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The Marian and Max Farash Center for Observational Astronomy
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Marian and Max Farash Center for Observational Astronomy clear sky chart from 2005-11-05 to 2021-11-10.

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
26%
20101
14%
63406
8%
20067
33%
20067
15%
45661

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
10%
959
6%
3346
3%
956
15%
956
5%
2793
January16th to endNight
10%
1024
8%
3356
2%
1024
18%
1024
6%
2782
February1st to 15thNight
7%
944
8%
3067
1%
941
15%
941
5%
2543
February16th to endNight
13%
843
10%
2636
3%
843
21%
843
8%
2075
March1st to 15thNight
15%
960
13%
2696
6%
960
23%
960
11%
2118
March16th to endNight
22%
1024
17%
2780
7%
1024
30%
1024
18%
2043
April1st to 15thNight
19%
958
14%
2396
4%
958
25%
958
17%
1825
April16th to endNight
28%
868
16%
2294
7%
868
34%
868
23%
1596
May1st to 15thNight
34%
576
16%
2016
10%
576
43%
576
17%
1352
May16th to endNight
38%
502
16%
2009
15%
502
48%
502
23%
1176
June1st to 15thNight
39%
480
16%
1920
16%
480
51%
480
19%
1174
June16th to endNight
43%
480
14%
1920
15%
480
51%
480
23%
1105
July1st to 15thNight
55%
460
17%
1840
21%
460
61%
460
27%
1012
July16th to endNight
49%
566
18%
1989
16%
541
55%
541
28%
1140
August1st to 15thNight
51%
710
19%
2120
13%
707
55%
707
32%
1293
August16th to endNight
52%
922
22%
2452
11%
922
56%
922
36%
1518
September1st to 15thNight
42%
960
19%
2400
9%
960
47%
960
30%
1606
September16th to endNight
49%
957
24%
2640
16%
957
54%
957
31%
1665
October1st to 15thNight
31%
960
15%
2880
10%
960
38%
960
19%
1995
October16th to endNight
16%
1024
11%
3080
4%
1024
25%
1024
12%
2343
November1st to 15thNight
24%
980
17%
3265
11%
980
33%
980
16%
2268
November16th to endNight
18%
960
10%
3360
5%
960
24%
960
10%
2536
December1st to 15thNight
12%
960
8%
3360
2%
960
18%
960
6%
2700
December16th to endNight
11%
1024
6%
3584
1%
1024
16%
1024
5%
3003

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
15%10%47%6%3445%6%29%
64566
Night
15%10%47%6%3445%6%29%
63580
Cloud CoverDay
15%10%47%6%35%45%6%29%
64576
Night
15%11%48%6%3445%6%29%
63585
TransparencyDay
54%5%10%19%9%
64259
Night
54%411%18%9%1
63406
SeeingDay
22%17%29%19%8%3
10778
Night
22%16%28%21%9%1
20103

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
12%17%8%14%10%46%43313%
1912
16th to endDay
11%17%8%15%12%5%444411%
2274
February1st to 15thDay
16%16%9%14%8%4443412%
2115
16th to endDay
17%15%5%13%8%3443417%
2002
March1st to 15thDay
14%16%7%11%7%4434422%
2571
16th to endDay
16%13%5%8%5%33345%29%
2852
April1st to 15thDay
19%12%47%5%24445%27%
2872
16th to endDay
19%11%36%5%23445%33%
2944
May1st to 15thDay
17%10%36%5%35%45%6%31%
3252
16th to endDay
14%6%25%5%45%45%8%37%
3514
June1st to 15thDay
18%6%36%5%25%45%7%34%
3360
16th to endDay
13%415%5%35%5%7%8%38%
3360
July1st to 15thDay
9%5%25%5%36%5%6%9%39%
3360
16th to endDay
12%5%35%6%45%6%6%9%34%
3485
August1st to 15thDay
11%6%25%6%35%6%7%9%35%
3072
16th to endDay
12%6%26%6%36%5%6%9%34%
3141
September1st to 15thDay
16%6%25%4345%6%8%35%
2880
16th to endDay
14%5%25%5%345%5%6%41%
2636
October1st to 15thDay
21%9%35%5%2345%6%33%
2400
16th to endDay
25%12%37%6%3443422%
2552
November1st to 15thDay
13%15%47%5%24445%30%
2124
16th to endDay
18%16%5%8%6%34445%21%
1920
December1st to 15thDay
16%19%7%12%7%3434417%
1920
16th to endDay
16%19%9%13%7%4443411%
2048
January1st to 15thNight
14%16%7%12%10%45%43414%
3346
16th to endNight
12%17%7%13%11%45%44414%
3356
February1st to 15thNight
15%15%8%14%8%3443416%
3065
16th to endNight
13%13%7%12%8%35%5%45%19%
2636
March1st to 15thNight
15%15%6%10%7%34345%23%
2684
16th to endNight
16%11%46%5%34345%32%
2780
April1st to 15thNight
18%11%46%5%34446%29%
2396
16th to endNight
17%9%35%5%2335%6%36%
2294
May1st to 15thNight
17%7%36%435%45%7%34%
2016
16th to endNight
11%5%245%25%46%8%42%
2007
June1st to 15thNight
14%5%25%5%25%5%5%7%39%
1920
16th to endNight
10%6%345%345%5%9%42%
1920
July1st to 15thNight
7%425%5%3445%8%47%
1920
16th to endNight
10%425%42446%8%45%
2088
August1st to 15thNight
8%425%5%345%5%8%46%
2131
16th to endNight
9%42443445%8%47%
2452
September1st to 15thNight
15%5%25%5%2445%7%42%
2400
16th to endNight
14%5%1432445%7%45%
2640
October1st to 15thNight
18%7%25%5%345%5%7%34%
2880
16th to endNight
27%10%36%5%34446%25%
3080
November1st to 15thNight
16%10%36%5%245%5%6%32%
3265
16th to endNight
17%14%5%8%7%345%46%22%
3360
December1st to 15thNight
16%18%6%10%7%3444417%
3360
16th to endNight
19%17%7%11%7%34445%12%
3584

