Dog-Star Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dog-Star Observatory clear sky chart from 2005-11-05 to 2017-12-04.

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
36%
15384
17%
47869
10%
15344
44%
15344
20%
32020

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
18%
717
13%
2440
6%
716
27%
716
10%
1798
January16th to endNight
16%
768
14%
2496
4%
768
29%
768
13%
1775
February1st to 15thNight
16%
704
13%
2287
4%
701
27%
701
11%
1626
February16th to endNight
18%
631
17%
1965
6%
631
32%
631
14%
1378
March1st to 15thNight
23%
720
17%
1986
8%
720
33%
720
17%
1409
March16th to endNight
25%
768
19%
2106
8%
768
34%
768
20%
1443
April1st to 15thNight
22%
718
13%
1796
4%
718
28%
718
19%
1319
April16th to endNight
36%
681
18%
1761
7%
681
42%
681
27%
1194
May1st to 15thNight
40%
507
16%
1587
9%
507
48%
507
20%
1093
May16th to endNight
49%
374
17%
1497
15%
374
57%
374
20%
911
June1st to 15thNight
49%
360
16%
1440
16%
360
56%
360
22%
860
June16th to endNight
55%
360
16%
1440
18%
360
63%
360
25%
821
July1st to 15thNight
54%
340
14%
1360
17%
340
58%
340
22%
806
July16th to endNight
65%
523
17%
1554
15%
490
68%
490
32%
908
August1st to 15thNight
64%
539
17%
1609
12%
536
66%
536
33%
979
August16th to endNight
63%
705
23%
1851
15%
705
65%
705
35%
1164
September1st to 15thNight
53%
720
24%
1800
13%
720
57%
720
33%
1171
September16th to endNight
52%
717
24%
1991
19%
717
56%
717
30%
1261
October1st to 15thNight
44%
720
19%
2160
15%
720
50%
720
24%
1400
October16th to endNight
35%
768
21%
2304
13%
768
46%
768
22%
1510
November1st to 15thNight
41%
760
20%
2447
15%
760
50%
760
24%
1524
November16th to endNight
28%
780
17%
2730
11%
780
38%
780
14%
1841
December1st to 15thNight
25%
736
11%
2574
6%
736
33%
736
11%
1854
December16th to endNight
19%
768
11%
2688
3%
768
30%
768
10%
1975

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
15%8%36%6%35%45%7%32%
48616
Night
14%7%35%5%3445%7%37%
48051
Cloud CoverDay
15%8%36%6%35%45%7%33%
48626
Night
15%7%36%5%3445%7%37%
48055
TransparencyDay
49%6%11%19%11%1
48316
Night
44%5%12%21%12%1
47869
SeeingDay
21%11%23%22%14%6%
5810
Night
21%12%24%28%12%1
15388

