C. E. Scovil Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the C. E. Scovil Observatory clear sky chart from 2005-11-05 to 2017-04-25.

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
35%
15120
15%
45592
9%
15080
41%
15080
20%
31766

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
16%
898
10%
2506
3%
895
23%
895
12%
1977
January16th to endNight
19%
847
9%
2575
3%
847
26%
847
12%
2014
February1st to 15thNight
16%
701
9%
2281
1%
701
24%
701
10%
1747
February16th to endNight
23%
631
14%
1893
6%
631
31%
631
14%
1405
March1st to 15thNight
24%
720
14%
2067
8%
720
30%
720
17%
1508
March16th to endNight
35%
768
17%
2112
9%
768
41%
768
22%
1483
April1st to 15thNight
27%
602
14%
1806
7%
602
34%
602
19%
1264
April16th to endNight
36%
525
20%
1575
8%
525
46%
525
26%
1016
May1st to 15thNight
40%
495
15%
1485
9%
495
47%
495
23%
1010
May16th to endNight
51%
506
15%
1532
12%
505
57%
505
29%
937
June1st to 15thNight
53%
330
17%
1155
17%
330
59%
330
26%
695
June16th to endNight
57%
337
16%
1162
17%
337
61%
337
29%
670
July1st to 15thNight
64%
465
17%
1240
15%
465
67%
465
40%
738
July16th to endNight
64%
522
14%
1388
11%
489
66%
489
36%
827
August1st to 15thNight
65%
494
19%
1474
15%
491
68%
491
34%
876
August16th to endNight
62%
525
22%
1575
16%
525
67%
525
36%
919
September1st to 15thNight
56%
621
23%
1769
17%
621
60%
621
31%
1097
September16th to endNight
58%
657
21%
1815
16%
657
61%
657
31%
1146
October1st to 15thNight
45%
660
19%
1911
14%
660
51%
660
27%
1258
October16th to endNight
25%
704
13%
2194
8%
704
33%
704
15%
1624
November1st to 15thNight
34%
700
20%
2276
16%
700
42%
700
22%
1493
November16th to endNight
25%
720
12%
2451
8%
720
30%
720
14%
1778
December1st to 15thNight
15%
732
8%
2532
3%
732
21%
732
10%
1955
December16th to endNight
14%
960
8%
2818
2%
960
20%
960
9%
2329

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%9%47%6%35%5%5%7%32%
46028
Night
14%8%36%5%3445%6%35%
45771
Cloud CoverDay
13%8%47%6%35%5%5%7%32%
46038
Night
14%8%46%5%3445%6%35%
45775
TransparencyDay
50%7%12%18%10%1
45725
Night
48%6%12%20%11%1
45592
SeeingDay
16%8%27%24%15%7%
5200
Night
18%9%29%29%11%1
15126

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
15%14%7%11%8%36%445%18%
1432
16th to endDay
13%18%7%11%10%45%44415%
1647
February1st to 15thDay
14%13%6%11%9%46%5%45%17%
1581
16th to endDay
12%13%5%10%9%45%447%22%
1580
March1st to 15thDay
15%11%5%9%7%35%345%27%
1882
16th to endDay
15%11%5%8%7%35%44429%
2112
April1st to 15thDay
18%10%5%5%5%3445%6%30%
2150
16th to endDay
15%8%25%6%35%35%6%37%
2273
May1st to 15thDay
18%7%36%5%35%45%6%33%
2136
16th to endDay
14%5%245%35%448%39%
2228
June1st to 15thDay
11%5%36%5%35%6%6%9%37%
2472
16th to endDay
8%6%36%6%45%5%7%9%36%
2464
July1st to 15thDay
6%425%6%35%6%7%8%41%
2310
16th to endDay
8%425%6%46%5%7%9%37%
2367
August1st to 15thDay
8%5%27%7%36%6%6%9%36%
2145
16th to endDay
11%5%35%5%35%5%6%8%40%
2275
September1st to 15thDay
11%5%35%5%45%6%6%8%37%
1849
16th to endDay
13%5%34435%5%6%8%37%
1815
October1st to 15thDay
14%7%36%5%35%5%45%37%
1719
16th to endDay
20%10%46%5%34436%30%
1675
November1st to 15thDay
14%8%48%6%345%47%33%
1582
16th to endDay
14%14%49%6%35%45%6%25%
1506
December1st to 15thDay
14%14%6%12%7%3444421%
1425
16th to endDay
19%15%8%10%6%34345%18%
1403
January1st to 15thNight
22%11%5%7%7%34445%24%
2506
16th to endNight
12%12%8%9%8%45%45%6%22%
2575
February1st to 15thNight
14%13%5%8%6%36%5%45%26%
2279
16th to endNight
15%11%47%8%35%446%27%
1893
March1st to 15thNight
16%10%5%7%5%23445%33%
2055
16th to endNight
16%7%35%5%36%45%6%35%
2112
April1st to 15thNight
19%8%36%43345%6%33%
1806
16th to endNight
15%6%25%5%2345%7%41%
1575
May1st to 15thNight
16%5%26%5%35%45%9%34%
1485
16th to endNight
11%416%434448%46%
1530
June1st to 15thNight
9%5%25%5%25%7%6%8%42%
1155
16th to endNight
7%6%25%43447%9%45%
1162
July1st to 15thNight
6%415%43335%9%52%
1320
16th to endNight
6%324425%5%6%9%49%
1492
August1st to 15thNight
6%415%435%5%6%9%47%
1485
16th to endNight
10%5%24323347%52%
1575
September1st to 15thNight
12%414425%446%48%
1769
16th to endNight
10%6%246%2445%7%46%
1815
October1st to 15thNight
14%6%15%425%5%6%6%41%
1911
16th to endNight
21%7%37%6%35%45%5%30%
2194
November1st to 15thNight
13%8%25%5%3445%6%39%
2276
16th to endNight
19%10%46%5%3445%6%26%
2451
December1st to 15thNight
18%13%5%8%6%3435%6%23%
2532
16th to endNight
19%15%6%10%7%24445%19%
2818

