Centennial
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Centennial clear sky chart from 2005-11-05 to 2018-01-12.

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
60%
16455
28%
48366
21%
16415
67%
16415
44%
25950

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
58%
953
31%
2662
23%
951
66%
951
51%
1369
January16th to endNight
56%
813
34%
2541
27%
813
66%
813
42%
1332
February1st to 15thNight
51%
699
25%
2235
18%
698
60%
698
39%
1202
February16th to endNight
47%
632
34%
1894
19%
632
61%
632
43%
1001
March1st to 15thNight
53%
720
28%
2124
17%
720
62%
720
45%
1128
March16th to endNight
50%
672
28%
2016
18%
672
60%
672
41%
1097
April1st to 15thNight
46%
539
25%
1798
20%
539
58%
539
37%
940
April16th to endNight
45%
540
22%
1800
18%
540
53%
540
29%
1057
May1st to 15thNight
53%
540
20%
1617
16%
540
59%
540
30%
1009
May16th to endNight
55%
562
18%
1498
12%
561
61%
561
40%
871
June1st to 15thNight
69%
540
22%
1440
17%
540
72%
540
52%
760
June16th to endNight
76%
540
26%
1440
22%
540
79%
540
56%
735
July1st to 15thNight
71%
510
18%
1360
16%
510
72%
510
37%
824
July16th to endNight
76%
564
25%
1438
22%
531
77%
531
44%
797
August1st to 15thNight
73%
539
18%
1680
19%
536
75%
536
36%
928
August16th to endNight
73%
573
28%
1910
31%
573
76%
573
40%
972
September1st to 15thNight
72%
540
29%
1800
30%
540
76%
540
40%
928
September16th to endNight
71%
537
35%
1939
34%
537
78%
537
46%
890
October1st to 15thNight
60%
697
30%
2137
21%
697
66%
697
44%
1112
October16th to endNight
68%
805
37%
2341
26%
805
73%
805
49%
1198
November1st to 15thNight
65%
950
34%
2470
21%
950
70%
950
55%
1303
November16th to endNight
64%
975
36%
2584
24%
975
68%
975
54%
1356
December1st to 15thNight
57%
975
27%
2730
17%
975
63%
975
46%
1479
December16th to endNight
52%
1040
29%
2912
19%
1040
60%
1040
41%
1662

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
5%42432445%8%53%
48983
Night
5%5%23323447%57%
48540
Cloud CoverDay
5%42432445%8%53%
48981
Night
5%5%24323447%57%
48540
TransparencyDay
27%410%24%22%9%
48660
Night
25%411%26%23%8%
48366
SeeingDay
9%6%24%31%20%7%
6204
Night
7%222%48%17%1
16464

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
26%24312247%61%
1520
16th to endDay
16%23312347%62%
1694
February1st to 15thDay
27%36%334347%55%
1625
16th to endDay
26%34424346%57%
1580
March1st to 15thDay
443432445%8%54%
1833
16th to endDay
6%6%2432446%9%49%
2208
April1st to 15thDay
7%6%2332445%8%52%
2150
16th to endDay
11%6%13335%45%8%46%
2160
May1st to 15thDay
10%6%25%4345%5%7%42%
2330
16th to endDay
9%5%23426%5%7%9%43%
2616
June1st to 15thDay
6%313335%6%7%8%50%
2520
16th to endDay
2213325%6%6%9%55%
2520
July1st to 15thDay
6%313435%6%8%10%45%
2520
16th to endDay
5%3245%35%6%7%9%46%
2630
August1st to 15thDay
5%324446%6%8%9%43%
2270
16th to endDay
4213435%6%6%9%51%
2292
September1st to 15thDay
7%31342445%7%56%
2160
16th to endDay
5%43223346%63%
2020
October1st to 15thDay
6%31222335%7%60%
1821
16th to endDay
5%5%13212236%65%
1869
November1st to 15thDay
142332336%8%60%
1718
16th to endDay
342321235%8%62%
1703
December1st to 15thDay
25%25%32335%7%56%
1560
16th to endDay
35%35%32335%7%56%
1664
January1st to 15thNight
1424422247%63%
2662
16th to endNight
26%25%323335%60%
2541
February1st to 15thNight
36%35%323347%54%
2225
16th to endNight
28%34322346%57%
1894
March1st to 15thNight
45%2341345%6%57%
2124
16th to endNight
6%5%24322347%56%
2016
April1st to 15thNight
7%6%2332435%6%55%
1798
16th to endNight
14%7%24323335%48%
1800
May1st to 15thNight
14%6%223235%5%8%44%
1616
16th to endNight
7%41432345%9%51%
1497
June1st to 15thNight
421222336%8%60%
1440
16th to endNight
22122235%7%8%61%
1440
July1st to 15thNight
5%2145%35%5%7%10%47%
1440
16th to endNight
5%213325%6%7%10%51%
1535
August1st to 15thNight
4315%435%5%6%9%51%
1689
16th to endNight
5%31342346%9%53%
1910
September1st to 15thNight
7%31432346%8%54%
1800
16th to endNight
5%312312346%65%
1939
October1st to 15thNight
7%5%13212345%61%
2137
16th to endNight
5%5%13322336%63%
2341
November1st to 15thNight
2313213346%65%
2470
16th to endNight
35%12312337%63%
2584
December1st to 15thNight
36%24422338%58%
2730
16th to endNight
37%34423348%54%
2912

