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 2017-09-19.

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%
16064
15%
46860
10%
16022
45%
16022
22%
32071

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%
539
15%
1797
11%
539
40%
539
18%
1256
April16th to endNight
44%
540
19%
1697
15%
540
49%
540
24%
1136
May1st to 15thNight
44%
540
15%
1557
10%
540
47%
540
23%
1073
May16th to endNight
55%
562
16%
1498
11%
561
58%
561
31%
986
June1st to 15thNight
58%
540
14%
1440
9%
540
61%
540
31%
934
June16th to endNight
60%
540
15%
1440
10%
540
63%
540
35%
902
July1st to 15thNight
73%
510
17%
1360
12%
510
74%
510
44%
784
July16th to endNight
68%
564
18%
1417
13%
531
70%
531
40%
852
August1st to 15thNight
72%
539
22%
1497
18%
536
74%
536
40%
857
August16th to endNight
62%
573
20%
1903
20%
573
66%
573
30%
1118
September1st to 15thNight
60%
549
23%
1809
23%
549
65%
549
31%
1045
September16th to endNight
56%
673
22%
1858
16%
673
61%
673
33%
1164
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
12%7%36%5%35%5%5%7%37%
47964
Night
13%7%35%5%3445%7%39%
47028
Cloud CoverDay
12%7%36%5%35%5%6%8%37%
47973
Night
14%7%36%5%3445%7%37%
47033
TransparencyDay
43%8%13%22%10%1
47650
Night
44%7%13%21%11%1
46860
SeeingDay
14%424%32%19%5%
6056
Night
17%6%28%30%15%2
16068

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
15%10%47%5%25%5%5%7%29%
2151
16th to endDay
19%8%35%5%24446%35%
2262
May1st to 15thDay
18%6%26%5%35%5%5%6%33%
2391
16th to endDay
10%425%5%35%5%6%7%43%
2617
June1st to 15thDay
11%5%25%5%346%6%8%41%
2520
16th to endDay
7%425%5%35%47%9%44%
2520
July1st to 15thDay
6%313426%5%7%10%48%
2520
16th to endDay
7%325%5%345%5%8%47%
2655
August1st to 15thDay
6%4245%35%6%6%9%44%
2454
16th to endDay
11%5%25%32445%8%45%
2297
September1st to 15thDay
11%415%42445%7%46%
2139
16th to endDay
9%5%35%6%35%46%9%40%
1848
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%
1797
16th to endNight
19%8%34424345%39%
1697
May1st to 15thNight
19%5%35%5%3446%7%35%
1557
16th to endNight
11%5%14435%46%9%42%
1496
June1st to 15thNight
11%5%145%25%5%6%7%43%
1440
16th to endNight
8%43443346%9%46%
1440
July1st to 15thNight
5%3133245%6%10%53%
1440
16th to endNight
5%335%5%2445%8%52%
1513
August1st to 15thNight
6%31332446%9%52%
1506
16th to endNight
10%4145%2345%7%50%
1903
September1st to 15thNight
9%323424447%52%
1809
16th to endNight
10%4144235%5%7%48%
1858
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%
2151
16th to endDay
18%8%25%5%3445%6%35%
2262
May1st to 15thDay
16%6%25%5%445%5%7%33%
2391
16th to endDay
10%5%25%5%345%6%8%42%
2617
June1st to 15thDay
11%5%26%4345%7%8%39%
2520
16th to endDay
7%415%5%35%47%9%45%
2520
July1st to 15thDay
5%213435%6%7%9%49%
2520
16th to endDay
6%3245%246%6%9%48%
2655
August1st to 15thDay
5%314436%6%6%9%46%
2454
16th to endDay
10%5%1442346%7%47%
2297
September1st to 15thDay
10%326%42445%8%45%
2139
16th to endDay
9%4345%45%46%9%41%
1848
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%6%24446%34%
1797
16th to endNight
19%8%34423345%39%
1697
May1st to 15thNight
18%5%26%5%245%6%7%34%
1556
16th to endNight
11%5%24425%46%9%41%
1496
June1st to 15thNight
11%5%24436%46%7%43%
1440
16th to endNight
8%5%244245%6%11%44%
1440
July1st to 15thNight
5%4133135%7%10%52%
1440
16th to endNight
4425%42445%9%51%
1513
August1st to 15thNight
6%2134235%7%11%49%
1506
16th to endNight
9%5%2442345%7%49%
1903
September1st to 15thNight
9%3145%2445%6%50%
1809
16th to endNight
10%425%4336%5%8%46%
1858
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
52%8%11%17%10%
2151
16th to endDay
48%6%12%18%12%2
2262
May1st to 15thDay
48%7%11%22%9%1
2391
16th to endDay
37%9%13%24%13%1
2621
June1st to 15thDay
38%9%12%26%12%
2520
16th to endDay
33%9%16%24%14%1
2520
July1st to 15thDay
28%9%13%31%14%2
2371
16th to endDay
32%9%14%23%16%3
2488
August1st to 15thDay
31%9%16%30%10%1
2439
16th to endDay
34%8%13%28%13%1
2297
September1st to 15thDay
35%8%12%27%14%
2139
16th to endDay
37%9%15%27%9%
1848
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
50%6%7%19%14%1
1797
16th to endNight
46%410%20%14%3
1697
May1st to 15thNight
46%6%12%21%12%
1557
16th to endNight
37%7%11%24%15%2
1498
June1st to 15thNight
36%7%11%27%15%
1440
16th to endNight
33%7%15%23%17%2
1440
July1st to 15thNight
24%7%14%29%21%3
1360
16th to endNight
28%7%14%28%17%3
1417
August1st to 15thNight
26%7%15%34%14%1
1497
16th to endNight
33%7%10%27%18%2
1903
September1st to 15thNight
32%7%11%25%22%1
1809
16th to endNight
34%6%11%35%11%1
1858
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
24%6%30%25%12%
270
16th to endDay
22%5%29%24%12%5%
270
May1st to 15thDay
20%331%29%13%2
348
16th to endDay
13%327%30%19%5%
517
June1st to 15thDay
12%221%38%21%2
495
16th to endDay
7%224%42%19%4
495
July1st to 15thDay
7%119%36%29%6%
475
16th to endDay
7%118%39%25%8%
515
August1st to 15thDay
6%115%37%29%8%
427
16th to endDay
14%316%28%28%9%
332
September1st to 15thDay
10%316%30%25%13%
315
16th to endDay
12%418%32%26%6%
266
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%32%29%8%
539
16th to endNight
22%324%34%12%2
540
May1st to 15thNight
20%224%37%14%1
540
16th to endNight
14%220%38%21%3
563
June1st to 15thNight
13%218%39%23%2
540
16th to endNight
10%120%40%25%2
540
July1st to 15thNight
7%11%41%35%4
510
16th to endNight
6%15%41%33%3
564
August1st to 15thNight
8%18%44%32%4
539
16th to endNight
12%216%31%31%5%
573
September1st to 15thNight
10%417%30%26%10%
549
16th to endNight
13%419%28%27%6%
673
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 2017-09-20 03:49:48. Version ac04

Copyright 2017 A. Danko


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