Photon's End Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Photon's End Observatory clear sky chart from 2005-11-05 to 2017-08-12.

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
33%
14503
14%
46487
9%
14471
39%
14471
18%
32646

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
19%
720
8%
2506
5%
716
24%
716
8%
2004
January16th to endNight
25%
768
12%
2653
7%
768
32%
768
12%
1958
February1st to 15thNight
23%
704
12%
2287
6%
701
30%
701
12%
1744
February16th to endNight
26%
631
15%
1940
8%
631
36%
631
15%
1451
March1st to 15thNight
22%
720
14%
2112
8%
720
30%
720
15%
1570
March16th to endNight
33%
768
21%
2025
10%
768
41%
768
24%
1387
April1st to 15thNight
26%
718
16%
1796
6%
718
32%
718
22%
1318
April16th to endNight
32%
643
18%
1723
8%
643
38%
643
23%
1197
May1st to 15thNight
35%
360
18%
1440
16%
360
44%
360
17%
934
May16th to endNight
39%
375
14%
1497
12%
374
50%
374
20%
934
June1st to 15thNight
41%
360
10%
1440
11%
360
48%
360
17%
950
June16th to endNight
45%
360
9%
1440
13%
360
50%
360
20%
890
July1st to 15thNight
57%
340
14%
1360
21%
340
61%
340
28%
748
July16th to endNight
56%
376
14%
1418
17%
354
60%
354
27%
792
August1st to 15thNight
54%
414
15%
1463
13%
412
59%
412
25%
876
August16th to endNight
55%
657
19%
1707
10%
657
58%
657
37%
1050
September1st to 15thNight
49%
660
16%
1650
8%
660
51%
660
30%
1121
September16th to endNight
49%
657
22%
1790
14%
657
53%
657
32%
1145
October1st to 15thNight
35%
660
19%
1980
12%
660
44%
660
22%
1359
October16th to endNight
29%
704
13%
2210
7%
704
36%
704
15%
1630
November1st to 15thNight
30%
700
18%
2322
12%
700
40%
700
18%
1603
November16th to endNight
22%
720
12%
2520
7%
720
28%
720
11%
1889
December1st to 15thNight
21%
720
8%
2520
4%
720
26%
720
10%
1975
December16th to endNight
17%
768
10%
2688
4%
768
25%
768
9%
2121

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
18%8%36%5%3445%6%32%
47495
Night
18%9%36%5%34445%33%
46656
Cloud CoverDay
18%8%36%5%34446%33%
47504
Night
18%9%36%5%34446%33%
46662
TransparencyDay
51%312%21%10%1
47182
Night
52%311%21%10%1
46487
SeeingDay
22%8%26%24%13%4
5342
Night
23%8%26%29%10%
14503

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
23%14%6%8%6%2343421%
1432
16th to endDay
15%15%48%6%35%5%45%24%
1569
February1st to 15thDay
14%13%5%11%6%4445%5%24%
1575
16th to endDay
18%13%48%6%345%35%25%
1532
March1st to 15thDay
18%9%47%6%46%44328%
1838
16th to endDay
17%6%35%5%23446%40%
2199
April1st to 15thDay
23%9%35%323335%33%
2152
16th to endDay
21%7%35%5%2434437%
2245
May1st to 15thDay
20%8%36%5%25%446%32%
2511
16th to endDay
18%5%25%6%4445%6%34%
2618
June1st to 15thDay
22%6%25%6%3445%7%30%
2520
16th to endDay
18%6%25%5%35%6%6%7%31%
2520
July1st to 15thDay
13%4245%36%6%7%8%37%
2520
16th to endDay
12%5%26%5%35%5%7%9%36%
2654
August1st to 15thDay
12%6%26%6%35%5%5%7%38%
2399
16th to endDay
10%425%435%5%5%9%43%
2132
September1st to 15thDay
16%4245%2435%7%41%
1980
16th to endDay
16%5%25%423346%45%
1839
October1st to 15thDay
21%7%26%434446%35%
1650
16th to endDay
27%8%36%8%3333426%
1661
November1st to 15thDay
17%8%45%5%4446%6%34%
1533
16th to endDay
24%12%37%6%24345%25%
1440
December1st to 15thDay
24%13%5%8%6%44445%18%
1440
16th to endDay
24%15%5%7%6%3434420%
1536
January1st to 15thNight
19%16%6%9%7%4434419%
2506
16th to endNight
14%15%5%8%6%35%345%26%
2653
February1st to 15thNight
13%13%6%11%6%45%5%45%23%
2285
16th to endNight
17%11%5%7%7%35%435%28%
1940
March1st to 15thNight
19%12%47%6%2334429%
2099
16th to endNight
16%8%36%5%3333441%
2025
April1st to 15thNight
25%7%34424335%35%
1796
16th to endNight
19%7%26%423345%38%
1723
May1st to 15thNight
22%7%35%423445%36%
1440
16th to endNight
17%6%35%425%45%6%37%
1495
June1st to 15thNight
19%6%25%6%345%6%6%32%
1440
16th to endNight
17%5%25%4245%6%7%37%
1440
July1st to 15thNight
10%3245%345%5%8%46%
1440
16th to endNight
8%5%24435%5%6%8%45%
1514
August1st to 15thNight
10%6%34425%5%6%9%40%
1473
16th to endNight
10%31443436%7%48%
1707
September1st to 15thNight
15%5%26%6%34346%41%
1650
16th to endNight
17%425%313325%48%
1790
October1st to 15thNight
19%7%35%5%34445%37%
1980
16th to endNight
24%9%35%5%24346%27%
2210
November1st to 15thNight
21%7%36%5%24346%33%
2322
16th to endNight
23%10%47%6%3444425%
2520
December1st to 15thNight
23%15%46%6%3443421%
2520
16th to endNight
25%15%5%8%5%2444420%
2688

