Martin Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Martin Observatory clear sky chart from 2005-11-05 to 2018-10-27.

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
41%
17230
18%
51292
12%
17191
48%
17191
22%
33773

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
20%
778
17%
2522
8%
776
32%
776
13%
1686
January16th to endNight
16%
832
18%
2704
6%
832
31%
832
15%
1789
February1st to 15thNight
19%
762
16%
2482
6%
761
32%
761
16%
1628
February16th to endNight
16%
683
18%
2028
7%
683
28%
683
14%
1412
March1st to 15thNight
24%
780
18%
2145
9%
780
32%
780
20%
1458
March16th to endNight
27%
832
15%
2288
8%
832
33%
832
20%
1605
April1st to 15thNight
30%
778
17%
2047
5%
778
38%
778
24%
1369
April16th to endNight
38%
662
19%
1818
8%
662
46%
662
24%
1225
May1st to 15thNight
42%
585
16%
1755
9%
585
47%
585
23%
1165
May16th to endNight
52%
609
13%
1828
9%
609
55%
609
24%
1236
June1st to 15thNight
65%
585
15%
1755
13%
585
68%
585
29%
1121
June16th to endNight
66%
585
16%
1755
13%
585
69%
585
30%
1083
July1st to 15thNight
65%
555
13%
1665
12%
555
65%
555
26%
1105
July16th to endNight
73%
612
14%
1739
12%
579
74%
579
29%
1099
August1st to 15thNight
65%
575
19%
1715
17%
572
66%
572
28%
1124
August16th to endNight
70%
712
18%
1954
14%
712
71%
712
30%
1289
September1st to 15thNight
61%
780
22%
2068
16%
780
62%
780
29%
1378
September16th to endNight
52%
777
19%
2145
16%
777
54%
777
25%
1448
October1st to 15thNight
50%
780
23%
2314
20%
780
57%
780
26%
1481
October16th to endNight
39%
816
27%
2447
19%
816
51%
816
28%
1480
November1st to 15thNight
43%
760
25%
2344
19%
760
52%
760
26%
1431
November16th to endNight
36%
780
25%
2535
17%
780
47%
780
23%
1525
December1st to 15thNight
25%
780
17%
2535
9%
780
35%
780
15%
1714
December16th to endNight
21%
832
17%
2704
7%
832
33%
832
13%
1922

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%7%36%6%35%5%5%7%34%
52251
Night
13%6%35%5%35%5%5%8%38%
51485
Cloud CoverDay
14%6%36%6%35%5%5%7%35%
52261
Night
13%5%25%5%3445%8%39%
51489
TransparencyDay
45%8%12%19%12%2
51962
Night
40%7%13%21%14%2
51292
SeeingDay
20%11%20%20%16%9%
7076
Night
18%12%21%27%17%2
17236

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
16%8%37%6%345%46%32%
1746
16th to endDay
15%8%36%435%436%37%
1872
February1st to 15thDay
14%9%37%5%45%445%34%
1710
16th to endDay
16%9%48%6%34447%31%
1728
March1st to 15thDay
16%6%36%5%25%45%5%38%
2134
16th to endDay
17%9%37%5%2335%5%35%
2288
April1st to 15thDay
13%6%36%5%23348%42%
2231
16th to endDay
17%6%26%6%345%45%37%
2428
May1st to 15thDay
18%7%36%5%35%5%6%7%29%
2526
16th to endDay
14%7%37%6%46%5%6%8%29%
2639
June1st to 15thDay
11%5%25%7%36%6%7%9%34%
2535
16th to endDay
9%5%36%6%5%6%5%7%9%35%
2535
July1st to 15thDay
14%6%37%7%36%5%6%8%29%
2535
16th to endDay
10%5%36%7%5%8%7%8%9%26%
2673
August1st to 15thDay
15%7%36%6%47%6%7%9%26%
2487
16th to endDay
11%6%36%7%5%7%6%7%8%30%
2586
September1st to 15thDay
14%5%36%6%35%5%6%7%35%
2219
16th to endDay
19%7%36%5%445%46%30%
2145
October1st to 15thDay
16%7%24423446%42%
1976
16th to endDay
15%6%24424345%46%
2034
November1st to 15thDay
12%7%245%24447%45%
1842
16th to endDay
14%7%34434246%43%
1755
December1st to 15thDay
16%8%36%5%3446%6%35%
1755
16th to endDay
19%10%35%5%25%346%32%
1872
January1st to 15thNight
16%6%36%6%46%5%5%7%31%
2522
16th to endNight
15%8%346%35%5%5%7%33%
2704
February1st to 15thNight
15%8%35%436%5%6%7%34%
2480
16th to endNight
13%7%47%7%45%5%6%6%31%
2028
March1st to 15thNight
15%6%25%5%35%5%6%7%35%
2133
16th to endNight
15%7%36%5%35%5%47%35%
2288
April1st to 15thNight
13%6%25%5%3446%8%39%
2047
16th to endNight
14%5%37%5%24448%39%
1818
May1st to 15thNight
15%5%36%6%34448%38%
1755
16th to endNight
12%8%35%5%345%5%8%37%
1826
June1st to 15thNight
7%424435%5%7%13%41%
1755
16th to endNight
7%424435%5%6%11%44%
1755
July1st to 15thNight
10%5%35%5%35%5%5%8%41%
1755
16th to endNight
5%325%6%46%6%7%12%39%
1847
August1st to 15thNight
12%435%5%2446%8%41%
1726
16th to endNight
9%425%5%36%6%7%11%39%
1954
September1st to 15thNight
11%5%15%5%3445%7%43%
2068
16th to endNight
16%6%245%245%46%40%
2145
October1st to 15thNight
13%5%25%433446%44%
2314
16th to endNight
13%5%25%424436%45%
2447
November1st to 15thNight
13%6%24324446%46%
2344
16th to endNight
14%5%25%423446%44%
2535
December1st to 15thNight
16%8%36%5%36%45%6%31%
2535
16th to endNight
17%10%47%6%35%5%5%6%28%
2704

