Kendrick Astro Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Kendrick Astro Observatory clear sky chart from 2005-11-06 to 2024-02-10.

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%
22929
13%
80456
10%
22835
43%
22835
17%
56550

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 10thNight
17%
753
8%
4405
5%
737
24%
737
6%
3282
January11th to 20thNight
18%
757
4%
4185
2%
740
23%
740
5%
3346
January21st to endNight
23%
829
6%
4528
5%
814
30%
814
7%
3626
February1st to 10thNight
19%
759
9%
2464
4%
759
26%
759
12%
1873
February11th to 20thNight
19%
700
11%
2275
4%
700
28%
700
12%
1720
February21st to endNight
21%
592
11%
1867
5%
592
28%
592
14%
1367
March1st to 10thNight
25%
720
15%
1980
6%
720
33%
720
19%
1412
March11th to 20thNight
25%
720
16%
1980
8%
720
33%
720
19%
1438
March21st to endNight
35%
792
19%
2178
11%
792
42%
792
23%
1515
April1st to 10thNight
30%
720
14%
1835
6%
720
34%
720
22%
1327
April11th to 20thNight
35%
660
17%
1724
7%
660
40%
660
25%
1224
April21st to endNight
39%
540
17%
1620
8%
540
46%
540
22%
1119
May1st to 10thNight
44%
540
15%
1620
9%
540
49%
540
25%
1087
May11th to 20thNight
52%
372
22%
1434
20%
372
62%
372
25%
833
May21st to endNight
58%
388
17%
1551
20%
388
64%
388
27%
845
June1st to 10thNight
55%
360
14%
1440
16%
360
63%
360
23%
845
June11th to 20thNight
52%
360
16%
1440
18%
360
59%
360
24%
825
June21st to endNight
57%
360
15%
1440
21%
360
62%
360
24%
834
July1st to 10thNight
71%
350
17%
1400
25%
350
75%
350
33%
701
July11th to 20thNight
62%
348
18%
1392
26%
348
66%
348
31%
732
July21st to endNight
67%
567
18%
1650
16%
536
69%
536
35%
945
August1st to 10thNight
68%
537
17%
1600
14%
534
69%
534
34%
970
August11th to 20thNight
69%
534
23%
1598
18%
534
72%
534
38%
919
August21st to endNight
61%
672
21%
1860
12%
672
63%
672
34%
1148
September1st to 10thNight
59%
720
17%
1800
8%
720
62%
720
34%
1183
September11th to 20thNight
60%
720
27%
1903
16%
720
65%
720
39%
1128
September21st to endNight
52%
720
20%
2016
16%
720
55%
720
27%
1338
October1st to 10thNight
45%
720
16%
2160
14%
720
49%
720
23%
1460
October11th to 20thNight
34%
720
14%
2160
10%
720
40%
720
19%
1532
October21st to endNight
27%
792
15%
2376
10%
792
34%
792
15%
1782
November1st to 10thNight
38%
740
18%
2462
15%
740
45%
740
20%
1613
November11th to 20thNight
27%
760
14%
2660
8%
760
36%
760
16%
1885
November21st to endNight
25%
760
9%
2660
6%
760
29%
760
13%
1973
December1st to 10thNight
19%
760
8%
2660
4%
760
23%
760
10%
2071
December11th to 20thNight
19%
760
6%
3254
2%
758
25%
758
8%
2512
December21st to endNight
17%
827
3%
4879
1%
817
22%
817
4%
4140

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%45%5%6%7%33%
78238
Night
16%9%47%6%35%5%5%6%34%
80706
TransparencyDay
47%9%15%19%10%1
77953
Night
49%8%14%18%10%1
80525
SeeingDay
16%8%27%28%15%5%
13393
Night
18%8%29%30%13%2
22959

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 10thDay
16%12%5%8%7%35%5%5%6%29%
2517
11th to 20thDay
