Anderson Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Anderson Observatory clear sky chart from 2005-11-05 to 2018-02-22.

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
37%
16132
16%
48778
11%
16090
42%
16090
20%
34193

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
16%
780
10%
2522
4%
776
23%
776
9%
2002
January16th to endNight
16%
832
12%
2704
5%
832
23%
832
10%
2119
February1st to 15thNight
15%
763
9%
2459
4%
761
20%
761
10%
1929
February16th to endNight
19%
659
11%
1977
4%
659
25%
659
11%
1555
March1st to 15thNight
25%
720
14%
2045
8%
720
30%
720
15%
1542
March16th to endNight
30%
768
15%
2112
9%
768
35%
768
20%
1529
April1st to 15thNight
29%
641
13%
1851
6%
641
34%
641
20%
1328
April16th to endNight
35%
540
19%
1620
7%
540
45%
540
24%
1088
May1st to 15thNight
38%
540
13%
1620
8%
540
43%
540
18%
1169
May16th to endNight
50%
561
17%
1684
14%
561
52%
561
28%
1080
June1st to 15thNight
54%
540
14%
1608
11%
540
58%
540
30%
994
June16th to endNight
58%
540
16%
1440
12%
540
61%
540
33%
921
July1st to 15thNight
62%
510
15%
1407
14%
510
63%
510
34%
885
July16th to endNight
68%
564
18%
1595
14%
531
72%
531
36%
919
August1st to 15thNight
68%
539
20%
1609
18%
536
69%
536
34%
971
August16th to endNight
69%
573
23%
1719
20%
573
72%
573
36%
1002
September1st to 15thNight
62%
705
25%
1965
18%
705
65%
705
35%
1181
September16th to endNight
59%
717
27%
1980
22%
717
62%
717
33%
1221
October1st to 15thNight
47%
720
21%
2085
18%
720
51%
720
28%
1346
October16th to endNight
29%
768
20%
2343
13%
768
38%
768
19%
1626
November1st to 15thNight
35%
760
20%
2471
14%
760
43%
760
23%
1594
November16th to endNight
25%
780
16%
2535
10%
780
32%
780
15%
1824
December1st to 15thNight
18%
780
8%
2723
5%
780
23%
780
10%
2148
December16th to endNight
15%
832
8%
2704
3%
832
21%
832
8%
2220

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
15%9%47%6%35%45%7%31%
49441
Night
14%9%46%5%3445%6%34%
48965
Cloud CoverDay
15%9%47%6%3445%7%31%
49451
Night
14%9%46%5%3445%6%34%
48969
TransparencyDay
52%5%10%18%10%1
49146
Night
50%410%19%12%1
48778
SeeingDay
19%7%25%22%16%8%
6116
Night
19%8%27%28%13%2
16135

By Month

Percentage Cloud Cover NE (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%14%7%10%8%5%444417%
1746
16th to endDay
13%17%8%13%9%4443415%
1872
February1st to 15thDay
16%15%7%10%8%445%3418%
1731
16th to endDay
15%13%6%11%7%35%346%23%
1643
March1st to 15thDay
20%12%6%9%6%25%336%22%
1903
16th to endDay
18%12%6%8%6%24445%27%
2112
April1st to 15thDay
17%11%36%5%345%5%6%29%
2106
16th to endDay
18%8%26%424347%36%
2340
May1st to 15thDay
18%7%48%5%35%45%6%30%
2331
16th to endDay
11%5%25%5%45%5%6%8%37%
2431
June1st to 15thDay
13%6%245%35%5%6%8%37%
2346
16th to endDay
11%5%25%5%36%5%6%9%36%
2520
July1st to 15thDay
11%6%25%5%35%5%6%10%37%
2466
16th to endDay
9%4245%35%6%7%10%38%
2465
August1st to 15thDay
8%5%25%5%36%6%8%10%36%
2340
16th to endDay
10%425%5%45%6%6%10%38%
2480
September1st to 15thDay
14%5%25%5%345%5%7%40%
1983
16th to endDay
15%6%35%5%23446%41%
1980
October1st to 15thDay
15%8%26%5%2446%6%37%
1874
16th to endDay
19%10%35%5%24446%32%
1878
November1st to 15thDay
12%11%5%6%5%24446%36%
1717
16th to endDay
17%14%5%6%6%25%246%27%
1748
December1st to 15thDay
18%16%8%11%7%23436%17%
1560
16th to endDay
19%17%8%10%7%33345%14%
1869
January1st to 15thNight
18%15%6%8%8%3434421%
2522
16th to endNight
14%16%7%8%8%4444421%
2704
February1st to 15thNight
17%14%6%10%6%3433424%
2457
16th to endNight
16%14%6%8%8%35%345%23%
1977
March1st to 15thNight
18%11%48%6%34345%29%
2033
16th to endNight
14%9%47%6%35%446%33%
2112
April1st to 15thNight
16%9%45%5%3445%6%32%
1851
16th to endNight
13%6%35%6%245%5%6%38%
1620
May1st to 15thNight
19%6%36%6%36%45%7%31%
1620
16th to endNight
11%5%345%245%6%9%41%
1682
June1st to 15thNight
7%6%24425%47%8%45%
1608
16th to endNight
8%325%435%6%7%11%41%
1440
July1st to 15thNight
8%315%5%35%5%6%8%46%
1491
16th to endNight
5%3244345%7%9%49%
1703
August1st to 15thNight
6%3145%345%7%8%46%
1620
16th to endNight
7%424424447%51%
1719
September1st to 15thNight
10%5%24323346%52%
1965
16th to endNight
11%5%2443345%6%49%
1980
October1st to 15thNight
14%6%25%434345%44%
2085
16th to endNight
20%6%36%5%33345%36%
2343
November1st to 15thNight
14%8%36%5%2346%7%38%
2471
16th to endNight
18%11%46%6%23446%29%
2535
December1st to 15thNight
19%16%6%9%5%34345%21%
2723
16th to endNight
19%17%7%9%6%34445%16%
2704