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
14%9%5%9%8%45%5%45%27%
1495
16th to endDay
13%14%5%10%8%5%5%45%5%20%
1728
February1st to 15thDay
14%16%6%7%5%35%45%6%23%
1575
16th to endDay
13%10%6%9%7%3445%5%26%
1507
March1st to 15thDay
17%9%47%7%35%446%28%
1962
16th to endDay
15%11%46%6%34446%33%
2118
April1st to 15thDay
17%9%45%6%3435%6%32%
2152
16th to endDay
19%7%25%434446%36%
2208
May1st to 15thDay
20%7%36%5%35%448%30%
2361
16th to endDay
16%6%25%6%35%5%5%7%34%
2618
June1st to 15thDay
13%6%26%6%46%46%8%35%
2520
16th to endDay
14%5%26%5%35%5%6%10%34%
2520
July1st to 15thDay
11%6%36%6%46%5%6%8%33%
2520
16th to endDay
9%5%35%6%45%5%7%10%34%
2504
August1st to 15thDay
12%426%6%47%6%8%9%31%
2340
16th to endDay
13%5%25%5%345%6%9%37%
2339
September1st to 15thDay
17%6%15%425%35%6%40%
2160
16th to endDay
15%6%25%42335%7%43%
1965
October1st to 15thDay
18%9%25%424446%37%
1800
16th to endDay
16%8%36%5%25%5%45%35%
1920
November1st to 15thDay
11%7%35%6%35%5%6%6%37%
1740
16th to endDay
20%8%35%5%45%45%6%30%
1560
December1st to 15thDay
16%12%5%9%6%35%446%24%
1468
16th to endDay
20%11%5%7%6%46%5%46%20%
1536
January1st to 15thNight
17%8%48%7%35%5%5%7%24%
2440
16th to endNight
13%11%47%6%4445%7%29%
2496
February1st to 15thNight
14%10%47%5%345%5%7%30%
2285
16th to endNight
12%8%47%6%46%35%5%34%
1965
March1st to 15thNight
16%8%36%5%25%446%35%
1974
16th to endNight
16%7%25%5%24446%40%
2106
April1st to 15thNight
17%9%47%5%24445%35%
1796
16th to endNight
16%5%244245%5%7%41%
1761
May1st to 15thNight
19%5%25%5%24446%39%
1587
16th to endNight
11%6%25%43446%8%41%
1495
June1st to 15thNight
13%43442446%9%42%
1440
16th to endNight
11%42443447%10%43%
1440
July1st to 15thNight
10%3345%3446%9%43%
1440
16th to endNight
7%3245%35%47%10%45%
1661
August1st to 15thNight
7%5%25%435%46%9%45%
1620
16th to endNight
11%42442445%7%49%
1851
September1st to 15thNight
15%5%23423446%48%
1800
16th to endNight
13%5%245%3445%7%46%
1991
October1st to 15thNight
17%6%24423447%42%
2160
16th to endNight
17%6%2442445%6%40%
2304
November1st to 15thNight
13%6%25%424446%44%
2447
16th to endNight
18%8%35%5%2445%6%34%
2730
December1st to 15thNight
19%8%37%5%35%5%5%8%27%
2574
16th to endNight
17%10%46%6%36%6%5%6%26%
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
15%9%5%10%7%445%45%28%
1495
16th to endDay
14%15%5%9%10%35%445%21%
1728
February1st to 15thDay
15%15%7%7%6%25%446%23%
1575
16th to endDay
14%10%5%11%7%345%4427%
1507
March1st to 15thDay
17%10%47%6%45%446%28%
1973
16th to endDay
16%11%37%434446%32%
2117
April1st to 15thDay
17%9%46%5%24346%32%
2152
16th to endDay
19%7%35%434346%36%
2208
May1st to 15thDay
21%7%26%5%25%45%7%30%
2361
16th to endDay
15%6%25%5%45%5%47%34%
2618
June1st to 15thDay
13%6%25%6%46%5%5%7%35%
2520
16th to endDay
13%5%26%5%35%5%7%9%35%
2520
July1st to 15thDay
10%6%36%6%46%5%7%8%34%
2520
16th to endDay
9%435%6%46%6%7%10%34%
2504
August1st to 15thDay
12%5%26%7%47%6%7%9%31%
2340
16th to endDay
13%5%245%35%6%5%9%37%
2339
September1st to 15thDay
17%6%145%24446%41%
2160
16th to endDay
15%5%245%2335%7%43%
1965
October1st to 15thDay
19%7%25%5%24346%38%
1800
16th to endDay
17%8%35%5%35%45%5%36%
1920
November1st to 15thDay
12%7%26%5%36%5%5%7%37%
1740
16th to endDay
19%11%35%5%35%45%5%30%
1560
December1st to 15thDay
16%12%5%10%5%44446%23%
1468
16th to endDay
20%12%48%6%36%5%5%5%21%
1536
January1st to 15thNight
17%9%49%7%35%46%7%24%
2440
16th to endNight
13%12%5%7%6%35%45%6%28%
2496
February1st to 15thNight
14%10%47%5%35%45%7%29%
2278
16th to endNight
12%8%48%6%46%45%434%
1965
March1st to 15thNight
17%8%26%5%34446%35%
1986
16th to endNight
16%8%345%24346%40%
2106
April1st to 15thNight
16%9%47%5%24446%34%
1796
16th to endNight
16%5%244345%47%41%
1761
May1st to 15thNight
19%6%25%434446%38%
1586
16th to endNight
12%6%2433446%9%41%
1495
June1st to 15thNight
13%435%42446%8%42%
1440
16th to endNight
11%414425%47%10%43%
1440
July1st to 15thNight
10%4246%35%46%8%43%
1440
16th to endNight
7%325%5%345%6%10%46%
1661
August1st to 15thNight
7%5%245%35%5%6%8%45%
1620
16th to endNight
10%5%23425%448%49%
1851
September1st to 15thNight
15%5%13423347%47%
1800
16th to endNight
13%5%24424347%46%
1991
October1st to 15thNight
