Stone Garden Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stone Garden Observatory clear sky chart from 2005-11-05 to 2017-12-20.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.
Observation TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(no limit)Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
41%
15228
8%
48007
6%
15201
44%
15201
15%
35699

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 15thNight
27%
809
5%
2747
3%
807
29%
807
7%
2330
January16th to endNight
30%
800
9%
2880
8%
800
33%
800
9%
2295
February1st to 15thNight
33%
703
6%
2400
5%
703
36%
703
11%
1874
February16th to endNight
42%
632
11%
2053
9%
632
46%
632
16%
1468
March1st to 15thNight
33%
720
10%
2112
7%
720
36%
720
14%
1642
March16th to endNight
48%
768
11%
2054
7%
767
50%
767
18%
1557
April1st to 15thNight
43%
659
10%
1739
6%
659
45%
659
17%
1318
April16th to endNight
40%
430
9%
1510
9%
430
43%
430
13%
1107
May1st to 15thNight
44%
359
4%
1419
4%
359
45%
359
14%
996
May16th to endNight
50%
374
0%
1222
0%
374
50%
374
17%
864
June1st to 15thNight
47%
360
0%
1080
0%
360
47%
360
19%
772
June16th to endNight
53%
360
0%
1080
0%
360
53%
360
21%
771
July1st to 15thNight
51%
340
0%
1066
0%
340
51%
340
20%
725
July16th to endNight
63%
376
3%
1239
1%
354
65%
354
30%
711
August1st to 15thNight
71%
360
10%
1385
14%
358
73%
358
30%
735
August16th to endNight
56%
542
11%
1688
12%
542
58%
542
23%
1139
September1st to 15thNight
62%
714
15%
1794
10%
714
63%
714
34%
1161
September16th to endNight
47%
716
14%
1977
9%
716
50%
716
21%
1424
October1st to 15thNight
44%
720
10%
2160
7%
720
48%
720
20%
1530
October16th to endNight
35%
768
9%
2537
5%
768
40%
768
12%
1939
November1st to 15thNight
32%
760
7%
2660
5%
760
35%
760
11%
2022
November16th to endNight
31%
918
8%
2938
5%
918
35%
918
11%
2307
December1st to 15thNight
35%
1020
7%
3120
5%
1020
37%
1020
12%
2470
December16th to endNight
30%
1020
8%
3147
4%
1020
34%
1020
10%
2542

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

Occurrence of each ForecastData
Points
Cloud CoverDay
11%9%47%7%46%6%6%7%28%
48875
Night
12%11%48%7%45%5%5%6%27%
48149
TransparencyDay
53%6%16%18%4
48517
Night
56%6%15%16%5%
48011
SeeingDay
14%8%24%27%19%4
7107
Night
19%6%20%31%19%3
15238

