Rock Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rock Lake clear sky chart from 2005-11-05 to 2017-09-21.

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%
14679
12%
46654
7%
14647
31%
14647
14%
34379

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
9%
720
4%
2506
1%
716
12%
716
4%
2129
January16th to endNight
17%
768
10%
2556
5%
768
24%
768
9%
2033
February1st to 15thNight
12%
704
8%
2287
3%
701
18%
701
8%
1844
February16th to endNight
15%
631
11%
2024
4%
631
24%
631
11%
1534
March1st to 15thNight
15%
720
12%
2010
4%
720
22%
720
13%
1545
March16th to endNight
27%
768
19%
2100
8%
768
36%
768
22%
1448
April1st to 15thNight
18%
718
14%
1796
4%
718
24%
718
17%
1352
April16th to endNight
28%
578
17%
1658
8%
578
35%
578
21%
1178
May1st to 15thNight
32%
408
16%
1488
12%
408
42%
408
17%
980
May16th to endNight
31%
374
13%
1497
8%
374
44%
374
18%
934
June1st to 15thNight
31%
360
9%
1440
7%
360
39%
360
16%
946
June16th to endNight
40%
360
10%
1260
9%
360
46%
360
19%
824
July1st to 15thNight
45%
340
15%
1271
17%
340
51%
340
28%
720
July16th to endNight
45%
382
14%
1424
13%
360
53%
360
24%
847
August1st to 15thNight
49%
539
15%
1609
10%
536
53%
536
27%
1029
August16th to endNight
45%
636
17%
1782
8%
636
51%
636
32%
1110
September1st to 15thNight
40%
720
15%
1800
7%
720
43%
720
29%
1227
September16th to endNight
41%
681
19%
1889
12%
681
45%
681
28%
1245
October1st to 15thNight
26%
660
16%
1980
9%
660
36%
660
17%
1424
October16th to endNight
16%
704
9%
2128
3%
704
22%
704
9%
1717
November1st to 15thNight
24%
700
14%
2421
11%
700
32%
700
12%
1776
November16th to endNight
17%
720
8%
2520
6%
720
22%
720
8%
2068
December1st to 15thNight
10%
720
6%
2520
1%
720
15%
720
5%
2161
December16th to endNight
8%
768
6%
2688
2%
768
13%
768
4%
2308

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%11%47%6%34446%28%
48213
Night
16%12%5%7%6%34445%29%
46822
Cloud CoverDay
18%11%47%6%34446%28%
48223
Night
15%12%5%8%6%34446%29%
46827
TransparencyDay
56%5%10%17%8%1
47899
Night
55%5%10%17%9%
46654
SeeingDay
24%14%30%19%7%2
5613
Night
22%15%31%21%8%1
14680

