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 2018-03-11.

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%
16424
14%
49143
9%
16386
42%
16386
20%
34483

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%
971
8%
2716
2%
970
25%
970
13%
2140
January16th to endNight
23%
990
8%
2862
3%
990
28%
990
12%
2281
February1st to 15thNight
22%
761
10%
2456
3%
761
29%
761
12%
1881
February16th to endNight
24%
683
13%
2049
6%
683
32%
683
14%
1556
March1st to 15thNight
33%
764
15%
2221
10%
764
36%
764
20%
1592
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
58%
651
20%
1911
16%
651
61%
651
34%
1139
September16th to endNight
58%
717
23%
1980
18%
717
60%
717
33%
1228
October1st to 15thNight
44%
720
18%
2065
15%
720
49%
720
25%
1393
October16th to endNight
27%
768
13%
2433
8%
768
33%
768
15%
1786
November1st to 15thNight
34%
760
17%
2471
14%
760
39%
760
18%
1705
November16th to endNight
24%
780
11%
2627
5%
780
30%
780
12%
1977
December1st to 15thNight
18%
874
7%
2824
2%
874
23%
874
11%
2213
December16th to endNight
18%
1040
9%
3029
3%
1040
23%
1040
10%
2473

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%
49469
Night
14%8%46%5%3445%6%35%
49317
Cloud CoverDay
13%8%36%6%35%45%7%34%
49479
Night
14%9%46%5%3445%6%35%
49321
TransparencyDay
47%6%13%20%10%1
49161
Night
48%6%12%19%11%1
49143
SeeingDay
16%6%26%26%16%7%
6427
Night
18%6%29%30%12%1
16432

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%8%6%46%5%5%6%19%
1552
16th to endDay
14%14%6%11%10%5%6%34417%
1713
February1st to 15thDay
11%15%5%10%7%46%5%5%6%20%
1733
16th to endDay
12%11%6%8%7%46%5%5%6%26%
1710
March1st to 15thDay
15%8%38%7%36%35%6%30%
1965
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
10%6%245%3445%9%44%
2037
16th to endDay
11%6%15%5%3446%7%42%
1980
October1st to 15thDay
16%6%27%6%34445%37%
1893
16th to endDay
20%9%36%6%34447%28%
1788
November1st to 15thDay
15%10%47%6%34346%33%
1717
16th to endDay
15%12%48%6%35%6%5%6%24%
1661
December1st to 15thDay
14%14%6%9%7%34345%24%
1462
16th to endDay
18%15%6%8%6%35%45%6%18%
1543
January1st to 15thNight
19%12%5%9%7%34445%23%
2716
16th to endNight
12%13%7%10%7%45%5%46%21%
2862
February1st to 15thNight
12%14%6%8%7%45%45%5%25%
2454
16th to endNight
15%12%5%9%7%44446%25%
2049
March1st to 15thNight
14%10%37%5%34435%36%
2209
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
10%323423447%51%
1911
16th to endNight
9%6%25%425%346%48%
1980
October1st to 15thNight
16%6%25%43445%6%40%
2065
16th to endNight
20%8%37%5%34446%30%
2433
November1st to 15thNight
15%8%26%5%34446%36%
2471
16th to endNight
19%10%46%6%345%5%6%25%
2627
December1st to 15thNight
18%15%6%8%6%24445%23%
2824
16th to endNight
20%13%6%9%6%3445%421%
3029

