Joseph Dale Perry Memorial Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Joseph Dale Perry Memorial Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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
41%
23964
19%
74598
13%
23909
47%
23909
22%
49980

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
18%
760
14%
2459
7%
757
28%
757
13%
1839
January11th to 20thNight
20%
744
15%
2417
8%
744
29%
744
11%
1831
January21st to endNight
19%
792
15%
2574
7%
792
30%
792
14%
1857
February1st to 10thNight
22%
720
13%
2331
6%
720
31%
720
13%
1719
February11th to 20thNight
16%
702
13%
2099
6%
700
23%
700
13%
1560
February21st to endNight
14%
592
16%
1776
6%
592
23%
592
13%
1347
March1st to 10thNight
24%
720
19%
2048
9%
720
32%
720
18%
1432
March11th to 20thNight
24%
720
17%
1980
7%
720
32%
720
19%
1423
March21st to endNight
29%
792
16%
2178
8%
792
35%
792
20%
1536
April1st to 10thNight
32%
720
19%
1980
8%
720
41%
720
24%
1320
April11th to 20thNight
37%
569
23%
1683
14%
569
46%
569
27%
1058
April21st to endNight
27%
540
20%
1620
7%
540
37%
540
23%
1084
May1st to 10thNight
38%
540
15%
1620
8%
540
43%
540
22%
1102
May11th to 20thNight
43%
531
15%
1592
10%
531
48%
531
22%
1095
May21st to endNight
58%
583
18%
1745
13%
582
62%
582
30%
1094
June1st to 10thNight
61%
540
17%
1620
15%
540
63%
540
32%
986
June11th to 20thNight
65%
540
16%
1620
14%
540
67%
540
32%
980
June21st to endNight
60%
540
18%
1620
15%
540
62%
540
32%
994
July1st to 10thNight
64%
525
15%
1575
15%
525
65%
525
29%
1012
July11th to 20thNight
68%
522
18%
1566
15%
522
70%
522
34%
945
July21st to endNight
66%
591
19%
1672
18%
558
68%
558
30%
1050
August1st to 10thNight
67%
537
20%
1600
18%
534
67%
534
29%
1003
August11th to 20thNight
66%
534
22%
1598
18%
534
68%
534
31%
976
August21st to endNight
69%
610
25%
1846
24%
610
70%
610
35%
1085
September1st to 10thNight
65%
720
23%
1980
18%
720
67%
720
35%
1209
September11th to 20thNight
60%
720
26%
1980
20%
720
63%
720
35%
1208
September21st to endNight
54%
720
26%
1980
19%
720
60%
720
32%
1246
October1st to 10thNight
57%
720
26%
2034
23%
720
61%
720
36%
1212
October11th to 20thNight
43%
720
25%
2160
19%
720
52%
720
27%
1366
October21st to endNight
39%
792
26%
2376
21%
792
48%
792
23%
1571
November1st to 10thNight
47%
740
28%
2378
24%
740
56%
740
30%
1381
November11th to 20thNight
35%
760
24%
2470
16%
760
47%
760
22%
1564
November21st to endNight
38%
760
22%
2470
17%
760
46%
760
22%
1595
December1st to 10thNight
24%
760
14%
2470
8%
760
31%
760
14%
1843
December11th to 20thNight
27%
759
17%
2988
11%
758
37%
758
13%
2094
December21st to endNight
23%
829
10%
4493
8%
817
32%
817
7%
3363

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
16%8%36%5%345%5%7%37%
74917
Night
16%8%36%5%3445%7%38%
74898
TransparencyDay
47%5%11%22%13%2
74640
Night
46%5%10%21%15%3
74694
SeeingDay
22%11%25%22%14%6%
13830
Night
21%9%23%29%16%2
23974

