NF/ Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the NF/ Observatory clear sky chart from 2005-11-05 to 2017-03-25.

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
62%
14722
34%
45190
24%
14680
72%
14680
47%
22321

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
59%
718
32%
2327
26%
716
70%
716
44%
1134
January16th to endNight
53%
768
37%
2496
28%
768
69%
768
43%
1222
February1st to 15thNight
56%
700
35%
2263
26%
698
71%
698
51%
1019
February16th to endNight
45%
632
42%
1805
23%
632
63%
632
50%
886
March1st to 15thNight
49%
720
39%
1980
20%
720
65%
720
52%
978
March16th to endNight
56%
744
38%
2046
20%
744
69%
744
58%
967
April1st to 15thNight
44%
527
38%
1681
17%
527
68%
527
49%
748
April16th to endNight
44%
495
40%
1650
21%
495
70%
495
56%
644
May1st to 15thNight
50%
494
34%
1624
22%
494
67%
494
56%
681
May16th to endNight
58%
515
33%
1540
21%
513
70%
513
56%
712
June1st to 15thNight
67%
495
31%
1485
24%
495
72%
495
57%
672
June16th to endNight
73%
495
21%
1485
16%
495
76%
495
47%
750
July1st to 15thNight
74%
465
19%
1395
17%
465
74%
465
31%
850
July16th to endNight
72%
522
15%
1467
14%
489
71%
489
26%
965
August1st to 15thNight
76%
494
20%
1526
21%
491
76%
491
30%
932
August16th to endNight
75%
525
20%
1750
22%
525
76%
525
25%
1102
September1st to 15thNight
74%
495
25%
1650
27%
495
75%
495
28%
990
September16th to endNight
74%
646
34%
1835
26%
646
80%
646
54%
926
October1st to 15thNight
71%
660
37%
1980
27%
660
77%
660
56%
928
October16th to endNight
75%
704
42%
2112
30%
704
83%
704
67%
890
November1st to 15thNight
69%
700
42%
2100
31%
700
79%
700
65%
899
November16th to endNight
62%
720
42%
2160
31%
720
71%
720
51%
1036
December1st to 15thNight
61%
720
36%
2337
30%
720
72%
720
47%
1110
December16th to endNight
54%
768
34%
2496
28%
768
64%
768
40%
1280

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
4313324446%59%
45756
Night
431332345%6%62%
45394
TransparencyDay
22%47%14%27%22%
45452
Night
20%47%16%28%21%
45199
SeeingDay
8%12%25%30%18%4
4472
Night
45%21%35%26%6%
14729

