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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 2019-07-11.

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%
17148
13%
54168
8%
17114
33%
17114
15%
39076

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%
839
7%
2926
3%
836
15%
836
5%
2433
January16th to endNight
9%
896
9%
2937
2%
896
17%
896
6%
2411
February1st to 15thNight
7%
824
7%
2677
1%
821
15%
821
6%
2205
February16th to endNight
14%
735
10%
2299
4%
735
22%
735
8%
1812
March1st to 15thNight
16%
840
13%
2360
6%
840
23%
840
11%
1861
March16th to endNight
22%
896
16%
2433
7%
896
29%
896
18%
1791
April1st to 15thNight
19%
838
14%
2096
4%
838
25%
838
17%
1599
April16th to endNight
31%
758
17%
2004
7%
758
37%
758
25%
1358
May1st to 15thNight
37%
504
16%
1764
11%
504
45%
504
18%
1180
May16th to endNight
37%
438
16%
1753
14%
438
47%
438
23%
1014
June1st to 15thNight
39%
420
15%
1680
14%
420
49%
420
18%
1037
June16th to endNight
41%
420
13%
1680
14%
420
49%
420
22%
979
July1st to 15thNight
58%
392
18%
1568
23%
392
64%
392
29%
846
July16th to endNight
49%
459
16%
1594
14%
434
55%
434
27%
921
August1st to 15thNight
51%
575
16%
1715
11%
572
55%
572
31%
1062
August16th to endNight
54%
749
22%
1991
12%
749
58%
749
38%
1206
September1st to 15thNight
46%
780
20%
1950
9%
780
51%
780
31%
1298
September16th to endNight
50%
777
23%
2146
17%
777
53%
777
30%
1377
October1st to 15thNight
32%
780
15%
2340
11%
780
39%
780
19%
1635
October16th to endNight
17%
832
11%
2502
4%
832
26%
832
12%
1898
November1st to 15thNight
25%
820
15%
2737
10%
820
32%
820
15%
1944
November16th to endNight
18%
840
11%
2940
6%
840
25%
840
10%
2209
December1st to 15thNight
12%
840
8%
2940
3%
840
19%
840
7%
2342
December16th to endNight
10%
896
5%
3136
0%
896
15%
896
4%
2658

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
16%10%47%6%3445%6%28%
55041
Night
15%10%47%6%3445%6%29%
54342
Cloud CoverDay
16%10%47%6%35%45%6%28%
55051
Night
15%10%48%6%3445%6%29%
54347
TransparencyDay
54%410%18%9%
54734
Night
54%411%18%9%1
54168
SeeingDay
22%17%27%19%9%3
7739
Night
22%16%28%21%9%1
17150

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%16%7%14%11%46%43313%
1672
16th to endDay
11%16%8%14%12%5%5%44412%
1989
February1st to 15thDay
15%16%10%14%9%4443413%
1845
16th to endDay
18%15%5%12%8%3444416%
1745
March1st to 15thDay
15%16%7%11%7%4434320%
2247
16th to endDay
15%13%5%8%5%3335%5%29%
2495
April1st to 15thDay
20%12%47%5%24445%26%
2512
16th to endDay
19%10%35%423445%35%
2572
May1st to 15thDay
17%10%26%5%35%45%7%32%
2846
16th to endDay
14%5%25%5%45%45%8%37%
3066
June1st to 15thDay
19%6%36%5%25%45%7%33%
2940
16th to endDay
14%5%15%5%35%6%7%8%36%
2940
July1st to 15thDay
9%5%25%5%36%5%6%8%40%
2874
16th to endDay
12%5%36%6%35%6%6%9%32%
2825
August1st to 15thDay
12%7%26%6%45%6%6%8%33%
2487
16th to endDay
13%6%26%6%36%5%6%9%34%
2548
September1st to 15thDay
17%7%25%4345%5%8%36%
2340
16th to endDay
15%5%25%5%345%5%6%39%
2142
October1st to 15thDay
22%9%25%5%2335%5%33%
1950
16th to endDay
25%12%37%6%34445%22%
2074
November1st to 15thDay
14%15%46%5%24446%29%
1780
16th to endDay
18%15%5%8%7%34446%21%
1680
December1st to 15thDay
15%19%7%11%7%3434418%
1680
16th to endDay
17%19%10%12%7%4343411%
1792
January1st to 15thNight
15%16%7%12%10%45%43414%
2926
16th to endNight
13%16%7%12%10%46%44414%
2937
February1st to 15thNight
14%15%8%14%8%35%44417%
2675
16th to endNight
13%13%6%12%9%45%5%45%19%
2299
March1st to 15thNight
16%15%6%10%7%34345%23%
2348
16th to endNight
17%11%47%5%34345%32%
2433
April1st to 15thNight
19%11%45%5%34446%28%
2096
16th to endNight
17%8%245%2336%6%39%
2004
May1st to 15thNight
17%6%26%435%45%7%34%
1764
16th to endNight
11%5%245%3446%8%44%
1751
June1st to 15thNight
15%5%25%6%25%5%5%7%37%
1680
16th to endNight
11%6%345%345%5%9%41%
1680
July1st to 15thNight
6%425%5%3446%7%49%
1648
16th to endNight
9%425%5%245%6%8%44%
1693
August1st to 15thNight
8%5%25%5%345%6%8%45%
1726
16th to endNight
9%42442445%8%48%
1991
September1st to 15thNight
15%5%25%424447%43%
1950
16th to endNight
14%5%13425%45%7%43%
2146
October1st to 15thNight
20%7%35%5%3445%6%34%
2340
16th to endNight
27%10%35%5%34446%25%
2502
November1st to 15thNight
17%10%36%6%245%5%6%30%
2737
16th to endNight
18%13%5%8%7%245%46%23%
2940
December1st to 15thNight
16%16%6%10%7%345%5%5%18%
2940
16th to endNight
19%17%8%11%7%35%445%11%
3136

