Mason Road
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mason Road clear sky chart from 2005-11-05 to 2017-09-10.

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
57%
15349
23%
46804
19%
15300
61%
15300
31%
28171

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
38%
900
23%
2327
11%
895
45%
895
29%
1571
January16th to endNight
39%
960
23%
2496
11%
960
45%
960
29%
1677
February1st to 15thNight
40%
835
24%
2238
11%
829
47%
829
30%
1448
February16th to endNight
36%
474
25%
1736
16%
474
47%
474
23%
1044
March1st to 15thNight
38%
540
24%
1980
17%
540
47%
540
22%
1215
March16th to endNight
49%
576
21%
2112
18%
576
54%
576
28%
1202
April1st to 15thNight
48%
539
23%
1899
19%
539
56%
539
26%
1115
April16th to endNight
45%
540
21%
1800
19%
540
52%
540
26%
1098
May1st to 15thNight
51%
539
18%
1784
17%
539
57%
539
26%
1102
May16th to endNight
68%
563
26%
1685
28%
561
71%
561
37%
956
June1st to 15thNight
85%
540
18%
1620
21%
540
85%
540
46%
855
June16th to endNight
75%
540
16%
1620
19%
540
76%
540
30%
1010
July1st to 15thNight
76%
510
17%
1530
21%
510
76%
510
36%
882
July16th to endNight
81%
564
18%
1594
21%
531
82%
531
34%
931
August1st to 15thNight
89%
539
24%
1658
27%
536
89%
536
49%
824
August16th to endNight
74%
573
14%
1910
16%
573
74%
573
25%
1218
September1st to 15thNight
76%
525
15%
1856
18%
525
76%
525
29%
1078
September16th to endNight
72%
492
25%
1815
30%
492
72%
492
30%
1016
October1st to 15thNight
74%
643
31%
1963
27%
643
75%
643
43%
1027
October16th to endNight
67%
704
35%
2112
28%
704
71%
704
45%
1100
November1st to 15thNight
60%
700
28%
2100
23%
700
63%
700
36%
1210
November16th to endNight
52%
720
33%
2160
24%
720
60%
720
36%
1240
December1st to 15thNight
43%
873
24%
2313
15%
873
48%
873
26%
1580
December16th to endNight
36%
960
18%
2496
10%
960
40%
960
24%
1772

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
12%6%36%6%35%5%6%7%35%
47812
Night
11%5%2442445%8%46%
47004
TransparencyDay
44%7%11%16%14%6%
47512
Night
34%5%13%20%16%8%
46809
SeeingDay
11%314%25%28%16%
5379
Night
13%418%31%27%4
15350

By Month

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
18%5%2442445%5%43%
1611
16th to endDay
19%7%34423345%41%
1728
February1st to 15thDay
19%7%25%424245%40%
1627
16th to endDay
20%8%34423345%39%
1738
March1st to 15thDay
23%6%24325%346%36%
1980
16th to endDay
15%6%36%425%446%40%
2110
April1st to 15thDay
15%6%36%5%3446%7%37%
2049
16th to endDay
14%6%35%5%36%46%7%36%
2160
May1st to 15thDay
12%6%36%6%46%5%7%7%33%
2163
16th to endDay
8%5%46%7%46%6%7%10%32%
2430
June1st to 15thDay
6%5%37%7%47%7%8%10%30%
2340
16th to endDay
6%6%47%9%6%9%7%7%10%23%
2340
July1st to 15thDay
10%437%7%46%8%8%11%25%
2340
16th to endDay
8%5%46%9%5%7%9%9%10%23%
2466
August1st to 15thDay
3426%7%5%8%8%9%11%32%
2289
16th to endDay
11%6%38%8%5%7%7%7%8%25%
2292
September1st to 15thDay
10%5%27%7%5%7%7%6%8%31%
1988
16th to endDay
11%6%35%7%46%5%7%6%35%
1815
October1st to 15thDay
7%425%435%5%5%6%48%
1656
16th to endDay
10%323313346%55%
1760
November1st to 15thDay
11%5%25%5%26%5%5%7%43%
1758
16th to endDay
13%6%25%423335%49%
1800
December1st to 15thDay
16%9%45%5%2335%7%36%
1644
16th to endDay
18%8%36%5%3434435%
1728
January1st to 15thNight
19%6%24323437%41%
2327
16th to endNight
18%7%35%323346%43%
2496
February1st to 15thNight
16%5%24334346%45%
2233
16th to endNight
16%7%25%423236%44%
1736
March1st to 15thNight
19%6%24422446%41%
1980
16th to endNight
11%5%25%324447%48%
2112
April1st to 15thNight
12%5%2442446%8%43%
1899
16th to endNight
12%6%25%43445%8%42%
1800
May1st to 15thNight
9%5%25%5%35%6%5%10%40%
1783
16th to endNight
5%42332448%11%48%
1683
June1st to 15thNight
321332437%12%55%
1620
16th to endNight
5%4245%26%6%9%11%40%
1620
July1st to 15thNight
5%42342447%12%47%
1620
16th to endNight
33245%25%5%8%13%45%
1702
August1st to 15thNight
223245%6%13%57%
1668
16th to endNight
7%425%6%35%5%7%13%38%
1910
September1st to 15thNight
7%425%4335%7%10%45%
1856
16th to endNight
8%425%42446%8%48%
1815
October1st to 15thNight
7%21332245%7%59%
1963
16th to endNight
9%213323235%63%
2112
November1st to 15thNight
8%424424447%52%
2100
16th to endNight
10%5%2442323455%
2160
December1st to 15thNight
14%8%345%33446%40%
2313
16th to endNight
19%8%35%5%24435%37%
2496

