The Stocker AstroScience Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Stocker AstroScience Center clear sky chart from 2005-11-05 to 2017-03-22.

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
62%
15650
18%
45203
15%
15610
66%
15610
28%
29196

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
54%
716
17%
2327
14%
716
60%
716
26%
1445
January16th to endNight
51%
768
25%
2463
19%
768
60%
768
32%
1415
February1st to 15thNight
51%
703
27%
2090
21%
699
59%
699
35%
1227
February16th to endNight
57%
631
31%
1735
20%
631
66%
631
40%
982
March1st to 15thNight
54%
720
26%
1980
16%
720
62%
720
38%
1168
March16th to endNight
59%
732
24%
2013
19%
732
63%
732
39%
1173
April1st to 15thNight
67%
658
26%
1811
22%
658
70%
658
48%
987
April16th to endNight
60%
660
23%
1656
13%
660
65%
660
41%
1004
May1st to 15thNight
69%
659
26%
1649
17%
659
72%
659
46%
958
May16th to endNight
65%
569
13%
1595
12%
569
66%
569
26%
1099
June1st to 15thNight
64%
495
9%
1485
8%
495
64%
495
16%
1118
June16th to endNight
76%
495
6%
1485
6%
495
76%
495
22%
1050
July1st to 15thNight
73%
465
5%
1395
5%
465
73%
465
19%
1026
July16th to endNight
81%
522
9%
1469
9%
489
80%
489
30%
941
August1st to 15thNight
75%
568
8%
1548
6%
565
75%
565
26%
1052
August16th to endNight
71%
700
5%
1858
4%
700
71%
700
22%
1358
September1st to 15thNight
68%
660
5%
1815
5%
660
68%
660
16%
1401
September16th to endNight
63%
657
5%
1815
6%
657
63%
657
15%
1433
October1st to 15thNight
65%
660
14%
1919
16%
660
66%
660
21%
1347
October16th to endNight
53%
704
18%
2112
16%
704
58%
704
22%
1452
November1st to 15thNight
60%
700
24%
2101
20%
700
66%
700
30%
1303
November16th to endNight
54%
720
26%
2160
21%
720
62%
720
28%
1375
December1st to 15thNight
56%
720
23%
2226
19%
720
62%
720
25%
1429
December16th to endNight
63%
768
24%
2496
24%
768
67%
768
31%
1453

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
8%6%38%8%5%7%7%7%9%26%
45664
Night
6%425%5%35%6%7%10%40%
45409
TransparencyDay
48%9%13%15%10%2
45365
Night
37%8%17%20%12%2
45212
SeeingDay
9%415%24%24%22%
5379
Night
8%215%31%28%13%
15658

By Month

Percentage Cloud Cover SE (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
9%6%37%7%5%6%6%7%9%29%
1611
16th to endDay
9%5%26%6%45%6%7%9%36%
1758
February1st to 15thDay
9%5%35%6%46%45%8%39%
1764
16th to endDay
7%425%6%35%5%7%9%42%
1738
March1st to 15thDay
6%436%6%47%6%7%11%36%
1980
16th to endDay
7%5%36%7%35%6%6%10%36%
2007
April1st to 15thDay
6%325%5%37%7%9%12%35%
1807
16th to endDay
7%425%6%48%6%8%10%35%
1972
May1st to 15thDay
4325%6%46%7%7%9%39%
1972
16th to endDay
10%6%49%9%5%11%7%7%9%18%
2175
June1st to 15thDay
13%8%410%10%6%9%7%7%7%14%
2145
16th to endDay
9%7%410%10%7%9%9%9%8%13%
2145
July1st to 15thDay
8%7%410%10%6%8%8%7%11%16%
2145
16th to endDay
6%5%38%8%7%9%9%9%10%19%
2283
August1st to 15thDay
7%6%310%8%5%10%9%8%10%17%
2058
16th to endDay
10%6%310%10%5%9%9%8%10%14%
1987
September1st to 15thDay
9%7%311%11%6%10%9%8%8%13%
1815
16th to endDay
13%10%411%11%6%8%7%6%6%13%
1815
October1st to 15thDay
9%7%39%10%5%7%6%9%10%19%
1711
16th to endDay
14%7%27%7%45%6%7%9%27%
1760
November1st to 15thDay
8%5%37%7%47%6%7%8%34%
1757
16th to endDay
10%6%36%7%48%6%5%7%34%
1800
December1st to 15thDay
9%7%48%7%45%7%6%8%31%
1731
16th to endDay
6%6%25%6%5%7%7%7%10%34%
1728
January1st to 15thNight
7%4245%46%6%7%10%38%
2327
16th to endNight
5%4245%245%7%10%46%
2463
February1st to 15thNight
8%425%42435%7%50%
2088
16th to endNight
4214435%45%9%54%
1735
March1st to 15thNight
33245%36%5%6%8%51%
1980
16th to endNight
5%2135%346%6%9%50%
2013
April1st to 15thNight
211333446%9%57%
1811
16th to endNight
6%3144345%6%10%50%
1656
May1st to 15thNight
2113425%46%11%56%
1649
16th to endNight
7%5%36%5%46%6%7%11%34%
1594
June1st to 15thNight
11%5%27%6%5%8%8%8%11%24%
1485
16th to endNight
4325%7%46%9%12%14%28%
1485
July1st to 15thNight
45%37%6%46%7%8%14%29%
1485
16th to endNight
3335%6%26%7%9%13%39%
1577
August1st to 15thNight
4425%5%46%7%9%13%35%
1559
16th to endNight
5%436%6%46%8%9%13%30%
1858
September1st to 15thNight
5%437%8%5%7%9%11%11%25%
1815
16th to endNight
8%6%39%8%6%6%8%9%10%22%
1815
October1st to 15thNight
6%5%26%7%5%7%7%8%12%30%
1919
16th to endNight
11%8%36%6%45%5%6%7%35%
2112
November1st to 15thNight
6%435%5%35%5%6%8%44%
2101
16th to endNight
8%336%6%46%5%5%7%43%
2160
December1st to 15thNight
8%5%35%5%35%6%7%11%38%
2226
16th to endNight
5%3245%26%6%6%10%46%
2496