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
26%24312347%61%
1520
16th to endDay
15%33322337%62%
1694
February1st to 15thDay
17%36%324347%55%
1625
16th to endDay
17%24323347%57%
1580
March1st to 15thDay
4435%42335%8%54%
1833
16th to endDay
6%6%2432446%8%49%
2206
April1st to 15thDay
7%5%2332345%8%52%
2150
16th to endDay
11%7%13325%45%8%46%
2160
May1st to 15thDay
10%7%25%5%25%5%5%8%42%
2330
16th to endDay
9%5%13436%5%7%9%43%
2616
June1st to 15thDay
5%313326%5%6%9%49%
2520
16th to endDay
2213335%6%6%10%55%
2520
July1st to 15thDay
6%313435%6%8%10%45%
2520
16th to endDay
5%3245%35%6%7%9%46%
2630
August1st to 15thDay
5%323437%6%7%9%44%
2270
16th to endDay
4313435%6%7%9%51%
2292
September1st to 15thDay
7%31242345%7%57%
2160
16th to endDay
6%32222346%63%
2020
October1st to 15thDay
6%31322335%7%60%
1821
16th to endDay
6%5%12212236%65%
1869
November1st to 15thDay
242331346%7%60%
1718
16th to endDay
342322235%8%62%
1703
December1st to 15thDay
25%25%32335%8%56%
1560
16th to endDay
35%35%423447%55%
1664
January1st to 15thNight
1435%412237%63%
2662
16th to endNight
26%25%32333460%
2541
February1st to 15thNight
37%35%33335%7%54%
2225
16th to endNight
28%34423336%56%
1894
March1st to 15thNight
36%2332345%6%57%
2124
16th to endNight
7%5%23322347%56%
2016
April1st to 15thNight
7%7%2232435%6%54%
1798
16th to endNight
14%7%24422436%48%
1800
May1st to 15thNight
14%7%133235%5%8%44%
1616
16th to endNight
7%4143335%5%9%51%
1497
June1st to 15thNight
431222336%9%60%
1440
16th to endNight
21132235%7%9%61%
1440
July1st to 15thNight
6%2145%25%5%7%9%47%
1440
16th to endNight
5%223325%6%7%10%50%
1535
August1st to 15thNight
4315%425%6%6%8%51%
1689
16th to endNight
5%31332446%9%54%
1910
September1st to 15thNight
7%31332346%8%54%
1800
16th to endNight
6%312222247%64%
1939
October1st to 15thNight
7%5%13212345%61%
2137
16th to endNight
5%5%12322335%63%
2341
November1st to 15thNight
2313223346%65%
2470
16th to endNight
3422313337%63%
2584
December1st to 15thNight
36%25%422338%58%
2730
16th to endNight
37%34423348%53%
2912

