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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 2017-03-26.

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%
14365
13%
45341
7%
14331
33%
14331
15%
32763

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%
719
6%
2506
3%
716
14%
716
5%
2082
January16th to endNight
11%
768
8%
2517
2%
768
18%
768
6%
2075
February1st to 15thNight
7%
704
7%
2287
1%
701
16%
701
6%
1877
February16th to endNight
15%
631
10%
1973
4%
631
23%
631
9%
1552
March1st to 15thNight
16%
720
12%
2022
5%
720
23%
720
11%
1592
March16th to endNight
22%
748
16%
2032
7%
748
30%
748
18%
1497
April1st to 15thNight
20%
658
15%
1646
4%
658
25%
658
18%
1242
April16th to endNight
33%
602
18%
1592
8%
602
39%
602
27%
1065
May1st to 15thNight
42%
396
18%
1386
13%
396
50%
396
20%
891
May16th to endNight
40%
342
16%
1369
15%
342
48%
342
24%
783
June1st to 15thNight
39%
330
14%
1320
13%
330
49%
330
17%
841
June16th to endNight
43%
330
12%
1320
14%
330
50%
330
22%
769
July1st to 15thNight
54%
310
16%
1240
20%
310
60%
310
28%
685
July16th to endNight
50%
391
14%
1346
12%
366
55%
366
28%
768
August1st to 15thNight
50%
494
17%
1474
11%
491
54%
491
31%
905
August16th to endNight
54%
633
21%
1683
11%
633
57%
633
37%
1028
September1st to 15thNight
46%
660
21%
1650
10%
660
51%
660
31%
1084
September16th to endNight
48%
657
22%
1816
15%
657
52%
657
28%
1181
October1st to 15thNight
33%
660
15%
1980
12%
660
39%
660
19%
1380
October16th to endNight
18%
704
9%
2117
3%
704
25%
704
12%
1635
November1st to 15thNight
25%
700
16%
2337
12%
700
32%
700
16%
1625
November16th to endNight
19%
720
11%
2520
7%
720
25%
720
10%
1891
December1st to 15thNight
12%
720
7%
2520
2%
720
17%
720
6%
2027
December16th to endNight
10%
768
5%
2688
1%
768
14%
768
5%
2288

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%
45636
Night
15%10%48%6%34446%29%
45515
Cloud CoverDay
16%10%47%6%35%45%6%28%
45646
Night
15%10%48%6%34446%29%
45520
TransparencyDay
54%411%18%9%
45329
Night
54%411%18%9%1
45341
SeeingDay
20%15%27%21%10%4
4792
Night
21%17%28%21%9%1
14367

