Ellwood H. May Environmental Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ellwood H. May Environmental Park clear sky chart from 2005-11-05 to 2017-04-07.

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
39%
15570
15%
45429
9%
15528
44%
15528
22%
31194

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
20%
900
10%
2506
3%
895
27%
895
15%
1909
January16th to endNight
20%
960
12%
2688
3%
960
27%
960
15%
2062
February1st to 15thNight
23%
818
13%
2250
3%
818
31%
818
17%
1642
February16th to endNight
26%
631
14%
1893
6%
631
35%
631
17%
1371
March1st to 15thNight
33%
720
13%
2160
7%
720
38%
720
21%
1486
March16th to endNight
40%
639
17%
2019
13%
639
46%
639
21%
1398
April1st to 15thNight
33%
515
16%
1717
12%
515
41%
515
19%
1196
April16th to endNight
45%
495
18%
1556
14%
495
49%
495
24%
1039
May1st to 15thNight
43%
495
16%
1427
11%
495
47%
495
22%
987
May16th to endNight
57%
514
15%
1370
11%
513
60%
513
31%
901
June1st to 15thNight
56%
495
14%
1320
9%
495
59%
495
30%
869
June16th to endNight
62%
495
13%
1320
9%
495
63%
495
34%
829
July1st to 15thNight
73%
465
18%
1240
13%
465
74%
465
44%
712
July16th to endNight
69%
522
17%
1305
12%
489
70%
489
40%
778
August1st to 15thNight
72%
494
23%
1371
19%
491
73%
491
40%
784
August16th to endNight
62%
525
19%
1743
19%
525
66%
525
30%
1023
September1st to 15thNight
59%
503
23%
1658
23%
503
64%
503
29%
976
September16th to endNight
56%
657
22%
1815
16%
657
60%
657
33%
1136
October1st to 15thNight
48%
660
20%
1897
14%
660
53%
660
28%
1234
October16th to endNight
31%
704
13%
2267
8%
704
37%
704
20%
1533
November1st to 15thNight
35%
700
20%
2276
16%
700
42%
700
22%
1474
November16th to endNight
27%
803
13%
2423
6%
803
33%
803
17%
1729
December1st to 15thNight
18%
900
7%
2520
2%
900
23%
900
12%
1968
December16th to endNight
16%
960
10%
2688
2%
960
23%
960
12%
2158

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
13%7%36%5%35%5%5%7%37%
45813
Night
14%7%35%5%3445%7%39%
45597
Cloud CoverDay
12%7%36%5%35%5%6%8%36%
45822
Night
14%8%36%5%3445%7%37%
45602
TransparencyDay
44%8%13%22%9%1
45499
Night
45%7%13%21%11%1
45429
SeeingDay
14%424%31%19%5%
5316
Night
18%7%28%29%14%1
15574

By Month

Percentage Cloud Cover NE (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%11%6%6%6%345%5%7%30%
1432
16th to endDay
12%11%7%9%6%35%46%7%25%
1536
February1st to 15thDay
12%12%5%7%4245%5%6%33%
1609
16th to endDay
12%9%47%6%35%447%32%
1580
March1st to 15thDay
14%9%37%5%345%5%9%31%
1790
16th to endDay
15%9%5%6%43445%7%33%
2215
April1st to 15thDay
16%10%47%5%25%45%6%29%
2046
16th to endDay
19%8%35%5%24446%36%
2073
May1st to 15thDay
19%6%26%5%35%5%6%6%31%
2191
16th to endDay
9%425%5%35%5%6%7%44%
2393
June1st to 15thDay
12%5%36%5%346%6%7%39%
2310
16th to endDay
7%425%5%35%47%9%45%
2310
July1st to 15thDay
6%313426%5%6%10%48%
2310
16th to endDay
8%325%5%345%6%8%45%
2459
August1st to 15thDay
6%424435%6%6%9%45%
2250
16th to endDay
11%5%25%32445%7%46%
2105
September1st to 15thDay
12%415%42446%8%44%
1961
16th to endDay
9%5%35%6%35%46%9%40%
1815
October1st to 15thDay
16%5%25%43445%7%40%
1730
16th to endDay
18%7%35%6%345%5%6%32%
1604
November1st to 15thDay
13%7%36%5%345%5%7%37%
1582
16th to endDay
16%9%35%6%46%45%7%29%
1536
December1st to 15thDay
17%13%45%5%25%5%5%8%28%
1440
16th to endDay
18%13%39%6%35%445%23%
1536
January1st to 15thNight
16%12%46%6%3434433%
2506
16th to endNight
12%11%5%9%5%36%5%5%7%28%
2688
February1st to 15thNight
14%10%5%6%434435%37%
2248
16th to endNight
14%12%46%5%34445%34%
1893
March1st to 15thNight
14%7%445%345%5%6%37%
2147
16th to endNight
15%7%36%5%3445%6%36%
2019
April1st to 15thNight
18%8%345%34446%34%
1717
16th to endNight
19%8%3441335%5%40%
1556
May1st to 15thNight
19%5%35%5%3445%8%35%
1427
16th to endNight
11%5%14425%45%9%43%
1368
June1st to 15thNight
12%5%145%25%5%6%8%41%
1320
16th to endNight
8%43443347%9%45%
1320
July1st to 15thNight
5%3133245%6%10%53%
1320
16th to endNight
4335%5%1445%8%52%
1401
August1st to 15thNight
6%31332446%9%53%
1380
16th to endNight
10%5%145%2335%6%50%
1743
September1st to 15thNight
9%423424447%51%
1658
16th to endNight
10%4144235%5%7%48%
1815
October1st to 15thNight
14%5%24433345%47%
1897
16th to endNight
15%8%25%5%23447%38%
2267
November1st to 15thNight
13%6%24434346%45%
2276
16th to endNight
17%8%26%5%3445%6%34%
2423
December1st to 15thNight
19%10%46%5%35%45%7%28%
2520
16th to endNight
18%13%48%5%25%445%26%
2688

