2014-04-05 17:45:13.000 – Tom Padham, Weather Observer/Meteorologist
Freezing rain events on the summit are relatively uncommon, since in order for freezing rain to occur temperatures at the summit need to be below freezing while above the summit has a deep layer of above freezing temperatures. Most often this layer of above freezing air is shallow and the summit may see sleet or wet snow. Last night into this morning was an unusual freezing rain event due to the long duration of the freezing rain seen on the summit, and how cold the temperatures were with the freezing rain.
For much of the night temperatures sat in the mid to upper teens, which is pretty cold for freezing rain to form (remember freezing rain forms as a liquid in above freezing temperatures aloft). Considering that it was only in the teens at 6,000 feet , the above freezing layer in which the rain was forming was probably several thousand feet above summit. Usually this would lend to sleet (ice pellets) for the summit, since the liquid rain would freeze on its way through air well below freezing . Because most of our precipitation fell in the form of freezing rain, the temperatures at say 8,000 or 9,000 feet may have been well above freezing, perhaps 40 degrees or so, a very balmy day for that high up!
Working in an ice storm on the summit is not as glamorous as it sounds (that is, if you think it sounds glamorous). Glaze ice forms very quickly if the winds are high and freezing rain is occurring. Glaze ice, or clear ice, is also much harder to knock off our instruments and tower, and doing so on an hourly basis does grow tiring. In addition sleet with a 50+ mph wind starts becoming uncomfortable, and with an 80+ mph wind becomes not very fun at all. Still, ice storms are a fascinating part of the weather we see here on Mount Washington and in New England; but I’m glad they’re not an everyday occurrence!
Tom Padham, Weather Observer/Meteorologist