Starlight Cascade Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starlight Cascade Observatory clear sky chart from 2005-11-05 to 2017-04-07.

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
29%
14299
14%
45467
8%
14268
37%
14268
18%
31774

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
13%
720
9%
2506
3%
716
20%
716
7%
1969
January16th to endNight
18%
768
12%
2583
4%
768
27%
768
11%
1944
February1st to 15thNight
15%
704
11%
2287
4%
701
23%
701
11%
1759
February16th to endNight
19%
631
14%
1967
5%
631
31%
631
14%
1442
March1st to 15thNight
21%
720
15%
2060
6%
720
30%
720
17%
1503
March16th to endNight
28%
768
20%
2061
9%
768
37%
768
24%
1403
April1st to 15thNight
21%
686
17%
1716
4%
686
28%
686
20%
1262
April16th to endNight
32%
605
17%
1595
7%
605
38%
605
25%
1100
May1st to 15thNight
38%
344
19%
1334
16%
344
47%
344
19%
841
May16th to endNight
39%
342
16%
1369
15%
342
50%
342
22%
802
June1st to 15thNight
37%
330
11%
1320
10%
330
46%
330
17%
865
June16th to endNight
49%
330
10%
1320
12%
330
55%
330
21%
804
July1st to 15thNight
53%
310
16%
1240
23%
310
59%
310
30%
665
July16th to endNight
54%
348
14%
1306
14%
326
59%
326
30%
709
August1st to 15thNight
53%
466
16%
1447
11%
464
57%
464
29%
878
August16th to endNight
52%
638
22%
1688
10%
638
58%
638
37%
1019
September1st to 15thNight
47%
660
20%
1650
9%
660
52%
660
35%
1064
September16th to endNight
49%
657
21%
1807
14%
657
53%
657
30%
1155
October1st to 15thNight
33%
660
17%
1980
12%
660
40%
660
19%
1387
October16th to endNight
22%
704
10%
2161
3%
704
29%
704
13%
1651
November1st to 15thNight
29%
700
18%
2342
14%
700
37%
700
18%
1591
November16th to endNight
22%
720
13%
2520
7%
720
30%
720
11%
1862
December1st to 15thNight
15%
720
7%
2520
3%
720
20%
720
9%
1939
December16th to endNight
13%
768
8%
2688
2%
768
20%
768
8%
2160

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
17%8%36%5%3445%6%33%
45778
Night
17%8%36%5%34446%34%
45637
Cloud CoverDay
17%8%36%5%3445%6%33%
45788
Night
17%9%36%5%3445%6%34%
45642
TransparencyDay
49%6%12%20%10%1
45466
Night
49%5%11%20%10%1
45467
SeeingDay
21%11%29%22%11%4
4820
Night
22%11%30%23%10%
14300

By Month

Percentage Cloud Cover NE (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
21%14%36%6%35%345%25%
1432
16th to endDay
13%14%6%10%8%45%43423%
1638
February1st to 15thDay
14%14%412%7%345%45%22%
1575
16th to endDay
18%14%47%7%3443426%
1506
March1st to 15thDay
17%12%5%7%8%44425%26%
1888
16th to endDay
17%8%35%5%3334439%
2163
April1st to 15thDay
22%11%345%23325%33%
2048
16th to endDay
19%8%25%42435%6%37%
2043
May1st to 15thDay
16%7%36%5%3445%8%34%
2286
16th to endDay
14%5%25%5%25%45%8%39%
2394
June1st to 15thDay
22%5%35%5%245%5%7%31%
2310
16th to endDay
16%6%346%25%5%5%8%34%
2310
July1st to 15thDay
13%424436%5%6%8%41%
2310
16th to endDay
11%5%25%5%36%5%8%9%36%
2458
August1st to 15thDay
12%5%26%435%6%7%8%38%
2173
16th to endDay
14%424425%46%8%43%
2151
September1st to 15thDay
16%5%24424448%42%
1980
16th to endDay
16%6%2432335%7%43%
1821
October1st to 15thDay
20%6%25%5%33346%36%
1650
16th to endDay
29%8%36%5%33445%25%
1711
November1st to 15thDay
15%7%46%5%35%45%6%34%
1515
16th to endDay
22%12%46%5%235%35%27%
1440
December1st to 15thDay
21%15%5%5%5%345%5%422%
1440
16th to endDay
23%15%5%9%5%2434421%
1536
January1st to 15thNight
21%13%410%6%34435%22%
2506
16th to endNight
14%13%5%8%7%35%45%5%25%
2583
February1st to 15thNight
16%12%5%8%6%36%445%25%
2285
16th to endNight
17%10%47%6%3435%5%29%
1967
March1st to 15thNight
20%9%46%6%34445%31%
2048
16th to endNight
16%8%35%423345%42%
2061
April1st to 15thNight
23%7%45%423345%34%
1716
16th to endNight
17%6%25%424445%40%
1595
May1st to 15thNight
19%6%2442345%6%38%
1334
16th to endNight
11%5%245%25%45%7%44%
1367
June1st to 15thNight
18%5%26%435%45%8%34%
1320
16th to endNight
14%3235%25%7%6%7%40%
1320
July1st to 15thNight
9%224435%5%5%9%48%
1320
16th to endNight
8%32343346%9%49%
1402
August1st to 15thNight
10%425%5%2446%8%46%
1457
16th to endNight
9%33232446%7%51%
1688
September1st to 15thNight
15%5%2442235%8%46%
1650
16th to endNight
15%424334346%46%
1807
October1st to 15thNight
20%6%35%5%24445%37%
1980
16th to endNight
23%10%27%6%335%46%26%
2161
November1st to 15thNight
18%9%25%424446%36%
2342
16th to endNight
24%8%36%435%45%5%28%
2520
December1st to 15thNight
21%15%47%5%24345%24%
2520
16th to endNight
22%15%5%7%6%34345%20%
2688