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
15%14%6%11%8%45%445%18%
1432
16th to endDay
13%16%8%12%8%45%5%4415%
1647
February1st to 15thDay
14%14%6%11%9%46%5%45%17%
1581
16th to endDay
12%14%5%9%9%45%447%23%
1580
March1st to 15thDay
16%11%6%8%7%35%445%27%
1893
16th to endDay
16%11%5%8%7%45%43429%
2111
April1st to 15thDay
18%10%5%5%5%2445%6%31%
2150
16th to endDay
16%8%35%5%3445%6%36%
2273
May1st to 15thDay
18%7%36%5%26%45%7%33%
2136
16th to endDay
14%5%35%5%35%45%8%39%
2228
June1st to 15thDay
11%5%36%5%35%5%6%8%38%
2472
16th to endDay
9%5%26%6%36%6%7%9%36%
2464
July1st to 15thDay
6%425%6%36%6%6%9%41%
2310
16th to endDay
8%435%6%36%6%7%9%37%
2367
August1st to 15thDay
8%5%26%7%45%6%7%8%37%
2145
16th to endDay
11%5%346%35%5%5%8%40%
2275
September1st to 15thDay
12%5%36%446%6%6%8%36%
1849
16th to endDay
13%5%25%5%246%6%9%37%
1815
October1st to 15thDay
14%7%36%5%345%5%5%37%
1719
16th to endDay
20%10%37%424436%30%
1675
November1st to 15thDay
14%9%36%6%34447%33%
1582
16th to endDay
15%12%48%6%45%45%6%25%
1506
December1st to 15thDay
15%13%7%12%8%3434421%
1425
16th to endDay
18%15%8%10%6%34435%18%
1403
January1st to 15thNight
21%11%5%8%6%34445%24%
2506
16th to endNight
12%12%8%8%7%45%45%6%23%
2575
February1st to 15thNight
13%14%5%8%6%45%5%45%26%
2272
16th to endNight
15%11%48%7%36%346%27%
1893
March1st to 15thNight
16%10%5%7%5%24436%32%
2067
16th to endNight
15%7%35%5%35%45%6%36%
2112
April1st to 15thNight
18%8%36%42445%6%34%
1806
16th to endNight
15%6%25%5%2345%7%41%
1575
May1st to 15thNight
16%5%26%6%35%5%5%8%35%
1484
16th to endNight
12%325%5%2445%7%47%
1530
June1st to 15thNight
9%425%5%35%6%5%9%43%
1155
16th to endNight
7%5%25%43447%10%45%
1162
July1st to 15thNight
6%425%43345%9%52%
1320
16th to endNight
5%3245%246%5%9%49%
1492
August1st to 15thNight
7%3244245%6%9%47%
1485
16th to endNight
10%5%23423346%53%
1575
September1st to 15thNight
12%423434446%48%
1769
16th to endNight
10%5%3442445%6%46%
1815
October1st to 15thNight
14%5%25%4345%6%6%41%
1911
16th to endNight
21%7%36%6%3445%5%30%
2194
November1st to 15thNight
14%7%35%4345%5%6%39%
2276
16th to endNight
19%11%36%5%3445%7%27%
2451
December1st to 15thNight
19%13%5%8%6%24446%23%
2532
16th to endNight
20%14%6%10%6%24445%19%
2818

