Fair View Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fair View Observatory clear sky chart from 2005-11-05 to 2017-04-28.

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
51%
15094
24%
45628
17%
15051
59%
15051
30%
27656

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
28%
720
24%
2327
10%
716
44%
716
22%
1415
January16th to endNight
29%
768
25%
2454
13%
768
44%
768
22%
1531
February1st to 15thNight
35%
704
26%
2111
12%
701
50%
701
27%
1286
February16th to endNight
28%
631
26%
1893
10%
631
43%
631
26%
1166
March1st to 15thNight
35%
720
25%
2052
13%
720
46%
720
30%
1262
March16th to endNight
44%
768
23%
2112
13%
768
51%
768
33%
1280
April1st to 15thNight
45%
659
26%
1917
18%
659
54%
659
36%
1094
April16th to endNight
51%
534
26%
1677
17%
534
61%
534
33%
951
May1st to 15thNight
51%
495
23%
1485
14%
495
58%
495
31%
908
May16th to endNight
65%
513
22%
1538
17%
513
69%
513
35%
912
June1st to 15thNight
71%
495
19%
1485
16%
495
73%
495
35%
898
June16th to endNight
79%
495
18%
1485
16%
495
80%
495
37%
858
July1st to 15thNight
71%
465
14%
1395
12%
465
71%
465
29%
896
July16th to endNight
77%
522
15%
1469
13%
489
77%
489
32%
908
August1st to 15thNight
72%
494
20%
1493
20%
491
72%
491
30%
927
August16th to endNight
66%
525
17%
1750
18%
525
67%
525
22%
1158
September1st to 15thNight
69%
657
21%
1812
18%
657
69%
657
29%
1201
September16th to endNight
61%
657
24%
1815
19%
657
64%
657
30%
1173
October1st to 15thNight
58%
660
33%
1829
26%
660
64%
660
36%
1102
October16th to endNight
57%
704
34%
2112
27%
704
68%
704
38%
1160
November1st to 15thNight
53%
700
32%
2241
27%
700
63%
700
37%
1179
November16th to endNight
44%
720
28%
2340
20%
720
57%
720
30%
1328
December1st to 15thNight
42%
720
25%
2340
18%
720
52%
720
26%
1412
December16th to endNight
35%
768
22%
2496
16%
768
44%
768
20%
1651

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%244345%5%8%42%
46061
Night
12%42442445%7%46%
45828
TransparencyDay
39%411%21%18%4
45762
Night
36%410%20%20%7%
45631
SeeingDay
14%415%21%25%18%
4848
Night
14%6%19%30%24%4
15096

