McCauley Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the McCauley Lake Observatory clear sky chart from 2005-11-05 to 2018-01-20.

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
25%
15158
12%
48322
7%
15127
32%
15127
15%
35327

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%
780
6%
2716
2%
776
16%
776
5%
2263
January16th to endNight
18%
788
10%
2636
4%
788
25%
788
9%
2060
February1st to 15thNight
13%
703
8%
2287
2%
701
20%
701
8%
1822
February16th to endNight
16%
631
12%
2015
4%
631
25%
631
11%
1510
March1st to 15thNight
15%
720
12%
2019
4%
720
22%
720
13%
1549
March16th to endNight
27%
768
18%
2091
7%
768
36%
768
22%
1432
April1st to 15thNight
19%
718
14%
1796
4%
718
25%
718
17%
1370
April16th to endNight
28%
588
17%
1668
8%
588
34%
588
21%
1177
May1st to 15thNight
33%
398
17%
1478
13%
398
42%
398
17%
968
May16th to endNight
31%
375
12%
1497
9%
374
42%
374
18%
941
June1st to 15thNight
30%
360
8%
1440
6%
360
40%
360
16%
939
June16th to endNight
37%
360
10%
1293
10%
360
43%
360
19%
845
July1st to 15thNight
41%
340
14%
1300
16%
340
48%
340
27%
728
July16th to endNight
42%
376
13%
1418
12%
354
51%
354
24%
814
August1st to 15thNight
49%
532
14%
1603
9%
530
54%
530
28%
1022
August16th to endNight
46%
644
18%
1790
8%
644
52%
644
33%
1102
September1st to 15thNight
40%
720
15%
1800
7%
720
43%
720
29%
1222
September16th to endNight
44%
717
19%
1991
13%
717
47%
717
28%
1306
October1st to 15thNight
27%
720
15%
2160
9%
720
36%
720
19%
1518
October16th to endNight
16%
768
10%
2334
4%
768
24%
768
11%
1861
November1st to 15thNight
24%
760
14%
2618
10%
760
31%
760
11%
1927
November16th to endNight
16%
780
8%
2730
5%
780
20%
780
8%
2223
December1st to 15thNight
10%
780
7%
2730
1%
780
16%
780
5%
2290
December16th to endNight
9%
832
7%
2912
2%
832
15%
832
5%
2438

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
17%10%47%6%34446%28%
49203
Night
15%11%48%6%34446%29%
48492
Cloud CoverDay
17%10%47%6%34446%29%
49213
Night
15%11%47%6%34446%30%
48497
TransparencyDay
55%5%10%17%9%1
48891
Night
54%6%11%17%9%
48322
SeeingDay
23%14%31%19%8%2
5887
Night
21%15%32%21%8%
15159

