Mayer Field Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mayer Field Observatory 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
46%
15346
23%
47500
15%
15302
55%
15302
26%
28453

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
27%
720
25%
2201
11%
716
41%
716
21%
1343
January16th to endNight
27%
768
25%
2304
11%
768
40%
768
21%
1472
February1st to 15thNight
29%
704
29%
2110
11%
700
44%
700
25%
1257
February16th to endNight
25%
631
24%
1893
9%
631
36%
631
20%
1212
March1st to 15thNight
28%
720
22%
2160
9%
720
40%
720
22%
1345
March16th to endNight
35%
649
26%
2018
14%
649
47%
649
27%
1155
April1st to 15thNight
40%
539
24%
1797
18%
539
50%
539
25%
1036
April16th to endNight
47%
540
29%
1800
20%
540
61%
540
33%
921
May1st to 15thNight
46%
539
21%
1763
14%
539
56%
539
30%
988
May16th to endNight
56%
561
22%
1682
16%
561
64%
561
29%
995
June1st to 15thNight
62%
540
15%
1620
11%
540
66%
540
28%
987
June16th to endNight
62%
540
15%
1620
14%
540
64%
540
27%
1024
July1st to 15thNight
72%
510
11%
1552
13%
510
72%
510
28%
989
July16th to endNight
69%
564
11%
1772
13%
531
75%
531
25%
1115
August1st to 15thNight
75%
539
9%
1788
11%
536
76%
536
25%
1118
August16th to endNight
64%
573
14%
1910
17%
573
65%
573
21%
1265
September1st to 15thNight
61%
596
18%
1856
17%
596
63%
596
26%
1169
September16th to endNight
60%
717
27%
1980
18%
717
66%
717
29%
1230
October1st to 15thNight
57%
720
31%
1980
22%
720
63%
720
42%
1083
October16th to endNight
52%
768
37%
2242
26%
768
63%
768
40%
1194
November1st to 15thNight
46%
700
31%
2276
23%
700
58%
700
31%
1229
November16th to endNight
40%
720
30%
2340
19%
720
56%
720
28%
1270
December1st to 15thNight
35%
720
25%
2340
17%
720
47%
720
23%
1399
December16th to endNight
25%
768
21%
2496
9%
768
40%
768
17%
1657

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
11%5%25%5%35%5%5%7%40%
48219
Night
10%42442445%8%47%
47717
TransparencyDay
41%7%10%16%16%7%
47935
Night
33%6%13%18%18%8%
47505
SeeingDay
11%12%15%22%21%16%
5287
Night
11%19%17%24%21%6%
15349