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
21%13%36%6%34435%26%
1432
16th to endDay
14%14%7%10%8%35%44422%
1638
February1st to 15thDay
15%14%413%7%34445%22%
1575
16th to endDay
18%14%47%8%4443425%
1506
March1st to 15thDay
17%13%48%8%44435%25%
1899
16th to endDay
17%9%45%5%2333439%
2162
April1st to 15thDay
22%11%445%2323434%
2048
16th to endDay
19%8%34424345%37%
2043
May1st to 15thDay
16%8%35%5%345%5%7%34%
2286
16th to endDay
14%6%25%435%46%7%38%
2394
June1st to 15thDay
22%7%245%245%5%7%31%
2310
16th to endDay
16%6%245%35%45%8%35%
2310
July1st to 15thDay
12%424435%6%5%9%41%
2310
16th to endDay
10%5%35%6%35%6%7%9%36%
2458
August1st to 15thDay
12%5%25%5%36%6%6%8%37%
2173
16th to endDay
13%5%25%42446%8%43%
2151
September1st to 15thDay
15%5%25%42335%7%42%
1980
16th to endDay
16%6%2432335%7%43%
1821
October1st to 15thDay
20%6%25%5%33347%36%
1650
16th to endDay
28%8%35%6%3345%5%25%
1711
November1st to 15thDay
15%7%46%5%345%5%6%34%
1515
16th to endDay
22%11%38%434346%27%
1440
December1st to 15thDay
21%15%35%6%26%45%5%21%
1440
16th to endDay
23%16%5%8%6%2434421%
1536
January1st to 15thNight
21%14%49%6%24435%22%
2506
16th to endNight
14%13%5%8%7%45%45%425%
2583
February1st to 15thNight
16%12%5%8%7%35%346%25%
2278
16th to endNight
17%10%47%7%3445%5%29%
1967
March1st to 15thNight
20%9%5%6%5%34345%31%
2060
16th to endNight
16%8%36%323445%41%
2061
April1st to 15thNight
24%7%35%424345%34%
1716
16th to endNight
17%6%25%425%445%40%
1595
May1st to 15thNight
18%7%3442445%5%39%
1334
16th to endNight
11%5%34435%45%8%43%
1367
June1st to 15thNight
17%6%25%6%15%5%6%7%34%
1320
16th to endNight
13%4245%26%6%6%8%40%
1320
July1st to 15thNight
9%3243345%5%8%48%
1320
16th to endNight
7%3244335%6%8%49%
1402
August1st to 15thNight
10%4245%335%6%8%45%
1457
16th to endNight
8%42333446%7%51%
1688
September1st to 15thNight
14%5%2432245%7%46%
1650
16th to endNight
16%32432445%6%46%
1807
October1st to 15thNight
20%6%35%434445%36%
1980
16th to endNight
23%9%27%6%345%45%26%
2161
November1st to 15thNight
19%9%24424446%36%
2342
16th to endNight
24%9%26%435%445%28%
2520
December1st to 15thNight
21%15%47%5%24346%24%
2520
16th to endNight
23%14%5%7%6%35%345%20%
2688

