Island Lake State Recreation Area
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Island Lake State Recreation Area clear sky chart from 2005-11-06 to 2024-03-23.

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
36%
24746
14%
81211
10%
24636
41%
24636
18%
57501

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 10thNight
19%
943
10%
4384
5%
926
26%
926
8%
3308
January11th to 20thNight
17%
947
6%
4415
3%
930
20%
930
6%
3570
January21st to endNight
21%
892
5%
4612
4%
871
26%
871
6%
3772
February1st to 10thNight
19%
760
9%
2470
4%
760
24%
760
10%
1923
February11th to 20thNight
20%
740
13%
2253
5%
740
28%
740
14%
1672
February21st to endNight
17%
628
13%
1884
3%
628
27%
628
15%
1370
March1st to 10thNight
25%
760
16%
2252
9%
760
31%
760
18%
1589
March11th to 20thNight
26%
760
20%
2090
8%
760
36%
760
22%
1427
March21st to endNight
30%
801
17%
2201
10%
801
36%
801
19%
1591
April1st to 10thNight
27%
604
15%
1864
8%
604
36%
604
19%
1271
April11th to 20thNight
31%
533
19%
1643
9%
533
42%
533
22%
1115
April21st to endNight
34%
540
17%
1620
6%
540
43%
540
22%
1107
May1st to 10thNight
36%
540
13%
1620
8%
540
40%
540
20%
1133
May11th to 20thNight
43%
531
17%
1593
12%
531
49%
531
24%
1068
May21st to endNight
53%
583
14%
1726
10%
582
58%
582
30%
1087
June1st to 10thNight
55%
540
16%
1440
12%
540
59%
540
35%
902
June11th to 20thNight
53%
540
16%
1440
13%
540
57%
540
31%
922
June21st to endNight
57%
540
19%
1440
13%
540
63%
540
36%
893
July1st to 10thNight
67%
525
16%
1400
14%
525
69%
525
39%
836
July11th to 20thNight
63%
522
22%
1392
17%
522
68%
522
40%
836
July21st to endNight
67%
591
19%
1606
15%
558
71%
558
40%
924
August1st to 10thNight
66%
537
21%
1600
17%
534
68%
534
35%
932
August11th to 20thNight
62%
534
23%
1598
18%
534
66%
534
33%
964
August21st to endNight
63%
594
23%
1824
19%
594
67%
594
34%
1060
September1st to 10thNight
57%
634
21%
1894
16%
634
62%
634
31%
1159
September11th to 20thNight
62%
720
29%
1980
22%
720
65%
720
38%
1170
September21st to endNight
53%
720
23%
1980
16%
720
57%
720
30%
1283
October1st to 10thNight
45%
720
21%
2016
16%
720
50%
720
28%
1314
October11th to 20thNight
31%
720
15%
2160
9%
720
40%
720
19%
1520
October21st to endNight
25%
792
16%
2538
10%
792
34%
792
17%
1811
November1st to 10thNight
35%
740
20%
2406
15%
740
43%
740
23%
1529
November11th to 20thNight
23%
760
15%
2470
9%
760
32%
760
16%
1741
November21st to endNight
22%
760
14%
2504
8%
760
30%
760
14%
1843
December1st to 10thNight
19%
760
8%
2660
5%
760
23%
760
9%
2088
December11th to 20thNight
17%
893
8%
3358
2%
891
24%
891
9%
2553
December21st to endNight
13%
1042
4%
4878
1%
1026
18%
1026
4%
4218

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
14%10%47%6%45%5%5%7%32%
78380
Night
16%10%47%6%3445%6%33%
81532
TransparencyDay
50%7%12%19%11%1
78089
Night
51%6%12%19%11%1
81344
SeeingDay
18%11%29%22%14%6%
14558
Night
19%9%29%29%12%1
24764