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
17%14%8%10%9%34336%17%
1552
16th to endDay
12%14%6%10%9%45%45%5%20%
1692
February1st to 15thDay
10%15%7%13%11%46%43418%
1575
16th to endDay
15%17%5%9%6%445%35%21%
1457
March1st to 15thDay
14%13%6%9%8%3443425%
1927
16th to endDay
13%9%5%7%7%34446%35%
2133
April1st to 15thDay
21%13%46%32423430%
2152
16th to endDay
21%9%36%32323437%
2301
May1st to 15thDay
19%10%47%5%34346%31%
2472
16th to endDay
16%7%35%6%35%45%6%35%
2618
June1st to 15thDay
22%8%46%6%2345%8%28%
2520
16th to endDay
17%6%25%5%36%6%5%8%31%
2661
July1st to 15thDay
14%7%35%5%35%6%6%8%34%
2574
16th to endDay
12%6%36%7%45%5%6%8%32%
2654
August1st to 15thDay
14%8%36%7%45%5%6%7%31%
2346
16th to endDay
13%7%25%6%36%6%5%9%32%
2399
September1st to 15thDay
20%7%35%43345%6%35%
2160
16th to endDay
17%7%35%423446%39%
1968
October1st to 15thDay
21%11%36%5%34445%30%
1800
16th to endDay
28%14%47%6%33235%19%
1890
November1st to 15thDay
17%13%5%6%6%3445%5%27%
1568
16th to endDay
20%16%8%11%6%34335%16%
1560
December1st to 15thDay
16%20%9%12%8%3333412%
1560
16th to endDay
18%19%8%11%6%23246%15%
1664
January1st to 15thNight
15%15%7%12%9%46%5%5%5%13%
2716
16th to endNight
11%13%6%11%8%5%6%5%5%6%20%
2636
February1st to 15thNight
11%15%7%12%9%45%45%5%18%
2285
16th to endNight
12%15%5%9%6%445%45%25%
2015
March1st to 15thNight
16%11%410%6%34435%27%
2007
16th to endNight
11%9%47%6%23346%39%
2091
April1st to 15thNight
19%12%5%6%5%2433432%
1796
16th to endNight
16%9%36%424346%36%
1668
May1st to 15thNight
19%9%36%32435%7%35%
1478
16th to endNight
13%7%35%425%5%5%7%39%
1495
June1st to 15thNight
17%8%3443445%8%35%
1440
16th to endNight
13%5%36%5%35%5%7%7%36%
1293
July1st to 15thNight
9%5%34424348%48%
1380
16th to endNight
9%5%235%25%5%6%8%44%
1514
August1st to 15thNight
9%5%24425%5%6%9%43%
1613
16th to endNight
10%32443445%9%46%
1790
September1st to 15thNight
14%5%25%434448%42%
1800
16th to endNight
14%7%25%33335%6%44%
1991
October1st to 15thNight
19%9%35%42335%6%36%
2160
16th to endNight
23%14%46%6%3435%5%21%
2334
November1st to 15thNight
17%12%5%6%5%345%5%5%28%
2618
16th to endNight
20%15%5%9%8%34335%19%
2730
December1st to 15thNight
17%19%9%10%7%4444415%
2730
16th to endNight
19%17%7%13%6%35%34415%
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
17%14%7%11%8%35%345%18%
1552
16th to endDay
12%13%6%10%9%46%45%5%20%
1692
February1st to 15thDay
9%15%7%13%11%46%445%19%
1575
16th to endDay
15%16%5%10%5%45%5%35%21%
1457
March1st to 15thDay
15%13%6%9%7%445%4325%
1938
16th to endDay
13%8%47%7%33446%35%
2132
April1st to 15thDay
21%12%5%6%424335%31%
2152
16th to endDay
21%9%36%32324437%
2301
May1st to 15thDay
19%10%36%5%34345%32%
2472
16th to endDay
16%7%45%5%35%45%6%35%
2618
June1st to 15thDay
22%7%45%6%3445%7%28%
2520
16th to endDay
17%5%35%5%36%5%5%8%31%
2661
July1st to 15thDay
15%6%25%6%25%5%6%8%34%
2574
16th to endDay
12%5%36%6%45%5%6%9%32%
2654
August1st to 15thDay
14%7%36%7%35%5%6%7%31%
2346
16th to endDay
13%6%25%6%45%6%6%8%33%
2399
September1st to 15thDay
19%8%25%423447%36%
2160
16th to endDay
17%8%34423446%40%
1968
October1st to 15thDay
22%11%35%5%35%445%30%
1800
16th to endDay
28%13%38%6%3334419%
1890
November1st to 15thDay
17%13%5%7%6%34446%27%
1568
16th to endDay
20%16%8%10%6%35%34417%
1560
December1st to 15thDay
16%20%8%13%8%3433413%
1560
16th to endDay
18%19%8%10%6%23346%16%
1664
January1st to 15thNight
15%14%7%12%8%46%5%5%5%14%
2716
16th to endNight
11%12%6%10%8%46%5%5%7%20%
2636
February1st to 15thNight
11%15%7%11%10%45%45%5%19%
2278
16th to endNight
12%15%5%8%6%445%45%26%
2015
March1st to 15thNight
16%11%410%7%34335%27%
2019
16th to endNight
11%9%47%6%23346%39%
2091
April1st to 15thNight
18%12%5%6%434335%33%
1796
16th to endNight
15%10%36%5%24346%36%
1668
May1st to 15thNight
18%9%26%42345%7%35%
1478
16th to endNight
13%7%35%425%5%5%7%39%
1495
June1st to 15thNight
17%7%35%42445%8%36%
1440
16th to endNight
12%6%27%5%35%5%7%8%35%
1293
July1st to 15thNight
9%415%42435%7%49%
1380
16th to endNight
9%5%235%25%5%6%8%45%
1514
August1st to 15thNight
10%5%245%2446%10%43%
1613
16th to endNight
10%32442445%9%47%
1790
September1st to 15thNight
14%6%24424448%42%
1800
16th to endNight
