MVAS Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the MVAS Observatory clear sky chart from 2005-11-05 to 2017-04-08.

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
25%
14393
11%
45450
7%
14362
31%
14362
13%
34175

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
9%
720
7%
2506
4%
716
14%
716
5%
2125
January16th to endNight
12%
768
6%
2601
2%
768
16%
768
6%
2175
February1st to 15thNight
8%
704
6%
2287
1%
701
15%
701
5%
1958
February16th to endNight
13%
631
8%
1906
4%
631
18%
631
8%
1604
March1st to 15thNight
15%
720
10%
2106
4%
720
21%
720
10%
1664
March16th to endNight
21%
768
16%
2025
6%
768
29%
768
15%
1517
April1st to 15thNight
19%
690
11%
1726
3%
690
23%
690
15%
1361
April16th to endNight
28%
653
16%
1643
6%
653
33%
653
22%
1173
May1st to 15thNight
31%
355
18%
1345
14%
355
40%
355
17%
883
May16th to endNight
39%
342
15%
1369
14%
342
46%
342
18%
859
June1st to 15thNight
38%
330
11%
1320
13%
330
45%
330
14%
915
June16th to endNight
46%
330
10%
1320
14%
330
51%
330
21%
806
July1st to 15thNight
50%
310
13%
1240
18%
310
54%
310
21%
740
July16th to endNight
56%
348
14%
1306
15%
326
60%
326
23%
765
August1st to 15thNight
47%
442
14%
1423
10%
440
52%
440
25%
912
August16th to endNight
52%
693
16%
1743
9%
693
54%
693
31%
1154
September1st to 15thNight
46%
660
16%
1650
9%
660
49%
660
29%
1145
September16th to endNight
45%
657
21%
1782
14%
657
50%
657
28%
1186
October1st to 15thNight
34%
660
15%
1980
12%
660
40%
660
17%
1432
October16th to endNight
16%
704
7%
2186
3%
704
22%
704
9%
1750
November1st to 15thNight
19%
700
14%
2277
9%
700
27%
700
13%
1691
November16th to endNight
19%
720
11%
2501
8%
720
25%
720
10%
1909
December1st to 15thNight
11%
720
5%
2520
1%
720
15%
720
5%
2106
December16th to endNight
9%
768
3%
2688
0%
768
12%
768
4%
2345

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%10%47%6%3445%6%28%
45811
Night
18%11%48%6%34445%28%
45619
Cloud CoverDay
18%10%47%6%3445%6%27%
45820
Night
17%11%48%6%34445%28%
45625
TransparencyDay
56%6%10%16%8%
45498
Night
57%6%10%16%8%
45450
SeeingDay
25%14%26%19%10%3
4963
Night
25%16%26%21%8%
14394

