Island Grove Observatory.
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Island Grove Observatory. clear sky chart from 2005-11-05 to 2018-02-14.

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
32%
15380
13%
48632
8%
15345
38%
15345
17%
34828

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
16%
779
8%
2700
3%
776
23%
776
8%
2188
January16th to endNight
20%
832
9%
2704
4%
832
25%
832
9%
2211
February1st to 15thNight
17%
757
9%
2468
3%
757
24%
757
9%
1977
February16th to endNight
22%
631
12%
2023
5%
631
30%
631
13%
1514
March1st to 15thNight
21%
720
13%
1980
6%
720
28%
720
16%
1483
March16th to endNight
32%
768
20%
2112
10%
768
39%
768
24%
1440
April1st to 15thNight
27%
718
15%
1815
6%
718
32%
718
21%
1340
April16th to endNight
36%
557
19%
1637
9%
557
44%
557
25%
1107
May1st to 15thNight
44%
477
16%
1557
12%
477
50%
477
23%
1018
May16th to endNight
47%
374
16%
1497
15%
374
57%
374
25%
828
June1st to 15thNight
44%
360
11%
1440
11%
360
53%
360
19%
865
June16th to endNight
50%
360
12%
1284
15%
360
54%
360
25%
770
July1st to 15thNight
60%
340
16%
1287
21%
340
64%
340
31%
699
July16th to endNight
58%
470
16%
1505
16%
441
61%
441
29%
881
August1st to 15thNight
64%
539
16%
1609
12%
536
67%
536
35%
944
August16th to endNight
60%
621
21%
1767
12%
621
64%
621
34%
1078
September1st to 15thNight
49%
720
18%
1806
8%
720
53%
720
32%
1183
September16th to endNight
54%
717
22%
2007
17%
717
57%
717
29%
1276
October1st to 15thNight
37%
720
16%
2160
13%
720
42%
720
20%
1526
October16th to endNight
21%
768
11%
2304
6%
768
28%
768
12%
1788
November1st to 15thNight
28%
760
15%
2598
12%
760
34%
760
16%
1853
November16th to endNight
21%
780
9%
2730
6%
780
27%
780
10%
2122
December1st to 15thNight
12%
780
5%
2730
1%
780
16%
780
6%
2261
December16th to endNight
9%
832
6%
2912
1%
832
15%
832
5%
2476

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%37%6%35%5%5%7%32%
49437
Night
14%9%47%6%35%45%6%32%
48808
Cloud CoverDay
15%9%37%6%35%5%5%7%31%
49447
Night
14%9%47%6%3445%6%32%
48812
TransparencyDay
50%7%12%18%10%
49133
Night
51%6%11%18%10%
48632
SeeingDay
18%7%27%26%14%5%
5978
Night
19%9%30%27%11%1
15385