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%6%8%7%46%5%5%6%19%
1552
16th to endDay
14%14%8%11%9%5%5%435%17%
1713
February1st to 15thDay
11%15%5%10%6%46%5%5%6%20%
1733
16th to endDay
12%11%5%8%7%37%5%5%6%26%
1710
March1st to 15thDay
15%9%38%8%45%45%6%29%
1976
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%5%15%5%3445%8%43%
2037
16th to endDay
11%5%245%3446%8%42%
1980
October1st to 15thDay
15%6%36%6%44446%36%
1893
16th to endDay
20%10%37%6%3435%6%28%
1788
November1st to 15thDay
15%10%46%6%3435%7%32%
1717
16th to endDay
15%12%5%6%7%36%6%5%7%23%
1661
December1st to 15thDay
14%15%6%9%6%44345%23%
1462
16th to endDay
18%13%8%9%7%335%5%6%17%
1543
January1st to 15thNight
19%12%5%8%7%34445%24%
2716
16th to endNight
12%13%6%10%8%45%5%5%6%21%
2862
February1st to 15thNight
12%14%6%8%7%4445%6%24%
2447
16th to endNight
15%11%5%9%7%44446%26%
2049
March1st to 15thNight
14%10%46%5%24435%35%
2221
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%51%
1911
16th to endNight
9%6%25%424446%48%
1980
October1st to 15thNight
17%6%25%43435%6%40%
2065
16th to endNight
20%8%37%6%34446%29%
2433
November1st to 15thNight
15%9%26%6%345%47%35%
2471
16th to endNight
20%10%46%6%345%47%25%
2627
December1st to 15thNight
17%15%7%8%6%23445%23%
2824
16th to endNight
20%14%6%9%6%24445%20%
3029

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
63%7%11%11%3
1553
16th to endDay
69%5%9%10%4
1713
February1st to 15thDay
63%7%11%13%3
1735
16th to endDay
57%6%12%16%6%
1710
March1st to 15thDay
54%6%12%18%8%
1976
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
2037
16th to endDay
38%6%15%27%12%
1980
October1st to 15thDay
47%5%10%22%11%1
1893
16th to endDay
56%5%16%16%4
1788
November1st to 15thDay
50%6%13%19%8%
1717
16th to endDay
58%7%14%14%5%
1661
December1st to 15thDay
62%6%13%12%3
1462
16th to endDay
64%6%12%11%3
1543
January1st to 15thNight
62%5%12%12%8%
2716
16th to endNight
61%7%14%12%3
2862
February1st to 15thNight
60%6%10%16%6%
2456
16th to endNight
59%410%17%8%
2049
March1st to 15thNight
50%5%11%20%10%1
2221
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
32%5%14%29%16%
1911
16th to endNight
34%6%14%30%13%
1980
October1st to 15thNight
44%5%10%24%13%1
2065
16th to endNight
54%6%13%19%5%
2433
November1st to 15thNight
47%8%13%20%9%
2471
16th to endNight
56%8%15%14%5%
2627
December1st to 15thNight
62%6%13%11%6%
2824
16th to endNight
65%6%10%11%5%
3029

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%6%34%26%11%
135
16th to endDay
23%10%35%26%3
144
February1st to 15thDay
24%11%41%20%1
135
16th to endDay
14%11%46%19%8%
120
March1st to 15thDay
27%8%26%30%7%
192
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
8%321%23%25%18%
315
16th to endDay
14%5%14%23%25%16%
314
October1st to 15thDay
19%8%24%25%17%5%
315
16th to endDay
25%9%32%26%4
204
November1st to 15thDay
18%10%29%25%11%4
135
16th to endDay
19%18%38%15%7%
113
December1st to 15thDay
28%12%37%16%4
90
16th to endDay
25%11%41%18%3
116
January1st to 15thNight
24%8%35%23%6%
975
16th to endNight
17%7%35%31%7%
990
February1st to 15thNight
20%8%39%26%4
764
16th to endNight
22%7%34%28%7%
683
March1st to 15thNight
20%6%32%32%8%
764
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
12%320%32%23%7%
651
16th to endNight
14%417%31%26%5%
717
October1st to 15thNight
20%6%22%32%16%1
720
16th to endNight
25%11%31%25%5%
768
November1st to 15thNight
19%9%31%26%12%
760
16th to endNight
24%11%33%23%7%
780
December1st to 15thNight
25%9%36%24%3
874
16th to endNight
26%8%35%24%3
1040
Page generated at 2018-03-12 13:28:14. Version ac04

Copyright 2018 A. Danko


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