[Chaos-l] [Medoc-mountain-men] Weather forecasting-- great article in S&T

[rfitzgerald1 at nc.rr.com]

Great information!  Yes, I've largely been disappointed with CSC and have been relying on AccuWeather.  They have a few astronomy folks on staff, update forecast more often and have been quick to respond to my questions concerning specific-area forecasts.

Rule from your email:
<70 @300 /700 mb RH = OK
Wind Data @300 mb, Jet Stream Impacts Seeing
Wind The Most When Isobars Are Close!

Got it!


---- Mark South <md_south at mac.com> wrote: 
> Hi,
> Sky and Telescope Feb 2010 issue has a great article on Astronomy  
> Weather forecasting that goes beyond the Clear sky clock.
> 
> The supplement to the issue online with some great links is here:
> http://www.skyandtelescope.com/howto/visualobserving/79770137.html
> 
> The big idea in this article is that we should cross check with  
> multiple weather models, starting with a general forcast and CSC, then  
> moving to more complex  models for more fine tuning such as the Global  
> Forecast System (GFS) .  GFS is a great modeling system and predictor  
> for the week (in addition to  CSC and Accu-weather) for info on  
> clouds, rain, etc.  and is updated four times a day unlike CSC which  
> is updated only twice a day.   The author says regarding the CSC,  
> "...that's good but not ideal; a lot can change in 12 hours."
> 
> Click here for GFS and NAM (North American Mesoscale)
> http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/
> 
> Quoting the article:
> "The GFS map...shows predicted precipitation and mean sea level  
> pressure (MSLP).  Rainy areas are best avoided while high-pressure  
> systems are most likely to have cloudless skies.  But if the isobars  
> (lines of equal pressure) are squeezed tight together, expect high  
> winds and poor seeing.
>       Diffrent layers in the atmosphere are labeled by pressure at  
> that altitude.  The map showing relative humidity @ 700 millibars  
> (about 10,000 feet) is labeled "700 mb RH."  Cloud cover is likely if  
> this value is above 70%.  High humitity at 300 mb (30,000 feet) is  
> likely to cause cirrus clouds.  If you see high winds at 300mb, it  
> meas that the jet stream is overhead, which usually causes poor seeing."
> 
> Great stuff.  I'm going to start looking at these sites in the future  
> to make better decisions.   For example, it looks like Friday is going  
> to be a quite clear according to NWS and the GFS.  GFS says at 84  
> hours out from today that 700 mb RH is "0" and 300mb is "0" so  it  
> apears that it will be quite clear and some good seeing.   I'm just  
> learning this.... does anyone agree with my findings or disagree for  
> Friday's weather?  :)
> 
> Kind regards,
> Mark South 
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