Nightfall Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Nightfall Observatory clear sky chart from 2005-11-05 to

2017-09-12
.

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%
15225
24%
46915
17%
15182
56%
15182
28%
28758

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
25%
720
24%
2327
9%
716
41%
716
21%
1475
January16th to endNight
24%
768
26%
2322
11%
768
37%
768
21%
1520
February1st to 15thNight
27%
704
25%
2112
9%
701
42%
701
26%
1324
February16th to endNight
26%
631
24%
1893
10%
631
37%
631
25%
1206
March1st to 15thNight
30%
720
20%
2155
10%
720
38%
720
24%
1387
March16th to endNight
37%
705
24%
2049
14%
705
46%
705
28%
1262
April1st to 15thNight
39%
539
24%
1797
16%
539
52%
539
30%
1030
April16th to endNight
45%
540
27%
1800
19%
540
57%
540
33%
987
May1st to 15thNight
51%
540
21%
1638
14%
540
59%
540
29%
1030
May16th to endNight
67%
561
23%
1682
19%
561
71%
561
36%
993
June1st to 15thNight
72%
540
18%
1620
15%
540
74%
540
33%
965
June16th to endNight
76%
540
20%
1620
18%
540
77%
540
36%
953
July1st to 15thNight
73%
510
14%
1530
13%
510
75%
510
29%
978
July16th to endNight
76%
564
17%
1617
17%
531
78%
531
29%
1035
August1st to 15thNight
82%
539
19%
1788
22%
536
82%
536
31%
1054
August16th to endNight
71%
573
20%
1910
24%
573
71%
573
24%
1235
September1st to 15thNight
64%
602
20%
1839
20%
602
65%
602
26%
1197
September16th to endNight
66%
657
27%
1815
22%
657
69%
657
35%
1098
October1st to 15thNight
56%
660
34%
1815
26%
660
62%
660
40%
1054
October16th to endNight
51%
704
33%
2134
28%
704
59%
704
36%
1208
November1st to 15thNight
50%
700
30%
2276
24%
700
61%
700
35%
1221
November16th to endNight
38%
720
27%
2340
18%
720
51%
720
27%
1374
December1st to 15thNight
32%
720
22%
2340
14%
720
43%
720
22%
1495
December16th to endNight
28%
768
21%
2496
14%
768
38%
768
19%
1677

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%40%
47737
Night
11%5%2442445%7%46%
47117
TransparencyDay
40%7%10%19%17%4
47441
Night
36%6%10%20%20%6%
46917
SeeingDay
15%7%19%23%21%12%
5134
Night
14%7%23%28%21%4
15227

