Today is Big Wind Day, commemorating the 231 mph wind gust recorded by Mount Washington Observatory staff on April 12, 1934.  

 

Since the earliest days of observing weather on the summit, measuring wind speeds has been a challenge. Heavy icing conditions and extreme winds are enough to damage common measurement devices, rendering them inadequate for maintaining our 90 years of continuous weather and climate data. In the early years of the Observatory, the necessity arose to have an instrument that could accurately measure high winds and maintain accuracy during severe icing.

 

To this day, there are no commercially available instruments that could survive a Mount Washington winter, let alone accurately measure wind speeds throughout the cold season. To combat this, MWOBS has accomplished numerous innovations in measuring wind speeds through the development of heated anemometers. Adding a heater allowed for these instruments to survive the summit’s icing conditions, and the Observatory has spent the decades since improving and perfecting a custom designed heated pitot anemometer.  

 

Beginning back in the late 1800s, the Blue Hill Observatory originally loaned some cup anemometers to the Observatory, beginning a record of wind speeds. However, these anemometers were non-heated, preventing a continuous record in the wintertime icing conditions. The cup anemometers remained in use as primary instruments through 1946. From then until 2005, the Observatory used them occasionally as backup anemometers in light wind and light icing conditions.

 

Attempts to overcome icing conditions led to the development of a heated anemometer, aptly named the Heated No. 1. With a new heating element, this anemometer could counter winter ice accumulation. Implemented on Nov. 9, 1932, Heated No. 1 was able to take measurements when winds were between 11-120 mph in icing conditions. 

 

After it went up, efforts to improve Heated No. 1 resulted in the Heated No. 2 becoming an operational instrument. Heated No. 2’s improvements over No. 1 included a sheltered heater with a vent around the shaft, a 700-watt double-circuit heating device, and vacuum contacts for electrical recording.

 

Heated No. 2 became the main instrument on the summit in 1933, replacing Heated No. 1. Heated No. 2 is most famous for recording The Big Wind of 231 mph on April 12, 1934, which still stands as the fastest surface wind speed ever observed by a human. Measured in extremely challenging icing conditions, the measurement was extensively verified, setting the standard of data quality for MWOBS weather observers throughout our history. The Heated No. 2 is currently on display in the Extreme Mount Washington™ museum on the summit. 

 

Shown above are Mount Washington Observatory staff Alex McKenzie, left, John Dick, and Aubrey Hustead, holding the Heated No. 2 Anemometer.   

 

 

Later on into the Heated No. 2’s lifespan, questions emerged surrounding its performance in periods of high winds and heavy icing. Beginning in the winter of 1944-45, testing for using an operational pitot tube anemometer began. The idea for using a pitot tube was borrowed from the aviation industry, since pitot tubes were proven to be able to measure wind speeds much faster than those experienced on the summit. The tubes were attached to the nose and wings of an airplane, analyzing the free-air pressure and the measured pressure at the plane, and then calculating the relative airspeed from the difference.

 

The tubes themselves were commercially available, so once determined that a pitot tube could properly measure wind speeds on the summit, all that was necessary was to build the housing. Observatory staff got creative and constructed a mast and skirt out of a repurposed tin vegetable can. With these, in 1946 the Grandfather Pitot became the Observatory’s main instrument for measuring and recording wind speeds. Its advantages over the Heated No. 2 included that it automatically corrected the barometer to free-air pressure, had no moving parts, and could accurately measure instantaneous gusts and average sustained wind speeds directly from the recorder. Previously, observers would calculate these two data points by hand.

 

The Grandfather worked well for speeds above 30 mph, but winds less than that often could not deliver the torque necessary to vane the tube into the right direction. In these instances of lighter winds, using the cup anemometers as backups came in handy. The Grandfather was then retired in 1992, and, through 2022, remains the summit’s longest-used primary anemometer. 

 

In 1990, the “Pitot Project” began, looking to build a replacement for the aging Grandfather. Primary goals of the project were to simplify maintenance and implement newer technologies to upgrade performance. The Pitot Project developed four similar pitot tubes used through the 1990s and 2000s – Pitot 92, Pitot 94, Pitot 97, and Pitot 99. Respectively, these pitots were functional instruments on the summit during 1992-2000, 1994-97, 1997-2011, and 1999-2011. 