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
15%16%9%12%7%35%445%15%
1432
16th to endDay
13%17%7%13%9%46%5%4413%
1621
February1st to 15thDay
15%15%8%14%11%45%5%3412%
1575
16th to endDay
16%16%8%13%8%3423318%
1566
March1st to 15thDay
19%16%6%10%5%3444421%
1841
16th to endDay
18%12%5%7%433335%32%
2198
April1st to 15thDay
21%12%5%7%42434429%
2062
16th to endDay
18%11%25%434345%35%
1985
May1st to 15thDay
19%8%35%5%2435%6%34%
2284
16th to endDay
16%7%25%5%245%6%8%34%
2394
June1st to 15thDay
24%7%35%4345%5%7%27%
2310
16th to endDay
19%6%35%6%35%5%6%8%31%
2310
July1st to 15thDay
13%6%35%6%36%6%6%8%33%
2310
16th to endDay
13%6%36%6%36%6%5%8%32%
2458
August1st to 15thDay
16%6%26%6%45%6%6%8%31%
2190
16th to endDay
14%6%346%46%5%6%7%35%
2100
September1st to 15thDay
18%6%244345%5%7%37%
1980
16th to endDay
15%6%25%5%25%346%41%
1844
October1st to 15thDay
22%8%35%5%33346%32%
1650
16th to endDay
27%13%36%4245%35%22%
1686
November1st to 15thDay
16%13%46%6%245%5%5%29%
1581
16th to endDay
18%13%5%10%6%3335%5%23%
1458
December1st to 15thDay
18%21%8%10%7%2333416%
1440
16th to endDay
21%20%10%12%6%333349%
1536
January1st to 15thNight
18%17%6%12%8%3444414%
2506
16th to endNight
14%16%7%12%9%5%5%43415%
2601
February1st to 15thNight
14%15%7%17%9%4444314%
2285
16th to endNight
15%14%7%13%9%45%43416%
1906
March1st to 15thNight
18%12%6%10%8%3343424%
2093
16th to endNight
20%11%5%7%423445%30%
2025
April1st to 15thNight
24%12%45%423435%28%
1726
16th to endNight
19%7%25%424345%39%
1643
May1st to 15thNight
19%6%35%5%24346%37%
1345
16th to endNight
14%5%36%425%45%8%39%
1367
June1st to 15thNight
23%6%25%5%25%45%6%31%
1320
16th to endNight
16%43442446%9%39%
1320
July1st to 15thNight
10%425%6%36%5%6%8%41%
1320
16th to endNight
12%32443445%7%46%
1402
August1st to 15thNight
12%6%25%5%235%5%9%40%
1433
16th to endNight
11%5%35%43345%7%45%
1743
September1st to 15thNight
16%6%24434445%42%
1650
16th to endNight
16%5%14324447%43%
1782
October1st to 15thNight
25%7%25%5%2435%5%32%
1980
16th to endNight
27%12%46%5%3444422%
2186
November1st to 15thNight
18%13%37%5%34445%29%
2277
16th to endNight
17%12%5%9%6%3445%6%24%
2501
December1st to 15thNight
21%18%7%9%6%2444415%
2520
16th to endNight
20%19%8%12%7%34335%11%
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
15%15%8%13%7%35%435%15%
1432
16th to endDay
12%16%8%13%10%47%5%4413%
1621
February1st to 15thDay
15%14%8%14%11%45%5%4313%
1575
16th to endDay
17%15%7%14%8%3423417%
1566
March1st to 15thDay
18%16%5%10%5%2444421%
1851
16th to endDay
18%12%6%7%423335%32%
2197
April1st to 15thDay
20%13%5%7%5%2334329%
2062
16th to endDay
17%11%35%433346%34%
1985
May1st to 15thDay
19%8%35%5%34446%34%
2284
16th to endDay
15%7%35%5%35%5%5%8%33%
2394
June1st to 15thDay
23%8%35%5%3446%8%26%
2310
16th to endDay
19%6%25%5%445%6%8%30%
2310
July1st to 15thDay
13%5%35%6%45%6%6%8%32%
2310
16th to endDay
14%5%36%6%46%6%6%8%31%
2458
August1st to 15thDay
16%6%26%7%45%5%7%7%30%
2190
16th to endDay
14%6%345%46%6%6%8%34%
2100
September1st to 15thDay
19%5%25%435%45%6%36%
1980
16th to endDay
15%6%246%3435%6%40%
1844
October1st to 15thDay
22%9%36%5%23346%32%
1650
16th to endDay
27%12%45%5%24445%21%
1686
November1st to 15thDay
16%15%36%434446%29%
1581
16th to endDay
18%13%6%9%6%2435%424%
1458
December1st to 15thDay
18%22%8%11%5%3233415%
1440
16th to endDay
21%20%10%11%7%433349%
1536
January1st to 15thNight
18%17%6%11%8%45%44414%
2506
16th to endNight
14%15%8%13%9%5%5%34315%
2601
February1st to 15thNight
13%15%7%18%9%4444314%
2278
16th to endNight
14%15%6%14%10%45%34416%
1906
March1st to 15thNight
18%12%5%11%7%34335%24%
2106
16th to endNight
19%12%5%8%423435%30%
2025
April1st to 15thNight
23%13%46%42343428%
1726
16th to endNight
18%8%25%42434439%
1643
May1st to 15thNight
19%7%36%424346%36%
1345
16th to endNight
13%6%26%425%46%7%39%
1367
June1st to 15thNight
23%6%25%435%45%6%31%
1320
16th to endNight
16%42442446%9%39%
1320
July1st to 15thNight
10%425%6%36%5%5%8%41%
1320
16th to endNight
13%3245%2445%7%46%
1402
August1st to 15thNight
12%5%25%5%235%6%9%40%
1433
16th to endNight
12%5%25%5%335%5%7%44%
1743
September1st to 15thNight
17%5%244245%36%42%
1650
16th to endNight
