AJP Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the AJP Observatory clear sky chart from 2005-11-06 to 2024-01-27.

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
20%
23271
14%
74990
5%
23212
31%
23212
15%
52856

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
12%
850
11%
2838
2%
847
23%
847
10%
2087
January11th to 20thNight
16%
823
14%
2793
3%
823
28%
823
11%
1995
January21st to endNight
19%
820
19%
2712
5%
820
35%
820
16%
1772
February1st to 10thNight
14%
720
14%
2340
4%
720
27%
720
13%
1647
February11th to 20thNight
10%
703
13%
2276
2%
700
24%
700
11%
1677
February21st to endNight
16%
592
18%
1881
4%
592
33%
592
14%
1338
March1st to 10thNight
15%
720
17%
2034
5%
720
26%
720
15%
1507
March11th to 20thNight
18%
720
16%
1980
5%
720
27%
720
16%
1442
March21st to endNight
16%
792
17%
2178
5%
792
27%
792
16%
1620
April1st to 10thNight
16%
590
12%
1842
4%
590
23%
590
11%
1397
April11th to 20thNight
17%
534
17%
1598
5%
534
27%
534
18%
1124
April21st to endNight
20%
540
15%
1620
6%
540
28%
540
14%
1202
May1st to 10thNight
21%
540
14%
1576
6%
540
29%
540
15%
1152
May11th to 20thNight
20%
532
14%
1417
5%
532
30%
532
18%
1037
May21st to endNight
19%
529
11%
1497
2%
528
27%
528
17%
1061
June1st to 10thNight
24%
360
9%
1260
5%
360
30%
360
15%
907
June11th to 20thNight
28%
360
11%
1260
4%
360
36%
360
17%
850
June21st to endNight
25%
360
7%
1260
4%
360
29%
360
14%
926
July1st to 10thNight
24%
350
11%
1225
3%
350
35%
350
18%
818
July11th to 20thNight
36%
348
11%
1218
8%
348
42%
348
20%
802
July21st to endNight
32%
516
12%
1488
8%
488
37%
488
21%
1031
August1st to 10thNight
31%
538
10%
1600
5%
534
37%
534
22%
1084
August11th to 20thNight
35%
532
12%
1596
7%
532
40%
532
21%
1119
August21st to endNight
37%
594
17%
1795
8%
594
44%
594
26%
1123
September1st to 10thNight
28%
540
17%
1800
7%
540
39%
540
24%
1102
September11th to 20thNight
31%
679
20%
1939
9%
679
42%
679
28%
1223
September21st to endNight
27%
720
22%
1988
9%
720
39%
720
26%
1292
October1st to 10thNight
29%
720
20%
2160
9%
720
38%
720
23%
1430
October11th to 20thNight
23%
720
20%
2160
7%
720
34%
720
19%
1461
October21st to endNight
16%
792
16%
2460
3%
792
29%
792
15%
1737
November1st to 10thNight
19%
811
16%
2554
5%
811
30%
811
15%
1798
November11th to 20thNight
19%
850
17%
2660
7%
850
30%
850
14%
1924
November21st to endNight
18%
850
12%
2660
3%
850
29%
850
12%
1943
December1st to 10thNight
13%
850
15%
2664
3%
850
25%
850
12%
1971
December11th to 20thNight
12%
850
13%
3475
3%
849
25%
849
9%
2617
December21st to endNight
13%
926
9%
5186
2%
907
26%
907
6%
3640

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
20%9%46%5%3445%6%33%
74782
Night
19%10%46%5%3445%6%34%
75257
TransparencyDay
52%5%11%20%11%1
74477
Night
52%5%11%20%11%1
75097
SeeingDay
28%17%31%18%6%1
15417
Night
26%15%33%20%6%
23280

