Fred's Backyard Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fred's Backyard Observatory clear sky chart from 2005-11-05 to 2017-09-16.

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%
14825
16%
46832
10%
14789
45%
14789
21%
31311

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
17%
717
11%
2467
4%
716
25%
716
10%
1881
January16th to endNight
20%
768
14%
2496
5%
768
30%
768
13%
1856
February1st to 15thNight
19%
701
11%
2287
3%
701
29%
701
13%
1716
February16th to endNight
25%
631
14%
2012
6%
631
36%
631
16%
1427
March1st to 15thNight
25%
720
15%
1980
7%
720
33%
720
18%
1437
March16th to endNight
33%
768
21%
2112
12%
768
41%
768
26%
1426
April1st to 15thNight
29%
718
16%
1822
6%
718
35%
718
24%
1288
April16th to endNight
41%
561
21%
1641
10%
561
49%
561
29%
1040
May1st to 15thNight
48%
498
18%
1578
12%
498
56%
498
26%
997
May16th to endNight
53%
374
18%
1497
18%
374
60%
374
27%
821
June1st to 15thNight
50%
360
14%
1440
14%
360
58%
360
24%
825
June16th to endNight
56%
360
14%
1391
18%
360
62%
360
28%
770
July1st to 15thNight
68%
340
17%
1360
25%
340
73%
340
37%
655
July16th to endNight
68%
497
18%
1529
19%
465
69%
465
36%
836
August1st to 15thNight
69%
539
19%
1609
14%
536
72%
536
39%
903
August16th to endNight
65%
623
25%
1769
17%
623
69%
623
37%
1030
September1st to 15thNight
58%
720
23%
1814
11%
720
63%
720
38%
1129
September16th to endNight
58%
658
22%
1837
16%
658
62%
658
35%
1112
October1st to 15thNight
44%
660
20%
1980
17%
660
50%
660
26%
1291
October16th to endNight
28%
704
14%
2112
8%
704
36%
704
17%
1540
November1st to 15thNight
39%
700
19%
2371
16%
700
46%
700
21%
1531
November16th to endNight
28%
720
12%
2520
8%
720
35%
720
15%
1782
December1st to 15thNight
20%
720
9%
2520
4%
720
26%
720
12%
1887
December16th to endNight
16%
768
8%
2688
3%
768
22%
768
9%
2131

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%6%35%5%5%7%33%
47858
Night
15%8%36%5%3445%6%35%
47013
Cloud CoverDay
14%7%36%6%35%5%5%7%33%
47868
Night
15%8%36%5%3445%6%36%
47017
TransparencyDay
47%413%22%11%1
47557
Night
47%312%23%11%1
46832
SeeingDay
17%5%24%26%17%8%
5339
Night
19%6%26%31%14%1
14832

