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 2018-01-12.

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
43%
16230
20%
48336
13%
16192
51%
16192
25%
30848

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
23%
763
20%
2472
9%
761
37%
761
16%
1595
January16th to endNight
18%
768
21%
2496
7%
768
36%
768
17%
1602
February1st to 15thNight
20%
701
20%
2287
7%
701
36%
701
18%
1427
February16th to endNight
19%
631
22%
1871
7%
631
34%
631
17%
1235
March1st to 15thNight
28%
720
21%
1980
11%
720
37%
720
23%
1321
March16th to endNight
30%
768
16%
2112
9%
768
36%
768
23%
1444
April1st to 15thNight
32%
718
19%
1886
6%
718
41%
718
27%
1228
April16th to endNight
41%
627
21%
1707
9%
627
48%
627
27%
1118
May1st to 15thNight
40%
540
15%
1620
7%
540
46%
540
23%
1069
May16th to endNight
57%
561
15%
1684
10%
561
60%
561
29%
1080
June1st to 15thNight
65%
540
15%
1620
13%
540
67%
540
32%
1006
June16th to endNight
67%
540
17%
1620
13%
540
70%
540
32%
977
July1st to 15thNight
67%
510
11%
1530
10%
510
68%
510
27%
995
July16th to endNight
75%
564
15%
1595
13%
531
77%
531
34%
963
August1st to 15thNight
67%
539
18%
1609
15%
536
68%
536
30%
1044
August16th to endNight
69%
663
19%
1809
15%
663
70%
663
32%
1158
September1st to 15thNight
63%
720
23%
1905
17%
720
65%
720
32%
1221
September16th to endNight
53%
717
22%
1980
17%
717
56%
717
28%
1287
October1st to 15thNight
51%
720
25%
2139
23%
720
57%
720
29%
1327
October16th to endNight
42%
768
31%
2304
21%
768
56%
768
31%
1341
November1st to 15thNight
46%
760
25%
2336
20%
760
55%
760
28%
1412
November16th to endNight
38%
780
28%
2535
19%
780
50%
780
26%
1473
December1st to 15thNight
28%
780
20%
2535
10%
780
40%
780
17%
1662
December16th to endNight
24%
832
19%
2704
8%
832
37%
832
14%
1863

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
13%6%26%6%35%5%6%7%36%
48988
Night
11%5%25%5%35%45%8%42%
48529
Cloud CoverDay
13%5%36%6%35%5%5%7%37%
48998
Night
11%5%25%5%345%5%8%42%
48533
TransparencyDay
44%5%12%21%13%2
48699
Night
39%5%13%23%15%2
48336
SeeingDay
18%9%20%21%19%11%
6004
Night
17%10%21%29%18%2
16237

