The Stellar Shed
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Stellar Shed 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
39%
15986
18%
46946
11%
15943
45%
15943
25%
30731

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
25%
900
14%
2506
6%
895
32%
895
21%
1771
January16th to endNight
22%
960
14%
2535
4%
960
29%
960
19%
1846
February1st to 15thNight
25%
876
12%
2288
3%
876
32%
876
20%
1660
February16th to endNight
26%
635
21%
1897
8%
635
37%
635
23%
1242
March1st to 15thNight
30%
651
17%
2091
9%
651
37%
651
21%
1375
March16th to endNight
27%
576
12%
2042
7%
576
35%
576
15%
1446
April1st to 15thNight
29%
539
17%
1797
12%
539
39%
539
22%
1178
April16th to endNight
36%
540
18%
1800
13%
540
45%
540
21%
1209
May1st to 15thNight
36%
540
16%
1535
10%
540
42%
540
23%
1067
May16th to endNight
48%
563
19%
1497
9%
561
54%
561
30%
993
June1st to 15thNight
54%
540
16%
1440
10%
540
57%
540
34%
905
June16th to endNight
50%
540
17%
1440
9%
540
55%
540
33%
921
July1st to 15thNight
69%
510
18%
1360
11%
510
70%
510
41%
812
July16th to endNight
71%
564
22%
1437
16%
531
74%
531
42%
835
August1st to 15thNight
74%
539
22%
1616
23%
536
74%
536
39%
898
August16th to endNight
67%
573
22%
1910
25%
573
71%
573
34%
1078
September1st to 15thNight
64%
540
28%
1800
28%
540
69%
540
37%
956
September16th to endNight
59%
624
27%
1871
20%
624
66%
624
36%
1070
October1st to 15thNight
44%
660
26%
1980
19%
660
51%
660
33%
1175
October16th to endNight
33%
704
19%
2148
10%
704
43%
704
25%
1352
November1st to 15thNight
34%
700
25%
2276
16%
700
46%
700
28%
1350
November16th to endNight
27%
852
18%
2472
8%
852
36%
852
23%
1652
December1st to 15thNight
22%
900
13%
2520
5%
900
30%
900
18%
1854
December16th to endNight
21%
960
13%
2688
5%
960
28%
960
14%
2086

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%7%35%5%3445%7%39%
47995
Night
13%7%35%424446%42%
47117
Cloud CoverDay
13%7%36%5%3445%7%38%
48003
Night
13%7%35%424446%42%
47121
TransparencyDay
44%6%13%21%12%1
47683
Night
41%5%12%22%14%2
46947
SeeingDay
13%7%26%28%18%5%
6012
Night
16%8%30%30%12%1
15990