By Month

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 10thDay
17%13%6%10%7%34435%28%
1706
11th to 20thDay
21%17%410%6%25%435%23%
1665
21st to endDay
19%14%5%7%5%34346%30%
1782
February1st to 10thDay
22%13%5%8%5%33345%28%
1624
11th to 20thDay
23%11%5%7%4335%46%29%
1748
21st to endDay
22%13%5%5%434445%30%
1480
March1st to 10thDay
18%11%45%43445%6%36%
1912
11th to 20thDay
21%9%47%6%3445%5%32%
1980
21st to endDay
21%9%47%5%34446%34%
2178
April1st to 10thDay
15%7%37%5%4446%7%39%
1980
11th to 20thDay
18%7%36%434446%42%
2239
21st to endDay
18%7%26%6%35%45%7%37%
2340
May1st to 10thDay
19%7%36%6%345%5%7%35%
2340
11th to 20thDay
19%7%37%6%35%5%5%6%33%
2301
21st to endDay
11%426%7%46%6%7%9%37%
2531
June1st to 10thDay
12%5%25%6%35%6%6%9%41%
2340
11th to 20thDay
10%5%26%5%45%6%6%10%39%
2340
21st to endDay
11%5%35%5%46%5%7%10%40%
2340
July1st to 10thDay
14%425%6%25%6%7%9%39%
2340
11th to 20thDay
11%5%26%7%46%6%7%9%37%
2340
21st to endDay
13%5%36%6%35%6%7%9%35%
2547
August1st to 10thDay
12%5%26%6%47%6%7%11%34%
2327
11th to 20thDay
13%6%26%6%46%6%8%9%34%
2303
21st to endDay
10%436%5%35%6%6%10%43%
2486
September1st to 10thDay
14%6%245%3445%6%47%
1980
11th to 20thDay
12%6%244345%5%8%46%
1980
21st to endDay
18%6%25%434445%45%
1980
October1st to 10thDay
13%425%4235%5%7%48%
1926
11th to 20thDay
17%5%245%33446%47%
1800
21st to endDay
22%6%35%423336%42%
1980
November1st to 10thDay
13%5%25%42345%452%
1695
11th to 20thDay
15%10%35%4245%5%6%40%
1710
21st to endDay
17%9%46%43445%5%40%
1710
December1st to 10thDay
25%13%47%5%34445%27%
1710
11th to 20thDay
20%13%5%7%5%2445%5%31%
2153
21st to endDay
19%17%48%6%45%5%5%6%20%
3124
January1st to 10thNight
18%12%5%9%7%34445%28%
2459
11th to 20thNight
25%12%5%7%6%24446%25%
2417
21st to endNight
19%13%5%8%5%44345%30%
2574
February1st to 10thNight
21%11%5%7%5%45%446%28%
2331
11th to 20thNight
24%12%47%5%24445%28%
2098
21st to endNight
26%13%46%5%34345%28%
1776
March1st to 10thNight
18%10%46%5%34335%38%
2048
11th to 20thNight
21%9%45%5%35%45%6%33%
1980
21st to endNight
17%8%36%6%36%5%48%34%
2178
April1st to 10thNight
14%7%36%5%35%45%8%40%
1980
11th to 20thNight
15%6%35%5%245%6%8%42%
1683
21st to endNight
16%7%35%5%35%5%5%7%39%
1620
May1st to 10thNight
20%6%26%5%35%5%5%6%37%
1620
11th to 20thNight
16%7%26%5%36%5%5%9%35%
1592
21st to endNight
9%5%35%6%35%5%6%11%41%
1744
June1st to 10thNight
10%4345%45%6%7%9%44%
1620
11th to 20thNight
7%5%25%436%7%7%10%44%
1620
21st to endNight
11%5%245%35%5%6%11%43%
1620
July1st to 10thNight
10%6%35%5%35%5%7%8%42%
1620
11th to 20thNight
7%4246%35%5%5%11%47%
1620
21st to endNight
9%5%35%6%46%5%6%8%44%
1771
August1st to 10thNight
9%5%36%5%445%6%9%42%
1611
11th to 20thNight
9%6%26%5%346%6%9%43%
1598
21st to endNight
9%5%244246%7%7%49%
1846
September1st to 10thNight
12%4245%35%5%6%8%47%
1980
11th to 20thNight
11%6%246%24448%49%
1980
21st to endNight
12%5%35%5%3445%6%47%
1980
October1st to 10thNight
12%5%25%423447%52%
2034
11th to 20thNight
16%6%24434446%46%
2160
21st to endNight
20%7%35%5%33445%42%
2376
November1st to 10thNight
14%6%335%33445%52%
2378
11th to 20thNight
17%7%35%424446%43%
2470
21st to endNight
16%10%36%43345%6%40%
2470
December1st to 10thNight
23%14%5%7%5%23445%28%
2470
11th to 20thNight
18%12%6%7%5%34346%31%
3042
21st to endNight
20%16%48%7%35%5%5%6%22%
4532