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
17%15%5%8%6%2435%6%30%
1327
11th to 20thDay
18%14%6%8%7%4445%427%
1382
21st to endDay
12%9%45%5%3445%7%41%
1785
February1st to 10thDay
15%11%5%7%6%45%5%46%32%
1620
11th to 20thDay
17%12%5%8%6%45%45%5%29%
1573
21st to endDay
11%11%5%9%7%35%45%6%34%
1372
March1st to 10thDay
18%16%5%5%5%25%5%45%30%
1921
11th to 20thDay
17%11%5%8%5%34446%32%
1980
21st to endDay
20%14%5%7%5%2434432%
2178
April1st to 10thDay
22%12%48%6%3445%6%26%
2113
11th to 20thDay
21%11%36%433446%35%
2312
21st to endDay
26%12%36%5%33345%29%
2340
May1st to 10thDay
27%10%47%5%34445%28%
2382
11th to 20thDay
26%9%45%434336%33%
2478
21st to endDay
21%7%35%5%35%5%6%7%33%
2793
June1st to 10thDay
28%9%36%5%345%5%6%25%
2700
11th to 20thDay
21%7%35%5%35%5%5%7%34%
2700
21st to endDay
29%8%36%5%3445%7%27%
2700
July1st to 10thDay
18%7%37%5%45%5%6%7%33%
2700
11th to 20thDay
15%5%26%6%46%6%6%8%34%
2700
21st to endDay
18%7%36%6%46%6%6%9%30%
2718
August1st to 10thDay
18%6%26%6%36%6%7%8%32%
2327
11th to 20thDay
16%7%36%7%46%6%7%8%31%
2304
21st to endDay
15%6%35%5%45%5%6%7%39%
2561
September1st to 10thDay
15%7%26%5%345%6%7%40%
2160
11th to 20thDay
18%8%35%5%23445%43%
2017
21st to endDay
20%6%25%5%3335%6%42%
1972
October1st to 10thDay
16%8%35%5%335%5%7%41%
1800
11th to 20thDay
21%7%36%6%35%347%36%
1800
21st to endDay
25%7%26%6%345%46%31%
1894
November1st to 10thDay
20%10%35%5%35%5%46%33%
1523
11th to 20thDay
18%11%47%5%3435%6%33%
1520
21st to endDay
20%11%38%5%35%446%32%
1520
December1st to 10thDay
22%13%46%5%4435%5%30%
1511
11th to 20thDay
19%12%6%10%6%44335%28%
1668
21st to endDay
18%10%5%7%6%3433435%
2431
January1st to 10thNight
15%12%6%8%6%45%6%5%6%28%
2838
11th to 20thNight
17%12%48%6%3445%6%32%
2793
21st to endNight
13%10%37%5%35%45%6%38%
2712
February1st to 10thNight
15%12%47%6%445%6%7%32%
2340
11th to 20thNight
18%14%5%7%5%45%445%30%
2273
21st to endNight
14%13%5%7%5%36%5%5%6%31%
1881
March1st to 10thNight
18%14%47%5%35%445%31%
2025
11th to 20thNight
18%9%47%6%35%6%5%6%31%
1979
21st to endNight
17%12%5%8%6%3443434%
2178
April1st to 10thNight
25%11%48%5%43445%27%
1842
11th to 20thNight
22%10%35%5%34446%34%
1598
21st to endNight
23%12%46%5%335%36%30%
1620
May1st to 10thNight
25%9%346%44446%32%
1576
11th to 20thNight
25%7%36%5%25%35%6%33%
1416
21st to endNight
15%8%37%6%45%5%6%7%34%
1496
June1st to 10thNight
27%8%25%6%35%446%31%
1260
11th to 20thNight
21%8%35%436%45%6%35%
1260
21st to endNight
28%8%25%5%35%35%6%29%
1260
July1st to 10thNight
17%7%36%5%35%5%6%6%36%
1260
11th to 20thNight
13%5%36%6%36%7%6%9%34%
1260
21st to endNight
17%8%37%5%46%46%9%33%
1575
August1st to 10thNight
16%5%25%6%5%5%6%5%7%39%
1612
11th to 20thNight
16%7%36%7%35%6%6%8%34%
1596
21st to endNight
13%6%35%4345%5%9%43%
1795
September1st to 10thNight
18%5%25%433447%45%
1800
11th to 20thNight
17%6%2442345%6%47%
1939
21st to endNight
19%5%35%42445%6%44%
1988
October1st to 10thNight
19%6%25%4335%5%6%41%
2160
11th to 20thNight
19%9%26%5%34447%38%
2160
21st to endNight
23%9%36%5%33446%35%
2460
November1st to 10thNight
20%9%46%5%3445%5%34%
2554
11th to 20thNight
21%10%46%5%35%447%31%
2660
21st to endNight
22%10%37%5%4445%5%31%
2660
December1st to 10thNight
23%12%47%5%34445%29%
2664
11th to 20thNight
22%12%5%6%6%34445%28%
3531
21st to endNight
21%11%5%9%6%3434430%
5236

