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 2017-03-24.

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%
14638
23%
45310
15%
14594
55%
14594
26%
27160

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%
628
26%
1948
14%
628
47%
628
27%
1113
April1st to 15thNight
37%
494
24%
1647
18%
494
48%
494
23%
972
April16th to endNight
46%
495
27%
1650
19%
495
60%
495
32%
851
May1st to 15thNight
45%
494
21%
1616
14%
494
55%
494
29%
923
May16th to endNight
56%
513
22%
1538
15%
513
64%
513
29%
903
June1st to 15thNight
63%
495
16%
1485
12%
495
67%
495
29%
886
June16th to endNight
64%
495
16%
1485
14%
495
65%
495
28%
919
July1st to 15thNight
71%
465
12%
1415
13%
465
71%
465
27%
909
July16th to endNight
68%
522
10%
1632
12%
489
74%
489
25%
1022
August1st to 15thNight
76%
494
10%
1638
12%
491
77%
491
26%
1013
August16th to endNight
66%
525
14%
1750
17%
525
67%
525
22%
1151
September1st to 15thNight
61%
546
18%
1701
18%
546
62%
546
24%
1101
September16th to endNight
57%
657
26%
1815
16%
657
64%
657
28%
1138
October1st to 15thNight
58%
660
33%
1815
23%
660
65%
660
43%
980
October16th to endNight
53%
704
36%
2055
25%
704
63%
704
40%
1095
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%
45591
Night
10%42442445%8%47%
45527
TransparencyDay
41%7%10%16%16%7%
45307
Night
33%6%13%18%18%8%
45315
SeeingDay
11%13%15%22%21%16%
4422
Night
11%19%17%24%20%5%
14641

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%
2125
April1st to 15thDay
14%5%25%5%25%447%42%
1971
16th to endDay
9%6%25%435%35%8%45%
1980
May1st to 15thDay
10%5%25%5%35%6%5%8%40%
2001
16th to endDay
7%5%26%5%45%6%7%7%42%
2223
June1st to 15thDay
6%426%8%47%7%9%12%30%
2145
16th to endDay
6%426%7%49%7%8%10%31%
2145
July1st to 15thDay
10%5%37%9%6%9%6%8%8%23%
2120
16th to endDay
10%7%38%8%47%7%9%9%22%
2108
August1st to 15thDay
8%5%36%7%46%8%9%11%25%
1980
16th to endDay
12%7%37%8%47%6%5%8%27%
2100
September1st to 15thDay
10%7%46%7%47%5%7%8%29%
1917
16th to endDay
9%425%6%45%5%5%6%44%
1815
October1st to 15thDay
7%3145%2445%6%54%
1815
16th to endDay
9%313424436%56%
1812
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
11%5%14323347%53%
1948
April1st to 15thNight
10%5%2443446%7%46%
1647
16th to endNight
7%21331445%7%57%
1650
May1st to 15thNight
8%424423448%50%
1616
16th to endNight
5%2244335%7%11%48%
1538
June1st to 15thNight
4324335%7%8%12%43%
1485
16th to endNight
6%315%5%36%7%7%11%40%
1485
July1st to 15thNight
33245%36%8%8%13%39%
1507
16th to endNight
4225%6%35%6%10%13%38%
1752
August1st to 15thNight
33145%36%8%10%14%40%
1650
16th to endNight
8%4245%46%6%7%10%37%
1750
September1st to 15thNight
8%5%25%5%35%6%8%11%36%
1701
16th to endNight
10%415%5%2446%9%45%
1815
October1st to 15thNight
6%312423447%58%
1815
16th to endNight
9%412322235%61%
2055
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
38%5%8%17%21%8%
2126
April1st to 15thDay
41%47%17%19%9%
1971
16th to endDay
35%6%9%21%20%7%
1980
May1st to 15thDay
38%8%10%17%16%7%
2001
16th to endDay
37%8%10%22%17%2
2227
June1st to 15thDay
40%11%15%22%8%1
2145
16th to endDay
41%11%16%18%9%1
2145
July1st to 15thDay
53%13%16%11%3
1983
16th to endDay
52%12%16%14%3
1965
August1st to 15thDay
47%12%19%13%6%
1968
16th to endDay
52%10%15%10%8%2
2100
September1st to 15thDay
49%11%12%12%10%3
1917
16th to endDay
39%6%10%17%17%8%
1815
October1st to 15thDay
31%411%15%21%15%
1815
16th to endDay
28%45%13%26%21%
1812
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%49%20%22%10%
1948
April1st to 15thNight
34%6%11%16%20%10%
1647
16th to endNight
26%412%26%23%7%
1650
May1st to 15thNight
31%6%14%21%19%7%
1617
16th to endNight
26%9%16%25%18%2
1540
June1st to 15thNight
28%9%22%25%12%1
1485
16th to endNight
32%10%22%22%10%1
1485
July1st to 15thNight
29%15%31%16%6%
1415
16th to endNight
30%14%30%20%2
1632
August1st to 15thNight
27%16%32%18%5%
1638
16th to endNight
38%12%23%14%8%3
1750
September1st to 15thNight
37%10%19%17%10%4
1701
16th to endNight
34%7%13%18%17%8%
1815
October1st to 15thNight
23%412%19%23%16%
1815
16th to endNight
25%35%13%27%23%
2055
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
14%18%26%24%15%1
233
April1st to 15thDay
20%22%22%15%16%1
210
16th to endDay
10%18%20%27%19%3
210
May1st to 15thDay
8%20%18%25%20%6%
228
16th to endDay
9%13%12%22%17%24%
267
June1st to 15thDay
10%12%7%21%22%25%
255
16th to endDay
5%12%320%25%33%
255
July1st to 15thDay
48%5%15%33%32%
245
16th to endDay
5%11%215%30%33%
270
August1st to 15thDay
9%7%413%32%32%
253
16th to endDay
8%6%319%34%26%
268
September1st to 15thDay
9%6%7%21%27%26%
255
16th to endDay
14%6%6%32%26%13%
254
October1st to 15thDay
310%18%32%25%8%
255
16th to endDay
10%7%21%29%17%11%
151
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%24%26%11%1
628
April1st to 15thNight
12%23%23%27%12%
494
16th to endNight
10%21%19%32%15%
495
May1st to 15thNight
10%20%18%32%16%1
495
16th to endNight
6%19%10%25%33%4
515
June1st to 15thNight
5%18%5%26%33%10%
495
16th to endNight
5%18%318%37%16%
495
July1st to 15thNight
413%119%42%20%
465
16th to endNight
317%118%37%21%
522
August1st to 15thNight
310%112%46%26%
494
16th to endNight
9%10%317%41%17%
525
September1st to 15thNight
10%9%6%18%38%16%
546
16th to endNight
12%9%9%25%35%6%
657
October1st to 15thNight
9%10%17%33%25%4
660
16th to endNight
10%12%20%27%25%3
704
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 2017-03-25 11:39:46. Version ac04

Copyright 2017 A. Danko


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