StarHome Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the StarHome Observatory clear sky chart from 2005-11-05 to 2017-12-02.

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%
16468
15%
47736
9%
16422
44%
16422
24%
32302

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
30%
900
12%
2506
7%
895
36%
895
21%
1811
January16th to endNight
23%
960
11%
2565
4%
960
28%
960
17%
1960
February1st to 15thNight
30%
879
14%
2288
4%
875
36%
875
22%
1636
February16th to endNight
30%
749
13%
2011
5%
749
36%
749
22%
1434
March1st to 15thNight
31%
594
14%
2034
10%
594
37%
594
19%
1363
March16th to endNight
34%
576
16%
2088
13%
576
42%
576
18%
1396
April1st to 15thNight
32%
539
16%
1797
13%
539
40%
539
20%
1207
April16th to endNight
30%
540
15%
1674
10%
540
37%
540
17%
1206
May1st to 15thNight
33%
540
14%
1476
7%
540
38%
540
22%
1053
May16th to endNight
45%
562
14%
1498
6%
561
49%
561
28%
1008
June1st to 15thNight
51%
540
12%
1440
5%
540
54%
540
32%
937
June16th to endNight
56%
540
15%
1344
7%
540
59%
540
39%
845
July1st to 15thNight
61%
510
14%
1351
7%
510
63%
510
43%
787
July16th to endNight
66%
564
20%
1417
10%
531
69%
531
45%
809
August1st to 15thNight
66%
539
21%
1605
18%
536
70%
536
38%
916
August16th to endNight
59%
573
21%
1794
21%
573
65%
573
33%
1048
September1st to 15thNight
59%
540
22%
1800
20%
540
67%
540
36%
956
September16th to endNight
44%
591
20%
1979
14%
591
53%
591
30%
1161
October1st to 15thNight
42%
720
22%
2160
14%
720
47%
720
31%
1309
October16th to endNight
34%
768
16%
2334
9%
768
40%
768
20%
1611
November1st to 15thNight
34%
899
18%
2610
10%
899
41%
899
23%
1758
November16th to endNight
29%
975
15%
2730
9%
975
35%
975
19%
1968
December1st to 15thNight
26%
910
9%
2547
3%
910
31%
910
16%
1955
December16th to endNight
20%
960
10%
2688
3%
960
27%
960
12%
2168

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
14%7%36%5%3445%7%37%
48699
Night
13%8%36%5%34346%40%
47904
Cloud CoverDay
25%7%25%423346%32%
48710
Night
24%7%25%423345%35%
47908
Cloud CoverDay
14%8%36%5%3445%7%36%
48708
Night
13%8%36%5%34346%40%
47908
TransparencyDay
46%6%14%22%8%
48385
Night
44%5%13%23%10%1
47736
SeeingDay
17%7%27%28%15%4
6376
Night
16%7%30%32%12%1
16470