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
42%45%16%21%9%
1612
16th to endDay
45%26%15%17%12%
1728
February1st to 15thDay
46%26%16%18%8%
1628
16th to endDay
47%37%14%18%8%
1738
March1st to 15thDay
48%47%12%19%6%
1980
16th to endDay
42%5%9%14%21%6%
2112
April1st to 15thDay
44%6%7%15%16%8%
2049
16th to endDay
45%6%11%16%14%6%
2160
May1st to 15thDay
46%7%10%14%13%7%
2163
16th to endDay
43%8%12%20%13%2
2434
June1st to 15thDay
42%9%15%16%15%1
2340
16th to endDay
49%11%15%15%7%
2340
July1st to 15thDay
45%10%19%18%5%
2201
16th to endDay
47%12%19%18%1
2311
August1st to 15thDay
37%11%21%23%6%
2275
16th to endDay
50%11%16%13%5%1
2292
September1st to 15thDay
47%10%14%15%10%2
1988
16th to endDay
44%8%10%16%14%5%
1815
October1st to 15thDay
33%6%9%19%16%14%
1656
16th to endDay
29%36%13%30%16%
1760
November1st to 15thDay
39%5%9%17%18%9%
1758
16th to endDay
38%35%14%22%15%
1800
December1st to 15thDay
46%49%17%14%7%
1644
16th to endDay
51%47%15%14%6%
1728
January1st to 15thNight
43%35%14%21%11%
2327
16th to endNight
43%36%16%17%13%
2496
February1st to 15thNight
40%36%14%22%11%
2243
16th to endNight
41%36%17%17%13%
1736
March1st to 15thNight
42%49%14%18%10%
1980
16th to endNight
35%413%16%20%8%
2112
April1st to 15thNight
36%5%10%19%16%10%
1899
16th to endNight
39%412%18%15%9%
1800
May1st to 15thNight
36%7%14%18%13%8%
1784
16th to endNight
26%8%15%30%15%3
1685
June1st to 15thNight
20%7%21%28%20%
1620
16th to endNight
33%10%21%25%9%
1620
July1st to 15thNight
28%7%30%26%7%
1530
16th to endNight
26%11%29%29%3
1594
August1st to 15thNight
17%7%30%36%8%
1658
16th to endNight
35%12%25%18%6%1
1910
September1st to 15thNight
31%9%24%20%10%3
1856
16th to endNight
32%6%14%19%18%7%
1815
October1st to 15thNight
24%410%24%19%15%
1963
16th to endNight
25%26%15%29%19%
2112
November1st to 15thNight
31%5%12%21%21%8%
2100
16th to endNight
32%36%14%25%16%
2160
December1st to 15thNight
44%48%19%14%8%
2313
16th to endNight
48%47%14%15%9%
2496

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
20%8%31%27%12%
90
16th to endDay
10%14%43%19%11%
96
February1st to 15thDay
11%7%40%35%5%
90
16th to endDay
16%8%38%30%6%
81
March1st to 15thDay
27%12%43%8%7%
90
16th to endDay
20%9%27%22%15%4
96
April1st to 15thDay
14%9%22%32%20%1
168
16th to endDay
21%321%30%21%1
270
May1st to 15thDay
13%5%19%36%22%3
300
16th to endDay
10%423%33%21%6%
517
June1st to 15thDay
8%9%34%34%12%
495
16th to endDay
9%17%27%33%21%
495
July1st to 15thDay
8%5%25%34%26%
475
16th to endDay
7%1318%35%33%
515
August1st to 15thDay
4216%42%33%
442
16th to endDay
16%149%34%34%
332
September1st to 15thDay
7%5%18%43%25%
185
16th to endDay
8%217%41%30%
90
October1st to 15thDay
31441%32%17%
90
16th to endDay
11%418%27%28%10%
96
November1st to 15thDay
13%324%32%22%4
90
16th to endDay
17%7%23%33%12%5%
90
December1st to 15thDay
24%322%33%11%5%
90
16th to endDay
26%14%34%19%41
96
January1st to 15thNight
21%5%28%33%10%
900
16th to endNight
20%6%28%35%8%
960
February1st to 15thNight
19%7%28%35%8%
835
16th to endNight
21%9%29%35%4
474
March1st to 15thNight
21%7%28%34%7%
540
16th to endNight
14%6%27%37%14%
576
April1st to 15thNight
13%7%26%40%11%
539
16th to endNight
16%5%26%36%15%
540
May1st to 15thNight
11%425%42%15%
540
16th to endNight
7%116%41%30%3
563
June1st to 15thNight
3437%50%4
540
16th to endNight
6%1326%52%10%
540
July1st to 15thNight
5%1218%55%16%
510
16th to endNight
3113%59%21%
564
August1st to 15thNight
310%66%18%
539
16th to endNight
8%316%54%16%
573
September1st to 15thNight
8%418%54%14%
525
16th to endNight
10%1426%47%9%
492
October1st to 15thNight
8%18%32%43%5%
643
16th to endNight
10%215%36%31%4
704
November1st to 15thNight
10%319%38%26%3
700
16th to endNight
13%425%37%17%1
720
December1st to 15thNight
18%6%25%32%16%
873
16th to endNight
24%6%26%31%10%
960
Page generated at 2017-09-11 18:35:24. Version ac04

Copyright 2017 A. Danko


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