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%16%8%13%11%45%44413%
1672
16th to endDay
10%16%7%15%12%5%5%43412%
1989
February1st to 15thDay
15%15%10%14%10%4434413%
1845
16th to endDay
18%14%6%12%8%3444416%
1745
March1st to 15thDay
15%17%6%11%8%3444420%
2258
16th to endDay
15%13%5%8%6%23345%29%
2494
April1st to 15thDay
20%12%5%6%6%24345%26%
2512
16th to endDay
19%10%35%423445%35%
2572
May1st to 15thDay
18%9%36%5%2445%6%32%
2846
16th to endDay
15%6%25%5%35%46%8%37%
3066
June1st to 15thDay
19%6%36%5%3445%7%32%
2940
16th to endDay
14%5%245%45%5%6%8%36%
2940
July1st to 15thDay
9%5%25%5%36%5%6%8%40%
2874
16th to endDay
12%5%36%6%36%6%7%8%32%
2825
August1st to 15thDay
13%6%26%6%35%6%6%9%33%
2487
16th to endDay
14%6%25%6%36%5%6%8%34%
2548
September1st to 15thDay
17%6%25%4345%5%7%35%
2340
16th to endDay
15%5%245%345%5%6%39%
2142
October1st to 15thDay
22%9%26%42435%5%33%
1950
16th to endDay
24%12%38%6%35%345%22%
2074
November1st to 15thDay
14%15%47%5%345%45%29%
1780
16th to endDay
18%15%5%8%6%25%45%5%21%
1680
December1st to 15thDay
15%19%8%11%7%2443318%
1680
16th to endDay
17%20%10%13%7%4443411%
1792
January1st to 15thNight
15%15%7%13%9%46%44414%
2926
16th to endNight
12%16%7%12%10%46%445%15%
2937
February1st to 15thNight
14%14%7%14%8%35%44417%
2668
16th to endNight
13%14%7%12%9%45%445%19%
2299
March1st to 15thNight
16%15%6%10%6%34335%23%
2360
16th to endNight
16%11%48%5%24345%32%
2433
April1st to 15thNight
19%11%46%5%44446%29%
2096
16th to endNight
17%8%25%42235%7%38%
2004
May1st to 15thNight
17%6%36%435%45%7%33%
1764
16th to endNight
11%5%2443445%8%43%
1751
June1st to 15thNight
15%5%26%5%25%5%5%7%38%
1680
16th to endNight
11%6%25%43445%10%41%
1680
July1st to 15thNight
6%425%5%345%6%8%48%
1648
16th to endNight
10%4245%3446%8%44%
1693
August1st to 15thNight
8%4246%35%5%6%7%44%
1726
16th to endNight
9%41442446%8%48%
1991
September1st to 15thNight
15%5%24424447%43%
1950
16th to endNight
14%5%24325%45%8%42%
2146
October1st to 15thNight
19%7%25%5%34447%34%
2340
16th to endNight
26%10%26%5%34436%25%
2502
November1st to 15thNight
17%10%36%5%245%46%30%
2737
16th to endNight
18%13%5%7%6%3445%6%23%
2940
December1st to 15thNight
16%16%6%10%7%35%45%418%
2940
16th to endNight
18%17%7%12%8%445%4412%
3136

