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 2005-11-05 to 2017-08-12.

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
38%
15766
15%
46651
10%
15724
43%
15724
21%
32587

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
17%
900
9%
2506
4%
895
21%
895
12%
1987
January16th to endNight
21%
864
8%
2592
3%
864
26%
864
11%
2069
February1st to 15thNight
19%
701
9%
2252
3%
701
25%
701
11%
1733
February16th to endNight
25%
631
13%
1893
6%
631
32%
631
16%
1383
March1st to 15thNight
27%
720
15%
2082
8%
720
32%
720
17%
1513
March16th to endNight
34%
768
18%
2112
10%
768
40%
768
21%
1482
April1st to 15thNight
30%
581
14%
1809
7%
581
37%
581
18%
1261
April16th to endNight
36%
540
19%
1620
8%
540
46%
540
25%
1087
May1st to 15thNight
39%
540
14%
1620
8%
540
45%
540
21%
1127
May16th to endNight
50%
562
15%
1671
12%
561
55%
561
28%
1070
June1st to 15thNight
57%
540
14%
1440
11%
540
60%
540
33%
915
June16th to endNight
58%
540
16%
1440
12%
540
63%
540
34%
911
July1st to 15thNight
66%
510
16%
1360
14%
510
68%
510
40%
804
July16th to endNight
69%
564
19%
1495
16%
531
72%
531
39%
875
August1st to 15thNight
66%
527
21%
1575
17%
524
69%
524
34%
936
August16th to endNight
65%
525
21%
1601
17%
525
68%
525
33%
950
September1st to 15thNight
58%
608
26%
1763
20%
608
63%
608
35%
1050
September16th to endNight
59%
657
23%
1815
17%
657
63%
657
33%
1134
October1st to 15thNight
47%
660
19%
1892
16%
660
52%
660
28%
1235
October16th to endNight
27%
704
14%
2211
8%
704
35%
704
17%
1577
November1st to 15thNight
37%
700
19%
2276
16%
700
43%
700
23%
1479
November16th to endNight
25%
720
13%
2361
9%
720
31%
720
14%
1727
December1st to 15thNight
19%
744
8%
2544
4%
744
24%
744
10%
1982
December16th to endNight
15%
960
7%
2721
1%
960
20%
960
8%
2300

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%8%46%6%35%45%7%32%
47307
Night
15%8%46%5%3445%6%35%
46829
Cloud CoverDay
14%8%47%6%35%45%7%32%
47317
Night
15%8%46%5%3445%6%35%
46833
TransparencyDay
49%6%12%19%10%1
47003
Night
48%5%12%20%11%1
46651
SeeingDay
17%7%26%24%16%7%
5698
Night
19%7%28%30%12%1
15770

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
16%16%5%10%7%46%445%16%
1432
16th to endDay
16%17%8%9%8%44446%14%
1629
February1st to 15thDay
14%14%6%10%9%36%45%6%18%
1607
16th to endDay
14%14%5%11%7%35%45%6%21%
1580
March1st to 15thDay
16%11%48%5%35%35%6%28%
1867
16th to endDay
17%9%5%8%6%35%335%30%
2112
April1st to 15thDay
19%10%35%5%34446%30%
2150
16th to endDay
16%8%36%5%24446%38%
2340
May1st to 15thDay
19%7%27%6%35%346%32%
2331
16th to endDay
13%6%25%5%35%45%9%38%
2441
June1st to 15thDay
10%5%36%5%35%46%8%40%
2520
16th to endDay
10%5%35%6%46%6%7%11%34%
2520
July1st to 15thDay
7%435%5%345%5%8%45%
2520
16th to endDay
8%5%25%6%346%7%10%38%
2568
August1st to 15thDay
8%5%25%6%46%6%7%7%38%
2288
16th to endDay
11%425%5%35%5%7%9%38%
2248
September1st to 15thDay
12%6%24435%45%9%40%
1856
16th to endDay
12%5%25%5%25%46%9%39%
1815
October1st to 15thDay
15%6%35%6%45%347%38%
1738
16th to endDay
21%9%45%6%235%46%31%
1658
November1st to 15thDay
14%8%36%5%3445%6%37%
1582
16th to endDay
17%12%5%8%6%35%446%27%
1595
December1st to 15thDay
16%13%6%11%6%45%446%21%
1413
16th to endDay
22%15%9%11%6%3434416%
1497
January1st to 15thNight
21%13%5%7%5%34345%23%
2506
16th to endNight
14%12%7%11%7%45%45%5%20%
2592
February1st to 15thNight
16%14%6%7%7%44445%26%
2250
16th to endNight
16%9%5%7%7%35%45%6%28%
1893
March1st to 15thNight
17%9%46%5%2445%5%33%
2070
16th to endNight
15%7%36%5%35%5%5%6%36%
2112
April1st to 15thNight
19%7%35%43445%6%33%
1809
16th to endNight
16%6%25%5%245%5%6%39%
1620
May1st to 15thNight
17%6%36%5%35%45%7%34%
1620
16th to endNight
12%425%5%25%448%44%
1669
June1st to 15thNight
10%4145%25%46%8%46%
1440
16th to endNight
9%325%4245%7%9%43%
1440
July1st to 15thNight
7%3144245%5%8%51%
1440
16th to endNight
5%3245%35%4410%52%
1598
August1st to 15thNight
5%324435%5%6%8%48%
1586
16th to endNight
10%5%24324347%51%
1601
September1st to 15thNight
12%424314346%52%
1763
16th to endNight
11%5%245%2445%7%47%
1815
October1st to 15thNight
15%6%25%425%347%42%
1892
16th to endNight
21%7%35%5%3445%5%33%
2211
November1st to 15thNight
14%7%35%435%35%6%40%
2276
16th to endNight
21%10%5%6%424446%28%
2361
December1st to 15thNight
21%12%5%9%5%35%445%22%
2544
16th to endNight
22%15%7%9%7%35%44416%
2721