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
9%11%7%8%8%45%45%6%29%
1432
16th to endDay
10%13%6%11%6%35%5%5%7%24%
1656
February1st to 15thDay
8%11%6%9%6%34447%32%
1575
16th to endDay
11%11%6%9%6%345%46%31%
1461
March1st to 15thDay
14%10%46%6%34347%33%
1927
16th to endDay
18%10%46%5%2445%6%31%
2135
April1st to 15thDay
17%9%35%5%24445%38%
2151
16th to endDay
23%10%36%5%34345%29%
2283
May1st to 15thDay
20%6%36%6%24447%31%
2473
16th to endDay
14%7%35%5%35%45%7%37%
2617
June1st to 15thDay
16%5%2443345%8%39%
2520
16th to endDay
9%4246%36%5%6%9%40%
2603
July1st to 15thDay
8%314335%5%5%8%51%
2520
16th to endDay
8%323425%5%7%9%46%
2655
August1st to 15thDay
10%425%435%47%8%42%
2346
16th to endDay
13%324423447%47%
2406
September1st to 15thDay
9%424425%46%7%46%
2160
16th to endDay
17%3344345%5%7%41%
1968
October1st to 15thDay
16%7%25%42335%6%42%
1800
16th to endDay
19%8%45%5%2335%5%36%
1890
November1st to 15thDay
13%11%47%5%2435%6%35%
1575
16th to endDay
16%9%36%5%25%45%7%31%
1560
December1st to 15thDay
16%11%6%9%8%34446%23%
1450
16th to endDay
17%17%6%11%6%3432420%
1536
January1st to 15thNight
11%9%5%8%5%25%45%6%33%
2506
16th to endNight
11%13%7%9%6%3345%5%29%
2565
February1st to 15thNight
7%12%5%7%6%34346%38%
2285
16th to endNight
10%8%46%7%5%5%446%36%
2011
March1st to 15thNight
12%9%45%7%24345%39%
2022
16th to endNight
19%7%46%5%23347%36%
2088
April1st to 15thNight
19%8%35%423336%38%
1797
16th to endNight
24%8%35%323445%32%
1674
May1st to 15thNight
19%6%25%5%24346%39%
1476
16th to endNight
11%4246%36%5%6%7%41%
1496
June1st to 15thNight
12%425%43446%8%45%
1440
16th to endNight
8%314325%45%7%52%
1344
July1st to 15thNight
6%21333446%8%55%
1431
16th to endNight
5%21342446%9%55%
1513
August1st to 15thNight
8%214335%35%8%53%
1614
16th to endNight
10%423434346%53%
1794
September1st to 15thNight
8%324423346%57%
1800
16th to endNight
13%424333346%49%
1979
October1st to 15thNight
15%6%23322336%50%
2160
16th to endNight
19%9%25%423346%38%
2334
November1st to 15thNight
15%8%37%423435%41%
2610
16th to endNight
15%9%46%6%35%347%33%
2730
December1st to 15thNight
13%13%5%9%7%34335%29%
2547
16th to endNight
16%16%7%9%7%3433422%
2688