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
45%2331244364%
1611
16th to endDay
7%5%14222346%60%
1728
February1st to 15thDay
331331243468%
1592
16th to endDay
241322344465%
1667
March1st to 15thDay
3414323335%64%
1980
16th to endDay
221211235%5%70%
2045
April1st to 15thDay
3212323235%68%
1937
16th to endDay
121221233476%
1980
May1st to 15thDay
1112223345%69%
1993
16th to endDay
3112113345%70%
2221
June1st to 15thDay
3212213347%68%
2145
16th to endDay
321332445%7%59%
2145
July1st to 15thDay
6%425%6%47%7%6%10%37%
2145
16th to endDay
8%5%36%7%5%8%8%8%11%27%
2285
August1st to 15thDay
7%325%6%47%7%8%9%36%
2093
16th to endDay
6%5%37%5%46%5%7%8%38%
2100
September1st to 15thDay
10%6%25%5%35%6%6%8%39%
1980
16th to endDay
6%33323446%61%
1792
October1st to 15thDay
42123135%45%65%
1650
16th to endDay
221212235%73%
1760
November1st to 15thDay
3212222236%72%
1759
16th to endDay
432331323467%
1800
December1st to 15thDay
5%412213446%63%
1620
16th to endDay
5%6%23323436%58%
1728
January1st to 15thNight
5%5%12313335%64%
2327
16th to endNight
6%422212346%62%
2496
February1st to 15thNight
221221445%6%65%
2260
16th to endNight
331222334467%
1805
March1st to 15thNight
3212212446%67%
1980
16th to endNight
221121322474%
2046
April1st to 15thNight
321222344468%
1681
16th to endNight
11221224477%
1650
May1st to 15thNight
311213345%71%
1624
16th to endNight
2112312246%69%
1540
June1st to 15thNight
2212213445%68%
1485
16th to endNight
2122325%6%6%9%56%
1485
July1st to 15thNight
4225%5%46%7%9%13%38%
1485
16th to endNight
4425%7%37%8%9%12%34%
1575
August1st to 15thNight
4325%5%247%11%12%38%
1535
16th to endNight
3325%7%48%8%8%10%36%
1750
September1st to 15thNight
6%4245%45%7%8%10%41%
1650
16th to endNight
5%22213235%68%
1835
October1st to 15thNight
3212213345%69%
1980
16th to endNight
11112235%78%
2112
November1st to 15thNight
122212236%75%
2100
16th to endNight
5%313212335%67%
2160
December1st to 15thNight
6%31221335%6%62%
2337
16th to endNight
6%5%2332335%5%58%
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
22%3415%33%20%
1612
16th to endDay
23%3415%32%19%
1728
February1st to 15thDay
18%25%15%29%27%
1593
16th to endDay
18%3416%35%22%
1667
March1st to 15thDay
21%2412%33%25%
1980
16th to endDay
14%2412%38%27%
2045
April1st to 15thDay
17%2413%36%26%
1937
16th to endDay
11%148%35%37%
1980
May1st to 15thDay
13%36%12%30%33%
1993
16th to endDay
15%35%8%29%36%
2224
June1st to 15thDay
14%25%8%25%43%
2145
16th to endDay
20%5%8%12%19%34%
2145
July1st to 15thDay
35%8%14%17%12%11%
2006
16th to endDay
42%12%18%17%6%
2130
August1st to 15thDay
35%11%15%20%14%2
2078
16th to endDay
36%9%15%15%15%6%
2100
September1st to 15thDay
36%7%11%19%17%7%
1980
16th to endDay
20%46%16%34%18%
1792
October1st to 15thDay
19%36%14%31%25%
1650
16th to endDay
14%2314%34%30%
1760
November1st to 15thDay
15%25%16%33%27%
1759
16th to endDay
21%3413%35%22%
1800
December1st to 15thDay
19%47%22%30%16%
1620
16th to endDay
23%48%21%30%11%
1728
January1st to 15thNight
22%36%14%34%17%
2327
16th to endNight
23%2319%33%17%
2496
February1st to 15thNight
16%46%17%30%25%
2270
16th to endNight
17%35%18%33%21%
1805
March1st to 15thNight
16%35%14%35%24%
1980
16th to endNight
14%1413%38%27%
2046
April1st to 15thNight
16%25%15%37%21%
1681
16th to endNight
11%2312%33%36%
1650
May1st to 15thNight
13%25%11%31%35%
1625
16th to endNight
16%36%12%27%35%
1541
June1st to 15thNight
15%35%9%25%40%
1485
16th to endNight
21%49%12%20%31%
1485
July1st to 15thNight
30%11%15%20%13%9%
1395
16th to endNight
35%12%22%21%6%1
1467
August1st to 15thNight
29%12%19%20%13%4
1526
16th to endNight
35%11%15%18%14%5%
1750
September1st to 15thNight
31%11%15%20%12%9%
1650
16th to endNight
19%37%17%35%17%
1835
October1st to 15thNight
16%37%15%31%24%
1980
16th to endNight
10%2418%31%33%
2112
November1st to 15thNight
12%1418%36%26%
2100
16th to endNight
19%2415%30%28%
2160
December1st to 15thNight
20%37%21%29%17%
2337
16th to endNight
25%49%20%29%11%
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%14%27%27%7%3
90
16th to endDay
11%14%22%30%13%7%
96
February1st to 15thDay
7%6%20%35%24%5%
90
16th to endDay
6%34%27%19%10%1
168
March1st to 15thDay
8%20%35%23%10%2
270
16th to endDay
6%28%35%20%7%3
264
April1st to 15thDay
9%30%36%18%4
209
16th to endDay
10%24%44%16%3
210
May1st to 15thDay
5%25%39%27%3
228
16th to endDay
412%43%30%8%1
266
June1st to 15thDay
5%9%30%40%13%1
255
16th to endDay
4225%41%23%3
255
July1st to 15thDay
6%11%42%31%6%
245
16th to endDay
7%210%28%36%14%
271
August1st to 15thDay
8%18%34%34%12%
255
16th to endDay
5%114%29%40%8%
268
September1st to 15thDay
16%114%40%23%4
255
16th to endDay
7%324%43%16%4
225
October1st to 15thDay
13%421%24%25%11%
90
16th to endDay
6%322%30%29%8%
96
November1st to 15thDay
8%17%18%33%16%4
90
16th to endDay
11%16%31%31%8%1
90
December1st to 15thDay
6%10%20%34%24%4
90
16th to endDay
13%19%25%35%42
96
January1st to 15thNight
6%7%23%35%21%6%
720
16th to endNight
8%7%24%36%18%4
768
February1st to 15thNight
36%29%33%20%5%
704
16th to endNight
413%34%34%12%
632
March1st to 15thNight
310%31%31%19%3
720
16th to endNight
29%28%39%17%1
744
April1st to 15thNight
313%35%35%9%2
527
16th to endNight
212%37%32%11%2
495
May1st to 15thNight
28%34%42%10%1
495
16th to endNight
3330%42%19%
515
June1st to 15thNight
3222%49%21%1
495
16th to endNight
3115%42%33%3
495
July1st to 15thNight
5%6%32%44%9%
465
16th to endNight
46%23%51%13%
522
August1st to 15thNight
4319%52%19%
494
16th to endNight
46%24%51%13%
525
September1st to 15thNight
7%5%32%45%7%
495
16th to endNight
6%112%36%36%8%
646
October1st to 15thNight
419%41%27%6%
660
16th to endNight
2217%39%30%8%
704
November1st to 15thNight
2221%36%29%8%
700
16th to endNight
6%419%33%26%8%
720
December1st to 15thNight
6%6%20%36%22%6%
720
16th to endNight
6%9%23%39%17%4
768
Page generated at 2017-03-26 11:16:39. Version ac04

Copyright 2017 A. Danko


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