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
14%8%26%5%35%447%36%
1710
16th to endDay
13%7%36%6%35%446%39%
1728
February1st to 15thDay
11%7%27%6%45%5%6%437%
1575
16th to endDay
13%5%38%7%4446%7%35%
1599
March1st to 15thDay
14%5%35%5%34446%42%
1969
16th to endDay
17%7%37%5%24446%36%
2112
April1st to 15thDay
11%5%35%433448%45%
2062
16th to endDay
16%5%25%6%345%6%6%37%
2262
May1st to 15thDay
17%6%35%6%36%5%6%7%29%
2331
16th to endDay
12%5%36%7%36%6%6%9%32%
2431
June1st to 15thDay
9%427%6%46%7%7%9%34%
2340
16th to endDay
7%425%6%47%6%7%10%35%
2340
July1st to 15thDay
11%5%37%6%47%7%8%8%28%
2340
16th to endDay
8%5%36%8%49%7%8%9%28%
2465
August1st to 15thDay
13%5%27%7%47%7%7%8%27%
2340
16th to endDay
10%5%36%7%47%6%6%9%31%
2381
September1st to 15thDay
13%6%26%5%3446%7%38%
2052
16th to endDay
18%7%35%6%35%45%6%34%
1980
October1st to 15thDay
14%6%24422346%45%
1821
16th to endDay
13%5%24423346%48%
1920
November1st to 15thDay
11%5%245%24448%46%
1848
16th to endDay
12%7%25%5%24336%45%
1755
December1st to 15thDay
14%6%25%5%35%45%7%39%
1755
16th to endDay
17%8%25%425%45%6%35%
1872
January1st to 15thNight
13%5%25%5%35%5%6%7%38%
2472
16th to endNight
14%7%25%435%5%6%7%37%
2496
February1st to 15thNight
13%6%244245%6%7%41%
2285
16th to endNight
11%5%35%5%36%6%6%7%38%
1871
March1st to 15thNight
14%5%25%435%45%7%39%
1968
16th to endNight
15%5%245%345%5%8%39%
2112
April1st to 15thNight
12%5%2443446%9%41%
1886
16th to endNight
12%5%25%5%25%45%7%42%
1707
May1st to 15thNight
13%5%26%6%4445%7%39%
1620
16th to endNight
10%5%246%35%46%10%40%
1682
June1st to 15thNight
7%315%5%25%5%6%10%44%
1620
16th to endNight
5%324435%46%11%47%
1620
July1st to 15thNight
7%425%6%37%5%5%9%41%
1620
16th to endNight
3315%5%45%7%8%13%41%
1703
August1st to 15thNight
10%5%25%6%2446%9%41%
1620
16th to endNight
8%425%5%36%5%6%10%41%
1809
September1st to 15thNight
9%426%435%446%48%
1905
16th to endNight
13%6%245%35%45%6%41%
1980
October1st to 15thNight
12%5%25%5%24336%47%
2139
16th to endNight
10%5%1442445%7%48%
2304
November1st to 15thNight
13%5%24423345%49%
2336
16th to endNight
13%4244235%46%48%
2535
December1st to 15thNight
14%7%36%5%3445%8%36%
2535
16th to endNight
15%7%37%5%45%45%7%31%
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
14%7%26%6%245%47%37%
1710
16th to endDay
13%6%36%6%25%446%39%
1728
February1st to 15thDay
11%7%27%6%46%5%5%5%37%
1575
16th to endDay
13%5%38%7%345%5%7%34%
1599
March1st to 15thDay
14%5%344345%5%6%42%
1980
16th to endDay
17%7%36%5%2445%6%37%
2111
April1st to 15thDay
11%5%36%434348%45%
2062
16th to endDay
15%5%35%6%25%45%6%37%
2262
May1st to 15thDay
18%6%36%6%35%5%6%7%30%
2331
16th to endDay
12%5%36%6%46%6%5%9%32%
2431
June1st to 15thDay
9%326%6%46%6%7%9%34%
2340
16th to endDay
7%425%6%5%6%6%7%10%36%
2340
July1st to 15thDay
11%5%47%6%47%6%7%9%29%
2340
16th to endDay
8%436%7%5%8%7%8%9%29%
2465
August1st to 15thDay
13%5%36%7%5%7%6%7%8%28%
2340
16th to endDay
10%5%36%6%46%6%7%9%32%
2381
September1st to 15thDay
13%6%25%5%3445%7%39%
2052
16th to endDay
18%6%26%6%35%45%5%34%
1980
October1st to 15thDay
15%5%25%332346%45%
1821
16th to endDay
13%424423346%48%
1920
November1st to 15thDay
11%5%2442435%7%47%
1848
16th to endDay
12%7%245%24336%45%
1755
December1st to 15thDay
13%6%25%5%35%5%5%7%39%
1755
16th to endDay
17%8%35%425%45%6%35%
1872
January1st to 15thNight
13%5%25%5%35%5%6%7%39%
2472
16th to endNight
13%7%245%25%5%6%7%38%
2496
February1st to 15thNight
12%6%24425%5%5%7%41%
2278
16th to endNight
11%5%26%5%36%6%5%7%38%
1871
March1st to 15thNight
14%5%35%4245%5%7%40%
1980
16th to endNight
14%6%25%5%25%5%5%7%39%
2112
April1st to 15thNight
12%5%245%3346%9%41%
1886
16th to endNight
12%5%25%4345%47%42%
1707
May1st to 15thNight
13%5%25%6%34447%39%
1619
16th to endNight
10%4245%35%5%6%9%41%
1682
June1st to 15thNight
8%4245%246%6%10%44%
1620
16th to endNight
5%324435%46%11%47%
1620
July1st to 15thNight
7%4246%37%45%8%42%
1620
16th to endNight
4224436%6%8%13%41%
1703
August1st to 15thNight
9%5%25%6%335%6%9%42%
1620
16th to endNight
7%425%6%45%5%6%10%42%
1809
September1st to 15thNight
9%425%5%34346%48%
1905
16th to endNight
13%5%26%425%5%5%6%42%
1980
October1st to 15thNight
12%425%423436%48%
2139
