Blazer Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blazer Observatory clear sky chart from 2005-11-05 to 2017-09-23.

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
48%
15297
24%
46804
17%
15253
56%
15253
29%
28441

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
27%
858
24%
2425
8%
853
41%
853
24%
1566
January16th to endNight
23%
768
25%
2304
10%
768
37%
768
22%
1517
February1st to 15thNight
27%
704
24%
2112
9%
701
40%
701
25%
1337
February16th to endNight
24%
631
25%
1893
10%
631
37%
631
25%
1201
March1st to 15thNight
29%
720
19%
2160
10%
720
37%
720
23%
1407
March16th to endNight
38%
633
24%
2012
15%
633
46%
633
28%
1197
April1st to 15thNight
40%
539
25%
1797
17%
539
52%
539
30%
1023
April16th to endNight
44%
540
26%
1800
19%
540
56%
540
33%
993
May1st to 15thNight
48%
540
22%
1692
15%
540
57%
540
30%
1035
May16th to endNight
65%
561
24%
1682
19%
561
69%
561
36%
974
June1st to 15thNight
72%
540
20%
1593
17%
540
73%
540
34%
958
June16th to endNight
75%
540
23%
1440
19%
540
76%
540
39%
868
July1st to 15thNight
76%
510
18%
1360
16%
510
77%
510
32%
881
July16th to endNight
76%
564
18%
1680
18%
531
78%
531
32%
1014
August1st to 15thNight
78%
539
19%
1788
24%
536
79%
536
32%
1052
August16th to endNight
72%
573
22%
1910
26%
573
73%
573
27%
1177
September1st to 15thNight
64%
576
21%
1836
21%
576
66%
576
31%
1104
September16th to endNight
66%
689
29%
1903
23%
689
69%
689
38%
1119
October1st to 15thNight
59%
660
35%
1815
27%
660
64%
660
41%
1049
October16th to endNight
51%
704
33%
2150
27%
704
59%
704
35%
1213
November1st to 15thNight
49%
700
30%
2276
25%
700
60%
700
35%
1233
November16th to endNight
39%
720
27%
2340
19%
720
52%
720
28%
1391
December1st to 15thNight
37%
720
23%
2340
16%
720
48%
720
24%
1466
December16th to endNight
27%
768
20%
2496
13%
768
37%
768
19%
1666

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
12%5%25%5%35%5%5%7%41%
48070
Night
12%5%2442445%7%47%
47001
TransparencyDay
40%6%10%19%17%4
47769
Night
35%5%10%20%20%6%
46806
SeeingDay
14%6%18%25%21%12%
5454
Night
14%7%23%27%21%4
15299

By Month

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
20%8%2431233442%
1491
16th to endDay
19%6%23323345%45%
1920
February1st to 15thDay
15%8%35%423335%43%
1750
16th to endDay
19%5%235%3235%6%41%
1580
March1st to 15thDay
17%7%45%5%25%5%4437%
1800
16th to endDay
14%5%25%5%245%6%7%40%
2219
April1st to 15thDay
13%42442445%7%46%
2151
16th to endDay
11%5%3442345%8%46%
2160
May1st to 15thDay
13%5%25%5%35%45%6%41%
2257
16th to endDay
8%426%7%46%5%5%8%39%
2431
June1st to 15thDay
6%5%25%6%47%5%8%10%38%
2362
16th to endDay
6%4145%46%6%6%10%43%
2520
July1st to 15thDay
8%5%26%7%47%7%8%11%30%
2520
16th to endDay
7%426%7%5%8%7%8%11%31%
2367
August1st to 15thDay
6%426%8%37%7%8%11%34%
2160
16th to endDay
10%5%36%6%5%6%6%8%8%32%
2292
September1st to 15thDay
11%5%26%5%45%5%7%8%38%
2111
16th to endDay
11%5%25%434436%47%
1894
October1st to 15thDay
10%4244235%46%50%
1815
16th to endDay
12%31332333458%
1720
November1st to 15thDay
11%413323346%55%
1582
16th to endDay
16%413213445%49%
1620
December1st to 15thDay
21%7%345%24435%37%
1620
16th to endDay
24%7%35%32334437%
1728
January1st to 15thNight
17%6%24423335%45%
2425
16th to endNight
17%6%35%42334442%
2304
February1st to 15thNight
17%5%25%42334446%
2103
16th to endNight
17%5%34424346%44%
1893
March1st to 15thNight
17%6%24433347%41%
2160
16th to endNight
14%5%24414347%48%
2012
April1st to 15thNight
10%5%2432445%8%48%
1797
16th to endNight
10%32432435%8%51%
1800
May1st to 15thNight
10%5%3442445%7%46%
1691
16th to endNight
6%4133245%7%10%49%
1682
June1st to 15thNight
44245%36%5%7%12%45%
1593
16th to endNight
3324335%5%6%11%50%
1440
July1st to 15thNight
5%325%5%37%6%7%9%42%
1440
16th to endNight
5%3245%35%5%8%12%42%
1795
August1st to 15thNight
5%3145%35%6%9%11%43%
1800
16th to endNight
7%4245%35%6%7%11%41%
1910
September1st to 15thNight
10%42442345%9%46%
1836
16th to endNight
8%42433347%7%50%
1903
October1st to 15thNight
10%413323345%57%
1815
16th to endNight
14%5%2231223457%
2150
November1st to 15thNight
10%423223335%56%
2276
16th to endNight
14%5%24423335%50%
2340
December1st to 15thNight
16%5%25%324446%43%
2340
16th to endNight
20%6%35%5%33346%38%
2496