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
16%6%25%334336%44%
1611
16th to endDay
17%5%2432345%6%43%
1768
February1st to 15thDay
15%5%15%4245%46%44%
1750
16th to endDay
17%5%24334445%43%
1580
March1st to 15thDay
14%5%25%424447%44%
1908
16th to endDay
16%41443345%7%44%
2111
April1st to 15thDay
12%5%25%424346%48%
2040
16th to endDay
10%324424448%50%
2229
May1st to 15thDay
9%435%5%245%6%7%44%
2136
16th to endDay
9%314435%6%6%9%43%
2223
June1st to 15thDay
8%4245%46%6%8%12%37%
2145
16th to endDay
3214435%6%9%11%48%
2145
July1st to 15thDay
10%5%36%6%37%6%8%11%31%
2145
16th to endDay
6%5%26%6%48%8%8%12%32%
2283
August1st to 15thDay
7%5%25%7%5%5%8%8%10%32%
2123
16th to endDay
14%5%36%6%46%6%7%9%28%
2090
September1st to 15thDay
13%5%25%6%445%6%8%36%
1815
16th to endDay
17%6%24323446%43%
1815
October1st to 15thDay
13%413312435%54%
1801
16th to endDay
11%313323335%58%
1760
November1st to 15thDay
12%323413345%55%
1615
16th to endDay
14%5%34323445%49%
1620
December1st to 15thDay
16%7%245%3335%5%42%
1620
16th to endDay
24%7%25%423346%36%
1728
January1st to 15thNight
16%6%34323345%45%
2327
16th to endNight
18%5%24424335%44%
2454
February1st to 15thNight
15%424424346%47%
2103
16th to endNight
15%425%324335%47%
1893
March1st to 15thNight
13%5%235%24346%49%
2052
16th to endNight
11%5%14424348%49%
2112
April1st to 15thNight
12%41231345%7%51%
1917
16th to endNight
9%3245%2445%7%50%
1677
May1st to 15thNight
8%435%5%35%45%7%46%
1484
16th to endNight
7%414425%5%6%8%49%
1538
June1st to 15thNight
7%4243346%7%13%42%
1485
16th to endNight
31235%46%6%7%12%45%
1485
July1st to 15thNight
8%325%5%46%7%8%11%36%
1485
16th to endNight
5%3246%36%7%9%13%37%
1577
August1st to 15thNight
5%326%5%45%6%8%13%37%
1504
16th to endNight
11%5%25%5%5%6%5%7%9%34%
1750
September1st to 15thNight
8%5%25%6%46%6%8%9%38%
1812
16th to endNight
13%5%24425%5%5%7%44%
1815
October1st to 15thNight
12%5%23324345%52%
1829
16th to endNight
9%323413335%59%
2112
November1st to 15thNight
11%312312336%58%
2241
16th to endNight
14%413323345%52%
2340
December1st to 15thNight
14%6%24423446%46%
2340
16th to endNight
20%6%25%434445%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
42%29%15%25%4
1612
16th to endDay
41%36%19%20%8%
1768
February1st to 15thDay
40%38%20%22%4
1752
16th to endDay
42%26%20%20%6%
1580
March1st to 15thDay
40%29%21%19%6%
1908
16th to endDay
40%311%22%18%4
2112
April1st to 15thDay
37%39%22%21%6%
2040
16th to endDay
34%38%24%25%4
2229
May1st to 15thDay
37%414%21%17%3
2136
16th to endDay
35%5%14%27%15%2
2227
June1st to 15thDay
38%6%17%26%8%1
2145
16th to endDay
26%8%18%27%17%2
2145
July1st to 15thDay
42%8%19%20%7%2
2006
16th to endDay
40%9%18%21%7%1
2128
August1st to 15thDay
41%8%17%22%9%1
2110
16th to endDay
48%8%15%15%11%
2090
September1st to 15thDay
43%7%13%18%15%2
1815
16th to endDay
40%49%20%20%4
1815
October1st to 15thDay
32%210%21%26%7%
1801
16th to endDay
30%16%17%33%10%
1760
November1st to 15thDay
32%25%17%31%10%
1615
16th to endDay
37%45%17%26%8%
1620
December1st to 15thDay
43%37%22%15%7%
1620
16th to endDay
49%37%18%13%6%
1728
January1st to 15thNight
40%26%19%24%5%
2327
16th to endNight
42%2418%21%9%
2454
February1st to 15thNight
38%25%20%21%11%
2112
16th to endNight
39%25%20%24%7%
1893
March1st to 15thNight
37%39%20%20%9%
2052
16th to endNight
33%410%22%22%6%
2112
April1st to 15thNight
31%39%25%22%8%
1917
16th to endNight
31%410%22%21%9%
1677
May1st to 15thNight
36%413%21%20%3
1485
16th to endNight
32%5%14%28%15%3
1540
June1st to 15thNight
31%7%20%28%10%1
1485
16th to endNight
29%7%19%24%17%2
1485
July1st to 15thNight
36%8%21%22%7%3
1395
16th to endNight
32%9%24%21%10%1
1469
August1st to 15thNight
35%7%17%26%10%1
1493
16th to endNight
41%9%17%17%13%
1750
September1st to 15thNight
38%8%15%19%13%4
1812
16th to endNight
37%7%11%20%17%6%
1815
October1st to 15thNight
34%38%18%26%8%
1829
16th to endNight
29%2417%32%14%
2112
November1st to 15thNight
28%25%17%31%14%
2241
16th to endNight
35%26%17%27%11%
2340
December1st to 15thNight
38%38%22%18%8%
2340
16th to endNight
47%37%16%18%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
18%12%34%23%6%4
90
16th to endDay
12%16%48%13%8%
96
February1st to 15thDay
8%24%35%23%7%
90
16th to endDay
25%7%33%27%6%
81
March1st to 15thDay
15%9%29%32%11%1
198
16th to endDay
16%6%25%33%17%
288
April1st to 15thDay
16%10%25%18%20%7%
270
16th to endDay
13%320%24%27%10%
259
May1st to 15thDay
13%425%19%17%19%
228
16th to endDay
11%111%19%31%24%
267
June1st to 15thDay
9%17%18%30%31%
255
16th to endDay
36%20%29%40%
255
July1st to 15thDay
8%5%18%28%37%
245
16th to endDay
6%114%29%48%
270
August1st to 15thDay
12%1119%33%31%
253
16th to endDay
16%1215%35%27%
268
September1st to 15thDay
15%16%12%36%28%
255
16th to endDay
22%17%23%34%11%
254
October1st to 15thDay
18%115%27%25%10%
255
16th to endDay
13%413%25%31%11%
272
November1st to 15thDay
26%421%22%20%5%
123
16th to endDay
12%6%22%30%23%5%
90
December1st to 15thDay
25%435%18%14%1
90
16th to endDay
31%15%19%22%9%1
96
January1st to 15thNight
20%15%28%25%9%
720
16th to endNight
20%12%30%30%5%
768
February1st to 15thNight
17%12%28%34%6%
704
16th to endNight
17%14%34%30%3
631
March1st to 15thNight
16%10%31%33%8%
720
16th to endNight
12%10%27%33%15%
768
April1st to 15thNight
16%8%27%30%17%
659
16th to endNight
11%6%22%33%23%2
534
May1st to 15thNight
10%423%32%24%4
495
16th to endNight
9%114%28%39%6%
515
June1st to 15thNight
7%28%31%37%12%
495
16th to endNight
415%28%46%13%
495
July1st to 15thNight
10%1323%46%14%
465
16th to endNight
5%424%49%15%
522
August1st to 15thNight
5%1325%48%14%
494
16th to endNight
13%422%46%12%
525
September1st to 15thNight
9%15%24%46%12%
657
16th to endNight
16%19%32%35%4
657
October1st to 15thNight
15%217%31%27%5%
660
16th to endNight
10%7%19%32%26%4
704
November1st to 15thNight
12%6%20%35%22%2
700
16th to endNight
16%10%23%32%16%1
720
December1st to 15thNight
16%9%24%34%13%1
720
16th to endNight
23%10%25%31%10%
768
Page generated at 2017-04-29 09:44:58. Version ac04

Copyright 2017 A. Danko


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