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Old 10-31-2006, 07:43 AM
 
164 posts, read 519,293 times
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Id like help interpreting some of the weather graphs on the city stats pages. For example:

On the Ashland page, the percent of sunshine for the month of January appears to be around 48%, yet the cloudy days reach 80% during the same month. There seems to be a 28% discrepancy.
The answer to the first bullet may answer this, but if you look at the chart for Brookings, the percent of sunshine in January is less than Ashland, yet the percent of cloudy days for January is the same.
On the Humidity graph, Brookings, which is on the coast, has the same afternoon humidity readings as Ashland or Klamath Falls, which are supposed to be more arid climates. It doesnt seem possible that a coastal city could even have humidity as low as 25%.

Thanks for any enlightenment.
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Old 10-31-2006, 08:12 AM
 
Location: Escondido, CA
344 posts, read 1,667,355 times
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Even though those are average figures, they show a range from the high to the low for that category. Partly cloudy days in January range from 80% to 92% and you can see the trend as the month progresses. At least, that is how I interpret the graphs. Each day is an average for that day over a number of years and so on. That average ranges from a bottom to a top for that day.

What is interesting about weather is microclimates. Distance from the ocean to deserts with altitude largely dictates local microclimate weather. If you are researching weather altitude of your city and surrounding mountains will play a huge roll in local weather conditions.

Based on Oregon microclimates, I would have to place an X on Roseburg as having some of the best weather in the state. On the coast, Brookings tops coastal cities for all the categories important to coastal weather. Draw a line over to Klamath Falls and you can see the effects of altitude and mountaintops have on local climate conditions. Rainfall totals change as a result of each cities microclimate conditions. If you want the best weather, you have to follow the Sun.

Dan
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Old 10-31-2006, 09:02 AM
 
21 posts, read 117,286 times
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It would be nice if city-data.com would give a little more detailed info about the the methodology of how those sunny/cloudy data were measured.
They say the data "were compiled from multiple government and commercial sources". Very likely the two graphs pertaining to cloud cover conditions (that are presented for every locale) use different metrics to measure the "amount of sun". Any one method of measurement may not tell the whole story. In a way, maybe its good that they are giving us two different numbers for each town, to alert us that these data should not be taken too absolutely. Considering both graphs should give a more realistic idea.
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Old 10-31-2006, 10:56 AM
 
164 posts, read 519,293 times
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Clear2land, the way I interpret that chart is, using Ashland in January as an example, 45% of the time it’s raining, 35% of the time it’s cloudy (without rain), 10% of the time it’s partly cloudy, and 10% of the time it’s clear. I sure don’t see how the sunshine chart corresponds.

Maybe you’re right, grapeguy, the charts don't seem real accurate, and I would have to say, they aren’t very meaningful, unless I’m not understanding something.
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Old 10-31-2006, 11:09 AM
 
1,313 posts, read 5,656,969 times
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The last time I revealed that the site fills climate information voids by linking clusters of different cities to the same climate info, my post was quickly deleted. Here's what I mean. These are links to the skycover profile for:

Medford
http://pics.city-data.com/w7/cld18045.png (broken link)

Grants Pass
http://pics.city-data.com/w7/cld17982.png (broken link)

Coos Bay
http://pics.city-data.com/w7/cld17906.png (broken link)

Brookings
http://pics.city-data.com/w7/cld17906.png (broken link)

Gold Beach
http://pics.city-data.com/w7/cld17977.png (broken link)

Now, how many of you think that the skycover graphs from these very different inland and coastal climates were individually constructed from sets of discrete locally-recorded data?
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Old 10-31-2006, 12:06 PM
 
164 posts, read 519,293 times
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Default hmmm...

Now that you mention it Steve, I looked at the charts for the southern CA area I recently moved from, and the charts are identical for the coast and inland valleys--two very different climates. (I lived there for 30 years.) Wonder how long this post will last...
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Old 10-31-2006, 12:22 PM
 
21 posts, read 117,286 times
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No argument on that Steve.