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
12%12%38%7%45%5%45%28%
1432
16th to endDay
15%14%6%9%7%34345%26%
1689
February1st to 15thDay
14%11%47%425%446%32%
1575
16th to endDay
13%9%47%5%3445%6%35%
1575
March1st to 15thDay
15%9%35%6%34436%36%
1869
16th to endDay
18%9%47%6%2445%6%30%
2181
April1st to 15thDay
16%10%46%5%24435%36%
2151
16th to endDay
21%7%36%5%34446%33%
2160
May1st to 15thDay
18%8%45%5%35%5%5%6%31%
2415
16th to endDay
14%6%25%6%35%5%5%7%36%
2617
June1st to 15thDay
11%5%25%5%35%45%7%40%
2520
16th to endDay
10%424435%5%6%9%43%
2520
July1st to 15thDay
7%3145%35%5%6%9%45%
2520
16th to endDay
6%315%5%45%5%6%10%46%
2631
August1st to 15thDay
7%4145%36%7%7%8%43%
2334
16th to endDay
10%42442445%8%46%
2292
September1st to 15thDay
11%31442435%7%51%
2160
16th to endDay
8%415%425%5%5%8%47%
1935
October1st to 15thDay
15%6%24323245%50%
1650
16th to endDay
17%7%25%423345%42%
1724
November1st to 15thDay
13%8%25%424446%43%
1582
16th to endDay
18%9%44333345%38%
1487
December1st to 15thDay
20%12%49%434345%27%
1440
16th to endDay
20%14%48%5%23345%27%
1536
January1st to 15thNight
13%9%5%6%5%44346%36%
2506
16th to endNight
12%10%6%8%5%34337%34%
2535
February1st to 15thNight
14%11%46%435%447%34%
2285
16th to endNight
14%9%36%42335%5%42%
1897
March1st to 15thNight
16%8%35%5%23435%41%
2079
16th to endNight
17%9%46%6%3445%5%32%
2042
April1st to 15thNight
16%8%35%42335%5%41%
1797
16th to endNight
18%7%25%5%2445%7%37%
1800
May1st to 15thNight
18%5%35%5%25%348%37%
1535
16th to endNight
9%5%245%36%5%7%8%42%
1496
June1st to 15thNight
10%5%244245%5%9%46%
1440
16th to endNight
9%425%5%2446%9%45%
1440
July1st to 15thNight
7%21242446%9%53%
1440
16th to endNight
5%213435%47%11%49%
1534
August1st to 15thNight
42144345%5%8%55%
1626
16th to endNight
9%424323346%55%
1910
September1st to 15thNight
10%413323346%56%
1800
16th to endNight
6%32443446%6%52%
1871
October1st to 15thNight
12%5%24423335%52%
1980
16th to endNight
16%6%25%423346%44%
2148
November1st to 15thNight
15%6%23312336%50%
2276
16th to endNight
18%7%25%423346%40%
2472
December1st to 15thNight
18%11%47%5%2434433%
2520
16th to endNight
22%14%47%42343428%
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
12%12%48%7%45%45%5%28%
1432
16th to endDay
15%13%6%9%8%34345%26%
1689
February1st to 15thDay
14%11%47%425%446%33%
1575
16th to endDay
13%9%47%5%3445%6%35%
1575
March1st to 15thDay
16%9%36%5%33436%36%
1879
16th to endDay
18%9%48%5%2445%6%30%
2179
April1st to 15thDay
15%10%47%5%33435%36%
2151
16th to endDay
21%8%36%5%24446%33%
2160
May1st to 15thDay
18%8%46%5%35%5%5%7%30%
2415
16th to endDay
14%6%25%6%35%5%5%7%36%
2617
June1st to 15thDay
11%6%35%5%36%45%7%40%
2520
16th to endDay
10%424435%5%5%10%42%
2520
July1st to 15thDay
7%415%5%35%5%6%9%45%
2520
16th to endDay
5%315%5%35%6%6%10%45%
2631
August1st to 15thDay
6%415%5%45%7%7%8%43%
2334
16th to endDay
10%43442446%8%46%
2292
September1st to 15thDay
11%314424348%51%
2160
16th to endDay
8%415%425%5%5%7%47%
1935
October1st to 15thDay
15%6%24322345%50%
1650
16th to endDay
17%7%25%423336%42%
1724
November1st to 15thDay
13%8%244245%47%42%
1582
16th to endDay
17%10%44323345%38%
1487
December1st to 15thDay
19%12%49%434345%27%
1440
16th to endDay
19%15%47%5%23345%27%
1536
January1st to 15thNight
13%9%5%6%5%44346%36%
2506
16th to endNight
12%10%6%8%5%34346%34%
2535
February1st to 15thNight
14%11%46%435%447%34%
2278
16th to endNight
13%10%35%5%23345%41%
1897
March1st to 15thNight
16%7%36%424335%41%
2091
16th to endNight
16%9%46%6%3445%5%31%
2042
April1st to 15thNight
15%8%35%42335%6%40%
1797
16th to endNight
18%7%35%5%2435%7%37%
1800
May1st to 15thNight
18%6%35%5%25%247%37%
1534
16th to endNight
9%5%245%36%5%7%9%41%
1496
June1st to 15thNight
9%5%245%345%49%46%
1440
16th to endNight
8%425%5%245%5%9%45%
1440
July1st to 15thNight
6%2134345%7%9%52%
1440
16th to endNight
4223435%5%7%11%49%
1534
August1st to 15thNight
32144345%5%8%55%
1626
16th to endNight
9%424323346%54%
1910
September1st to 15thNight
10%32332335%6%56%
1800
16th to endNight
6%32443446%7%52%
1871
October1st to 15thNight
11%5%24423345%52%
1980
16th to endNight
