Marysville Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Marysville Observatory clear sky chart from 2005-11-05 to 2018-10-08.

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
42%
15827
9%
50823
9%
15799
43%
15799
14%
38322

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
33%
814
8%
2862
10%
810
34%
810
8%
2356
January16th to endNight
31%
832
8%
2894
9%
832
31%
832
10%
2313
February1st to 15thNight
36%
760
8%
2483
9%
760
36%
760
10%
2022
February16th to endNight
34%
684
10%
2180
11%
684
36%
684
12%
1719
March1st to 15thNight
28%
780
5%
2252
5%
780
29%
780
10%
1879
March16th to endNight
27%
832
5%
2230
3%
832
27%
832
10%
1900
April1st to 15thNight
32%
779
5%
1949
3%
779
32%
779
11%
1675
April16th to endNight
37%
579
6%
1737
5%
579
38%
579
12%
1401
May1st to 15thNight
53%
389
12%
1559
18%
389
55%
389
17%
1007
May16th to endNight
47%
406
5%
1624
8%
406
48%
406
11%
1192
June1st to 15thNight
46%
390
3%
1437
4%
390
47%
390
14%
1042
June16th to endNight
52%
390
7%
1365
7%
390
53%
390
16%
974
July1st to 15thNight
69%
370
13%
1295
16%
370
70%
370
32%
713
July16th to endNight
74%
408
16%
1539
27%
386
76%
386
34%
758
August1st to 15thNight
80%
456
19%
1600
25%
454
81%
454
40%
786
August16th to endNight
69%
696
20%
1938
17%
696
69%
696
38%
1131
September1st to 15thNight
69%
780
21%
1950
12%
780
70%
780
40%
1204
September16th to endNight
51%
776
16%
2132
13%
776
52%
776
23%
1531
October1st to 15thNight
49%
752
11%
2256
12%
752
50%
752
20%
1599
October16th to endNight
39%
768
8%
2387
8%
768
41%
768
13%
1865
November1st to 15thNight
24%
760
5%
2636
5%
760
25%
760
7%
2232
November16th to endNight
29%
780
5%
2730
5%
780
30%
780
8%
2236
December1st to 15thNight
37%
780
8%
2730
9%
780
38%
780
11%
2156
December16th to endNight
22%
866
5%
3058
5%
866
23%
866
6%
2631

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
25%8%35%424445%31%
52334
Night
28%8%35%424345%29%
50980
Cloud CoverDay
27%8%35%5%24345%29%
52334
Night
29%8%35%423345%29%
50983
TransparencyDay
57%5%12%16%6%1
51994
Night
58%5%12%15%6%1
50824
SeeingDay
27%6%18%25%15%5%
7295
Night
33%5%11%23%21%5%
15833

By Month

Percentage Cloud Cover NW (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
41%9%3443223320%
1404
16th to endDay
38%8%36%323345%17%
1680
February1st to 15thDay
32%10%46%6%34445%18%
1711
16th to endDay
31%11%36%5%3333421%
1580
March1st to 15thDay
36%10%45%5%35%43316%
2038
16th to endDay
34%10%48%5%2434415%
2346
April1st to 15thDay
29%11%46%5%46%45%5%15%
2329
16th to endDay
25%10%37%6%45%45%5%20%
2495
May1st to 15thDay
19%7%26%5%35%46%6%32%
2721
16th to endDay
24%8%35%5%3345%6%27%
2839
June1st to 15thDay
24%8%26%5%3445%6%28%
2850
16th to endDay
20%7%27%5%35%5%5%6%31%
2925
July1st to 15thDay
12%424312346%54%
2925
16th to endDay
13%312213236%58%
2884
August1st to 15thDay
9%423313346%55%
2602
16th to endDay
11%424324447%49%
2616
September1st to 15thDay
11%5%24413336%52%
2340
16th to endDay
21%6%25%42335%6%36%
2157
October1st to 15thDay
24%8%26%5%2445%6%29%
1873
16th to endDay
37%7%25%5%24345%21%
1836
November1st to 15thDay
42%8%35%6%2443414%
1549
16th to endDay
40%9%3443334418%
1560
December1st to 15thDay
32%12%46%41443322%
1560
16th to endDay
39%11%46%43333316%
1514
January1st to 15thNight
39%8%345%2333421%
2862
16th to endNight
36%9%35%423345%20%
2894
February1st to 15thNight
34%9%35%5%35%23421%
2471
16th to endNight
31%10%36%5%24335%23%
2180
March1st to 15thNight
34%11%35%434445%19%
2252
16th to endNight
35%11%36%42344417%
2226
April1st to 15thNight
28%10%45%7%35%5%5%6%18%
1949
16th to endNight
27%8%47%6%25%445%22%
1737
May1st to 15thNight
18%6%26%5%24336%40%
1559
16th to endNight
21%6%46%6%25%5%5%6%29%
1624
June1st to 15thNight
25%7%25%5%24336%31%
1437
16th to endNight
21%6%246%345%6%6%32%
1365
July1st to 15thNight
10%313423335%56%
1365
16th to endNight
8%323323246%60%
1634
August1st to 15thNight
7%213212347%62%
1608
16th to endNight
8%5%14313346%55%
1938
September1st to 15thNight
9%425%313445%56%
1950
16th to endNight
20%6%35%5%23345%39%
2132
October1st to 15thNight
22%8%35%5%23335%36%
2256
16th to endNight
33%7%24433446%25%
2387
November1st to 15thNight
41%9%445%2333317%
2636
16th to endNight
37%10%25%42433419%
2730
December1st to 15thNight
32%9%26%43444324%
2730
16th to endNight
39%13%36%42332315%
3058

