Perry Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Perry Observatory clear sky chart from 2005-11-06 to 2024-01-14.

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
36%
23131
12%
74579
7%
23090
42%
23090
12%
57075

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
22%
760
13%
2649
5%
757
32%
757
11%
1998
January11th to 20thNight
21%
736
11%
2574
4%
736
30%
736
8%
2073
January21st to endNight
20%
792
14%
2704
4%
792
32%
792
11%
1983
February1st to 10thNight
21%
720
10%
2254
3%
720
30%
720
10%
1758
February11th to 20thNight
17%
703
12%
2100
4%
700
28%
700
11%
1656
February21st to endNight
20%
592
17%
1776
6%
592
33%
592
11%
1371
March1st to 10thNight
25%
720
14%
2160
7%
720
34%
720
14%
1595
March11th to 20thNight
26%
720
13%
2107
5%
720
34%
720
12%
1663
March21st to endNight
28%
792
16%
1980
5%
792
36%
792
16%
1562
April1st to 10thNight
29%
720
13%
1800
5%
720
34%
720
15%
1447
April11th to 20thNight
38%
711
13%
1775
5%
711
41%
711
15%
1429
April21st to endNight
36%
632
13%
1712
6%
632
39%
632
15%
1355
May1st to 10thNight
37%
540
10%
1620
5%
540
40%
540
11%
1312
May11th to 20thNight
34%
478
13%
1540
8%
478
38%
478
12%
1200
May21st to endNight
52%
388
10%
1551
12%
388
54%
388
10%
1178
June1st to 10thNight
46%
360
10%
1440
11%
360
50%
360
10%
1105
June11th to 20thNight
57%
360
11%
1440
13%
360
60%
360
11%
1072
June21st to endNight
58%
360
8%
1440
10%
360
60%
360
10%
1094
July1st to 10thNight
56%
350
7%
1400
10%
350
57%
350
10%
1074
July11th to 20thNight
61%
348
9%
1392
12%
348
62%
348
12%
1040
July21st to endNight
62%
394
12%
1486
13%
372
64%
372
11%
1111
August1st to 10thNight
67%
454
11%
1518
9%
452
69%
452
14%
1144
August11th to 20thNight
59%
710
11%
1774
7%
710
60%
710
16%
1404
August21st to endNight
64%
792
10%
1980
5%
792
65%
792
16%
1588
September1st to 10thNight
51%
720
14%
1800
7%
720
53%
720
17%
1433
September11th to 20thNight
57%
720
18%
1929
12%
720
60%
720
20%
1430
September21st to endNight
44%
720
14%
1980
9%
720
49%
720
15%
1543
October1st to 10thNight
37%
720
12%
1993
8%
720
41%
720
14%
1556
October11th to 20thNight
40%
720
13%
2165
8%
720
47%
720
14%
1648
October21st to endNight
28%
792
10%
2574
5%
792
35%
792
10%
2022
November1st to 10thNight
37%
740
13%
2407
8%
740
44%
740
14%
1800
November11th to 20thNight
28%
760
16%
2470
10%
760
37%
760
12%
1881
November21st to endNight
30%
760
13%
2470
6%
760
38%
760
12%
1866
December1st to 10thNight
25%
760
10%
2645
3%
760
33%
760
9%
2043
December11th to 20thNight
22%
760
13%
3177
3%
759
32%
759
8%
2294
December21st to endNight
22%
827
8%
4797
4%
817
31%
817
5%
3347

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%6%35%5%3445%7%42%
74796
Night
17%7%35%5%3445%7%41%
74948
TransparencyDay
26%38%9%15%10%1
74501
Night
28%38%8%15%10%1
74777
SeeingDay
19%8%25%29%15%3
13968
Night
20%8%29%28%13%2
23141

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
14%6%36%43446%5%44%
1517
11th to 20thDay
16%9%35%5%35%45%6%39%