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%15%11%45%43313%
1432
16th to endDay
10%16%8%15%12%5%444411%
1705
February1st to 15thDay
15%16%10%13%9%4443313%
1575
16th to endDay
17%15%5%11%8%45%44417%
1499
March1st to 15thDay
16%16%7%10%7%4434421%
1925
16th to endDay
15%14%5%7%5%3335%6%29%
2079
April1st to 15thDay
19%12%47%5%24445%29%
1972
16th to endDay
18%9%25%42345%6%37%
2046
May1st to 15thDay
13%9%26%5%35%5%5%7%35%
2234
16th to endDay
15%5%245%35%45%8%39%
2394
June1st to 15thDay
20%6%36%5%25%45%7%30%
2310
16th to endDay
14%415%5%35%6%7%8%37%
2310
July1st to 15thDay
9%6%25%5%36%5%6%8%38%
2310
16th to endDay
11%5%36%7%35%6%7%9%32%
2413
August1st to 15thDay
12%7%26%5%46%5%6%8%33%
2145
16th to endDay
14%6%26%5%36%46%9%35%
2154
September1st to 15thDay
18%6%25%3345%5%7%37%
1980
16th to endDay
16%5%25%5%345%5%5%38%
1812
October1st to 15thDay
21%9%25%5%2335%5%33%
1650
16th to endDay
25%12%37%6%34435%21%
1755
November1st to 15thDay
13%15%46%5%24446%31%
1520
16th to endDay
18%13%5%8%7%34446%22%
1440
December1st to 15thDay
16%20%7%10%7%3434417%
1440
16th to endDay
17%19%11%12%7%3343411%
1536
January1st to 15thNight
15%17%7%12%9%35%43414%
2506
16th to endNight
12%16%7%12%10%46%44414%
2517
February1st to 15thNight
13%14%8%14%8%35%44417%
2285
16th to endNight
13%14%6%12%8%45%5%45%19%
1973
March1st to 15thNight
17%14%6%10%6%33345%24%
2010
16th to endNight
16%11%5%6%5%24346%31%
2032
April1st to 15thNight
19%11%45%5%33446%30%
1646
16th to endNight
15%8%245%2336%6%40%
1592
May1st to 15thNight
14%5%26%436%45%8%37%
1386
16th to endNight
11%5%245%2436%7%45%
1367
June1st to 15thNight
17%5%25%6%25%5%5%7%35%
1320
16th to endNight
10%6%345%345%5%9%42%
1320
July1st to 15thNight
7%425%5%35%46%8%46%
1320
16th to endNight
9%3245%25%5%6%9%44%
1445
August1st to 15thNight
8%425%5%345%6%8%45%
1485
16th to endNight
10%32442445%9%48%
1683
September1st to 15thNight
16%425%424347%45%
1650
16th to endNight
15%6%24425%45%7%42%
1816
October1st to 15thNight
20%7%36%5%34446%34%
1980
16th to endNight
27%9%36%5%34346%23%
2117
November1st to 15thNight
17%10%36%5%2445%7%32%
2337
16th to endNight
18%13%5%8%6%235%46%24%
2520
December1st to 15thNight
18%16%6%10%7%345%5%5%17%
2520
16th to endNight
19%17%8%11%7%35%445%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
14%15%8%14%11%45%44413%
1432
16th to endDay
10%16%8%16%12%5%5%435%11%
1705
February1st to 15thDay
15%15%10%13%10%4443313%
1575
16th to endDay
18%15%6%11%8%445%4417%
1499
March1st to 15thDay
16%16%6%11%7%3444421%
1936
16th to endDay
15%13%5%8%5%3335%5%29%
2078
April1st to 15thDay
19%12%46%5%24345%29%
1972
16th to endDay
18%9%35%423446%37%
2046
May1st to 15thDay
14%9%26%5%25%5%5%6%35%
2234
16th to endDay
16%6%245%35%35%8%38%
2394
June1st to 15thDay
20%6%36%5%35%5%5%7%30%
2310
16th to endDay
14%4245%46%5%6%8%37%
2310
July1st to 15thDay
10%6%25%6%36%5%6%8%38%
2310
16th to endDay
12%5%36%7%36%6%7%8%32%
2413
August1st to 15thDay
13%6%26%6%35%6%6%9%33%
2145
16th to endDay
15%6%25%6%35%5%6%8%34%
2154
September1st to 15thDay
18%6%25%4245%5%7%37%
1980
16th to endDay
17%5%25%5%35%5%5%6%37%
1812
October1st to 15thDay
21%9%36%425%35%5%33%
1650
16th to endDay
25%12%37%6%25%335%22%
1755
November1st to 15thDay
13%15%46%6%3445%5%31%
1520
16th to endDay
18%13%5%8%7%26%45%6%21%
1440
December1st to 15thDay
16%20%7%10%7%2443318%
1440
16th to endDay
17%19%11%13%7%3443411%
1536
January1st to 15thNight
15%16%7%13%9%35%44414%
2506
16th to endNight
12%16%7%12%10%46%44414%
2517
February1st to 15thNight
13%14%8%15%8%35%43417%
2278
16th to endNight
12%15%6%12%8%35%445%19%
1973
March1st to 15thNight
16%15%6%10%6%34345%24%
2022
16th to endNight
16%11%5%8%5%33445%31%
2032
April1st to 15thNight
19%11%45%444445%31%
1646
16th to endNight
16%8%25%42335%7%39%
1592
May1st to 15thNight
14%5%36%436%45%8%37%
1386
16th to endNight
11%5%25%42445%8%44%
1367
June1st to 15thNight
16%6%26%5%25%6%5%6%36%
1320
16th to endNight
10%5%25%4345%5%10%41%
1320
July1st to 15thNight
7%425%6%345%5%9%45%
1320
16th to endNight
9%3145%345%6%9%44%
1445
August1st to 15thNight
8%4245%35%5%5%7%45%
1485
16th to endNight
10%42442446%8%47%
1683
September1st to 15thNight
16%424423446%45%
1650
16th to endNight