Percentage Cloud Cover SW (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
43%9%3442222320%
1404
16th to endDay
40%10%34423335%18%
1680
February1st to 15thDay
36%10%36%6%2333418%
1711
16th to endDay
33%11%46%5%3333321%
1580
March1st to 15thDay
39%12%36%5%2423215%
2038
16th to endDay
37%11%37%7%3334314%
2346
April1st to 15thDay
32%11%48%6%35%35%5%13%
2329
16th to endDay
27%10%48%6%35%45%5%17%
2495
May1st to 15thDay
21%6%36%6%345%5%5%29%
2721
16th to endDay
26%10%46%6%33445%25%
2839
June1st to 15thDay
27%8%36%5%34445%25%
2850
16th to endDay
21%8%36%5%36%45%6%28%
2925
July1st to 15thDay
12%5%1341345%6%51%
2925
16th to endDay
12%422323335%55%
2884
August1st to 15thDay
11%5%13323346%53%
2602
16th to endDay
12%4245%24446%47%
2616
September1st to 15thDay
12%5%24422236%51%
2340
16th to endDay
22%7%25%5%23346%36%
2157
October1st to 15thDay
26%7%26%424347%29%
1873
16th to endDay
40%7%25%32334421%
1836
November1st to 15thDay
45%9%35%42333413%
1549
16th to endDay
40%11%25%41333417%
1560
December1st to 15thDay
34%12%45%32333421%
1560
16th to endDay
41%12%46%42332314%
1514
January1st to 15thNight
43%7%2442333320%
2861
16th to endNight
38%10%35%42333420%
2894
February1st to 15thNight
35%10%36%43344421%
2471
16th to endNight
33%11%35%42333423%
2180
March1st to 15thNight
38%10%345%23335%18%
2252
16th to endNight
37%12%45%5%22345%16%
2230
April1st to 15thNight
29%10%47%6%3445%6%16%
1949
16th to endNight
28%10%47%6%35%345%21%
1737
May1st to 15thNight
18%5%35%424346%39%
1559
16th to endNight
22%7%37%6%245%5%6%28%
1624
June1st to 15thNight
26%7%26%5%32436%31%
1437
16th to endNight
21%5%35%5%345%5%6%33%
1365
July1st to 15thNight
9%424323335%56%
1365
16th to endNight
8%323313245%59%
1634
August1st to 15thNight
7%312222247%62%
1608
16th to endNight
9%414323336%56%
1938
September1st to 15thNight
10%5%24413336%55%
1950
16th to endNight
22%7%34423345%38%
2132
October1st to 15thNight
24%7%25%5%3333436%
2256
16th to endNight
35%6%2443345%5%23%
2387
November1st to 15thNight
44%9%35%42322315%
2636
16th to endNight
41%8%25%42333419%
2730
December1st to 15thNight
34%10%35%42334323%
2730
16th to endNight
42%12%36%42232314%
3058

