This page made possible by the sponsorship of: Joseph Comeau.

Orchard Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Orchard Hill Observatory clear sky chart from 2005-11-05 to 2020-06-03.

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
25%
18126
11%
57810
7%
18095
30%
18095
12%
43560

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
11%
900
6%
3136
3%
896
15%
896
5%
2635
January16th to endNight
15%
960
8%
3360
4%
960
20%
960
7%
2697
February1st to 15thNight
13%
884
6%
2876
3%
881
19%
881
6%
2440
February16th to endNight
18%
791
10%
2373
5%
791
26%
791
9%
1901
March1st to 15thNight
20%
900
10%
2700
7%
900
25%
900
10%
2138
March16th to endNight
22%
960
19%
2500
7%
960
31%
960
16%
1852
April1st to 15thNight
19%
898
12%
2246
3%
898
24%
898
13%
1784
April16th to endNight
22%
764
13%
2100
4%
764
30%
764
14%
1562
May1st to 15thNight
24%
534
16%
1884
10%
534
34%
534
13%
1297
May16th to endNight
31%
470
12%
1881
10%
470
41%
470
15%
1242
June1st to 15thNight
28%
425
9%
1701
10%
425
35%
425
12%
1197
June16th to endNight
38%
420
9%
1680
10%
420
44%
420
16%
1094
July1st to 15thNight
46%
400
13%
1600
18%
400
52%
400
21%
978
July16th to endNight
47%
440
12%
1674
16%
418
54%
418
20%
1025
August1st to 15thNight
48%
445
14%
1676
14%
443
51%
443
18%
1081
August16th to endNight
49%
882
18%
2220
10%
882
52%
882
32%
1464
September1st to 15thNight
44%
840
14%
2103
7%
840
46%
840
27%
1466
September16th to endNight
43%
837
20%
2310
14%
837
46%
837
29%
1488
October1st to 15thNight
28%
840
14%
2449
9%
840
34%
840
17%
1782
October16th to endNight
20%
896
9%
2879
5%
896
26%
896
10%
2271
November1st to 15thNight
20%
880
13%
2862
9%
880
26%
880
11%
2170
November16th to endNight
17%
900
9%
3090
6%
900
23%
900
8%
2454
December1st to 15thNight
11%
900
4%
3150
1%
900
14%
900
5%
2686
December16th to endNight
10%
960
5%
3360
2%
960
14%
960
4%
2856

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%9%36%6%3445%6%31%
58612
Night
18%10%47%5%34446%30%
57980
Cloud CoverDay
18%9%36%5%3445%6%31%
58622
Night
19%10%47%5%34445%29%
57985
TransparencyDay
55%6%11%17%8%
58300
Night
58%5%11%16%8%
57810
SeeingDay
25%19%27%18%8%2
8985
Night
23%22%23%21%8%
18127

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
20%16%5%9%7%45%44416%
1792
16th to endDay
13%16%410%7%25%446%23%
1920
February1st to 15thDay
16%15%5%12%8%35%43420%
1975
16th to endDay
16%15%6%8%6%33346%24%
1980
March1st to 15thDay
16%14%5%9%7%35%445%24%
2240
16th to endDay
18%9%47%5%33335%35%
2775
April1st to 15thDay
22%12%36%5%34345%28%
2692
16th to endDay
21%7%35%6%23436%35%
2795
May1st to 15thDay
20%7%36%5%34446%33%
3070
16th to endDay
17%5%35%6%345%6%8%33%
3290
June1st to 15thDay
24%6%25%5%35%45%7%29%
2968
16th to endDay
18%5%25%6%35%46%7%33%
2940
July1st to 15thDay
12%425%5%35%5%6%7%39%
2940
16th to endDay
12%5%25%5%35%6%6%9%35%
3102
August1st to 15thDay
12%5%36%6%45%6%6%7%34%
2842
16th to endDay
11%325%5%345%6%8%44%
2683
September1st to 15thDay
16%5%25%42345%7%42%
2517
16th to endDay
12%424434347%47%
2310
October1st to 15thDay
21%7%25%5%35%45%6%31%
2170
16th to endDay
22%11%47%6%34335%26%
2048
November1st to 15thDay
20%10%37%6%3445%5%29%
1986
16th to endDay
22%11%48%43444425%
1857
December1st to 15thDay
21%14%6%9%6%35%345%18%
1800
16th to endDay
22%16%6%8%8%34345%16%
1920
January1st to 15thNight
18%15%6%10%7%35%44418%
3136
16th to endNight
14%14%5%9%8%34445%25%
3360
February1st to 15thNight
16%13%7%11%8%5%5%34419%
2875
16th to endNight
15%13%5%9%5%34445%27%
2373
March1st to 15thNight
21%14%5%7%5%3443426%
2687
16th to endNight
19%10%36%5%3333436%
2500
April1st to 15thNight
23%10%46%6%3434428%
2246
16th to endNight
21%9%25%5%24335%35%
2100
May1st to 15thNight
21%8%27%424346%34%
1884
16th to endNight
17%6%243445%5%8%37%
1879
June1st to 15thNight
24%6%345%2345%7%30%
1701
16th to endNight
18%5%24435%46%8%35%
1680
July1st to 15thNight
10%3235%45%5%6%10%41%
1680
16th to endNight
12%424435%6%7%8%41%
1770
August1st to 15thNight
13%4345%345%6%8%40%
1686
16th to endNight
12%5%24434347%47%
2220
September1st to 15thNight
15%425%433447%44%
2103
16th to endNight
16%414423446%47%
2310
October1st to 15thNight
18%7%26%5%24446%36%
2449
16th to endNight
25%9%36%6%34445%26%
2879
November1st to 15thNight
21%9%36%5%34446%29%
2862
16th to endNight
22%12%37%5%3444426%
3090
December1st to 15thNight
21%16%5%8%7%35%43417%
3150
16th to endNight
20%17%5%8%6%3433420%
3360