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
66%6%9%12%4
1433
16th to endDay
71%6%8%9%4
1647
February1st to 15thDay
66%7%9%12%4
1583
16th to endDay
61%5%9%14%7%1
1580
March1st to 15thDay
58%6%11%16%7%
1893
16th to endDay
57%5%10%17%7%1
2112
April1st to 15thDay
52%6%10%19%10%
2150
16th to endDay
46%5%14%16%13%2
2273
May1st to 15thDay
50%6%11%20%9%1
2136
16th to endDay
41%6%12%23%13%2
2232
June1st to 15thDay
41%8%12%21%14%1
2472
16th to endDay
41%8%13%20%14%1
2464
July1st to 15thDay
36%7%11%25%17%1
2161
16th to endDay
39%9%15%20%13%2
2208
August1st to 15thDay
40%8%14%20%13%1
2132
16th to endDay
38%8%11%26%12%1
2275
September1st to 15thDay
41%7%16%22%10%1
1849
16th to endDay
40%7%13%26%11%
1815
October1st to 15thDay
45%7%11%21%12%1
1719
16th to endDay
55%5%14%17%6%
1675
November1st to 15thDay
49%6%12%19%10%
1582
16th to endDay
58%5%13%16%5%
1506
December1st to 15thDay
64%7%12%11%3
1425
16th to endDay
67%413%10%3
1403
January1st to 15thNight
61%5%11%14%7%
2506
16th to endNight
61%6%13%14%3
2575
February1st to 15thNight
59%6%10%14%7%
2281
16th to endNight
56%5%11%18%7%
1893
March1st to 15thNight
53%411%19%9%1
2067
16th to endNight
48%5%12%22%10%1
2112
April1st to 15thNight
49%5%11%19%13%
1806
16th to endNight
41%5%11%19%18%3
1575
May1st to 15thNight
45%6%12%21%11%2
1485
16th to endNight
36%5%12%23%16%4
1532
June1st to 15thNight
35%8%12%26%16%
1155
16th to endNight
34%6%15%24%18%1
1162
July1st to 15thNight
29%5%8%31%21%2
1240
16th to endNight
28%9%18%23%18%2
1388
August1st to 15thNight
29%8%14%30%13%2
1474
16th to endNight
31%5%12%31%16%2
1575
September1st to 15thNight
36%5%11%28%16%1
1769
16th to endNight
35%7%12%29%15%
1815
October1st to 15thNight
40%7%12%21%17%
1911
16th to endNight
54%6%12%19%5%
2194
November1st to 15thNight
43%6%13%23%11%1
2276
16th to endNight
55%5%15%16%6%
2451
December1st to 15thNight
61%5%13%13%5%
2532
16th to endNight
66%6%10%11%4
2818

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
16%23%40%16%21
90
16th to endDay
34%13%35%15%1
96
February1st to 15thDay
18%23%43%13%1
90
16th to endDay
16%22%40%17%3
81
March1st to 15thDay
26%15%31%21%5%
183
16th to endDay
23%6%33%23%10%2
288
April1st to 15thDay
22%11%30%22%10%2
270
16th to endDay
22%7%30%18%16%6%
250
May1st to 15thDay
21%7%26%25%13%4
228
16th to endDay
16%7%23%25%18%9%
267
June1st to 15thDay
14%7%30%29%13%4
417
16th to endDay
10%7%28%27%20%6%
420
July1st to 15thDay
9%5%23%32%18%11%
400
16th to endDay
7%328%29%19%11%
353
August1st to 15thDay
7%217%28%22%20%
253
16th to endDay
14%416%20%22%21%
268
September1st to 15thDay
13%319%20%23%19%
255
16th to endDay
16%5%12%25%29%10%
254
October1st to 15thDay
16%5%25%29%18%5%
255
16th to endDay
24%13%34%20%5%
187
November1st to 15thDay
10%15%33%23%16%1
90
16th to endDay
25%21%36%11%5%
71
December1st to 15thDay
18%21%41%16%1
60
16th to endDay
21%29%43%5%
74
January1st to 15thNight
25%14%35%18%41
900
16th to endNight
18%12%38%24%5%
847
February1st to 15thNight
20%16%39%20%3
704
16th to endNight
21%13%31%27%5%
631
March1st to 15thNight
22%11%34%25%5%
720
16th to endNight
19%10%30%30%8%1
768
April1st to 15thNight
22%12%33%27%4
602
16th to endNight
18%6%34%28%9%2
525
May1st to 15thNight
17%5%28%35%10%1
495
16th to endNight
13%323%38%19%1
507
June1st to 15thNight
11%227%47%11%
330
16th to endNight
9%324%45%16%
337
July1st to 15thNight
8%118%40%26%3
465
16th to endNight
6%319%45%22%2
522
August1st to 15thNight
8%116%42%27%4
494
16th to endNight
12%117%35%29%3
525
September1st to 15thNight
14%5%19%31%23%6%
621
16th to endNight
13%417%35%24%4
657
October1st to 15thNight
17%5%25%31%17%2
660
16th to endNight
23%12%33%24%5%
704
November1st to 15thNight
17%11%32%24%13%1
700
16th to endNight
22%14%32%21%7%
720
December1st to 15thNight
25%13%37%19%3
732
16th to endNight
26%11%36%21%2
960
Page generated at 2017-04-26 17:21:46. Version ac04

Copyright 2017 A. Danko


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