16th to endNight
10%5%1442346%6%49%
2304
November1st to 15thNight
13%5%25%423445%49%
2336
16th to endNight
12%424433446%49%
2535
December1st to 15thNight
14%6%36%6%3445%8%36%
2535
16th to endNight
14%8%37%6%35%5%5%7%32%
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
46%410%23%11%3
1711
16th to endDay
45%310%25%13%2
1728
February1st to 15thDay
47%49%22%14%1
1577
16th to endDay
47%413%20%12%1
1599
March1st to 15thDay
42%310%23%15%3
1980
16th to endDay
48%5%9%23%11%1
2112
April1st to 15thDay
37%313%26%14%5%
2062
16th to endDay
45%5%10%20%13%4
2262
May1st to 15thDay
50%6%14%17%9%2
2331
16th to endDay
46%6%15%21%7%1
2435
June1st to 15thDay
42%9%16%20%11%
2340
16th to endDay
41%8%15%18%13%2
2340
July1st to 15thDay
48%8%13%15%11%2
2201
16th to endDay
43%9%17%17%11%
2310
August1st to 15thDay
48%7%14%19%8%
2327
16th to endDay
43%7%17%18%11%1
2381
September1st to 15thDay
42%6%11%19%17%2
2052
16th to endDay
48%49%21%14%1
1980
October1st to 15thDay
39%410%25%16%4
1821
16th to endDay
37%29%26%20%3
1920
November1st to 15thDay
35%49%20%24%5%
1848
16th to endDay
40%28%24%22%1
1755
December1st to 15thDay
43%412%19%16%3
1755
16th to endDay
48%412%20%12%1
1872
January1st to 15thNight
43%5%11%19%15%5%
2472
16th to endNight
43%410%23%15%1
2496
February1st to 15thNight
41%312%24%15%2
2287
16th to endNight
43%5%11%27%11%1
1871
March1st to 15thNight
42%5%11%26%11%2
1980
16th to endNight
43%6%12%23%13%1
2112
April1st to 15thNight
38%313%24%15%4
1886
16th to endNight
40%413%20%15%4
1707
May1st to 15thNight
43%5%16%21%12%
1620
16th to endNight
37%7%21%23%7%1
1684
June1st to 15thNight
32%9%21%24%11%
1620
16th to endNight
30%9%17%24%15%2
1620
July1st to 15thNight
37%9%16%19%13%3
1530
16th to endNight
28%10%22%24%12%1
1595
August1st to 15thNight
36%8%17%21%14%
1609
16th to endNight
36%7%17%25%12%1
1809
September1st to 15thNight
35%7%12%23%17%3
1905
16th to endNight
40%5%10%24%17%1
1980
October1st to 15thNight
38%48%27%17%3
2139
16th to endNight
34%28%29%19%4
2304
November1st to 15thNight
36%49%20%22%6%
2336
16th to endNight
36%38%27%21%3
2535
December1st to 15thNight
46%310%22%12%3
2535
16th to endNight
50%411%18%13%1
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
31%22%24%13%7%
123
16th to endDay
33%28%21%10%6%
96
February1st to 15thDay
24%31%38%41
90
16th to endDay
25%25%29%11%6%
112
March1st to 15thDay
23%17%27%20%11%
270
16th to endDay
20%15%28%23%10%2
288
April1st to 15thDay
20%14%24%20%18%2
270
16th to endDay
21%7%22%19%18%10%
270
May1st to 15thDay
23%13%28%15%11%7%
288
16th to endDay
14%322%21%21%16%
331
June1st to 15thDay
10%6%15%25%24%16%
315
16th to endDay
11%6%24%26%18%13%
315
July1st to 15thDay
16%119%28%20%14%
305
16th to endDay
7%19%24%33%22%
326
August1st to 15thDay
19%113%20%25%19%
313
16th to endDay
11%18%18%28%32%
332
September1st to 15thDay
14%5%12%18%29%19%
315
16th to endDay
20%212%25%24%14%
314
October1st to 15thDay
20%6%15%24%28%5%
315
16th to endDay
14%11%24%23%20%5%
336
November1st to 15thDay
23%7%22%24%17%4
266
16th to endDay
17%24%15%25%14%2
135
December1st to 15thDay
26%22%29%11%8%
135
16th to endDay
36%17%27%15%2
144
January1st to 15thNight
24%20%26%23%4
765
16th to endNight
22%21%33%21%1
768
February1st to 15thNight
25%19%29%23%1
704
16th to endNight
21%23%31%20%2
631
March1st to 15thNight
21%15%30%28%4
720
16th to endNight
19%12%32%27%9%
768
April1st to 15thNight
19%17%26%28%7%
718
16th to endNight
16%10%23%31%17%
627
May1st to 15thNight
16%9%25%30%16%2
540
16th to endNight
12%315%29%34%4
563
June1st to 15thNight
9%115%35%32%4
540
16th to endNight
6%112%38%34%5%
540
July1st to 15thNight
10%17%39%37%3
510
16th to endNight
5%16%33%45%7%
564
August1st to 15thNight
11%16%38%37%4
539
16th to endNight
11%431%44%7%
663
September1st to 15thNight
10%210%32%38%4
720
16th to endNight
17%215%31%29%3
717
October1st to 15thNight
16%7%16%31%24%3
720
16th to endNight
15%10%24%31%15%1
768
November1st to 15thNight
17%9%20%33%16%1
760
16th to endNight
19%15%22%28%13%
780
December1st to 15thNight
22%16%26%26%7%
780
16th to endNight
21%18%28%27%3
832
Page generated at 2018-01-12 22:01:35. Version ac04

Copyright 2018 A. Danko


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