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
61%39%17%9%1
1707
11th to 20thDay
66%39%15%6%
1665
21st to endDay
56%39%21%9%1
1782
February1st to 10thDay
60%48%19%9%1
1624
11th to 20thDay
57%48%19%10%2
1758
21st to endDay
58%28%18%11%3
1480
March1st to 10thDay
49%310%24%12%2
1912
11th to 20thDay
55%5%8%18%12%2
1980
21st to endDay
52%5%8%23%10%2
2178
April1st to 10thDay
44%410%24%15%3
1980
11th to 20thDay
44%39%21%18%5%
2239
21st to endDay
47%5%12%22%11%3
2340
May1st to 10thDay
48%5%13%22%11%2
2340
11th to 20thDay
51%5%12%20%10%1
2305
21st to endDay
41%7%16%23%13%1
2531
June1st to 10thDay
38%7%13%26%16%1
2340
11th to 20thDay
39%7%14%20%17%2
2340
21st to endDay
39%7%14%22%16%3
2340
July1st to 10thDay
40%8%16%19%15%2
2275
11th to 20thDay
40%8%14%21%14%3
2271
21st to endDay
42%7%13%24%12%2
2405
August1st to 10thDay
42%8%17%21%11%1
2314
11th to 20thDay
44%7%14%24%11%1
2303
21st to endDay
35%7%15%25%15%3
2486
September1st to 10thDay
37%5%11%24%18%6%
1980
11th to 20thDay
36%5%11%28%18%1
1980
21st to endDay
42%49%24%20%2
1980
October1st to 10thDay
34%5%13%26%20%3
1926
11th to 20thDay
39%39%27%20%2
1800
21st to endDay
46%29%25%16%2
1980
November1st to 10thDay
35%48%26%24%3
1695
11th to 20thDay
45%38%22%19%3
1710
21st to endDay
47%39%24%16%1
1710
December1st to 10thDay
60%49%20%6%1
1710
11th to 20thDay
56%310%18%13%1
2150
21st to endDay
64%5%9%17%4
3124
January1st to 10thNight
59%48%15%12%2
2459
11th to 20thNight
62%38%17%10%1
2417
21st to endNight
56%310%22%7%2
2574
February1st to 10thNight
58%49%19%9%1
2331
11th to 20thNight
59%38%18%11%1
2099
21st to endNight
61%39%14%10%3
1776
March1st to 10thNight
51%36%21%17%3
2048
11th to 20thNight
51%410%22%11%2
1980
21st to endNight
48%5%11%19%14%2
2178
April1st to 10thNight
43%5%9%22%18%3
1980
11th to 20thNight
40%410%22%16%7%
1683
21st to endNight
45%6%11%22%15%2
1620
May1st to 10thNight
47%5%12%20%13%3
1620
11th to 20thNight
46%6%12%22%12%2
1593
21st to endNight
37%6%16%23%16%1
1745
June1st to 10thNight
35%7%16%23%17%3
1620
11th to 20thNight
33%8%17%18%20%4
1620
21st to endNight
34%7%16%24%15%4
1620
July1st to 10thNight
37%8%15%19%17%4
1575
11th to 20thNight
31%8%16%24%16%5%
1566
21st to endNight
36%8%14%26%14%2
1672
August1st to 10thNight
37%7%13%26%14%2
1600
11th to 20thNight
35%7%16%26%16%1
1598
21st to endNight
32%6%11%27%20%4
1846
September1st to 10thNight
34%6%13%23%17%7%
1980
11th to 20thNight
34%5%11%22%24%3
1980
21st to endNight
37%5%10%23%23%2
1980
October1st to 10thNight
33%410%27%20%5%
2034
11th to 20thNight
40%5%7%24%21%3
2160
21st to endNight
45%46%23%18%4
2376
November1st to 10thNight
36%38%24%24%5%
2378
11th to 20thNight
43%47%20%21%5%
2470
21st to endNight
46%39%25%16%2
2470
December1st to 10thNight
60%39%19%8%1
2470
11th to 20thNight
55%38%23%10%1
3044
21st to endNight
63%48%16%8%
4532

