CRUST Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the CRUST Observatory clear sky chart from 2005-11-05 to 2017-09-24.

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
38%
16250
14%
46851
8%
16204
43%
16204
23%
32503

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
29%
900
9%
2685
6%
895
33%
895
15%
2043
January16th to endNight
26%
960
11%
2685
5%
960
31%
960
14%
2118
February1st to 15thNight
38%
878
11%
2288
4%
875
42%
875
19%
1725
February16th to endNight
33%
747
13%
2009
7%
747
37%
747
19%
1522
March1st to 15thNight
32%
609
12%
2049
8%
609
37%
609
17%
1470
March16th to endNight
33%
576
14%
2112
11%
576
41%
576
17%
1437
April1st to 15thNight
35%
539
17%
1747
13%
539
44%
539
24%
1106
April16th to endNight
35%
540
14%
1620
11%
540
40%
540
20%
1147
May1st to 15thNight
35%
540
13%
1543
6%
540
38%
540
22%
1085
May16th to endNight
41%
563
13%
1369
4%
561
45%
561
34%
899
June1st to 15thNight
49%
540
10%
1260
6%
540
52%
540
36%
842
June16th to endNight
52%
540
10%
1260
5%
540
55%
540
41%
819
July1st to 15thNight
62%
510
14%
1190
7%
510
65%
510
53%
685
July16th to endNight
62%
564
18%
1304
8%
531
63%
531
48%
759
August1st to 15thNight
66%
539
21%
1610
15%
536
69%
536
42%
877
August16th to endNight
57%
573
22%
1719
20%
573
63%
573
41%
942
September1st to 15thNight
59%
540
20%
1830
20%
540
65%
540
38%
947
September16th to endNight
47%
519
23%
1914
19%
519
56%
519
30%
1067
October1st to 15thNight
38%
632
20%
1952
15%
632
42%
632
26%
1220
October16th to endNight
33%
806
13%
2214
6%
806
37%
806
20%
1600
November1st to 15thNight
31%
875
15%
2412
6%
875
38%
875
21%
1739
November16th to endNight
28%
900
12%
2520
7%
900
32%
900
17%
1905
December1st to 15thNight
26%
900
7%
2679
4%
900
29%
900
13%
2130
December16th to endNight
19%
960
7%
2880
3%
960
24%
960
9%
2419

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
13%8%37%5%3445%7%35%
48098
Night
11%8%47%6%3445%6%36%
47004
Cloud CoverDay
13%8%36%6%3445%7%35%
48108
Night
11%8%47%6%3445%6%36%
47007
Cloud CoverDay
13%8%36%5%3445%7%35%
48109
Night
11%9%47%6%3445%6%36%
47008
Cloud CoverDay
13%8%36%5%3445%7%35%
48107
Night
11%9%47%6%3445%6%36%
47008
TransparencyDay
47%5%15%22%7%
47768
Night
47%5%14%22%8%
46851
SeeingDay
16%7%27%29%16%3
6238
Night
15%6%30%33%12%1
16252