1464
21st to endDay
16%6%45%435%5%5%7%42%
1647
February1st to 10thDay
18%7%36%43446%7%38%
1705
11th to 20thDay
16%5%35%5%34446%45%
1748
21st to endDay
20%8%345%3445%6%38%
1480
March1st to 10thDay
14%7%35%5%3435%7%45%
1797
11th to 20thDay
15%6%345%345%6%8%42%
1847
21st to endDay
19%7%35%434346%41%
2376
April1st to 10thDay
17%8%35%43445%6%41%
2160
11th to 20thDay
17%6%245%25%45%6%44%
2134
21st to endDay
20%5%2443446%6%42%
2246
May1st to 10thDay
22%8%34433447%38%
2340
11th to 20thDay
18%6%25%43445%7%42%
2370
21st to endDay
14%6%244245%6%9%43%
2725
June1st to 10thDay
17%5%245%345%5%10%39%
2520
11th to 20thDay
14%6%35%445%5%6%9%40%
2520
21st to endDay
11%7%25%4345%5%10%43%
2520
July1st to 10thDay
11%5%25%5%35%6%6%9%44%
2520
11th to 20thDay
10%5%245%35%5%6%9%44%
2520
21st to endDay
13%5%25%5%35%5%7%9%42%
2744
August1st to 10thDay
10%5%245%45%5%7%11%43%
2387
11th to 20thDay
12%5%35%6%345%6%9%43%
2126
21st to endDay
11%5%35%5%345%6%9%44%
2376
September1st to 10thDay
14%5%25%5%3445%8%46%
2160
11th to 20thDay
12%6%34423447%52%
2030
21st to endDay
18%6%25%5%34446%42%
1980
October1st to 10thDay
22%5%2443335%7%43%
1963
11th to 20thDay
15%5%35%43445%8%45%
1793
21st to endDay
19%5%26%5%3445%7%40%
1782
November1st to 10thDay
14%6%345%34335%50%
1671
11th to 20thDay
17%6%24424347%48%
1710
21st to endDay
15%6%34435%5%5%7%44%
1710
December1st to 10thDay
19%6%25%5%35%5%5%8%38%
1530
11th to 20thDay
22%7%24322435%46%
1906
21st to endDay
18%10%48%5%345%46%33%
2772
January1st to 10thNight
17%6%2443445%6%45%
2649
11th to 20thNight
21%7%35%434446%40%
2574
21st to endNight
14%8%35%42445%7%44%
2704
February1st to 10thNight
17%9%36%6%24446%39%
2254
11th to 20thNight
18%8%25%4345%46%40%
2098
21st to endNight
21%5%235%34445%42%
1776
March1st to 10thNight
16%6%25%424447%45%
2150
11th to 20thNight
17%6%25%435%36%6%41%
2106
21st to endNight
16%9%35%433447%41%
1980
April1st to 10thNight
18%7%36%6%34446%39%
1800
11th to 20thNight
18%8%245%33447%42%
1775
21st to endNight
20%7%25%434446%40%
1712
May1st to 10thNight
20%9%35%6%25%5%5%6%33%
1620
11th to 20thNight
19%7%35%5%35%47%7%34%
1539
21st to endNight
19%7%36%5%3447%9%35%
1550
June1st to 10thNight
19%6%345%35%45%8%38%
1440
11th to 20thNight
16%6%24335%5%6%9%40%
1440
21st to endNight
11%6%36%5%36%5%6%9%40%
1440
July1st to 10thNight
11%6%35%6%35%6%8%8%38%
1440
11th to 20thNight
12%7%35%5%25%6%6%9%40%
1440
21st to endNight
12%6%35%5%46%46%8%41%
1574
August1st to 10thNight
6%425%5%46%6%8%10%43%
1528
11th to 20thNight
10%6%36%7%46%6%7%9%37%
1774
21st to endNight
12%5%245%345%7%9%44%
1980
September1st to 10thNight
15%6%25%6%35%45%7%42%
1800
11th to 20thNight
14%5%243235%46%52%
1929
21st to endNight
18%5%25%5%34446%41%
1980
October1st to 10thNight
20%7%36%5%34347%40%
1993
11th to 20thNight
16%6%25%424446%48%
2165
21st to endNight
21%6%35%5%33446%40%
2574
November1st to 10thNight
13%6%35%6%34447%47%
2407
11th to 20thNight
19%6%34423445%46%
2470
21st to endNight
15%425%43436%7%47%