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
16%17%5%9%7%45%5%45%17%
1432
16th to endDay
17%17%8%9%8%45%446%14%
1629
February1st to 15thDay
14%14%6%11%8%46%446%18%
1607
16th to endDay
14%14%5%11%8%3445%6%21%
1580
March1st to 15thDay
17%11%48%6%3445%6%28%
1878
16th to endDay
17%9%48%6%24446%30%
2111
April1st to 15thDay
19%10%45%5%35%446%30%
2150
16th to endDay
16%7%36%433445%38%
2340
May1st to 15thDay
19%7%36%6%35%446%32%
2331
16th to endDay
13%5%35%5%3445%9%38%
2441
June1st to 15thDay
10%5%36%5%35%5%6%8%40%
2520
16th to endDay
10%425%6%46%6%7%11%34%
2520
July1st to 15thDay
7%425%5%35%46%8%45%
2520
16th to endDay
8%426%6%445%7%10%38%
2568
August1st to 15thDay
8%5%25%7%46%6%6%8%38%
2288
16th to endDay
11%425%5%35%5%6%9%38%
2248
September1st to 15thDay
12%5%25%445%46%8%40%
1856
16th to endDay
12%425%5%35%5%6%9%39%
1815
October1st to 15thDay
14%6%25%6%34446%38%
1738
16th to endDay
20%8%46%5%34446%31%
1658
November1st to 15thDay
14%8%35%6%3445%6%37%
1582
16th to endDay
17%11%48%6%35%446%27%
1595
December1st to 15thDay
16%12%7%11%7%34437%21%
1413
16th to endDay
21%15%9%11%6%33245%15%
1497
January1st to 15thNight
21%13%5%7%7%24445%23%
2506
16th to endNight
14%12%7%10%7%45%45%5%20%
2592
February1st to 15thNight
16%13%6%8%7%3444426%
2243
16th to endNight
16%10%5%7%7%35%446%28%
1893
March1st to 15thNight
18%9%46%6%2445%6%32%
2082
16th to endNight
15%7%36%5%345%5%6%36%
2112
April1st to 15thNight
18%8%26%5%3445%6%33%
1809
16th to endNight
15%6%25%4245%5%7%38%
1620
May1st to 15thNight
17%6%26%5%35%45%8%34%
1619
16th to endNight
12%5%245%25%447%44%
1669
June1st to 15thNight
10%4245%25%46%8%45%
1440
16th to endNight
8%4244246%7%9%43%
1440
July1st to 15thNight
7%214425%46%7%52%
1440
16th to endNight
43245%344411%51%
1598
August1st to 15thNight
5%3345%36%5%6%8%49%
1586
16th to endNight
10%424423447%51%
1601
September1st to 15thNight
12%414323445%52%
1763
16th to endNight
10%5%245%2345%7%47%
1815
October1st to 15thNight
15%5%35%434448%42%
1892
16th to endNight
20%8%26%5%3445%5%33%
2211
November1st to 15thNight
14%7%3443445%6%40%
2276
16th to endNight
21%10%46%5%34446%28%
2361
December1st to 15thNight
21%11%5%8%6%35%445%22%
2544
16th to endNight
22%14%6%9%6%34445%16%
2721

