W. Armitage Memorial Dark Sky Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the W. Armitage Memorial Dark Sky Site clear sky chart from 2005-11-05 to 2018-01-12.

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
26%
14991
11%
48235
7%
14960
31%
14960
14%
36092

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
15%
765
6%
2662
3%
761
19%
761
6%
2225
January16th to endNight
20%
768
10%
2667
5%
768
27%
768
9%
2104
February1st to 15thNight
21%
704
10%
2287
5%
701
28%
701
10%
1796
February16th to endNight
18%
631
10%
1982
5%
631
25%
631
10%
1563
March1st to 15thNight
19%
720
11%
2091
5%
720
26%
720
12%
1635
March16th to endNight
27%
768
19%
2042
9%
768
33%
768
20%
1456
April1st to 15thNight
24%
718
15%
1796
6%
718
29%
718
19%
1339
April16th to endNight
26%
579
17%
1659
8%
579
33%
579
20%
1144
May1st to 15thNight
31%
360
15%
1440
16%
360
39%
360
15%
993
May16th to endNight
30%
374
11%
1497
11%
374
41%
374
15%
1018
June1st to 15thNight
28%
360
7%
1440
4%
360
34%
360
13%
986
June16th to endNight
37%
360
8%
1316
6%
360
41%
360
20%
850
July1st to 15thNight
42%
340
10%
1333
12%
340
46%
340
22%
816
July16th to endNight
48%
376
11%
1418
13%
354
51%
354
20%
877
August1st to 15thNight
45%
416
12%
1487
12%
414
50%
414
20%
971
August16th to endNight
46%
675
18%
1821
9%
675
51%
675
30%
1185
September1st to 15thNight
36%
720
13%
1800
5%
720
39%
720
27%
1255
September16th to endNight
38%
717
17%
1967
10%
717
43%
717
25%
1345
October1st to 15thNight
26%
720
13%
2160
8%
720
33%
720
15%
1602
October16th to endNight
20%
768
10%
2409
6%
768
26%
768
11%
1922
November1st to 15thNight
18%
760
13%
2589
7%
760
26%
760
10%
2010
November16th to endNight
15%
780
8%
2730
5%
780
20%
780
6%
2261
December1st to 15thNight
15%
780
7%
2730
2%
780
21%
780
6%
2287
December16th to endNight
14%
832
10%
2912
5%
832
19%
832
6%
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
20%11%47%6%34445%25%
49095
Night
19%12%48%6%34445%26%
48404
TransparencyDay
59%39%17%8%
48782
Night
59%39%18%7%
48235
SeeingDay
27%11%30%19%8%2
5838
Night
27%10%28%24%8%1
14992