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
13%6%25%42345%7%44%
1734
16th to endDay
18%5%2442233446%
1920
February1st to 15thDay
13%5%24424447%47%
1750
16th to endDay
16%6%25%5%24346%42%
1580
March1st to 15thDay
13%5%344235%47%44%
1800
16th to endDay
12%5%24434445%48%
2211
April1st to 15thDay
13%5%25%5%25%447%44%
2151
16th to endDay
9%6%15%435%45%8%46%
2160
May1st to 15thDay
9%5%25%5%35%5%5%8%41%
2184
16th to endDay
8%5%26%6%45%6%6%7%41%
2431
June1st to 15thDay
8%427%8%47%7%8%11%29%
2340
16th to endDay
8%5%26%7%49%7%8%10%29%
2340
July1st to 15thDay
9%5%37%9%6%9%6%8%8%23%
2313
16th to endDay
10%6%38%8%47%7%9%8%23%
2276
August1st to 15thDay
9%5%36%7%47%8%9%11%25%
2160
16th to endDay
13%7%37%8%47%6%5%8%27%
2292
September1st to 15thDay
10%7%36%7%46%5%7%8%32%
2091
16th to endDay
9%425%6%45%5%5%6%45%
1980
October1st to 15thDay
7%3145%3445%6%52%
1980
16th to endDay
9%313423445%56%
1976
November1st to 15thDay
11%313423337%56%
1582
16th to endDay
9%413433345%54%
1620
December1st to 15thDay
12%8%245%24445%45%
1620
16th to endDay
20%9%36%413336%35%
1728
January1st to 15thNight
12%6%24425%447%46%
2201
16th to endNight
18%7%24313336%44%
2304
February1st to 15thNight
14%5%23313345%51%
2103
16th to endNight
15%6%35%42334445%
1893
March1st to 15thNight
13%6%25%32445%6%44%
2160
16th to endNight
10%5%14323347%52%
2018
April1st to 15thNight
9%5%2443446%7%48%
1797
16th to endNight
7%21331445%8%57%
1800
May1st to 15thNight
8%424423449%51%
1763
16th to endNight
6%3244335%7%11%47%
1682
June1st to 15thNight
5%424335%6%8%12%41%
1620
16th to endNight
7%315%5%36%7%7%11%39%
1620
July1st to 15thNight
33145%36%8%8%12%41%
1644
16th to endNight
3215%6%35%6%10%13%38%
1892
August1st to 15thNight
43145%36%8%9%13%39%
1800
16th to endNight
8%5%25%6%46%6%7%10%37%
1910
September1st to 15thNight
8%425%5%346%7%12%38%
1856
16th to endNight
9%4145%3446%8%46%
1980
October1st to 15thNight
7%31242345%7%57%
1980
16th to endNight
9%312322235%61%
2242
November1st to 15thNight
8%41442235%5%56%
2276
16th to endNight
8%424323345%56%
2340
December1st to 15thNight
12%6%24423346%48%
2340
16th to endNight
18%7%26%324345%39%
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
39%47%14%22%11%
1735
16th to endDay
42%3415%24%10%
1920
February1st to 15thDay
36%49%15%23%11%
1752
16th to endDay
42%45%15%22%9%
1580
March1st to 15thDay
39%5%7%18%21%7%
1800
16th to endDay
37%5%8%18%20%9%
2212
April1st to 15thDay
39%47%17%20%9%
2151
16th to endDay
34%6%10%20%20%7%
2160
May1st to 15thDay
37%7%10%16%18%8%
2184
16th to endDay
39%8%10%21%16%3
2435
June1st to 15thDay
43%10%14%21%8%1
2340
16th to endDay
44%11%15%17%8%1
2340
July1st to 15thDay
52%14%16%11%4
2176
16th to endDay
52%12%15%15%3
2133
August1st to 15thDay
48%12%20%12%6%
2148
16th to endDay
52%10%15%11%7%2
2292
September1st to 15thDay
47%11%12%12%11%4
2091
16th to endDay
38%7%11%17%17%7%
1980
October1st to 15thDay
32%410%16%20%14%
1980
16th to endDay
28%45%13%26%21%
1976
November1st to 15thDay
29%46%17%28%13%
1582
16th to endDay
30%5%7%15%22%18%
1620
December1st to 15thDay
40%5%6%19%20%6%
1620
16th to endDay
50%4419%15%5%
1728
January1st to 15thNight
38%47%14%25%9%
2201
16th to endNight
42%36%13%23%10%
2304
February1st to 15thNight
35%35%19%22%14%
2112
16th to endNight
41%5%5%13%20%13%
1893
March1st to 15thNight
38%410%17%20%7%
2160
16th to endNight
32%410%21%21%9%
2018
April1st to 15thNight
32%6%11%16%22%10%
1797
16th to endNight
25%412%27%23%7%
1800
May1st to 15thNight
30%5%13%20%22%7%
1764
16th to endNight
27%9%16%23%18%3
1684
June1st to 15thNight
30%9%21%24%11%1
1620
16th to endNight
33%10%22%21%10%
1620
July1st to 15thNight
28%15%30%17%6%
1552
16th to endNight
30%15%30%20%2
1772
August1st to 15thNight
29%16%31%17%4
1788
16th to endNight
39%12%23%14%7%3
1910
September1st to 15thNight
35%10%19%17%11%6%
1856
16th to endNight
33%8%13%20%17%7%
1980
October1st to 15thNight
24%413%20%22%15%
1980
16th to endNight
25%35%13%28%22%
2242
November1st to 15thNight
29%36%17%27%14%
2276
16th to endNight
29%47%17%22%18%
2340
December1st to 15thNight
37%48%20%22%7%
2340
16th to endNight
46%47%20%15%6%
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
17%20%27%20%11%3
90
16th to endDay
14%33%26%19%6%
96
February1st to 15thDay
11%27%28%23%8%
90
16th to endDay
13%24%33%27%1
81
March1st to 15thDay
18%24%43%10%21
90
16th to endDay
13%17%29%24%13%1
261
April1st to 15thDay
18%20%23%16%19%1
270
16th to endDay
11%16%20%26%20%4
270
May1st to 15thDay
7%19%20%23%22%5%
288
16th to endDay
10%12%14%25%16%19%
331
June1st to 15thDay
13%9%8%24%19%24%
315
16th to endDay
10%10%421%23%28%
315
July1st to 15thDay
5%7%413%33%36%
305
16th to endDay
7%9%415%31%31%
326
August1st to 15thDay
10%6%415%31%31%
313
16th to endDay
10%5%418%33%26%
332
September1st to 15thDay
9%7%12%21%26%23%
315
16th to endDay
13%5%6%32%28%14%
314
October1st to 15thDay
6%8%18%31%25%8%
315
16th to endDay
10%10%24%28%17%8%
204
November1st to 15thDay
21%330%31%12%2
90
16th to endDay
7%16%35%27%8%3
90
December1st to 15thDay
18%15%41%16%5%2
90
16th to endDay
31%11%22%28%6%
96
January1st to 15thNight
14%27%27%23%6%
720
16th to endNight
15%27%25%23%7%
768
February1st to 15thNight
15%26%26%23%7%
704
16th to endNight
16%26%29%21%6%
631
March1st to 15thNight
14%26%27%23%7%
720
16th to endNight
12%23%25%26%11%1
649
April1st to 15thNight
11%22%22%28%14%1
539
16th to endNight
9%19%19%32%17%1
540
May1st to 15thNight
9%19%18%33%17%1
540
16th to endNight
7%17%11%26%33%3
563
June1st to 15thNight
7%17%5%25%33%10%
540
16th to endNight
6%16%419%37%15%
540
July1st to 15thNight
412%117%41%23%
510
16th to endNight
316%118%38%21%
564
August1st to 15thNight
49%111%46%26%
539
16th to endNight
10%9%416%40%18%
573
September1st to 15thNight
9%9%8%19%37%15%
596
16th to endNight
11%9%9%25%36%7%
717
October1st to 15thNight
9%9%18%32%25%5%
720
16th to endNight
10%12%20%27%25%3
768
November1st to 15thNight
9%18%20%31%17%2
700
16th to endNight
11%21%22%31%12%
720
December1st to 15thNight
13%23%25%23%13%1
720
16th to endNight
18%25%26%22%7%
768
Page generated at 2017-11-01 16:23:42. Version ac04

Copyright 2017 A. Danko


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