How to use

1.What is 7Timer! and why called 7Timer!?

7Timer! is a tool for astronomers to get a glimpse on how the weather will be on next 180 hours.

For the former name might made you confuse with A.Danko's Clear Sky Clock, I change the name to "7Timer!". In Chinese this tool calls "Qing-Tian-Zhong", and "seven" pronounce as "Qi", similar to "Qing", so the new name is "7Timer!".

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2.What's the differences between normal weather forecast and 7Timer!?

7Timer! is design for astronomy so here're the differences:

1. Difference on time resolution. The time resolution of normal weather forecast is 8-hour at most but 7Timer's time resolution is 3-hour.
2. Difference on forecast elements. 7Timer! forecasts cloud cover or transparency, which are rarely seem in normal weather forecasts.

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3.Why to work on 7Timer!?

The 7Timer! of North America (http://cleardarksky.com/csk/) is a weather forecast program for astronomer, its accuracy rate could reach 90% or more, but it's only available to USA, Canada, and parts of Caribbean. In June 2005, I began to design another program like 7Timer!, which can be use in China. With Mr.Bug, Zuqiang Li and many other friends' help and support, the 7Timer! came out in later June. Due to the data I use, it also makes it possible to design a "International 7Timer!", so the Global Service 7Timer! came out.

 

4.Where does the data of 7Timer! comes from?

Global Forecast System, a free produce, is supported by The National Center of Environmental Prediction in USA. The data which the project use comes from here. The name of these files are PGRBF, released by NCEP four times a day, and would gives a 384-hour forecast every time. Every PGRBF file include hundreds of elements. The project will download an 120-hour forecast every day.

5.How does 7Timer! process the data?

In 10:00GMT everyday, the program will download the PGRBF files automatically and save them to the FTP, so the project can work. GrADS is a program that use widely in meteorological centers, it can read the PGRBF files. With the command files the GrADS will output the forecast maps and clocks, these images will save to this website and a new forecast is release in this way.

6.How many hours could 7Timer! predict and how large could it predict?

GFS contains data for a 384-hour (16-day) forecast purpose, but now 7Timer! will only guarantee an 120-hour forecast. How large? Anywhere in the world (even include Antarctica).

7.What does 7Timer! predict?

The forecast of cloud cover: The PGRBF files can output cloud cover directly, or in another way, could output "Low Cloud", "Mid Cloud", "High Cloud" etc. But I found the directly one is always put the cover rate much higher than the real one, so I had to put low together with mid and high. For a better solution I slightly discard the high cloud output.

The forecast of transparency: If not consider the humanely pollution, transparency will only relates to humidity. So I sum the humidity value from different geopotential. According to the North America one, I use a 5-lever system for transparency forecast.

Temperature, Humidity, Wind Speed: These can get directly from PGRBF files.

The forecast of snow depth: PGRBF hasn't a direct snow depth forecast, it could only tell how heavy the snow is in a square meter. I use a arrange rate to calculate snow depth: 100kg per cubic meter. But the density of snow relate to the time the snow have reach the ground. The flesh snow might only weight 50kg per cubic meter, but the snow in spring cloud weight 200-400kg per cubic meter. So it's only a attempt to know how the "real" snow depth is.

8.How about the accuracy?

Unlike the Clear Sky Clock of North America, which with Canadian Meteorological Center's support, this project using the free product from NCEP, so it unlikely to reach a 90% accuracy. Though, after several weeks' test, the accuracy could reach 60-70%.

According to the observed result, there might still be some error in clocks and maps, although I've tried my best to discard them. e.g. the 'overcast' might be very thin, thin enough to see the moon, planet or even star, but the project might still put it to 'overcast' class. For more detailed information please read the explanation in a clock or in the forecast maps page.

9.How does 7Timer! works?

7Timer! Auto Run Program (ARP) will run once everyday, and release new forecast. You could go to "Weather Maps"(forecast maps) for 7Timer! forecast.

10.I need weather forecast for a place, does 7Timer! give me this kind of service?

Actually, from July 8, 2005 to May 4, 2006, 7Timer! offer forecast for local weather, and this kind of service called "7Timer! Panel", however now things are different.
That's because GFS, the data 7Timer! uses, is of low resolutions (or say, of highest resolution among the free data). After nearly one year's operating, we find GFS is far from suitable for give forecast for local weather, "Global Forecast System" is not "Local Forecast System".
So we decide to suspend "7Timer! Panel" and only offer weather maps, this is which GFS be good at. However, we still have 7Timer! Panel operating for those in real need.We still encourage you to use "Weather maps" for more accurate weather forecast.

