Abbey Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Abbey Ridge Observatory clear sky chart from 2005-11-05 to 2017-09-10.

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
19%
15178
12%
46646
5%
15133
27%
15133
12%
34480

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
11%
750
11%
2506
2%
746
22%
746
7%
1902
January16th to endNight
11%
771
11%
2518
2%
771
22%
771
8%
1919
February1st to 15thNight
10%
704
7%
2286
1%
701
18%
701
7%
1777
February16th to endNight
12%
631
9%
2030
2%
631
20%
631
7%
1577
March1st to 15thNight
15%
720
13%
1988
3%
720
24%
720
12%
1500
March16th to endNight
16%
768
14%
2112
4%
768
24%
768
12%
1575
April1st to 15thNight
13%
541
13%
1798
5%
541
24%
541
10%
1334
April16th to endNight
17%
540
14%
1643
5%
540
25%
540
14%
1193
May1st to 15thNight
20%
540
10%
1521
4%
540
25%
540
11%
1171
May16th to endNight
20%
561
10%
1496
3%
560
26%
560
15%
1129
June1st to 15thNight
18%
540
6%
1440
2%
540
22%
540
13%
1149
June16th to endNight
25%
414
7%
1314
3%
414
29%
414
13%
1001
July1st to 15thNight
33%
465
7%
1315
4%
465
36%
465
19%
940
July16th to endNight
29%
565
9%
1465
7%
532
33%
532
15%
1141
August1st to 15thNight
37%
539
12%
1608
8%
535
40%
535
18%
1147
August16th to endNight
36%
573
17%
1791
9%
573
43%
573
20%
1198
September1st to 15thNight
31%
525
16%
1749
10%
525
39%
525
19%
1142
September16th to endNight
33%
638
23%
1834
13%
638
41%
638
24%
1190
October1st to 15thNight
25%
660
19%
1980
8%
660
35%
660
19%
1326
October16th to endNight
16%
704
14%
2112
4%
704
25%
704
15%
1519
November1st to 15thNight
23%
729
13%
2412
8%
729
29%
729
14%
1733
November16th to endNight
16%
750
13%
2520
4%
750
26%
750
10%
1849
December1st to 15thNight
9%
750
10%
2520
1%
750
20%
750
7%
1943
December16th to endNight
8%
800
9%
2688
1%
800
17%
800
6%
2125

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
22%9%46%5%34446%28%
47977
Night
21%9%36%5%3445%6%28%
46823
TransparencyDay
55%6%10%17%8%
47672
Night
54%6%11%18%8%
46646
SeeingDay
26%23%26%15%6%1
7495
Night
24%25%25%17%6%
15178