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
24%14%6%8%6%3333420%
1432
16th to endDay
14%15%5%9%6%35%445%24%
1569
February1st to 15thDay
14%13%411%7%35%445%25%
1575
16th to endDay
19%12%5%7%6%35%445%25%
1532
March1st to 15thDay
18%9%38%6%36%44430%
1848
16th to endDay
17%6%345%23446%41%
2198
April1st to 15thDay
23%10%35%423235%33%
2152
16th to endDay
21%7%35%424335%36%
2245
May1st to 15thDay
19%7%36%5%33445%36%
2511
16th to endDay
17%5%25%6%34446%38%
2618
June1st to 15thDay
22%6%25%6%345%47%30%
2520
16th to endDay
18%6%25%5%36%6%5%8%31%
2520
July1st to 15thDay
13%5%245%36%5%7%9%37%
2520
16th to endDay
12%5%26%5%35%5%7%9%36%
2654
August1st to 15thDay
17%5%26%5%35%5%6%6%35%
2399
16th to endDay
14%424425%5%5%8%41%
2132
September1st to 15thDay
16%5%25%5%33448%40%
1980
16th to endDay
15%6%24413346%45%
1839
October1st to 15thDay
21%6%35%5%34446%34%
1650
16th to endDay
27%8%36%6%3433426%
1661
November1st to 15thDay
17%8%35%6%445%5%7%33%
1533
16th to endDay
24%11%46%6%23445%26%
1440
December1st to 15thDay
24%14%48%6%34445%18%
1440
16th to endDay
24%15%5%8%5%25%33320%
1536
January1st to 15thNight
20%16%6%9%7%4443419%
2506
16th to endNight
15%15%5%8%6%25%445%25%
2653
February1st to 15thNight
13%13%6%11%6%46%445%23%
2278
16th to endNight
18%11%47%7%25%44428%
1940
March1st to 15thNight
19%11%46%6%2334432%
2112
16th to endNight
15%8%35%5%2334344%
2025
April1st to 15thNight
25%9%2442333435%
1796
16th to endNight
19%8%26%423346%38%
1723
May1st to 15thNight
22%7%26%423346%37%
1440
16th to endNight
17%6%2443445%6%39%
1495
June1st to 15thNight
19%7%25%5%345%5%8%31%
1440
16th to endNight
17%5%25%4245%6%7%37%
1440
July1st to 15thNight
10%3245%345%6%8%45%
1440
16th to endNight
8%4245%346%5%9%44%
1514
August1st to 15thNight
13%6%244245%6%9%39%
1473
16th to endNight
13%32433346%6%47%
1707
September1st to 15thNight
14%5%26%6%34346%41%
1650
16th to endNight
17%5%23322335%49%
1790
October1st to 15thNight
19%8%25%435%446%37%
1980
16th to endNight
25%9%35%5%33346%27%
2210
November1st to 15thNight
21%8%26%5%34346%33%
2322
16th to endNight
23%10%48%5%35%44425%
2520
December1st to 15thNight
23%15%5%6%5%345%4421%
2520
16th to endNight
25%15%5%7%5%2444420%
2688