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
18%17%5%10%7%46%44416%
1792
16th to endDay
12%16%5%10%7%35%45%5%22%
1920
February1st to 15thDay
15%14%5%11%9%45%435%19%
1975
16th to endDay
15%15%7%8%6%33346%24%
1980
March1st to 15thDay
17%14%5%8%7%34435%23%
2250
16th to endDay
19%9%47%5%33345%34%
2775
April1st to 15thDay
21%10%35%5%34445%28%
2692
16th to endDay
21%8%26%5%24335%36%
2795
May1st to 15thDay
20%7%35%5%34446%33%
3070
16th to endDay
17%6%25%5%345%6%7%35%
3290
June1st to 15thDay
23%6%25%43436%8%30%
2968
16th to endDay
17%5%35%6%35%5%6%8%33%
2940
July1st to 15thDay
12%5%25%5%36%5%5%8%39%
2940
16th to endDay
13%5%245%36%5%6%8%37%
3102
August1st to 15thDay
12%5%26%6%45%6%7%7%35%
2842
16th to endDay
11%31443447%7%45%
2683
September1st to 15thDay
17%5%24424347%43%
2517
16th to endDay
13%5%1342435%7%47%
2310
October1st to 15thDay
22%7%36%5%25%446%31%
2170
16th to endDay
25%12%35%5%3444426%
2048
November1st to 15thDay
21%11%37%6%3445%5%27%
1986
16th to endDay
20%14%5%7%6%3434424%
1857
December1st to 15thDay
22%16%38%6%36%44418%
1800
16th to endDay
24%15%5%9%6%35%44415%
1920
January1st to 15thNight
19%16%6%9%8%3444417%
3136
16th to endNight
15%15%5%10%7%44345%22%
3360
February1st to 15thNight
16%14%6%13%9%4443318%
2868
16th to endNight
16%13%6%9%7%3444425%
2373
March1st to 15thNight
22%14%5%6%6%2333425%
2700
16th to endNight
19%12%36%42333435%
2499
April1st to 15thNight
23%11%47%5%3434426%
2246
16th to endNight
23%9%25%6%3344433%
2100
May1st to 15thNight
22%8%35%423346%33%
1884
16th to endNight
17%5%25%43446%7%37%
1879
June1st to 15thNight
25%6%36%424347%30%
1701
16th to endNight
17%6%245%245%6%9%36%
1680
July1st to 15thNight
11%315%5%35%47%9%41%
1680
16th to endNight
13%4235%345%7%8%40%
1770
August1st to 15thNight
12%5%25%5%46%45%9%38%
1686
16th to endNight
12%5%1442345%8%47%
2220
September1st to 15thNight
16%5%245%2445%6%43%
2103
16th to endNight
16%42432335%6%47%
2310
October1st to 15thNight
21%6%26%5%3435%6%34%
2449
16th to endNight
27%9%46%5%35%34425%
2879
November1st to 15thNight
23%10%36%5%33446%27%
2862
16th to endNight
23%13%48%5%3433424%
3090
December1st to 15thNight
23%18%5%9%6%3434316%
3150
16th to endNight
22%17%6%9%6%3443317%
3360

