Delta College Planetarium
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Delta College Planetarium clear sky chart from 2005-11-05 to

2017-09-12
.

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
37%
15653
14%
46811
10%
15615
42%
15615
20%
32837

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
18%
896
8%
2506
2%
895
23%
895
12%
1990
January16th to endNight
23%
914
8%
2642
4%
914
28%
914
12%
2110
February1st to 15thNight
22%
701
9%
2263
4%
701
28%
701
12%
1743
February16th to endNight
25%
631
13%
1893
6%
631
33%
631
14%
1441
March1st to 15thNight
33%
720
15%
2091
11%
720
37%
720
20%
1498
March16th to endNight
36%
768
17%
2112
11%
768
42%
768
23%
1485
April1st to 15thNight
31%
566
14%
1788
9%
566
37%
566
20%
1225
April16th to endNight
37%
540
19%
1620
10%
540
46%
540
25%
1071
May1st to 15thNight
40%
540
15%
1620
10%
540
45%
540
23%
1090
May16th to endNight
47%
562
16%
1614
11%
561
53%
561
29%
1043
June1st to 15thNight
48%
384
15%
1284
14%
384
53%
384
26%
790
June16th to endNight
60%
399
16%
1299
15%
399
64%
399
29%
778
July1st to 15thNight
67%
510
16%
1360
14%
510
68%
510
42%
797
July16th to endNight
64%
564
17%
1453
14%
531
66%
531
38%
877
August1st to 15thNight
65%
539
18%
1609
15%
536
68%
536
34%
954
August16th to endNight
62%
573
22%
1740
18%
573
66%
573
34%
1009
September1st to 15thNight
57%
638
20%
1875
16%
638
61%
638
34%
1123
September16th to endNight
57%
657
20%
1815
16%
657
59%
657
32%
1140
October1st to 15thNight
45%
660
20%
1893
16%
660
50%
660
26%
1265
October16th to endNight
26%
704
11%
2230
7%
704
32%
704
14%
1659
November1st to 15thNight
35%
700
18%
2276
15%
700
40%
700
19%
1550
November16th to endNight
25%
720
11%
2425
6%
720
30%
720
12%
1848
December1st to 15thNight
17%
807
7%
2607
2%
807
22%
807
11%
2054
December16th to endNight
18%
960
8%
2796
3%
960
23%
960
10%
2297

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%8%36%6%35%5%5%7%35%
47833
Night
14%8%46%5%34446%35%
46985
Cloud CoverDay
13%8%36%6%35%45%7%34%
47843
Night
15%8%46%5%3445%6%35%
46989
TransparencyDay
47%6%13%20%10%1
47525
Night
48%6%12%20%11%1
46811
SeeingDay
16%5%26%26%17%8%
5876
Night
18%6%28%31%12%1
15661

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
16%12%6%9%6%46%5%5%6%18%
1432
16th to endDay
14%14%7%11%10%5%6%34416%
1581
February1st to 15thDay
10%15%6%10%7%46%5%5%6%20%
1596
16th to endDay
12%11%6%8%7%46%5%5%6%26%
1580
March1st to 15thDay
15%7%38%8%36%45%6%29%
1858
16th to endDay
14%9%5%7%7%35%445%32%
2112
April1st to 15thDay
18%11%36%5%34447%31%
2169
16th to endDay
15%7%25%5%2445%6%37%
2340
May1st to 15thDay
18%7%24425%5%46%37%
2331
16th to endDay
12%5%25%5%35%45%8%42%
2499
June1st to 15thDay
11%6%25%5%25%5%6%8%40%
2673
16th to endDay
9%5%245%35%7%6%10%38%
2657
July1st to 15thDay
6%424435%5%7%8%48%
2520
16th to endDay
8%425%5%35%46%10%44%
2614
August1st to 15thDay
9%425%5%35%6%6%9%41%
2340
16th to endDay
10%6%15%4345%5%8%44%
2460
September1st to 15thDay
11%6%245%3445%9%44%
1993
16th to endDay
12%6%15%5%2446%7%41%
1815
October1st to 15thDay
15%6%27%6%34445%37%
1735
16th to endDay
21%9%37%6%3445%6%27%
1639
November1st to 15thDay
14%10%37%6%34346%34%
1582
16th to endDay
15%12%48%7%35%6%5%6%24%
1533
December1st to 15thDay
14%14%6%9%8%35%345%24%
1350
16th to endDay
18%15%6%8%6%35%5%46%18%
1424
January1st to 15thNight
19%12%5%9%7%34445%23%
2506
16th to endNight
13%13%7%10%7%45%5%5%6%21%
2642
February1st to 15thNight
13%14%6%7%7%45%45%5%25%
2261
16th to endNight
14%12%5%9%7%445%47%25%
1893
March1st to 15thNight
14%9%47%5%35%435%36%
2079
16th to endNight
15%7%46%5%25%447%37%
2112
April1st to 15thNight
20%8%35%42345%6%34%
1788
16th to endNight
16%7%25%5%2345%6%40%
1620
May1st to 15thNight
15%7%245%4445%8%36%
1620
16th to endNight
12%4146%35%448%44%
1612
June1st to 15thNight
10%5%35%4245%6%6%44%
1284
16th to endNight
8%415%5%35%5%5%10%44%
1299
July1st to 15thNight
7%324334348%54%
1440
16th to endNight
7%3233245%6%8%52%
1552
August1st to 15thNight
6%4144345%7%7%49%
1620
16th to endNight
10%41431445%7%52%
1740
September1st to 15thNight
11%4244235%46%51%
1875
16th to endNight
10%6%245%25%346%47%
1815
October1st to 15thNight
16%6%25%434446%41%
1893
16th to endNight
20%8%37%6%34445%29%
2230
November1st to 15thNight
14%8%26%5%34446%37%
2276
16th to endNight
20%11%46%6%3445%6%25%
2425
December1st to 15thNight
19%15%6%7%6%24445%23%
2607
16th to endNight
21%13%6%8%5%3445%420%
2796

