatological data, the research conducted by our summit interns
has given MWO a clearer understanding of what our “new normal” on the summit of
Mount Washington is. If you’re curious to learn what your “normal” weather is
in your backyard, we encourage you to visit ncei.noaa.gov to search for climate
normals near your town. Additionally, to learn more about MWO’s recent climate
normals project and read the summary report, visit mountwashington.org/research.
MWO Observers Jay Broccolo and Sam Robinson, and MWO
summer interns Alexandra Branton, Michael Brown, Madeline DeGroot, and AJ
Mastrangelo contributed to this story.