Dry Creek Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dry Creek Observatory clear sky chart from 2005-11-05 to 2017-09-24.

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
47%
15442
24%
47025
16%
15399
55%
15399
29%
28628

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
24%
720
23%
2327
9%
716
40%
716
20%
1488
January16th to endNight
26%
768
25%
2419
12%
768
41%
768
22%
1552
February1st to 15thNight
28%
704
25%
2112
10%
701
42%
701
25%
1293
February16th to endNight
22%
631
24%
1893
9%
631
36%
631
22%
1199
March1st to 15thNight
29%
720
22%
2094
12%
720
38%
720
25%
1328
March16th to endNight
35%
768
22%
2112
13%
768
42%
768
29%
1329
April1st to 15thNight
42%
584
26%
1842
15%
584
54%
584
33%
1032
April16th to endNight
44%
540
27%
1729
19%
540
54%
540
32%
986
May1st to 15thNight
50%
540
21%
1620
12%
540
58%
540
30%
992
May16th to endNight
65%
561
22%
1682
16%
561
69%
561
36%
979
June1st to 15thNight
71%
540
17%
1620
15%
540
73%
540
35%
975
June16th to endNight
76%
540
18%
1620
15%
540
78%
540
40%
922
July1st to 15thNight
73%
510
15%
1530
13%
510
74%
510
30%
951
July16th to endNight
69%
564
17%
1595
15%
531
71%
531
29%
1015
August1st to 15thNight
74%
539
21%
1681
22%
536
74%
536
31%
1008
August16th to endNight
68%
573
20%
1910
21%
573
70%
573
25%
1218
September1st to 15thNight
63%
675
18%
1935
17%
675
64%
675
29%
1261
September16th to endNight
62%
693
27%
1914
20%
693
67%
693
35%
1154
October1st to 15thNight
54%
660
35%
1815
27%
660
61%
660
40%
1042
October16th to endNight
50%
704
33%
2123
26%
704
59%
704
36%
1186
November1st to 15thNight
47%
700
30%
2276
24%
700
59%
700
35%
1223
November16th to endNight
37%
720
28%
2340
18%
720
52%
720
29%
1343
December1st to 15thNight
29%
720
23%
2340
14%
720
42%
720
22%
1477
December16th to endNight
30%
768
20%
2496
14%
768
39%
768
18%
1675

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%5%25%5%35%45%7%40%
47896
Night
12%5%2442445%7%45%
47224
TransparencyDay
41%411%20%17%4
47597
Night
37%411%21%20%5%
47027
SeeingDay
15%7%18%23%21%13%
5328
Night
15%8%22%28%21%4
15444