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
18%15%6%11%8%4443417%
1746
16th to endDay
14%17%8%13%9%45%43415%
1872
February1st to 15thDay
16%16%7%10%9%445%3418%
1731
16th to endDay
15%13%6%10%7%34445%23%
1643
March1st to 15thDay
20%13%7%9%5%34336%21%
1914
16th to endDay
18%11%5%8%5%24446%26%
2111
April1st to 15thDay
18%11%35%6%25%5%5%6%29%
2106
16th to endDay
19%7%35%434347%36%
2340
May1st to 15thDay
18%8%38%5%35%5%5%6%30%
2331
16th to endDay
12%336%6%35%6%6%9%37%
2431
June1st to 15thDay
14%5%25%435%5%6%8%36%
2346
16th to endDay
12%425%5%36%6%6%9%36%
2520
July1st to 15thDay
11%5%25%5%35%5%6%9%37%
2466
16th to endDay
9%4246%35%6%7%10%37%
2465
August1st to 15thDay
8%5%25%5%46%6%8%10%37%
2340
16th to endDay
10%5%25%5%35%6%6%10%38%
2480
September1st to 15thDay
14%5%245%34447%40%
1983
16th to endDay
16%6%35%5%24446%41%
1980
October1st to 15thDay
16%7%25%4245%5%6%37%
1874
16th to endDay
20%10%35%5%33446%32%
1878
November1st to 15thDay
12%10%5%6%5%24446%36%
1717
16th to endDay
17%15%5%6%6%24345%27%
1748
December1st to 15thDay
18%15%8%11%7%23335%18%
1560
16th to endDay
20%17%9%10%7%34345%14%
1869
January1st to 15thNight
19%15%6%8%7%3443421%
2522
16th to endNight
14%16%7%8%8%44445%21%
2704
February1st to 15thNight
17%13%7%10%6%3433424%
2450
16th to endNight
16%14%6%9%7%36%345%23%
1977
March1st to 15thNight
18%12%47%6%3434429%
2045
16th to endNight
14%9%46%6%35%45%6%32%
2112
April1st to 15thNight
16%10%46%5%345%5%6%32%
1851
16th to endNight
14%6%26%6%25%5%5%6%38%
1620
May1st to 15thNight
19%5%35%5%45%5%5%7%31%
1619
16th to endNight
12%5%25%5%25%46%9%41%
1682
June1st to 15thNight
8%5%34425%5%6%8%44%
1608
16th to endNight
8%425%435%5%7%10%41%
1440
July1st to 15thNight
8%315%4445%6%8%47%
1491
16th to endNight
5%314425%5%7%9%49%
1703
August1st to 15thNight
7%3135%445%6%8%46%
1620
16th to endNight
8%424424447%51%
1719
September1st to 15thNight
11%423423437%51%
1965
16th to endNight
11%5%2342335%6%50%
1980
October1st to 15thNight
15%6%24433346%44%
2085
16th to endNight
21%6%36%5%34345%36%
2343
November1st to 15thNight
14%9%25%5%2346%8%38%
2471
16th to endNight
18%11%46%6%34446%29%
2535
December1st to 15thNight
19%16%6%8%6%33445%21%
2723
16th to endNight
19%17%7%8%6%35%45%5%16%
2704