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
14%11%5%6%5%36%5%6%9%25%
1432
16th to endDay
13%13%5%10%5%36%7%6%7%21%
1536
February1st to 15thDay
12%11%6%7%4245%6%7%30%
1609
16th to endDay
12%9%47%6%45%5%6%6%31%
1580
March1st to 15thDay
15%7%37%6%35%5%5%8%31%
1800
16th to endDay
14%9%46%6%3445%7%33%
2214
April1st to 15thDay
16%9%46%6%35%5%46%30%
2046
16th to endDay
18%7%25%5%3445%6%36%
2073
May1st to 15thDay
17%7%26%5%445%6%8%31%
2191
16th to endDay
9%5%25%5%345%6%8%44%
2393
June1st to 15thDay
12%5%36%4345%7%8%38%
2310
16th to endDay
7%415%5%3446%9%45%
2310
July1st to 15thDay
5%214435%6%7%9%49%
2310
16th to endDay
6%3245%246%6%9%46%
2459
August1st to 15thDay
5%314436%6%6%10%46%
2250
16th to endDay
10%5%2442446%7%47%
2105
September1st to 15thDay
11%426%4245%6%9%43%
1961
16th to endDay
9%5%345%45%46%9%41%
1815
October1st to 15thDay
15%5%35%42445%8%39%
1730
16th to endDay
16%8%27%5%45%5%5%6%32%
1604
November1st to 15thDay
12%7%36%6%3446%7%36%
1582
16th to endDay
17%9%47%6%36%5%5%6%27%
1536
December1st to 15thDay
18%12%36%6%46%5%6%7%22%
1440
16th to endDay
19%12%5%8%8%35%45%5%20%
1536
January1st to 15thNight
16%12%5%7%5%2445%6%28%
2506
16th to endNight
12%11%6%8%7%45%5%6%8%23%
2688
February1st to 15thNight
13%11%5%6%5%345%46%34%
2241
16th to endNight
13%12%5%8%434445%32%
1893
March1st to 15thNight
14%7%36%5%35%46%7%35%
2160
16th to endNight
15%7%36%5%3445%6%36%
2019
April1st to 15thNight
18%8%45%5%24446%34%
1717
16th to endNight
19%8%34423345%39%
1556
May1st to 15thNight
19%5%35%5%245%6%7%34%
1426
16th to endNight
11%5%25%425%46%8%42%
1368
June1st to 15thNight
12%6%24436%46%7%41%
1320
16th to endNight
8%4244245%6%11%44%
1320
July1st to 15thNight
5%4133235%7%10%52%
1320
16th to endNight
4325%42445%9%51%
1401
August1st to 15thNight
6%2134235%7%10%50%
1380
16th to endNight
9%5%2442345%7%50%
1743
September1st to 15thNight
10%415%5%2445%6%48%
1658
16th to endNight
10%425%4336%5%7%46%
1815
October1st to 15thNight
14%6%25%433446%45%
1897
16th to endNight
17%7%36%5%3345%5%37%
2267
November1st to 15thNight
13%7%26%435%45%6%41%
2276
16th to endNight
17%7%36%5%35%5%5%6%32%
2423
December1st to 15thNight
19%11%46%6%46%5%5%7%21%
2520
16th to endNight
19%13%48%6%35%44423%
2688