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
17%7%26%5%4445%6%34%
1746
16th to endDay
14%8%45%5%24446%38%
1872
February1st to 15thDay
14%8%37%5%45%35%5%36%
1710
16th to endDay
17%7%47%6%34447%32%
1728
March1st to 15thDay
16%5%35%5%35%45%6%40%
2145
16th to endDay
18%7%37%5%33346%36%
2287
April1st to 15thDay
12%6%36%43335%7%43%
2231
16th to endDay
17%6%25%6%35%446%37%
2428
May1st to 15thDay
18%7%36%5%35%5%6%6%29%
2526
16th to endDay
14%7%37%7%36%5%6%8%30%
2639
June1st to 15thDay
10%4347%46%6%7%10%33%
2535
16th to endDay
8%5%35%6%46%6%6%10%34%
2535
July1st to 15thDay
13%5%37%7%46%6%6%9%29%
2535
16th to endDay
10%5%36%7%5%8%8%7%9%26%
2673
August1st to 15thDay
15%6%26%6%5%6%7%7%9%26%
2487
16th to endDay
11%6%26%7%5%7%6%7%8%31%
2586
September1st to 15thDay
14%5%26%5%35%5%6%7%36%
2219
16th to endDay
20%7%36%6%345%5%6%31%
2145
October1st to 15thDay
17%6%2442335%6%43%
1976
16th to endDay
15%6%24424335%47%
2034
November1st to 15thDay
12%6%2442435%7%45%
1842
16th to endDay
14%6%25%424347%44%
1755
December1st to 15thDay
15%7%36%5%2445%7%37%
1755
16th to endDay
20%8%35%435%445%33%
1872
January1st to 15thNight
15%5%26%6%35%5%6%7%34%
2522
16th to endNight
15%7%35%5%345%5%7%36%
2704
February1st to 15thNight
14%7%35%5%35%5%6%8%36%
2473
16th to endNight
12%7%37%6%46%46%7%33%
2028
March1st to 15thNight
16%5%25%6%35%5%6%6%37%
2145
16th to endNight
16%6%35%5%35%5%5%6%36%
2288
April1st to 15thNight
13%6%25%5%3346%8%39%
2047
16th to endNight
14%5%35%435%447%40%
1818
May1st to 15thNight
13%5%37%5%34447%39%
1754
16th to endNight
13%6%25%6%2445%9%37%
1826
June1st to 15thNight
7%4245%245%7%13%41%
1755
16th to endNight
7%3245%345%5%11%45%
1755
July1st to 15thNight
9%5%25%6%35%5%5%9%42%
1755
16th to endNight
4315%6%36%6%7%12%39%
1847
August1st to 15thNight
12%425%425%46%8%41%
1726
16th to endNight
8%415%5%36%5%7%11%39%
1954
September1st to 15thNight
11%5%25%5%3446%7%44%
2068
16th to endNight
16%5%25%43445%6%40%
2145
October1st to 15thNight
13%6%25%42336%6%44%
2314
16th to endNight
12%415%434447%46%
2447
November1st to 15thNight
14%6%23323346%47%
2344
16th to endNight
14%5%235%23446%46%
2535
December1st to 15thNight
17%8%36%4245%47%34%
2535
16th to endNight
18%8%37%5%345%5%6%30%
2704

