Annual International Video Astronomy Star Party
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Annual International Video Astronomy Star Party clear sky chart from 2005-11-05 to 2018-01-12.

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
27%
15165
13%
48370
8%
15133
34%
15133
15%
35248

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
13%
765
5%
2662
1%
761
17%
761
6%
2206
January16th to endNight
17%
768
9%
2637
5%
768
23%
768
9%
2087
February1st to 15thNight
13%
704
8%
2287
3%
701
20%
701
8%
1840
February16th to endNight
17%
631
11%
1931
5%
631
25%
631
10%
1524
March1st to 15thNight
19%
720
13%
2109
7%
720
26%
720
14%
1598
March16th to endNight
26%
768
18%
2026
7%
768
34%
768
20%
1439
April1st to 15thNight
22%
718
15%
1796
5%
718
27%
718
19%
1352
April16th to endNight
27%
671
16%
1751
6%
671
33%
671
22%
1246
May1st to 15thNight
34%
360
17%
1440
15%
360
44%
360
16%
953
May16th to endNight
32%
375
14%
1496
10%
374
43%
374
17%
941
June1st to 15thNight
34%
360
10%
1440
11%
360
42%
360
14%
994
June16th to endNight
38%
360
8%
1440
11%
360
43%
360
19%
905
July1st to 15thNight
49%
340
14%
1360
19%
340
56%
340
24%
777
July16th to endNight
52%
376
13%
1418
15%
354
56%
354
24%
832
August1st to 15thNight
46%
443
13%
1514
11%
441
50%
441
21%
992
August16th to endNight
48%
729
21%
1875
11%
729
52%
729
36%
1183
September1st to 15thNight
46%
720
16%
1800
8%
720
49%
720
31%
1222
September16th to endNight
47%
717
24%
1952
16%
717
52%
717
30%
1257
October1st to 15thNight
31%
720
16%
2160
11%
720
39%
720
19%
1508
October16th to endNight
23%
768
11%
2403
5%
768
31%
768
12%
1851
November1st to 15thNight
25%
760
16%
2501
11%
760
33%
760
15%
1788
November16th to endNight
22%
780
11%
2730
7%
780
28%
780
9%
2087
December1st to 15thNight
13%
780
6%
2730
1%
780
18%
780
6%
2257
December16th to endNight
14%
832
8%
2912
4%
832
18%
832
6%
2409

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%8%36%5%34446%32%
48971
Night
19%10%47%5%34345%31%
48540
Cloud CoverDay
19%9%36%5%34446%32%
48980
Night
19%10%47%5%34446%31%
48546
TransparencyDay
52%6%11%19%10%1
48658
Night
54%5%10%18%9%
48371
SeeingDay
25%12%27%20%9%3
5845
Night
25%12%27%23%9%
15165

