Richard S. Perkin Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Richard S. Perkin Observatory clear sky chart from 2005-11-05 to 2018-02-13.

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
30%
15453
12%
48813
8%
15421
35%
15421
16%
35118

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
12%
779
7%
2716
4%
776
17%
776
6%
2242
January16th to endNight
13%
832
8%
2746
3%
832
19%
832
7%
2248
February1st to 15thNight
11%
752
7%
2444
2%
750
18%
750
7%
1980
February16th to endNight
16%
631
10%
1957
4%
631
23%
631
11%
1509
March1st to 15thNight
20%
720
11%
2042
6%
720
26%
720
13%
1582
March16th to endNight
24%
768
15%
2070
7%
768
30%
768
19%
1531
April1st to 15thNight
24%
718
13%
1796
4%
718
28%
718
19%
1349
April16th to endNight
33%
681
18%
1761
8%
681
38%
681
27%
1200
May1st to 15thNight
40%
414
17%
1494
13%
414
47%
414
18%
994
May16th to endNight
46%
374
16%
1497
18%
374
52%
374
23%
892
June1st to 15thNight
43%
360
13%
1440
14%
360
50%
360
18%
907
June16th to endNight
51%
360
12%
1440
15%
360
57%
360
24%
846
July1st to 15thNight
60%
340
14%
1360
19%
340
64%
340
27%
760
July16th to endNight
58%
400
15%
1440
17%
376
61%
376
26%
834
August1st to 15thNight
55%
539
15%
1609
10%
536
59%
536
33%
978
August16th to endNight
59%
708
21%
1854
13%
708
61%
708
36%
1153
September1st to 15thNight
50%
720
18%
1800
10%
720
54%
720
30%
1206
September16th to endNight
51%
717
23%
1974
17%
717
54%
717
31%
1261
October1st to 15thNight
35%
720
15%
2160
13%
720
39%
720
20%
1489
October16th to endNight
20%
768
10%
2327
5%
768
27%
768
13%
1752
November1st to 15thNight
27%
760
14%
2514
11%
760
33%
760
16%
1772
November16th to endNight
21%
780
12%
2730
7%
780
28%
780
11%
2014
December1st to 15thNight
14%
780
6%
2730
2%
780
19%
780
7%
2167
December16th to endNight
11%
832
5%
2912
1%
832
15%
832
5%
2452

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
14%9%47%7%35%45%7%30%
49233
Night
15%9%47%6%35%45%6%31%
48986
Cloud CoverDay
14%9%47%6%35%5%5%7%30%
49243
Night
15%9%47%6%35%45%6%31%
48991
TransparencyDay
52%6%12%17%9%
48924
Night
52%6%13%17%9%
48813
SeeingDay
19%13%28%21%12%4
5935
Night
21%14%29%23%10%1
15456

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
15%12%6%12%10%47%5%4415%
1552
16th to endDay
11%14%6%12%11%5%7%445%15%
1827
February1st to 15thDay
14%14%8%13%10%46%44413%
1683
16th to endDay
17%13%5%10%9%47%345%18%
1515
March1st to 15thDay
16%12%6%10%8%36%445%21%
1906
16th to endDay
16%10%47%6%35%446%28%
2154
April1st to 15thDay
18%10%37%5%35%436%30%
2152
16th to endDay
15%7%36%424347%37%
2208
May1st to 15thDay
14%6%36%7%35%448%34%
2457
16th to endDay
13%6%25%5%35%5%6%7%38%
2618
June1st to 15thDay
18%6%36%5%345%5%8%32%
2520
16th to endDay
10%5%25%5%45%5%7%9%36%
2520
July1st to 15thDay
8%5%25%6%35%5%6%9%39%
2520
16th to endDay
10%436%7%47%6%7%8%34%
2627
August1st to 15thDay
10%5%25%6%46%6%7%9%33%
2340
16th to endDay
12%5%25%6%46%5%6%7%35%
2336
September1st to 15thDay
15%6%25%5%3445%7%39%
2160
16th to endDay
13%6%346%3445%7%40%
1984
October1st to 15thDay
17%8%36%5%3435%6%35%
1800
16th to endDay
22%9%37%7%4446%6%23%
1896
November1st to 15thDay
13%11%38%6%26%45%6%30%
1674
16th to endDay
17%11%48%6%26%5%5%7%24%
1560
December1st to 15thDay
15%15%6%10%8%35%445%19%
1560
16th to endDay
18%16%7%12%7%35%445%13%
1664
January1st to 15thNight
17%15%5%10%8%46%5%5%5%16%
2716
16th to endNight
14%13%6%9%9%5%7%446%17%
2746
February1st to 15thNight
15%13%7%12%7%45%44419%
2442
16th to endNight
14%10%5%12%7%45%5%5%6%22%
1957
March1st to 15thNight
18%10%5%8%7%35%445%25%
2030
16th to endNight
17%9%47%5%24446%33%
2070
April1st to 15thNight
19%7%36%6%445%36%31%
1796
16th to endNight
16%6%25%5%2345%6%41%
1761
May1st to 15thNight
16%6%26%5%35%5%47%35%
1494
16th to endNight
10%5%25%5%35%45%9%42%
1495
June1st to 15thNight
15%6%26%4335%48%38%
1440
16th to endNight
9%425%5%35%5%6%9%42%
1440
July1st to 15thNight
5%425%436%5%6%8%46%
1440
16th to endNight
9%4335%35%5%5%9%44%
1538
August1st to 15thNight
8%425%4245%6%8%46%
1620
16th to endNight
8%425%5%2445%7%49%
1854
September1st to 15thNight
13%5%2443445%7%43%
1800
16th to endNight
12%5%144345%6%7%44%
1974
October1st to 15thNight
20%7%25%434446%36%
2160
16th to endNight
24%9%37%6%24446%26%
2327
November1st to 15thNight
17%9%36%6%3435%7%31%
2514
16th to endNight
16%12%47%6%35%45%6%27%
2730
December1st to 15thNight
19%13%48%6%36%5%6%6%19%
2730
16th to endNight
20%15%6%9%8%45%45%5%13%
2912

