Sam,
I’m sorry I didn’t reply to your suggestion to have some scopes go to BMCC as I
missed your email. I did see the cancellation email, however. Here’s a
suggestion for BMCC star parties, since I live so close. In future I would be
happy to pack my scope at the last second and go there. It’s not a big deal
since I don’t load up my car for BMCC events until just before setup time.
Pete Turner
From: pasmembers-bounce@xxxxxxxxxxxxx [mailto:pasmembers-bounce@xxxxxxxxxxxxx] ;
On Behalf Of Redacted sender "insanas" for DMARC
Sent: Friday, April 29, 2016 8:23 AM
To: pasweatherwatchers@xxxxxxxxxxxxx; pasmembers@xxxxxxxxxxxxx; insanas@xxxxxxx
Subject: [pasmembers] Re: [pasweatherwatchers] Weather Watching
Alex, at the Annual Flagstaff Festival of Science last September I attended the
open house at NOAA. They spent an hour going through all their complicated
model predictions. I then looked up at the computer screen and asked them why
their model said the sky was only 10% cloud cover in Flagstaff, when looking
out the window you could clearly see it was very cloudy?
The meteorologist looked bewildered and then said, they were probably measuring
how thick the cloud cover was!!! I asked how we could use their numerical cloud
percentage predictions for astronomy star parties. He said our best bet is to
look at the satellite photos as close to the events as possible.
Last night I suggested since 5 weather forecasts were bad and 5 were good, that
we look at the satellite pictures. I noticed a gap in the clouds but couldn't
be certain the gap would remain. I also mentioned that my barometer had been
going up steadily so that we might get lucky.
I then suggested that I go out to PVCC Blk Mt with my scope along with maybe
one or two others but not have a large number of scopes since it was so hard to
predict. No one else volunteered to drive out there. Also with Mike being sick
we didn't have a presentation for backup in case the clouds came in. Several
people commented on the weather: Terri, William, Don, Eric, Alex, Howard and
myself, and it got cancelled at the last minute based on best guesses.
I think a better solution is to have a policy that when the weather is in doubt
(like 50/50 weather predictions), that we reduce the number of scopes so that
at least some scopes are there if it clears and some people can see some
objects. Most star parties in the US have clouds and very few have great
nights. Roger has told us how the Sedona star parties are never cancelled.
When Alex and I did the weather forecast analysis 2 years ago we came up with
the model that if 8 out of 8 , or 7 out of 8, or 6 out of 8 weather forecasts
agreed , you could count on the predictions. But when it was like last night, 5
out of 10, there is no way to tell. We can look at other factors like the
satellite photos and barometric pressure, but I still think having a backup
policy of having a couple scopes show up is the best bet. I don't mind showing
up, since I have more free time, am centrally located, and have a smaller
easier scope to set up , but I wouldn't expect some of the other members to
make a long drive in rush hour traffic with a 50/50 chance of not showing
anything especially when they are rushing home from work and have a large scope
to set up. If they want to show up, that is fine, but I wouldn't expect them to
do so.
Alex, if you want to look at weather models, that is fine, but we will still
have situations like last night where I think we need a policy of having a
couple smaller scopes go out there, and maybe not unload until it looks good
enough to show things. Of course whoever is hosting the event, public or
private, needs to agree to our back up plan and we would need to warn anyone
who rsvp'd that the weather is iffy but we will still have a few scopes since
there is a 50/50 chance of showing some objects.
Any other suggestions are welcomed. Sam
-----Original Message-----
From: Alex Vrenios <axv@xxxxxxx>
To: pasweatherwatchers <pasweatherwatchers@xxxxxxxxxxxxx>
Sent: Fri, Apr 29, 2016 12:03 am
Subject: [pasweatherwatchers] Weather Watching
At 8pm this evening, the sky looked clear facing south from my backyard in
north Phoenix. So much for the weather reporting websites?
Sound familiar? We did a fairly reasonable test of the more popular sites and
about the best that could be concluded came from Sam, if I remember right: If
seven or eight out of the eight reporting sites say it will be clear, then it
will be clear. Nobody brought up the question f how likely seven or eight sites
would agree…
Someone said something back then that stayed with me. Something about certain
websites reporting the results of computer simulation models, and that some of
the sites used the same models.
Let me guess that there are only a few of these models. If so, can we get these
results directly? And if that’s so, can we compare their results to the actual
sky and wind conditions within perhaps an eight hour window? We could skip the
usual websites and use the model results to determine whether an event is to be
cancelled.
I’d like to volunteer to help gather and analyze such results. I don’t even
know the names of these models at this point. (I seem to remember that the
website that explains the Clear Sky Charts gave some insight.) Does anyone else
think this would be a worthy cause before we expend any effort?
First order of business would be to see if we can access these results (for
free). Even historical data would help the analysis. And before we expend any
shoe leather there might be a journal article on the subject of how well they
perform, and when and why they might be unreliable.
Alex
P.S. The important forecast time is the time that a model was run. Some models
may be more accurate than others, depending on the season of the year, the
sensitivity of their input data (like which data might have a wide range of
values that are likely to fluctuate).