By Month

Percentage Cloud Cover NW (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
13%15%6%11%10%5%6%7%5%313%
1203
16th to endDay
11%15%6%9%7%46%6%47%19%
1344
February1st to 15thDay
16%12%38%7%45%45%6%23%
1462
16th to endDay
7%12%48%7%47%5%5%6%29%
1421
March1st to 15thDay
9%16%6%8%6%46%6%5%6%23%
1847
16th to endDay
7%10%5%7%8%47%6%6%8%26%
2165
April1st to 15thDay
9%11%5%10%8%47%6%5%6%22%
2206
16th to endDay
15%11%5%9%6%5%6%5%5%5%23%
2449
May1st to 15thDay
11%9%48%7%46%5%5%6%28%
2530
16th to endDay
11%7%38%8%5%7%6%6%7%27%
2889
June1st to 15thDay
14%6%37%7%5%6%6%5%8%29%
2880
16th to endDay
13%6%36%7%46%6%7%8%27%
2880
July1st to 15thDay
12%5%35%6%46%6%6%8%33%
2829
16th to endDay
9%425%5%36%6%7%8%40%
2846
August1st to 15thDay
5%425%6%46%5%5%8%45%
2567
16th to endDay
11%6%37%5%45%6%6%7%34%
2512
September1st to 15thDay
9%5%25%5%445%7%7%43%
2166
16th to endDay
14%6%27%7%45%5%6%7%30%
1983
October1st to 15thDay
14%9%36%7%346%6%7%28%
1800
16th to endDay
17%12%37%6%46%5%48%24%
1686
November1st to 15thDay
15%14%5%8%6%4445%5%25%
1528
16th to endDay
11%14%5%11%10%49%6%46%16%
1336
December1st to 15thDay
12%12%5%9%8%36%5%6%6%22%
1170
16th to endDay
8%18%6%8%10%47%5%5%5%19%
1176
January1st to 15thNight
13%17%6%11%9%46%5%45%15%
2747
16th to endNight
15%14%5%8%7%45%5%5%5%21%
2880
February1st to 15thNight
13%16%5%9%8%44445%23%
2388
16th to endNight
8%10%6%10%7%35%5%5%7%29%
2053
March1st to 15thNight
10%14%5%9%7%46%6%5%5%24%
2112
16th to endNight
7%11%48%6%48%7%7%7%25%
2054
April1st to 15thNight
11%13%5%8%6%45%5%5%7%27%
1739
16th to endNight
11%11%47%7%47%6%5%6%27%
1510
May1st to 15thNight
12%9%46%7%47%5%6%7%28%
1418
16th to endNight
13%6%37%6%47%6%7%9%27%
1222
June1st to 15thNight
14%6%36%6%36%6%7%7%29%
1080
16th to endNight
12%437%7%5%7%5%5%9%30%
1080
July1st to 15thNight
12%5%25%8%45%5%8%7%33%
1130
16th to endNight
9%5%3443436%8%47%
1323
August1st to 15thNight
6%3244345%6%8%50%
1392
16th to endNight
11%6%35%6%45%6%6%7%37%
1688
September1st to 15thNight
8%5%25%5%4435%7%47%
1794
16th to endNight
15%7%35%6%35%5%5%7%32%
1977
October1st to 15thNight
14%9%36%6%35%45%6%33%
2160
16th to endNight
16%11%47%7%35%5%6%6%23%
2537
November1st to 15thNight
14%12%37%7%47%6%5%6%23%
2660
16th to endNight
11%16%5%9%6%36%5%5%6%22%
2938
December1st to 15thNight
14%13%5%7%7%45%5%4426%
3120
16th to endNight
9%15%6%10%10%5%6%45%6%19%
3147

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
72%6%12%7%
1203
16th to endDay
66%6%12%8%4
1344
February1st to 15thDay
61%6%15%12%4
1462
16th to endDay
54%416%16%6%
1421
March1st to 15thDay
59%5%12%16%5%
1847
16th to endDay
54%5%19%17%3
2165
April1st to 15thDay
59%6%13%16%4
2206
16th to endDay
62%5%11%15%4
2449
May1st to 15thDay
54%5%13%18%6%
2530
16th to endDay
52%7%16%18%3
2893
June1st to 15thDay
50%7%13%21%6%
2880
16th to endDay
51%7%16%19%4
2880
July1st to 15thDay
45%7%16%21%7%
2664
16th to endDay
36%9%24%24%4
2667
August1st to 15thDay
34%8%25%26%5%
2549
16th to endDay
47%7%20%21%3
2512
September1st to 15thDay
38%6%24%24%5%
2166
16th to endDay
51%6%16%21%3
1983
October1st to 15thDay
54%5%19%17%2
1800
16th to endDay
58%7%19%12%1
1686
November1st to 15thDay
60%5%15%11%6%
1528
16th to endDay
69%5%10%12%1
1336
December1st to 15thDay
62%7%15%12%2
1170
16th to endDay
65%6%14%10%2
1176
January1st to 15thNight
71%6%12%8%1
2747
16th to endNight
64%6%13%9%5%1
2880
February1st to 15thNight
64%414%10%5%
2400
16th to endNight
54%417%16%6%
2053
March1st to 15thNight
60%5%10%15%6%1
2112
16th to endNight
53%7%16%16%5%
2058
April1st to 15thNight
55%5%10%20%7%
1739
16th to endNight
57%5%13%16%7%
1510
May1st to 15thNight
54%5%12%17%10%
1419
16th to endNight
50%7%14%23%4
1222
June1st to 15thNight
50%6%12%22%6%
1080
16th to endNight
50%6%17%21%4
1080
July1st to 15thNight
47%6%14%19%11%1
1066
16th to endNight
33%6%26%28%5%
1239
August1st to 15thNight
30%6%19%34%8%
1385
16th to endNight
44%7%21%21%4
1688
September1st to 15thNight
37%419%29%8%
1794
16th to endNight
48%7%15%21%6%
1977
October1st to 15thNight
50%5%19%19%4
2160
16th to endNight
58%7%16%15%1
2537
November1st to 15thNight
59%6%16%11%4
2660
16th to endNight
62%6%14%13%3
2938
December1st to 15thNight
61%7%14%14%2
3120
16th to endNight
65%6%13%11%3
3147