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
7%10%6%12%7%45%5%7%7%24%
1253
16th to endDay
10%15%6%11%7%47%6%7%5%16%
1536
February1st to 15thDay
8%11%5%9%8%46%5%5%6%26%
1575
16th to endDay
10%12%5%11%10%5%7%5%6%6%19%
1476
March1st to 15thDay
15%11%5%8%6%2435%6%28%
1899
16th to endDay
14%12%48%6%3445%8%27%
2112
April1st to 15thDay
12%9%46%5%35%5%5%6%34%
2198
16th to endDay
20%10%36%5%2445%5%30%
2340
May1st to 15thDay
20%8%36%6%3445%6%31%
2406
16th to endDay
16%6%25%5%2445%9%35%
2743
June1st to 15thDay
19%6%25%42446%8%35%
2700
16th to endDay
11%425%5%36%5%6%7%40%
2700
July1st to 15thDay
9%3145%245%6%9%46%
2700
16th to endDay
6%313435%6%7%9%49%
2774
August1st to 15thDay
9%416%5%35%6%6%9%42%
2340
16th to endDay
10%5%23323347%52%
2483
September1st to 15thDay
12%5%15%42335%7%47%
2126
16th to endDay
13%6%245%23347%46%
1904
October1st to 15thDay
16%10%26%5%23337%39%
1667
16th to endDay
17%10%46%5%25%447%31%
1658
November1st to 15thDay
14%11%49%424435%35%
1446
16th to endDay
12%13%5%11%7%35%435%26%
1440
December1st to 15thDay
11%16%7%11%8%45%5%4418%
1278
16th to endDay
13%15%7%10%9%4434419%
1344
January1st to 15thNight
7%11%7%10%8%45%5%6%6%24%
2685
16th to endNight
11%12%5%9%7%5%6%5%6%6%23%
2685
February1st to 15thNight
9%10%5%7%6%5%7%6%5%6%29%
2285
16th to endNight
8%10%5%8%10%45%5%6%6%27%
2009
March1st to 15thNight
12%10%6%8%6%35%45%6%31%
2037
16th to endNight
13%9%38%6%35%446%33%
2112
April1st to 15thNight
11%8%36%4235%6%6%41%
1747
16th to endNight
19%10%45%423445%34%
1620
May1st to 15thNight
18%8%35%424445%36%
1543
16th to endNight
12%42432446%8%45%
1368
June1st to 15thNight
13%3244246%6%10%42%
1260
16th to endNight
6%315%5%345%5%10%47%
1260
July1st to 15thNight
4332146%5%7%60%
1260
16th to endNight
411432446%10%56%
1393
August1st to 15thNight
7%21442245%9%54%
1620
16th to endNight
6%31342335%7%56%
1719
September1st to 15thNight
8%312323348%57%
1830
16th to endNight
13%423313447%50%
1914
October1st to 15thNight
15%6%25%423348%41%
1952
16th to endNight
19%9%35%5%2445%6%33%
2214
November1st to 15thNight
11%10%5%9%5%33445%34%
2412
16th to endNight
13%10%5%7%7%46%45%6%28%
2520
December1st to 15thNight
11%13%6%10%8%46%5%5%5%20%
2679
16th to endNight
14%17%7%11%10%4443417%
2880

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
7%10%7%11%7%445%7%7%24%
1254
16th to endDay
10%15%7%11%7%47%6%7%417%
1536
February1st to 15thDay
7%12%5%9%9%5%6%6%5%6%26%
1575
16th to endDay
9%12%5%10%10%5%7%5%5%6%19%
1476
March1st to 15thDay
15%11%6%8%7%24446%28%
1910
16th to endDay
14%12%47%6%25%45%8%27%
2110
April1st to 15thDay
13%8%46%5%3446%7%34%
2198
16th to endDay
20%10%36%5%2445%6%30%
2340
May1st to 15thDay
20%8%36%6%3435%6%31%
2406
16th to endDay
17%6%35%5%3445%8%35%
2743
June1st to 15thDay
19%6%25%42445%8%36%
2700
16th to endDay
11%425%5%35%5%6%8%40%
2700
July1st to 15thDay
8%3145%246%6%9%46%
2700
16th to endDay
5%314425%5%6%10%49%
2774
August1st to 15thDay
9%415%5%35%6%6%8%42%
2340
16th to endDay
10%5%24324347%52%
2483
September1st to 15thDay
12%425%43335%6%48%
2126
16th to endDay
13%5%25%5%23347%46%
1904
October1st to 15thDay
16%9%25%5%23346%39%
1667
16th to endDay
18%10%46%5%25%346%31%
1658
November1st to 15thDay
14%11%5%9%424435%35%
1446
16th to endDay
12%13%5%11%7%25%435%27%
1440
December1st to 15thDay
11%16%7%11%9%46%5%4418%
1278
16th to endDay
13%15%6%11%9%4435%419%
1344
January1st to 15thNight
7%11%7%11%8%46%5%6%6%24%
2685
16th to endNight
11%12%5%9%8%5%6%5%6%5%22%
2685
February1st to 15thNight
9%11%47%7%47%6%5%6%29%
2278
16th to endNight
8%10%5%9%10%45%5%6%6%27%
2009
March1st to 15thNight
12%9%5%8%7%35%5%46%31%
2049
16th to endNight
13%9%48%6%3445%6%33%
2110
April1st to 15thNight
12%8%25%4235%6%6%41%
1747
16th to endNight
19%11%35%5%23445%34%
1620
May1st to 15thNight
18%7%36%42445%5%36%
1542
16th to endNight
12%435%32445%9%44%
1369
June1st to 15thNight
12%325%3346%5%10%42%
1260
16th to endNight
6%3245%35%5%6%9%47%
1260
July1st to 15thNight
42122235%6%7%60%
1260
16th to endNight
421342447%9%55%
1393
August1st to 15thNight
6%21442346%8%55%
1620
16th to endNight
7%32342335%6%57%
1719
September1st to 15thNight
8%31332335%7%57%
1830
16th to endNight
13%32331335%7%50%
1914
October1st to 15thNight
15%6%25%423348%42%
1952
16th to endNight
19%9%35%5%245%47%33%
2214
November1st to 15thNight
11%10%5%9%5%33445%34%
2412
16th to endNight
13%10%5%7%7%45%5%5%6%28%
2520
December1st to 15thNight
11%14%6%9%8%46%5%5%5%20%
2679
16th to endNight
14%18%7%11%10%3434417%
2880

