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 2017-10-31.

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
30%
14912
15%
47389
8%
14881
37%
14881
18%
32946

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
22%
718
16%
1796
4%
718
28%
718
21%
1308
April16th to endNight
30%
660
17%
1740
7%
660
37%
660
25%
1200
May1st to 15thNight
37%
375
17%
1455
15%
375
46%
375
18%
933
May16th to endNight
39%
374
15%
1497
14%
374
50%
374
21%
892
June1st to 15thNight
38%
360
11%
1440
10%
360
46%
360
18%
928
June16th to endNight
46%
360
10%
1440
13%
360
52%
360
20%
892
July1st to 15thNight
53%
340
15%
1360
22%
340
58%
340
29%
746
July16th to endNight
55%
376
15%
1418
16%
354
60%
354
30%
771
August1st to 15thNight
54%
509
15%
1580
11%
507
58%
507
29%
956
August16th to endNight
53%
696
24%
1842
11%
696
59%
696
38%
1097
September1st to 15thNight
49%
720
20%
1800
9%
720
54%
720
36%
1147
September16th to endNight
51%
717
24%
1971
17%
717
56%
717
32%
1238
October1st to 15thNight
34%
720
16%
2160
12%
720
41%
720
20%
1503
October16th to endNight
22%
768
12%
2356
5%
768
31%
768
14%
1763
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%
48371
Night
17%8%36%5%34446%35%
47559
Cloud CoverDay
17%8%36%5%3445%6%33%
48381
Night
17%8%36%5%3445%6%34%
47564
TransparencyDay
49%6%12%20%10%1
48059
Night
49%5%11%20%11%1
47389
SeeingDay
21%11%29%21%11%4
5638
Night
22%11%30%24%10%1
14913