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%210%32%25%6%
1521
16th to endDay
22%28%33%24%8%
1694
February1st to 15thDay
29%211%34%16%4
1626
16th to endDay
26%36%28%27%7%
1580
March1st to 15thDay
27%210%26%24%9%
1833
16th to endDay
30%412%23%21%6%
2208
April1st to 15thDay
29%311%25%20%8%
2150
16th to endDay
36%5%11%22%19%5%
2160
May1st to 15thDay
39%6%12%23%15%3
2330
16th to endDay
34%8%13%23%13%6%
2620
June1st to 15thDay
26%7%13%20%18%12%
2520
16th to endDay
22%6%10%20%28%12%
2520
July1st to 15thDay
31%7%11%20%16%11%
2371
16th to endDay
31%7%12%25%16%7%
2465
August1st to 15thDay
31%8%12%20%15%10%
2255
16th to endDay
25%7%10%24%24%8%
2292
September1st to 15thDay
27%39%22%21%15%
2160
16th to endDay
21%45%22%35%10%
2020
October1st to 15thDay
22%49%22%29%11%
1821
16th to endDay
21%26%27%28%13%
1869
November1st to 15thDay
20%210%27%26%12%
1718
16th to endDay
20%17%24%33%12%
1703
December1st to 15thDay
24%212%30%22%6%
1560
16th to endDay
26%313%26%22%6%
1664
January1st to 15thNight
21%311%30%26%6%
2662
16th to endNight
26%37%29%23%9%
2541
February1st to 15thNight
28%312%31%19%4
2235
16th to endNight
26%26%29%25%9%
1894
March1st to 15thNight
24%38%25%29%7%
2124
16th to endNight
27%310%25%26%6%
2016
April1st to 15thNight
28%312%25%20%8%
1798
16th to endNight
37%311%24%17%5%
1800
May1st to 15thNight
36%6%14%21%15%5%
1617
16th to endNight
27%7%21%24%12%6%
1498
June1st to 15thNight
19%5%18%28%15%12%
1440
16th to endNight
17%413%24%28%11%
1440
July1st to 15thNight
29%7%15%21%15%9%
1360
16th to endNight
23%7%17%29%18%4
1438
August1st to 15thNight
26%8%17%23%16%7%
1680
16th to endNight
25%411%27%24%7%
1910
September1st to 15thNight
26%412%23%21%12%
1800
16th to endNight
20%39%25%32%8%
1939
October1st to 15thNight
24%411%21%26%11%
2137
16th to endNight
22%36%25%30%12%
2341
November1st to 15thNight
19%37%26%27%14%
2470
16th to endNight
20%28%25%31%11%
2584
December1st to 15thNight
25%312%30%21%7%
2730
16th to endNight
28%413%26%23%3
2912

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
6%6%14%48%20%3
123
16th to endDay
7%220%52%17%
96
February1st to 15thDay
46%38%42%7%
90
16th to endDay
46%24%40%20%2
81
March1st to 15thDay
5%8%31%42%10%1
123
16th to endDay
17%19%36%20%5%1
288
April1st to 15thDay
13%18%32%23%9%3
269
16th to endDay
21%18%33%16%8%
270
May1st to 15thDay
14%8%28%29%16%2
428
16th to endDay
14%9%19%29%19%7%
517
June1st to 15thDay
7%423%32%21%10%
495
16th to endDay
4424%31%27%8%
495
July1st to 15thDay
10%116%25%33%12%
475
16th to endDay
6%114%28%37%11%
489
August1st to 15thDay
9%323%33%20%10%
315
16th to endDay
6%324%34%21%9%
332
September1st to 15thDay
8%5%25%30%20%8%
315
16th to endDay
8%6%26%28%18%11%
175
October1st to 15thDay
9%422%30%19%13%
135
16th to endDay
8%220%38%20%8%
144
November1st to 15thDay
2215%42%26%9%
135
16th to endDay
9%425%47%11%
135
December1st to 15thDay
5%435%42%11%
135
16th to endDay
3228%53%10%2
144
January1st to 15thNight
3227%53%10%2
956
16th to endNight
4326%52%11%1
813
February1st to 15thNight
7%229%51%8%
704
16th to endNight
6%333%50%5%
632
March1st to 15thNight
5%231%49%10%
720
16th to endNight
8%5%29%47%9%
672
April1st to 15thNight
11%6%31%42%7%
539
16th to endNight
18%5%25%37%12%
540
May1st to 15thNight
17%220%43%14%1
540
16th to endNight
10%224%39%21%1
563
June1st to 15thNight
5%218%48%23%2
540
16th to endNight
3213%50%30%
540
July1st to 15thNight
8%19%39%38%4
510
16th to endNight
5%7%38%43%3
564
August1st to 15thNight
5%18%47%34%2
539
16th to endNight
6%110%46%32%2
573
September1st to 15thNight
9%10%45%28%5%
540
16th to endNight
7%16%44%29%1
537
October1st to 15thNight
10%221%44%17%3
697
16th to endNight
7%216%49%21%2
805
November1st to 15thNight
4222%52%16%1
950
16th to endNight
4223%54%13%1
975
December1st to 15thNight
5%227%53%10%
975
16th to endNight
5%328%49%10%1
1040
Page generated at 2018-01-12 20:01:27. Version ac04

Copyright 2018 A. Danko


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