16%6%25%424346%44%
2148
November1st to 15thNight
14%6%24322336%50%
2276
16th to endNight
18%8%25%423346%40%
2472
December1st to 15thNight
18%11%47%5%34335%33%
2520
16th to endNight
22%13%47%5%2343427%
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
56%5%12%14%9%
1433
16th to endDay
60%5%12%14%7%
1689
February1st to 15thDay
51%6%15%19%5%
1576
16th to endDay
48%6%14%20%8%
1575
March1st to 15thDay
49%5%15%21%7%
1879
16th to endDay
53%6%14%19%5%1
2181
April1st to 15thDay
50%411%21%11%
2151
16th to endDay
51%5%10%17%12%1
2160
May1st to 15thDay
51%7%12%20%8%
2415
16th to endDay
45%8%13%18%13%1
2621
June1st to 15thDay
41%7%12%22%15%1
2520
16th to endDay
35%8%13%22%16%2
2520
July1st to 15thDay
33%8%15%25%13%3
2371
16th to endDay
31%8%18%24%14%2
2466
August1st to 15thDay
32%9%15%24%16%1
2320
16th to endDay
34%7%13%26%14%2
2292
September1st to 15thDay
31%6%9%26%21%4
2160
16th to endDay
34%6%12%27%17%1
1935
October1st to 15thDay
36%48%27%20%1
1650
16th to endDay
43%413%24%12%2
1724
November1st to 15thDay
41%412%24%14%2
1582
16th to endDay
47%417%21%8%
1487
December1st to 15thDay
59%5%12%16%5%
1440
16th to endDay
61%411%12%8%
1536
January1st to 15thNight
49%414%18%12%
2506
16th to endNight
51%5%16%17%8%
2535
February1st to 15thNight
49%6%14%19%9%
2288
16th to endNight
43%413%25%11%1
1897
March1st to 15thNight
45%5%13%23%10%1
2091
16th to endNight
53%5%12%19%8%
2042
April1st to 15thNight
45%410%23%14%2
1797
16th to endNight
45%6%11%19%13%3
1800
May1st to 15thNight
45%6%12%22%12%
1535
16th to endNight
36%9%14%19%17%2
1498
June1st to 15thNight
34%6%12%24%17%3
1440
16th to endNight
34%7%12%19%21%4
1440
July1st to 15thNight
27%7%15%28%17%3
1360
16th to endNight
26%7%16%29%18%2
1437
August1st to 15thNight
25%8%14%30%18%3
1616
16th to endNight
30%6%10%27%19%5%
1910
September1st to 15thNight
28%49%27%24%4
1800
16th to endNight
28%6%13%26%21%3
1871
October1st to 15thNight
34%49%23%23%4
1980
16th to endNight
41%412%23%16%1
2148
November1st to 15thNight
36%411%24%18%4
2276
16th to endNight
44%412%26%11%
2472
December1st to 15thNight
54%412%20%7%
2520
16th to endNight
60%410%15%8%
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
27%14%36%16%4
90
16th to endDay
19%10%40%17%10%1
96
February1st to 15thDay
17%16%42%15%7%
90
16th to endDay
19%12%37%17%7%6%
81
March1st to 15thDay
23%15%37%18%31
90
16th to endDay
27%15%28%16%9%1
165
April1st to 15thDay
18%13%31%24%12%
270
16th to endDay
26%6%30%22%11%2
270
May1st to 15thDay
18%12%30%26%10%1
417
16th to endDay
17%8%31%26%11%4
517
June1st to 15thDay
9%6%27%32%18%5%
495
16th to endDay
10%6%31%29%17%4
495
July1st to 15thDay
9%225%33%20%9%
475
16th to endDay
5%20%35%29%7%
515
August1st to 15thDay
6%119%37%25%8%
487
16th to endDay
8%414%33%28%11%
332
September1st to 15thDay
9%215%31%33%7%
315
16th to endDay
6%5%18%31%30%7%
260
October1st to 15thDay
13%5%23%33%14%10%
90
16th to endDay
20%9%31%29%9%
96
November1st to 15thDay
48%31%28%18%7%
90
16th to endDay
41%14%30%11%21
90
December1st to 15thDay
22%18%35%14%7%1
90
16th to endDay
29%21%41%5%2
96
January1st to 15thNight
16%14%39%22%6%
900
16th to endNight
16%12%39%27%3
960
February1st to 15thNight
19%10%37%26%5%
880
16th to endNight
19%11%38%26%3
635
March1st to 15thNight
20%10%34%26%7%
651
16th to endNight
17%13%35%26%6%
576
April1st to 15thNight
19%11%35%28%4
539
16th to endNight
19%9%30%32%7%
540
May1st to 15thNight
19%5%32%32%9%
540
16th to endNight
9%432%38%14%
563
June1st to 15thNight
10%324%43%16%
540
16th to endNight
9%329%38%18%
540
July1st to 15thNight
8%115%42%28%2
510
16th to endNight
6%15%43%32%2
564
August1st to 15thNight
4111%46%31%3
539
16th to endNight
9%14%41%28%4
573
September1st to 15thNight
12%215%35%29%5%
540
16th to endNight
7%5%21%34%27%3
624
October1st to 15thNight
14%5%29%31%18%1
660
16th to endNight
20%8%33%27%9%
704
November1st to 15thNight
18%8%35%26%10%
700
16th to endNight
21%10%36%24%6%
852
December1st to 15thNight
23%11%37%23%4
900
16th to endNight
27%11%33%23%4
960
Page generated at 2017-09-25 08:02:24. Version ac04

Copyright 2017 A. Danko


The Stellar Shed Clear Sky Chart | Charts Home