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
57%411%16%11%1
1328
11th to 20thDay
60%5%9%13%11%1
1382
21st to endDay
43%412%22%18%2
1785
February1st to 10thDay
52%5%11%18%12%2
1620
11th to 20thDay
56%5%9%19%10%1
1581
21st to endDay
50%6%8%21%13%2
1372
March1st to 10thDay
58%48%21%9%1
1925
11th to 20thDay
55%410%19%9%3
1980
21st to endDay
56%48%17%11%4
2178
April1st to 10thDay
60%37%15%11%3
2113
11th to 20thDay
51%5%9%21%13%2
2312
21st to endDay
58%48%15%11%4
2340
May1st to 10thDay
59%37%18%12%1
2382
11th to 20thDay
54%5%8%21%11%1
2482
21st to endDay
50%6%12%22%10%1
2793
June1st to 10thDay
60%5%10%17%8%1
2700
11th to 20thDay
50%5%12%20%12%1
2700
21st to endDay
59%411%16%9%
2700
July1st to 10thDay
48%7%17%20%8%
2625
11th to 20thDay
45%7%16%23%9%1
2619
21st to endDay
50%8%14%20%8%
2565
August1st to 10thDay
47%7%15%23%8%
2314
11th to 20thDay
49%8%15%22%7%
2304
21st to endDay
43%6%15%25%11%
2561
September1st to 10thDay
41%8%14%24%13%
2160
11th to 20thDay
44%411%25%15%1
2017
21st to endDay
44%411%25%15%1
1972
October1st to 10thDay
43%5%11%27%12%1
1800
11th to 20thDay
49%5%14%23%9%1
1800
21st to endDay
53%5%11%19%10%1
1894
November1st to 10thDay
52%5%10%21%10%1
1523
11th to 20thDay
53%5%13%16%12%1
1520
21st to endDay
55%415%17%8%
1520
December1st to 10thDay
59%413%18%6%
1511
11th to 20thDay
61%5%8%15%10%1
1668
21st to endDay
54%411%18%11%3
2431
January1st to 10thNight
57%5%11%17%9%1
2838
11th to 20thNight
54%5%12%18%10%1
2793
21st to endNight
47%411%24%13%2
2712
February1st to 10thNight
52%412%16%13%2
2340
11th to 20thNight
58%49%17%11%2
2276
21st to endNight
53%47%18%15%2
1881
March1st to 10thNight
56%38%19%11%2
2034
11th to 20thNight
52%5%9%19%14%2
1980
21st to endNight
55%47%19%12%3
2178
April1st to 10thNight
61%47%14%11%4
1842
11th to 20thNight
51%49%20%14%2
1598
21st to endNight
57%5%8%14%13%3
1620
May1st to 10thNight
54%5%9%19%11%2
1576
11th to 20thNight
51%6%10%20%12%1
1417
21st to endNight
48%7%14%20%10%1
1497
June1st to 10thNight
55%5%10%20%9%1
1260
11th to 20thNight
49%5%11%24%9%2
1260
21st to endNight
56%6%12%17%7%1
1260
July1st to 10thNight
45%8%15%23%8%
1225
11th to 20thNight
43%9%16%24%9%1
1218
21st to endNight
48%6%16%21%8%
1488
August1st to 10thNight
44%8%15%27%7%
1600
11th to 20thNight
46%8%19%21%5%
1596
21st to endNight
38%7%18%26%12%
1795
September1st to 10thNight
39%5%13%28%13%1
1800
11th to 20thNight
39%5%14%27%15%1
1939
21st to endNight
40%5%11%28%15%1
1988
October1st to 10thNight
44%5%11%26%14%1
2160
11th to 20thNight
47%412%27%9%1
2160
21st to endNight
52%411%22%11%1
2460
November1st to 10thNight
51%5%12%21%10%1
2554
11th to 20thNight
53%6%12%19%10%1
2660
21st to endNight
54%6%13%16%10%
2660
December1st to 10thNight
58%311%20%7%
2664
11th to 20thNight
60%47%18%10%1
3532
21st to endNight
59%411%17%8%1
5236