Percentage Cloud Cover SW (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
7%10%7%12%6%5%45%7%7%24%
1253
16th to endDay
9%16%6%12%7%47%6%7%5%17%
1536
February1st to 15thDay
8%11%49%9%47%5%5%6%26%
1575
16th to endDay
10%12%5%10%10%5%6%5%6%6%19%
1476
March1st to 15thDay
15%11%6%8%7%24446%28%
1910
16th to endDay
14%11%5%7%6%3435%7%28%
2112
April1st to 15thDay
13%9%45%5%45%5%5%6%35%
2198
16th to endDay
20%10%36%5%2445%6%30%
2340
May1st to 15thDay
21%7%36%5%3435%7%30%
2406
16th to endDay
17%6%25%5%2446%8%36%
2743
June1st to 15thDay
19%6%25%42445%8%36%
2700
16th to endDay
11%425%5%36%5%5%7%41%
2700
July1st to 15thDay
9%3145%246%6%8%46%
2700
16th to endDay
6%2144245%7%10%48%
2774
August1st to 15thDay
10%4145%345%6%8%43%
2340
16th to endDay
10%5%24323337%52%
2483
September1st to 15thDay
13%415%42335%6%47%
2126
16th to endDay
14%425%5%23447%45%
1904
October1st to 15thDay
17%10%25%423336%39%
1667
16th to endDay
18%10%37%435%446%31%
1658
November1st to 15thDay
14%11%5%8%433345%35%
1446
16th to endDay
12%13%6%10%8%25%435%26%
1440
December1st to 15thDay
11%16%7%11%9%36%5%5%318%
1278
16th to endDay
13%15%7%10%9%4444419%
1344
January1st to 15thNight
7%11%7%11%8%46%5%6%6%24%
2685
16th to endNight
11%12%6%9%7%5%6%5%6%5%22%
2685
February1st to 15thNight
8%11%47%6%47%6%5%6%29%
2278
16th to endNight
8%11%5%8%9%45%5%5%6%27%
2009
March1st to 15thNight
12%10%5%9%6%35%446%31%
2049
16th to endNight
13%8%38%6%35%35%6%34%
2112
April1st to 15thNight
12%7%35%4245%46%41%
1747
16th to endNight
20%10%45%413435%34%
1620
May1st to 15thNight
19%7%35%5%14445%36%
1542
16th to endNight
13%41442446%8%44%
1368
June1st to 15thNight
13%3244236%5%10%42%
1260
16th to endNight
7%325%5%35%47%9%47%
1260
July1st to 15thNight
43122136%6%8%60%
1260
16th to endNight
421432446%10%55%
1393
August1st to 15thNight
7%21442235%9%55%
1620
16th to endNight
7%31431345%7%56%
1719
September1st to 15thNight
8%313223347%57%
1830
16th to endNight
13%42322345%6%50%
1914
October1st to 15thNight
16%6%24423448%42%
1952
16th to endNight
19%9%345%24446%33%
2214
November1st to 15thNight
11%10%5%9%6%335%45%33%
2412
16th to endNight
13%11%5%7%7%45%45%6%27%
2520
December1st to 15thNight
11%14%6%10%9%46%5%5%421%
2679
16th to endNight
14%17%7%12%9%3434416%
2880

