[AZ-Observing] Re: Predicting Dew
- From: Brian Skiff <bas@xxxxxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Wed, 18 Jan 2017 13:51:58 -0700
On Wed, 2017-01-18 at 15:31 -0500, Paul Lind wrote:
This morning I noticed large amount of dew on things in my yard, reminding me
of observing sessions that were ruined by severe dew. I'm talking about
puddles of water on my observing table and water dripping off my scope.
So, my question is this: Is there a way to predict dewing from the
Clear-Sky-Charts and other data, say, by comparing transparency, humidity,
and temperature? The air-temperature/dewpoint relationship is not a good
indicator of dewing because radiative cooling from a clear sky can cool
objects well below both the air temperature and dewpoint. It's a good
predictor of fog.
This is likely to be a fairly local effect, so you're
probably best off simply measuring it. An easy way is with
a metal plate facing up with a contact thermometer attached
plus a thermometer measuring free air. If the temperature of
the metal plate drops down to or below the ambient air temp
(assuming the two thermometers are the same on really dry,
breezy nights), then dew/frost is going to condense onto
exposed surfaces. With some experience watching, you ought
to be able to predict the trend an hour or something ahead
of time.
\Brian
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