Blue Dome
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blue Dome clear sky chart from 2005-11-05 to 2018-02-13.

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
56%
15980
19%
48761
15%
15947
61%
15947
30%
29787

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
55%
796
11%
2736
9%
796
59%
796
19%
1849
January16th to endNight
53%
832
17%
2827
14%
832
59%
832
22%
1826
February1st to 15thNight
46%
747
11%
2444
8%
746
51%
746
21%
1636
February16th to endNight
44%
632
13%
1920
9%
632
51%
632
21%
1318
March1st to 15thNight
52%
720
13%
2066
8%
720
57%
720
26%
1377
March16th to endNight
47%
768
14%
2112
8%
768
51%
768
27%
1413
April1st to 15thNight
45%
651
16%
1791
7%
651
50%
651
27%
1187
April16th to endNight
47%
540
18%
1620
12%
540
51%
540
28%
1023
May1st to 15thNight
50%
540
18%
1619
13%
539
55%
539
35%
926
May16th to endNight
51%
517
12%
1550
11%
516
53%
516
24%
1038
June1st to 15thNight
56%
360
16%
1260
16%
360
61%
360
26%
752
June16th to endNight
70%
360
25%
1260
29%
360
77%
360
46%
581
July1st to 15thNight
79%
340
21%
1278
30%
340
82%
340
48%
538
July16th to endNight
79%
441
28%
1476
35%
414
81%
414
59%
583
August1st to 15thNight
72%
539
26%
1611
23%
536
75%
536
47%
823
August16th to endNight
72%
573
35%
1719
28%
573
75%
573
51%
836
September1st to 15thNight
71%
693
29%
1908
21%
693
75%
693
48%
1025
September16th to endNight
68%
716
32%
1980
25%
716
72%
716
43%
1116
October1st to 15thNight
60%
720
24%
2083
18%
720
65%
720
38%
1193
October16th to endNight
62%
768
24%
2406
19%
768
69%
768
35%
1367
November1st to 15thNight
56%
760
19%
2470
17%
760
60%
760
27%
1504
November16th to endNight
52%
952
17%
2707
12%
952
57%
952
27%
1749
December1st to 15thNight
49%
975
11%
2798
6%
975
54%
975
21%
1964
December16th to endNight
44%
1040
13%
3120
7%
1040
50%
1040
20%
2163

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
5%6%36%5%35%5%6%7%44%
49274
Night
45%26%5%35%5%5%7%47%
48937
TransparencyDay
35%8%15%20%14%5%
48949
Night
33%8%15%22%14%5%
48762
SeeingDay
8%9%28%33%16%4
6161
Night
6%422%40%21%4
15990

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
18%39%6%47%6%8%8%34%
1542
16th to endDay
28%47%5%35%7%7%8%38%
1746
February1st to 15thDay
15%37%7%36%6%6%10%39%
1683
16th to endDay
27%6%9%6%46%5%7%10%32%
1552
March1st to 15thDay
37%37%6%37%7%7%7%37%
1893
16th to endDay
5%7%47%7%45%5%7%8%35%
2112
April1st to 15thDay
6%9%47%7%36%46%8%37%
2153
16th to endDay
6%7%36%5%35%5%5%7%43%
2340
May1st to 15thDay
6%7%26%6%35%5%5%7%43%
2331
16th to endDay
12%9%48%7%5%5%5%6%7%26%
2558
June1st to 15thDay
9%6%36%6%35%5%7%9%34%
2700
16th to endDay
331443445%7%56%
2700
July1st to 15thDay
43144245%5%8%55%
2601
16th to endDay
421332445%5%59%
2589
August1st to 15thDay
4313435%6%6%6%53%
2340
16th to endDay
321332445%7%61%
2483
September1st to 15thDay
7%213423446%59%
2049
16th to endDay
7%42442345%7%54%
1980
October1st to 15thDay
9%5%245%345%5%5%47%
1875
16th to endDay
44245%36%6%6%7%48%
1815
November1st to 15thDay
46%37%6%35%5%7%6%42%
1719
16th to endDay
26%37%7%35%5%6%8%42%
1569
December1st to 15thDay
26%46%10%46%5%7%8%37%
1488
16th to endDay
310%5%9%6%345%5%6%38%
1456
January1st to 15thNight
16%48%5%46%6%7%9%39%
2736
16th to endNight
27%46%6%36%46%7%43%
2827
February1st to 15thNight
16%49%7%35%5%6%8%41%
2433
16th to endNight
26%5%8%9%35%5%5%7%37%
1920
March1st to 15thNight
26%38%6%35%6%6%10%40%
2066
16th to endNight
7%7%25%5%346%6%7%41%
2112
April1st to 15thNight
7%9%25%5%35%5%6%8%39%
1791
16th to endNight
7%6%36%6%35%5%46%45%
1620
May1st to 15thNight
5%5%25%325%45%8%51%
1619
16th to endNight
13%6%27%6%35%45%8%37%
1549
June1st to 15thNight
8%416%5%26%6%6%8%43%
1260
16th to endNight
3313323346%64%
1260
July1st to 15thNight
112325%36%8%62%
1356
16th to endNight
2111213446%69%
1577
August1st to 15thNight
22235%236%5%6%59%
1620
16th to endNight
321231335%6%66%
1719
September1st to 15thNight
4313323345%64%
1908
16th to endNight
6%314323335%59%
1980
October1st to 15thNight
7%41342346%8%52%
2083
16th to endNight
34244345%5%7%52%
2406
November1st to 15thNight
46%35%5%36%5%7%8%45%
2470
16th to endNight
25%26%6%45%6%6%9%44%
2707
December1st to 15thNight
26%38%7%46%5%6%8%38%
2798
16th to endNight
39%5%9%7%45%5%5%7%37%
3120

