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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 2018-03-11.

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%
15561
13%
49143
8%
15527
33%
15527
15%
35411

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%
779
6%
2716
3%
776
14%
776
5%
2259
January16th to endNight
10%
832
8%
2727
2%
832
18%
832
6%
2241
February1st to 15thNight
7%
764
7%
2482
1%
761
15%
761
6%
2042
February16th to endNight
14%
683
10%
2136
4%
683
22%
683
9%
1678
March1st to 15thNight
16%
764
12%
2147
5%
764
23%
764
11%
1690
March16th to endNight
22%
768
16%
2085
6%
768
29%
768
18%
1546
April1st to 15thNight
20%
718
14%
1796
4%
718
25%
718
18%
1355
April16th to endNight
32%
657
19%
1737
8%
657
38%
657
27%
1161
May1st to 15thNight
40%
432
17%
1512
12%
432
48%
432
19%
995
May16th to endNight
39%
374
17%
1497
15%
374
49%
374
23%
863
June1st to 15thNight
40%
360
14%
1440
13%
360
50%
360
18%
896
June16th to endNight
41%
360
13%
1440
13%
360
49%
360
22%
842
July1st to 15thNight
54%
340
15%
1360
19%
340
60%
340
28%
749
July16th to endNight
50%
423
16%
1462
14%
398
55%
398
28%
834
August1st to 15thNight
51%
539
16%
1609
11%
536
55%
536
32%
983
August16th to endNight
54%
691
23%
1837
12%
691
59%
691
38%
1111
September1st to 15thNight
45%
720
20%
1800
9%
720
50%
720
31%
1191
September16th to endNight
51%
717
24%
1981
18%
717
54%
717
30%
1260
October1st to 15thNight
33%
720
15%
2160
11%
720
39%
720
19%
1498
October16th to endNight
18%
768
11%
2310
5%
768
27%
768
13%
1744
November1st to 15thNight
25%
760
15%
2537
11%
760
32%
760
15%
1778
November16th to endNight
18%
780
11%
2730
6%
780
26%
780
10%
2038
December1st to 15thNight
12%
780
7%
2730
2%
780
18%
780
6%
2185
December16th to endNight
9%
832
5%
2912
0%
832
15%
832
4%
2472

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%29%
49488
Night
15%10%47%6%3445%6%29%
49317
Cloud CoverDay
16%10%47%6%35%45%6%29%
49498
Night
15%10%48%6%34446%29%
49322
TransparencyDay
54%411%18%9%
49181
Night
54%411%18%9%1
49143
SeeingDay
21%16%27%19%9%4
6000
Night
21%17%28%21%9%1
15563