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
54%10%14%15%4
1433
16th to endDay
58%8%14%14%3
1536
February1st to 15thDay
50%9%11%20%6%1
1611
16th to endDay
50%9%12%18%7%1
1580
March1st to 15thDay
49%9%14%18%7%1
1800
16th to endDay
49%8%14%20%6%
2215
April1st to 15thDay
53%7%11%17%10%
2046
16th to endDay
48%6%12%18%12%2
2073
May1st to 15thDay
49%7%11%23%7%
2191
16th to endDay
36%9%12%25%14%1
2397
June1st to 15thDay
40%9%12%25%11%
2310
16th to endDay
33%8%15%24%15%1
2310
July1st to 15thDay
28%8%13%31%14%2
2161
16th to endDay
33%9%15%23%14%3
2292
August1st to 15thDay
30%9%16%30%10%1
2235
16th to endDay
34%8%13%28%14%1
2105
September1st to 15thDay
36%8%12%27%13%
1961
16th to endDay
37%9%15%27%10%
1815
October1st to 15thDay
42%8%11%25%11%
1730
16th to endDay
51%7%13%20%7%
1604
November1st to 15thDay
45%7%12%23%10%1
1582
16th to endDay
54%7%17%16%4
1536
December1st to 15thDay
55%10%15%14%4
1440
16th to endDay
62%8%13%10%4
1536
January1st to 15thNight
55%7%13%15%7%
2506
16th to endNight
55%8%16%15%4
2688
February1st to 15thNight
50%7%11%20%8%1
2250
16th to endNight
52%6%13%17%9%
1893
March1st to 15thNight
45%7%15%18%11%1
2160
16th to endNight
48%5%11%24%8%1
2019
April1st to 15thNight
49%6%7%19%14%1
1717
16th to endNight
46%410%20%14%3
1556
May1st to 15thNight
46%6%13%22%11%
1427
16th to endNight
37%7%11%24%16%2
1370
June1st to 15thNight
38%7%11%27%14%
1320
16th to endNight
33%7%16%21%18%2
1320
July1st to 15thNight
24%7%14%28%21%3
1240
16th to endNight
28%7%15%29%17%2
1305
August1st to 15thNight
26%7%15%33%15%1
1371
16th to endNight
33%7%10%27%18%2
1743
September1st to 15thNight
33%7%11%25%20%1
1658
16th to endNight
34%6%11%34%11%1
1815
October1st to 15thNight
39%6%11%27%14%1
1897
16th to endNight
45%7%16%19%10%
2267
November1st to 15thNight
42%6%12%21%14%2
2276
16th to endNight
50%6%18%17%5%
2423
December1st to 15thNight
57%8%15%13%4
2520
16th to endNight
61%7%12%12%5%
2688

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%10%30%36%3
90
16th to endDay
19%430%35%9%1
96
February1st to 15thDay
16%15%44%15%7%
90
16th to endDay
19%11%34%27%7%
81
March1st to 15thDay
22%15%32%23%6%
90
16th to endDay
26%5%26%26%13%1
252
April1st to 15thDay
27%5%29%22%13%
235
16th to endDay
22%326%25%14%7%
210
May1st to 15thDay
22%331%26%12%2
283
16th to endDay
12%324%31%21%5%
437
June1st to 15thDay
14%221%36%20%3
420
16th to endDay
7%221%41%21%5%
420
July1st to 15thDay
7%120%35%28%7%
400
16th to endDay
7%118%39%25%7%
445
August1st to 15thDay
6%117%37%27%8%
358
16th to endDay
14%415%27%28%9%
268
September1st to 15thDay
11%318%30%23%11%
255
16th to endDay
12%418%31%25%6%
254
October1st to 15thDay
15%5%22%34%18%4
170
16th to endDay
19%8%35%29%7%
96
November1st to 15thDay
413%24%35%18%3
90
16th to endDay
27%15%32%15%8%
90
December1st to 15thDay
24%12%47%13%2
90
16th to endDay
26%20%39%11%2
96
January1st to 15thNight
22%11%37%22%5%
900
16th to endNight
18%9%40%25%5%
960
February1st to 15thNight
20%10%36%26%5%
821
16th to endNight
21%8%35%25%8%
631
March1st to 15thNight
19%7%31%29%10%
720
16th to endNight
16%331%32%12%2
639
April1st to 15thNight
22%6%33%29%8%
515
16th to endNight
22%324%34%13%2
495
May1st to 15thNight
20%225%36%13%1
495
16th to endNight
13%218%40%22%2
515
June1st to 15thNight
14%218%38%24%2
495
16th to endNight
10%118%40%27%2
495
July1st to 15thNight
7%12%41%34%4
465
16th to endNight
5%14%41%33%2
522
August1st to 15thNight
8%19%43%33%4
494
16th to endNight
12%216%31%31%5%
525
September1st to 15thNight
11%417%30%26%9%
503
16th to endNight
13%420%27%28%6%
657
October1st to 15thNight
18%6%22%29%21%2
660
16th to endNight
22%9%30%26%10%
704
November1st to 15thNight
17%8%33%28%11%
700
16th to endNight
22%13%31%23%9%
803
December1st to 15thNight
26%14%34%21%4
900
16th to endNight
25%10%39%21%3
960
Page generated at 2017-04-08 04:35:18. Version ac04

Copyright 2017 A. Danko


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