17%5%1442445%7%42%
1782
October1st to 15thNight
24%8%25%5%2345%6%32%
1980
16th to endNight
26%13%37%6%25%34422%
2186
November1st to 15thNight
17%13%47%5%34345%29%
2277
16th to endNight
17%12%5%9%6%34446%24%
2501
December1st to 15thNight
21%18%7%9%6%3444416%
2520
16th to endNight
20%19%8%11%8%34335%11%
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
71%5%8%9%5%1
1433
16th to endDay
72%5%9%8%3
1621
February1st to 15thDay
74%6%5%9%2
1577
16th to endDay
72%28%10%5%
1566
March1st to 15thDay
65%410%12%5%
1851
16th to endDay
54%410%14%14%1
2198
April1st to 15thDay
58%39%18%7%1
2062
16th to endDay
49%5%7%20%14%2
1985
May1st to 15thDay
50%5%10%19%12%1
2284
16th to endDay
47%7%14%19%10%
2398
June1st to 15thDay
55%7%11%17%7%
2310
16th to endDay
50%7%14%18%8%
2310
July1st to 15thDay
46%9%10%22%9%
2161
16th to endDay
47%8%15%20%7%
2291
August1st to 15thDay
49%9%12%19%8%
2176
16th to endDay
45%8%13%22%9%
2100
September1st to 15thDay
46%6%10%24%11%
1980
16th to endDay
44%6%9%24%13%1
1844
October1st to 15thDay
53%6%8%21%8%1
1650
16th to endDay
63%6%11%12%4
1686
November1st to 15thDay
54%6%13%16%7%1
1581
16th to endDay
61%7%12%12%6%
1458
December1st to 15thDay
72%5%10%8%3
1440
16th to endDay
79%46%6%2
1536
January1st to 15thNight
71%7%6%9%5%
2506
16th to endNight
71%5%8%9%3
2601
February1st to 15thNight
73%5%6%9%3
2287
16th to endNight
70%49%9%5%
1906
March1st to 15thNight
64%411%14%6%
2106
16th to endNight
55%49%17%10%2
2025
April1st to 15thNight
58%5%10%15%8%1
1726
16th to endNight
47%5%8%20%16%2
1643
May1st to 15thNight
48%5%10%18%15%2
1345
16th to endNight
41%9%12%22%12%1
1369
June1st to 15thNight
50%7%12%20%8%
1320
16th to endNight
39%7%15%24%11%
1320
July1st to 15thNight
38%7%12%26%12%1
1240
16th to endNight
36%7%15%24%14%2
1306
August1st to 15thNight
39%8%15%26%10%
1423
16th to endNight
37%7%14%27%13%
1743
September1st to 15thNight
41%6%13%25%11%
1650
16th to endNight
40%6%10%27%14%1
1782
October1st to 15thNight
52%5%10%17%12%
1980
16th to endNight
64%6%11%11%5%
2186
November1st to 15thNight
56%5%10%14%9%2
2277
16th to endNight
59%6%11%15%6%
2501
December1st to 15thNight
71%5%10%9%2
2520
16th to endNight
75%6%9%6%2
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
28%30%20%16%5%
60
16th to endDay
39%21%31%7%
79
February1st to 15thDay
43%35%17%3
90
16th to endDay
28%28%29%12%1
225
March1st to 15thDay
31%23%24%17%2
270
16th to endDay
28%24%23%17%5%1
288
April1st to 15thDay
32%22%22%13%7%1
240
16th to endDay
28%12%25%16%10%6%
210
May1st to 15thDay
30%8%25%18%12%4
228
16th to endDay
19%10%33%19%13%2
267
June1st to 15thDay
29%9%25%23%10%1
255
16th to endDay
23%10%28%24%11%1
255
July1st to 15thDay
17%6%28%30%11%5%
245
16th to endDay
12%9%31%31%10%4
270
August1st to 15thDay
18%7%24%26%16%5%
253
16th to endDay
14%5%22%26%19%11%
268
September1st to 15thDay
17%9%17%23%22%9%
255
16th to endDay
17%10%26%19%14%11%
254
October1st to 15thDay
25%9%25%18%17%4
255
16th to endDay
36%18%27%10%6%
259
November1st to 15thDay
24%15%28%22%8%
235
16th to endDay
30%21%29%16%1
78
December1st to 15thDay
30%30%23%13%11
60
16th to endDay
39%26%29%4
64
January1st to 15thNight
30%26%30%10%1
720
16th to endNight
25%25%31%16%1
768
February1st to 15thNight
25%25%33%13%1
704
16th to endNight
25%25%31%14%2
631
March1st to 15thNight
28%22%29%17%2
720
16th to endNight
28%21%24%20%4
768
April1st to 15thNight
28%19%29%18%2
690
16th to endNight
25%15%28%20%9%
653
May1st to 15thNight
23%7%30%30%7%
355
16th to endNight
16%7%29%34%10%
343
June1st to 15thNight
23%9%20%33%11%
330
16th to endNight
17%5%23%42%11%
330
July1st to 15thNight
11%424%41%16%1
310
16th to endNight
14%223%42%15%1
348
August1st to 15thNight
16%325%35%17%2
442
16th to endNight
14%6%20%32%23%2
693
September1st to 15thNight
20%6%22%32%17%1
660
16th to endNight
19%7%23%26%20%2
657
October1st to 15thNight
30%11%19%23%14%1
660
16th to endNight
35%16%26%18%2
704
November1st to 15thNight
26%16%32%16%7%
700
16th to endNight
25%23%26%18%5%
720
December1st to 15thNight
34%25%25%12%1
720
16th to endNight
34%25%26%12%1
768
Page generated at 2017-04-09 06:54:09. Version ac04

Copyright 2017 A. Danko


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