2470
December1st to 10thNight
21%6%35%43445%6%39%
2645
11th to 20thNight
20%7%24424445%43%
3288
21st to endNight
19%9%36%5%34446%38%
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
25%40%10%18%6%
1518
11th to 20thDay
32%42%9%11%6%
1464
21st to endDay
27%38%8%18%9%1
1647
February1st to 10thDay
29%36%9%16%10%1
1705
11th to 20thDay
26%38%9%17%8%2
1757
21st to endDay
31%37%7%13%10%2
1480
March1st to 10thDay
25%38%9%17%10%1
1800
11th to 20thDay
27%38%9%16%9%1
1847
21st to endDay
28%37%6%14%12%2
2376
April1st to 10thDay
26%38%8%14%12%3
2160
11th to 20thDay
27%37%9%14%10%3
2134
21st to endDay
26%38%8%13%12%3
2246
May1st to 10thDay
29%39%7%14%10%1
2340
11th to 20thDay
27%39%7%14%11%2
2374
21st to endDay
23%40%13%14%9%2
2725
June1st to 10thDay
26%39%10%15%8%1
2520
11th to 20thDay
26%40%10%16%7%1
2520
21st to endDay
25%40%12%16%7%1
2520
July1st to 10thDay
23%41%10%15%9%1
2450
11th to 20thDay
23%39%9%18%9%1
2445
21st to endDay
23%41%9%14%11%1
2591
August1st to 10thDay
23%40%13%15%9%
2373
11th to 20thDay
26%39%9%16%10%1
2126
21st to endDay
27%39%9%11%13%1
2376
September1st to 10thDay
24%39%9%13%13%2
2160
11th to 20thDay
20%38%9%17%15%2
2030
21st to endDay
30%37%6%13%13%2
1980
October1st to 10thDay
26%37%8%16%13%1
1963
11th to 20thDay
25%38%10%17%10%1
1793
21st to endDay
30%37%8%15%10%1
1782
November1st to 10thDay
23%41%8%15%12%1
1671
11th to 20thDay
24%40%9%15%9%1
1710
21st to endDay
27%41%9%16%7%1
1710
December1st to 10thDay
27%41%11%14%6%1
1530
11th to 20thDay
30%32%12%11%14%1
1906
21st to endDay
38%29%10%17%6%
2772
January1st to 10thNight
26%40%10%16%8%1
2649
11th to 20thNight
30%42%7%14%6%1
2574
21st to endNight
25%38%9%18%10%1
2704
February1st to 10thNight
30%37%9%14%9%1
2254
11th to 20thNight
30%38%7%15%8%2
2100
21st to endNight
30%37%5%16%11%2
1776
March1st to 10thNight
24%37%10%17%10%2
2160
11th to 20thNight
30%37%8%14%8%2
2107
21st to endNight
28%37%5%14%12%3
1980
April1st to 10thNight
30%37%7%12%12%3
1800
11th to 20thNight
31%36%5%13%13%1
1775
21st to endNight
29%37%6%13%11%4
1712
May1st to 10thNight
33%38%7%11%10%2
1620
11th to 20thNight
29%39%8%11%10%3
1540
21st to endNight
28%40%10%12%9%1
1551
June1st to 10thNight
30%39%9%13%9%1
1440
11th to 20thNight
26%39%11%16%7%
1440
21st to endNight
28%39%11%15%7%
1440
July1st to 10thNight
27%42%11%13%7%1
1400
11th to 20thNight
25%41%9%17%8%1
1392
21st to endNight
24%42%8%15%9%2
1486
August1st to 10thNight
24%41%12%15%8%
1518
11th to 20thNight
28%37%8%17%9%
1774
21st to endNight
27%40%8%15%10%1
1980
September1st to 10thNight
28%38%6%14%12%2
1800
11th to 20thNight
21%38%9%16%15%1
1929
21st to endNight
27%38%6%12%14%2
1980
October1st to 10thNight
29%37%7%15%11%1
1993
11th to 20thNight
27%37%10%17%9%
2165
21st to endNight
31%38%8%14%9%1
2574
November1st to 10thNight
22%41%8%15%11%2
2407
11th to 20thNight
26%39%7%17%9%1
2470
21st to endNight
24%41%9%18%8%
2470
December1st to 10thNight
27%41%11%12%8%1
2645
11th to 20thNight