17%6%24424447%42%
2160
16th to endNight
18%6%2442445%6%39%
2304
November1st to 15thNight
13%6%25%5%24446%44%
2447
16th to endNight
19%8%35%5%35%45%6%34%
2730
December1st to 15thNight
19%8%28%5%35%5%5%7%27%
2574
16th to endNight
17%9%5%7%5%35%5%6%6%25%
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%6%13%15%7%
1496
16th to endDay
64%411%14%5%
1728
February1st to 15thDay
60%5%10%16%5%1
1577
16th to endDay
57%5%11%16%7%
1507
March1st to 15thDay
56%5%11%19%6%
1973
16th to endDay
52%410%20%10%1
2118
April1st to 15thDay
51%410%18%13%1
2152
16th to endDay
47%48%18%17%3
2208
May1st to 15thDay
51%6%10%18%11%1
2361
16th to endDay
47%7%13%17%11%2
2622
June1st to 15thDay
45%6%12%21%13%
2520
16th to endDay
42%7%15%22%11%1
2520
July1st to 15thDay
45%9%11%18%13%2
2371
16th to endDay
39%9%14%22%14%
2348
August1st to 15thDay
45%9%13%20%11%
2327
16th to endDay
40%7%10%24%14%2
2339
September1st to 15thDay
43%6%9%21%17%1
2160
16th to endDay
38%5%9%24%19%2
1965
October1st to 15thDay
46%5%11%21%14%1
1800
16th to endDay
47%6%12%24%9%
1920
November1st to 15thDay
44%5%13%19%12%4
1740
16th to endDay
53%5%11%21%8%
1560
December1st to 15thDay
59%6%13%14%5%
1468
16th to endDay
63%5%11%14%4
1536
January1st to 15thNight
56%5%12%15%7%1
2440
16th to endNight
53%414%19%8%
2496
February1st to 15thNight
52%5%13%19%8%
2287
16th to endNight
50%5%9%23%10%
1965
March1st to 15thNight
48%5%12%22%10%
1986
16th to endNight
45%5%12%21%14%1
2106
April1st to 15thNight
51%410%18%13%1
1796
16th to endNight
42%410%22%16%4
1761
May1st to 15thNight
45%7%11%19%14%1
1587
16th to endNight
39%8%15%20%14%2
1497
June1st to 15thNight
37%7%13%26%14%
1440
16th to endNight
34%7%14%27%15%1
1440
July1st to 15thNight
38%7%12%23%14%2
1360
16th to endNight
31%7%16%24%16%2
1554
August1st to 15thNight
33%7%17%24%16%
1609
16th to endNight
33%6%11%26%18%3
1851
September1st to 15thNight
36%6%10%25%18%2
1800
16th to endNight
36%6%9%26%19%2
1991
October1st to 15thNight
41%6%13%22%15%1
2160
16th to endNight
43%412%26%12%
2304
November1st to 15thNight
40%414%21%14%4
2447
16th to endNight
49%5%11%21%11%1
2730
December1st to 15thNight
53%6%14%16%7%
2574
16th to endNight
56%6%15%16%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
32%28%22%7%8%1
71
16th to endDay
37%19%30%11%1
96
February1st to 15thDay
26%28%35%8%
90
16th to endDay
26%24%27%21%1
166
March1st to 15thDay
28%17%24%24%5%
270
16th to endDay
22%17%29%19%6%4
288
April1st to 15thDay
25%18%23%21%9%1
270
16th to endDay
22%12%24%18%14%7%
270
May1st to 15thDay
32%16%19%14%11%5%
288
16th to endDay
23%10%23%20%15%6%
331
June1st to 15thDay
17%12%22%30%13%3
315
16th to endDay
18%8%30%26%12%4
315
July1st to 15thDay
19%6%26%24%16%6%
305
16th to endDay
11%5%22%27%23%8%
326
August1st to 15thDay
16%319%23%26%10%
313
16th to endDay
13%315%24%21%19%
332
September1st to 15thDay
19%5%17%22%22%12%
315
16th to endDay
19%413%22%25%13%
314
October1st to 15thDay
26%5%15%24%21%5%
315
16th to endDay
22%14%26%26%9%
336
November1st to 15thDay
19%8%24%30%14%1
263
16th to endDay
17%18%38%15%7%1
90
December1st to 15thDay
20%22%23%22%7%2
67
16th to endDay
40%17%31%10%
64
January1st to 15thNight
26%18%29%19%4
720
16th to endNight
23%19%33%20%1
768
February1st to 15thNight
26%19%31%21%1
704
16th to endNight
24%19%32%21%2
631
March1st to 15thNight
25%16%29%24%3
720
16th to endNight
23%16%29%22%7%
768
April1st to 15thNight
25%15%33%20%5%
718
16th to endNight
22%11%24%31%10%
681
May1st to 15thNight
22%7%23%33%12%
507
16th to endNight
15%7%21%34%20%1
375
June1st to 15thNight
13%7%23%35%19%
360
16th to endNight
11%421%45%17%
360
July1st to 15thNight
10%421%40%21%1
340
16th to endNight
9%314%45%25%2
523
August1st to 15thNight
10%115%42%26%3
539
16th to endNight
13%213%34%31%4
705
September1st to 15thNight
17%417%31%24%3
720
16th to endNight
16%5%18%23%29%6%
717
October1st to 15thNight
21%9%19%27%19%2
720
16th to endNight
23%14%22%30%7%
768
November1st to 15thNight
19%10%25%32%11%1
760
16th to endNight
26%18%21%23%7%1
780
December1st to 15thNight
28%14%26%24%6%
736
16th to endNight
27%18%28%23%2
768
Page generated at 2017-12-05 10:19:00. Version ac04

Copyright 2017 A. Danko


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