12%16%7%14%10%45%35%5%19%
2758
21st to endDay
22%18%6%10%7%3444418%
3124
February1st to 10thDay
16%13%5%11%9%46%5%5%5%22%
1701
11th to 20thDay
13%13%7%10%8%46%446%27%
1573
21st to endDay
18%12%5%8%7%4445%6%26%
1386
March1st to 10thDay
14%9%49%7%35%6%6%7%30%
1977
11th to 20thDay
14%10%5%7%7%36%5%5%5%32%
1980
21st to endDay
18%10%47%6%45%446%33%
2178
April1st to 10thDay
16%11%47%7%45%5%47%30%
2124
11th to 20thDay
18%9%36%5%2445%7%36%
2199
21st to endDay
20%7%37%5%45%5%5%6%33%
2340
May1st to 10thDay
15%8%38%5%345%6%9%34%
2340
11th to 20thDay
14%7%35%5%45%46%7%41%
2457
21st to endDay
12%425%5%35%5%6%8%44%
2725
June1st to 10thDay
14%5%35%6%346%7%8%39%
2520
11th to 20thDay
12%5%25%5%45%6%7%10%40%
2520
21st to endDay
12%425%5%45%6%6%10%41%
2520
July1st to 10thDay
7%4245%46%7%7%9%45%
2520
11th to 20thDay
11%435%5%37%6%6%10%41%
2520
21st to endDay
9%5%25%6%46%7%9%10%37%
2567
August1st to 10thDay
8%5%26%6%35%7%7%10%41%
2327
11th to 20thDay
8%5%35%6%45%5%7%9%42%
2303
21st to endDay
11%6%25%5%35%6%6%9%42%
2477
September1st to 10thDay
13%5%26%5%35%5%6%9%41%
2160
11th to 20thDay
11%5%345%35%5%6%8%46%
2053
21st to endDay
12%5%36%7%36%5%6%9%38%
1944
October1st to 10thDay
19%8%36%5%35%45%7%35%
1800
11th to 20thDay
20%8%47%6%45%6%5%7%29%
1800
21st to endDay
24%10%47%7%35%5%7%6%22%
1980
November1st to 10thDay
14%8%46%7%36%5%6%8%34%
1610
11th to 20thDay
15%10%48%7%35%7%5%8%26%
1520
21st to endDay
20%12%48%6%35%47%7%24%
1520
December1st to 10thDay
18%13%5%10%8%5%6%5%6%5%19%
1520
11th to 20thDay
20%11%5%8%7%45%6%6%6%23%
1906
21st to endDay
30%15%5%9%6%4445%5%14%
2772
January1st to 10thNight
18%14%5%9%7%45%5%46%23%
4429
11th to 20thNight
16%12%5%10%11%5%6%5%5%6%20%
4187
21st to endNight
22%13%5%8%9%46%5%45%20%
4532
February1st to 10thNight
15%14%5%8%7%45%5%5%6%25%
2464
11th to 20thNight
16%13%5%7%8%45%6%46%27%
2273
21st to endNight
16%11%49%7%35%46%5%30%
1867
March1st to 10thNight
13%8%5%7%7%45%5%5%6%35%
1970
11th to 20thNight
15%11%5%9%6%34445%34%
1979
21st to endNight
16%9%37%5%3445%5%39%
2178
April1st to 10thNight
18%8%46%7%35%45%7%33%
1835
11th to 20thNight
16%7%46%6%35%447%38%
1724
21st to endNight
18%6%46%5%35%6%5%7%36%
1620
May1st to 10thNight
17%6%25%5%45%47%7%39%
1620
11th to 20thNight
15%435%5%3445%8%46%
1433
21st to endNight
11%4244346%5%8%50%
1550
June1st to 10thNight
12%425%6%45%5%6%9%43%
1440
11th to 20thNight
10%5%35%6%35%5%6%10%43%
1440
21st to endNight
12%5%25%5%245%6%8%45%
1440
July1st to 10thNight
5%423435%45%7%58%
1440
11th to 20thNight
10%325%435%46%9%50%
1440
21st to endNight
8%3245%245%8%8%50%
1747
August1st to 10thNight
8%325%6%45%5%6%8%49%
1611
11th to 20thNight
8%325%4335%6%9%53%
1598
21st to endNight
10%4245%35%5%6%7%48%
1860
September1st to 10thNight
10%5%25%435%5%6%8%46%
1800
11th to 20thNight
11%42443345%6%55%
1903
21st to endNight
14%5%25%6%3446%7%43%
2016
October1st to 10thNight
16%7%36%6%345%5%7%39%
2160
11th to 20thNight
19%9%37%6%245%47%35%
2160
21st to endNight
22%9%37%5%445%6%6%29%
2376