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%17%7%11%8%24345%16%
1432
16th to endDay
12%15%7%12%7%45%445%19%
1665
February1st to 15thDay
11%16%7%13%10%36%445%17%
1575
16th to endDay
15%17%6%9%8%25%5%36%19%
1449
March1st to 15thDay
15%13%6%9%7%45%43424%
1939
16th to endDay
12%10%49%6%33445%35%
2124
April1st to 15thDay
22%13%5%6%423335%29%
2152
16th to endDay
21%10%35%423335%37%
2313
May1st to 15thDay
20%10%46%6%33346%31%
2463
16th to endDay
16%7%36%5%3445%7%35%
2618
June1st to 15thDay
22%9%46%5%24447%28%
2520
16th to endDay
18%7%26%6%35%5%5%7%31%
2695
July1st to 15thDay
16%5%25%6%36%45%7%35%
2607
16th to endDay
13%7%27%6%45%6%6%8%32%
2647
August1st to 15thDay
16%7%37%6%45%5%5%6%31%
2340
16th to endDay
15%6%26%6%35%5%6%8%32%
2408
September1st to 15thDay
21%7%36%423346%36%
2160
16th to endDay
19%7%25%5%23446%38%
1862
October1st to 15thDay
25%11%36%6%23335%28%
1650
16th to endDay
30%16%47%5%2333417%
1742
November1st to 15thDay
17%13%6%7%6%34346%26%
1436
16th to endDay
22%17%9%11%6%3333416%
1440
December1st to 15thDay
17%23%8%11%8%3324410%
1440
16th to endDay
19%20%8%11%7%3335%412%
1536
January1st to 15thNight
16%17%8%11%10%4444412%
2506
16th to endNight
11%15%7%11%8%45%445%20%
2556
February1st to 15thNight
10%15%8%11%9%5%5%45%5%17%
2285
16th to endNight
12%15%7%10%6%45%45%5%23%
2024
March1st to 15thNight
15%11%7%8%7%35%445%27%
1998
16th to endNight
11%9%5%7%6%24336%39%
2100
April1st to 15thNight
20%13%45%42334433%
1796
16th to endNight
18%9%35%423446%35%
1658
May1st to 15thNight
19%8%25%42345%8%34%
1488
16th to endNight
14%6%35%4345%47%40%
1495
June1st to 15thNight
17%6%36%434446%35%
1440
16th to endNight
15%6%36%5%35%5%5%7%36%
1260
July1st to 15thNight
10%5%245%2345%7%48%
1348
16th to endNight
10%5%25%5%346%5%8%43%
1520
August1st to 15thNight
10%5%25%5%245%5%7%44%
1620
16th to endNight
10%5%135%3346%9%45%
1782
September1st to 15thNight
15%6%245%2445%7%42%
1800
16th to endNight
16%8%23423436%44%
1889
October1st to 15thNight
20%11%35%423446%33%
1980
16th to endNight
26%16%46%5%2334420%
2128
November1st to 15thNight
17%13%5%6%436%45%5%28%
2421
16th to endNight
20%17%6%8%7%3433418%
2520
December1st to 15thNight
18%21%9%10%6%3433314%
2520
16th to endNight
19%19%8%12%7%3433313%
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
18%16%8%11%8%24335%16%
1432
16th to endDay
13%14%7%12%8%35%5%45%20%
1665
February1st to 15thDay
11%16%7%12%10%35%44418%
1575
16th to endDay
15%17%6%10%7%35%445%20%
1449
March1st to 15thDay
15%14%6%9%8%4433425%
1950
16th to endDay
12%10%5%8%6%34345%35%
2123
April1st to 15thDay
22%13%46%324335%30%
2152
16th to endDay
20%10%35%5%23235%37%
2313
May1st to 15thDay
19%11%46%6%33335%31%
2463
16th to endDay
16%8%35%6%2445%7%35%
2618
June1st to 15thDay
22%9%37%5%33447%28%
2520
16th to endDay
17%7%36%5%25%6%6%7%31%
2695
July1st to 15thDay
15%6%25%6%36%45%7%35%
2607
16th to endDay
13%6%36%7%35%6%6%8%32%
2647
August1st to 15thDay
16%7%37%7%45%5%5%7%30%
2340
16th to endDay
15%6%26%5%45%5%6%8%32%
2408
September1st to 15thDay
20%7%35%5%23445%35%
2160
16th to endDay
19%7%25%5%2345%6%37%
1862
October1st to 15thDay
24%10%36%5%34336%28%
1650
16th to endDay
29%16%5%7%433335%17%
1742
November1st to 15thDay
17%13%5%8%6%33346%26%
1436
16th to endDay
21%17%8%11%5%3323416%
1440
December1st to 15thDay
18%22%7%12%7%3423411%
1440
16th to endDay
19%20%8%11%5%33345%13%
1536
January1st to 15thNight
16%17%7%13%9%45%44412%
2506
16th to endNight
11%14%7%12%8%46%5%45%19%
2556
February1st to 15thNight
10%15%9%11%9%45%45%5%18%
2278
16th to endNight
12%16%5%10%6%35%445%23%
2024
March1st to 15thNight
16%12%5%9%7%3444427%
2010
16th to endNight
10%11%48%5%23346%39%
2100
April1st to 15thNight
19%13%5%5%42333432%
1796
16th to endNight
18%9%45%424345%36%
1658
May1st to 15thNight
19%8%26%42345%7%34%
1488
16th to endNight
14%6%25%5%245%5%7%40%
1495
June1st to 15thNight
17%7%36%5%34447%35%
1440
16th to endNight
13%7%36%6%3445%7%36%
1260
July1st to 15thNight
10%5%2442345%7%48%
1348
16th to endNight
10%5%345%345%5%9%43%
1520
August1st to 15thNight
10%5%25%4245%5%8%44%
1620
16th to endNight
10%4145%3346%8%45%
1782
September1st to 15thNight
13%7%245%2445%8%42%
1800
16th to endNight