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
73%5%7%9%3
1793
16th to endDay
65%5%12%11%4
1920
February1st to 15thDay
70%5%6%14%2
1978
16th to endDay
65%5%9%11%7%
1980
March1st to 15thDay
66%410%12%41
2250
16th to endDay
56%39%16%12%2
2775
April1st to 15thDay
59%47%17%9%1
2692
16th to endDay
53%49%17%12%3
2795
May1st to 15thDay
53%49%17%12%1
3070
16th to endDay
48%7%12%19%10%1
3294
June1st to 15thDay
54%6%11%16%9%
2968
16th to endDay
48%7%11%20%9%1
2940
July1st to 15thDay
40%7%14%24%12%
2791
16th to endDay
44%9%15%22%8%
2935
August1st to 15thDay
47%9%16%19%6%
2828
16th to endDay
37%7%15%25%12%
2683
September1st to 15thDay
42%6%11%26%12%
2517
16th to endDay
37%6%16%27%11%1
2310
October1st to 15thDay
55%6%10%18%8%
2170
16th to endDay
63%6%11%14%3
2048
November1st to 15thDay
61%5%11%14%5%1
1986
16th to endDay
64%5%11%11%6%
1857
December1st to 15thDay
70%6%10%9%3
1800
16th to endDay
75%6%7%5%4
1920
January1st to 15thNight
73%410%8%3
3136
16th to endNight
67%5%10%11%5%
3360
February1st to 15thNight
72%5%7%9%4
2876
16th to endNight
65%49%11%8%
2373
March1st to 15thNight
64%49%15%5%
2700
16th to endNight
55%37%18%13%2
2500
April1st to 15thNight
62%38%14%10%
2246
16th to endNight
54%5%8%15%14%2
2100
May1st to 15thNight
52%47%17%15%2
1884
16th to endNight
46%7%13%18%12%1
1881
June1st to 15thNight
53%6%11%17%9%1
1701
16th to endNight
45%7%13%22%9%
1680
July1st to 15thNight
37%9%15%23%12%
1600
16th to endNight
38%9%16%22%12%
1674
August1st to 15thNight
42%8%17%22%9%
1676
16th to endNight
36%6%14%27%14%
2220
September1st to 15thNight
43%6%13%25%10%1
2103
16th to endNight
37%6%13%29%12%1
2310
October1st to 15thNight
52%5%11%20%9%
2449
16th to endNight
63%6%11%14%4
2879
November1st to 15thNight
59%5%12%14%6%1
2862
16th to endNight
65%5%10%13%4
3090
December1st to 15thNight
74%5%9%8%1
3150
16th to endNight
74%49%7%2
3360

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
30%23%24%15%42
150
16th to endDay
29%18%35%12%3
160
February1st to 15thDay
29%33%28%6%1
244
16th to endDay
25%27%30%12%2
399
March1st to 15thDay
31%23%24%18%2
450
16th to endDay
26%27%22%15%6%1
480
April1st to 15thDay
30%25%24%15%31
450
16th to endDay
29%24%23%14%6%1
439
May1st to 15thDay
31%19%26%13%6%1
468
16th to endDay
20%21%31%18%7%
523
June1st to 15thDay
31%15%28%16%7%
443
16th to endDay
19%17%34%21%5%
435
July1st to 15thDay
16%10%31%27%11%2
425
16th to endDay
16%10%29%30%11%1
454
August1st to 15thDay
16%11%29%27%11%3
418
16th to endDay
15%11%24%24%17%6%
460
September1st to 15thDay
18%13%22%21%16%7%
435
16th to endDay
13%14%25%23%14%9%
434
October1st to 15thDay
27%15%24%17%12%2
435
16th to endDay
37%18%24%14%4
396
November1st to 15thDay
34%21%24%11%7%
370
16th to endDay
33%27%19%13%5%
207
December1st to 15thDay
28%19%34%16%2
150
16th to endDay
32%26%29%10%1
160
January1st to 15thNight
24%30%28%14%3
900
16th to endNight
23%27%25%19%3
960
February1st to 15thNight
21%26%29%20%2
884
16th to endNight
21%28%26%19%3
791
March1st to 15thNight
29%25%20%21%2
900
16th to endNight
24%25%22%19%7%
960
April1st to 15thNight
27%24%22%20%4
898
16th to endNight
27%25%21%18%6%
764
May1st to 15thNight
26%20%24%19%8%
534
16th to endNight
17%20%27%26%7%1
471
June1st to 15thNight
24%18%23%25%8%
425
16th to endNight
17%17%21%31%10%
420
July1st to 15thNight
10%12%25%34%17%1
400
16th to endNight
15%15%16%36%16%
440
August1st to 15thNight
14%10%19%36%17%1
445
16th to endNight
14%10%18%29%23%2
882
September1st to 15thNight
19%12%19%28%17%2
840
16th to endNight
16%12%24%22%20%3
837
October1st to 15thNight
26%15%24%21%11%
840
16th to endNight
31%18%25%18%5%
896
November1st to 15thNight
27%25%23%16%6%1
880
16th to endNight
29%28%20%13%7%
900
December1st to 15thNight
31%28%23%13%4
900
16th to endNight
27%30%23%15%3
960
Page generated at 2020-06-04 03:18:54. Version ac04

Copyright 2020 A. Danko


Orchard Hill Observatory Clear Sky Chart |Charts Home