November1st to 10thNight
17%7%36%5%345%47%39%
2462
11th to 20thNight
16%9%47%6%45%6%5%6%31%
2660
21st to endNight
20%10%46%6%45%5%5%7%28%
2660
December1st to 10thNight
21%13%5%7%6%45%5%5%5%24%
2660
11th to 20thNight
15%16%5%8%7%35%5%6%6%23%
3288
21st to endNight
31%13%6%8%7%345%45%14%
4884

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 10thDay
53%12%19%10%6%
2518
11th to 20thDay
68%6%14%8%2
2758
21st to endDay
69%7%12%9%3
3124
February1st to 10thDay
61%8%14%13%21
1701
11th to 20thDay
59%7%13%14%6%1
1582
21st to endDay
56%8%15%14%6%1
1386
March1st to 10thDay
50%9%15%16%8%1
1980
11th to 20thDay
52%8%11%17%11%2
1980
21st to endDay
50%7%11%18%12%2
2178
April1st to 10thDay
52%6%12%18%10%1
2124
11th to 20thDay
47%6%11%21%15%1
2199
21st to endDay
48%9%11%18%11%3
2340
May1st to 10thDay
45%7%13%20%14%1
2340
11th to 20thDay
41%7%12%24%13%2
2461
21st to endDay
35%8%17%24%14%2
2725
June1st to 10thDay
39%9%14%22%15%2
2520
11th to 20thDay
36%9%15%24%15%1
2520
21st to endDay
35%9%15%25%15%1
2520
July1st to 10thDay
29%10%16%24%18%3
2450
11th to 20thDay
35%9%17%27%12%1
2445
21st to endDay
36%11%17%22%12%1
2423
August1st to 10thDay
34%10%18%23%13%2
2314
11th to 20thDay
34%10%18%26%11%1
2303
21st to endDay
35%9%15%27%12%1
2477
September1st to 10thDay
37%10%16%26%10%1
2160
11th to 20thDay
33%8%17%28%14%1
2053
21st to endDay
40%10%16%25%8%
1944
October1st to 10thDay
46%8%16%18%11%1
1800
11th to 20thDay
52%8%14%19%6%1
1800
21st to endDay
58%9%14%14%5%1
1980
November1st to 10thDay
46%9%16%21%7%1
1610
11th to 20thDay
53%9%16%15%7%
1520
21st to endDay
56%10%17%14%3
1520
December1st to 10thDay
64%9%14%10%3
1520
11th to 20thDay
60%10%16%10%4
1906
21st to endDay
71%8%12%8%1
2772
January1st to 10thNight
58%11%15%13%31
4429
11th to 20thNight
63%12%15%7%2
4187
21st to endNight
64%9%14%9%31
4532
February1st to 10thNight
58%7%14%16%31
2464
11th to 20thNight
58%7%13%15%7%1
2275
21st to endNight
54%7%15%17%7%
1867
March1st to 10thNight
49%6%14%20%8%1
1980
11th to 20thNight
52%5%11%19%12%2
1980
21st to endNight
46%7%9%21%15%3
2178
April1st to 10thNight
49%6%12%19%13%1
1835
11th to 20thNight
46%6%10%20%15%2
1724
21st to endNight
45%8%11%19%14%2
1620
May1st to 10thNight
43%7%10%20%17%3
1620
11th to 20thNight
37%6%12%26%16%4
1434
21st to endNight
31%9%14%24%19%5%
1551
June1st to 10thNight
38%7%13%23%17%2
1440
11th to 20thNight
36%7%12%22%21%2
1440
21st to endNight
36%8%13%24%18%1
1440
July1st to 10thNight
27%7%12%26%26%4
1400
11th to 20thNight
30%6%15%29%18%2
1392
21st to endNight
28%9%15%28%17%3
1650
August1st to 10thNight
32%8%18%28%13%2
1600
11th to 20thNight
27%8%18%33%13%1
1598
21st to endNight
33%8%14%28%16%1
1860
September1st to 10thNight
34%9%17%25%14%1
1800
11th to 20thNight
29%6%14%34%16%
1903
21st to endNight
39%8%13%27%12%
2016
October1st to 10thNight
43%8%14%20%14%1
2160
11th to 20thNight
49%7%15%21%7%
2160
21st to endNight
55%8%11%17%9%1
2376
November1st to 10thNight
44%7%15%22%11%1
2462
11th to 20thNight
49%9%15%17%8%1
2660
