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 2018-11-30.

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
26%
16368
11%
51700
7%
16337
31%
16337
13%
38762

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%
780
7%
2716
4%
776
13%
776
5%
2300
January16th to endNight
12%
832
6%
2818
2%
832
15%
832
6%
2348
February1st to 15thNight
9%
764
7%
2482
1%
761
15%
761
5%
2122
February16th to endNight
12%
683
7%
2063
4%
683
17%
683
8%
1732
March1st to 15thNight
14%
780
9%
2282
3%
780
20%
780
10%
1829
March16th to endNight
23%
832
16%
2194
6%
832
30%
832
16%
1644
April1st to 15thNight
20%
778
11%
1946
4%
778
24%
778
16%
1529
April16th to endNight
27%
762
16%
1918
6%
762
32%
762
22%
1381
May1st to 15thNight
31%
419
17%
1589
14%
419
38%
419
16%
1069
May16th to endNight
37%
406
14%
1625
13%
406
45%
406
18%
1030
June1st to 15thNight
40%
390
12%
1560
13%
390
48%
390
15%
1051
June16th to endNight
44%
390
11%
1560
13%
390
50%
390
20%
961
July1st to 15thNight
54%
370
14%
1480
19%
370
58%
370
23%
865
July16th to endNight
56%
408
15%
1546
18%
386
60%
386
24%
904
August1st to 15thNight
47%
513
13%
1654
10%
511
51%
511
24%
1070
August16th to endNight
53%
820
17%
2062
9%
820
55%
820
32%
1362
September1st to 15thNight
45%
780
15%
1950
9%
780
48%
780
28%
1368
September16th to endNight
47%
777
22%
2106
15%
777
52%
777
29%
1393
October1st to 15thNight
34%
780
15%
2340
11%
780
39%
780
17%
1691
October16th to endNight
15%
832
9%
2584
5%
832
22%
832
10%
2055
November1st to 15thNight
19%
820
13%
2667
8%
820
26%
820
12%
2004
November16th to endNight
18%
840
11%
2916
7%
840
24%
840
10%
2244
December1st to 15thNight
11%
780
5%
2730
1%
780
16%
780
5%
2280
December16th to endNight
8%
832
3%
2912
0%
832
12%
832
4%
2530

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%34446%28%
52607
Night
18%11%48%6%34445%28%
51869
Cloud CoverDay
18%10%47%6%3445%6%27%
52616
Night
17%11%48%6%34445%28%
51875
TransparencyDay
56%6%10%17%8%
52294
Night
56%6%10%16%8%
51700
SeeingDay
26%15%26%18%9%3
7100
Night
25%16%27%22%8%
16369