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
12%17%9%13%10%45%44412%
1912
16th to endDay
10%17%7%16%12%5%5%43411%
2274
February1st to 15thDay
15%16%9%14%9%4433413%
2115
16th to endDay
18%15%6%14%8%3444416%
2002
March1st to 15thDay
14%16%7%11%8%3443422%
2582
16th to endDay
16%13%5%8%5%23345%29%
2851
April1st to 15thDay
19%12%46%6%24345%27%
2872
16th to endDay
19%10%36%5%23445%33%
2944
May1st to 15thDay
18%9%36%5%3445%6%31%
3252
16th to endDay
15%6%25%5%45%45%8%37%
3514
June1st to 15thDay
18%6%36%5%35%45%7%34%
3360
16th to endDay
13%5%245%45%5%6%8%37%
3360
July1st to 15thDay
10%5%25%5%36%5%6%8%39%
3360
16th to endDay
12%5%36%6%35%6%7%8%34%
3485
August1st to 15thDay
12%5%25%6%36%6%7%9%34%
3072
16th to endDay
13%6%25%6%36%5%6%8%34%
3141
September1st to 15thDay
16%6%25%4345%5%7%35%
2880
16th to endDay
14%5%245%345%5%6%42%
2636
October1st to 15thDay
21%9%25%42435%6%33%
2400
16th to endDay
25%12%37%6%35%335%22%
2552
November1st to 15thDay
13%15%47%6%345%45%30%
2124
16th to endDay
18%16%5%8%6%25%445%21%
1920
December1st to 15thDay
16%19%8%11%7%2443418%
1920
16th to endDay
16%19%9%13%7%4443411%
2048
January1st to 15thNight
14%16%7%13%9%45%44414%
3346
16th to endNight
12%16%7%13%10%45%445%14%
3356
February1st to 15thNight
15%15%8%15%8%35%43416%
3058
16th to endNight
13%14%7%12%8%45%445%19%
2636
March1st to 15thNight
14%16%6%10%6%34345%24%
2696
16th to endNight
16%11%48%5%24445%32%
2780
April1st to 15thNight
18%11%47%5%34446%29%
2396
16th to endNight
17%9%36%42235%7%36%
2294
May1st to 15thNight
17%7%36%435%45%7%33%
2016
16th to endNight
11%5%245%35%5%5%9%41%
2007
June1st to 15thNight
14%5%26%5%25%5%5%7%39%
1920
16th to endNight
10%5%25%4345%5%10%41%
1920
July1st to 15thNight
8%425%5%3345%9%46%
1920
16th to endNight
10%4245%3446%8%44%
2088
August1st to 15thNight
8%425%6%35%5%5%7%46%
2131
16th to endNight
10%41443446%8%47%
2452
September1st to 15thNight
15%5%245%245%5%7%41%
2400
16th to endNight
14%424325%45%8%45%
2640
October1st to 15thNight
18%7%25%5%34447%34%
2880
16th to endNight
27%10%26%5%34436%25%
3080
November1st to 15thNight
16%10%36%5%25%5%46%32%
3265
16th to endNight
17%14%5%7%6%3445%6%23%
3360
December1st to 15thNight
16%18%6%10%7%35%45%417%
3360
16th to endNight
18%17%7%11%7%4444413%
3584