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
19%7%25%42324442%
1611
16th to endDay
18%6%24323335%46%
1901
February1st to 15thDay
17%8%35%422346%41%
1750
16th to endDay
20%5%25%333335%41%
1580
March1st to 15thDay
17%7%25%5%33445%39%
1803
16th to endDay
14%6%36%434447%41%
2184
April1st to 15thDay
12%5%25%5%2445%6%45%
2151
16th to endDay
10%425%5%3445%7%45%
2160
May1st to 15thDay
12%5%25%435%45%8%42%
2313
16th to endDay
8%5%25%6%46%5%6%8%39%
2431
June1st to 15thDay
6%5%26%6%5%7%7%8%8%35%
2340
16th to endDay
5%3245%46%6%8%10%42%
2340
July1st to 15thDay
9%426%6%48%7%7%10%31%
2340
16th to endDay
7%415%7%5%8%8%9%11%30%
2438
August1st to 15thDay
7%426%8%46%7%8%11%32%
2160
16th to endDay
10%6%36%7%47%6%7%8%29%
2292
September1st to 15thDay
10%5%35%5%46%5%7%7%38%
2029
16th to endDay
13%4145%25%36%6%46%
1815
October1st to 15thDay
10%4144245%5%7%50%
1815
16th to endDay
13%42331233358%
1734
November1st to 15thDay
12%5%23313245%55%
1582
16th to endDay
15%42431445%5%47%
1620
December1st to 15thDay
19%8%25%324345%39%
1620
16th to endDay
23%7%45%43333435%
1728
January1st to 15thNight
17%6%35%42334443%
2327
16th to endNight
17%6%345%2335%5%41%
2322
February1st to 15thNight
17%6%23323336%46%
2103
16th to endNight
16%5%25%423345%45%
1893
March1st to 15thNight
16%6%25%424446%43%
2155
16th to endNight
12%6%2442336%6%47%
2049
April1st to 15thNight
13%41242445%7%48%
1797
16th to endNight
8%4244235%5%7%52%
1800
May1st to 15thNight
9%4245%26%5%48%45%
1637
16th to endNight
4314435%5%6%10%49%
1682
June1st to 15thNight
42145%36%6%8%10%45%
1620
16th to endNight
3223436%5%7%11%48%
1620
July1st to 15thNight
8%3246%35%6%8%10%40%
1620
16th to endNight
4425%6%47%6%7%11%40%
1727
August1st to 15thNight
4214446%6%8%12%44%
1800
16th to endNight
8%5%246%45%6%6%9%40%
1910
September1st to 15thNight
8%5%25%5%35%6%6%7%42%
1839
16th to endNight
7%4245%25%45%7%50%
1815
October1st to 15thNight
9%41432344457%
1815
16th to endNight
12%5%2331222358%
2134
November1st to 15thNight
11%322323346%56%
2276
16th to endNight
13%5%24423235%50%
2340
December1st to 15thNight
17%6%25%423445%42%
2340
16th to endNight
21%6%35%423346%37%
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%15%23%4
1612
16th to endDay
42%35%21%20%6%
1901
February1st to 15thDay
44%36%23%17%3
1752
16th to endDay
44%47%15%23%5%
1580
March1st to 15thDay
46%48%15%18%5%
1803
16th to endDay
43%5%10%21%17%2
2185
April1st to 15thDay
39%5%10%19%18%6%
2151
16th to endDay
37%5%9%22%21%3
2160
May1st to 15thDay
38%7%10%19%18%4
2313
16th to endDay
38%8%12%24%13%2
2435
June1st to 15thDay
40%10%15%19%13%1
2340
16th to endDay
32%10%14%23%14%4
2340
July1st to 15thDay
41%12%18%18%7%1
2201
16th to endDay
40%14%17%18%8%
2285
August1st to 15thDay
39%12%17%16%10%2
2148
16th to endDay
47%10%12%17%8%2
2292
September1st to 15thDay
41%9%13%17%13%5%
2029
16th to endDay
37%6%10%19%20%5%
1815
October1st to 15thDay
31%6%9%18%24%9%
1815
16th to endDay
31%3317%33%10%
1734
November1st to 15thDay
32%26%18%30%9%
1582
16th to endDay
36%47%16%25%8%
1620
December1st to 15thDay
46%5%7%18%17%5%
1620
16th to endDay
52%37%18%13%3
1728
January1st to 15thNight
43%36%16%24%5%
2327
16th to endNight
44%45%18%20%6%
2322
February1st to 15thNight
40%36%21%20%8%
2112
16th to endNight
41%36%19%24%5%
1893
March1st to 15thNight
41%48%19%18%6%
2155
16th to endNight
35%5%9%25%20%3
2049
April1st to 15thNight
34%410%23%18%8%
1797
16th to endNight
30%410%23%23%6%
1800
May1st to 15thNight
35%8%11%17%23%4
1638
16th to endNight
28%9%14%27%14%5%
1684
June1st to 15thNight
28%10%17%23%17%1
1620
16th to endNight
27%9%15%23%20%3
1620
July1st to 15thNight
33%11%20%21%8%4
1530
16th to endNight
33%11%18%21%13%
1617
August1st to 15thNight
27%12%17%23%14%3
1788
16th to endNight
38%10%15%19%12%3
1910
September1st to 15thNight
38%9%14%17%14%5%
1839
16th to endNight
32%6%9%20%22%8%
1815
October1st to 15thNight
29%48%19%24%13%
1815
16th to endNight
32%2412%33%14%
2134
November1st to 15thNight
29%36%17%27%14%
2276
16th to endNight
36%35%17%25%10%
2340
December1st to 15thNight
43%5%7%17%21%5%
2340
16th to endNight
47%47%18%16%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
24%20%34%16%31
90
16th to endDay
25%26%39%6%3
96
February1st to 15thDay
25%31%32%10%1
90
16th to endDay
32%16%37%13%1
81
March1st to 15thDay
31%22%32%8%5%
93
16th to endDay
19%11%34%21%12%1
288
April1st to 15thDay
18%10%29%22%17%1
270
16th to endDay
14%8%25%26%22%2
270
May1st to 15thDay
14%6%30%23%16%9%
288
16th to endDay
13%5%22%25%18%14%
331
June1st to 15thDay
10%210%25%29%21%
315
16th to endDay
11%12%24%25%25%
315
July1st to 15thDay
6%110%26%29%23%
305
16th to endDay
9%26%15%34%31%
326
August1st to 15thDay
12%19%25%28%23%
313
16th to endDay
15%6%28%32%15%
332
September1st to 15thDay
12%112%25%30%18%
299
16th to endDay
15%314%30%26%9%
254
October1st to 15thDay
14%422%31%20%6%
255
16th to endDay
18%5%17%31%23%3
157
November1st to 15thDay
18%17%27%21%13%1
90
16th to endDay
15%17%35%18%10%2
90
December1st to 15thDay
21%23%35%16%21
90
16th to endDay
31%17%32%14%31
96
January1st to 15thNight
21%16%33%20%7%
720
16th to endNight
21%15%35%23%3
768
February1st to 15thNight
20%13%34%26%4
704
16th to endNight
21%12%37%25%2
631
March1st to 15thNight
20%13%33%26%5%
720
16th to endNight
16%10%31%26%13%1
705
April1st to 15thNight
14%8%33%26%14%1
539
16th to endNight
12%6%31%31%16%1
540
May1st to 15thNight
11%327%29%24%3
540
16th to endNight
6%117%37%30%6%
563
June1st to 15thNight
5%11%30%39%11%
540
16th to endNight
319%26%45%14%
540
July1st to 15thNight
7%16%26%42%15%
510
16th to endNight
6%6%23%43%19%
564
August1st to 15thNight
45%29%45%15%
539
16th to endNight
10%16%30%39%11%
573
September1st to 15thNight
11%111%28%35%10%
602
16th to endNight
10%113%38%32%3
657
October1st to 15thNight
12%322%29%26%4
660
16th to endNight
13%7%21%30%23%3
704
November1st to 15thNight
13%7%24%32%19%3
700
16th to endNight
17%11%30%27%13%
720
December1st to 15thNight
23%10%30%25%9%
720
16th to endNight
26%12%29%24%7%
768
Page generated at 2017-09-13 06:39:08. Version ac04

Copyright 2017 A. Danko


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