By Month

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 10thDay
16%20%6%9%7%45%445%21%
2527
11th to 20thDay
16%17%6%11%9%5%7%5%5%5%13%
2530
21st to endDay
27%20%7%9%6%3333414%
3028
February1st to 10thDay
14%13%6%11%9%46%5%47%21%
1710
11th to 20thDay
14%12%5%10%11%4445%6%24%
1811
21st to endDay
15%15%5%11%6%3445%6%26%
1570
March1st to 10thDay
15%11%48%7%35%5%6%6%29%
1927
11th to 20thDay
13%11%5%8%7%3445%7%33%
2090
21st to endDay
19%12%38%7%35%446%29%
2200
April1st to 10thDay
17%12%5%6%6%35%5%5%6%31%
2112
11th to 20thDay
17%9%46%6%4446%6%35%
2265
21st to endDay
18%9%47%6%345%47%34%
2340
May1st to 10thDay
17%8%37%6%45%5%5%7%32%
2340
11th to 20thDay
18%8%36%6%35%5%5%7%35%
2301
21st to endDay
12%6%36%5%35%5%6%10%39%
2546
June1st to 10thDay
10%5%36%5%35%5%6%9%42%
2520
11th to 20thDay
11%5%36%5%45%6%6%9%40%
2520
21st to endDay
10%5%35%6%46%6%7%11%38%
2520
July1st to 10thDay
7%5%25%6%35%5%6%9%47%
2520
11th to 20thDay
9%425%6%45%5%7%9%43%
2520
21st to endDay
8%5%26%6%446%7%9%42%
2613
August1st to 10thDay
8%5%25%7%36%7%7%10%41%
2327
11th to 20thDay
10%6%26%6%5%6%6%7%8%38%
2303
21st to endDay
10%5%25%5%35%5%7%9%42%
2529
September1st to 10thDay
11%6%26%6%5%5%5%6%9%38%
2048
11th to 20thDay
10%425%5%35%6%6%9%45%
1980
21st to endDay
13%6%36%5%45%5%7%8%39%
1980
October1st to 10thDay
14%6%35%6%45%5%5%6%41%
1944
11th to 20thDay
18%9%47%6%45%45%7%32%
1800
21st to endDay
20%10%47%6%3445%6%30%
1816
November1st to 10thDay
12%9%46%6%35%5%5%7%38%
1672
11th to 20thDay
15%12%5%7%7%445%5%6%30%
1710
21st to endDay
19%12%47%6%35%45%6%29%
1670
December1st to 10thDay
14%15%7%11%8%46%5%36%22%
1520
11th to 20thDay
16%14%6%11%5%45%6%5%7%21%
1788
21st to endDay
26%19%8%11%7%34435%10%
2783
January1st to 10thNight
16%15%7%10%8%34445%24%
4428
11th to 20thNight
15%16%8%13%8%46%5%6%5%15%
4440
21st to endNight
24%16%10%10%6%3334417%
4628
February1st to 10thNight
17%14%6%9%8%45%5%45%24%
2470
11th to 20thNight
14%12%5%8%7%45%5%5%6%28%
2252
21st to endNight
18%10%5%9%6%3445%6%29%
1884
March1st to 10thNight
17%9%48%7%3445%5%35%
2252
11th to 20thNight
12%10%45%6%25%5%5%8%38%
2090
21st to endNight
19%8%47%6%345%45%35%
2201
April1st to 10thNight
15%9%37%6%4446%7%36%
1864
11th to 20thNight
18%9%25%5%345%6%7%37%
1643
21st to endNight
18%7%37%5%25%5%47%38%
1620
May1st to 10thNight
15%9%48%5%45%45%8%33%
1620
11th to 20thNight
19%6%25%5%3446%7%40%
1592
21st to endNight
10%5%25%6%35%5%6%9%45%
1725
June1st to 10thNight
11%4245%35%45%8%47%
1440
11th to 20thNight
10%5%35%5%35%5%7%8%44%
1440
21st to endNight
10%425%4236%6%9%48%
1440
July1st to 10thNight
8%3145%35%45%8%53%
1440
11th to 20thNight
8%4345%245%5%9%50%
1440
21st to endNight
5%4246%345%6%11%51%
1701
August1st to 10thNight
7%435%5%35%5%6%9%50%
1611
11th to 20thNight
8%435%5%35%46%8%49%
1598
21st to endNight
8%5%35%4245%5%8%52%
1824
September1st to 10thNight
10%5%35%435%45%7%48%
1894
11th to 20thNight
11%5%2443345%6%54%
1980
21st to endNight
13%6%35%5%345%5%7%44%
1980
October1st to 10thNight
14%7%35%5%34447%45%
2016
11th to 20thNight
19%9%36%6%445%46%34%
2160
21st to endNight
21%9%37%5%4445%5%32%
2538
November1st to 10thNight
14%7%45%5%3445%6%43%
2406
11th to 20thNight
16%10%47%6%45%5%6%7%31%
2470
21st to endNight
19%13%5%7%5%34446%29%
2504
December1st to 10thNight
18%14%6%10%7%45%5%5%6%20%
2660
11th to 20thNight
15%14%5%11%7%45%6%5%6%23%
3397
21st to endNight
27%23%7%9%6%3334412%
4884