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
7%11%6%12%7%45%5%7%6%24%
1253
16th to endDay
10%15%6%12%6%5%7%5%6%5%17%
1536
February1st to 15thDay
8%11%5%9%9%47%6%5%6%26%
1575
16th to endDay
9%13%410%10%6%6%6%47%18%
1476
March1st to 15thDay
15%12%6%7%7%2435%6%28%
1910
16th to endDay
14%11%5%8%6%3435%8%27%
2110
April1st to 15thDay
13%9%45%5%445%6%6%34%
2198
16th to endDay
20%10%36%5%235%5%6%30%
2340
May1st to 15thDay
20%9%35%5%34447%30%
2406
16th to endDay
16%7%35%5%2445%8%35%
2743
June1st to 15thDay
19%7%25%42445%8%35%
2700
16th to endDay
11%435%5%36%5%6%8%39%
2700
July1st to 15thDay
8%3245%35%5%6%8%46%
2700
16th to endDay
5%3244346%8%9%48%
2774
August1st to 15thDay
9%425%5%346%7%9%42%
2340
16th to endDay
10%5%24323346%52%
2483
September1st to 15thDay
12%5%15%5%2335%7%47%
2126
16th to endDay
13%5%245%24347%45%
1904
October1st to 15thDay
17%10%25%423246%39%
1667
16th to endDay
17%11%47%42445%6%30%
1658
November1st to 15thDay
13%11%49%433445%34%
1446
16th to endDay
12%13%5%11%9%34435%26%
1440
December1st to 15thDay
12%15%7%11%8%46%6%4417%
1278
16th to endDay
12%16%6%11%8%5%5%44419%
1344
January1st to 15thNight
7%11%7%10%9%45%5%6%6%24%
2685
16th to endNight
11%13%5%10%7%5%6%5%6%6%22%
2685
February1st to 15thNight
8%11%5%7%7%46%6%5%7%29%
2278
16th to endNight
7%11%5%9%10%36%5%6%6%27%
2009
March1st to 15thNight
12%10%5%9%5%46%45%6%30%
2049
16th to endNight
13%8%48%6%35%446%34%
2112
April1st to 15thNight
11%8%35%4335%5%7%40%
1747
16th to endNight
18%11%45%414435%34%
1620
May1st to 15thNight
19%8%26%5%24345%36%
1542
16th to endNight
12%4244245%6%7%44%
1368
June1st to 15thNight
12%425%4245%6%9%42%
1260
16th to endNight
6%325%5%246%6%8%47%
1260
July1st to 15thNight
431221446%8%60%
1260
16th to endNight
42234245%6%9%55%
1393
August1st to 15thNight
6%31343335%9%55%
1620
16th to endNight
7%41332435%7%56%
1719
September1st to 15thNight
8%41331335%7%57%
1830
16th to endNight
12%5%23323447%50%
1914
October1st to 15thNight
15%6%25%42335%8%41%
1952
16th to endNight
18%10%35%5%2435%6%33%
2214
November1st to 15thNight
12%11%5%8%6%33445%33%
2412
16th to endNight
12%11%5%7%7%45%45%6%26%
2520
December1st to 15thNight
10%14%6%10%9%46%5%5%421%
2679
16th to endNight
14%17%8%12%9%3444416%
2880