14%7%24423347%44%
1991
October1st to 15thNight
20%8%35%5%23346%36%
2160
16th to endNight
23%13%47%5%3435%6%22%
2334
November1st to 15thNight
17%11%46%6%3445%5%28%
2618
16th to endNight
20%14%5%9%8%34436%19%
2730
December1st to 15thNight
17%18%9%9%6%4443415%
2730
16th to endNight
19%16%6%12%7%35%43416%
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
68%48%11%6%
1553
16th to endDay
65%5%9%11%6%2
1692
February1st to 15thDay
67%5%9%11%5%
1577
16th to endDay
64%47%12%10%
1457
March1st to 15thDay
62%410%15%5%1
1938
16th to endDay
49%47%18%15%4
2133
April1st to 15thDay
57%38%17%10%2
2152
16th to endDay
50%37%21%14%2
2301
May1st to 15thDay
53%410%16%12%2
2472
16th to endDay
48%6%11%19%11%2
2622
June1st to 15thDay
55%6%10%18%9%
2520
16th to endDay
49%7%12%19%10%1
2661
July1st to 15thDay
43%6%12%25%11%1
2425
16th to endDay
47%8%13%22%8%
2487
August1st to 15thDay
50%7%14%18%8%
2332
16th to endDay
44%7%15%23%7%
2399
September1st to 15thDay
47%5%13%22%9%
2160
16th to endDay
44%6%12%28%8%
1968
October1st to 15thDay
56%6%10%16%9%
1800
16th to endDay
67%5%10%11%4
1890
November1st to 15thDay
56%7%13%14%6%
1568
16th to endDay
70%5%8%11%31
1560
December1st to 15thDay
75%47%9%3
1560
16th to endDay
70%47%11%4
1664
January1st to 15thNight
69%7%8%8%5%
2716
16th to endNight
62%6%9%13%7%
2636
February1st to 15thNight
66%5%11%11%5%
2287
16th to endNight
58%5%9%17%8%
2015
March1st to 15thNight
59%410%16%7%
2019
16th to endNight
45%5%10%18%16%2
2091
April1st to 15thNight
55%36%18%12%1
1796
16th to endNight
49%48%20%15%2
1668
May1st to 15thNight
48%5%10%18%15%2
1478
16th to endNight
41%7%14%20%13%1
1497
June1st to 15thNight
47%6%13%20%12%
1440
16th to endNight
43%8%14%22%10%
1293
July1st to 15thNight
33%6%14%27%18%
1300
16th to endNight
35%6%16%28%11%
1418
August1st to 15thNight
35%8%18%25%10%
1603
16th to endNight
32%7%19%30%8%
1790
September1st to 15thNight
40%6%16%25%11%
1800
16th to endNight
40%5%14%31%7%
1991
October1st to 15thNight
49%5%12%20%12%
2160
16th to endNight
63%5%11%14%4
2334
November1st to 15thNight
56%6%13%15%8%
2618
16th to endNight
66%6%10%12%3
2730
December1st to 15thNight
71%5%8%9%3
2730
16th to endNight
72%46%9%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%24%34%10%4
90
16th to endDay
26%21%32%17%2
93
February1st to 15thDay
27%30%35%6%
90
16th to endDay
37%21%27%8%4
116
March1st to 15thDay
25%19%34%17%3
270
16th to endDay
21%19%31%17%7%1
288
April1st to 15thDay
25%20%32%15%5%
270
16th to endDay
26%18%28%13%11%1
270
May1st to 15thDay
30%13%26%17%7%3
288
16th to endDay
19%17%33%18%9%2
331
June1st to 15thDay
26%12%34%18%8%
315
16th to endDay
18%11%38%21%7%2
456
July1st to 15thDay
16%10%37%25%8%1
359
16th to endDay
12%10%32%31%10%2
326
August1st to 15thDay
17%6%29%30%10%6%
313
16th to endDay
17%6%28%29%10%6%
332
September1st to 15thDay
20%8%27%19%14%9%
315
16th to endDay
20%7%25%25%14%5%
314
October1st to 15thDay
24%18%27%19%7%2
315
16th to endDay
36%18%28%13%3
328
November1st to 15thDay
29%18%30%18%2
132
16th to endDay
30%24%37%6%1
90
December1st to 15thDay
27%28%25%17%
90
16th to endDay
28%33%26%10%2
96
January1st to 15thNight
23%23%33%15%3
780
16th to endNight
20%15%37%19%5%
788
February1st to 15thNight
18%19%41%15%5%
704
16th to endNight
21%20%35%19%3
631
March1st to 15thNight
23%21%33%17%3
720
16th to endNight
17%17%32%21%9%1
768
April1st to 15thNight
25%18%32%19%4
718
16th to endNight
21%15%31%20%10%
588
May1st to 15thNight
22%10%28%27%10%1
398
16th to endNight
18%10%34%26%9%
375
June1st to 15thNight
20%8%33%28%7%
360
16th to endNight
15%8%31%34%9%
360
July1st to 15thNight
11%435%32%15%
340
16th to endNight
9%6%35%33%14%1
376
August1st to 15thNight
11%426%34%19%3
532
16th to endNight
11%6%31%33%15%2
644
September1st to 15thNight
17%8%30%24%15%3
720
16th to endNight
18%8%25%27%17%2
717
October1st to 15thNight
25%12%30%20%9%1
720
16th to endNight
31%17%29%16%5%
768
November1st to 15thNight
24%17%28%20%8%
760
16th to endNight
29%18%30%15%4
780
December1st to 15thNight
27%22%34%12%3
780
16th to endNight
30%18%32%15%2
832
Page generated at 2018-01-21 12:19:29. Version ac04

Copyright 2018 A. Danko


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