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 2017-08-12.

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%
14676
8%
46376
6%
14649
43%
14649
15%
34544

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%
352
10%
1353
14%
350
73%
350
30%
719
August16th to endNight
55%
496
10%
1546
11%
496
56%
496
22%
1047
September1st to 15thNight
62%
654
15%
1644
10%
654
63%
654
34%
1066
September16th to endNight
46%
656
14%
1812
8%
656
49%
656
21%
1311
October1st to 15thNight
45%
660
10%
1980
8%
660
48%
660
20%
1397
October16th to endNight
34%
704
8%
2326
5%
704
39%
704
11%
1798
November1st to 15thNight
31%
700
7%
2450
6%
700
35%
700
11%
1866
November16th to endNight
32%
842
8%
2712
5%
842
36%
842
12%
2116
December1st to 15thNight
33%
930
7%
2880
5%
930
34%
930
11%
2299
December16th to endNight
30%
992
7%
3072
3%
992
33%
992
10%
2495

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%
47639
Night
12%11%47%7%45%5%5%6%27%
46518
TransparencyDay
53%6%16%18%4
47281
Night
56%6%15%16%5%
46380
SeeingDay
14%8%24%27%20%4
6705
Night
19%6%20%31%19%3
14686

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%6%8%45%
2514
16th to endDay
12%6%37%5%45%6%6%7%34%
2302
September1st to 15thDay
8%5%25%5%445%7%7%43%
1986
16th to endDay
15%6%26%7%45%5%6%7%31%
1818
October1st to 15thDay
15%9%36%7%45%6%7%7%27%
1650
16th to endDay
17%12%47%6%46%5%48%23%
1545
November1st to 15thDay
16%14%46%6%445%5%5%24%
1408
16th to endDay
12%14%5%11%9%39%6%45%17%
1233
December1st to 15thDay
13%13%5%9%8%36%5%6%5%21%
1080
16th to endDay
8%18%5%8%10%47%5%5%5%18%
1152
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
7%3244345%6%8%50%
1360
16th to endNight
11%6%35%6%45%6%6%7%36%
1546
September1st to 15thNight
8%5%25%5%4445%7%46%
1644
16th to endNight
15%8%46%7%35%5%5%7%32%
1812
October1st to 15thNight
14%9%36%5%35%45%7%33%
1980
16th to endNight
17%11%47%7%35%5%6%6%22%
2326
November1st to 15thNight
15%12%37%7%37%6%5%6%23%
2450
16th to endNight
11%16%5%8%6%36%5%5%6%23%
2712
December1st to 15thNight
14%14%6%7%7%35%44425%
2880
16th to endNight
9%15%6%10%10%5%6%45%6%19%
3072

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%24%26%5%
2496
16th to endDay
46%7%20%21%3
2302
September1st to 15thDay
37%7%26%23%5%
1986
16th to endDay
50%7%16%21%3
1818
October1st to 15thDay
55%6%20%16%2
1650
16th to endDay
59%7%19%11%1
1545
November1st to 15thDay
60%5%16%11%5%
1408
16th to endDay
69%5%9%13%1
1233
December1st to 15thDay
63%6%14%12%2
1080
16th to endDay
66%6%14%10%2
1152
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
31%5%19%34%8%
1353
16th to endNight
45%7%21%20%4
1546
September1st to 15thNight
36%5%20%28%8%
1644
16th to endNight
49%6%15%21%7%
1812
October1st to 15thNight
49%5%20%19%3
1980
16th to endNight
60%7%16%14%1
2326
November1st to 15thNight
59%6%17%11%4
2450
16th to endNight
61%6%14%14%3
2712
December1st to 15thNight
63%6%13%14%2
2880
16th to endNight
66%6%13%11%2
3072

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%
347
16th to endDay
14%8%25%33%16%1
268
September1st to 15thDay
11%7%27%29%21%3
255
16th to endDay
17%8%33%24%14%1
255
October1st to 15thDay
20%8%23%24%20%3
255
16th to endDay
23%6%24%23%17%3
131
November1st to 15thDay
28%6%31%21%110%
60
16th to endDay
20%320%28%18%10%
60
December1st to 15thDay
15%118%20%33%11%
60
16th to endDay
15%110%34%25%12%
64
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%
352
16th to endNight
17%115%31%30%3
496
September1st to 15thNight
10%214%33%34%3
654
16th to endNight
20%5%17%33%18%4
656
October1st to 15thNight
21%419%32%18%3
660
16th to endNight
25%8%21%29%13%1
704
November1st to 15thNight
24%9%25%29%9%2
700
16th to endNight
23%8%24%29%11%2
842
December1st to 15thNight
23%6%21%30%16%1
930
16th to endNight
18%8%24%31%14%2
992
Page generated at 2017-08-13 11:16:16. Version ac04

Copyright 2017 A. Danko


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