McElroy Mountain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the McElroy Mountain clear sky chart from 2005-11-05 to 2017-09-23.

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%
15504
22%
47007
15%
15461
54%
15461
26%
29556

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
25%
720
21%
2327
8%
716
41%
716
17%
1496
January16th to endNight
24%
768
23%
2457
10%
768
40%
768
20%
1584
February1st to 15thNight
27%
704
24%
2112
10%
701
40%
701
24%
1293
February16th to endNight
22%
631
23%
1893
8%
631
36%
631
21%
1216
March1st to 15thNight
28%
720
22%
2069
11%
720
38%
720
23%
1355
March16th to endNight
36%
768
19%
2112
11%
768
43%
768
27%
1362
April1st to 15thNight
40%
626
24%
1884
15%
626
51%
626
31%
1095
April16th to endNight
46%
540
24%
1698
17%
540
55%
540
29%
1011
May1st to 15thNight
49%
540
20%
1620
11%
540
56%
540
26%
1038
May16th to endNight
59%
561
19%
1683
14%
561
63%
561
31%
1033
June1st to 15thNight
66%
540
14%
1620
12%
540
68%
540
28%
1052
June16th to endNight
76%
540
17%
1620
14%
540
77%
540
32%
998
July1st to 15thNight
69%
510
13%
1530
12%
510
70%
510
26%
1012
July16th to endNight
72%
564
16%
1595
14%
531
74%
531
28%
1045
August1st to 15thNight
69%
539
18%
1630
17%
536
70%
536
27%
1048
August16th to endNight
63%
573
18%
1910
19%
573
65%
573
22%
1296
September1st to 15thNight
61%
699
17%
1959
15%
699
62%
699
26%
1331
September16th to endNight
59%
689
24%
1903
19%
689
64%
689
31%
1221
October1st to 15thNight
52%
660
34%
1823
25%
660
60%
660
37%
1066
October16th to endNight
48%
704
32%
2112
24%
704
59%
704
34%
1193
November1st to 15thNight
48%
700
30%
2274
24%
700
60%
700
33%
1225
November16th to endNight
37%
720
26%
2340
17%
720
50%
720
25%
1392
December1st to 15thNight
33%
720
22%
2340
13%
720
45%
720
20%
1494
December16th to endNight
28%
768
18%
2496
12%
768
37%
768
17%
1700

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
14%5%25%5%35%5%5%7%38%
47898
Night
13%5%2442445%7%44%
47205
TransparencyDay
42%7%11%17%16%4
47599
Night
37%6%11%19%18%5%
47008
SeeingDay
17%7%19%22%19%13%
5381
Night
16%9%21%27%20%4
15506