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%13%5%9%8%36%5%5%6%18%
1567
16th to endDay
12%14%6%11%10%46%5%5%6%16%
1872
February1st to 15thDay
11%14%5%13%8%47%5%5%5%19%
1695
16th to endDay
15%12%5%9%7%45%45%5%23%
1448
March1st to 15thDay
13%8%49%8%36%45%5%29%
1969
16th to endDay
14%7%47%434446%38%
2112
April1st to 15thDay
19%9%35%5%35%5%5%5%31%
2131
16th to endDay
15%8%35%423446%40%
2334
May1st to 15thDay
15%5%36%5%345%5%7%36%
2394
16th to endDay
12%5%25%5%25%5%6%7%41%
2618
June1st to 15thDay
16%6%25%425%46%8%36%
2520
16th to endDay
13%5%25%5%35%5%6%8%38%
2670
July1st to 15thDay
9%4246%45%6%6%8%41%
2592
16th to endDay
9%5%25%6%36%5%7%9%37%
2558
August1st to 15thDay
9%5%25%6%35%6%5%9%40%
2340
16th to endDay
10%5%25%425%7%7%9%39%
2423
September1st to 15thDay
16%6%26%43446%7%37%
2151
16th to endDay
14%5%25%6%34446%41%
1953
October1st to 15thDay
19%8%37%7%34446%31%
1800
16th to endDay
24%11%48%7%33445%21%
1920
November1st to 15thDay
15%13%47%6%35%45%7%26%
1586
16th to endDay
18%15%5%9%7%36%446%17%
1560
December1st to 15thDay
15%16%7%12%8%46%44413%
1560
16th to endDay
18%14%6%10%8%46%446%13%
1664
January1st to 15thNight
17%14%6%8%8%46%5%5%5%17%
2700
16th to endNight
13%13%6%10%10%5%7%5%5%416%
2704
February1st to 15thNight
11%14%6%10%9%46%5%46%19%
2466
16th to endNight
13%11%5%10%7%35%46%6%24%
2023
March1st to 15thNight
15%10%5%8%7%3433431%
1968
16th to endNight
14%7%46%424436%41%
2112
April1st to 15thNight
19%8%45%5%34436%34%
1815
16th to endNight
14%8%26%5%34347%40%
1637
May1st to 15thNight
15%5%25%5%3446%9%37%
1557
16th to endNight
10%425%32445%7%48%
1495
June1st to 15thNight
13%5%35%5%3446%8%40%
1440
16th to endNight
9%5%246%35%46%7%44%
1284
July1st to 15thNight
6%3245%345%46%53%
1365
16th to endNight
8%3234345%7%8%46%
1608
August1st to 15thNight
7%3135%245%7%10%48%
1620
16th to endNight
8%5%244235%5%6%51%
1767
September1st to 15thNight
14%6%24424347%45%
1806
16th to endNight
13%6%24422446%46%
2007
October1st to 15thNight
16%7%36%6%34346%35%
2160
16th to endNight
21%9%38%6%35%5%5%5%24%
2304
November1st to 15thNight
18%10%47%5%3445%7%30%
2598
16th to endNight
19%12%5%8%6%34446%22%
2730
December1st to 15thNight
17%14%6%11%8%36%5%45%15%
2730
16th to endNight
19%14%7%14%8%35%5%4413%
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
16%13%6%9%8%35%5%6%6%18%
1567
16th to endDay
12%14%6%12%9%45%5%5%6%16%
1872
February1st to 15thDay
12%14%6%12%8%46%5%45%19%
1695
16th to endDay
15%13%5%8%8%4445%5%23%
1448
March1st to 15thDay
14%9%48%8%45%45%5%28%
1980
16th to endDay
15%8%37%5%24346%38%
2111
April1st to 15thDay
19%10%35%6%2445%5%31%
2131
16th to endDay
16%8%35%323446%40%
2334
May1st to 15thDay
16%6%35%5%35%5%47%36%
2394
16th to endDay
12%5%245%25%5%6%6%40%
2618
June1st to 15thDay
17%5%245%35%46%8%35%
2520
16th to endDay
13%5%15%6%35%46%8%37%
2670
July1st to 15thDay
9%4246%46%5%5%8%41%
2592
16th to endDay
9%6%25%5%46%6%6%9%37%
2558
August1st to 15thDay
9%6%25%6%35%5%6%9%39%
2340
16th to endDay
10%6%24435%7%6%8%39%
2423
September1st to 15thDay
16%6%35%5%25%45%8%37%
2151
16th to endDay
14%5%26%5%43446%42%
1953
October1st to 15thDay
19%8%46%6%34445%32%
1800
16th to endDay
25%10%48%7%33345%22%
1920
November1st to 15thDay
15%13%47%5%345%5%7%26%
1586
16th to endDay
18%15%5%8%7%45%5%46%18%
1560
December1st to 15thDay
15%17%7%13%8%36%5%4413%
1560
16th to endDay
18%14%7%10%8%45%446%14%
1664
January1st to 15thNight
16%15%6%9%7%46%5%45%17%
2700
16th to endNight
13%13%6%11%9%5%7%5%45%17%
2704
February1st to 15thNight
12%15%7%9%9%5%5%5%45%19%
2459
16th to endNight
13%11%5%9%7%45%45%6%24%
2023
March1st to 15thNight
16%11%5%7%7%34335%31%
1980
16th to endNight
14%7%46%5%24435%41%
2112
April1st to 15thNight
19%8%45%6%24436%34%
1815
16th to endNight
14%7%26%433447%40%
1637
May1st to 15thNight
15%6%25%5%3446%8%37%
1556
16th to endNight
10%5%14415%45%7%48%
1495
June1st to 15thNight
13%5%25%5%25%46%8%40%
1440
16th to endNight
10%5%245%3446%7%44%
1284
July1st to 15thNight
6%324434447%52%
1365
16th to endNight
8%424425%5%7%8%46%
1608
August1st to 15thNight
7%323425%5%6%10%48%
1620
16th to endNight
8%5%145%3345%6%51%
1767
September1st to 15thNight
14%5%23424347%45%
1806
16th to endNight
13%6%335%22436%47%