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
46%7%11%18%10%5%
1612
16th to endDay
41%6%12%18%16%5%
1758
February1st to 15thDay
40%5%8%21%18%5%
1766
16th to endDay
34%6%10%26%17%4
1738
March1st to 15thDay
38%7%10%23%16%3
1980
16th to endDay
39%8%10%21%13%5%
2008
April1st to 15thDay
34%9%14%24%14%2
1807
16th to endDay
37%8%12%19%17%4
1972
May1st to 15thDay
35%8%13%23%14%4
1972
16th to endDay
56%11%11%15%5%
2179
June1st to 15thDay
63%10%12%9%3
2145
16th to endDay
61%12%15%8%1
2145
July1st to 15thDay
57%14%20%7%
2006
16th to endDay
50%13%25%10%
2128
August1st to 15thDay
54%14%19%11%
2045
16th to endDay
57%14%19%8%
1987
September1st to 15thDay
61%13%16%6%1
1815
16th to endDay
66%12%11%6%2
1815
October1st to 15thDay
53%11%14%12%7%1
1711
16th to endDay
49%6%11%14%13%4
1760
November1st to 15thDay
44%6%10%15%18%5%
1757
16th to endDay
45%6%8%11%20%7%
1800
December1st to 15thDay
48%6%8%16%17%2
1731
16th to endDay
40%7%10%21%16%3
1728
January1st to 15thNight
38%6%16%22%11%3
2327
16th to endNight
31%6%12%27%17%4
2463
February1st to 15thNight
32%49%25%20%7%
2097
16th to endNight
26%6%13%26%21%5%
1735
March1st to 15thNight
30%412%28%19%5%
1980
16th to endNight
28%6%16%26%18%4
2013
April1st to 15thNight
22%5%18%34%16%2
1811
16th to endNight
29%5%15%24%20%3
1656
May1st to 15thNight
23%7%15%33%16%3
1650
16th to endNight
42%8%16%24%7%
1596
June1st to 15thNight
51%11%20%13%3
1485
16th to endNight
39%15%31%12%
1485
July1st to 15thNight
42%16%29%10%
1395
16th to endNight
33%11%37%15%2
1469
August1st to 15thNight
36%13%32%16%
1548
16th to endNight
42%14%31%11%
1858
September1st to 15thNight
47%16%24%9%1
1815
16th to endNight
51%14%20%9%3
1815
October1st to 15thNight
44%10%17%15%10%1
1919
16th to endNight
46%6%10%19%12%4
2112
November1st to 15thNight
38%5%10%19%22%4
2101
16th to endNight
39%5%9%18%19%7%
2160
December1st to 15thNight
39%7%13%19%17%2
2226
16th to endNight
33%6%11%27%19%2
2496

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
18%13%38%24%4
90
16th to endDay
12%19%38%23%32
96
February1st to 15thDay
7%14%40%20%15%
105
16th to endDay
8%7%30%29%22%1
239
March1st to 15thDay
5%10%31%34%15%2
270
16th to endDay
6%7%33%25%22%6%
250
April1st to 15thDay
6%221%26%30%12%
210
16th to endDay
5%123%28%27%12%
210
May1st to 15thDay
5%216%25%32%17%
228
16th to endDay
8%27%25%32%23%
267
June1st to 15thDay
11%38%18%25%32%
255
16th to endDay
7%1114%29%46%
255
July1st to 15thDay
6%113%31%46%
245
16th to endDay
6%2219%20%48%
270
August1st to 15thDay
8%1216%22%48%
253
16th to endDay
11%1216%27%39%
268
September1st to 15thDay
7%2314%22%49%
255
16th to endDay
13%1114%27%42%
254
October1st to 15thDay
7%211%30%32%15%
255
16th to endDay
15%223%29%17%11%
272
November1st to 15thDay
7%220%33%29%7%
265
16th to endDay
12%7%26%32%17%3
270
December1st to 15thDay
19%217%35%19%3
201
16th to endDay
8%7%22%51%9%1
96
January1st to 15thNight
9%5%22%36%22%3
720
16th to endNight
6%5%29%40%15%1
768
February1st to 15thNight
10%328%37%19%
704
16th to endNight
6%5%26%41%19%
631
March1st to 15thNight
5%428%40%18%2
720
16th to endNight
6%324%43%20%1
732
April1st to 15thNight
3221%42%26%2
658
16th to endNight
6%322%41%23%2
660
May1st to 15thNight
3116%45%29%3
660
16th to endNight
9%19%34%34%11%
571
June1st to 15thNight
12%1420%39%22%
495
16th to endNight
4213%40%38%
495
July1st to 15thNight
5%118%47%34%
465
16th to endNight
39%38%47%
522
August1st to 15thNight
6%11%42%37%
568
16th to endNight
7%1316%38%33%
700
September1st to 15thNight
9%1214%33%38%
660
16th to endNight
10%1116%37%33%
657
October1st to 15thNight
9%19%31%37%11%
660
16th to endNight
15%116%29%26%10%
704
November1st to 15thNight
8%218%38%26%5%
700
16th to endNight
10%321%36%23%4
720
December1st to 15thNight
10%418%38%25%2
720
16th to endNight
8%318%41%25%4
768
Page generated at 2017-03-23 07:36:18. Version ac04

Copyright 2017 A. Danko


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