21st to endNight
55%9%19%14%3
2660
December1st to 10thNight
59%9%15%13%4
2660
11th to 20thNight
60%9%15%13%3
3288
21st to endNight
71%10%12%6%1
4884

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 10thDay
19%13%34%23%8%2
180
11th to 20thDay
19%20%37%14%8%2
249
21st to endDay
22%12%35%24%6%
297
February1st to 10thDay
21%15%42%18%5%
267
11th to 20thDay
20%18%41%18%2
240
21st to endDay
27%24%29%19%1
216
March1st to 10thDay
18%12%40%24%7%
420
11th to 20thDay
18%16%32%25%9%1
420
21st to endDay
25%8%32%25%8%1
462
April1st to 10thDay
17%12%33%29%9%
420
11th to 20thDay
22%9%34%20%10%3
412
21st to endDay
21%7%33%28%10%2
420
May1st to 10thDay
18%8%28%28%13%5%
423
11th to 20thDay
15%5%26%31%18%5%
447
21st to endDay
14%319%34%22%7%
485
June1st to 10thDay
12%427%38%17%3
450
11th to 20thDay
13%5%23%33%23%3
450
21st to endDay
13%5%19%36%21%5%
450
July1st to 10thDay
7%314%35%30%11%
445
11th to 20thDay
12%316%36%25%9%
444
21st to endDay
8%317%42%24%7%
488
August1st to 10thDay
9%416%30%28%13%
446
11th to 20thDay
9%315%34%27%13%
439
21st to endDay
11%5%19%29%24%11%
495
September1st to 10thDay
13%420%30%22%12%
450
11th to 20thDay
10%419%28%24%15%
450
21st to endDay
12%6%29%27%17%9%
450
October1st to 10thDay
21%8%24%24%16%7%
450
11th to 20thDay
19%12%34%24%9%2
450
21st to endDay
27%11%29%25%8%1
495
November1st to 10thDay
16%15%28%28%12%2
265
11th to 20thDay
21%18%31%22%7%1
180
21st to endDay
23%11%39%23%31
180
December1st to 10thDay
23%14%36%20%6%1
180
11th to 20thDay
24%21%31%19%4
180
21st to endDay
25%16%39%18%2
198
January1st to 10thNight
23%14%37%20%6%
760
11th to 20thNight
26%13%32%24%4
760
21st to endNight
19%8%39%26%7%
836
February1st to 10thNight
21%13%40%23%3
759
11th to 20thNight
22%12%38%24%5%
703
21st to endNight
20%12%42%23%4
592
March1st to 10thNight
18%10%39%26%8%
720
11th to 20thNight
20%12%36%24%7%1
720
21st to endNight
20%8%29%31%10%1
792
April1st to 10thNight
22%8%33%30%7%
720
11th to 20thNight
18%9%33%29%10%2
660
21st to endNight
21%6%26%34%13%
540
May1st to 10thNight
17%427%31%18%3
540
11th to 20thNight
15%224%41%17%
372
21st to endNight
9%323%38%25%2
389
June1st to 10thNight
12%221%44%19%1
360
11th to 20thNight
11%226%37%23%1
360
21st to endNight
10%419%43%24%1
360
July1st to 10thNight
6%114%48%27%3
350
11th to 20thNight
11%318%38%26%3
348
21st to endNight
8%115%47%26%3
567
August1st to 10thNight
9%212%40%32%4
537
11th to 20thNight
8%114%40%33%5%
534
21st to endNight
11%219%36%29%4
672
September1st to 10thNight
11%420%33%24%7%
720
11th to 20thNight
13%317%31%29%7%
720
21st to endNight
16%5%20%32%22%5%
720
October1st to 10thNight
18%6%24%28%20%3
720
11th to 20thNight
20%9%30%29%10%2
720
21st to endNight
26%8%30%30%6%1
792
November1st to 10thNight
20%9%27%31%13%1
740
11th to 20thNight
19%10%36%25%8%2
760
21st to endNight
24%9%34%26%6%
760
December1st to 10thNight
28%11%35%20%6%
760
11th to 20thNight
21%13%41%21%4
760
21st to endNight
30%11%34%23%2
836
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