Negative Relative Humidity? Is that possible?

2012-12-31 17:40:00.000 – Brian Fitzgerald,  Weather Observer/Education Specialist

-30% ??

It is really dry in our weather room right now.

How dry is it, you ask? Well our mini temperature/humidity meter next to my computer was reading less than 0% for relative humidity, and if there was a number where the arrow were pointing it might have read -30%. Is that possible? (Answer: no, it’s not).

It certainly feels that dry, no matter how much water I drink, and I’ve been drinking nearly continuously today; my throat and mouth are parched and my eyes feel like they should be submerged in a pool in order to keep them open.

Conversely, we are in the clouds with freezing fog right now, meaning relative humidity is at 100%, or put another way, we have reached a point outside where the air contains 100% of the moisture it possibly can and has reached saturation. At the saturation point, we have water vapor in the air that has condensed into ‘dew’, or in this case freezing fog.

So why aren’t we moisture-rich inside then? It was easy figuring out the answer to this question last night when the winds were howling up to 118mph out of the northwest slamming right into our weather room, positioned perfectly in the wind’s path. At -16 degrees ambient air temperature our wind chill reached -62 degrees with our peak wind forcing a tremendous amount of cold air rushing into our windows, which by the way are triple-paned and bulletproof. As sealed as our building is in winter, it was pretty easy to find the seals where wind and cold air were sneaking their way indoors causing our heaters to work extra hard and therefore dry up all of the moisture in the air. Even with two full-time humidifiers running, we are desperate for some water vapor. Investments in caulking and more humidifiers are sure to ensue.

Happy New Year! We are especially grateful for all of our supporters who have helped us through yet another year (and 8th decade) of observing some of the most unique weather on the planet. If you’d like to make a New Year’s Resolution to support the non-profit Mount Washington Observatory, please do! Thanks again!


Brian Fitzgerald,  Weather Observer/Education Specialist

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