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
67%6%11%11%3
1433
16th to endDay
71%6%8%9%4
1629
February1st to 15thDay
65%7%8%12%5%
1609
16th to endDay
63%6%10%13%5%
1580
March1st to 15thDay
56%6%11%16%7%1
1878
16th to endDay
55%411%19%7%1
2112
April1st to 15thDay
54%5%10%19%10%
2150
16th to endDay
46%5%13%16%14%2
2340
May1st to 15thDay
52%5%11%18%9%2
2331
16th to endDay
42%6%12%24%12%1
2445
June1st to 15thDay
39%7%12%24%14%1
2520
16th to endDay
40%9%13%19%15%
2520
July1st to 15thDay
34%7%11%25%18%2
2371
16th to endDay
37%9%14%20%15%2
2408
August1st to 15thDay
40%7%13%24%12%1
2275
16th to endDay
39%8%12%22%15%2
2248
September1st to 15thDay
40%6%13%24%13%
1856
16th to endDay
40%6%10%29%12%
1815
October1st to 15thDay
44%6%12%22%12%1
1738
16th to endDay
53%5%14%17%7%
1658
November1st to 15thDay
46%5%11%22%11%1
1582
16th to endDay
58%412%18%5%
1595
December1st to 15thDay
64%6%12%13%3
1413
16th to endDay
72%410%9%3
1497
January1st to 15thNight
63%412%12%6%
2506
16th to endNight
63%6%13%11%4
2592
February1st to 15thNight
60%6%11%14%6%
2252
16th to endNight
55%414%17%6%
1893
March1st to 15thNight
52%5%10%18%10%1
2082
16th to endNight
48%5%12%22%9%1
2112
April1st to 15thNight
49%5%10%19%14%
1809
16th to endNight
43%5%12%18%17%3
1620
May1st to 15thNight
48%6%11%20%11%2
1620
16th to endNight
38%6%12%23%15%3
1671
June1st to 15thNight
35%7%13%27%15%1
1440
16th to endNight
33%7%15%24%17%1
1440
July1st to 15thNight
30%5%11%29%21%2
1360
16th to endNight
28%6%16%24%20%3
1495
August1st to 15thNight
30%7%12%30%15%2
1575
16th to endNight
32%6%11%28%17%3
1601
September1st to 15thNight
32%5%10%29%20%1
1763
16th to endNight
35%5%11%29%17%
1815
October1st to 15thNight
41%5%13%21%17%1
1892
16th to endNight
51%5%13%21%8%
2211
November1st to 15thNight
44%5%13%23%12%1
2276
16th to endNight
56%5%12%18%6%
2361
December1st to 15thNight
62%6%12%13%5%
2544
16th to endNight
70%6%10%9%3
2721

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
20%14%40%18%5%1
90
16th to endDay
30%8%41%17%2
96
February1st to 15thDay
20%22%43%14%
90
16th to endDay
22%12%40%23%1
81
March1st to 15thDay
30%12%29%20%7%
168
16th to endDay
23%8%29%27%9%1
288
April1st to 15thDay
21%10%32%24%9%2
270
16th to endDay
21%10%30%17%13%7%
270
May1st to 15thDay
27%6%26%20%13%5%
288
16th to endDay
17%8%24%23%17%9%
341
June1st to 15thDay
12%431%29%16%5%
495
16th to endDay
12%5%32%26%16%6%
495
July1st to 15thDay
9%6%23%28%21%10%
475
16th to endDay
9%322%27%24%12%
428
August1st to 15thDay
10%213%28%23%20%
297
16th to endDay
14%214%17%27%21%
268
September1st to 15thDay
13%220%19%27%17%
255
16th to endDay
16%315%24%29%11%
254
October1st to 15thDay
17%6%21%27%19%7%
255
16th to endDay
28%7%32%25%6%
170
November1st to 15thDay
12%14%26%26%17%2
90
16th to endDay
24%17%34%17%5%
85
December1st to 15thDay
20%26%30%18%5%
60
16th to endDay
26%22%41%8%
89
January1st to 15thNight
26%12%34%19%5%
900
16th to endNight
19%11%34%28%5%
864
February1st to 15thNight
23%13%36%23%4
704
16th to endNight
22%10%33%29%3
631
March1st to 15thNight
22%11%32%27%5%
720
16th to endNight
18%9%30%30%9%1
768
April1st to 15thNight
22%12%29%29%5%
581
16th to endNight
19%6%34%28%9%1
540
May1st to 15thNight
20%5%27%36%8%1
540
16th to endNight
14%323%36%18%2
563
June1st to 15thNight
11%123%48%14%
540
16th to endNight
10%222%42%20%1
540
July1st to 15thNight
10%116%40%27%3
510
16th to endNight
5%115%48%25%3
564
August1st to 15thNight
6%116%43%27%3
527
16th to endNight
12%113%32%34%4
525
September1st to 15thNight
14%418%29%27%5%
608
16th to endNight
12%5%15%32%28%5%
657
October1st to 15thNight
18%424%32%17%2
660
16th to endNight
24%11%33%24%5%
704
November1st to 15thNight
17%9%30%28%12%2
700
16th to endNight
26%12%30%21%8%
720
December1st to 15thNight
26%12%35%21%4
744
16th to endNight
29%10%35%20%3
960
Page generated at 2017-08-13 14:16:39. Version ac04

Copyright 2017 A. Danko


Island Lake State Recreation Area Clear Sky Chart | Charts Home