AI2 Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the AI2 Observatory clear sky chart from 2005-11-05 to 2017-09-10.

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%
15003
19%
46794
12%
14971
47%
14971
22%
29869

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
28%
720
19%
2506
11%
716
39%
716
18%
1608
January16th to endNight
28%
768
21%
2547
11%
768
42%
768
21%
1593
February1st to 15thNight
25%
704
17%
2269
8%
701
38%
701
18%
1495
February16th to endNight
25%
631
25%
1893
11%
631
43%
631
22%
1197
March1st to 15thNight
27%
720
19%
2102
9%
720
38%
720
22%
1386
March16th to endNight
29%
768
22%
2026
9%
768
40%
768
24%
1339
April1st to 15thNight
28%
718
17%
1796
7%
718
33%
718
24%
1239
April16th to endNight
35%
720
18%
1800
6%
720
41%
720
26%
1207
May1st to 15thNight
33%
477
18%
1557
9%
477
43%
477
17%
1027
May16th to endNight
47%
374
15%
1497
13%
374
54%
374
17%
926
June1st to 15thNight
45%
360
15%
1440
16%
360
51%
360
19%
893
June16th to endNight
55%
360
17%
1440
20%
360
63%
360
23%
802
July1st to 15thNight
55%
340
13%
1360
17%
340
57%
340
18%
835
July16th to endNight
56%
379
16%
1421
18%
357
64%
357
24%
792
August1st to 15thNight
58%
571
18%
1641
14%
568
61%
568
28%
1039
August16th to endNight
60%
764
20%
1910
12%
764
62%
764
33%
1262
September1st to 15thNight
52%
700
23%
1750
12%
700
56%
700
33%
1144
September16th to endNight
55%
657
26%
1776
19%
657
61%
657
31%
1117
October1st to 15thNight
45%
660
22%
1980
20%
660
50%
660
26%
1241
October16th to endNight
39%
704
23%
2161
14%
704
51%
704
27%
1327
November1st to 15thNight
38%
700
21%
2277
15%
700
47%
700
24%
1385
November16th to endNight
33%
720
20%
2437
13%
720
44%
720
20%
1534
December1st to 15thNight
29%
720
15%
2520
8%
720
39%
720
15%
1703
December16th to endNight
24%
768
18%
2688
8%
768
38%
768
16%
1778

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
16%5%25%5%35%45%7%38%
47839
Night
16%5%2442445%7%42%
46965
Cloud CoverDay
16%5%25%5%35%45%7%38%
47848
Night
16%5%2442445%7%42%
46971
TransparencyDay
43%5%11%22%14%1
47528
Night
41%412%23%15%2
46794
SeeingDay
18%12%17%25%18%7%
5684
Night
16%17%20%32%12%1
15004