11.How long will my request be proceed? How to do if I'm hurry to use it?

Usually I will proceed the request in 1-3 weeks, you could click "top" on the right and then click "Requests status" to see when will I proceed. If you're hurry to use, please contact me by the feedback form on the first page or mail me.

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12.I don't know what the image means.

Every 7Timer!'s page should has a detailed explanation. 7Timer! uses different color to represent different value, but if you still confuse, feel free to contact me by feedback form on the first page or email.

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13.The forecasts of cloud cover or transparency doesn't get right! What's wrong?

Here're some incorrect cloud cover forecast reasons:

1. Thunderstorms. Because the thunder cloud appeared and disappeared quickly, it's hard to predict thunder cloud accurately. Consider the geo-resolution and time resolution of 7Timer! (100km/3-hour), it's really not an easy job to give an accurate forecast of thunder clouds. But I think, thunderstorms won't block your observing project.
2. Haze/Fog. They're not high enough to get into "cloud" class in GFS, and it's hard to be predict in transparency, so 7Timer! may miss haze/fog. You could use this way to determine whether it will be clear: usually haze/fog will appear in no wind or wet environment, and you could use the forecast of wind/humidity to determine whether haze/fog will lift. Maybe you'll say why I don't add the effect of wind/humidity into 7Timer!? Actually I've added, but it's hard to know how much will them effected, so the haze/fog's effect may still be missed.
3. Wrong cloud cover percent. E.g. 7Timer! says 30% but actually is 40%. In my opinion that's reasonable, consider the resolution of 7Timer!, it's hard to make cloud cover rate is 30% in all 100 cubic kilometer. So please keep in mind: this is NOT "exact" forecast, it will only tell you the "trend" of weather. I feel 7Timer!'s "trend forecast" is quite accurate (that's because GFS is good at "trend" forecast but not so good at "exact" forecast).

About transparency, in theory it only related to humidity, but actually it related to many elements, GFS is still unable to consider all or most of these elements, so please combine the forecast with environment.

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14.My place is quite near to sea, why the temperature is always 26C?

Because 7Timer!'s low resolutions, near-sea place may be effected by the sea more than it actually did, so the temperature might be more steady than it actually is.

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15.Some time would be "Clear and -9C"?

Sometimes the data of some time might be unreachable, so the program could not calculate during this time, all the values at this time will be return to undefined value which is "Clear, -9C".

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16.Could 7Timer! guarantee seeing forecast?

Yes, please see "forecast maps".

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17.100km's resolution is too low, do you have some higher resolution data?

GFS data is now the most accurate and highest resolution and FREE data I can find.

18.What can I do for 7Timer!?

Three way: Mental, Tech and Economic, please see here

19.How to read Cloud Cover forecast maps?

Similar with looking satellite images. Please see the comparison below, white is cloud while black is land.

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Maybe you have noticed, some "black" places in the satellite image are "white" in the forecast map. Is 7Timer! wrong? Sometimes not. Please see FAQ #20 (next one).

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20.It's scattered cloud here, but forecast maps tell me it's overcast?

Also answer the last question of #19. Those "black region" in the satellite image (basically infrared images) actually sometimes have "mini" clouds. We can see them on a high resolution visible image below:

We can confirm that the black region on MTSAT-1R image are actually "scattered cloud region", as the image of NOAA-18 shown. These clouds can affect the quality of observing greatly, we could see its effect on all-sky cam image on right, by Hong Kong Observatory.

As the low resolution of 7Timer! (~111km), small structure of clouds will be mis-detect by it, as the example below:

We could see, 7Timer! can predict the big structure prefect-ably, but it has nothing to do with small structure. As a cloud as big as 10-20km will affect the observing greatly, please note this "mis-detect" effect when you use 7Timer!.

21.Why appear "Entire grid undefined"?

Usually, on the early time (e.g. Release day - 03h/06h/09h), some parameter will say "entire grid undefined" because they require more data to calculate. To solve this problem, you can simply roll down your mouse and see later time.

22.The animation page doesn't work!

Because the size (20-50k) and the amount of the images, it's possible that when your connection is slow, the animation page does not taken effect. To solve this problem, you can click "skip forward" icon to load the image manually. I'm sorry about this problem, I'm still trying to develop a more "powerful" animation page.

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