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
60%410%17%5%1
1433
16th to endDay
63%5%9%11%8%
1638
February1st to 15thDay
64%5%8%15%5%
1577
16th to endDay
61%5%10%12%9%1
1506
March1st to 15thDay
61%412%15%5%1
1899
16th to endDay
48%47%19%14%4
2163
April1st to 15thDay
54%38%18%11%2
2048
16th to endDay
48%46%20%16%3
2043
May1st to 15thDay
47%5%10%19%13%2
2286
16th to endDay
42%7%14%21%12%2
2398
June1st to 15thDay
50%6%13%18%10%
2310
16th to endDay
44%6%13%21%12%1
2310
July1st to 15thDay
35%7%14%29%12%
2161
16th to endDay
40%8%17%23%8%
2291
August1st to 15thDay
40%8%15%23%11%
2159
16th to endDay
37%6%15%28%11%
2151
September1st to 15thDay
40%7%14%26%11%
1980
16th to endDay
40%6%10%30%11%
1821
October1st to 15thDay
47%6%14%21%11%
1650
16th to endDay
58%6%12%17%5%
1711
November1st to 15thDay
47%8%12%19%10%
1515
16th to endDay
58%5%12%14%8%
1440
December1st to 15thDay
62%7%13%13%3
1440
16th to endDay
67%5%9%12%5%
1536
January1st to 15thNight
64%5%9%13%5%
2506
16th to endNight
59%5%9%16%8%
2583
February1st to 15thNight
60%6%10%17%5%
2287
16th to endNight
55%5%10%18%9%
1967
March1st to 15thNight
55%310%21%7%
2060
16th to endNight
44%49%20%17%2
2061
April1st to 15thNight
51%37%19%15%1
1716
16th to endNight
44%49%19%18%3
1595
May1st to 15thNight
44%5%9%19%15%4
1334
16th to endNight
38%6%13%21%17%2
1369
June1st to 15thNight
46%7%13%20%12%
1320
16th to endNight
39%7%14%22%15%
1320
July1st to 15thNight
30%6%11%29%20%1
1240
16th to endNight
30%7%16%29%14%1
1306
August1st to 15thNight
34%8%15%26%14%1
1447
16th to endNight
30%6%13%34%14%
1688
September1st to 15thNight
35%5%15%32%11%
1650
16th to endNight
37%5%11%30%13%
1807
October1st to 15thNight
48%6%11%21%12%
1980
16th to endNight
57%6%13%14%7%
2161
November1st to 15thNight
48%6%12%19%11%1
2342
16th to endNight
57%6%10%18%6%1
2520
December1st to 15thNight
61%5%14%14%4
2520
16th to endNight
66%5%11%10%5%
2688

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
25%23%30%11%10%
60
16th to endDay
32%18%29%13%6%
81
February1st to 15thDay
28%28%34%7%
90
16th to endDay
32%20%30%12%4
165
March1st to 15thDay
27%15%29%21%7%
270
16th to endDay
26%15%33%14%8%1
288
April1st to 15thDay
29%17%27%12%11%
235
16th to endDay
21%14%29%16%10%7%
210
May1st to 15thDay
21%9%29%25%10%4
228
16th to endDay
16%9%33%23%12%4
267
June1st to 15thDay
24%7%31%24%9%2
255
16th to endDay
16%5%29%30%12%5%
255
July1st to 15thDay
14%422%33%16%7%
245
16th to endDay
13%235%30%12%6%
270
August1st to 15thDay
13%424%31%17%7%
253
16th to endDay
13%5%25%26%15%13%
268
September1st to 15thDay
14%5%28%20%17%13%
255
16th to endDay
18%9%25%22%15%8%
254
October1st to 15thDay
22%11%29%18%14%3
255
16th to endDay
33%16%26%19%4
263
November1st to 15thDay
17%10%33%28%9%1
169
16th to endDay
25%10%31%25%6%1
60
December1st to 15thDay
25%21%25%20%8%
60
16th to endDay
43%25%25%6%
64
January1st to 15thNight
30%17%29%17%4
720
16th to endNight
23%14%35%21%4
768
February1st to 15thNight
24%16%38%18%2
704
16th to endNight
23%13%37%20%4
631
March1st to 15thNight
26%14%33%21%3
720
16th to endNight
20%13%32%22%9%1
768
April1st to 15thNight
27%12%35%20%4
686
16th to endNight
19%12%31%23%11%
605
May1st to 15thNight
22%430%27%13%
344
16th to endNight
11%6%37%32%11%1
343
June1st to 15thNight
18%6%31%30%12%
330
16th to endNight
14%424%42%13%
330
July1st to 15thNight
8%326%39%22%
310
16th to endNight
8%130%40%17%
348
August1st to 15thNight
12%422%34%24%2
466
16th to endNight
10%327%32%23%2
638
September1st to 15thNight
16%5%25%28%20%2
660
16th to endNight
17%7%22%27%21%3
657
October1st to 15thNight
25%10%27%19%15%1
660
16th to endNight
28%14%28%22%6%
704
November1st to 15thNight
24%10%30%23%10%
700
16th to endNight
32%16%25%16%8%
720
December1st to 15thNight
32%18%29%16%3
720
16th to endNight
32%15%32%15%2
768
Page generated at 2017-04-08 05:35:20. Version ac04

Copyright 2017 A. Danko


Starlight Cascade Observatory Clear Sky Chart | Charts Home