29%33%10%13%14%1
3288
21st to endNight
37%27%10%18%8%
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%19%31%23%7%1
180
11th to 20thDay
19%24%34%17%6%
166
21st to endDay
21%13%38%20%7%1
204
February1st to 10thDay
25%14%35%21%5%
325
11th to 20thDay
21%16%40%20%3
416
21st to endDay
25%15%33%22%4
346
March1st to 10thDay
16%14%38%26%5%
420
11th to 20thDay
17%11%40%25%6%1
420
21st to endDay
21%11%37%22%7%2
462
April1st to 10thDay
22%10%35%23%10%1
420
11th to 20thDay
19%10%29%31%10%1
412
21st to endDay
25%9%29%29%7%2
420
May1st to 10thDay
28%7%30%25%9%2
423
11th to 20thDay
21%8%24%33%13%1
447
21st to endDay
20%218%30%25%5%
485
June1st to 10thDay
17%320%36%20%3
450
11th to 20thDay
16%420%38%18%4
450
21st to endDay
14%317%39%23%4
450
July1st to 10thDay
14%411%38%26%7%
445
11th to 20thDay
11%39%40%29%9%
444
21st to endDay
14%215%40%26%3
488
August1st to 10thDay
11%213%39%30%5%
446
11th to 20thDay
13%310%38%29%8%
439
21st to endDay
12%415%34%25%9%
495
September1st to 10thDay
20%319%26%23%9%
450
11th to 20thDay
14%320%32%20%11%
450
21st to endDay
22%5%23%30%17%3
450
October1st to 10thDay
26%6%19%23%19%7%
450
11th to 20thDay
15%7%28%30%15%3
446
21st to endDay
23%11%31%22%12%1
396
November1st to 10thDay
17%8%26%32%15%3
365
11th to 20thDay
19%16%29%25%11%
370
21st to endDay
16%14%32%26%11%1
370
December1st to 10thDay
19%15%34%25%7%1
190
11th to 20thDay
23%23%29%20%4
180
21st to endDay
25%12%38%15%8%2
198
January1st to 10thNight
20%14%41%20%5%
760
11th to 20thNight
26%15%32%23%4
736
21st to endNight
20%13%43%21%3
792
February1st to 10thNight
21%13%39%25%2
720
11th to 20thNight
25%13%41%18%2
703
21st to endNight
23%13%39%21%4
592
March1st to 10thNight
19%13%37%24%6%
720
11th to 20thNight
20%12%38%23%6%1
720
21st to endNight
20%8%38%25%8%1
792
April1st to 10thNight
23%8%35%26%8%
720
11th to 20thNight
21%6%30%32%10%
711
21st to endNight
24%430%33%9%1
632
May1st to 10thNight
24%5%25%31%13%2
540
11th to 20thNight
22%330%34%11%
478
21st to endNight
21%312%37%24%2
389
June1st to 10thNight
21%319%32%23%2
360
11th to 20thNight
18%215%43%21%2
360
21st to endNight
14%218%41%24%1
360
July1st to 10thNight
13%5%13%41%25%3
350
11th to 20thNight
13%113%41%28%4
348
21st to endNight
12%415%45%23%2
394
August1st to 10thNight
8%213%46%29%2
454
11th to 20thNight
13%214%37%30%4
710
21st to endNight
14%211%37%28%7%
792
September1st to 10thNight
17%220%33%23%5%
720
11th to 20thNight
17%317%32%23%8%
720
21st to endNight
23%421%30%19%3
720
October1st to 10thNight
24%6%25%21%19%4
720
11th to 20thNight
20%8%26%29%16%1
720
21st to endNight
25%9%30%25%10%1
792
November1st to 10thNight
16%8%32%27%14%2
740
11th to 20thNight
22%12%32%23%10%1
760
21st to endNight
17%15%34%25%8%1
760
December1st to 10thNight
24%14%32%22%6%1
760
11th to 20thNight
23%15%35%23%4
760
21st to endNight
23%13%37%23%4
836
Page generated at 2024-01-11 13:31:59. Version ac07

Copyright 2024 Attilla Danko


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