Amazing Glaze!

2020-04-13 12:34:08.000 – AJ Grimes, Weather Observer


Early April.  Astronomical and meteorological Spring.  In the valleys below, birds are fluttering in the trees, crickets are chirping in the woods, and new life is beginning to emerge from the ground.  However, as weather observers and those familiar with Mount Washington know, winter still has the summit firmly in its frozen grip.  On April 3rd, the observers on the summit battled one of the most intense icing events of the current winter season, resulting in some stunning photos and helping to illustrate why the Observatory needs to be manned throughout the year to maintain its operations. 

This particular event actually began on April 2nd, with light snow beginning just after midnight.  Snow lasted throughout the entire day, with rime ice also coating everything on the summit in typical winter fashion.  However, once again around midnight, things were about to change.  As the wind direction started to shift slightly to the east, warmer temperatures aloft allowed the snow to switch to a messy mix of freezing rain and ice pellets (sleet).  Instead of the light, feathery, and relatively-easy-to-remove rime ice formations, these types of precipitation form hard glaze ice.  Glaze is one of the least-enjoyed weather phenomena among observers.  Not only does it make it treacherous to navigate outside, but it can be very difficult to adequately remove from our instrumentation.  


The instrument tower coated in glaze ice.

During normal winter conditions, observers typically go to the top of the tower to de-ice our instrumentation once per hour, usually right before taking an observation.  On this day, the glazing was so severe that observers were going outside every 15-30 minutes to smash thick layers of ice off the wind vane and anemometers.  At one point, it was estimated that around 8 inches of ice was accumulating per hour! 

The top of the instrument tower and pitot anemometer prior to de-icing.

The Stevenson screen, or “thermoshack”, which houses several of our thermometers.

These extreme conditions were due to a combination of constant freezing rain and sleet, high winds, and moisture-laden air from the east that resulted in dense, wet fog.  Some of the pieces of ice had grown to over 2 feet in length, forcing the observers to be exceptionally careful and mindful of their positioning while removing the ice in strong winds. 

A massive chunk of ice on the instrument tower, with a glove for scale.

These photos help illustrate why the Mount Washington Observatory is still a manned weather station in a time when many weather stations have transitioned to automatic or semi-automatic status. Without the enormous efforts of the observers on duty, the relentless accretion of ice would have frozen our instruments in place and likely caused damage to the systems. It would not be possible to record accurate data on a day like this without manual intervention. The hardy team of observers remain on the summit to battle the elements because we truly do see some of the worst weather conditions in the world. 


AJ Grimes, Weather Observer

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