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
13%15%7%14%11%46%43313%
1552
16th to endDay
10%16%8%15%11%5%444412%
1847
February1st to 15thDay
15%16%10%13%9%4434413%
1710
16th to endDay
19%15%5%11%8%4444417%
1622
March1st to 15thDay
16%16%7%10%7%3434320%
2037
16th to endDay
15%13%5%7%6%3335%5%28%
2139
April1st to 15thDay
19%12%46%5%24345%29%
2152
16th to endDay
18%9%35%423446%37%
2232
May1st to 15thDay
15%10%26%5%3445%7%33%
2438
16th to endDay
16%5%25%5%35%45%8%37%
2618
June1st to 15thDay
20%6%36%5%25%45%7%32%
2520
16th to endDay
14%415%5%35%6%7%8%36%
2520
July1st to 15thDay
10%5%25%6%36%5%7%8%38%
2520
16th to endDay
12%5%36%7%35%6%6%9%32%
2605
August1st to 15thDay
11%7%26%6%45%6%7%8%34%
2340
16th to endDay
13%6%26%5%36%5%6%9%35%
2351
September1st to 15thDay
17%6%25%4345%5%7%37%
2160
16th to endDay
15%5%25%5%345%5%6%39%
1977
October1st to 15thDay
21%9%25%5%2335%5%34%
1800
16th to endDay
24%11%37%6%34445%23%
1914
November1st to 15thDay
13%14%46%5%24446%30%
1650
16th to endDay
17%14%5%8%7%34446%22%
1560
December1st to 15thDay
16%19%7%11%7%3434418%
1560
16th to endDay
17%18%10%12%7%4343411%
1664
January1st to 15thNight
15%16%7%12%9%45%43414%
2716
16th to endNight
12%17%7%12%10%46%44415%
2727
February1st to 15thNight
14%15%8%14%8%35%44417%
2480
16th to endNight
13%14%6%12%8%45%5%35%20%
2136
March1st to 15thNight
17%14%6%9%6%34345%23%
2135
16th to endNight
17%11%46%5%24446%30%
2085
April1st to 15thNight
20%11%45%5%33446%30%
1796
16th to endNight
15%7%245%2346%6%40%
1737
May1st to 15thNight
16%6%26%436%45%8%35%
1512
16th to endNight
11%5%245%3436%7%44%
1495
June1st to 15thNight
16%5%25%5%25%5%5%7%37%
1440
16th to endNight
10%6%345%345%5%9%41%
1440
July1st to 15thNight
7%425%5%35%46%8%46%
1440
16th to endNight
9%4245%245%6%9%44%
1561
August1st to 15thNight
7%425%5%35%5%6%7%46%
1620
16th to endNight
9%32442445%8%48%
1837
September1st to 15thNight
15%425%424447%44%
1800
16th to endNight
14%5%13425%45%7%44%
1981
October1st to 15thNight
20%6%36%5%34446%34%
2160
16th to endNight
27%9%35%5%34346%25%
2310
November1st to 15thNight
17%10%36%5%245%5%6%31%
2537
16th to endNight
17%13%5%8%7%235%46%24%
2730
December1st to 15thNight
17%16%6%10%7%345%5%5%17%
2730
16th to endNight
19%17%8%11%7%35%445%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
13%15%8%13%11%45%44413%
1552
16th to endDay
10%16%8%15%12%5%5%435%12%
1847
February1st to 15thDay
15%15%10%14%10%4434313%
1710
16th to endDay
19%14%6%11%8%4444417%
1622
March1st to 15thDay
16%16%6%11%8%3444420%
2048
16th to endDay
15%13%5%8%5%3335%5%28%
2138
April1st to 15thDay
19%12%46%5%24345%29%
2152
16th to endDay
18%9%35%423446%37%
2232
May1st to 15thDay
16%9%26%5%25%5%5%6%33%
2438
16th to endDay
16%6%25%5%35%45%8%37%
2618
June1st to 15thDay
20%6%36%5%3445%7%32%
2520
16th to endDay
14%5%245%46%5%7%8%36%
2520
July1st to 15thDay
10%5%25%6%36%5%6%8%38%
2520
16th to endDay
12%5%36%7%36%6%7%8%32%
2605
August1st to 15thDay
12%6%26%6%36%6%7%9%33%
2340
16th to endDay
14%6%25%6%35%5%6%8%34%
2351
September1st to 15thDay
17%6%25%4345%5%7%37%
2160
16th to endDay
16%5%245%35%5%5%6%39%
1977
October1st to 15thDay
21%9%35%425%35%5%34%
1800
16th to endDay
24%11%37%6%35%345%23%
1914
November1st to 15thDay
13%14%46%6%345%45%30%
1650
16th to endDay
17%14%5%8%6%25%45%5%22%
1560
December1st to 15thDay
15%20%7%11%7%2443318%
1560
16th to endDay
17%18%11%13%7%4443411%
1664
January1st to 15thNight
15%16%7%13%9%46%44414%
2716
16th to endNight
12%16%7%12%10%46%445%15%
2727
February1st to 15thNight
13%14%8%15%8%35%43417%
2473
16th to endNight
12%14%6%12%8%35%445%20%
2136
March1st to 15thNight
16%15%6%10%6%34335%24%
2147
16th to endNight
17%11%5%8%5%34445%31%
2085
April1st to 15thNight
19%11%45%444445%31%
1796
16th to endNight
15%7%25%42245%7%39%
1737
May1st to 15thNight
16%5%36%436%45%7%34%
1512
16th to endNight
11%5%25%5%3445%8%43%
1495
June1st to 15thNight
15%6%25%5%25%5%5%7%37%
1440
16th to endNight
11%6%25%4345%5%10%40%
1440
July1st to 15thNight
6%425%6%345%6%9%45%
1440
16th to endNight
9%4145%345%6%9%44%
1561
August1st to 15thNight
8%4246%35%5%6%7%45%
1620
16th to endNight
9%41442446%8%48%
1837
September1st to 15thNight
15%5%24424446%44%
1800
16th to endNight