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
17%13%49%7%345%5%5%22%
1468
16th to endDay
13%14%7%11%8%46%46%5%17%
1728
February1st to 15thDay
14%12%5%12%9%45%44421%
1575
16th to endDay
17%11%47%7%235%46%27%
1458
March1st to 15thDay
15%8%48%7%35%45%6%28%
1969
16th to endDay
15%8%47%5%25%346%34%
2112
April1st to 15thDay
18%10%36%5%3445%6%31%
2125
16th to endDay
17%7%35%5%24345%38%
2330
May1st to 15thDay
14%6%36%6%345%5%8%35%
2373
16th to endDay
11%425%5%35%5%6%8%41%
2618
June1st to 15thDay
14%5%25%5%35%47%8%38%
2520
16th to endDay
12%4245%36%6%6%9%37%
2520
July1st to 15thDay
7%325%5%36%6%7%9%41%
2520
16th to endDay
9%425%5%47%6%7%10%37%
2532
August1st to 15thDay
7%425%7%45%7%6%8%40%
2340
16th to endDay
9%5%246%345%5%9%42%
2420
September1st to 15thDay
13%5%245%35%45%8%41%
2144
16th to endDay
13%5%35%5%35%35%8%40%
1796
October1st to 15thDay
17%8%26%5%35%45%6%34%
1650
16th to endDay
24%9%46%6%346%5%6%23%
1760
November1st to 15thDay
13%8%36%6%3345%9%33%
1484
16th to endDay
18%12%5%7%5%445%5%8%24%
1440
December1st to 15thDay
18%14%5%9%7%445%5%5%18%
1440
16th to endDay
20%11%6%9%7%36%5%6%6%17%
1536
January1st to 15thNight
20%13%5%9%5%345%45%21%
2467
16th to endNight
14%11%6%9%7%35%5%5%6%23%
2496
February1st to 15thNight
14%12%6%8%7%35%45%5%25%
2285
16th to endNight
14%9%5%7%7%35%45%6%28%
2012
March1st to 15thNight
18%8%37%6%35%45%5%31%
1968
16th to endNight
14%9%36%5%2233442%
2112
April1st to 15thNight
18%7%35%5%45%446%35%
1822
16th to endNight
12%7%25%434446%44%
1641
May1st to 15thNight
15%415%6%35%5%5%6%40%
1578
16th to endNight
12%42342446%6%47%
1495
June1st to 15thNight
11%5%25%43445%9%41%
1440
16th to endNight
9%5%246%245%6%8%43%
1391
July1st to 15thNight
5%31343445%8%56%
1440
16th to endNight
8%3134345%6%8%49%
1635
August1st to 15thNight
6%2145%345%6%8%50%
1620
16th to endNight
8%4144345%45%53%
1769
September1st to 15thNight
11%41442346%7%48%
1814
16th to endNight
12%5%15%414349%47%
1837
October1st to 15thNight
16%5%26%5%23447%39%
1980
16th to endNight
20%9%36%6%34445%30%
2112
November1st to 15thNight
16%6%25%5%35%45%7%37%
2371
16th to endNight
20%9%36%5%35%5%5%7%26%
2520
December1st to 15thNight
20%13%5%6%6%25%45%6%23%
2520
16th to endNight
21%13%6%9%7%35%5%5%5%17%
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
18%13%49%7%35%45%5%22%
1468
16th to endDay
13%14%6%11%8%46%5%6%417%
1728
February1st to 15thDay
14%12%6%11%9%45%5%45%21%
1575
16th to endDay
17%12%48%6%245%5%6%26%
1458
March1st to 15thDay
16%8%48%6%35%5%5%6%28%
1980
16th to endDay
15%8%47%5%35%346%34%
2111
April1st to 15thDay
18%9%46%43445%6%31%
2125
16th to endDay
17%7%26%5%34445%38%
2330
May1st to 15thDay
14%6%26%5%3446%8%35%
2373
16th to endDay
11%5%25%5%25%5%6%8%41%
2618
June1st to 15thDay
14%5%245%35%5%6%8%38%
2520
16th to endDay
12%425%436%6%7%9%38%
2520
July1st to 15thDay
7%4245%46%7%7%9%42%
2520
16th to endDay
9%425%5%46%6%8%9%37%
2532
August1st to 15thDay
7%425%7%35%7%6%9%40%
2340
16th to endDay
9%5%246%245%5%9%43%
2420
September1st to 15thDay
14%424435%5%5%8%41%
2144
16th to endDay
13%5%35%5%3445%8%40%
1796
October1st to 15thDay
18%7%25%5%3445%6%35%
1650
16th to endDay
24%9%47%5%445%5%6%23%
1760
November1st to 15thDay
13%8%36%6%345%5%9%33%
1484
16th to endDay
18%12%47%5%25%45%8%23%
1440
December1st to 15thDay
19%13%5%9%7%35%5%5%5%19%
1440
16th to endDay
20%11%6%9%6%37%46%5%17%
1536
January1st to 15thNight
20%13%5%8%6%34445%22%
2467
16th to endNight
14%11%6%9%7%45%45%5%24%
2496
February1st to 15thNight
14%14%5%7%7%45%445%25%
2278
16th to endNight
15%9%49%6%35%45%6%29%
2012
March1st to 15thNight
18%8%37%6%35%446%30%
1980
16th to endNight
14%9%36%5%2333442%
2112
April1st to 15thNight
18%7%35%5%35%346%35%
1822
16th to endNight
12%6%25%4245%46%44%
1641
May1st to 15thNight
15%415%6%3445%7%39%
1577
16th to endNight
12%42443435%6%47%
1495
June1st to 15thNight
12%5%25%4345%5%9%41%
1440
16th to endNight
9%425%6%245%5%8%43%
1391
July1st to 15thNight
5%313325%448%56%
1440
16th to endNight
8%22343446%8%49%
1635
August1st to 15thNight
6%2145%345%7%8%50%
1620
16th to endNight
8%314435%45%5%53%
1769
September1st to 15thNight
11%41432346%7%48%
1814
16th to endNight
12%5%2441435%8%47%