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
32%18%36%14%1
180
11th to 20thDay
38%21%24%12%41
180
21st to endDay
23%18%35%19%6%
341
February1st to 10thDay
29%22%29%16%41
340
11th to 20thDay
28%24%30%13%41
336
21st to endDay
24%20%34%17%4
298
March1st to 10thDay
33%21%32%11%31
420
11th to 20thDay
29%18%31%17%41
420
21st to endDay
32%19%30%14%41
462
April1st to 10thDay
38%21%28%10%3
420
11th to 20thDay
31%23%27%14%41
412
21st to endDay
35%18%26%14%6%1
420
May1st to 10thDay
35%20%25%15%41
465
11th to 20thDay
32%15%27%16%7%2
624
21st to endDay
31%16%33%16%4
680
June1st to 10thDay
36%14%29%13%7%1
630
11th to 20thDay
28%15%30%21%5%1
630
21st to endDay
30%13%29%22%6%
630
July1st to 10thDay
22%14%35%20%8%1
620
11th to 20thDay
17%11%39%24%8%1
618
21st to endDay
18%13%36%25%7%1
605
August1st to 10thDay
16%12%39%24%8%2
446
11th to 20thDay
20%11%30%28%10%1
439
21st to endDay
20%13%29%26%10%2
495
September1st to 10thDay
16%18%32%23%10%1
450
11th to 20thDay
24%15%32%20%7%2
450
21st to endDay
25%14%35%15%6%4
446
October1st to 10thDay
20%16%29%19%13%3
360
11th to 20thDay
28%16%29%16%8%3
360
21st to endDay
33%19%27%15%5%1
396
November1st to 10thDay
31%17%30%15%5%1
365
11th to 20thDay
29%19%29%16%5%1
370
21st to endDay
32%21%30%13%41
370
December1st to 10thDay
32%17%30%17%41
361
11th to 20thDay
38%22%31%7%2
180
21st to endDay
35%19%30%13%3
198
January1st to 10thNight
26%19%33%19%3
850
11th to 20thNight
26%19%32%19%4
823
21st to endNight
22%18%35%20%5%
820
February1st to 10thNight
24%20%35%17%41
720
11th to 20thNight
29%19%35%13%41
703
21st to endNight
24%16%37%19%4
592
March1st to 10thNight
26%18%36%18%2
720
11th to 20thNight
26%17%33%18%6%
720
21st to endNight
25%17%36%17%5%1
792
April1st to 10thNight
32%19%27%17%3
590
11th to 20thNight
30%13%34%16%7%
534
21st to endNight
33%15%28%20%41
540
May1st to 10thNight
32%15%28%20%4
540
11th to 20thNight
26%15%34%18%7%
532
21st to endNight
21%21%35%18%4
529
June1st to 10thNight
31%8%31%26%5%
360
11th to 20thNight
25%11%30%26%8%
360
21st to endNight
33%8%28%26%6%
360
July1st to 10thNight
20%10%42%21%8%
350
11th to 20thNight
15%8%36%32%9%
348
21st to endNight
20%7%35%28%9%
516
August1st to 10thNight
17%8%38%28%9%
538
11th to 20thNight
17%7%33%33%10%1
532
21st to endNight
17%10%30%30%11%1
594
September1st to 10thNight
21%10%37%25%7%
540
11th to 20thNight
22%10%34%25%9%1
679
21st to endNight
21%14%34%23%8%
720
October1st to 10thNight
23%12%33%23%9%
720
11th to 20thNight
23%15%34%19%8%
720
21st to endNight
30%17%32%17%4
792
November1st to 10thNight
29%14%31%20%41
811
11th to 20thNight
30%16%30%16%7%1
850
21st to endNight
30%19%27%20%4
850
December1st to 10thNight
30%17%33%16%4
850
11th to 20thNight
30%20%32%14%3
850
21st to endNight
32%19%28%16%41
935
Page generated at 2024-01-24 10:37:28. Version ac07

Copyright 2024 Attilla Danko


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