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%34%
2152
16th to endDay
19%8%25%424346%37%
2229
May1st to 15thDay
18%8%35%5%3445%7%33%
2495
16th to endDay
15%5%25%5%35%45%8%38%
2618
June1st to 15thDay
22%5%35%5%245%5%7%32%
2520
16th to endDay
16%6%345%25%5%5%8%34%
2520
July1st to 15thDay
13%424436%5%6%8%39%
2520
16th to endDay
11%5%25%6%35%5%7%9%35%
2654
August1st to 15thDay
11%5%26%435%6%7%8%37%
2370
16th to endDay
14%42442446%8%43%
2348
September1st to 15thDay
15%5%24424448%43%
2160
16th to endDay
15%5%2432336%7%45%
1986
October1st to 15thDay
21%6%35%5%33346%36%
1800
16th to endDay
27%8%36%5%33445%26%
1866
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
22%7%45%423345%35%
1796
16th to endNight
16%6%25%5%2445%6%40%
1740
May1st to 15thNight
21%6%2442345%6%37%
1455
16th to endNight
11%5%25%5%25%45%7%43%
1495
June1st to 15thNight
18%5%26%435%45%8%35%
1440
16th to endNight
15%4235%25%7%6%7%38%
1440
July1st to 15thNight
9%324425%5%49%47%
1440
16th to endNight
8%32343346%9%49%
1514
August1st to 15thNight
10%425%5%2446%8%46%
1590
16th to endNight
8%33232446%7%51%
1842
September1st to 15thNight
15%5%1332235%7%47%
1800
16th to endNight
15%313434346%47%
1971
October1st to 15thNight
20%6%35%5%24445%38%
2160
16th to endNight
23%9%27%6%33446%28%
2356
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%23335%34%
2152
16th to endDay
19%8%34424345%38%
2229
May1st to 15thDay
18%8%35%5%3445%7%32%
2495
16th to endDay
14%6%25%435%46%8%37%
2618
June1st to 15thDay
21%6%245%245%5%7%32%
2520
16th to endDay
16%6%25%5%35%45%8%34%
2520
July1st to 15thDay
13%4245%35%6%5%9%40%
2520
16th to endDay
10%5%35%6%35%5%7%10%35%
2654
August1st to 15thDay
11%5%25%5%36%5%7%8%37%
2370
16th to endDay
12%5%25%425%46%8%43%
2348
September1st to 15thDay
15%5%25%42345%7%43%
2160
16th to endDay
15%5%2432235%7%46%
1986
October1st to 15thDay
20%6%25%5%33347%36%
1800
16th to endDay
26%8%35%5%3345%5%26%
1866
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
23%7%35%423345%35%
1796
16th to endNight
17%5%25%425%445%40%
1740
May1st to 15thNight
20%7%3432345%5%38%
1455
16th to endNight
11%5%34436%45%8%42%
1495
June1st to 15thNight
17%6%25%6%15%5%6%8%35%
1440
16th to endNight
14%4245%25%6%6%7%38%
1440
July1st to 15thNight
9%4243345%5%8%48%
1440
16th to endNight
8%4244335%6%8%49%
1514
August1st to 15thNight
9%4245%335%6%8%45%
1590
16th to endNight
8%42332446%8%51%
1842
September1st to 15thNight
14%5%2432245%7%48%
1800
16th to endNight
15%32432435%6%48%
1971
October1st to 15thNight
20%6%35%434445%37%
2160
16th to endNight
22%9%26%6%335%45%28%
2356
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
53%38%19%12%2
2152
16th to endDay
48%47%20%15%3
2229
May1st to 15thDay
50%5%10%18%12%2
2495
16th to endDay
43%7%14%20%11%1
2622
June1st to 15thDay
49%6%13%19%10%
2520
16th to endDay
45%7%14%20%11%
2520
July1st to 15thDay
37%7%14%28%12%
2371
16th to endDay
41%8%17%23%8%
2487
August1st to 15thDay
40%8%16%22%10%
2356
16th to endDay
37%6%15%29%11%
2348
September1st to 15thDay
38%7%14%26%12%
2160
16th to endDay
37%6%11%31%12%
1986
October1st to 15thDay
47%5%13%22%10%
1800
16th to endDay
57%6%13%17%5%
1866
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
50%47%19%15%1
1796
16th to endNight
44%5%10%19%17%3
1740
May1st to 15thNight
46%5%9%19%14%4
1455
16th to endNight
39%6%13%21%16%2
1497
June1st to 15thNight
45%6%13%20%12%
1440
16th to endNight
40%7%14%21%14%
1440
July1st to 15thNight
31%7%11%27%20%1
1360
16th to endNight
30%7%16%29%15%1
1418
August1st to 15thNight
34%8%16%26%13%
1580
16th to endNight
29%6%13%34%14%
1842
September1st to 15thNight
34%5%15%31%12%1
1800
16th to endNight
35%5%11%31%14%
1971
October1st to 15thNight
47%6%11%22%12%
2160
16th to endNight
55%6%14%16%7%
2356
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
28%17%30%12%10%
270
16th to endDay
22%19%27%15%9%5%
270
May1st to 15thDay
27%10%27%23%8%3
288
16th to endDay
19%11%34%20%11%3
331
June1st to 15thDay
24%7%34%23%8%1
315
16th to endDay
19%8%30%26%10%4
315
July1st to 15thDay
15%5%25%31%16%6%
305
16th to endDay
14%333%29%13%6%
326
August1st to 15thDay
13%325%31%17%7%
313
16th to endDay
13%7%25%25%15%13%
332
September1st to 15thDay
13%6%27%21%16%13%
315
16th to endDay
15%8%23%21%21%9%
314
October1st to 15thDay
23%11%30%17%12%4
315
16th to endDay
31%18%24%21%4
322
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
26%12%35%21%4
718
16th to endNight
19%13%33%22%11%
660
May1st to 15thNight
25%5%28%28%12%
375
16th to endNight
11%6%37%32%11%1
375
June1st to 15thNight
18%6%31%30%13%
360
16th to endNight
15%426%40%11%
360
July1st to 15thNight
8%227%38%21%
340
16th to endNight
8%130%40%18%1
376
August1st to 15thNight
12%421%35%24%2
509
16th to endNight
10%327%32%23%3
696
September1st to 15thNight
16%5%24%29%21%3
720
16th to endNight
17%7%20%26%23%4
717
October1st to 15thNight
25%10%26%19%15%2
720
16th to endNight
27%14%28%22%6%
768
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 2017-11-01 17:23:42. Version ac04

Copyright 2017 A. Danko


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