2007
October1st to 15thNight
17%7%36%6%34445%36%
2160
16th to endNight
21%9%37%6%35%45%6%24%
2304
November1st to 15thNight
18%11%45%5%24446%31%
2598
16th to endNight
19%13%49%5%3445%6%22%
2730
December1st to 15thNight
17%15%6%11%8%46%5%45%15%
2730
16th to endNight
19%14%7%12%8%3444413%
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
63%7%11%11%5%
1568
16th to endDay
66%6%11%9%6%
1872
February1st to 15thDay
65%7%8%13%3
1697
16th to endDay
61%5%10%14%7%
1448
March1st to 15thDay
57%5%13%15%6%
1980
16th to endDay
48%49%17%17%1
2112
April1st to 15thDay
53%5%10%18%11%
2131
16th to endDay
44%6%10%20%15%2
2334
May1st to 15thDay
46%7%10%20%14%1
2394
16th to endDay
40%8%13%22%13%1
2622
June1st to 15thDay
44%7%12%22%11%
2520
16th to endDay
43%7%14%21%12%
2670
July1st to 15thDay
37%8%13%23%15%1
2442
16th to endDay
42%9%13%22%10%1
2399
August1st to 15thDay
40%9%15%20%13%1
2327
16th to endDay
38%8%16%24%10%1
2423
September1st to 15thDay
44%7%13%23%10%
2151
16th to endDay
42%7%12%27%9%
1953
October1st to 15thDay
54%5%9%20%9%
1800
16th to endDay
63%6%13%11%4
1920
November1st to 15thDay
55%7%13%15%7%
1586
16th to endDay
65%8%12%10%3
1560
December1st to 15thDay
71%7%11%9%1
1560
16th to endDay
70%6%9%10%3
1664
January1st to 15thNight
66%6%10%10%5%
2700
16th to endNight
66%7%9%12%3
2704
February1st to 15thNight
64%7%9%14%4
2468
16th to endNight
57%5%12%15%7%
2023
March1st to 15thNight
56%412%19%6%
1980
16th to endNight
44%5%10%21%16%1
2112
April1st to 15thNight
51%5%9%19%14%
1815
16th to endNight
43%6%9%18%18%2
1637
May1st to 15thNight
43%6%12%18%16%2
1557
16th to endNight
34%6%14%26%15%2
1497
June1st to 15thNight
40%7%12%24%15%
1440
16th to endNight
37%6%14%24%15%
1284
July1st to 15thNight
29%7%10%29%21%1
1287
16th to endNight
32%8%13%28%15%1
1505
August1st to 15thNight
28%8%20%27%14%
1609
16th to endNight
32%7%13%29%15%1
1767
September1st to 15thNight
38%5%15%26%13%1
1806
16th to endNight
38%5%11%30%13%
2007
October1st to 15thNight
47%7%10%21%12%
2160
16th to endNight
58%8%13%13%6%
2304
November1st to 15thNight
52%6%12%17%9%1
2598
16th to endNight
61%7%14%12%3
2730
December1st to 15thNight
69%6%11%9%2
2730
16th to endNight
72%6%8%8%3
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
20%22%34%17%6%
94
16th to endDay
28%11%36%22%
144
February1st to 15thDay
23%12%47%16%
130
16th to endDay
23%20%31%23%1
89
March1st to 15thDay
20%14%34%25%4
270
16th to endDay
24%5%31%26%9%2
288
April1st to 15thDay
25%10%32%21%8%1
270
16th to endDay
18%9%30%24%12%5%
270
May1st to 15thDay
21%428%26%13%5%
288
16th to endDay
15%6%27%31%15%3
331
June1st to 15thDay
21%5%22%31%16%2
315
16th to endDay
16%428%32%15%2
465
July1st to 15thDay
9%325%34%19%7%
376
16th to endDay
8%323%35%19%9%
326
August1st to 15thDay
12%219%29%23%12%
313
16th to endDay
15%319%24%24%14%
332
September1st to 15thDay
13%418%26%24%14%
315
16th to endDay
14%319%25%24%12%
314
October1st to 15thDay
23%5%30%19%14%6%
315
16th to endDay
28%12%32%20%5%
336
November1st to 15thDay
22%12%28%24%9%2
121
16th to endDay
31%16%34%13%4
90
December1st to 15thDay
14%23%32%25%4
90
16th to endDay
22%18%45%11%1
96
January1st to 15thNight
23%14%37%18%5%
780
16th to endNight
20%11%36%24%6%
832
February1st to 15thNight
20%10%42%22%3
760
16th to endNight
20%11%36%26%4
631
March1st to 15thNight
21%13%36%23%4
720
16th to endNight
18%9%34%25%10%1
768
April1st to 15thNight
22%11%33%27%5%
718
16th to endNight
19%7%31%29%10%1
557
May1st to 15thNight
19%325%34%14%2
477
16th to endNight
12%429%35%17%1
375
June1st to 15thNight
13%6%29%36%14%
360
16th to endNight
11%326%41%17%
360
July1st to 15thNight
9%221%46%18%2
340
16th to endNight
9%222%39%24%1
470
August1st to 15thNight
8%218%41%27%2
539
16th to endNight
9%320%34%28%3
621
September1st to 15thNight
16%423%29%20%6%
720
16th to endNight
17%419%31%21%6%
717
October1st to 15thNight
20%8%27%27%14%1
720
16th to endNight
27%12%32%21%5%
768
November1st to 15thNight
25%10%28%23%10%
760
16th to endNight
25%15%30%22%6%
780
December1st to 15thNight
27%15%38%16%2
780
16th to endNight
25%13%39%17%2
832
Page generated at 2018-02-15 10:58:41. Version ac04

Copyright 2018 A. Danko


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