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
55%5%14%20%4
1254
16th to endDay
64%6%12%12%3
1536
February1st to 15thDay
56%416%17%5%
1576
16th to endDay
63%5%12%14%4
1476
March1st to 15thDay
56%5%15%18%4
1910
16th to endDay
54%6%15%19%3
2112
April1st to 15thDay
47%5%14%22%9%1
2198
16th to endDay
53%413%17%9%1
2340
May1st to 15thDay
53%412%22%7%
2406
16th to endDay
45%5%13%23%10%
2747
June1st to 15thDay
45%5%19%23%6%
2700
16th to endDay
40%6%18%27%8%
2700
July1st to 15thDay
32%7%16%31%11%
2541
16th to endDay
29%7%20%30%11%
2600
August1st to 15thDay
36%7%17%27%9%1
2326
16th to endDay
32%415%32%14%
2483
September1st to 15thDay
36%317%32%10%
2126
16th to endDay
38%417%32%6%
1904
October1st to 15thDay
46%416%24%8%
1667
16th to endDay
53%5%16%17%7%
1658
November1st to 15thDay
52%315%18%9%
1446
16th to endDay
59%6%13%14%6%
1440
December1st to 15thDay
68%312%12%2
1278
16th to endDay
67%412%11%4
1344
January1st to 15thNight
57%6%11%19%5%
2685
16th to endNight
60%6%12%15%5%
2685
February1st to 15thNight
53%6%14%19%5%
2288
16th to endNight
55%5%12%19%6%
2009
March1st to 15thNight
53%5%13%20%5%
2049
16th to endNight
50%5%15%21%6%
2112
April1st to 15thNight
41%5%13%24%12%2
1747
16th to endNight
52%310%19%10%2
1620
May1st to 15thNight
49%412%19%12%1
1543
16th to endNight
36%6%14%27%12%2
1369
June1st to 15thNight
35%5%18%28%9%1
1260
16th to endNight
30%6%19%30%10%1
1260
July1st to 15thNight
19%6%19%36%16%1
1190
16th to endNight
23%5%17%32%17%1
1304
August1st to 15thNight
26%5%14%36%14%2
1610
16th to endNight
26%417%32%17%1
1719
September1st to 15thNight
26%5%16%38%12%
1830
16th to endNight
33%5%14%32%13%
1914
October1st to 15thNight
41%316%27%10%
1952
16th to endNight
50%5%15%21%6%
2214
November1st to 15thNight
51%413%20%8%1
2412
16th to endNight
55%6%16%14%6%
2520
December1st to 15thNight
63%415%12%3
2679
16th to endNight
71%49%10%3
2880

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%6%30%28%13%2
90
16th to endDay
25%322%31%17%
96
February1st to 15thDay
16%16%40%21%5%
90
16th to endDay
18%7%37%32%31
81
March1st to 15thDay
21%10%32%26%8%1
90
16th to endDay
19%6%28%33%11%1
96
April1st to 15thDay
15%13%32%24%12%
317
16th to endDay
26%10%28%24%9%1
450
May1st to 15thDay
24%10%26%26%10%2
468
16th to endDay
19%6%28%27%14%3
517
June1st to 15thDay
20%9%26%27%14%2
495
16th to endDay
12%9%27%27%17%5%
495
July1st to 15thDay
11%425%26%24%7%
475
16th to endDay
6%325%35%20%7%
515
August1st to 15thDay
9%221%34%26%5%
493
16th to endDay
11%424%31%23%4
523
September1st to 15thDay
12%6%24%37%16%2
281
16th to endDay
15%8%35%23%9%6%
114
October1st to 15thDay
15%6%32%35%10%
90
16th to endDay
22%11%23%22%16%2
96
November1st to 15thDay
11%6%26%36%16%2
90
16th to endDay
34%13%28%17%5%
90
December1st to 15thDay
24%231%32%8%1
90
16th to endDay
17%6%43%18%9%4
96
January1st to 15thNight
13%7%34%32%11%1
900
16th to endNight
17%9%34%29%7%
960
February1st to 15thNight
14%7%26%35%13%2
880
16th to endNight
12%7%35%29%11%3
747
March1st to 15thNight
16%5%34%31%10%2
609
16th to endNight
17%7%29%31%11%1
576
April1st to 15thNight
16%8%34%32%7%
539
16th to endNight
25%7%24%31%10%
540
May1st to 15thNight
23%6%27%32%8%1
540
16th to endNight
15%333%33%14%
563
June1st to 15thNight
15%426%40%12%
540
16th to endNight
7%329%39%19%
540
July1st to 15thNight
5%225%44%20%1
510
16th to endNight
5%224%43%21%1
564
August1st to 15thNight
8%117%47%23%2
539
16th to endNight
9%325%37%21%2
573
September1st to 15thNight
11%222%41%19%2
540
16th to endNight
14%5%28%35%14%
519
October1st to 15thNight
21%6%28%34%9%
632
16th to endNight
24%6%28%29%9%
806
November1st to 15thNight
16%6%35%30%9%
875
16th to endNight
18%9%36%27%7%1
900
December1st to 15thNight
17%7%31%32%10%
900
16th to endNight
23%7%30%28%8%1
960
Page generated at 2017-09-25 08:02:25. Version ac04

Copyright 2017 A. Danko


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