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
29%22%32%11%41
270
11th to 20thDay
35%21%32%11%1
255
21st to endDay
33%25%30%10%2
264
February1st to 10thDay
35%18%33%10%4
240
11th to 20thDay
48%21%25%6%1
240
21st to endDay
40%16%34%9%1
198
March1st to 10thDay
32%18%31%16%4
352
11th to 20thDay
29%18%33%15%5%
420
21st to endDay
31%17%31%16%5%
462
April1st to 10thDay
24%16%31%20%8%1
420
11th to 20thDay
25%15%31%16%10%3
412
21st to endDay
27%14%31%20%6%2
420
May1st to 10thDay
26%16%30%17%8%4
423
11th to 20thDay
21%11%27%24%13%4
447
21st to endDay
13%8%23%26%20%11%
485
June1st to 10thDay
13%5%24%30%19%9%
450
11th to 20thDay
13%7%19%32%20%9%
450
21st to endDay
12%7%28%22%22%9%
450
July1st to 10thDay
14%317%22%24%19%
445
11th to 20thDay
9%320%31%23%13%
444
21st to endDay
15%216%30%26%12%
488
August1st to 10thDay
13%316%34%22%12%
446
11th to 20thDay
16%315%29%25%12%
439
21st to endDay
11%215%32%27%13%
495
September1st to 10thDay
16%313%26%28%12%
450
11th to 20thDay
14%412%31%28%12%
450
21st to endDay
21%7%21%26%18%8%
450
October1st to 10thDay
17%7%21%29%20%6%
450
11th to 20thDay
20%10%29%25%12%4
450
21st to endDay
27%9%28%22%11%2
495
November1st to 10thDay
19%11%32%27%10%2
293
11th to 20thDay
27%14%31%18%8%1
270
21st to endDay
28%13%34%19%6%1
270
December1st to 10thDay
34%17%27%14%7%1
270
11th to 20thDay
29%17%34%14%5%1
270
21st to endDay
32%19%31%13%5%
297
January1st to 10thNight
29%17%29%19%5%
760
11th to 20thNight
34%15%26%21%4
744
21st to endNight
28%16%31%22%3
792
February1st to 10thNight
30%12%31%25%2
720
11th to 20thNight
33%18%30%18%1
703
21st to endNight
35%15%32%16%2
592
March1st to 10thNight
25%15%31%25%4
720
11th to 20thNight
27%15%31%20%7%
720
21st to endNight
23%13%31%25%7%
792
April1st to 10thNight
20%14%29%29%8%
720
11th to 20thNight
18%11%30%27%12%1
569
21st to endNight
22%7%37%26%7%1
540
May1st to 10thNight
22%9%26%28%13%2
540
11th to 20thNight
18%7%25%31%17%2
531
21st to endNight
13%318%35%27%5%
584
June1st to 10thNight
11%218%38%28%4
540
11th to 20thNight
9%314%41%27%5%
540
21st to endNight
13%218%37%27%3
540
July1st to 10thNight
14%310%33%32%8%
525
11th to 20thNight
7%213%32%39%6%
522
21st to endNight
11%38%36%36%6%
591
August1st to 10thNight
12%27%39%35%5%
537
11th to 20thNight
11%310%34%37%7%
534
21st to endNight
12%28%36%34%8%
610
September1st to 10thNight
12%310%33%35%7%
720
11th to 20thNight
13%214%28%38%5%
720
21st to endNight
15%419%30%28%4
720
October1st to 10thNight
14%418%32%26%5%
720
11th to 20thNight
20%8%25%29%16%2
720
21st to endNight
23%10%23%30%14%1
792
November1st to 10thNight
16%8%24%33%17%2
740
11th to 20thNight
22%13%25%29%11%1
760
21st to endNight
23%10%23%33%11%1
760
December1st to 10thNight
33%12%25%24%5%
760
11th to 20thNight
25%11%30%27%6%1
760
21st to endNight
30%15%26%26%4
836
Page generated at 2024-01-13 09:37:56. Version ac07

Copyright 2024 Attilla Danko


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