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 10thDay
64%7%11%13%6%
2528
11th to 20thDay
70%7%13%7%3
2530
21st to endDay
76%410%7%31
3028
February1st to 10thDay
62%7%9%14%7%
1710
11th to 20thDay
61%5%9%15%8%1
1821
21st to endDay
59%6%11%16%7%2
1570
March1st to 10thDay
55%6%13%17%8%1
1927
11th to 20thDay
50%6%11%19%11%2
2090
21st to endDay
57%5%10%18%8%1
2200
April1st to 10thDay
53%6%11%18%12%
2112
11th to 20thDay
49%5%12%19%13%2
2265
21st to endDay
49%7%14%15%13%2
2340
May1st to 10thDay
50%6%12%20%10%2
2340
11th to 20thDay
49%7%10%19%13%2
2305
21st to endDay
40%7%14%23%14%2
2546
June1st to 10thDay
37%8%12%27%13%3
2520
11th to 20thDay
39%7%13%23%16%2
2520
21st to endDay
37%9%14%22%16%2
2520
July1st to 10thDay
32%8%12%26%18%4
2451
11th to 20thDay
35%8%13%23%18%2
2445
21st to endDay
35%9%13%23%18%2
2468
August1st to 10thDay
36%9%14%26%13%1
2314
11th to 20thDay
41%9%13%23%13%2
2303
21st to endDay
36%9%11%25%17%2
2529
September1st to 10thDay
42%8%14%21%13%2
2048
11th to 20thDay
34%8%12%32%14%1
1980
21st to endDay
42%7%13%25%14%
1980
October1st to 10thDay
42%7%12%24%13%2
1944
11th to 20thDay
51%7%12%19%10%
1800
21st to endDay
54%6%13%17%10%
1816
November1st to 10thDay
45%7%11%23%13%1
1672
11th to 20thDay
54%5%13%19%7%2
1710
21st to endDay
57%5%12%18%7%
1670
December1st to 10thDay
63%7%11%14%4
1520
11th to 20thDay
61%7%13%15%4
1784
21st to endDay
77%5%9%6%3
2783
January1st to 10thNight
62%6%12%15%6%1
4428
11th to 20thNight
68%7%13%8%4
4440
21st to endNight
71%5%10%11%31
4628
February1st to 10thNight
62%7%10%13%7%1
2470
11th to 20thNight
56%5%11%17%9%1
2253
21st to endNight
56%5%13%17%8%2
1884
March1st to 10thNight
51%5%12%21%10%1
2252
11th to 20thNight
43%7%12%21%15%2
2090
21st to endNight
52%5%9%21%11%2
2201
April1st to 10thNight
47%6%10%21%14%2
1864
11th to 20thNight
46%6%11%17%18%2
1643
21st to endNight
46%6%11%19%15%3
1620
May1st to 10thNight
49%6%12%20%11%2
1620
11th to 20thNight
44%6%10%19%18%3
1593
21st to endNight
35%8%14%24%15%3
1726
June1st to 10thNight
35%6%11%28%18%3
1440
11th to 20thNight
35%9%14%24%16%2
1440
21st to endNight
32%7%14%26%20%1
1440
July1st to 10thNight
30%6%12%28%20%4
1400
11th to 20thNight
31%5%13%29%20%2
1392
21st to endNight
27%8%17%24%20%3
1606
August1st to 10thNight
30%8%14%31%16%1
1600
11th to 20thNight
32%8%13%30%13%3
1598
21st to endNight
30%8%13%28%20%2
1824
September1st to 10thNight
34%8%12%27%17%2
1894
11th to 20thNight
31%5%10%32%20%1
1980
21st to endNight
38%6%12%28%14%1
1980
October1st to 10thNight
40%5%11%24%19%1
2016
11th to 20thNight
50%5%12%20%12%1
2160
21st to endNight
52%5%11%21%9%1
2538
November1st to 10thNight
42%5%12%25%15%1
2406
11th to 20thNight
52%5%14%19%8%1
2470
21st to endNight
56%6%12%19%7%
2504
December1st to 10thNight
64%7%11%13%6%
2660
11th to 20thNight
59%7%13%14%6%1
3400
21st to endNight
76%6%10%6%2
4884

