Intrusted Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Intrusted Observatory clear sky chart from 2005-11-05 to 2017-09-23.

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
42%
15868
26%
46984
15%
15821
52%
15821
35%
26730

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
33%
900
29%
2327
11%
895
45%
895
38%
1392
January16th to endNight
34%
960
32%
2496
12%
960
46%
960
40%
1435
February1st to 15thNight
30%
854
21%
2262
8%
850
38%
850
31%
1457
February16th to endNight
30%
632
27%
1894
10%
632
43%
632
31%
1089
March1st to 15thNight
34%
561
25%
2001
13%
561
47%
561
28%
1088
March16th to endNight
26%
576
18%
2112
12%
576
36%
576
22%
1279
April1st to 15thNight
30%
539
21%
1929
12%
539
46%
539
27%
1059
April16th to endNight
30%
540
21%
1621
14%
540
41%
540
28%
1002
May1st to 15thNight
35%
539
21%
1620
14%
539
46%
539
30%
998
May16th to endNight
47%
563
19%
1684
16%
561
54%
561
32%
989
June1st to 15thNight
52%
540
18%
1620
11%
540
59%
540
39%
889
June16th to endNight
56%
540
23%
1620
15%
540
62%
540
49%
810
July1st to 15thNight
67%
510
20%
1530
17%
510
70%
510
43%
818
July16th to endNight
73%
564
24%
1594
25%
531
76%
531
43%
836
August1st to 15thNight
75%
539
25%
1610
28%
536
78%
536
42%
866
August16th to endNight
68%
573
28%
1755
29%
573
72%
573
41%
951
September1st to 15thNight
57%
540
23%
1980
24%
540
64%
540
32%
1061
September16th to endNight
55%
516
31%
1903
27%
516
65%
516
36%
938
October1st to 15thNight
45%
590
31%
1910
23%
590
52%
590
34%
1064
October16th to endNight
42%
704
33%
2112
16%
704
55%
704
47%
1050
November1st to 15thNight
40%
828
30%
2228
12%
828
52%
828
44%
1230
November16th to endNight
35%
900
29%
2340
10%
900
48%
900
39%
1358
December1st to 15thNight
33%
900
25%
2340
10%
900
44%
900
34%
1470
December16th to endNight
34%
960
28%
2496
12%
960
45%
960
32%
1601

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
10%5%24424447%49%
47924
Night
9%423323447%53%
47180
Cloud CoverDay
10%5%2442445%7%49%
47922
Night
9%423323447%53%
47180
TransparencyDay
34%412%27%17%3
47622
Night
31%311%27%20%5%
46985
SeeingDay
11%6%26%33%18%3
5868
Night
12%8%32%34%12%1
15869

By Month

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%6%23433235%55%
1611
16th to endDay
9%5%25%423336%51%
1728
February1st to 15thDay
8%8%36%423347%47%
1610
16th to endDay
9%6%2332345%7%50%
1580
March1st to 15thDay
11%5%35%43445%6%44%
1959
16th to endDay
18%7%25%423346%42%
2112
April1st to 15thDay
13%5%24434447%45%
2019
16th to endDay
16%7%25%433345%43%
2337
May1st to 15thDay
13%6%35%5%14346%44%
2331
16th to endDay
12%5%25%5%35%5%5%7%40%
2430
June1st to 15thDay
7%313325%45%8%51%
2340
16th to endDay
5%134245%6%10%55%
2340
July1st to 15thDay
8%3234346%6%9%47%
2340
16th to endDay
5%2145%35%5%6%9%50%
2466
August1st to 15thDay
5%3245%36%5%5%8%48%
2340
16th to endDay
6%32442445%8%54%
2444
September1st to 15thDay
10%6%245%24347%48%
1980
16th to endDay
7%314423345%57%
1893
October1st to 15thDay
12%5%1332235%6%53%
1708
16th to endDay
8%413314345%58%
1760
November1st to 15thDay
6%313324346%60%
1628
16th to endDay
11%323312215%60%
1620
December1st to 15thDay
13%6%15%423336%48%
1620
16th to endDay
12%7%27%423346%44%
1728
January1st to 15thNight
7%5%24423246%55%
2327
16th to endNight
7%433313335%59%
2496
February1st to 15thNight
9%7%45%323336%48%
2252
16th to endNight
9%424423436%54%
1894
March1st to 15thNight
10%6%2332346%6%49%
2001
16th to endNight
17%7%23323346%45%
2112
April1st to 15thNight
12%5%14423347%50%
1929
16th to endNight
12%7%25%413346%47%
1621
May1st to 15thNight
13%424324446%47%
1619
16th to endNight
8%433415%46%10%46%
1683
June1st to 15thNight
42234235%5%9%53%
1620
16th to endNight
41222446%9%59%
1620
July1st to 15thNight
5%2133345%6%9%55%
1620
16th to endNight
421342446%11%53%
1702
August1st to 15thNight
42143346%7%10%52%
1620
16th to endNight
6%313424448%55%
1755
September1st to 15thNight
9%414423436%54%
1980
16th to endNight
6%31342435%7%57%
1903
October1st to 15thNight
13%414313245%54%
1910
16th to endNight
7%313212236%65%
2112
November1st to 15thNight
7%413313336%61%
2228
16th to endNight
11%5%22212336%57%
2340
December1st to 15thNight
11%6%23323446%49%
2340
16th to endNight
11%7%35%423346%47%
2496