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
15%14%6%11%8%5%8%5%5%414%
1552
16th to endDay
11%14%7%11%11%5%6%5%45%16%
1827
February1st to 15thDay
16%14%7%12%10%46%44414%
1683
16th to endDay
17%13%5%10%9%46%445%19%
1515
March1st to 15thDay
16%12%6%9%8%36%5%45%21%
1917
16th to endDay
15%10%48%6%35%447%28%
2153
April1st to 15thDay
18%9%37%5%34446%31%
2152
16th to endDay
15%8%35%5%24447%38%
2208
May1st to 15thDay
14%6%36%6%35%448%34%
2457
16th to endDay
13%6%25%5%245%5%8%38%
2618
June1st to 15thDay
18%6%36%5%25%5%5%7%33%
2520
16th to endDay
11%5%25%5%35%5%7%10%36%
2520
July1st to 15thDay
9%425%6%35%6%5%9%40%
2520
16th to endDay
10%5%35%6%46%5%7%9%34%
2627
August1st to 15thDay
11%5%25%6%46%5%7%9%34%
2340
16th to endDay
11%6%25%6%46%6%6%8%36%
2336
September1st to 15thDay
15%5%25%434446%39%
2160
16th to endDay
13%6%25%5%2446%6%41%
1984
October1st to 15thDay
17%9%35%42445%6%35%
1800
16th to endDay
22%10%36%5%45%45%6%24%
1896
November1st to 15thDay
14%10%47%6%45%45%6%31%
1674
16th to endDay
17%11%5%7%5%35%5%46%25%
1560
December1st to 15thDay
15%16%5%11%7%35%445%19%
1560
16th to endDay
19%15%7%11%8%35%5%4414%
1664
January1st to 15thNight
17%15%411%8%45%5%45%15%
2716
16th to endNight
14%14%6%10%9%46%5%45%17%
2746
February1st to 15thNight
15%14%8%11%8%35%445%19%
2435
16th to endNight
14%11%5%11%7%46%5%5%6%22%
1957
March1st to 15thNight
19%11%48%8%35%345%26%
2042
16th to endNight
17%9%47%5%34446%32%
2070
April1st to 15thNight
19%9%36%6%345%5%5%31%
1796
16th to endNight
16%6%35%5%33345%42%
1761
May1st to 15thNight
16%6%25%6%246%5%5%36%
1494
16th to endNight
11%5%25%6%345%5%9%41%
1495
June1st to 15thNight
16%5%26%5%15%45%7%38%
1440
16th to endNight
10%325%435%46%9%43%
1440
July1st to 15thNight
6%325%5%35%5%5%10%45%
1440
16th to endNight
10%42443446%9%44%
1538
August1st to 15thNight
8%4244245%5%8%47%
1620
16th to endNight
10%4235%2445%7%49%
1854
September1st to 15thNight
14%425%43445%7%43%
1800
16th to endNight
12%414325%5%6%7%44%
1974
October1st to 15thNight
19%8%35%5%33446%35%
2160
16th to endNight
24%9%36%6%33446%26%
2327
November1st to 15thNight
16%11%37%5%24446%32%
2514
16th to endNight
16%13%37%6%35%5%5%6%27%
2730
December1st to 15thNight
19%14%48%7%36%5%5%5%19%
2730
16th to endNight
20%15%6%10%8%45%445%14%
2912