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
43%13%18%17%5%2
1542
16th to endDay
42%10%19%17%7%2
1746
February1st to 15thDay
38%14%22%17%6%
1683
16th to endDay
45%11%16%19%5%1
1552
March1st to 15thDay
40%12%19%19%7%
1893
16th to endDay
43%10%20%19%5%
2112
April1st to 15thDay
43%7%20%19%8%
2153
16th to endDay
37%7%16%25%11%
2340
May1st to 15thDay
38%6%13%27%13%
2331
16th to endDay
52%10%13%16%6%
2561
June1st to 15thDay
42%7%14%22%10%2
2700
16th to endDay
23%5%10%19%31%9%
2700
July1st to 15thDay
24%5%10%20%23%16%
2450
16th to endDay
22%47%12%23%29%
2427
August1st to 15thDay
25%6%11%16%26%15%
2325
16th to endDay
20%5%10%22%26%14%
2483
September1st to 15thDay
25%49%18%30%11%
2049
16th to endDay
27%6%13%25%21%5%
1980
October1st to 15thDay
36%7%16%26%10%2
1875
16th to endDay
31%9%18%24%14%
1815
November1st to 15thDay
39%10%18%18%12%1
1719
16th to endDay
38%9%21%19%7%2
1569
December1st to 15thDay
41%13%19%17%7%
1488
16th to endDay
47%8%18%16%6%1
1456
January1st to 15thNight
39%14%19%17%7%2
2736
16th to endNight
37%11%16%23%8%2
2827
February1st to 15thNight
41%10%20%21%6%
2444
16th to endNight
44%9%18%21%5%1
1920
March1st to 15thNight
36%11%20%21%8%
2066
16th to endNight
37%10%21%22%7%
2112
April1st to 15thNight
38%8%18%22%10%
1791
16th to endNight
37%6%16%26%12%
1620
May1st to 15thNight
29%6%15%32%16%
1620
16th to endNight
42%7%16%20%11%
1550
June1st to 15thNight
35%8%12%26%13%3
1260
16th to endNight
20%38%22%32%11%
1260
July1st to 15thNight
17%410%22%28%17%
1278
16th to endNight
13%28%13%32%30%
1476
August1st to 15thNight
21%5%8%20%23%19%
1611
16th to endNight
18%47%20%28%19%
1719
September1st to 15thNight
21%5%6%21%30%13%
1908
16th to endNight
26%5%9%28%24%6%
1980
October1st to 15thNight
27%7%16%31%14%2
2083
16th to endNight
27%8%16%29%17%
2406
November1st to 15thNight
35%7%19%23%10%3
2470
16th to endNight
33%11%18%23%10%2
2707
December1st to 15thNight
41%12%20%16%8%
2798
16th to endNight
45%8%18%17%7%1
3120

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
6%2443%30%13%
90
16th to endDay
4115%50%22%6%
116
February1st to 15thDay
332%38%18%5%
126
16th to endDay
6%6%38%36%9%4
211
March1st to 15thDay
7%433%41%13%
270
16th to endDay
8%11%33%34%11%1
288
April1st to 15thDay
6%15%29%26%14%6%
269
16th to endDay
9%13%38%24%13%
270
May1st to 15thDay
10%17%30%26%11%3
288
16th to endDay
17%7%21%26%20%6%
417
June1st to 15thDay
11%12%23%31%16%4
495
16th to endDay
5%10%28%30%21%3
495
July1st to 15thDay
6%8%21%33%25%4
384
16th to endDay
6%11%37%28%11%3
327
August1st to 15thDay
49%33%32%16%3
315
16th to endDay
39%28%33%17%7%
332
September1st to 15thDay
10%7%29%29%15%7%
315
16th to endDay
12%8%26%32%17%2
315
October1st to 15thDay
13%7%30%33%13%1
210
16th to endDay
6%6%31%38%13%2
144
November1st to 15thDay
8%320%42%18%6%
135
16th to endDay
7%11%29%40%8%1
135
December1st to 15thDay
6%17%51%15%7%
118
16th to endDay
6%228%44%14%4
96
January1st to 15thNight
5%322%46%18%4
800
16th to endNight
6%423%41%19%4
832
February1st to 15thNight
3429%43%15%3
752
16th to endNight
5%426%43%17%3
632
March1st to 15thNight
4326%43%19%2
720
16th to endNight
9%8%24%39%16%1
768
April1st to 15thNight
10%7%27%32%17%4
651
16th to endNight
9%6%28%36%16%2
540
May1st to 15thNight
6%6%30%30%21%4
540
16th to endNight
16%218%33%24%3
518
June1st to 15thNight
9%5%19%39%22%2
360
16th to endNight
4217%44%27%3
360
July1st to 15thNight
3110%40%40%4
340
16th to endNight
211%44%36%4
441
August1st to 15thNight
5%112%42%34%2
539
16th to endNight
5%114%38%33%6%
573
September1st to 15thNight
8%211%33%33%11%
693
16th to endNight
9%214%31%31%11%
716
October1st to 15thNight
9%320%39%22%4
720
16th to endNight
6%420%40%22%6%
768
November1st to 15thNight
6%5%22%43%20%3
760
16th to endNight
45%28%41%16%3
952
December1st to 15thNight
5%426%48%13%2
975
16th to endNight
7%6%25%45%12%2
1040
Page generated at 2018-02-13 18:46:01. Version ac04

Copyright 2018 A. Danko


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