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
48%6%10%20%11%2
1747
16th to endDay
45%6%9%23%12%2
1872
February1st to 15thDay
49%5%10%20%13%1
1712
16th to endDay
50%5%12%18%11%1
1728
March1st to 15thDay
43%5%11%22%13%3
2145
16th to endDay
49%6%9%22%11%1
2288
April1st to 15thDay
39%5%12%24%13%4
2231
16th to endDay
46%6%9%18%14%4
2428
May1st to 15thDay
50%9%13%16%8%1
2526
16th to endDay
49%11%12%18%7%1
2643
June1st to 15thDay
42%12%14%18%11%
2535
16th to endDay
42%10%13%17%13%2
2535
July1st to 15thDay
47%10%11%14%12%2
2396
16th to endDay
46%12%14%15%9%
2518
August1st to 15thDay
49%10%14%17%8%
2474
16th to endDay
45%9%16%15%10%1
2586
September1st to 15thDay
43%8%13%18%14%2
2219
16th to endDay
51%7%9%17%13%
2145
October1st to 15thDay
40%5%11%23%13%4
1976
16th to endDay
38%49%24%19%2
2034
November1st to 15thDay
36%5%10%19%22%5%
1842
16th to endDay
40%5%9%23%20%1
1755
December1st to 15thDay
43%7%12%17%14%3
1755
16th to endDay
49%5%12%18%11%1
1872
January1st to 15thNight
45%6%13%16%13%4
2522
16th to endNight
43%7%11%22%13%1
2704
February1st to 15thNight
42%7%13%21%13%2
2482
16th to endNight
47%6%12%22%8%2
2028
March1st to 15thNight
42%6%12%23%11%2
2145
16th to endNight
45%7%13%19%12%1
2288
April1st to 15thNight
40%5%14%21%14%3
2047
16th to endNight
42%6%12%18%16%4
1818
May1st to 15thNight
42%7%15%21%12%1
1755
16th to endNight
40%9%19%21%7%1
1828
June1st to 15thNight
32%12%19%22%12%
1755
16th to endNight
30%11%16%23%15%1
1755
July1st to 15thNight
37%11%14%18%13%4
1665
16th to endNight
30%13%19%23%11%1
1739
August1st to 15thNight
37%9%15%22%13%
1715
16th to endNight
35%10%15%25%12%1
1954
September1st to 15thNight
37%9%13%20%16%2
2068
16th to endNight
42%6%11%21%16%
2145
October1st to 15thNight
38%6%10%24%15%3
2314
16th to endNight
35%5%9%26%18%4
2447
November1st to 15thNight
37%49%20%21%6%
2344
16th to endNight
36%5%9%25%19%2
2535
December1st to 15thNight
47%6%12%19%11%2
2535
16th to endNight
50%7%12%16%12%1
2704

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
33%22%27%11%4
135
16th to endDay
32%25%25%13%2
144
February1st to 15thDay
29%34%30%5%
135
16th to endDay
28%26%29%10%4
149
March1st to 15thDay
25%24%26%16%7%
330
16th to endDay
23%21%26%20%6%1
352
April1st to 15thDay
22%20%21%21%12%1
330
16th to endDay
24%12%23%16%16%5%
319
May1st to 15thDay
22%14%24%17%11%8%
348
16th to endDay
20%422%21%19%12%
395
June1st to 15thDay
12%5%21%24%24%12%
375
16th to endDay
10%8%28%23%17%11%
375
July1st to 15thDay
15%120%27%21%13%
365
16th to endDay
12%212%30%23%18%
390
August1st to 15thDay
22%115%20%22%17%
358
16th to endDay
12%210%21%25%26%
396
September1st to 15thDay
16%6%14%18%25%18%
375
16th to endDay
22%415%25%18%12%
374
October1st to 15thDay
19%10%17%22%25%5%
375
16th to endDay
17%16%23%21%17%3
382
November1st to 15thDay
23%10%21%25%16%2
260
16th to endDay
20%25%10%34%7%2
135
December1st to 15thDay
26%27%27%11%6%
135
16th to endDay
38%20%24%13%2
144
January1st to 15thNight
26%23%25%20%4
780
16th to endNight
23%25%30%19%1
832
February1st to 15thNight
25%21%30%21%1
764
16th to endNight
21%25%31%19%1
683
March1st to 15thNight
23%18%31%22%3
780
16th to endNight
21%15%31%23%8%
832
April1st to 15thNight
21%18%26%26%7%
778
16th to endNight
17%13%22%31%14%
662
May1st to 15thNight
14%10%24%31%16%1
585
16th to endNight
14%317%29%31%4
611
June1st to 15thNight
8%115%37%32%3
585
16th to endNight
8%114%36%33%5%
585
July1st to 15thNight
11%19%36%36%4
555
16th to endNight
5%17%33%43%7%
612
August1st to 15thNight
14%17%39%33%4
575
16th to endNight
11%16%28%44%7%
712
September1st to 15thNight
12%312%29%35%6%
780
16th to endNight
20%314%30%27%3
777
October1st to 15thNight
18%8%16%29%24%2
780
16th to endNight
17%12%25%28%15%1
816
November1st to 15thNight
17%11%21%31%15%1
760
16th to endNight
19%16%22%27%12%
780
December1st to 15thNight
24%17%26%23%7%
780
16th to endNight
24%18%28%24%3
832
Page generated at 2018-10-28 08:41:04. Version ac04

Copyright 2018 A. Danko


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