Marathon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Marathon clear sky chart from 2005-11-05 to 2017-10-31.

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
62%
15539
31%
47534
23%
15497
70%
15497
45%
24305

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
55%
719
34%
2151
23%
719
65%
719
42%
1144
January16th to endNight
56%
768
37%
2304
25%
768
67%
768
44%
1190
February1st to 15thNight
57%
703
35%
2108
22%
698
70%
698
48%
1043
February16th to endNight
50%
632
34%
1894
19%
632
64%
632
49%
913
March1st to 15thNight
51%
720
33%
2160
17%
720
65%
720
45%
1086
March16th to endNight
50%
622
35%
1996
22%
622
64%
622
43%
969
April1st to 15thNight
44%
539
34%
1798
21%
539
62%
539
42%
881
April16th to endNight
50%
540
36%
1800
26%
540
68%
540
46%
826
May1st to 15thNight
45%
539
26%
1799
20%
539
58%
539
41%
904
May16th to endNight
54%
562
25%
1715
22%
561
63%
561
38%
959
June1st to 15thNight
66%
540
24%
1620
22%
540
72%
540
53%
788
June16th to endNight
73%
540
24%
1620
25%
540
76%
540
45%
854
July1st to 15thNight
76%
510
19%
1636
21%
510
77%
510
41%
862
July16th to endNight
79%
564
26%
1771
30%
531
82%
531
41%
914
August1st to 15thNight
87%
539
26%
1789
32%
536
88%
536
48%
840
August16th to endNight
79%
573
22%
1910
26%
573
79%
573
32%
1097
September1st to 15thNight
77%
540
21%
1839
24%
540
78%
540
33%
1031
September16th to endNight
70%
537
25%
1980
27%
537
72%
537
30%
1092
October1st to 15thNight
69%
540
32%
1980
32%
540
73%
540
43%
917
October16th to endNight
70%
732
40%
2268
29%
732
77%
732
55%
1048
November1st to 15thNight
69%
820
36%
2220
22%
820
74%
820
59%
1084
November16th to endNight
63%
900
37%
2340
20%
900
70%
900
53%
1219
December1st to 15thNight
61%
900
37%
2340
22%
900
67%
900
48%
1289
December16th to endNight
54%
960
36%
2496
19%
960
64%
960
48%
1355

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
5%31332445%7%59%
48179
Night
431232345%8%60%
47757
Cloud CoverDay
5%31332445%7%59%
48177
Night
431332345%8%60%
47757
TransparencyDay
23%5%9%19%24%18%
47899
Night
21%5%10%19%23%19%
47540
SeeingDay
6%6%22%33%24%6%
5397
Night
6%422%41%23%2
15546

By Month

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
8%423323335%60%
1790
16th to endDay
6%312413235%64%
1920
February1st to 15thDay
2212212346%68%
1750
16th to endDay
3212212337%69%
1580
March1st to 15thDay
242332445%6%59%
1800
16th to endDay
4313313335%65%
2223
April1st to 15thDay
4212323345%65%
2150
16th to endDay
3212223346%68%
2160
May1st to 15thDay
3212323447%63%
2151
16th to endDay
421221445%8%61%
2396
June1st to 15thDay
11112235%6%8%64%
2340
16th to endDay
5%213435%5%6%8%51%
2340
July1st to 15thDay
7%414435%5%7%8%46%
2220
16th to endDay
6%314436%6%7%10%45%
2277
August1st to 15thDay
3314436%6%6%10%49%
2160
16th to endDay
7%4245%5%6%6%7%10%39%
2292
September1st to 15thDay
9%5%25%7%45%46%8%40%
2121
16th to endDay
9%425%5%3445%7%46%
1980
October1st to 15thDay
4313313337%63%
1980
16th to endDay
421221223471%
1951
November1st to 15thDay
6%2221223470%
1624
16th to endDay
5%31321222371%
1620
December1st to 15thDay
6%42213335%65%
1620
16th to endDay
4412414446%61%
1734
January1st to 15thNight
6%423323335%60%
2151
16th to endNight
6%312322447%60%
2304
February1st to 15thNight
3313322237%65%
2102
16th to endNight
5%212313446%64%
1894
March1st to 15thNight
3412324347%62%
2160
16th to endNight
4312223435%65%
1996
April1st to 15thNight
5%212423346%62%
1798
16th to endNight
2213223336%67%
1800
May1st to 15thNight
5%32324346%61%
1799
16th to endNight
5%413325%5%6%8%54%
1714
June1st to 15thNight
2123236%6%11%59%
1620
16th to endNight
32133246%7%11%54%
1620
July1st to 15thNight
4213225%6%7%10%52%
1735
16th to endNight
4213335%46%10%54%
1891
August1st to 15thNight
3122145%8%14%53%
1800
16th to endNight
5%214425%5%9%12%44%
1910
September1st to 15thNight
5%41442446%11%49%
1839
16th to endNight
8%4144346%6%10%46%
1980
October1st to 15thNight
5%212313447%62%
1980
16th to endNight
43212222472%
2268
November1st to 15thNight
4211112336%70%
2220
16th to endNight
5%312322235%68%
2340
December1st to 15thNight
5%312323447%62%
2340
16th to endNight
4412323336%64%
2496