16%8%24323445%44%
1889
October1st to 15thNight
20%10%35%423346%33%
1980
16th to endNight
26%15%5%7%5%24445%20%
2128
November1st to 15thNight
17%13%5%6%435%446%28%
2421
16th to endNight
20%17%6%9%7%3433418%
2520
December1st to 15thNight
18%21%8%11%6%2433314%
2520
16th to endNight
19%19%8%12%7%35%32413%
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
70%47%10%6%
1433
16th to endDay
65%5%7%12%6%2
1665
February1st to 15thDay
68%5%7%12%6%
1577
16th to endDay
66%47%12%9%
1449
March1st to 15thDay
63%310%14%6%1
1950
16th to endDay
50%47%18%15%4
2124
April1st to 15thDay
57%37%17%11%2
2152
16th to endDay
50%37%21%13%2
2313
May1st to 15thDay
54%49%17%12%1
2463
16th to endDay
48%6%11%20%11%2
2622
June1st to 15thDay
55%5%10%19%8%
2520
16th to endDay
49%7%11%20%10%
2695
July1st to 15thDay
44%6%11%26%10%1
2455
16th to endDay
48%7%12%23%8%
2480
August1st to 15thDay
51%7%13%18%8%
2327
16th to endDay
47%7%13%23%7%
2408
September1st to 15thDay
49%5%12%22%9%
2160
16th to endDay
46%6%10%28%7%
1862
October1st to 15thDay
58%411%15%9%
1650
16th to endDay
70%48%10%5%
1742
November1st to 15thDay
58%6%11%15%7%
1436
16th to endDay
73%38%9%31
1440
December1st to 15thDay
77%46%8%2
1440
16th to endDay
73%5%6%10%4
1536
January1st to 15thNight
74%5%8%6%4
2506
16th to endNight
65%5%7%13%7%1
2556
February1st to 15thNight
67%5%9%12%5%
2287
16th to endNight
61%49%16%8%
2024
March1st to 15thNight
60%310%15%8%1
2010
16th to endNight
46%410%19%16%2
2100
April1st to 15thNight
55%36%19%13%1
1796
16th to endNight
50%47%20%15%1
1658
May1st to 15thNight
47%5%10%18%15%1
1488
16th to endNight
42%7%13%21%13%1
1497
June1st to 15thNight
47%5%12%20%12%
1440
16th to endNight
45%6%13%23%10%
1260
July1st to 15thNight
33%7%12%29%16%
1271
16th to endNight
37%6%16%27%11%
1424
August1st to 15thNight
36%9%16%26%10%
1609
16th to endNight
33%7%19%29%9%
1782
September1st to 15thNight
39%7%15%25%10%
1800
16th to endNight
41%5%14%31%7%
1889
October1st to 15thNight
52%5%10%19%11%
1980
16th to endNight
65%5%10%12%5%
2128
November1st to 15thNight
56%5%12%15%8%
2421
16th to endNight
69%5%9%11%3
2520
December1st to 15thNight
74%5%7%9%3
2520
16th to endNight
75%45%7%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
33%28%26%8%3
60
16th to endDay
31%18%34%11%3
85
February1st to 15thDay
23%37%32%6%
90
16th to endDay
39%20%28%9%1
108
March1st to 15thDay
28%19%31%17%2
270
16th to endDay
22%19%31%17%7%1
288
April1st to 15thDay
25%21%32%14%5%
270
16th to endDay
27%20%25%15%9%2
270
May1st to 15thDay
32%10%27%17%8%3
288
16th to endDay
20%18%32%19%6%2
331
June1st to 15thDay
26%13%31%21%6%
315
16th to endDay
19%13%36%20%7%2
490
July1st to 15thDay
15%10%35%26%8%2
389
16th to endDay
14%10%32%28%11%3
326
August1st to 15thDay
18%5%30%28%8%7%
313
16th to endDay
19%8%28%27%10%6%
332
September1st to 15thDay
20%9%26%20%13%8%
315
16th to endDay
21%9%29%20%13%5%
275
October1st to 15thDay
27%15%29%17%8%1
255
16th to endDay
40%15%26%13%3
269
November1st to 15thDay
21%18%38%15%5%
90
16th to endDay
38%16%31%13%
60
December1st to 15thDay
33%21%30%15%
60
16th to endDay
28%43%23%4
64
January1st to 15thNight
27%23%32%13%2
720
16th to endNight
21%17%35%18%6%
768
February1st to 15thNight
19%19%41%15%4
704
16th to endNight
21%19%37%17%3
631
March1st to 15thNight
23%23%32%17%2
720
16th to endNight
17%17%33%20%9%1
768
April1st to 15thNight
26%18%31%18%4
718
16th to endNight
23%14%30%21%9%
578
May1st to 15thNight
23%10%29%25%10%1
408
16th to endNight
18%9%36%25%9%
375
June1st to 15thNight
20%11%32%28%7%
360
16th to endNight
16%8%30%35%9%
360
July1st to 15thNight
13%432%35%13%
340
16th to endNight
10%7%32%35%13%1
382
August1st to 15thNight
12%5%25%33%19%3
539
16th to endNight
12%6%31%30%17%1
636
September1st to 15thNight
17%9%29%25%15%3
720
16th to endNight
20%8%25%27%15%2
681
October1st to 15thNight
27%14%26%21%8%
660
16th to endNight
33%17%27%15%5%
704
November1st to 15thNight
26%19%25%20%8%
700
16th to endNight
31%17%27%17%4
720
December1st to 15thNight
29%22%32%11%2
720
16th to endNight
32%17%31%14%21
768
Page generated at 2017-09-22 07:35:30. Version ac04

Copyright 2017 A. Danko


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