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
18%14%5%7%6%36%5%6%5%20%
1432
16th to endDay
18%11%5%8%7%36%45%6%21%
1704
February1st to 15thDay
17%13%5%9%7%45%5%45%20%
1575
16th to endDay
13%14%7%10%6%34436%24%
1443
March1st to 15thDay
21%11%48%7%35%33426%
1960
16th to endDay
17%11%5%7%6%24436%29%
2112
April1st to 15thDay
24%13%36%5%33345%25%
2150
16th to endDay
23%9%35%424346%30%
2316
May1st to 15thDay
27%9%47%6%2345%6%24%
2429
16th to endDay
25%9%45%5%24446%27%
2618
June1st to 15thDay
29%9%47%5%34335%22%
2520
16th to endDay
27%8%35%434447%26%
2652
July1st to 15thDay
22%7%343245%5%8%32%
2547
16th to endDay
25%7%36%5%3445%7%26%
2602
August1st to 15thDay
20%6%36%6%245%6%7%29%
2340
16th to endDay
17%6%2442446%8%40%
2411
September1st to 15thDay
22%6%24433447%37%
2099
16th to endDay
17%6%24424246%44%
1796
October1st to 15thDay
22%5%2442335%7%37%
1650
16th to endDay
24%8%36%6%3445%6%26%
1760
November1st to 15thDay
24%9%37%5%23346%27%
1445
16th to endDay
22%11%38%6%36%346%23%
1440
December1st to 15thDay
27%9%5%9%5%35%446%18%
1440
16th to endDay
24%13%5%8%6%34445%18%
1536
January1st to 15thNight
18%9%38%7%35%5%6%7%23%
2506
16th to endNight
17%11%5%7%6%35%5%6%7%21%
2518
February1st to 15thNight
18%11%38%6%47%6%6%6%19%
2285
16th to endNight
15%12%5%8%8%46%5%46%22%
2030
March1st to 15thNight
20%10%47%5%35%5%46%27%
1976
16th to endNight
18%9%46%6%33445%30%
2112
April1st to 15thNight
25%10%35%5%3335%5%27%
1798
16th to endNight
24%8%36%43335%5%31%
1643
May1st to 15thNight
28%8%4442445%6%25%
1521
16th to endNight
22%8%46%5%24448%29%
1494
June1st to 15thNight
30%10%46%433346%24%
1440
16th to endNight
25%10%45%5%24446%26%
1314
July1st to 15thNight
20%9%3442445%9%31%
1395
16th to endNight
22%9%35%4345%46%27%
1565
August1st to 15thNight
19%8%25%5%3445%5%35%
1620
16th to endNight
17%5%35%5%24347%39%
1791
September1st to 15thNight
18%6%25%42435%6%39%
1749
16th to endNight
19%5%24323346%43%
1834
October1st to 15thNight
20%6%25%433347%38%
1980
16th to endNight
25%7%245%24446%33%
2112
November1st to 15thNight
24%8%35%5%34447%30%
2412
16th to endNight
23%7%36%5%35%35%5%29%
2520
December1st to 15thNight
24%10%37%6%3445%6%22%
2520
16th to endNight
25%11%48%6%35%5%36%19%
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
60%7%12%13%4
1433
16th to endDay
58%7%9%15%8%
1704
February1st to 15thDay
63%7%9%12%6%1
1578
16th to endDay
61%5%9%14%6%1
1443
March1st to 15thDay
61%47%15%9%1
1971
16th to endDay
56%5%8%18%9%1
2112
April1st to 15thDay
59%5%7%15%11%1
2150
16th to endDay
54%48%18%11%1
2316
May1st to 15thDay
60%5%10%16%7%
2429
16th to endDay
57%6%12%15%6%1
2622
June1st to 15thDay
64%5%9%12%6%
2520
16th to endDay
57%6%10%15%8%
2652
July1st to 15thDay
48%8%14%18%9%
2399
16th to endDay
56%8%10%18%5%
2439
August1st to 15thDay
50%8%13%18%8%
2327
16th to endDay
40%7%15%26%10%
2411
September1st to 15thDay
47%5%12%21%12%1
2099
16th to endDay
41%48%28%16%
1796
October1st to 15thDay
46%411%23%13%
1650
16th to endDay
55%6%11%19%6%
1760
November1st to 15thDay
58%5%12%15%7%1
1445
16th to endDay
60%7%12%12%7%
1440
December1st to 15thDay
64%7%8%15%4
1440
16th to endDay
65%6%8%11%7%
1536
January1st to 15thNight
57%7%12%16%5%
2506
16th to endNight
57%7%11%18%4
2518
February1st to 15thNight
61%6%13%13%5%
2286
16th to endNight
61%6%11%14%5%
2030
March1st to 15thNight
55%5%11%17%9%
1988
16th to endNight
54%5%9%19%10%1
2112
April1st to 15thNight
57%5%7%15%10%2
1798
16th to endNight
54%48%18%12%2
1643
May1st to 15thNight
59%5%9%18%6%
1521
16th to endNight
55%5%12%18%6%1
1496
June1st to 15thNight
62%5%9%16%6%
1440
16th to endNight
58%5%10%15%8%
1314
July1st to 15thNight
48%7%16%18%8%
1315
16th to endNight
56%8%10%17%6%
1465
August1st to 15thNight
49%7%12%22%7%
1608
16th to endNight
44%7%12%24%11%
1791
September1st to 15thNight
45%5%10%25%12%1
1749
16th to endNight
41%49%29%13%
1834
October1st to 15thNight
44%5%12%25%11%
1980
16th to endNight
50%6%11%21%10%
2112
November1st to 15thNight
53%6%13%17%9%
2412
16th to endNight
54%7%12%16%8%
2520
December1st to 15thNight
59%7%10%17%4
2520
16th to endNight
63%6%8%14%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
21%32%29%15%1
240
16th to endDay
23%29%34%9%2
256
February1st to 15thDay
22%32%27%14%2
236
16th to endDay
23%32%29%11%4
212
March1st to 15thDay
23%36%24%11%3
269
16th to endDay
28%33%23%9%31
288
April1st to 15thDay
30%31%26%8%3
270
16th to endDay
21%31%30%11%4
270
May1st to 15thDay
33%22%23%14%5%1
385
16th to endDay
27%23%28%14%41
519
June1st to 15thDay
31%21%25%16%5%
495
16th to endDay
29%20%25%15%5%2
495
July1st to 15thDay
26%13%26%21%9%1
475
16th to endDay
30%15%23%19%10%1
463
August1st to 15thDay
24%12%26%23%9%2
313
16th to endDay
22%13%26%21%13%3
332
September1st to 15thDay
22%15%32%18%8%2
294
16th to endDay
21%17%27%19%10%4
247
October1st to 15thDay
24%16%31%14%10%2
225
16th to endDay
27%27%26%12%5%1
240
November1st to 15thDay
22%25%25%14%9%2
235
16th to endDay
27%31%22%12%5%
240
December1st to 15thDay
30%31%23%11%3
240
16th to endDay
33%29%26%7%2
256
January1st to 15thNight
22%32%28%14%2
750
16th to endNight
23%33%28%11%2
771
February1st to 15thNight
24%33%27%13%
704
16th to endNight
23%33%25%12%4
631
March1st to 15thNight
23%32%24%14%4
720
16th to endNight
23%34%21%14%5%
768
April1st to 15thNight
25%29%27%13%4
541
16th to endNight
24%26%27%16%4
540
May1st to 15thNight
30%23%22%15%8%
540
16th to endNight
23%23%26%18%6%
561
June1st to 15thNight
28%22%26%19%3
540
16th to endNight
28%19%19%23%7%
414
July1st to 15thNight
24%13%23%29%9%
465
16th to endNight
23%19%21%23%11%
565
August1st to 15thNight
25%11%19%26%15%1
539
16th to endNight
19%11%27%26%13%1
573
September1st to 15thNight
20%15%28%23%11%
525
16th to endNight
21%17%24%23%11%1
638
October1st to 15thNight
21%19%28%20%7%1
660
16th to endNight
25%23%31%15%4
704
November1st to 15thNight
24%24%25%17%6%1
729
16th to endNight
25%32%22%13%6%
750
December1st to 15thNight
29%30%25%11%3
750
16th to endNight
30%31%25%11%1
800
Page generated at 2017-09-11 20:35:26. Version ac04

Copyright 2017 A. Danko


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