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
67%27%15%5%
1433
16th to endDay
60%411%14%8%
1569
February1st to 15thDay
61%212%18%4
1577
16th to endDay
60%39%16%9%1
1532
March1st to 15thDay
59%311%16%7%1
1848
16th to endDay
46%29%19%16%5%
2199
April1st to 15thDay
53%27%20%13%2
2152
16th to endDay
50%26%21%14%4
2245
May1st to 15thDay
52%37%21%13%2
2511
16th to endDay
49%411%20%11%1
2622
June1st to 15thDay
53%411%21%8%
2520
16th to endDay
48%5%14%21%10%
2520
July1st to 15thDay
39%415%28%12%
2371
16th to endDay
43%5%17%23%10%
2487
August1st to 15thDay
44%416%24%9%
2385
16th to endDay
37%417%28%11%
2132
September1st to 15thDay
42%312%29%11%
1980
16th to endDay
39%413%31%10%
1839
October1st to 15thDay
50%213%22%10%
1650
16th to endDay
62%212%15%6%
1661
November1st to 15thDay
50%315%21%8%
1533
16th to endDay
61%313%14%5%
1440
December1st to 15thDay
68%312%13%2
1440
16th to endDay
69%29%12%5%
1536
January1st to 15thNight
68%39%13%5%
2506
16th to endNight
60%39%18%7%
2653
February1st to 15thNight
62%39%18%5%
2287
16th to endNight
58%38%19%9%
1940
March1st to 15thNight
58%29%19%8%1
2112
16th to endNight
47%29%20%16%4
2025
April1st to 15thNight
52%37%19%16%1
1796
16th to endNight
48%38%19%18%3
1723
May1st to 15thNight
49%37%19%15%4
1440
16th to endNight
45%311%22%14%2
1497
June1st to 15thNight
49%411%23%9%1
1440
16th to endNight
43%5%13%21%15%
1440
July1st to 15thNight
33%5%13%30%15%1
1360
16th to endNight
35%415%27%15%
1418
August1st to 15thNight
37%6%18%24%12%
1463
16th to endNight
34%317%33%11%
1707
September1st to 15thNight
43%312%28%11%
1650
16th to endNight
39%310%36%10%
1790
October1st to 15thNight
49%310%24%11%
1980
16th to endNight
58%213%19%6%
2210
November1st to 15thNight
52%313%19%10%
2322
16th to endNight
61%311%17%4
2520
December1st to 15thNight
65%313%14%3
2520
16th to endNight
67%310%13%5%
2688

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
30%6%28%26%6%1
60
16th to endDay
31%5%30%26%41
69
February1st to 15thDay
35%10%38%14%1
90
16th to endDay
34%12%26%20%6%
191
March1st to 15thDay
25%10%33%21%8%
270
16th to endDay
22%11%28%23%10%3
288
April1st to 15thDay
27%16%27%20%8%
270
16th to endDay
24%11%25%22%12%3
270
May1st to 15thDay
29%7%27%20%10%4
288
16th to endDay
21%11%30%19%14%2
331
June1st to 15thDay
27%5%27%25%11%2
315
16th to endDay
23%6%25%26%16%2
315
July1st to 15thDay
13%328%30%17%5%
305
16th to endDay
12%223%34%20%6%
326
August1st to 15thDay
12%5%20%31%21%8%
297
16th to endDay
10%420%31%21%12%
268
September1st to 15thDay
19%320%20%20%15%
255
16th to endDay
20%6%21%24%20%7%
254
October1st to 15thDay
21%9%24%23%17%2
255
16th to endDay
34%9%22%22%9%
254
November1st to 15thDay
19%9%27%27%13%2
187
16th to endDay
33%10%20%30%6%
60
December1st to 15thDay
28%10%30%25%6%
60
16th to endDay
43%12%35%7%
64
January1st to 15thNight
28%12%29%23%5%
720
16th to endNight
22%9%30%28%8%
768
February1st to 15thNight
19%12%33%27%6%
704
16th to endNight
25%9%30%28%4
631
March1st to 15thNight
26%12%30%27%3
720
16th to endNight
21%11%28%28%10%
768
April1st to 15thNight
29%7%30%26%5%
718
16th to endNight
25%11%26%27%8%
643
May1st to 15thNight
27%6%23%31%9%1
360
16th to endNight
20%5%28%33%10%1
375
June1st to 15thNight
21%325%37%11%
360
16th to endNight
18%322%38%14%1
360
July1st to 15thNight
9%324%45%17%
340
16th to endNight
9%221%43%21%1
376
August1st to 15thNight
16%316%36%24%2
414
16th to endNight
11%419%38%24%1
657
September1st to 15thNight
18%221%34%20%1
660
16th to endNight
21%421%28%21%2
657
October1st to 15thNight
23%8%25%28%13%
660
16th to endNight
31%8%23%27%8%
704
November1st to 15thNight
26%8%26%24%13%
700
16th to endNight
29%14%24%22%9%
720
December1st to 15thNight
31%11%28%24%3
720
16th to endNight
33%8%29%21%5%1
768
Page generated at 2017-08-13 14:16:52. Version ac04

Copyright 2017 A. Danko


Photon's End Observatory Clear Sky Chart | Charts Home