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
13%6%36%6%45%5%45%38%
1432
16th to endDay
14%6%45%5%345%5%7%37%
1674
February1st to 15thDay
15%6%36%5%35%46%7%35%
1592
16th to endDay
14%6%36%5%35%45%5%38%
1580
March1st to 15thDay
16%7%25%5%35%5%5%7%35%
1847
16th to endDay
17%7%24424346%40%
2196
April1st to 15thDay
18%7%25%424447%39%
2152
16th to endDay
15%425%5%335%6%6%41%
2160
May1st to 15thDay
21%5%245%25%45%6%35%
2405
16th to endDay
16%6%245%25%5%6%9%34%
2618
June1st to 15thDay
15%5%25%436%5%7%9%34%
2520
16th to endDay
14%425%6%35%46%8%38%
2520
July1st to 15thDay
11%5%25%6%36%5%7%10%35%
2520
16th to endDay
10%425%6%45%6%7%9%36%
2648
August1st to 15thDay
14%5%246%45%7%6%7%35%
2295
16th to endDay
14%424425%347%44%
2292
September1st to 15thDay
15%424434447%43%
2098
16th to endDay
16%5%25%323446%44%
1851
October1st to 15thDay
17%5%15%42335%7%43%
1650
16th to endDay
19%414335%346%41%
1711
November1st to 15thDay
17%7%2442333445%
1581
16th to endDay
19%5%13324347%42%
1521
December1st to 15thDay
17%7%26%325%46%7%35%
1440
16th to endDay
21%7%35%4245%5%6%34%
1536
January1st to 15thNight
17%6%25%434446%39%
2506
16th to endNight
15%8%3442445%6%41%
2547
February1st to 15thNight
13%8%36%5%34446%39%
2268
16th to endNight
15%5%35%32445%5%43%
1893
March1st to 15thNight
17%5%24324346%42%
2089
16th to endNight
16%6%25%323446%43%
2026
April1st to 15thNight
17%5%25%5%24447%39%
1796
16th to endNight
18%42432345%7%43%
1800
May1st to 15thNight
19%7%2433445%6%37%
1557
16th to endNight
17%5%15%3345%47%41%
1495
June1st to 15thNight
17%5%2342345%7%42%
1440
16th to endNight
10%4135%245%6%9%45%
1440
July1st to 15thNight
12%325%6%36%46%9%40%
1440
16th to endNight
9%423425%5%6%11%44%
1517
August1st to 15thNight
12%4245%235%6%8%43%
1652
16th to endNight
12%5%245%3445%9%42%
1910
September1st to 15thNight
15%5%14424346%47%
1750
16th to endNight
13%5%24422437%48%
1776
October1st to 15thNight
18%6%23323346%45%
1980
16th to endNight
19%5%1322335%6%46%
2161
November1st to 15thNight
14%6%24324346%46%
2277
16th to endNight
18%5%3442345%6%41%
2437
December1st to 15thNight
19%5%35%435%5%46%35%
2520
16th to endNight
19%7%24434446%37%
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
14%6%35%6%35%5%4439%
1432
16th to endDay
13%6%45%6%245%5%7%37%
1674
February1st to 15thDay
15%7%36%435%5%5%6%36%
1592
16th to endDay
15%6%36%6%35%45%5%37%
1580
March1st to 15thDay
16%7%25%6%35%45%8%34%
1857
16th to endDay
17%7%24434446%40%
2195
April1st to 15thDay
18%7%35%424347%39%
2152
16th to endDay
15%425%5%3346%6%42%
2160
May1st to 15thDay
21%5%245%25%45%6%35%
2405
16th to endDay
17%6%24435%5%6%9%35%
2618
June1st to 15thDay
15%425%436%5%6%10%33%
2520
16th to endDay
13%5%25%5%35%46%8%39%
2520
July1st to 15thDay
11%5%25%7%45%5%7%10%35%
2520
16th to endDay
10%5%25%5%36%5%7%9%37%
2648
August1st to 15thDay
14%6%25%5%46%6%6%7%34%
2295
16th to endDay
14%425%435%346%44%
2292
September1st to 15thDay
15%424435%447%43%
2098
16th to endDay
15%5%25%324446%44%
1851
October1st to 15thDay
16%5%25%423446%43%
1650
16th to endDay
19%414435%35%6%41%
1711
November1st to 15thDay
17%7%24423335%45%
1581
16th to endDay
19%5%2341335%6%43%
1521
December1st to 15thDay
17%6%35%43446%7%35%
1440
16th to endDay
20%7%344245%5%6%34%
1536
January1st to 15thNight
17%6%35%43445%6%39%
2506
16th to endNight
16%8%34424446%41%
2547
February1st to 15thNight
13%8%36%5%34446%39%
2261
16th to endNight
15%5%3432445%5%44%
1893
March1st to 15thNight
18%5%24424346%42%
2102
16th to endNight
16%6%25%423437%43%
2026
April1st to 15thNight
17%5%25%5%2445%6%39%
1796
16th to endNight
18%5%2332335%6%44%
1800
May1st to 15thNight
19%7%2443445%6%38%
1557
16th to endNight
16%5%23425%447%42%
1495
June1st to 15thNight
17%5%2442345%7%41%
1440
16th to endNight
10%4244245%7%9%44%
1440
July1st to 15thNight
11%425%6%35%5%6%9%39%
1440
16th to endNight
9%423425%6%6%11%43%
1517
August1st to 15thNight
12%4245%245%6%7%44%
1652
16th to endNight
13%5%245%3445%9%42%
1910
September1st to 15thNight
15%5%1442335%5%47%
1750
16th to endNight
13%5%24423437%48%
1776
October1st to 15thNight
18%6%23323346%45%
1980
16th to endNight
19%5%13213346%46%
2161