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
16%13%7%8%7%46%5%5%6%18%
1432
16th to endDay
14%14%8%11%9%5%5%435%16%
1581
February1st to 15thDay
11%15%5%10%6%5%6%5%5%6%19%
1596
16th to endDay
11%12%5%8%7%47%5%5%6%25%
1580
March1st to 15thDay
15%8%38%8%45%45%7%28%
1869
16th to endDay
14%10%48%6%35%45%5%31%
2111
April1st to 15thDay
18%10%46%5%34446%31%
2169
16th to endDay
15%7%25%5%345%46%38%
2340
May1st to 15thDay
18%7%24425%446%37%
2331
16th to endDay
11%5%35%5%2445%8%42%
2499
June1st to 15thDay
11%6%25%5%35%5%5%8%40%
2673
16th to endDay
9%425%6%36%6%7%9%39%
2657
July1st to 15thDay
6%4245%35%5%7%8%47%
2520
16th to endDay
7%425%5%35%46%9%44%
2614
August1st to 15thDay
9%415%5%45%5%7%9%40%
2340
16th to endDay
10%5%244345%5%8%44%
2460
September1st to 15thDay
11%415%5%3445%8%43%
1993
16th to endDay
12%5%2443446%8%41%
1815
October1st to 15thDay
15%6%36%6%34446%37%
1735
16th to endDay
21%10%37%5%3435%6%27%
1639
November1st to 15thDay
14%10%46%6%3435%7%33%
1582
16th to endDay
15%12%5%6%7%36%6%5%7%23%
1533
December1st to 15thDay
14%15%7%9%6%44445%23%
1350
16th to endDay
19%14%8%9%7%345%5%6%16%
1424
January1st to 15thNight
20%12%5%9%7%33445%23%
2506
16th to endNight
13%13%6%10%8%45%5%5%6%20%
2642
February1st to 15thNight
13%14%6%8%6%4445%5%25%
2254
16th to endNight
15%12%5%9%7%44446%25%
1893
March1st to 15thNight
15%9%46%5%25%445%36%
2091
16th to endNight
15%8%47%5%23447%36%
2112
April1st to 15thNight
21%7%35%32345%7%33%
1788
16th to endNight
17%7%25%4235%36%40%
1620
May1st to 15thNight
15%6%25%6%345%5%7%36%
1619
16th to endNight
11%415%435%45%8%43%
1612
June1st to 15thNight
10%5%345%235%47%44%
1284
16th to endNight
8%4145%35%47%9%43%
1299
July1st to 15thNight
7%32442436%7%54%
1440
16th to endNight
7%3243245%5%8%52%
1552
August1st to 15thNight
6%4245%245%6%8%48%
1620
16th to endNight
9%42332335%8%51%
1740
September1st to 15thNight
11%42332345%6%50%
1875
16th to endNight
10%6%25%424446%47%
1815
October1st to 15thNight
16%5%25%43435%5%41%
1893
16th to endNight
20%8%37%6%34446%28%
2230
November1st to 15thNight
14%8%26%6%245%47%36%
2276
16th to endNight
21%10%47%6%345%47%25%
2425
December1st to 15thNight
18%15%7%7%6%23446%22%
2607
16th to endNight
21%13%6%8%6%345%45%19%
2796