1837
October1st to 15thNight
16%5%26%5%23447%39%
1980
16th to endNight
20%9%35%6%345%45%29%
2112
November1st to 15thNight
16%6%35%5%35%447%37%
2371
16th to endNight
20%9%36%5%345%5%7%27%
2520
December1st to 15thNight
21%13%46%5%25%45%6%23%
2520
16th to endNight
21%13%6%9%6%45%45%5%17%
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
62%311%16%6%
1469
16th to endDay
66%39%13%6%
1728
February1st to 15thDay
63%311%16%3
1577
16th to endDay
56%312%18%7%1
1458
March1st to 15thDay
55%412%19%8%
1980
16th to endDay
50%39%21%13%1
2112
April1st to 15thDay
51%311%20%12%
2125
16th to endDay
47%29%22%15%2
2330
May1st to 15thDay
45%411%24%13%
2373
16th to endDay
39%315%24%15%1
2622
June1st to 15thDay
41%412%27%13%
2520
16th to endDay
39%5%15%25%14%
2520
July1st to 15thDay
34%5%11%27%18%2
2371
16th to endDay
39%5%15%25%12%2
2375
August1st to 15thDay
37%416%24%15%1
2327
16th to endDay
36%413%30%13%1
2420
September1st to 15thDay
39%5%14%27%12%1
2144
16th to endDay
41%313%30%9%
1796
October1st to 15thDay
47%312%24%10%1
1650
16th to endDay
58%415%16%5%
1760
November1st to 15thDay
47%416%22%8%1
1484
16th to endDay
57%415%16%5%
1440
December1st to 15thDay
65%313%15%2
1440
16th to endDay
65%411%15%2
1536
January1st to 15thNight
63%210%15%6%
2467
16th to endNight
60%211%18%6%
2496
February1st to 15thNight
59%310%18%6%
2287
16th to endNight
55%212%21%7%
2012
March1st to 15thNight
54%211%22%7%
1980
16th to endNight
46%28%23%16%2
2112
April1st to 15thNight
49%210%21%15%1
1822
16th to endNight
40%410%23%18%3
1641
May1st to 15thNight
42%310%25%16%2
1578
16th to endNight
35%313%27%16%3
1497
June1st to 15thNight
38%411%26%17%1
1440
16th to endNight
36%314%26%18%1
1391
July1st to 15thNight
26%311%28%26%3
1360
16th to endNight
31%215%28%18%3
1529
August1st to 15thNight
29%417%32%13%2
1609
16th to endNight
32%310%33%18%1
1769
September1st to 15thNight
33%413%31%16%1
1814
16th to endNight
34%412%34%13%
1837
October1st to 15thNight
43%310%28%13%
1980
16th to endNight
55%412%19%8%
2112
November1st to 15thNight
45%312%22%13%1
2371
16th to endNight
54%415%20%5%
2520
December1st to 15thNight
60%413%17%4
2520
16th to endNight
67%311%13%3
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%18%43%9%10%1
66
16th to endDay
36%13%32%15%2
96
February1st to 15thDay
16%12%50%16%4
90
16th to endDay
21%12%35%28%2
90
March1st to 15thDay
21%8%33%24%11%
270
16th to endDay
22%5%31%26%10%3
288
April1st to 15thDay
22%7%30%29%8%1
270
16th to endDay
18%7%31%23%14%5%
270
May1st to 15thDay
21%323%25%15%10%
288
16th to endDay
14%426%26%20%7%
331
June1st to 15thDay
16%5%18%32%22%4
315
16th to endDay
14%421%28%25%5%
315
July1st to 15thDay
10%16%33%26%13%
305
16th to endDay
9%219%34%23%11%
326
August1st to 15thDay
8%117%27%26%17%
313
16th to endDay
12%214%24%24%20%
332
September1st to 15thDay
13%115%25%25%17%
315
16th to endDay
17%314%27%23%12%
254
October1st to 15thDay
19%5%24%24%18%8%
255
16th to endDay
27%8%26%27%9%
272
November1st to 15thDay
9%12%20%37%17%3
94
16th to endDay
23%11%26%28%8%1
60
December1st to 15thDay
16%10%45%20%6%1
60
16th to endDay
29%17%40%12%
64
January1st to 15thNight
27%13%31%21%5%
720
16th to endNight
22%7%35%27%6%
768
February1st to 15thNight
22%11%35%23%5%
704
16th to endNight
19%9%35%28%5%
631
March1st to 15thNight
24%8%33%27%6%
720
16th to endNight
19%7%30%29%11%1
768
April1st to 15thNight
21%7%33%29%6%
718
16th to endNight
15%5%28%35%12%1
561
May1st to 15thNight
16%223%35%19%2
498
16th to endNight
13%223%34%24%
375
June1st to 15thNight
13%224%38%19%
360
16th to endNight
8%120%44%24%
360
July1st to 15thNight
7%16%46%27%2
340
16th to endNight
9%113%47%24%3
497
August1st to 15thNight
8%10%44%31%4
539
16th to endNight
11%112%37%32%4
623
September1st to 15thNight
13%317%31%26%6%
720
16th to endNight
15%215%31%30%4
658
October1st to 15thNight
18%423%29%21%3
660
16th to endNight
25%7%28%30%7%
704
November1st to 15thNight
19%5%27%31%13%2
700
16th to endNight
25%8%27%26%9%1
720
December1st to 15thNight
29%8%33%22%5%
720
16th to endNight
28%8%36%22%4
768
Page generated at 2017-09-16 17:07:01. Version ac04

Copyright 2017 A. Danko


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