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
7%42332233460%
1790
16th to endDay
6%312413235%64%
1920
February1st to 15thDay
2212213346%68%
1750
16th to endDay
3312212337%68%
1580
March1st to 15thDay
242431445%7%59%
1800
16th to endDay
4313313335%65%
2221
April1st to 15thDay
4212313345%65%
2150
16th to endDay
3213223246%67%
2160
May1st to 15thDay
3213323346%63%
2151
16th to endDay
421222336%8%61%
2396
June1st to 15thDay
111221346%8%64%
2340
16th to endDay
5%213435%5%6%9%51%
2340
July1st to 15thDay
6%414435%5%7%8%46%
2220
16th to endDay
6%314436%6%7%9%45%
2277
August1st to 15thDay
3314435%6%6%10%49%
2160
16th to endDay
6%4246%47%5%7%9%39%
2292
September1st to 15thDay
9%435%7%35%5%6%8%40%
2121
16th to endDay
9%5%25%5%3446%6%46%
1980
October1st to 15thDay
4313223337%64%
1980
16th to endDay
422312235%71%
1951
November1st to 15thDay
6%2131223470%
1624
16th to endDay
5%31321223371%
1620
December1st to 15thDay
6%42313336%64%
1620
16th to endDay
3412314446%61%
1734
January1st to 15thNight
5%423323335%60%
2151
16th to endNight
6%312322347%60%
2304
February1st to 15thNight
3313322247%65%
2102
16th to endNight
421221345%6%65%
1894
March1st to 15thNight
3413324347%62%
2160
16th to endNight
4312223446%64%
1996
April1st to 15thNight
5%312433347%61%
1798
16th to endNight
2213223336%67%
1800
May1st to 15thNight
5%33314346%61%
1799
16th to endNight
5%313325%5%6%7%54%
1714
June1st to 15thNight
11123135%7%11%59%
1620
16th to endNight
32133237%8%11%53%
1620
July1st to 15thNight
4213326%5%7%10%52%
1735
16th to endNight
4213435%46%10%54%
1891
August1st to 15thNight
3122145%8%15%53%
1800
16th to endNight
5%314435%5%8%12%44%
1910
September1st to 15thNight
5%414425%5%6%11%49%
1839
16th to endNight
8%4144246%6%10%46%
1980
October1st to 15thNight
5%212323446%62%
1980
16th to endNight
431221213472%
2268
November1st to 15thNight
421112335%71%
2220
16th to endNight
5%31232223469%
2340
December1st to 15thNight
5%312323347%62%
2340
16th to endNight
4412323336%64%
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
27%35%16%30%16%
1791
16th to endDay
23%26%13%32%22%
1920
February1st to 15thDay
16%36%15%25%32%
1751
16th to endDay
17%1414%33%28%
1580
March1st to 15thDay
23%46%16%21%27%
1800
16th to endDay
21%35%12%26%30%
2223
April1st to 15thDay
19%47%10%23%34%
2150
16th to endDay
17%35%11%25%36%
2160
May1st to 15thDay
20%36%14%25%29%
2151
16th to endDay
19%410%20%24%20%
2399
June1st to 15thDay
14%5%11%23%28%16%
2340
16th to endDay
26%7%12%21%22%10%
2340
July1st to 15thDay
31%7%13%26%19%1
2091
16th to endDay
26%9%17%31%14%1
2134
August1st to 15thDay
24%8%15%30%18%1
2147
16th to endDay
34%9%18%21%11%4
2292
September1st to 15thDay
38%7%15%19%14%3
2121
16th to endDay
34%7%10%19%19%7%
1980
October1st to 15thDay
19%6%12%26%19%16%
1980
16th to endDay
16%35%15%27%31%
1951
November1st to 15thDay
17%26%21%30%21%
1624
16th to endDay
19%26%12%28%29%
1620
December1st to 15thDay
23%25%19%28%19%
1620
16th to endDay
22%35%19%33%15%