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
22%15%5%9%8%3443418%
1520
16th to endDay
16%13%6%9%8%45%345%21%
1584
February1st to 15thDay
16%13%6%11%7%45%5%4420%
1575
16th to endDay
19%15%6%8%7%3344423%
1541
March1st to 15thDay
19%11%5%10%7%35%23326%
1838
16th to endDay
19%9%34424236%39%
2197
April1st to 15thDay
23%11%345%2333432%
2152
16th to endDay
19%9%25%423445%37%
2220
May1st to 15thDay
20%6%26%434446%35%
2511
16th to endDay
16%6%25%42445%8%36%
2618
June1st to 15thDay
23%6%34434447%32%
2520
16th to endDay
19%5%25%5%35%46%8%32%
2520
July1st to 15thDay
13%435%425%47%7%39%
2520
16th to endDay
12%425%5%35%6%6%8%36%
2654
August1st to 15thDay
12%6%26%6%35%6%5%7%36%
2433
16th to endDay
12%325%436%45%8%43%
2315
September1st to 15thDay
18%5%25%433446%42%
2160
16th to endDay
16%5%24313347%46%
2005
October1st to 15thDay
21%7%36%424446%34%
1800
16th to endDay
26%11%26%6%2345%5%24%
1821
November1st to 15thDay
16%7%37%7%35%447%31%
1683
16th to endDay
22%13%38%6%33437%23%
1560
December1st to 15thDay
24%17%5%7%6%34435%17%
1560
16th to endDay
26%17%6%7%5%3432419%
1664
January1st to 15thNight
20%18%6%9%6%3433319%
2662
16th to endNight
15%16%6%9%7%4444422%
2637
February1st to 15thNight
17%13%6%13%7%3444420%
2285
16th to endNight
17%13%7%9%6%35%335%25%
1931
March1st to 15thNight
20%13%47%5%2333431%
2096
16th to endNight
19%10%35%42333438%
2026
April1st to 15thNight
23%8%45%42334433%
1796
16th to endNight
21%7%15%424345%38%
1751
May1st to 15thNight
20%6%345%3435%7%36%
1440
16th to endNight
17%5%25%5%2445%7%38%
1495
June1st to 15thNight
21%6%25%5%2435%8%31%
1440
16th to endNight
16%6%244335%5%10%35%
1440
July1st to 15thNight
11%324436%46%8%44%
1440
16th to endNight
9%4244446%6%9%42%
1514
August1st to 15thNight
12%5%27%5%245%5%8%39%
1524
16th to endNight
11%425%42345%7%49%
1875
September1st to 15thNight
16%6%245%23336%45%
1800
16th to endNight
15%32442345%6%47%
1952
October1st to 15thNight
19%7%36%424446%36%
2160
16th to endNight
26%9%36%6%33345%27%
2403
November1st to 15thNight
20%9%36%434336%33%
2501
16th to endNight
23%12%47%6%24345%25%
2730
December1st to 15thNight
23%17%5%8%6%3433419%
2730
16th to endNight
24%16%5%8%6%3433419%
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
22%16%410%8%3433319%
1520
16th to endDay
16%14%7%9%8%3444421%
1584
February1st to 15thDay
16%14%6%11%8%35%5%3420%
1575
16th to endDay
20%15%6%8%7%3333423%
1541
March1st to 15thDay
20%12%6%9%7%3423425%
1848
16th to endDay
19%8%35%423235%39%
2196
April1st to 15thDay
24%10%35%42333432%
2152
16th to endDay
20%8%26%423436%36%
2220
May1st to 15thDay
20%7%25%5%24446%35%
2511
16th to endDay
16%7%25%5%345%5%8%35%
2618
June1st to 15thDay
24%6%25%43445%7%31%
2520
16th to endDay
19%5%25%6%35%46%7%33%
2520
July1st to 15thDay
14%5%25%435%47%7%39%
2520
16th to endDay
12%425%5%35%5%7%8%36%
2654
August1st to 15thDay
12%7%36%5%35%6%6%7%35%
2433
16th to endDay
12%415%5%35%45%8%42%
2315
September1st to 15thDay
18%5%245%2335%6%41%
2160
16th to endDay
16%6%24323346%46%
2005
October1st to 15thDay
21%6%35%5%3335%7%33%
1800
16th to endDay
26%11%27%5%33445%24%
1821
November1st to 15thDay
16%8%46%7%345%47%31%
1683
16th to endDay
23%13%48%5%23336%23%
1560
December1st to 15thDay
24%18%5%8%6%3434416%
1560
16th to endDay
26%17%6%7%6%3332419%
1664
January1st to 15thNight
20%18%6%10%6%3433318%
2662
16th to endNight
15%17%6%9%7%35%43422%
2637
February1st to 15thNight
16%15%6%12%7%3334420%
2278
16th to endNight
17%15%6%8%7%3343424%
1931
March1st to 15thNight
20%13%47%5%3323430%
2109
16th to endNight
19%10%4442333438%
2026
April1st to 15thNight
23%8%45%5%2244433%
1796
16th to endNight
21%7%25%433345%38%
1751
May1st to 15thNight
19%7%345%24347%36%
1440
16th to endNight
16%6%25%435%448%38%
1495
June1st to 15thNight
22%7%25%5%3435%8%31%
1440
16th to endNight
16%6%245%335%5%10%35%
1440
July1st to 15thNight
11%424435%5%6%8%43%
1440
16th to endNight
9%325%5%35%5%7%8%42%
1514
August1st to 15thNight
12%5%27%5%336%5%7%38%
1524
16th to endNight
12%425%42235%8%48%
1875
September1st to 15thNight
17%5%245%23337%44%
1800
16th to endNight
14%42432335%7%46%
1952
October1st to 15thNight