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
73%46%11%3
1673
16th to endDay
74%310%8%2
1989
February1st to 15thDay
74%38%10%2
1847
16th to endDay
69%48%12%4
1745
March1st to 15thDay
68%39%13%4
2258
16th to endDay
56%38%19%10%1
2495
April1st to 15thDay
58%310%16%9%
2512
16th to endDay
50%38%19%16%2
2572
May1st to 15thDay
51%5%10%21%10%1
2846
16th to endDay
44%5%12%23%12%1
3070
June1st to 15thDay
49%5%10%20%13%
2940
16th to endDay
42%6%12%23%14%1
2940
July1st to 15thDay
39%7%9%26%16%1
2725
16th to endDay
45%7%14%19%12%
2662
August1st to 15thDay
45%5%15%21%11%
2474
16th to endDay
44%6%11%26%10%1
2548
September1st to 15thDay
45%6%10%24%11%
2340
16th to endDay
42%5%11%24%14%
2142
October1st to 15thDay
52%412%18%11%
1950
16th to endDay
64%313%14%3
2074
November1st to 15thDay
56%5%12%15%8%1
1780
16th to endDay
63%412%16%3
1680
December1st to 15thDay
70%312%12%1
1680
16th to endDay
77%48%7%2
1792
January1st to 15thNight
72%39%9%4
2926
16th to endNight
70%310%12%3
2937
February1st to 15thNight
69%48%12%4
2677
16th to endNight
65%210%14%5%
2299
March1st to 15thNight
63%39%17%5%
2360
16th to endNight
54%48%19%12%1
2433
April1st to 15thNight
55%410%18%10%
2096
16th to endNight
44%312%21%16%2
2004
May1st to 15thNight
48%5%11%18%13%1
1764
16th to endNight
37%5%15%24%14%2
1753
June1st to 15thNight
43%5%12%22%15%
1680
16th to endNight
38%5%12%24%16%1
1680
July1st to 15thNight
32%5%12%25%20%3
1568
16th to endNight
35%6%14%27%14%2
1594
August1st to 15thNight
36%6%15%30%11%
1715
16th to endNight
32%414%32%13%2
1991
September1st to 15thNight
40%413%26%13%2
1950
16th to endNight
37%5%12%27%15%
2146
October1st to 15thNight
49%411%20%12%
2340
16th to endNight
60%314%15%5%
2502
November1st to 15thNight
53%5%12%17%8%2
2737
16th to endNight
60%413%15%5%
2940
December1st to 15thNight
66%5%12%13%2
2940
16th to endNight
74%49%8%2
3136

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
18%35%30%7%6%1
120
16th to endDay
21%38%29%10%
185
February1st to 15thDay
26%42%24%6%
180
16th to endDay
27%33%29%8%
248
March1st to 15thDay
23%29%27%15%3
390
16th to endDay
24%22%30%15%5%1
416
April1st to 15thDay
33%24%24%13%21
390
16th to endDay
26%18%26%15%9%2
379
May1st to 15thDay
28%17%26%16%7%3
408
16th to endDay
16%17%32%23%6%3
459
June1st to 15thDay
23%14%31%22%6%
435
16th to endDay
17%12%33%24%9%1
435
July1st to 15thDay
10%5%28%33%16%5%
406
16th to endDay
14%10%30%27%12%4
390
August1st to 15thDay
17%6%24%28%13%9%
358
16th to endDay
14%430%22%16%11%
396
September1st to 15thDay
18%6%21%21%19%11%
375
16th to endDay
16%11%22%20%18%11%
374
October1st to 15thDay
28%11%23%20%13%4
375
16th to endDay
32%22%26%13%5%
398
November1st to 15thDay
25%18%29%18%8%
254
16th to endDay
33%26%26%13%
120
December1st to 15thDay
27%28%20%16%5%
120
16th to endDay
32%35%23%7%
128
January1st to 15thNight
24%28%30%12%2
840
16th to endNight
21%29%30%15%2
896
February1st to 15thNight
27%28%32%10%1
824
16th to endNight
23%28%28%16%2
735
March1st to 15thNight
26%23%29%18%2
840
16th to endNight
24%15%33%17%7%
896
April1st to 15thNight
25%19%31%20%2
838
16th to endNight
21%15%28%25%8%1
758
May1st to 15thNight
21%7%25%32%11%
504
16th to endNight
12%9%35%28%13%
439
June1st to 15thNight
16%10%26%31%14%
420
16th to endNight
13%7%31%36%11%
420
July1st to 15thNight
7%422%41%20%2
392
16th to endNight
11%327%34%20%3
459
August1st to 15thNight
10%426%33%21%3
575
16th to endNight
11%424%31%25%2
749
September1st to 15thNight
18%6%21%27%22%3
780
16th to endNight
16%9%20%23%23%6%
777
October1st to 15thNight
24%12%25%21%14%1
780
16th to endNight
33%15%28%17%4
832
November1st to 15thNight
26%15%28%19%7%1
820
16th to endNight
26%23%25%16%7%1
840
December1st to 15thNight
29%24%27%13%4
840
16th to endNight
30%24%29%13%2
896
Page generated at 2019-07-12 07:32:35. Version ac04

Copyright 2019 A. Danko


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