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
19%7%24324345%42%
1611
16th to endDay
17%5%25%434345%44%
1803
February1st to 15thDay
17%8%2432335%6%41%
1750
16th to endDay
19%6%26%423235%41%
1580
March1st to 15thDay
17%7%25%42445%6%39%
1866
16th to endDay
16%5%345%2445%6%41%
2111
April1st to 15thDay
13%5%24425%446%45%
2115
16th to endDay
11%5%25%5%35%446%45%
2229
May1st to 15thDay
12%5%26%5%35%45%6%42%
2331
16th to endDay
8%425%6%36%5%7%7%40%
2431
June1st to 15thDay
8%425%6%5%7%6%8%9%35%
2340
16th to endDay
6%325%5%36%6%7%12%40%
2340
July1st to 15thDay
11%426%7%46%6%7%10%31%
2340
16th to endDay
7%435%7%5%7%8%9%11%29%
2465
August1st to 15thDay
7%415%6%5%7%7%9%11%32%
2265
16th to endDay
12%5%37%8%5%8%6%6%9%27%
2292
September1st to 15thDay
11%6%26%6%36%5%7%8%34%
2013
16th to endDay
15%5%245%3445%5%44%
1905
October1st to 15thDay
11%414323335%54%
1815
16th to endDay
13%5%2331222358%
1744
November1st to 15thDay
13%413322335%54%
1582
16th to endDay
16%433423245%48%
1620
December1st to 15thDay
18%6%15%4235%46%40%
1620
16th to endDay
25%8%25%5%13345%34%
1728
January1st to 15thNight
19%5%245%24346%41%
2327
16th to endNight
18%7%34423435%42%
2419
February1st to 15thNight
15%6%24413336%47%
2103
16th to endNight
18%5%25%433336%43%
1893
March1st to 15thNight
13%6%24424446%43%
2094
16th to endNight
12%7%34423446%46%
2112
April1st to 15thNight
12%42331335%7%51%
1842
16th to endNight
9%42342445%6%51%
1729
May1st to 15thNight
9%4245%345%5%7%46%
1619
16th to endNight
7%3145%25%5%7%9%47%
1682
June1st to 15thNight
4335%435%5%8%11%44%
1620
16th to endNight
4214435%5%7%11%48%
1620
July1st to 15thNight
7%3145%36%6%8%11%39%
1620
16th to endNight
4425%6%47%6%7%11%38%
1703
August1st to 15thNight
5%3246%346%6%11%43%
1692
16th to endNight
10%5%35%5%245%7%11%37%
1910
September1st to 15thNight
10%426%5%36%46%8%40%
1935
16th to endNight
11%41442445%8%48%
1914
October1st to 15thNight
10%413313346%57%
1815
16th to endNight
10%42442232458%
2123
November1st to 15thNight
12%313313246%56%
2276
16th to endNight
14%6%23322446%49%
2340
December1st to 15thNight
16%6%26%5%2345%5%42%
2340
16th to endNight
22%8%24424346%35%
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
44%28%17%22%4
1612
16th to endDay
43%26%21%20%5%
1803
February1st to 15thDay
43%28%21%20%2
1752
16th to endDay
46%25%20%20%4
1580
March1st to 15thDay
44%39%18%20%4
1866
16th to endDay
43%211%23%15%2
2112
April1st to 15thDay
39%29%21%20%5%
2115
16th to endDay
37%48%22%21%5%
2229
May1st to 15thDay
39%5%11%22%17%3
2331
16th to endDay
38%5%15%23%13%3
2435
June1st to 15thDay
41%6%17%22%10%1
2340
16th to endDay
33%7%16%25%14%3
2340
July1st to 15thDay
41%7%18%18%9%2
2201
16th to endDay
41%8%20%18%10%1
2310
August1st to 15thDay
38%8%17%22%10%2
2252
16th to endDay
49%7%13%16%10%2
2292
September1st to 15thDay
44%5%14%18%13%4
2013
16th to endDay
40%49%20%20%4
1905
October1st to 15thDay
32%37%20%27%9%
1815
16th to endDay
33%25%18%30%10%
1744
November1st to 15thDay
33%2417%33%8%
1582
16th to endDay
38%26%18%27%6%
1620
December1st to 15thDay
45%28%21%17%5%
1620
16th to endDay
53%27%17%14%3
1728
January1st to 15thNight
44%36%18%22%4
2327
16th to endNight
44%25%20%20%6%
2419
February1st to 15thNight
40%17%22%20%7%
2112
16th to endNight
43%2423%22%3
1893
March1st to 15thNight
40%48%20%18%7%
2094
16th to endNight
38%29%27%18%2
2112
April1st to 15thNight
32%310%25%22%6%
1842
16th to endNight
33%39%25%21%6%
1729
May1st to 15thNight
36%414%20%21%2
1620
16th to endNight
30%6%16%26%16%3
1684
June1st to 15thNight
31%7%21%26%12%1
1620
16th to endNight
27%6%21%23%16%3
1620
July1st to 15thNight
34%8%19%23%11%2
1530
16th to endNight
34%9%19%20%12%2
1595
August1st to 15thNight
32%8%18%23%14%2
1681
16th to endNight
39%8%17%18%14%2
1910
September1st to 15thNight
39%6%17%18%13%4
1935
16th to endNight
32%5%10%25%20%5%
1914
October1st to 15thNight
28%48%21%26%10%
1815
16th to endNight
32%1316%32%12%
2123
November1st to 15thNight
30%25%18%30%12%
2276
16th to endNight
35%26%20%27%8%
2340
December1st to 15thNight
43%28%19%20%5%
2340
16th to endNight
50%28%18%17%3
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
20%22%36%14%42
90
16th to endDay
18%29%44%34
96
February1st to 15thDay
21%27%37%11%2
90
16th to endDay
29%17%37%16%
81
March1st to 15thDay
24%17%30%23%21
156
16th to endDay
19%10%34%21%12%1
288
April1st to 15thDay
20%14%27%18%17%2
270
16th to endDay
13%5%27%27%21%4
270
May1st to 15thDay
15%9%25%21%13%14%
288
16th to endDay
10%218%32%20%15%
331
June1st to 15thDay
10%111%22%29%23%
315
16th to endDay
10%212%24%22%28%
315
July1st to 15thDay
10%28%24%25%28%
305
16th to endDay
9%15%20%35%27%
326
August1st to 15thDay
12%27%28%30%18%
313
16th to endDay
14%26%24%29%22%
332
September1st to 15thDay
13%49%22%27%22%
315
16th to endDay
15%212%30%28%10%
287
October1st to 15thDay
16%5%18%28%22%9%
255
16th to endDay
17%8%20%21%25%6%
239
November1st to 15thDay
26%12%17%30%11%2
90
16th to endDay
17%12%40%14%13%2
90
December1st to 15thDay
27%18%30%18%31
90
16th to endDay
36%12%28%18%31
96
January1st to 15thNight
23%17%29%22%7%
720
16th to endNight
22%15%31%26%3
768
February1st to 15thNight
20%15%32%28%3
704
16th to endNight
20%19%34%22%3
631
March1st to 15thNight
19%15%32%26%6%
720
16th to endNight
15%12%29%28%13%
768
April1st to 15thNight
14%10%30%28%15%
584
16th to endNight
11%9%29%31%17%1
540
May1st to 15thNight
10%5%25%30%23%3
540
16th to endNight
9%114%35%31%6%
563
June1st to 15thNight
6%110%34%36%10%
540
16th to endNight
5%17%30%42%12%
540
July1st to 15thNight
8%25%26%44%13%
510
16th to endNight
6%7%24%45%14%
564
August1st to 15thNight
8%1431%43%11%
539
16th to endNight
12%1429%41%10%
573
September1st to 15thNight
12%38%28%38%8%
675
16th to endNight
14%113%34%31%3
693
October1st to 15thNight
13%422%31%24%4
660
16th to endNight
12%9%22%30%22%3
704
November1st to 15thNight
13%7%26%29%20%2
700
16th to endNight
18%13%27%27%13%
720
December1st to 15thNight
20%13%29%26%9%
720
16th to endNight
26%13%27%24%7%
768
Page generated at 2017-09-25 09:02:20. Version ac04

Copyright 2017 A. Danko


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