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
20%6%34424335%41%
1611
16th to endDay
18%6%25%42334444%
1766
February1st to 15thDay
18%7%2443345%6%39%
1750
16th to endDay
20%5%25%423445%40%
1580
March1st to 15thDay
19%5%245%2445%6%39%
1890
16th to endDay
15%7%25%43445%6%39%
2111
April1st to 15thDay
14%5%25%425%5%6%6%41%
2073
16th to endDay
13%4245%35%45%6%44%
2262
May1st to 15thDay
12%5%35%5%35%45%7%40%
2331
16th to endDay
11%5%26%6%36%6%6%8%36%
2431
June1st to 15thDay
9%5%36%6%48%6%7%10%31%
2340
16th to endDay
6%315%5%47%8%7%10%38%
2340
July1st to 15thDay
10%6%46%6%5%8%7%8%9%27%
2340
16th to endDay
7%6%37%7%6%8%8%7%9%27%
2465
August1st to 15thDay
8%5%26%7%5%7%7%8%10%30%
2316
16th to endDay
14%7%37%8%5%6%7%7%7%25%
2292
September1st to 15thDay
12%6%36%6%46%5%6%6%33%
1989
16th to endDay
16%425%425%45%7%41%
1894
October1st to 15thDay
13%423313345%54%
1807
16th to endDay
13%41431323457%
1760
November1st to 15thDay
14%5%13213236%54%
1582
16th to endDay
18%5%14324346%45%
1620
December1st to 15thDay
20%6%3332435%6%38%
1620
16th to endDay
26%7%3442343435%
1728
January1st to 15thNight
20%424324445%41%
2327
16th to endNight
17%6%35%424345%41%
2457
February1st to 15thNight
15%5%2441335%5%46%
2103
16th to endNight
17%5%25%423445%42%
1893
March1st to 15thNight
14%6%244246%46%43%
2069
16th to endNight
12%6%25%5%24346%46%
2112
April1st to 15thNight
13%4142235%47%50%
1884
16th to endNight
9%5%244235%6%6%48%
1698
May1st to 15thNight
12%425%435%45%7%44%
1619
16th to endNight
8%425%425%5%5%10%45%
1682
June1st to 15thNight
7%3246%46%6%7%10%40%
1620
16th to endNight
5%3145%37%6%8%11%43%
1620
July1st to 15thNight
8%415%5%36%7%8%10%36%
1620
16th to endNight
5%4145%5%5%6%9%12%38%
1703
August1st to 15thNight
7%425%6%26%6%6%12%39%
1641
16th to endNight
12%5%36%5%45%5%7%9%35%
1910
September1st to 15thNight
9%5%25%5%45%5%6%8%40%
1959
16th to endNight
11%41442446%7%47%
1903
October1st to 15thNight
12%314223335%57%
1823
16th to endNight
10%42442323357%
2112
November1st to 15thNight
11%423312337%55%
2274
16th to endNight
16%5%23323345%48%
2340
December1st to 15thNight
16%7%36%333346%40%
2340
16th to endNight
22%8%25%433345%34%
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
45%47%15%21%5%
1612
16th to endDay
42%37%19%19%6%
1766
February1st to 15thDay
43%39%19%20%3
1752
16th to endDay
44%48%20%18%5%
1580
March1st to 15thDay
44%5%9%16%19%5%
1890
16th to endDay
43%5%12%19%15%3
2112
April1st to 15thDay
39%5%11%20%17%4
2073
16th to endDay
38%6%10%20%19%5%
2262
May1st to 15thDay
41%6%12%19%16%3
2331
16th to endDay
41%10%13%18%12%2
2435
June1st to 15thDay
43%12%16%20%6%1
2340
16th to endDay
35%11%17%21%12%2
2340
July1st to 15thDay
46%13%17%16%6%1
2201
16th to endDay
45%13%17%14%7%1
2310
August1st to 15thDay
43%12%16%18%7%1
2303
16th to endDay
52%10%13%13%7%1
2292
September1st to 15thDay
45%9%13%15%12%3
1989
16th to endDay
40%6%13%16%19%4
1894
October1st to 15thDay
32%5%9%16%27%8%
1807
16th to endDay
31%35%19%29%11%
1760
November1st to 15thDay
32%26%16%32%10%
1582
16th to endDay
39%47%14%25%8%
1620
December1st to 15thDay
45%5%8%16%16%7%
1620
16th to endDay
51%39%15%15%5%
1728
January1st to 15thNight
42%5%8%17%21%5%
2327
16th to endNight
44%36%18%20%6%
2457
February1st to 15thNight
38%29%20%20%7%
2112
16th to endNight
41%47%20%21%4
1893
March1st to 15thNight
39%7%9%18%18%7%
2069
16th to endNight
39%411%24%17%3
2112
April1st to 15thNight
32%5%12%23%21%5%
1884
16th to endNight
34%5%10%21%20%6%
1698
May1st to 15thNight
37%8%13%21%17%1
1620
16th to endNight
32%8%17%25%12%2
1684
June1st to 15thNight
34%11%21%21%9%1
1620
16th to endNight
30%11%19%22%13%2
1620
July1st to 15thNight
37%11%21%18%9%1
1530
16th to endNight
33%13%20%20%9%2
1595
August1st to 15thNight
34%11%18%21%11%1
1630
16th to endNight
42%10%16%16%12%1
1910
September1st to 15thNight
39%9%15%15%15%3
1959
16th to endNight
34%9%12%22%16%5%
1903
October1st to 15thNight
30%5%10%17%27%8%
1823
16th to endNight
31%35%18%28%12%
2112
November1st to 15thNight
29%36%18%29%12%
2274
16th to endNight
37%46%17%25%8%
2340
December1st to 15thNight
42%49%17%17%7%
2340
16th to endNight
50%39%15%16%4
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
32%13%33%17%3
90
16th to endDay
25%28%34%10%2
96
February1st to 15thDay
24%25%41%8%
90
16th to endDay
38%17%35%6%2
81
March1st to 15thDay
25%18%28%18%7%1
180
16th to endDay
20%13%28%24%11%1
288
April1st to 15thDay
20%11%28%22%14%3
270
16th to endDay
17%5%25%24%21%5%
270
May1st to 15thDay
17%9%27%17%17%11%
288
16th to endDay
16%6%17%25%19%14%
331
June1st to 15thDay
13%13%25%23%23%
315
16th to endDay
9%117%24%22%25%
315
July1st to 15thDay
12%19%22%27%26%
305
16th to endDay
7%10%17%32%30%
326
August1st to 15thDay
18%11%24%20%24%
313
16th to endDay
15%210%21%32%17%
332
September1st to 15thDay
15%414%21%25%18%
315
16th to endDay
16%214%27%27%10%
283
October1st to 15thDay
18%421%26%21%7%
255
16th to endDay
15%8%18%28%24%5%
272
November1st to 15thDay
27%13%25%16%14%2
90
16th to endDay
22%16%26%22%8%3
90
December1st to 15thDay
28%20%26%22%2
90
16th to endDay
37%10%34%16%1
96
January1st to 15thNight
27%16%25%23%5%
720
16th to endNight
21%17%32%24%3
768
February1st to 15thNight
20%16%31%27%4
704
16th to endNight
21%18%33%22%3
631
March1st to 15thNight
18%17%32%24%5%
720
16th to endNight
17%13%26%29%12%
768
April1st to 15thNight
16%12%27%27%14%
626
16th to endNight
12%8%25%34%17%1
540
May1st to 15thNight
12%6%24%31%21%3
540
16th to endNight
13%214%29%34%6%
563
June1st to 15thNight
9%111%30%36%10%
540
16th to endNight
5%17%31%41%11%
540
July1st to 15thNight
8%18%24%44%12%
510
16th to endNight
6%7%23%47%13%
564
August1st to 15thNight
10%18%24%44%10%
539
16th to endNight
14%10%23%40%10%
573
September1st to 15thNight
12%213%25%37%8%
699
16th to endNight
14%217%35%27%2
689
October1st to 15thNight
15%5%23%28%21%5%
660
16th to endNight
12%9%24%28%21%3
704
November1st to 15thNight
14%9%21%29%20%3
700
16th to endNight
19%14%25%26%13%
720
December1st to 15thNight
21%15%25%27%9%1
720
16th to endNight
27%11%28%25%6%
768
Page generated at 2017-09-24 09:15:45. Version ac04

Copyright 2017 A. Danko


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