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
71%38%11%5%
1747
16th to endDay
73%39%9%3
1872
February1st to 15thDay
69%5%7%11%6%
1733
16th to endDay
63%410%15%5%
1643
March1st to 15thDay
65%48%15%5%
1914
16th to endDay
58%49%19%6%
2112
April1st to 15thDay
54%5%12%16%10%
2106
16th to endDay
49%310%20%12%3
2340
May1st to 15thDay
54%5%11%19%8%1
2331
16th to endDay
42%6%12%24%12%1
2435
June1st to 15thDay
43%6%11%25%12%
2346
16th to endDay
42%7%14%19%14%1
2520
July1st to 15thDay
42%6%10%20%17%2
2321
16th to endDay
37%7%15%24%12%2
2310
August1st to 15thDay
39%8%13%23%13%1
2327
16th to endDay
39%7%13%20%14%4
2480
September1st to 15thDay
42%6%9%21%16%2
1983
16th to endDay
44%39%20%21%1
1980
October1st to 15thDay
45%6%10%19%16%1
1874
16th to endDay
53%312%19%9%
1878
November1st to 15thDay
48%49%21%12%3
1717
16th to endDay
59%310%17%7%
1748
December1st to 15thDay
69%37%13%4
1560
16th to endDay
73%38%10%3
1869
January1st to 15thNight
67%38%13%6%
2522
16th to endNight
65%310%15%5%
2704
February1st to 15thNight
64%49%14%7%
2459
16th to endNight
63%47%17%5%
1977
March1st to 15thNight
57%49%18%8%1
2045
16th to endNight
51%5%11%20%8%2
2112
April1st to 15thNight
51%411%15%15%
1851
16th to endNight
45%410%19%15%4
1620
May1st to 15thNight
52%5%10%19%10%1
1620
16th to endNight
38%7%11%23%15%2
1684
June1st to 15thNight
36%6%12%24%18%1
1608
16th to endNight
36%6%16%23%14%4
1440
July1st to 15thNight
35%5%13%22%20%3
1407
16th to endNight
29%7%15%28%15%3
1595
August1st to 15thNight
32%6%13%26%19%1
1609
16th to endNight
31%5%14%25%19%3
1719
September1st to 15thNight
33%412%24%20%4
1965
16th to endNight
34%5%8%25%24%1
1980
October1st to 15thNight
41%5%9%23%18%2
2085
16th to endNight
50%39%24%10%1
2343
November1st to 15thNight
44%411%21%14%3
2471
16th to endNight
55%310%20%8%
2535
December1st to 15thNight
65%39%14%5%
2723
16th to endNight
69%411%11%2
2704

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
22%15%40%9%10%
135
16th to endDay
22%20%43%10%2
144
February1st to 15thDay
33%17%38%11%
135
16th to endDay
27%18%37%16%2
100
March1st to 15thDay
27%15%29%21%4
204
16th to endDay
27%9%34%19%7%1
288
April1st to 15thDay
25%10%31%20%10%1
270
16th to endDay
23%9%30%18%11%7%
270
May1st to 15thDay
27%431%21%10%4
288
16th to endDay
17%426%28%14%8%
331
June1st to 15thDay
15%321%31%21%6%
321
16th to endDay
16%6%27%29%15%5%
495
July1st to 15thDay
15%322%28%20%9%
425
16th to endDay
9%115%25%29%18%
326
August1st to 15thDay
13%211%25%29%17%
313
16th to endDay
12%312%22%31%17%
332
September1st to 15thDay
14%215%23%25%19%
315
16th to endDay
17%412%19%25%21%
314
October1st to 15thDay
17%6%23%23%20%8%
315
16th to endDay
20%11%33%24%7%2
294
November1st to 15thDay
17%10%27%22%18%3
135
16th to endDay
22%13%41%18%3
133
December1st to 15thDay
14%17%50%8%5%3
90
16th to endDay
25%23%37%11%1
143
January1st to 15thNight
26%16%34%18%3
780
16th to endNight
23%15%36%20%3
832
February1st to 15thNight
24%14%36%21%3
764
16th to endNight
24%11%36%23%3
659
March1st to 15thNight
23%12%30%27%5%
720
16th to endNight
19%9%35%25%9%
768
April1st to 15thNight
21%12%32%26%5%
641
16th to endNight
19%7%34%24%12%2
540
May1st to 15thNight
22%5%26%31%12%1
540
16th to endNight
13%325%32%22%3
563
June1st to 15thNight
9%322%42%19%1
540
16th to endNight
10%221%43%20%2
540
July1st to 15thNight
9%117%42%26%2
510
16th to endNight
6%13%42%30%5%
564
August1st to 15thNight
10%110%44%27%5%
539
16th to endNight
10%110%34%36%7%
573
September1st to 15thNight
13%214%31%32%5%
705
16th to endNight
15%215%29%28%7%
717
October1st to 15thNight
18%324%31%18%3
720
16th to endNight
24%10%31%23%8%
768
November1st to 15thNight
19%10%29%26%11%2
760
16th to endNight
26%14%28%21%8%
780
December1st to 15thNight
27%13%32%20%5%
780
16th to endNight
27%15%34%19%3
832
Page generated at 2018-02-23 11:21:27. Version ac04

Copyright 2018 A. Danko


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