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%8%12%7%35%435%16%
1552
16th to endDay
12%17%7%14%9%46%5%4413%
1756
February1st to 15thDay
15%15%8%14%11%45%5%3412%
1710
16th to endDay
17%16%7%12%8%3423317%
1695
March1st to 15thDay
19%18%6%10%5%3443320%
1995
16th to endDay
18%11%5%7%423335%32%
2381
April1st to 15thDay
21%12%5%8%5%2434328%
2332
16th to endDay
19%11%25%433345%35%
2315
May1st to 15thDay
20%8%35%5%24346%33%
2702
16th to endDay
16%7%25%6%2446%8%34%
2842
June1st to 15thDay
23%6%35%4245%5%7%28%
2730
16th to endDay
18%6%25%6%35%5%6%8%31%
2730
July1st to 15thDay
12%5%35%6%46%6%6%7%35%
2730
16th to endDay
14%6%36%6%36%6%5%8%33%
2878
August1st to 15thDay
16%6%26%6%45%5%6%8%31%
2540
16th to endDay
13%5%25%6%45%5%6%8%35%
2484
September1st to 15thDay
18%7%244345%5%7%36%
2340
16th to endDay
15%6%245%35%45%6%41%
2180
October1st to 15thDay
24%9%25%5%33346%32%
1950
16th to endDay
26%13%36%4345%35%23%
1992
November1st to 15thDay
19%13%47%5%24445%28%
1851
16th to endDay
18%15%5%9%6%33345%23%
1698
December1st to 15thDay
18%20%8%10%7%2333416%
1560
16th to endDay
21%20%10%12%7%333349%
1664
January1st to 15thNight
18%17%6%11%8%45%44413%
2716
16th to endNight
14%16%7%12%9%5%5%43416%
2818
February1st to 15thNight
15%15%7%16%9%4444314%
2480
16th to endNight
16%14%7%12%9%45%44417%
2063
March1st to 15thNight
19%14%6%10%8%2333423%
2269
16th to endNight
19%11%5%7%42344431%
2194
April1st to 15thNight
23%12%45%423435%29%
1946
16th to endNight
20%8%25%423345%38%
1918
May1st to 15thNight
19%7%35%6%24346%35%
1589
16th to endNight
13%5%36%426%46%8%38%
1623
June1st to 15thNight
21%6%25%5%35%45%6%33%
1560
16th to endNight
16%4245%2446%9%39%
1560
July1st to 15thNight
9%4246%35%5%6%8%43%
1560
16th to endNight
12%32443445%7%46%
1642
August1st to 15thNight
13%6%25%5%235%5%9%40%
1664
16th to endNight
11%435%5%3445%7%44%
2062
September1st to 15thNight
16%6%245%34446%41%
1950
16th to endNight
16%5%1342445%7%44%
2106
October1st to 15thNight
24%7%25%5%24345%32%
2340
16th to endNight
27%12%36%5%3444422%
2584
November1st to 15thNight
19%13%37%5%34446%27%
2667
16th to endNight
18%14%5%8%5%34446%23%
2916
December1st to 15thNight
20%18%7%9%7%2444415%
2730
16th to endNight
19%19%8%12%7%34335%11%
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%15%8%13%7%35%435%16%
1552
16th to endDay
12%16%8%14%10%36%44413%
1756
February1st to 15thDay
15%15%8%13%11%45%5%4312%
1710
16th to endDay
17%15%7%14%8%3423417%
1695
March1st to 15thDay
19%18%6%10%5%2444320%
2005
16th to endDay
18%11%6%7%423335%32%
2380
April1st to 15thDay
20%13%5%7%5%2333328%
2332
16th to endDay
19%11%35%423345%34%
2315
May1st to 15thDay
20%9%35%5%34446%32%
2702
16th to endDay
16%7%35%6%35%5%5%8%33%
2842
June1st to 15thDay
22%8%35%43445%8%28%
2730
16th to endDay
19%6%35%5%445%6%8%31%
2730
July1st to 15thDay
12%5%35%6%45%6%6%8%34%
2730
16th to endDay
14%5%36%6%36%6%6%7%32%
2878
August1st to 15thDay
16%6%26%7%35%5%7%8%29%
2540
16th to endDay
13%5%35%6%46%6%6%8%34%
2484
September1st to 15thDay
19%6%25%43445%7%35%
2340
16th to endDay
15%6%25%5%35%35%6%40%
2180
October1st to 15thDay
23%9%36%5%23445%31%
1950
16th to endDay
26%13%35%5%34445%23%
1992
November1st to 15thDay
18%14%37%5%34436%28%
1851
16th to endDay
18%15%6%9%6%2435%423%
1698
December1st to 15thDay
17%21%8%11%6%2234415%
1560
16th to endDay
20%20%10%11%8%4333410%
1664
January1st to 15thNight
17%16%6%11%8%46%445%14%
2716
16th to endNight
14%15%8%13%9%5%5%33316%
2818
February1st to 15thNight
14%15%7%17%9%4444314%
2473
16th to endNight
15%14%6%13%9%45%44417%
2063
March1st to 15thNight
18%14%6%11%6%3433422%
2282
16th to endNight
18%11%5%7%4245%35%30%
2194
April1st to 15thNight
22%12%46%5%24435%29%
1946
16th to endNight
20%8%25%42434439%
1918
May1st to 15thNight
19%7%37%424346%34%
1589
16th to endNight
12%5%36%5%25%5%6%7%38%
1623
June1st to 15thNight
21%5%25%5%3445%6%33%
1560
16th to endNight
15%425%43446%9%38%
1560
July1st to 15thNight
9%425%6%36%5%5%8%43%
1560
16th to endNight
13%325%5%2445%7%45%
1642
August1st to 15thNight
13%5%25%5%335%6%8%39%
1664
16th to endNight
11%5%25%5%3345%7%44%
2062
September1st to 15thNight
16%5%25%5%345%46%40%
1950
16th to endNight