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
22%18%7%11%7%32335%13%
1520
16th to endDay
16%15%6%11%6%36%46%5%16%
1554
February1st to 15thDay
9%16%8%12%10%5%5%45%6%16%
1575
16th to endDay
16%19%6%10%6%3343422%
1491
March1st to 15thDay
17%15%47%6%25%5%25%26%
1856
16th to endDay
13%10%5%6%5%25%5%45%34%
2181
April1st to 15thDay
24%14%45%422335%28%
2152
16th to endDay
23%9%37%423335%33%
2310
May1st to 15thDay
23%9%35%5%34346%28%
2511
16th to endDay
23%7%37%434445%30%
2618
June1st to 15thDay
21%9%37%6%35%5%6%5%25%
2520
16th to endDay
17%6%26%6%46%6%6%7%28%
2636
July1st to 15thDay
18%6%36%6%45%5%6%8%29%
2541
16th to endDay
17%8%36%6%35%5%5%7%30%
2654
August1st to 15thDay
18%9%38%6%5%6%447%25%
2461
16th to endDay
17%7%36%6%45%45%6%32%
2369
September1st to 15thDay
20%8%26%433346%35%
2160
16th to endDay
21%7%34423346%36%
1992
October1st to 15thDay
24%12%46%423346%26%
1800
16th to endDay
32%17%48%6%2322415%
1814
November1st to 15thDay
19%17%6%8%5%2233424%
1596
16th to endDay
26%17%9%10%5%3423314%
1560
December1st to 15thDay
23%20%8%11%6%3443410%
1560
16th to endDay
21%19%6%10%7%3344313%
1664
January1st to 15thNight
21%17%6%13%7%34335%13%
2662
16th to endNight
14%16%6%10%8%46%46%6%15%
2667
February1st to 15thNight
10%13%6%10%12%6%5%5%5%6%18%
2285
16th to endNight
15%16%6%10%7%4444420%
1982
March1st to 15thNight
18%15%5%7%6%35%5%45%22%
2078
16th to endNight
15%10%46%42434436%
2042
April1st to 15thNight
22%10%46%6%2323433%
1796
16th to endNight
20%8%25%5%23445%36%
1659
May1st to 15thNight
22%9%36%5%2434433%
1440
16th to endNight
20%8%36%5%34447%31%
1495
June1st to 15thNight
20%8%46%4345%6%6%28%
1440
16th to endNight
17%6%35%5%26%5%5%7%35%
1316
July1st to 15thNight
14%6%25%5%3446%8%37%
1413
16th to endNight
13%5%25%5%25%5%7%8%37%
1514
August1st to 15thNight
16%6%26%5%25%46%7%36%
1497
16th to endNight
11%6%36%4245%6%7%42%
1821
September1st to 15thNight
19%7%25%5%2435%6%38%
1800
16th to endNight
19%7%25%423436%40%
1967
October1st to 15thNight
24%10%47%42344430%
2160
16th to endNight
28%15%36%5%24335%20%
2409
November1st to 15thNight
21%14%5%7%7%3433423%
2589
16th to endNight
27%17%6%8%6%2323316%
2730
December1st to 15thNight
21%20%7%10%5%24335%13%
2730
16th to endNight
19%19%7%11%8%3443412%
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
75%25%11%4
1521
16th to endDay
68%16%15%7%
1554
February1st to 15thDay
69%16%14%6%
1577
16th to endDay
67%16%15%9%
1491
March1st to 15thDay
61%27%16%9%1
1866
16th to endDay
51%38%17%14%3
2181
April1st to 15thDay
59%27%17%11%2
2152
16th to endDay
54%17%18%14%2
2310
May1st to 15thDay
56%37%19%11%1
2511
16th to endDay
54%38%19%12%1
2622
June1st to 15thDay
58%49%17%9%
2520
16th to endDay
52%5%12%21%8%
2636
July1st to 15thDay
50%413%21%9%
2392
16th to endDay
53%413%20%7%
2487
August1st to 15thDay
58%313%19%4
2447
16th to endDay
51%314%21%7%
2369
September1st to 15thDay
49%313%20%11%
2160
16th to endDay
49%315%24%6%
1992
October1st to 15thDay
60%310%18%6%
1800
16th to endDay
74%27%11%3
1814
November1st to 15thDay
64%211%14%7%
1596
16th to endDay
76%26%9%5%
1560
December1st to 15thDay
78%36%10%2
1560
16th to endDay
74%35%11%5%
1664
January1st to 15thNight
75%27%11%3
2662
16th to endNight
67%36%14%8%
2667
February1st to 15thNight
66%27%16%5%
2287
16th to endNight
66%17%14%9%
1982
March1st to 15thNight
63%38%15%9%
2091
16th to endNight
50%47%20%15%1
2042
April1st to 15thNight
55%16%19%13%1
1796
16th to endNight
49%38%21%14%2
1659
May1st to 15thNight
54%37%18%12%2
1440
16th to endNight
53%39%21%11%
1497
June1st to 15thNight
54%410%20%9%
1440
16th to endNight
47%313%24%10%
1316
July1st to 15thNight
42%415%26%10%
1333
16th to endNight
44%5%16%27%7%
1418
August1st to 15thNight
45%5%17%26%4
1487
16th to endNight
39%5%18%30%6%
1821
September1st to 15thNight
46%317%23%8%
1800
16th to endNight
46%316%28%5%
1967
October1st to 15thNight
57%310%18%9%
2160
16th to endNight
67%210%16%3
2409
November1st to 15thNight
65%29%15%6%
2589
16th to endNight
73%27%11%4
2730
December1st to 15thNight
74%27%11%3
2730
16th to endNight
74%35%10%5%
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
26%14%43%10%21
82
16th to endDay
38%10%34%11%4
67
February1st to 15thDay
21%15%44%15%21
90
16th to endDay
36%15%30%14%21
150
March1st to 15thDay
29%16%29%18%5%
270
16th to endDay
21%18%34%18%5%2
288
April1st to 15thDay
35%15%23%18%6%1
270
16th to endDay
28%14%30%16%7%2
270
May1st to 15thDay
35%10%27%15%7%3
288
16th to endDay
30%14%26%18%8%1
331
June1st to 15thDay
31%10%33%19%4
315
16th to endDay
21%9%35%21%10%2
431
July1st to 15thDay
20%7%38%25%6%1
326
16th to endDay
19%8%28%26%13%3
326
August1st to 15thDay
21%6%30%24%11%5%
313
16th to endDay
24%331%23%10%7%
332
September1st to 15thDay
23%431%20%15%4
315
16th to endDay
22%9%26%21%15%5%
314
October1st to 15thDay
29%12%29%18%8%1
315
16th to endDay
39%11%24%16%6%
309
November1st to 15thDay
28%13%30%20%6%1
160
16th to endDay
40%22%25%10%2
90
December1st to 15thDay
35%10%37%14%11
90
16th to endDay
31%16%39%9%3
96
January1st to 15thNight
31%12%30%19%4
765
16th to endNight
26%9%31%23%7%
768
February1st to 15thNight
18%14%34%22%7%
704
16th to endNight
25%14%31%23%4
631
March1st to 15thNight
28%14%29%22%3
720
16th to endNight
20%14%30%24%9%
768
April1st to 15thNight
31%13%25%24%4
718
16th to endNight
25%11%31%22%7%
579
May1st to 15thNight
28%7%24%27%11%
360
16th to endNight
25%7%30%27%8%
375
June1st to 15thNight
27%6%28%25%10%1
360
16th to endNight
21%5%27%31%13%
360
July1st to 15thNight
16%330%35%13%
340
16th to endNight
15%325%41%13%1
376
August1st to 15thNight
20%319%32%22%2
416
16th to endNight
16%425%31%20%1
675
September1st to 15thNight
24%427%27%13%2
720
16th to endNight
23%7%25%28%11%2
717
October1st to 15thNight
30%8%28%21%10%
720
16th to endNight
37%10%26%19%6%
768
November1st to 15thNight
31%12%29%16%8%1
760
16th to endNight
38%15%20%18%6%1
780
December1st to 15thNight
36%13%26%19%4
780
16th to endNight
31%13%28%20%41
832
Page generated at 2018-01-12 22:01:32. Version ac04

Copyright 2018 A. Danko


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