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%6%23423245%55%
1611
16th to endDay
9%5%24423346%51%
1728
February1st to 15thDay
8%8%36%423347%47%
1610
16th to endDay
9%6%2342335%7%50%
1580
March1st to 15thDay
11%5%35%43445%6%44%
1959
16th to endDay
18%7%25%324345%42%
2110
April1st to 15thDay
13%5%2442435%6%45%
2019
16th to endDay
16%7%25%43434443%
2337
May1st to 15thDay
13%6%3442335%6%44%
2331
16th to endDay
13%5%345%35%5%5%7%40%
2430
June1st to 15thDay
7%313425%46%8%51%
2340
16th to endDay
5%1242446%10%55%
2340
July1st to 15thDay
8%313435%6%6%9%46%
2340
16th to endDay
5%2145%35%5%6%9%50%
2466
August1st to 15thDay
5%315%5%36%6%5%9%47%
2340
16th to endDay
6%32442445%8%54%
2444
September1st to 15thDay
10%6%24434346%48%
1980
16th to endDay
7%314323445%58%
1893
October1st to 15thDay
12%5%1332235%6%53%
1708
16th to endDay
8%413324336%58%
1760
November1st to 15thDay
6%313323346%60%
1628
16th to endDay
12%323312225%60%
1620
December1st to 15thDay
13%6%15%423336%49%
1620
16th to endDay
13%7%26%5%23346%44%
1728
January1st to 15thNight
8%5%135%23346%55%
2327
16th to endNight
7%433313335%59%
2496
February1st to 15thNight
9%7%45%333435%48%
2252
16th to endNight
9%424423436%54%
1894
March1st to 15thNight
10%6%2332346%6%49%
2001
16th to endNight
17%7%23323346%45%
2112
April1st to 15thNight
12%5%14423347%50%
1929
16th to endNight
12%7%25%413347%47%
1621
May1st to 15thNight
14%424314446%47%
1619
16th to endNight
8%434415%46%10%46%
1683
June1st to 15thNight
5%2234335%5%10%53%
1620
16th to endNight
4111325%46%9%60%
1620
July1st to 15thNight
5%2133245%5%9%55%
1620
16th to endNight
421343446%10%53%
1702
August1st to 15thNight
42143345%7%9%52%
1620
16th to endNight
6%313414448%55%
1755
September1st to 15thNight
9%414424436%54%
1980
16th to endNight
6%31342435%7%57%
1903
October1st to 15thNight
13%414313245%54%
1910
16th to endNight
7%313212236%65%
2112
November1st to 15thNight
7%422222336%61%
2228
16th to endNight
11%5%22212345%58%
2340
December1st to 15thNight
11%6%2342345%6%49%
2340
16th to endNight
11%7%35%423346%47%
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
32%211%29%20%2
1612
16th to endDay
34%313%29%17%2
1728
February1st to 15thDay
37%313%28%11%3
1611
16th to endDay
33%311%29%18%3
1580
March1st to 15thDay
40%39%24%18%4
1959
16th to endDay
45%39%24%13%2
2112
April1st to 15thDay
39%311%26%16%2
2019
16th to endDay
44%410%27%11%2
2337
May1st to 15thDay
41%5%11%21%18%1
2331
16th to endDay
42%5%13%23%12%1
2434
June1st to 15thDay
30%416%27%18%3
2340
16th to endDay
24%5%14%27%24%4
2340
July1st to 15thDay
31%6%12%30%16%2
2201
16th to endDay
28%5%14%31%16%3
2311
August1st to 15thDay
31%6%15%27%15%4
2326
16th to endDay
29%413%30%16%6%
2444
September1st to 15thDay
36%411%23%16%7%
1980
16th to endDay
27%310%32%21%4
1893
October1st to 15thDay
31%411%23%24%4
1708
16th to endDay
27%311%28%23%5%
1760
November1st to 15thDay
25%310%27%23%8%
1628
16th to endDay
29%29%30%23%4
1620
December1st to 15thDay
38%312%29%15%1
1620