16%5%1442445%7%43%
2106
October1st to 15thNight
24%7%25%5%2435%6%32%
2340
16th to endNight
26%13%37%6%25%34422%
2584
November1st to 15thNight
18%14%47%5%34445%28%
2667
16th to endNight
18%14%5%8%6%34446%24%
2916
December1st to 15thNight
20%17%7%10%7%3444416%
2730
16th to endNight
20%18%8%11%7%34335%11%
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%8%9%5%1
1553
16th to endDay
72%5%9%7%3
1756
February1st to 15thDay
75%6%5%9%2
1712
16th to endDay
72%28%10%5%
1695
March1st to 15thDay
67%410%11%5%
2005
16th to endDay
55%310%14%14%1
2381
April1st to 15thDay
59%39%18%8%1
2332
16th to endDay
50%5%8%19%14%2
2315
May1st to 15thDay
52%5%10%19%11%1
2702
16th to endDay
47%7%13%20%10%
2846
June1st to 15thDay
53%7%11%18%8%
2730
16th to endDay
49%7%13%19%9%
2730
July1st to 15thDay
45%9%10%23%10%
2581
16th to endDay
47%8%14%20%8%
2711
August1st to 15thDay
48%9%13%19%7%
2526
16th to endDay
44%8%13%23%9%
2484
September1st to 15thDay
47%6%10%23%11%
2340
16th to endDay
42%6%10%25%14%
2180
October1st to 15thDay
53%6%9%21%8%
1950
16th to endDay
62%6%11%13%4
1992
November1st to 15thDay
57%5%12%15%7%1
1851
16th to endDay
62%6%12%12%6%
1698
December1st to 15thDay
72%5%10%8%3
1560
16th to endDay
79%47%5%2
1664
January1st to 15thNight
71%7%6%9%4
2716
16th to endNight
71%5%9%9%3
2818
February1st to 15thNight
73%5%7%9%3
2482
16th to endNight
70%5%9%9%5%
2063
March1st to 15thNight
65%410%13%5%
2282
16th to endNight
55%49%17%11%2
2194
April1st to 15thNight
57%6%9%16%8%1
1946
16th to endNight
48%5%9%19%16%2
1918
May1st to 15thNight
49%5%10%17%14%2
1589
16th to endNight
41%9%12%23%11%1
1625
June1st to 15thNight
48%7%11%21%9%
1560
16th to endNight
40%7%15%23%12%
1560
July1st to 15thNight
36%8%12%26%15%1
1480
16th to endNight
36%7%15%24%14%1
1546
August1st to 15thNight
39%9%15%25%9%
1654
16th to endNight
37%6%15%27%12%
2062
September1st to 15thNight
42%6%13%22%12%
1950
16th to endNight
39%6%11%27%14%
2106
October1st to 15thNight
51%6%11%18%11%
2340
16th to endNight
63%5%11%12%6%
2584
November1st to 15thNight
58%5%10%14%8%2
2667
16th to endNight
61%6%11%14%6%
2916
December1st to 15thNight
71%5%10%9%2
2730
16th to endNight
75%5%8%7%2
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
27%25%28%13%4
90
16th to endDay
34%20%38%6%
118
February1st to 15thDay
41%34%20%3
135
16th to endDay
30%29%27%10%1
276
March1st to 15thDay
33%22%26%15%2
330
16th to endDay
27%23%25%17%4
352
April1st to 15thDay
34%20%25%11%5%
330
16th to endDay
31%13%25%14%10%4
319
May1st to 15thDay
32%14%24%15%10%3
348
16th to endDay
21%11%34%20%10%2
395
June1st to 15thDay
27%10%27%22%9%1
375
16th to endDay
21%14%30%22%9%1
375
July1st to 15thDay
15%7%28%31%12%5%
365
16th to endDay
15%7%31%29%11%4
390
August1st to 15thDay
19%8%24%24%16%6%
358
16th to endDay
12%7%26%29%15%8%
396
September1st to 15thDay
19%8%20%23%20%7%
375
16th to endDay
16%10%25%19%15%12%
374
October1st to 15thDay
27%10%26%17%12%4
375
16th to endDay
34%21%26%10%6%
373
November1st to 15thDay
31%15%25%19%7%
325
16th to endDay
41%21%25%11%
140
December1st to 15thDay
30%33%22%12%11
90
16th to endDay
41%26%28%4
96
January1st to 15thNight
30%27%30%10%1
780
16th to endNight
25%24%32%16%1
832
February1st to 15thNight
26%25%33%13%1
764
16th to endNight
26%25%31%13%2
683
March1st to 15thNight
29%22%29%17%1
780
16th to endNight
27%20%24%22%4
832
April1st to 15thNight
28%18%29%19%2
778
16th to endNight
27%14%27%20%8%
762
May1st to 15thNight
25%9%28%29%6%
419
16th to endNight
16%7%33%33%9%
407
June1st to 15thNight
21%9%22%34%11%
390
16th to endNight
16%5%26%41%10%
390
July1st to 15thNight
10%424%42%16%1
370
16th to endNight
13%224%41%16%2
408
August1st to 15thNight
16%324%33%19%2
513
16th to endNight
13%6%20%34%23%2
820
September1st to 15thNight
20%5%23%30%18%1
780
16th to endNight
18%8%22%25%21%3
777
October1st to 15thNight
28%10%21%23%12%1
780
16th to endNight
35%17%27%17%2
832
November1st to 15thNight
27%17%30%16%7%
820
16th to endNight
27%22%25%17%5%
840
December1st to 15thNight
32%25%26%13%1
780
16th to endNight
33%25%26%12%1
832
Page generated at 2018-12-01 11:35:34. Version ac04

Copyright 2018 A. Danko


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