1734
January1st to 15thNight
26%35%16%28%19%
2151
16th to endNight
24%25%15%31%21%
2304
February1st to 15thNight
20%36%11%25%33%
2112
16th to endNight
18%37%11%28%30%
1894
March1st to 15thNight
22%27%16%21%28%
2160
16th to endNight
20%47%15%23%28%
1996
April1st to 15thNight
23%38%12%21%30%
1798
16th to endNight
17%47%16%23%30%
1800
May1st to 15thNight
22%5%8%16%20%25%
1800
16th to endNight
25%8%9%20%17%17%
1716
June1st to 15thNight
15%6%15%25%27%9%
1620
16th to endNight
20%7%16%22%22%10%
1620
July1st to 15thNight
22%8%18%31%16%2
1636
16th to endNight
21%8%17%33%17%1
1771
August1st to 15thNight
16%7%20%28%24%1
1789
16th to endNight
27%11%17%26%14%2
1910
September1st to 15thNight
28%9%21%23%13%4
1839
16th to endNight
31%7%16%21%17%7%
1980
October1st to 15thNight
20%5%14%25%17%16%
1980
16th to endNight
17%25%15%29%29%
2268
November1st to 15thNight
15%36%20%33%21%
2220
16th to endNight
19%26%11%26%33%
2340
December1st to 15thNight
23%36%19%25%22%
2340
16th to endNight
22%26%18%31%18%
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
14%5%34%32%13%
90
16th to endDay
9%19%28%22%17%2
96
February1st to 15thDay
46%22%26%30%10%
90
16th to endDay
9%14%25%34%12%2
81
March1st to 15thDay
5%5%37%32%13%5%
90
16th to endDay
417%42%24%7%3
255
April1st to 15thDay
418%47%24%4
269
16th to endDay
418%43%26%6%
270
May1st to 15thDay
316%44%29%4
288
16th to endDay
6%6%25%41%18%
483
June1st to 15thDay
221%35%35%5%
495
16th to endDay
414%33%40%6%
495
July1st to 15thDay
6%111%34%37%9%
365
16th to endDay
3110%40%30%13%
327
August1st to 15thDay
415%39%33%15%
315
16th to endDay
10%7%39%29%11%
332
September1st to 15thDay
6%18%43%29%10%
276
16th to endDay
20%15%24%34%13%
135
October1st to 15thDay
8%215%27%33%13%
135
16th to endDay
2420%25%31%15%
144
November1st to 15thDay
10%7%24%36%14%6%
90
16th to endDay
13%12%23%34%12%4
90
December1st to 15thDay
12%5%17%40%22%2
90
16th to endDay
5%7%38%34%14%
96
January1st to 15thNight
8%425%39%19%1
723
16th to endNight
8%5%23%43%16%1
768
February1st to 15thNight
5%7%25%38%19%2
704
16th to endNight
6%7%33%42%10%
632
March1st to 15thNight
6%6%30%37%16%1
720
16th to endNight
5%9%30%36%16%1
622
April1st to 15thNight
5%8%38%39%7%
539
16th to endNight
29%35%43%8%
540
May1st to 15thNight
6%6%39%37%10%
540
16th to endNight
5%332%43%14%
563
June1st to 15thNight
2126%50%20%
540
16th to endNight
315%51%28%
540
July1st to 15thNight
6%11%49%30%1
510
16th to endNight
48%46%36%2
564
August1st to 15thNight
2342%47%4
539
16th to endNight
5%5%40%45%2
573
September1st to 15thNight
6%7%40%41%3
540
16th to endNight
8%12%43%32%2
537
October1st to 15thNight
5%117%43%29%1
540
16th to endNight
6%217%36%29%7%
732
November1st to 15thNight
5%219%39%27%6%
820
16th to endNight
7%418%38%25%5%
900
December1st to 15thNight
7%422%42%19%3
900
16th to endNight
7%7%26%41%15%1
960
Page generated at 2017-11-01 16:23:31. Version ac04

Copyright 2017 A. Danko


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