Seeing (when cloud cover <= 80%)
Color Meanings:
Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
11%111%23%38%13%
60
16th to endDay
26%320%20%18%10%
64
February1st to 15thDay
22%8%28%20%15%4
149
16th to endDay
15%9%23%30%16%6%
211
March1st to 15thDay
16%14%37%23%6%1
266
16th to endDay
15%14%28%25%14%
288
April1st to 15thDay
17%16%28%23%11%2
269
16th to endDay
16%16%32%22%10%1
270
May1st to 15thDay
15%13%26%28%13%3
307
16th to endDay
12%7%22%28%22%5%
603
June1st to 15thDay
16%6%22%27%22%4
675
16th to endDay
12%425%30%20%6%
675
July1st to 15thDay
14%6%20%27%25%5%
598
16th to endDay
9%7%20%30%27%4
515
August1st to 15thDay
5%317%33%31%8%
362
16th to endDay
13%7%27%33%15%2
332
September1st to 15thDay
12%7%26%26%21%4
315
16th to endDay
16%8%31%26%15%2
315
October1st to 15thDay
21%9%23%23%17%4
315
16th to endDay
23%9%23%23%16%2
176
November1st to 15thDay
26%7%24%24%6%10%
90
16th to endDay
18%424%27%15%8%
90
December1st to 15thDay
11%115%25%34%12%
90
16th to endDay
15%212%36%22%11%
72
January1st to 15thNight
25%8%21%27%14%2
812
16th to endNight
24%8%25%27%12%1
800
February1st to 15thNight
25%7%18%28%17%2
708
16th to endNight
14%6%18%35%22%2
632
March1st to 15thNight
18%9%25%32%11%2
720
16th to endNight
13%7%17%34%23%3
768
April1st to 15thNight
18%5%17%32%20%4
659
16th to endNight
18%5%22%31%18%2
430
May1st to 15thNight
16%5%20%35%18%3
360
16th to endNight
15%5%17%30%28%3
375
June1st to 15thNight
16%321%29%26%3
360
16th to endNight
12%118%36%27%2
360
July1st to 15thNight
14%216%32%31%3
340
16th to endNight
9%215%36%31%4
376
August1st to 15thNight
8%9%30%40%10%
360
16th to endNight
17%114%33%29%3
542
September1st to 15thNight
11%214%32%34%4
714
16th to endNight
20%416%32%20%4
716
October1st to 15thNight
21%420%31%17%4
720
16th to endNight
25%8%21%29%14%1
768
November1st to 15thNight
23%9%24%29%10%1
760
16th to endNight
23%8%26%28%10%2
918
December1st to 15thNight
22%5%20%32%18%1
1020
16th to endNight
18%7%25%31%14%2
1020
Page generated at 2017-12-21 04:04:42. Version ac04

Copyright 2017 A. Danko


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