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 2017-12-02.

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%
15558
34%
47757
24%
15516
72%
15516
47%
23532

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
55%
768
38%
2112
20%
768
69%
768
58%
1000
April1st to 15thNight
45%
575
36%
1834
16%
575
67%
575
50%
809
April16th to endNight
45%
540
42%
1800
23%
540
72%
540
57%
692
May1st to 15thNight
51%
539
33%
1772
22%
539
67%
539
56%
740
May16th to endNight
57%
563
35%
1684
22%
561
70%
561
57%
770
June1st to 15thNight
68%
540
29%
1620
23%
540
73%
540
56%
743
June16th to endNight
73%
540
22%
1620
17%
540
76%
540
46%
822
July1st to 15thNight
75%
510
18%
1530
16%
510
75%
510
31%
937
July16th to endNight
74%
564
15%
1593
14%
531
73%
531
27%
1023
August1st to 15thNight
75%
539
18%
1666
19%
536
75%
536
30%
1020
August16th to endNight
76%
573
22%
1910
24%
573
77%
573
27%
1180
September1st to 15thNight
75%
540
24%
1800
26%
540
76%
540
30%
1057
September16th to endNight
74%
705
36%
2002
27%
705
79%
705
54%
1012
October1st to 15thNight
72%
720
36%
2160
26%
720
78%
720
57%
1006
October16th to endNight
75%
768
44%
2304
32%
768
83%
768
67%
975
November1st to 15thNight
70%
760
41%
2280
30%
760
79%
760
63%
986
November16th to endNight
64%
780
44%
2340
34%
780
72%
780
53%
1107
December1st to 15thNight
61%
728
36%
2363
29%
728
71%
728
46%
1134
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%
48681
Night
331332345%6%62%
47961
TransparencyDay
22%47%14%27%22%
48377
Night
20%48%16%28%21%
47766
SeeingDay
7%11%24%31%19%5%
5404
Night
45%21%35%26%6%
15565