14%5%24325%45%8%43%
1981
October1st to 15thNight
19%7%25%5%34437%35%
2160
16th to endNight
26%10%26%5%34436%26%
2310
November1st to 15thNight
17%10%36%5%25%5%46%31%
2537
16th to endNight
17%13%5%7%6%3345%6%24%
2730
December1st to 15thNight
17%16%6%10%7%35%45%417%
2730
16th to endNight
18%17%7%12%8%445%4412%
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
73%46%11%3
1553
16th to endDay
74%310%8%2
1847
February1st to 15thDay
75%38%9%2
1712
16th to endDay
68%48%13%5%
1622
March1st to 15thDay
68%39%13%5%
2048
16th to endDay
56%38%19%9%
2139
April1st to 15thDay
56%310%17%10%1
2152
16th to endDay
47%38%20%17%2
2232
May1st to 15thDay
49%5%10%21%11%1
2438
16th to endDay
44%413%21%13%1
2622
June1st to 15thDay
50%411%20%11%
2520
16th to endDay
42%6%13%24%12%
2520
July1st to 15thDay
40%6%10%25%15%
2371
16th to endDay
45%6%15%20%11%
2442
August1st to 15thDay
44%6%15%21%12%
2327
16th to endDay
44%6%11%25%11%1
2351
September1st to 15thDay
44%6%10%25%12%1
2160
16th to endDay
43%5%11%24%14%
1977
October1st to 15thDay
51%411%19%12%
1800
16th to endDay
63%314%14%3
1914
November1st to 15thDay
54%5%12%16%8%1
1650
16th to endDay
62%412%16%3
1560
December1st to 15thDay
69%312%12%1
1560
16th to endDay
76%48%7%2
1664
January1st to 15thNight
72%38%9%5%
2716
16th to endNight
70%310%11%3
2727
February1st to 15thNight
69%48%13%4
2482
16th to endNight
66%210%14%6%
2136
March1st to 15thNight
63%310%16%5%
2147
16th to endNight
54%49%17%12%1
2085
April1st to 15thNight
54%49%18%11%
1796
16th to endNight
42%312%22%16%2
1737
May1st to 15thNight
46%5%11%20%14%1
1512
16th to endNight
37%5%15%23%14%2
1497
June1st to 15thNight
43%5%13%22%14%
1440
16th to endNight
38%6%13%23%16%1
1440
July1st to 15thNight
34%413%26%18%2
1360
16th to endNight
34%6%15%27%14%2
1462
August1st to 15thNight
35%5%16%30%11%
1609
16th to endNight
32%413%32%14%2
1837
September1st to 15thNight
39%412%26%13%2
1800
16th to endNight
37%5%11%28%16%
1981
October1st to 15thNight
49%411%20%13%
2160
16th to endNight
59%314%15%5%
2310
November1st to 15thNight
51%5%12%17%9%2
2537
16th to endNight
60%413%16%5%
2730
December1st to 15thNight
66%5%12%12%3
2730
16th to endNight
74%49%8%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
15%36%34%5%6%1
90
16th to endDay
18%35%34%11%
139
February1st to 15thDay
25%46%21%5%
135
16th to endDay
29%31%29%9%
203
March1st to 15thDay
25%27%27%15%3
312
16th to endDay
25%21%29%15%5%2
288
April1st to 15thDay
31%19%27%15%31
270
16th to endDay
21%15%30%18%10%3
270
May1st to 15thDay
26%16%24%18%9%3
288
16th to endDay
16%16%34%20%7%4
331
June1st to 15thDay
24%11%30%23%9%
315
16th to endDay
17%12%32%25%10%1
315
July1st to 15thDay
11%6%31%32%14%3
305
16th to endDay
14%11%29%27%13%4
326
August1st to 15thDay
14%7%26%27%13%10%
313
16th to endDay
15%5%26%24%16%12%
332
September1st to 15thDay
17%7%23%21%19%11%
315
16th to endDay
15%9%20%20%20%13%
314
October1st to 15thDay
25%11%24%19%14%4
315
16th to endDay
31%20%26%15%6%
334
November1st to 15thDay
21%16%30%20%9%
214
16th to endDay
26%28%27%16%
90
December1st to 15thDay
28%27%20%16%6%
90
16th to endDay
30%40%21%7%
96
January1st to 15thNight
25%29%30%12%2
780
16th to endNight
21%28%30%16%2
832
February1st to 15thNight
26%28%33%10%1
764
16th to endNight
22%28%29%16%2
683
March1st to 15thNight
26%22%29%18%2
764
16th to endNight
23%16%33%17%7%
768
April1st to 15thNight
25%18%32%21%2
718
16th to endNight
19%15%29%26%7%1
657
May1st to 15thNight
20%8%23%34%12%
432
16th to endNight
11%9%33%29%14%
375
June1st to 15thNight
17%9%25%33%13%
360
16th to endNight
12%8%32%35%11%
360
July1st to 15thNight
8%425%39%20%2
340
16th to endNight
10%426%35%20%3
423
August1st to 15thNight
9%427%33%21%3
539
16th to endNight
10%424%31%25%3
691
September1st to 15thNight
18%7%21%27%22%2
720
16th to endNight
16%9%19%22%25%6%
717
October1st to 15thNight
24%11%24%22%15%1
720
16th to endNight
31%15%29%18%4
768
November1st to 15thNight
25%14%29%20%8%1
760
16th to endNight
26%23%26%15%7%1
780
December1st to 15thNight
30%25%26%12%3
780
16th to endNight
30%25%29%12%2
832
Page generated at 2018-03-12 13:28:03. Version ac04

Copyright 2018 A. Danko


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