Interesting day at the top of Mt. Washington
- 17:38 PM Mon Oct 9th
The summit has, in effect, been a desert for the past three days.
With strong subsidence beneath a massive ridge of high pressure the
air was compressed and warmed. There was no feed of moisture from
any direction as winds were nearly calm through a considerable
portion of the lower atmosphere. The result was progressively
lowering relative humidity values which bottomed out last night at
Let me say that again, 1.4%.
That is extreme.
What is even more impressive, between the 4 am and 5 am
observations, subsidence ended which allowed the temperature to go
from 48.5 degrees Fahrenheit with humidity of 4.2% down to 41.3
degrees Fahrenheit with humidity of 83%. When I was forecasting this
morning, I did not expect us to moisten up as quickly as it did. I
was expecting it to gradually rise through the day not shoot up in
one hour. But this example illustrates how rapidly the weather can
change on the summit and to remind visitors to always be prepared
for rapidly changing conditions.
Ryan Knapp Meteorologist