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
70%5%10%9%3
1553
16th to endDay
69%5%13%8%3
1827
February1st to 15thDay
73%5%8%8%3
1685
16th to endDay
67%410%12%4
1515
March1st to 15thDay
63%5%12%12%5%
1917
16th to endDay
56%5%9%18%9%
2154
April1st to 15thDay
54%5%10%17%9%1
2152
16th to endDay
46%5%7%20%18%2
2208
May1st to 15thDay
48%6%12%20%11%1
2457
16th to endDay
43%7%14%20%12%1
2622
June1st to 15thDay
49%7%11%20%10%
2520
16th to endDay
40%10%14%22%11%
2520
July1st to 15thDay
38%9%12%24%13%1
2371
16th to endDay
43%9%15%20%9%
2462
August1st to 15thDay
44%8%15%20%10%
2327
16th to endDay
42%8%13%23%10%
2336
September1st to 15thDay
44%6%10%23%13%1
2160
16th to endDay
42%6%10%23%15%1
1984
October1st to 15thDay
48%5%13%18%12%
1800
16th to endDay
58%6%15%14%3
1896
November1st to 15thDay
52%7%14%15%8%1
1674
16th to endDay
56%6%16%16%3
1560
December1st to 15thDay
67%5%13%10%2
1560
16th to endDay
72%6%10%6%2
1664
January1st to 15thNight
68%6%10%9%4
2716
16th to endNight
67%6%11%11%3
2746
February1st to 15thNight
67%5%10%12%4
2444
16th to endNight
61%415%13%4
1957
March1st to 15thNight
60%412%17%4
2042
16th to endNight
53%411%17%12%
2070
April1st to 15thNight
52%5%11%17%10%1
1796
16th to endNight
42%411%21%16%2
1761
May1st to 15thNight
45%7%10%19%13%2
1494
16th to endNight
38%7%15%22%14%2
1497
June1st to 15thNight
43%7%14%23%11%
1440
16th to endNight
36%7%15%23%15%1
1440
July1st to 15thNight
33%7%15%24%17%2
1360
16th to endNight
34%7%14%25%14%2
1440
August1st to 15thNight
32%7%17%31%10%
1609
16th to endNight
31%7%14%30%14%1
1854
September1st to 15thNight
39%5%14%22%14%2
1800
16th to endNight
36%6%12%26%16%1
1974
October1st to 15thNight
48%5%13%18%13%
2160
16th to endNight
58%5%16%14%4
2327
November1st to 15thNight
51%5%14%17%8%2
2514
16th to endNight
57%5%14%16%5%
2730
December1st to 15thNight
64%7%14%11%2
2730
16th to endNight
71%5%11%9%1
2912

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
18%27%37%10%5%
90
16th to endDay
23%23%41%10%1
134
February1st to 15thDay
26%37%31%4
126
16th to endDay
25%20%37%15%1
174
March1st to 15thDay
24%21%26%22%5%
270
16th to endDay
25%19%29%17%7%1
288
April1st to 15thDay
28%15%30%15%8%1
270
16th to endDay
21%14%29%19%11%4
270
May1st to 15thDay
23%18%24%18%11%3
288
16th to endDay
13%12%35%20%14%3
331
June1st to 15thDay
20%9%30%26%11%2
315
16th to endDay
14%9%34%26%11%3
315
July1st to 15thDay
10%329%32%18%5%
305
16th to endDay
10%6%29%27%21%5%
326
August1st to 15thDay
14%328%24%17%11%
313
16th to endDay
13%420%27%18%16%
332
September1st to 15thDay
16%8%18%22%21%12%
315
16th to endDay
15%8%20%22%18%14%
314
October1st to 15thDay
21%8%26%22%15%5%
315
16th to endDay
28%17%30%17%6%
330
November1st to 15thDay
25%9%30%23%9%1
238
16th to endDay
24%27%26%18%2
90
December1st to 15thDay
23%17%36%15%42
90
16th to endDay
34%28%29%8%
96
January1st to 15thNight
26%23%33%14%2
780
16th to endNight
24%19%35%18%1
832
February1st to 15thNight
23%22%35%16%2
753
16th to endNight
23%22%33%17%3
631
March1st to 15thNight
25%21%28%21%3
720
16th to endNight
22%16%31%21%7%
768
April1st to 15thNight
24%15%31%24%3
718
16th to endNight
19%11%31%26%10%1
681
May1st to 15thNight
20%7%26%34%10%
414
16th to endNight
12%6%28%33%18%
375
June1st to 15thNight
17%8%24%32%16%
360
16th to endNight
12%5%25%42%12%1
360
July1st to 15thNight
9%121%43%22%1
340
16th to endNight
10%224%39%20%3
400
August1st to 15thNight
9%227%32%23%4
539
16th to endNight
12%418%34%27%1
708
September1st to 15thNight
17%6%20%30%21%3
720
16th to endNight
13%8%21%23%25%6%
717
October1st to 15thNight
24%9%25%21%16%1
720
16th to endNight
29%13%30%21%4
768
November1st to 15thNight
22%15%30%22%7%1
760
16th to endNight
23%21%28%18%6%1
780
December1st to 15thNight
27%21%32%15%2
780
16th to endNight
29%21%32%14%2
832
Page generated at 2018-02-13 20:46:06. Version ac04

Copyright 2018 A. Danko


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