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
321211235%5%70%
2112
April1st to 15thDay
2212323236%68%
2114
16th to endDay
12112232477%
2160
May1st to 15thDay
2112213345%70%
2175
16th to endDay
3112113346%70%
2429
June1st to 15thDay
2212213347%67%
2340
16th to endDay
321332445%7%60%
2340
July1st to 15thDay
6%425%6%46%8%7%10%37%
2340
16th to endDay
8%5%36%6%5%8%8%8%11%27%
2467
August1st to 15thDay
8%325%6%37%7%8%9%36%
2283
16th to endDay
6%437%5%46%5%7%8%40%
2292
September1st to 15thDay
9%5%25%5%35%6%6%8%41%
2160
16th to endDay
6%33323446%62%
1954
October1st to 15thDay
4212313445%66%
1800
16th to endDay
221212235%73%
1920
November1st to 15thDay
2212222236%70%
1909
16th to endDay
431331323468%
1950
December1st to 15thDay
5%412213446%63%
1630
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%
2112
April1st to 15thNight
3212213345%68%
1834
16th to endNight
11221223478%
1800
May1st to 15thNight
311312345%72%
1772
16th to endNight
2112312246%70%
1684
June1st to 15thNight
2212213446%67%
1620
16th to endNight
2222425%6%6%8%57%
1620
July1st to 15thNight
4125%5%5%6%7%9%12%38%
1620
16th to endNight
3425%6%37%7%9%12%35%
1701
August1st to 15thNight
4425%5%247%11%12%38%
1675
16th to endNight
3425%6%48%8%8%10%38%
1910
September1st to 15thNight
6%4245%35%6%8%10%43%
1800
16th to endNight
5%212213235%68%
2002
October1st to 15thNight
3212213345%70%
2160
16th to endNight
1111223478%
2304
November1st to 15thNight
122212236%73%
2280
16th to endNight
4313212335%67%
2340
December1st to 15thNight
6%31221335%6%62%
2363
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%25%13%38%26%
2112
April1st to 15thDay
16%1412%38%26%
2114
16th to endDay
10%149%33%39%
2160
May1st to 15thDay
13%26%12%31%32%
2175
16th to endDay
14%35%9%29%37%
2432
June1st to 15thDay
15%25%9%25%42%
2340
16th to endDay
19%5%8%12%19%34%
2340
July1st to 15thDay
34%9%14%17%11%12%
2201
16th to endDay
42%13%19%16%6%
2312
August1st to 15thDay
35%11%15%20%14%3
2268
16th to endDay
35%9%14%15%17%7%
2292
September1st to 15thDay
35%7%10%18%19%8%
2160
16th to endDay
20%46%16%33%18%
1954
October1st to 15thDay
18%37%13%31%26%
1800
16th to endDay
14%2315%34%29%
1920
November1st to 15thDay
15%25%18%32%25%
1909
16th to endDay
20%2413%36%22%
1950
December1st to 15thDay
19%47%22%30%15%
1630
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%26%
2112
April1st to 15thNight
16%25%14%39%21%
1834
16th to endNight
10%2313%33%36%
1800
May1st to 15thNight
13%25%10%32%34%
1773
16th to endNight
15%35%11%27%36%
1685
June1st to 15thNight
15%35%10%24%39%
1620
16th to endNight
21%5%9%12%19%32%
1620
July1st to 15thNight
30%11%14%19%13%9%
1530
16th to endNight
34%12%25%21%5%1
1593
August1st to 15thNight
30%11%20%19%12%5%
1666
16th to endNight
34%10%15%19%14%5%
1910
September1st to 15thNight
30%10%14%20%14%10%
1800
16th to endNight
19%37%17%34%17%
2002
October1st to 15thNight
16%37%15%30%26%
2160
16th to endNight
10%2318%30%33%
2304
November1st to 15thNight
13%15%19%35%24%
2280
16th to endNight
18%2415%31%27%
2340
December1st to 15thNight
20%37%21%29%16%
2363
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%19%6%3
288
April1st to 15thDay
7%26%35%20%8%1
269
16th to endDay
8%24%40%20%41
270
May1st to 15thDay
5%22%36%27%7%
288
16th to endDay
313%41%32%7%1
330
June1st to 15thDay
5%7%29%41%14%2
315
16th to endDay
4122%42%24%3
315
July1st to 15thDay
5%10%40%33%9%
305
16th to endDay
7%29%27%35%16%
327
August1st to 15thDay
9%7%32%36%13%
315
16th to endDay
5%12%28%40%11%
332
September1st to 15thDay
13%13%41%24%5%
315
16th to endDay
7%427%41%15%3
282
October1st to 15thDay
8%6%20%28%26%8%
135
16th to endDay
6%320%26%35%7%
144
November1st to 15thDay
5%14%22%38%15%3
135
16th to endDay
7%12%25%34%17%2
135
December1st to 15thDay
6%9%19%36%24%4
94
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
39%29%38%17%1
768
April1st to 15thNight
312%35%35%9%2
575
16th to endNight
213%37%32%11%2
540
May1st to 15thNight
28%33%42%11%1
540
16th to endNight
3331%41%19%
563
June1st to 15thNight
2221%48%22%2
540
16th to endNight
2115%42%33%3
540
July1st to 15thNight
5%6%32%45%10%
510
16th to endNight
45%22%52%14%
564
August1st to 15thNight
5%320%52%17%
539
16th to endNight
45%23%52%13%
573
September1st to 15thNight
6%5%31%48%7%
540
16th to endNight
6%112%37%34%7%
705
October1st to 15thNight
318%43%28%6%
720
16th to endNight
2216%37%32%8%
768
November1st to 15thNight
2220%38%28%7%
760
16th to endNight
6%419%34%27%8%
780
December1st to 15thNight
7%6%19%37%22%6%
728
16th to endNight
6%9%23%39%17%4
768
Page generated at 2017-12-03 09:16:42. Version ac04

Copyright 2017 A. Danko


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