16th to endDay
41%210%26%14%3
1728
January1st to 15thNight
31%28%30%22%3
2327
16th to endNight
28%211%30%21%4
2496
February1st to 15thNight
38%313%25%15%4
2262
16th to endNight
32%412%26%19%5%
1894
March1st to 15thNight
34%210%24%20%6%
2001
16th to endNight
41%410%24%16%2
2112
April1st to 15thNight
34%311%24%22%3
1929
16th to endNight
37%413%20%18%4
1621
May1st to 15thNight
37%313%24%18%2
1620
16th to endNight
32%6%19%25%13%2
1685
June1st to 15thNight
27%5%16%29%17%2
1620
16th to endNight
20%5%14%32%22%5%
1620
July1st to 15thNight
25%413%31%20%4
1530
16th to endNight
24%5%14%31%22%1
1594
August1st to 15thNight
25%5%15%31%17%4
1610
16th to endNight
26%411%26%23%6%
1755
September1st to 15thNight
31%411%23%18%9%
1980
16th to endNight
26%410%26%27%5%
1903
October1st to 15thNight
33%29%22%23%8%
1910
16th to endNight
22%28%29%30%6%
2112
November1st to 15thNight
25%39%25%25%10%
2228
16th to endNight
29%28%29%23%6%
2340
December1st to 15thNight
34%411%30%17%1
2340
16th to endNight
38%311%25%14%6%
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
21%10%34%27%6%
90
16th to endDay
11%12%53%19%21
96
February1st to 15thDay
7%21%44%23%3
90
16th to endDay
319%44%27%4
81
March1st to 15thDay
14%17%51%13%3
90
16th to endDay
23%10%35%26%4
96
April1st to 15thDay
17%10%36%26%7%
138
16th to endDay
21%10%40%20%5%1
447
May1st to 15thDay
16%10%34%26%9%2
468
16th to endDay
16%8%31%29%11%3
517
June1st to 15thDay
7%428%37%20%2
495
16th to endDay
6%226%42%19%3
495
July1st to 15thDay
9%116%44%23%5%
475
16th to endDay
5%9%40%36%7%
515
August1st to 15thDay
5%112%39%35%4
493
16th to endDay
8%214%34%34%6%
484
September1st to 15thDay
5%17%42%27%6%
135
16th to endDay
5%325%38%18%8%
111
October1st to 15thDay
6%7%28%35%10%11%
90
16th to endDay
7%5%43%28%10%5%
96
November1st to 15thDay
6%136%30%21%4
90
16th to endDay
31%20%25%18%31
90
December1st to 15thDay
13%14%47%15%5%3
90
16th to endDay
22%12%35%22%6%
96
January1st to 15thNight
11%11%39%29%6%
900
16th to endNight
10%11%39%33%5%
960
February1st to 15thNight
14%12%36%31%4
854
16th to endNight
12%14%37%30%4
632
March1st to 15thNight
13%11%37%31%6%
561
16th to endNight
21%12%37%24%4
576
April1st to 15thNight
17%11%39%24%6%
539
16th to endNight
16%11%38%25%7%
540
May1st to 15thNight
17%7%35%28%10%1
540
16th to endNight
10%6%30%37%12%2
563
June1st to 15thNight
6%332%39%17%
540
16th to endNight
4134%44%14%1
540
July1st to 15thNight
6%118%51%19%2
510
16th to endNight
5%11%48%32%2
564
August1st to 15thNight
5%19%50%31%2
539
16th to endNight
7%114%37%35%3
573
September1st to 15thNight
11%223%39%21%1
540
16th to endNight
8%326%36%21%3
516
October1st to 15thNight
16%430%29%18%1
590
16th to endNight
9%8%37%31%12%
704
November1st to 15thNight
8%10%36%31%10%1
828
16th to endNight
14%13%34%30%7%
900
December1st to 15thNight
17%9%37%30%5%
900
16th to endNight
15%10%35%34%4
960
Page generated at 2017-09-24 08:15:53. Version ac04

Copyright 2017 A. Danko


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