 

Pitot 92’s design process focused on building the heated vaning assembly. It featured an improved heating system capable of fully automated and ice-free operation and custom-machined aluminum body parts alongside other commercially available components. These allowed for modular design and easier standardization of repair processes.  

 

Pitot 94 then included a new and improved heater control system, as well as a custom chart recorder interface for the Observatory’s wind direction instrument. The design improvements built a linkage between the wind direction instrument and the Pitot 94, thereby eliminating the need for one of the wind vanes. MWOBS used Pitot 94 primarily as a backup for Pitot 92. In the summer, the Observatory used the Grandfather Pitot as a backup as well.

 

As the Pitot Project continued, the Observatory analyzed various retired pitots and identified instances of inconsistent performance and calibration. Observers found very slight variances in wind direction and speed from one pitot to the next, although each measurement was within reasonable margin of error. Observers looked to ensure that all measurement tools on the summit remained consistent to one another.

 

Measures to rebuild Pitot 94 birthed the Pitot 97, which had a new heater controller subsystem, weather room display and control subsystem, pressure transducer, and data subsystem. When implemented, Pitot 97 was the primary means of accurately measuring winds up to 250 mph in any conditions. The Observatory then later rebuilt the Grandfather Pitot as the Pitot 99, serving to supplement Pitots 92 and 97 as summer and light icing backups.

 

In the 2000s, new technologies and instruments arose. Beginning in summer 2005, the Observatory has used various RM Young propeller anemometers for wind speeds below 30 mph with light-to-no icing conditions. The RM Young models replaced the use of cup anemometers. RM Young wind monitors are now used in conjunction with the pitot system throughout the summer months.

 

 

As time went on, Pitots 97 and 99 began to show their age. Work began to develop new pitots to replace the models. Pitot 97, the main instrument, had begun to experience recording issues before the Observatory was able to replace it. In this instance, Pitot 99 and an unnamed backup pitot served as the main recording devices.

 

Early in January 2011, work on the Pitot 11 concluded. Pitot 11 went up as Pitot 97 came down, and Observatory staff found that Pitot 97’s housing contained about a cup of water, the pressure line became disconnected, and there was significant corrosion on the wires. Pitot 11’s improvements over 97 included new heat tapes, a heated tube, and new insulation. Pitot 11 served as the Observatory’s main instrument through 2017, when Pitot 17 took its place.

 

Pitot 17, referred to as the “sister” to Pitot 11, is structurally identical to Pitot 11, with improved skirt heaters and bearings. In 2019, Pitot 17’s bearings needed replacement, so Pitot 19 took its place. Pitot 19 is again a sister pitot to Pitot 11, structurally identical to the prior two pitots. Pitot 19 included repaired bearings and features to enhance heating and to simplify data transmission. Pitot 19 is currently in use on the summit, functioning as the current primary pitot and air pressure measurement device.

 

In April 2013, a group of UMass Lowell students published a paper analyzing certain factors and their effect on the Observatory’s wind speed measurement system: tubing length between the transducer and pitot tube, system leaks, and the pitot tube’s angular orientation. They concluded and recommended to the Observatory to shorten the tubing length, implement methods to minimize leak zones, and to maintain the current pitot tube angle and mount. With these recommendations, work began to develop the Pitot 22.

 

Conceptualized as the next generation of pitot anemometers, Pitot 22 resulted from a multi-year collaboration between MWOBS, General Electric, and UMass Lowell. Its improvements include a more simplified design for easier removal and installation, shorter tube length, improved gust sensitivity, and an upgraded heating system. Construction began in 2015, and Pitot 22 was first installed on the summit in August of 2018, having been recently reinstalled in January 2022 after third-party testing from the University of New Hampshire. Currently, MWOBS is in the final stages of testing before designating Pitot 22 as the primary wind measurement instrument.

 

 

 

Adam Muhith earned a B.S. in Environmental Engineering from the University of Texas at Austin in 2021. He joined our summit team as an intern in fall 2021.