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
71%37%10%6%
1404
16th to endDay
69%49%11%31
1680
February1st to 15thDay
69%6%9%8%41
1711
16th to endDay
67%48%13%6%
1580
March1st to 15thDay
74%49%9%2
2038
16th to endDay
74%5%8%10%
2346
April1st to 15thDay
72%6%11%9%1
2329
16th to endDay
67%6%11%10%4
2495
May1st to 15thDay
54%6%14%17%6%
2721
16th to endDay
60%7%16%13%2
2843
June1st to 15thDay
59%6%15%11%5%
2850
16th to endDay
55%5%16%17%3
2925
July1st to 15thDay
33%6%14%28%14%2
2766
16th to endDay
29%5%14%32%15%1
2716
August1st to 15thDay
31%6%18%29%11%1
2585
16th to endDay
36%6%15%29%9%2
2616
September1st to 15thDay
35%414%24%17%2
2340
16th to endDay
50%5%16%17%8%1
2157
October1st to 15thDay
54%5%15%16%7%
1873
16th to endDay
66%411%13%4
1836
November1st to 15thDay
74%6%8%5%21
1549
16th to endDay
70%5%6%8%7%
1560
December1st to 15thDay
67%48%11%7%
1560
16th to endDay
75%47%8%3
1514
January1st to 15thNight
68%6%7%11%5%1
2862
16th to endNight
67%39%11%5%1
2894
February1st to 15thNight
67%5%9%10%42
2483
16th to endNight
64%410%14%5%
2180
March1st to 15thNight
68%6%10%12%2
2252
16th to endNight
71%5%12%10%
2230
April1st to 15thNight
67%8%10%11%2
1949
16th to endNight
64%5%12%11%5%
1737
May1st to 15thNight
46%6%17%19%8%
1560
16th to endNight
55%9%17%14%2
1624
June1st to 15thNight
56%6%18%14%4
1437
16th to endNight
51%8%16%19%21
1365
July1st to 15thNight
32%414%30%13%4
1295
16th to endNight
26%5%13%30%20%3
1539
August1st to 15thNight
24%5%19%32%15%3
1600
16th to endNight
30%5%19%31%10%2
1938
September1st to 15thNight
31%414%26%17%4
1950
16th to endNight
48%5%12%21%8%2
2132
October1st to 15thNight
51%414%20%8%
2256
16th to endNight
60%6%13%13%5%
2387
November1st to 15thNight
73%48%8%22
2636
16th to endNight
69%5%8%9%6%
2730
December1st to 15thNight
65%411%12%5%
2730
16th to endNight
76%36%7%3
3058

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
26%3320%22%24%
90
16th to endDay
59%6%8%13%8%3
112
February1st to 15thDay
45%416%19%11%1
281
16th to endDay
41%10%20%20%6%1
260
March1st to 15thDay
45%14%19%11%7%
330
16th to endDay
46%8%21%10%9%3
352
April1st to 15thDay
37%12%21%16%9%2
329
16th to endDay
27%10%24%22%10%4
318
May1st to 15thDay
20%11%24%26%14%2
348
16th to endDay
26%415%28%16%8%
394
June1st to 15thDay
22%6%23%28%15%2
495
16th to endDay
20%6%24%29%17%2
570
July1st to 15thDay
12%320%35%24%3
550
16th to endDay
10%217%35%24%10%
393
August1st to 15thDay
11%111%36%24%13%
359
16th to endDay
12%219%34%22%9%
396
September1st to 15thDay
17%418%32%20%7%
375
16th to endDay
21%6%18%29%17%6%
375
October1st to 15thDay
33%6%21%20%15%2
345
16th to endDay
42%7%9%19%15%5%
252
November1st to 15thDay
55%9%17%12%31
95
16th to endDay
53%5%12%11%7%10%
90
December1st to 15thDay
46%410%8%15%14%
90
16th to endDay
50%7%7%18%12%4
96
January1st to 15thNight
44%7%6%15%20%4
814
16th to endNight
42%5%12%18%16%3
832
February1st to 15thNight
41%48%27%13%3
764
16th to endNight
39%5%12%23%15%3
684
March1st to 15thNight
42%10%12%18%13%2
780
16th to endNight
42%8%14%21%11%1
832
April1st to 15thNight
33%7%16%24%15%2
779
16th to endNight
31%8%13%24%18%3
579
May1st to 15thNight
20%5%12%27%28%4
390
16th to endNight
23%49%26%29%6%
407
June1st to 15thNight
29%29%28%25%3
390
16th to endNight
23%210%35%23%3
390
July1st to 15thNight
12%28%33%37%6%
370
16th to endNight
8%28%27%41%10%
408
August1st to 15thNight
10%321%44%18%
456
16th to endNight
10%48%25%38%12%
696
September1st to 15thNight
12%37%27%36%13%
780
16th to endNight
26%310%23%28%7%
776
October1st to 15thNight
26%49%28%26%4
752
16th to endNight
38%412%20%18%4
768
November1st to 15thNight
47%6%13%23%8%
760
16th to endNight
44%414%17%13%5%
780
December1st to 15thNight
40%5%7%24%18%4
780
16th to endNight
47%6%15%18%11%
866
Page generated at 2018-10-09 07:39:09. Version ac04

Copyright 2018 A. Danko


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