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
23%7%5%6%7%35%446%26%
1432
16th to endDay
25%11%49%6%34446%19%
1656
February1st to 15thDay
23%10%5%6%5%33336%27%
1575
16th to endDay
23%10%5%8%5%24335%26%
1461
March1st to 15thDay
26%8%36%6%22336%29%
1938
16th to endDay
30%9%36%323345%27%
2135
April1st to 15thDay
30%7%3442333431%
2151
16th to endDay
36%9%35%42333423%
2283
May1st to 15thDay
32%6%26%5%33345%26%
2473
16th to endDay
29%7%25%424336%30%
2617
June1st to 15thDay
30%5%235%2335%6%31%
2520
16th to endDay
25%41443446%8%32%
2603
July1st to 15thDay
23%21332345%6%42%
2520
16th to endDay
23%31342346%7%38%
2655
August1st to 15thDay
17%415%4345%6%8%38%
2346
16th to endDay
19%424423346%44%
2406
September1st to 15thDay
16%41432446%7%42%
2160
16th to endDay
22%42442345%6%40%
1968
October1st to 15thDay
23%6%24413345%39%
1800
16th to endDay
24%7%25%423345%34%
1890
November1st to 15thDay
23%9%36%413345%32%
1575
16th to endDay
28%7%36%424446%27%
1560
December1st to 15thDay
29%11%48%7%3334419%
1450
16th to endDay
29%14%5%10%5%2232317%
1536
January1st to 15thNight
24%7%37%5%24345%30%
2506
16th to endNight
26%12%48%5%22345%23%
2565
February1st to 15thNight
22%11%46%422245%32%
2278
16th to endNight
22%7%35%7%45%335%31%
2011
March1st to 15thNight
24%8%345%3423435%
2034
16th to endNight
32%6%35%422235%32%
2088
April1st to 15thNight
31%6%25%413335%32%
1797
16th to endNight
36%8%2432333426%
1674
May1st to 15thNight
32%6%24423235%31%
1475
16th to endNight
25%425%434346%34%
1496
June1st to 15thNight
26%31442335%6%37%
1440
16th to endNight
23%33223346%44%
1344
July1st to 15thNight
22%21332335%6%45%
1431
16th to endNight
21%113323447%47%
1513
August1st to 15thNight
16%3342425%7%48%
1614
16th to endNight
17%413424235%51%
1794
September1st to 15thNight
15%223423336%52%
1800
16th to endNight
19%313422345%48%
1979
October1st to 15thNight
22%6%13313335%45%
2160
16th to endNight
25%8%25%422235%35%
2334
November1st to 15thNight
25%7%25%32333437%
2610
16th to endNight
26%8%36%433346%29%
2730
December1st to 15thNight
28%11%38%6%2323425%
2547
16th to endNight
28%14%5%9%6%3323419%
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
9%11%7%8%8%45%5%36%29%
1432
16th to endDay
10%13%6%11%6%46%45%7%23%
1656
February1st to 15thDay
8%12%6%8%7%34447%32%
1575
16th to endDay
10%11%6%9%6%34446%31%
1461
March1st to 15thDay
14%10%46%6%24347%33%
1938
16th to endDay
18%10%37%5%24447%31%
2133
April1st to 15thDay
17%8%36%434445%37%
2151
16th to endDay
22%10%36%5%34345%29%
2283
May1st to 15thDay
20%7%36%6%35%446%31%
2473
16th to endDay
14%6%25%6%35%45%7%36%
2617
June1st to 15thDay
16%6%2442446%8%38%
2520
16th to endDay
9%425%5%35%5%7%8%40%
2603
July1st to 15thDay
7%314425%46%8%50%
2520
16th to endDay
7%4145%25%5%6%9%47%
2655
August1st to 15thDay
9%425%5%35%6%7%8%42%
2346
16th to endDay
13%415%42335%7%47%
2406
September1st to 15thDay
9%4245%25%45%8%47%
2160
16th to endDay
16%42443445%7%41%
1968
October1st to 15thDay
16%7%25%41335%6%42%
1800
16th to endDay
19%8%46%5%2335%5%35%
1890
November1st to 15thDay
13%11%48%5%2345%6%34%
1575
16th to endDay
16%9%36%5%35%5%5%8%30%
1560
December1st to 15thDay
16%12%5%9%8%3445%5%23%
1450
16th to endDay
18%17%7%11%6%3433420%
1536
January1st to 15thNight
11%9%6%7%6%35%5%5%6%33%
2506
16th to endNight
12%13%6%10%6%2445%6%28%
2565
February1st to 15thNight
7%12%5%7%6%3435%7%37%
2278
16th to endNight
10%8%46%6%5%5%446%35%
2011
March1st to 15thNight
11%10%45%5%34445%39%
2034
16th to endNight
18%8%46%5%23346%36%
2088
April1st to 15thNight
19%8%26%414336%38%
1797
16th to endNight
23%9%35%423446%32%
1674
May1st to 15thNight
19%6%25%5%33347%37%
1475
16th to endNight
10%5%245%35%5%6%8%41%
1496
June1st to 15thNight
12%415%5%2346%8%44%
1440
16th to endNight
9%314425%46%7%51%
1344
July1st to 15thNight
5%31333347%7%55%
1431
16th to endNight
5%11342447%9%55%
1513
August1st to 15thNight
8%21442446%6%53%
1614
16th to endNight
10%423434336%54%
1794
September1st to 15thNight
8%313424347%56%
1800
16th to endNight
13%323433447%49%
1979
October1st to 15thNight
15%5%23313346%49%
2160
16th to endNight
19%9%25%5%23345%37%