15%5%24425%45%8%42%
1816
October1st to 15thNight
19%7%25%5%34447%33%
1980
16th to endNight
27%10%26%6%34446%24%
2117
November1st to 15thNight
16%10%36%5%25%5%46%32%
2337
16th to endNight
17%14%6%7%6%33446%24%
2520
December1st to 15thNight
17%16%6%10%7%35%45%417%
2520
16th to endNight
18%17%8%12%7%345%45%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
73%46%10%3
1433
16th to endDay
76%39%8%2
1705
February1st to 15thDay
75%38%9%2
1577
16th to endDay
68%48%12%4
1499
March1st to 15thDay
67%310%13%5%
1936
16th to endDay
56%38%20%10%
2079
April1st to 15thDay
56%310%17%10%1
1972
16th to endDay
47%37%20%18%2
2046
May1st to 15thDay
46%5%10%22%12%1
2234
16th to endDay
43%413%22%14%1
2398
June1st to 15thDay
51%5%11%19%11%
2310
16th to endDay
42%6%13%24%13%
2310
July1st to 15thDay
40%6%9%25%15%
2161
16th to endDay
45%7%15%20%11%1
2250
August1st to 15thDay
45%5%14%20%12%1
2132
16th to endDay
44%5%11%26%10%1
2154
September1st to 15thDay
44%6%10%25%11%
1980
16th to endDay
45%5%11%23%14%
1812
October1st to 15thDay
51%411%18%12%
1650
16th to endDay
64%413%13%3
1755
November1st to 15thDay
53%5%12%16%9%1
1520
16th to endDay
62%412%16%3
1440
December1st to 15thDay
70%313%11%1
1440
16th to endDay
76%49%7%2
1536
January1st to 15thNight
72%38%9%5%
2506
16th to endNight
71%39%11%3
2517
February1st to 15thNight
69%48%13%4
2287
16th to endNight
66%211%14%5%
1973
March1st to 15thNight
63%310%16%5%
2022
16th to endNight
54%39%18%12%1
2032
April1st to 15thNight
54%49%18%11%1
1646
16th to endNight
43%311%22%16%3
1592
May1st to 15thNight
44%5%11%21%15%1
1386
16th to endNight
36%5%16%22%16%2
1369
June1st to 15thNight
45%6%13%21%13%
1320
16th to endNight
38%5%12%24%17%1
1320
July1st to 15thNight
34%413%26%18%2
1240
16th to endNight
33%6%16%26%14%2
1346
August1st to 15thNight
35%5%15%29%12%
1474
16th to endNight
33%313%32%14%2
1683
September1st to 15thNight
39%312%28%13%2
1650
16th to endNight
39%5%11%27%14%
1816
October1st to 15thNight
49%411%20%12%
1980
16th to endNight
61%414%14%4
2117
November1st to 15thNight
51%5%13%17%9%2
2337
16th to endNight
60%413%15%5%
2520
December1st to 15thNight
67%5%12%12%2
2520
16th to endNight
74%410%8%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
16%41%26%310%1
60
16th to endDay
21%36%31%10%
93
February1st to 15thDay
26%47%18%6%
90
16th to endDay
24%27%34%12%
158
March1st to 15thDay
24%27%27%17%4
270
16th to endDay
23%21%29%16%6%2
267
April1st to 15thDay
29%20%26%18%41
210
16th to endDay
20%12%29%20%12%4
210
May1st to 15thDay
19%14%28%21%12%4
228
16th to endDay
15%14%32%23%8%5%
267
June1st to 15thDay
23%12%28%23%10%1
255
16th to endDay
18%9%28%29%12%2
255
July1st to 15thDay
11%5%28%33%16%4
245
16th to endDay
11%12%31%27%11%5%
270
August1st to 15thDay
16%6%24%28%13%10%
253
16th to endDay
16%224%23%18%14%
268
September1st to 15thDay
17%7%21%23%17%13%
255
16th to endDay
17%9%24%20%16%11%
254
October1st to 15thDay
23%11%23%20%16%4
255
16th to endDay
33%18%28%15%4
271
November1st to 15thDay
17%16%33%20%10%
174
16th to endDay
25%25%25%25%
60
December1st to 15thDay
25%31%21%15%6%
60
16th to endDay
32%37%25%4
64
January1st to 15thNight
25%29%30%12%2
720
16th to endNight
21%28%31%16%2
768
February1st to 15thNight
25%28%32%11%1
704
16th to endNight
22%28%28%17%2
631
March1st to 15thNight
26%23%28%18%2
720
16th to endNight
23%16%33%17%7%
748
April1st to 15thNight
24%19%32%20%2
658
16th to endNight
19%15%27%26%8%1
602
May1st to 15thNight
17%8%25%35%12%
396
16th to endNight
11%9%33%30%15%
343
June1st to 15thNight
17%10%25%32%13%
330
16th to endNight
11%7%31%36%12%
330
July1st to 15thNight
8%424%39%20%2
310
16th to endNight
10%427%35%19%2
391
August1st to 15thNight
10%426%33%21%3
494
16th to endNight
11%424%31%25%3
633
September1st to 15thNight
18%7%21%27%22%2
660
16th to endNight
17%9%21%23%23%5%
657
October1st to 15thNight
24%12%23%21%15%1
660
16th to endNight
32%15%29%18%3
704
November1st to 15thNight
25%14%30%20%7%1
700
16th to endNight
26%23%25%15%7%1
720
December1st to 15thNight
30%25%27%12%3
720
16th to endNight
30%24%29%12%2
768
Page generated at 2017-03-27 11:15:16. Version ac04

Copyright 2017 A. Danko


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