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 10thDay
24%17%37%15%6%1
270
11th to 20thDay
25%14%45%14%11
270
21st to endDay
28%15%34%18%41
297
February1st to 10thDay
23%21%38%14%21
270
11th to 20thDay
24%21%38%15%2
270
21st to endDay
27%26%35%11%1
225
March1st to 10thDay
26%24%31%15%3
297
11th to 20thDay
23%13%34%23%7%
460
21st to endDay
26%17%30%21%5%1
470
April1st to 10thDay
21%13%35%21%9%1
420
11th to 20thDay
25%17%30%16%7%6%
412
21st to endDay
25%14%29%18%11%2
420
May1st to 10thDay
25%12%27%21%11%4
423
11th to 20thDay
21%10%28%21%13%7%
447
21st to endDay
14%6%23%28%19%9%
500
June1st to 10thDay
11%6%30%30%18%4
630
11th to 20thDay
14%7%30%27%18%4
630
21st to endDay
11%7%30%30%17%5%
630
July1st to 10thDay
8%5%23%27%26%12%
621
11th to 20thDay
10%7%27%27%20%8%
618
21st to endDay
9%5%24%30%23%10%
554
August1st to 10thDay
7%419%28%27%15%
446
11th to 20thDay
14%417%28%24%13%
439
21st to endDay
11%422%25%25%13%
495
September1st to 10thDay
13%6%23%24%23%11%
450
11th to 20thDay
11%319%24%28%15%
450
21st to endDay
14%10%24%24%19%9%
450
October1st to 10thDay
18%8%26%23%17%8%
450
11th to 20thDay
21%16%28%26%9%1
450
21st to endDay
28%16%34%18%3
331
November1st to 10thDay
16%18%36%18%11%1
270
11th to 20thDay
22%22%31%17%6%1
270
21st to endDay
26%19%36%14%4
250
December1st to 10thDay
24%19%34%14%7%1
180
11th to 20thDay
24%19%41%12%41
196
21st to endDay
28%22%33%16%1
297
January1st to 10thNight
22%15%35%22%6%1
950
11th to 20thNight
25%14%34%22%5%1
950
21st to endNight
21%12%34%28%5%
893
February1st to 10thNight
24%12%37%23%3
760
11th to 20thNight
22%15%35%24%4
743
21st to endNight
26%13%38%21%2
628
March1st to 10thNight
21%12%35%26%5%1
760
11th to 20thNight
17%15%37%25%5%1
760
21st to endNight
24%11%29%27%8%1
801
April1st to 10thNight
18%15%34%28%41
604
11th to 20thNight
23%8%33%27%7%1
533
21st to endNight
21%8%32%30%9%
540
May1st to 10thNight
19%7%31%32%8%1
540
11th to 20thNight
22%426%34%12%1
531
21st to endNight
12%423%37%21%2
584
June1st to 10thNight
12%323%48%13%1
540
11th to 20thNight
13%424%41%19%
540
21st to endNight
10%421%44%20%1
540
July1st to 10thNight
8%216%40%30%4
525
11th to 20thNight
10%317%41%25%4
522
21st to endNight
5%218%48%25%2
591
August1st to 10thNight
8%116%43%29%3
537
11th to 20thNight
8%219%38%29%4
534
21st to endNight
10%217%35%33%3
594
September1st to 10thNight
13%419%34%26%4
634
11th to 20thNight
13%417%34%29%5%
720
21st to endNight
15%7%20%32%22%5%
720
October1st to 10thNight
17%5%27%30%18%3
720
11th to 20thNight
23%12%30%26%8%1
720
21st to endNight
26%10%34%23%5%
792
November1st to 10thNight
18%10%32%28%11%1
740
11th to 20thNight
22%14%35%22%7%1
760
21st to endNight
25%13%34%21%6%
760
December1st to 10thNight
23%17%34%21%6%
760
11th to 20thNight
24%14%38%21%3
893
21st to endNight
32%12%35%19%2
1045
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