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
45%36%16%23%5%
1492
16th to endDay
41%35%22%21%5%
1920
February1st to 15thDay
43%27%22%18%4
1752
16th to endDay
43%47%15%24%4
1580
March1st to 15thDay
47%6%7%15%17%5%
1800
16th to endDay
41%5%11%21%17%1
2220
April1st to 15thDay
36%5%10%21%18%7%
2151
16th to endDay
34%6%8%24%22%2
2160
May1st to 15thDay
41%7%9%19%17%4
2257
16th to endDay
40%8%13%22%12%2
2435
June1st to 15thDay
37%9%13%21%15%1
2362
16th to endDay
33%9%14%20%19%3
2520
July1st to 15thDay
42%10%18%18%8%2
2371
16th to endDay
41%11%18%18%9%
2219
August1st to 15thDay
38%11%15%19%11%2
2148
16th to endDay
45%10%13%19%8%2
2292
September1st to 15thDay
41%8%13%18%13%5%
2111
16th to endDay
37%5%9%20%19%6%
1894
October1st to 15thDay
33%48%18%24%9%
1815
16th to endDay
30%3418%33%9%
1720
November1st to 15thDay
31%35%18%30%9%
1582
16th to endDay
35%47%20%24%8%
1620
December1st to 15thDay
48%5%6%18%14%6%
1620
16th to endDay
51%39%18%14%2
1728
January1st to 15thNight
42%37%17%24%4
2425
16th to endNight
44%46%17%20%6%
2304
February1st to 15thNight
41%36%21%20%6%
2112
16th to endNight
41%45%20%22%5%
1893
March1st to 15thNight
43%49%18%17%8%
2160
16th to endNight
36%39%25%21%3
2012
April1st to 15thNight
33%410%23%19%7%
1797
16th to endNight
30%5%10%23%24%5%
1800
May1st to 15thNight
34%7%10%19%21%5%
1692
16th to endNight
27%8%15%26%16%5%
1684
June1st to 15thNight
31%8%14%24%19%2
1593
16th to endNight
26%9%15%22%23%2
1440
July1st to 15thNight
32%11%18%23%10%4
1360
16th to endNight
29%10%21%23%12%1
1680
August1st to 15thNight
28%11%17%24%14%3
1788
16th to endNight
34%10%18%22%11%3
1910
September1st to 15thNight
35%5%17%20%13%7%
1836
16th to endNight
30%5%10%21%23%8%
1903
October1st to 15thNight
29%37%19%25%14%
1815
16th to endNight
32%3313%32%14%
2150
November1st to 15thNight
30%36%18%27%14%
2276
16th to endNight
37%35%17%25%10%
2340
December1st to 15thNight
41%48%20%19%5%
2340
16th to endNight
47%48%18%15%5%
2496

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
22%22%33%15%5%1
90
16th to endDay
28%28%33%7%21
96
February1st to 15thDay
25%25%33%14%1
90
16th to endDay
27%19%35%16%1
81
March1st to 15thDay
28%26%31%10%21
90
16th to endDay
22%7%34%26%9%1
252
April1st to 15thDay
17%13%30%20%15%2
270
16th to endDay
12%10%24%30%20%2
270
May1st to 15thDay
18%7%24%27%11%11%
288
16th to endDay
14%223%27%19%13%
331
June1st to 15thDay
10%113%26%28%19%
337
16th to endDay
9%112%29%28%17%
495
July1st to 15thDay
8%112%30%30%17%
475
16th to endDay
9%6%18%28%35%
328
August1st to 15thDay
12%8%22%31%23%
313
16th to endDay
13%16%29%28%20%
332
September1st to 15thDay
13%38%23%32%18%
315
16th to endDay
11%210%28%35%10%
283
October1st to 15thDay
13%121%33%23%5%
255
16th to endDay
18%5%20%35%18%2
97
November1st to 15thDay
22%16%25%24%11%
90
16th to endDay
20%10%36%25%6%1
90
December1st to 15thDay
27%20%30%17%31
90
16th to endDay
25%16%38%15%4
96
January1st to 15thNight
22%15%31%21%7%
858
16th to endNight
20%14%38%24%2
768
February1st to 15thNight
21%12%35%26%4
704
16th to endNight
19%16%36%24%2
631
March1st to 15thNight
21%13%31%26%6%
720
16th to endNight
16%9%31%27%13%
633
April1st to 15thNight
13%11%32%26%14%2
539
16th to endNight
11%7%31%30%16%1
540
May1st to 15thNight
12%326%31%22%3
540
16th to endNight
8%117%34%31%5%
563
June1st to 15thNight
6%12%32%38%9%
540
16th to endNight
419%27%42%14%
540
July1st to 15thNight
6%7%30%43%12%
510
16th to endNight
5%6%23%42%21%
564
August1st to 15thNight
7%326%43%17%
539
16th to endNight
9%8%27%41%12%
573
September1st to 15thNight
12%111%28%37%8%
576
16th to endNight
10%213%31%36%5%
689
October1st to 15thNight
12%418%32%27%5%
660
16th to endNight
17%7%19%29%23%3
704
November1st to 15thNight
12%9%23%30%20%4
700
16th to endNight
17%10%30%27%13%1
720
December1st to 15thNight
20%10%27%30%10%
720
16th to endNight
25%12%30%23%7%
768
Page generated at 2017-09-24 08:15:46. Version ac04

Copyright 2017 A. Danko


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