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 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
27%
14672
12%
46780
8%
14640
33%
14640
15%
34156

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%
720
6%
2506
2%
716
17%
716
6%
2082
January16th to endNight
18%
768
9%
2637
5%
768
23%
768
9%
2087
February1st to 15thNight
14%
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
25%
720
14%
1598
March16th to endNight
26%
768
18%
2026
7%
768
34%
768
20%
1439
April1st to 15thNight
21%
718
15%
1796
5%
718
26%
718
19%
1352
April16th to endNight
27%
671
16%
1751
6%
671
33%
671
22%
1246
May1st to 15thNight
33%
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
35%
360
10%
1440
11%
360
44%
360
14%
994
June16th to endNight
38%
360
8%
1440
11%
360
42%
360
19%
905
July1st to 15thNight
48%
340
14%
1360
19%
340
55%
340
24%
777
July16th to endNight
52%
376
13%
1418
15%
354
56%
354
24%
832
August1st to 15thNight
47%
443
14%
1514
11%
441
51%
441
21%
992
August16th to endNight
47%
729
21%
1875
11%
729
52%
729
36%
1183
September1st to 15thNight
45%
700
16%
1750
8%
700
48%
700
30%
1200
September16th to endNight
44%
657
21%
1789
14%
657
49%
657
28%
1179
October1st to 15thNight
31%
660
17%
1980
11%
660
39%
660
19%
1395
October16th to endNight
24%
704
9%
2203
5%
704
30%
704
12%
1719
November1st to 15thNight
25%
700
16%
2304
11%
700
32%
700
15%
1653
November16th to endNight
22%
720
12%
2520
8%
720
29%
720
9%
1935
December1st to 15thNight
14%
720
5%
2520
1%
720
18%
720
6%
2083
December16th to endNight
13%
768
7%
2688
4%
768
17%
768
6%
2247

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
19%8%36%5%34446%32%
47852
Night
19%10%47%5%34346%31%
46950
Cloud CoverDay
19%9%36%5%34446%32%
47861
Night
19%10%47%5%34446%31%
46956
TransparencyDay
52%6%10%19%10%1
47539
Night
54%5%10%18%9%
46781
SeeingDay
25%12%27%20%9%3
5492
Night
26%12%27%23%9%
14672

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%7%3433419%
1432
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%41%
2098
16th to endDay
17%6%24423347%43%
1838
October1st to 15thDay
21%7%36%424446%33%
1650
16th to endDay
28%11%27%6%2344423%
1669
November1st to 15thDay
15%7%37%7%45%45%6%32%
1551
16th to endDay
22%13%38%5%33337%24%
1440
December1st to 15thDay
25%17%5%7%6%34435%17%
1440
16th to endDay
26%17%6%8%5%3332418%
1536
January1st to 15thNight
20%18%6%9%6%3433318%
2506
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%43%
1750
16th to endNight
16%32442345%6%45%
1789
October1st to 15thNight
20%7%35%434447%34%
1980
16th to endNight
27%9%36%6%23345%25%
2203
November1st to 15thNight
20%9%36%435%346%32%
2304
16th to endNight
23%11%47%6%24345%25%
2520
December1st to 15thNight
24%16%5%8%6%3433420%
2520
16th to endNight
25%17%5%8%6%3433418%
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
22%15%410%8%3433419%
1432
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
19%5%245%2335%5%40%
2098
16th to endDay
17%6%24424346%43%
1838
October1st to 15thDay
22%6%35%6%3335%6%32%
1650
16th to endDay
28%12%27%5%3334423%
1669
November1st to 15thDay
14%8%46%7%35%5%46%31%
1551
16th to endDay
23%13%48%5%23345%23%
1440
December1st to 15thDay
25%18%5%7%5%3434416%
1440
16th to endDay
26%17%6%7%6%3332317%
1536
January1st to 15thNight
21%18%6%10%5%3433318%
2506
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%43%
1750
16th to endNight
15%425%33436%6%44%
1789
October1st to 15thNight
19%9%36%423447%34%
1980
16th to endNight
28%9%37%5%33345%25%
2203
November1st to 15thNight
19%9%46%5%2435%6%32%
2304
16th to endNight
23%12%47%5%24435%25%
2520
December1st to 15thNight
24%17%5%8%6%3433319%
2520
16th to endNight
25%17%6%9%5%3433417%
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
70%47%10%5%
1433
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
44%6%10%25%12%
2098
16th to endDay
41%5%9%31%11%
1838
October1st to 15thDay
51%6%11%20%9%
1650
16th to endDay
63%6%11%12%6%
1669
November1st to 15thDay
51%6%13%19%7%
1551
16th to endDay
63%5%10%13%6%
1440
December1st to 15thDay
71%5%10%11%1
1440
16th to endDay
72%5%8%8%4
1536
January1st to 15thNight
70%5%9%9%4
2506
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
42%5%11%29%11%
1750
16th to endNight
39%5%9%30%13%
1789
October1st to 15thNight
49%5%11%21%11%
1980
16th to endNight
61%5%12%14%5%
2203
November1st to 15thNight
52%6%12%15%10%1
2304
16th to endNight
61%5%11%15%5%
2520
December1st to 15thNight
69%6%10%11%2
2520
16th to endNight
72%5%9%9%3
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
26%26%20%15%11%
60
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
24%5%24%21%12%11%
294
16th to endDay
19%11%24%20%16%7%
254
October1st to 15thDay
25%13%25%18%13%3
255
16th to endDay
37%11%27%18%4
255
November1st to 15thDay
16%14%35%19%11%2
205
16th to endDay
38%6%30%18%6%
60
December1st to 15thDay
31%21%33%6%6%
60
16th to endDay
50%23%21%4
64
January1st to 15thNight
32%19%27%16%3
720
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
22%5%22%31%16%1
700
16th to endNight
17%9%25%26%19%1
657
October1st to 15thNight
26%11%27%21%13%
660
16th to endNight
34%12%23%22%7%
704
November1st to 15thNight
26%11%30%20%10%1
700
16th to endNight
31%17%23%18%8%
720
December1st to 15thNight
36%19%25%15%3
720
16th to endNight
35%15%27%17%2
768
Page generated at 2017-09-11 19:35:18. Version ac04

Copyright 2017 A. Danko


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