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
64%8%11%12%3
1433
16th to endDay
70%5%8%10%4
1581
February1st to 15thDay
63%7%11%13%3
1598
16th to endDay
57%7%11%15%6%
1580
March1st to 15thDay
54%6%12%18%7%
1869
16th to endDay
53%6%13%18%7%1
2112
April1st to 15thDay
53%5%10%21%9%
2169
16th to endDay
45%6%15%17%14%1
2340
May1st to 15thDay
46%6%12%21%10%2
2331
16th to endDay
38%7%14%24%14%
2503
June1st to 15thDay
39%7%13%24%13%
2673
16th to endDay
37%8%15%23%14%
2657
July1st to 15thDay
30%7%12%28%18%2
2371
16th to endDay
35%7%15%23%15%2
2450
August1st to 15thDay
36%7%16%24%13%1
2327
16th to endDay
36%7%12%27%13%2
2460
September1st to 15thDay
37%6%16%27%10%1
1993
16th to endDay
39%6%15%27%11%
1815
October1st to 15thDay
47%5%11%22%12%
1735
16th to endDay
57%6%16%15%4
1639
November1st to 15thDay
49%7%13%19%9%
1582
16th to endDay
58%7%13%14%5%
1533
December1st to 15thDay
63%6%14%12%3
1350
16th to endDay
65%7%12%11%2
1424
January1st to 15thNight
63%5%11%12%7%
2506
16th to endNight
61%7%13%13%2
2642
February1st to 15thNight
60%6%10%16%6%
2263
16th to endNight
59%410%16%7%
1893
March1st to 15thNight
50%5%11%20%9%1
2091
16th to endNight
47%5%11%21%11%1
2112
April1st to 15thNight
48%5%11%19%13%1
1788
16th to endNight
44%411%19%17%3
1620
May1st to 15thNight
44%6%12%20%12%3
1620
16th to endNight
38%6%11%23%14%4
1614
June1st to 15thNight
37%7%12%22%18%1
1284
16th to endNight
33%8%15%24%17%
1299
July1st to 15thNight
27%6%11%30%21%2
1360
16th to endNight
29%7%16%25%19%1
1453
August1st to 15thNight
31%7%14%29%15%1
1609
16th to endNight
30%7%13%29%18%1
1740
September1st to 15thNight
33%5%14%29%16%
1875
16th to endNight
36%6%15%29%12%
1815
October1st to 15thNight
42%6%10%25%14%1
1893
16th to endNight
55%6%13%18%5%
2230
November1st to 15thNight
46%8%14%21%9%
2276
16th to endNight
57%8%13%14%5%
2425
December1st to 15thNight
62%6%13%11%5%
2607
16th to endNight
65%6%11%11%4
2796

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
23%6%37%22%10%
90
16th to endDay
25%9%32%28%41
96
February1st to 15thDay
18%13%45%21%1
90
16th to endDay
13%9%39%24%12%
81
March1st to 15thDay
27%8%24%32%7%
159
16th to endDay
26%425%28%13%2
288
April1st to 15thDay
23%6%30%25%11%1
270
16th to endDay
19%8%27%26%11%6%
270
May1st to 15thDay
22%5%29%21%14%6%
288
16th to endDay
16%6%25%25%18%8%
399
June1st to 15thDay
14%5%28%29%14%7%
495
16th to endDay
11%428%28%19%6%
495
July1st to 15thDay
8%223%31%22%10%
475
16th to endDay
8%223%33%22%10%
474
August1st to 15thDay
9%114%25%29%19%
313
16th to endDay
14%314%22%28%15%
332
September1st to 15thDay
9%322%24%24%16%
299
16th to endDay
17%415%24%23%14%
254
October1st to 15thDay
18%7%24%26%17%4
255
16th to endDay
26%9%33%26%4
151
November1st to 15thDay
8%13%30%28%12%6%
90
16th to endDay
14%21%40%13%10%
75
December1st to 15thDay
28%10%43%16%1
60
16th to endDay
28%12%41%16%
77
January1st to 15thNight
25%8%36%22%6%
900
16th to endNight
18%7%34%31%7%
914
February1st to 15thNight
21%8%38%25%4
704
16th to endNight
22%7%32%29%7%
631
March1st to 15thNight
19%6%33%32%7%
720
16th to endNight
17%7%28%34%9%1
768
April1st to 15thNight
21%8%33%27%7%1
566
16th to endNight
22%331%29%10%2
540
May1st to 15thNight
16%431%35%10%1
540
16th to endNight
13%426%33%19%2
563
June1st to 15thNight
13%327%40%15%
384
16th to endNight
10%123%40%22%1
399
July1st to 15thNight
8%116%44%25%3
510
16th to endNight
8%117%43%25%2
564
August1st to 15thNight
8%114%44%27%3
539
16th to endNight
12%117%33%31%4
573
September1st to 15thNight
13%320%33%22%6%
638
16th to endNight
15%417%32%24%5%
657
October1st to 15thNight
20%6%22%32%16%1
660
16th to endNight
26%11%30%25%5%
704
November1st to 15thNight
18%9%31%26%12%
700
16th to endNight
25%11%32%23%8%
720
December1st to 15thNight
25%9%36%23%3
807
16th to endNight
27%8%35%23%4
960
Page generated at 2017-09-13 07:39:06. Version ac04

Copyright 2017 A. Danko


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