18%9%36%423446%35%
2160
16th to endNight
27%9%36%5%33345%26%
2403
November1st to 15thNight
20%9%45%5%23346%32%
2501
16th to endNight
23%12%47%5%24435%25%
2730
December1st to 15thNight
23%17%5%8%6%3433319%
2730
16th to endNight
24%17%6%9%6%3433418%
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
70%5%7%10%5%
1521
16th to endDay
65%5%11%10%7%
1584
February1st to 15thDay
66%6%7%15%3
1577
16th to endDay
64%49%11%8%1
1541
March1st to 15thDay
64%410%13%7%
1848
16th to endDay
49%38%17%15%5%
2197
April1st to 15thDay
55%46%18%12%2
2152
16th to endDay
48%48%19%15%3
2220
May1st to 15thDay
49%5%9%19%14%1
2511
16th to endDay
45%7%12%20%11%2
2622
June1st to 15thDay
51%5%10%20%10%
2520
16th to endDay
48%7%11%20%10%
2520
July1st to 15thDay
39%7%12%28%12%
2371
16th to endDay
43%8%15%22%9%
2487
August1st to 15thDay
45%7%15%21%9%
2419
16th to endDay
38%6%15%27%11%
2315
September1st to 15thDay
43%6%10%26%13%
2160
16th to endDay
39%5%10%32%12%
2005
October1st to 15thDay
50%6%11%21%9%
1800
16th to endDay
60%6%13%13%6%
1821
November1st to 15thDay
52%6%13%18%7%
1683
16th to endDay
63%5%10%13%6%
1560
December1st to 15thDay
70%5%9%11%2
1560
16th to endDay
71%5%7%9%5%
1664
January1st to 15thNight
70%5%10%9%4
2662
16th to endNight
65%48%14%5%
2637
February1st to 15thNight
67%48%14%4
2287
16th to endNight
63%5%7%15%7%
1931
March1st to 15thNight
59%310%17%7%
2109
16th to endNight
50%38%18%14%3
2026
April1st to 15thNight
53%47%18%14%
1796
16th to endNight
48%48%19%15%3
1751
May1st to 15thNight
48%6%8%18%15%3
1440
16th to endNight
44%6%12%21%12%2
1497
June1st to 15thNight
51%6%13%17%9%
1440
16th to endNight
43%7%15%20%13%
1440
July1st to 15thNight
34%7%12%29%14%
1360
16th to endNight
36%7%15%23%15%
1418
August1st to 15thNight
42%8%16%20%11%
1514
16th to endNight
34%5%14%31%14%
1875
September1st to 15thNight
41%5%11%29%11%
1800
16th to endNight
37%6%10%31%13%
1952
October1st to 15thNight
48%5%11%22%11%
2160
16th to endNight
59%5%13%15%5%
2403
November1st to 15thNight
52%6%12%16%10%1
2501
16th to endNight
61%5%11%15%5%
2730
December1st to 15thNight
69%6%9%11%2
2730
16th to endNight
70%5%8%10%4
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
26%23%23%14%12%
82
16th to endDay
33%18%30%13%4
72
February1st to 15thDay
37%30%26%5%
90
16th to endDay
36%16%26%19%2
200
March1st to 15thDay
27%19%26%21%5%
270
16th to endDay
28%15%28%16%6%3
288
April1st to 15thDay
34%17%27%13%6%1
270
16th to endDay
27%15%28%15%9%3
270
May1st to 15thDay
30%12%27%18%8%2
288
16th to endDay
21%18%30%18%9%2
331
June1st to 15thDay
31%9%27%22%7%1
315
16th to endDay
23%10%33%21%8%1
315
July1st to 15thDay
17%11%26%26%13%4
305
16th to endDay
16%7%30%29%12%3
326
August1st to 15thDay
18%5%23%32%14%5%
313
16th to endDay
12%8%28%25%15%11%
332
September1st to 15thDay
22%423%22%13%13%
315
16th to endDay
16%11%21%22%19%8%
314
October1st to 15thDay
25%13%26%17%12%4
315
16th to endDay
35%12%29%18%4
311
November1st to 15thDay
21%13%31%21%10%2
247
16th to endDay
37%11%32%14%4
90
December1st to 15thDay
32%22%26%11%6%1
90
16th to endDay
43%22%27%6%
96
January1st to 15thNight
31%19%27%17%3
765
16th to endNight
26%17%30%20%5%
768
February1st to 15thNight
25%20%32%18%2
704
16th to endNight
27%15%32%19%4
631
March1st to 15thNight
30%16%29%20%3
720
16th to endNight
24%14%29%21%8%
768
April1st to 15thNight
30%13%30%21%4
718
16th to endNight
28%13%28%21%8%
671
May1st to 15thNight
26%7%27%28%9%1
360
16th to endNight
20%8%35%26%9%
375
June1st to 15thNight
23%10%25%31%9%
360
16th to endNight
19%5%31%28%13%1
360
July1st to 15thNight
11%426%41%15%
340
16th to endNight
10%327%42%14%1
376
August1st to 15thNight
17%424%33%18%1
443
16th to endNight
14%326%34%18%1
729
September1st to 15thNight
21%5%22%31%17%2
720
16th to endNight
16%9%23%26%21%2
717
October1st to 15thNight
25%11%28%20%14%
720
16th to endNight
33%13%24%21%6%
768
November1st to 15thNight
27%11%29%20%10%
760
16th to endNight
32%17%22%18%8%
780
December1st to 15thNight
35%19%25%16%3
780
16th to endNight
34%15%28%18%1
832
Page generated at 2018-01-12 22:01:34. Version ac04

Copyright 2018 A. Danko


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