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
74%46%10%3
1913
16th to endDay
76%39%8%2
2274
February1st to 15thDay
75%38%9%2
2117
16th to endDay
70%37%12%5%
2002
March1st to 15thDay
65%49%14%5%
2582
16th to endDay
56%37%18%11%1
2852
April1st to 15thDay
57%49%18%9%1
2872
16th to endDay
52%38%18%15%2
2944
May1st to 15thDay
51%5%9%21%11%
3252
16th to endDay
44%5%12%23%11%1
3518
June1st to 15thDay
47%5%10%20%14%
3360
16th to endDay
40%6%13%23%14%1
3360
July1st to 15thDay
39%6%11%26%14%1
3211
16th to endDay
43%6%14%21%12%
3322
August1st to 15thDay
42%6%14%23%12%
3059
16th to endDay
44%6%11%26%10%1
3141
September1st to 15thDay
44%7%11%25%10%1
2880
16th to endDay
40%5%11%26%15%
2636
October1st to 15thDay
50%412%18%12%
2400
16th to endDay
64%311%15%4
2552
November1st to 15thDay
54%5%11%16%9%1
2124
16th to endDay
64%312%15%3
1920
December1st to 15thDay
70%212%11%1
1920
16th to endDay
76%49%7%2
2048
January1st to 15thNight
72%38%9%4
3346
16th to endNight
71%39%11%3
3356
February1st to 15thNight
70%48%12%4
3067
16th to endNight
65%29%14%6%
2636
March1st to 15thNight
62%39%17%5%
2696
16th to endNight
54%38%19%12%1
2780
April1st to 15thNight
55%410%18%10%
2396
16th to endNight
47%311%20%15%2
2294
May1st to 15thNight
48%5%10%19%14%1
2016
16th to endNight
38%5%15%24%14%2
2009
June1st to 15thNight
42%5%11%23%15%
1920
16th to endNight
37%5%13%24%17%1
1920
July1st to 15thNight
33%5%13%26%17%2
1840
16th to endNight
34%5%14%27%14%2
1989
August1st to 15thNight
34%6%14%31%12%
2120
16th to endNight
34%414%32%12%1
2452
September1st to 15thNight
39%5%14%26%12%2
2400
16th to endNight
36%5%12%28%16%
2640
October1st to 15thNight
48%5%12%20%12%
2880
16th to endNight
60%413%14%6%
3080
November1st to 15thNight
51%5%11%18%9%2
3265
16th to endNight
60%414%15%4
3360
December1st to 15thNight
67%411%12%2
3360
16th to endNight
72%410%9%2
3584

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
20%35%27%10%5%1
180
16th to endDay
23%36%29%8%1
278
February1st to 15thDay
30%35%28%4
270
16th to endDay
30%30%30%7%
343
March1st to 15thDay
24%28%30%13%2
510
16th to endDay
27%21%28%15%5%1
544
April1st to 15thDay
31%23%25%14%31
510
16th to endDay
27%19%28%15%7%2
499
May1st to 15thDay
28%17%28%15%6%2
528
16th to endDay
16%16%32%22%8%3
587
June1st to 15thDay
20%16%30%24%7%1
555
16th to endDay
16%12%34%23%10%2
555
July1st to 15thDay
11%5%29%32%15%4
545
16th to endDay
14%9%33%29%10%3
582
August1st to 15thDay
14%6%25%30%15%7%
538
16th to endDay
13%6%31%25%14%8%
588
September1st to 15thDay
17%12%24%22%14%7%
555
16th to endDay
14%11%28%18%17%8%
554
October1st to 15thDay
25%13%27%18%10%3
555
16th to endDay
34%20%27%13%4
588
November1st to 15thDay
25%19%29%17%7%
362
16th to endDay
32%26%27%12%1
180
December1st to 15thDay
30%28%25%11%3
180
16th to endDay
28%33%26%11%
192
January1st to 15thNight
24%28%30%13%3
960
16th to endNight
21%29%30%15%2
1024
February1st to 15thNight
27%27%31%11%1
944
16th to endNight
24%29%28%15%2
843
March1st to 15thNight
27%22%30%17%2
960
16th to endNight
25%16%32%18%7%
1024
April1st to 15thNight
25%18%32%20%3
958
16th to endNight
22%16%28%24%7%1
868
May1st to 15thNight
21%10%26%30%10%
576
16th to endNight
12%8%34%30%12%
503
June1st to 15thNight
16%9%27%31%14%
480
16th to endNight
11%7%31%37%11%
480
July1st to 15thNight
8%5%23%41%18%2
460
16th to endNight
11%427%36%17%2
566
August1st to 15thNight
10%424%36%20%3
710
16th to endNight
11%5%25%32%22%2
922
September1st to 15thNight
18%7%24%27%19%2
960
16th to endNight
15%8%22%26%21%5%
957
October1st to 15thNight
23%12%27%22%12%1
960
16th to endNight
34%15%30%16%3
1024
November1st to 15thNight
25%15%30%20%6%1
980
16th to endNight
26%23%26%15%7%
960
December1st to 15thNight
30%24%28%13%3
960
16th to endNight
30%24%28%13%2
1024
Page generated at 2021-11-11 18:33:34. Version ac04

Copyright 2021 A. Danko


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