2334
November1st to 15thNight
15%8%36%423435%41%
2610
16th to endNight
14%9%46%6%34347%33%
2730
December1st to 15thNight
13%14%49%6%34335%29%
2547
16th to endNight
16%16%6%10%7%34335%22%
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
55%5%12%19%6%
1433
16th to endDay
59%6%16%13%4
1656
February1st to 15thDay
51%5%15%20%6%1
1576
16th to endDay
54%5%12%22%5%
1461
March1st to 15thDay
49%6%16%19%6%
1938
16th to endDay
52%5%14%22%4
2135
April1st to 15thDay
48%412%21%11%1
2151
16th to endDay
57%5%12%15%9%
2283
May1st to 15thDay
53%6%12%19%7%
2473
16th to endDay
45%7%12%21%11%1
2621
June1st to 15thDay
41%6%15%27%7%
2520
16th to endDay
37%8%16%26%9%1
2603
July1st to 15thDay
29%7%15%29%15%1
2371
16th to endDay
31%9%17%24%15%1
2488
August1st to 15thDay
36%7%16%28%9%1
2331
16th to endDay
35%6%15%28%12%1
2406
September1st to 15thDay
33%7%15%33%9%
2160
16th to endDay
41%6%14%30%6%
1968
October1st to 15thDay
42%5%14%25%11%
1800
16th to endDay
49%5%13%21%7%
1890
November1st to 15thDay
49%413%19%11%
1575
16th to endDay
51%8%18%14%6%1
1560
December1st to 15thDay
62%5%13%13%4
1450
16th to endDay
68%5%9%11%4
1536
January1st to 15thNight
50%5%14%21%7%
2506
16th to endNight
56%415%16%5%
2565
February1st to 15thNight
47%6%14%23%7%
2288
16th to endNight
47%6%14%22%8%
2011
March1st to 15thNight
47%5%14%21%10%
2034
16th to endNight
49%414%24%6%
2088
April1st to 15thNight
47%48%23%14%1
1797
16th to endNight
52%5%9%17%12%2
1674
May1st to 15thNight
47%6%13%18%12%1
1476
16th to endNight
39%7%12%23%14%1
1498
June1st to 15thNight
36%7%14%28%11%1
1440
16th to endNight
30%7%14%29%15%3
1344
July1st to 15thNight
25%7%16%31%17%1
1351
16th to endNight
23%7%16%29%18%4
1417
August1st to 15thNight
29%5%14%30%14%4
1605
16th to endNight
32%6%13%28%15%3
1794
September1st to 15thNight
28%415%33%16%
1800
16th to endNight
34%5%15%30%12%
1979
October1st to 15thNight
36%411%30%14%1
2160
16th to endNight
48%413%20%11%
2334
November1st to 15thNight
45%412%23%12%
2610
16th to endNight
50%6%17%17%7%1
2730
December1st to 15thNight
58%5%14%17%4
2547
16th to endNight
65%412%12%4
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
16%7%34%30%8%2
90
16th to endDay
26%5%32%29%7%
96
February1st to 15thDay
12%18%43%23%2
90
16th to endDay
20%13%38%20%41
81
March1st to 15thDay
18%8%35%31%41
90
16th to endDay
28%9%27%24%8%1
119
April1st to 15thDay
21%9%29%27%10%1
270
16th to endDay
28%8%31%22%8%1
393
May1st to 15thDay
24%11%29%25%8%2
468
16th to endDay
18%10%27%24%14%4
517
June1st to 15thDay
16%6%28%31%13%3
495
16th to endDay
10%5%31%30%16%5%
495
July1st to 15thDay
9%422%29%23%10%
475
16th to endDay
7%423%35%21%7%
515
August1st to 15thDay
9%221%32%28%5%
493
16th to endDay
15%6%17%34%18%6%
446
September1st to 15thDay
11%323%34%20%5%
315
16th to endDay
22%425%32%11%3
189
October1st to 15thDay
14%8%34%19%17%5%
135
16th to endDay
22%10%35%18%13%
144
November1st to 15thDay
16%8%34%24%14%
135
16th to endDay
31%11%35%18%3
135
December1st to 15thDay
25%435%28%6%
94
16th to endDay
33%11%37%16%1
96
January1st to 15thNight
15%9%33%30%9%1
900
16th to endNight
18%9%37%27%6%
960
February1st to 15thNight
13%8%36%31%8%1
880
16th to endNight
14%8%37%27%10%
749
March1st to 15thNight
15%9%35%29%9%
594
16th to endNight
22%7%30%27%10%2
576
April1st to 15thNight
22%7%33%29%7%
539
16th to endNight
27%6%30%25%8%
540
May1st to 15thNight
20%8%32%30%7%
540
16th to endNight
11%6%28%36%15%1
563
June1st to 15thNight
12%425%45%11%
540
16th to endNight
9%425%44%15%
540
July1st to 15thNight
6%224%41%23%1
510
16th to endNight
6%120%46%23%1
564
August1st to 15thNight
9%115%45%25%1
539
16th to endNight
12%220%37%24%1
573
September1st to 15thNight
8%322%40%19%4
540
16th to endNight
13%5%30%30%18%1
591
October1st to 15thNight
20%5%28%30%12%1
720
16th to endNight
25%7%26%31%8%
768
November1st to 15thNight
20%8%29%30%9%1
899
16th to endNight
18%11%34%26%8%
975
December1st to 15thNight
20%8%36%27%6%
910
16th to endNight
23%9%28%29%7%
960
Page generated at 2017-12-03 10:16:48. Version ac04

Copyright 2017 A. Danko


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