November1st to 15thNight
14%6%34323346%46%
2277
16th to endNight
18%5%3442345%6%41%
2437
December1st to 15thNight
20%5%25%5%35%45%5%35%
2520
16th to endNight
19%7%245%34446%37%
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
47%5%11%23%10%2
1433
16th to endDay
45%413%23%12%1
1674
February1st to 15thDay
45%5%12%20%13%1
1595
16th to endDay
46%412%24%10%1
1580
March1st to 15thDay
47%414%20%10%1
1857
16th to endDay
45%310%21%17%2
2196
April1st to 15thDay
44%410%22%13%4
2152
16th to endDay
40%410%20%20%3
2160
May1st to 15thDay
48%49%20%15%2
2405
16th to endDay
44%6%13%20%13%1
2622
June1st to 15thDay
44%7%14%22%10%
2520
16th to endDay
41%6%13%25%11%1
2520
July1st to 15thDay
43%6%11%22%15%1
2371
16th to endDay
39%6%12%24%13%1
2481
August1st to 15thDay
44%6%12%19%17%
2282
16th to endDay
39%48%25%20%2
2292
September1st to 15thDay
40%410%21%21%1
2098
16th to endDay
40%36%22%23%3
1851
October1st to 15thDay
41%413%22%15%2
1650
16th to endDay
42%311%26%14%1
1711
November1st to 15thDay
43%213%19%18%3
1581
16th to endDay
40%312%26%14%1
1521
December1st to 15thDay
46%5%17%19%9%1
1440
16th to endDay
49%5%15%18%11%
1536
January1st to 15thNight
44%413%21%12%2
2506
16th to endNight
43%312%25%13%1
2547
February1st to 15thNight
45%412%21%12%2
2269
16th to endNight
41%39%25%17%2
1893
March1st to 15thNight
43%413%22%13%2
2102
16th to endNight
41%410%22%18%2
2026
April1st to 15thNight
44%410%21%16%2
1796
16th to endNight
40%49%20%22%3
1800
May1st to 15thNight
45%5%10%19%17%2
1557
16th to endNight
41%7%15%17%15%3
1497
June1st to 15thNight
42%6%12%22%16%
1440
16th to endNight
33%6%14%31%13%
1440
July1st to 15thNight
41%7%12%22%14%1
1360
16th to endNight
32%7%17%25%14%2
1421
August1st to 15thNight
35%7%13%23%17%2
1641
16th to endNight
37%5%10%22%21%2
1910
September1st to 15thNight
38%410%24%21%1
1750
16th to endNight
36%46%23%26%2
1776
October1st to 15thNight
41%311%25%16%2
1980
16th to endNight
38%412%27%16%
2161
November1st to 15thNight
39%312%21%17%4
2277
16th to endNight
43%311%25%13%2
2437
December1st to 15thNight
49%5%13%20%10%
2520
16th to endNight
47%413%21%11%
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
18%16%33%25%5%1
60
16th to endDay
20%8%26%31%13%
87
February1st to 15thDay
17%11%40%26%3
109
16th to endDay
17%15%27%33%6%
239
March1st to 15thDay
17%24%21%27%8%
270
16th to endDay
18%17%25%24%10%3
288
April1st to 15thDay
18%16%23%24%13%2
270
16th to endDay
17%13%23%20%17%7%
270
May1st to 15thDay
32%18%14%17%12%4
288
16th to endDay
18%13%14%25%19%8%
331
June1st to 15thDay
16%13%19%21%21%7%
315
16th to endDay
18%14%16%26%19%5%
315
July1st to 15thDay
17%7%11%26%26%9%
305
16th to endDay
13%10%10%23%29%13%
326
August1st to 15thDay
17%7%9%24%26%14%
313
16th to endDay
12%5%5%26%28%20%
332
September1st to 15thDay
14%8%18%21%20%16%
294
16th to endDay
20%7%8%22%21%19%
254
October1st to 15thDay
18%8%11%29%23%7%
255
16th to endDay
16%10%26%29%15%
263
November1st to 15thDay
17%14%18%26%18%2
235
16th to endDay
17%17%22%28%12%2
141
December1st to 15thDay
18%18%28%21%10%3
60
16th to endDay
42%6%23%25%3
64
January1st to 15thNight
16%20%28%28%5%
720
16th to endNight
17%19%27%31%3
768
February1st to 15thNight
15%21%29%31%2
704
16th to endNight
16%20%31%28%3
631
March1st to 15thNight
20%20%27%26%4
720
16th to endNight
16%19%26%27%8%
768
April1st to 15thNight
16%21%28%27%5%
718
16th to endNight
15%21%21%29%11%
720
May1st to 15thNight
22%19%18%28%9%
477
16th to endNight
16%18%11%39%13%1
375
June1st to 15thNight
17%19%10%34%17%
360
16th to endNight
8%17%9%48%15%
360
July1st to 15thNight
12%12%9%42%22%1
340
16th to endNight
8%17%8%39%22%1
379
August1st to 15thNight
15%10%5%40%25%1
571
16th to endNight
13%9%6%35%32%3
764
September1st to 15thNight
16%10%13%36%22%2
700
16th to endNight
16%10%8%34%26%3
657
October1st to 15thNight
18%11%16%33%19%1
660
16th to endNight
19%11%25%33%10%
704
November1st to 15thNight
15%17%22%29%13%1
700
16th to endNight
15%20%23%31%8%
720
December1st to 15thNight
21%19%21%28%7%1
720
16th to endNight
20%20%26%28%3
768
Page generated at 2017-09-11 19:35:20. Version ac04

Copyright 2017 A. Danko


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