The "cloudy days/yr" data from Sperlings best places e.g.

(broken link)

are little better, although they at least are not identical data for the cities you mentioned, and seem to show at least some kind of correlation:

City Sunny days Precipitation Days
Medford 195 103
Grants Pass 196 127
Coos Bay 186 131
Brookings 191 126
Gold Beach 192 127

Notice how much greater the differences are in precipitation days than in sunny days.

I wonder if the low data density on cloud cover might be due to difficulty and/or expense in quantitatively measuring cloud cover with automatic instruments? It seems this is sometimes done with cloud cover radiometers that measure light input (reflectance from clouds), but its not hard to imagine ways such an instrument could get fouled up and give bad data.

Last edited by Yac; 10-31-2006 at 01:29 PM.. Reason: link removed
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Old 12-30-2007, 08:29 PM
 
Location: Michigan
2 posts, read 17,115 times
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Does anyone know where the data for making the graphs comes from? I am interested in finding a good weather site that has the same information as the graphs but in the raw number form.
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Old 12-31-2007, 08:23 AM
 
Location: DC Area, for now
3,517 posts, read 11,799,092 times
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Quote:
Originally Posted by fxdwg03 View Post
Does anyone know where the data for making the graphs comes from? I am interested in finding a good weather site that has the same information as the graphs but in the raw number form.
http://www.ncdc.noaa.gov/oa/mpp/freedata.html is the page for the National Climatic Data Center pages of data. All the data they have managed to get onto the web is free to download. The charges are for data that are on CDs or paper to cover the cost of the media and printing. A lot of the data are voluminous. This is the official repository for all official weather data by the US government and is the base source for most of what is reported by others. You will have to drill down and hunt for what you are looking for. Unlike a lot of commercial sources, they do tell you exactly what is being measured and for what time period.

In answer to the previous discussion, the sunshine data are old data since direct measurements of sunshine were discontinued a long time ago. Sunshine is measured as a percent of available sunshine. Meaning all nighttime hours are not counted. Because of the tilt of the earth, southern climes will have a more even day length year around and northern climes have a bigger difference.

Cloud cover does not translate directly to sunshine. They are different measures. You can have high thin overcasts of cirrus clouds that let a lot of sun thru. Partly cloudy ranges from a 10% cloud cover to 90% cloud cover. Obviously on the lower end, you can have a pretty sunny day. Also, cloud cover is measured during the nighttime hours as well as day.

Instrumentation has changed the data dramatically in some cases. During the period sunshine was being measured, humans reported the cloud cover. Now, the instruments can't detect clouds above 12,000 ft. Satellite data must be used to see the higher clouds. That can make a big difference to how a human experiences the day.

The more you know about the data and how it is measured, the more sense you can make of the different measures. They should always be taken as a comparative informational source and understand that any one day or week or even a year can vary dramatically from averages. A rough way to look at it is look at the averages (high, low, and daily), look at the records, then understand the climate will be roughly a third of the time close to the average (i.e normal), a third below, and a third above.

It is useful to look at the data for where you live now and compare what it says to a place you are interested in. Then you can get a better feel for what the differences are.

Reporting stations are at controlled airports. Less dense data are also collected in a bunch of places to add to the picture. It is common practice to do a smoothing function for places that fall between data points. This works a lot better in the Great Plains than it does in the mountainous west where it can look ridiculous.
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Old 12-31-2007, 08:23 AM
 
Location: Bayside, NY
823 posts, read 3,309,379 times
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The best way to measure how dry the air is is by dew point which measures the amount of moisture in the air. Humidity measures the moisture as compared to the temperature whereas the dew point is a pure measure irregardless of the temperature. A good site for this is: http://www.ask.com/web?q=climate+in+...city+ut&qsrc=8
this site gives you all weather data by month plus the annual averages.
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