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 2005-11-06 to 2024-01-14.

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
45%
23724
23%
74434
16%
23668
54%
23668
27%
45763

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 10thNight
22%
760
22%
2459
9%
757
39%
757
19%
1575
January11th to 20thNight
26%
736
22%
2391
11%
736
41%
736
19%
1593
January21st to endNight
25%
792
30%
2458
13%
792
42%
792
23%
1533
February1st to 10thNight
28%
720
25%
2160
12%
720
40%
720
24%
1374
February11th to 20thNight
21%
703
20%
2098
7%
699
32%
699
19%
1400
February21st to endNight
17%
592
21%
1776
7%
592
30%
592
19%
1194
March1st to 10thNight
29%
720
24%
2150
13%
720
39%
720
26%
1320
March11th to 20thNight
28%
720
20%
1980
9%
720
37%
720
25%
1304
March21st to endNight
32%
792
22%
2178
11%
792
40%
792
26%
1422
April1st to 10thNight
39%
608
26%
1868
17%
608
49%
608
31%
1089
April11th to 20thNight
36%
533
28%
1775
16%
533
51%
533
29%
1013
April21st to endNight
47%
540
29%
1695
21%
540
57%
540
33%
960
May1st to 10thNight
51%
540
24%
1620
14%
540
60%
540
34%
950
May11th to 20thNight
53%
531
18%
1592
12%
531
58%
531
29%
980
May21st to endNight
66%
582
20%
1744
17%
582
68%
582
33%
1053
June1st to 10thNight
66%
540
18%
1620
15%
540
68%
540
30%
1030
June11th to 20thNight
71%
540
19%
1620
15%
540
74%
540
41%
905
June21st to endNight
73%
540
17%
1620
14%
540
75%
540
36%
946
July1st to 10thNight
69%
525
15%
1575
14%
525
70%
525
28%
1009
July11th to 20thNight
74%
522
14%
1566
13%
522
74%
522
29%
984
July21st to endNight
68%
591
16%
1672
15%
558
69%
558
27%
1096
August1st to 10thNight
71%
537
18%
1616
18%
534
71%
534
29%
1015
August11th to 20thNight
70%
534
18%
1776
20%
534
70%
534
26%
1116
August21st to endNight
64%
594
20%
1980
22%
594
65%
594
24%
1286
September1st to 10thNight
65%
652
20%
1912
19%
652
67%
652
31%
1203
September11th to 20thNight
59%
720
23%
1980
18%
720
62%
720
31%
1269
September21st to endNight
63%
720
30%
1980
21%
720
69%
720
39%
1155
October1st to 10thNight
56%
720
33%
1980
25%
720
63%
720
41%
1118
October11th to 20thNight
48%
720
32%
2038
22%
720
58%
720
37%
1186
October21st to endNight
49%
792
31%
2425
26%
792
59%
792
33%
1392
November1st to 10thNight
49%
740
28%
2406
24%
740
59%
740
33%
1318
November11th to 20thNight
38%
760
30%
2470
18%
760
55%
760
32%
1367
November21st to endNight
36%
760
26%
2470
17%
760
50%
760
27%
1481
December1st to 10thNight
26%
760
23%
2470
13%
760
40%
760
19%
1622
December11th to 20thNight
31%
759
26%
2905
16%
758
43%
758
20%
1725
December21st to endNight
29%
829
14%
4409
13%
817
39%
817
12%
2780

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%6%25%5%35%5%6%8%41%
74866
Night
13%6%25%5%345%5%8%45%
74903
TransparencyDay
42%411%21%18%4
74589
Night
39%410%22%20%5%
74699
SeeingDay
18%10%22%23%18%10%
13645
Night
17%9%22%29%20%4
23734

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 10thDay
19%8%24434447%42%
1706
11th to 20thDay
21%9%35%32444441%
1647
21st to endDay
17%7%35%5%34345%45%
1894
February1st to 10thDay
20%8%345%3445%6%38%
1800
11th to 20thDay
22%8%35%434446%39%
1748
21st to endDay
23%7%26%6%33345%38%
1480
March1st to 10thDay
17%5%15%5%2445%7%44%
1808
11th to 20thDay
20%7%36%5%245%5%6%38%
1980
21st to endDay
16%7%35%6%45%5%6%7%39%
2178
April1st to 10thDay
14%5%25%435%5%6%7%45%
2106
11th to 20thDay
13%6%36%6%34445%47%
2134
21st to endDay
10%425%5%35%5%5%8%47%
2263
May1st to 10thDay
11%5%25%435%45%8%47%
2340
11th to 20thDay
12%6%26%6%45%6%6%7%41%
2301
21st to endDay
9%5%36%6%46%5%7%9%41%
2531
June1st to 10thDay
10%6%36%7%5%6%6%8%9%35%
2340
11th to 20thDay
6%425%6%46%7%8%12%42%
2340
21st to endDay
8%5%26%5%5%7%7%7%11%36%
2340
July1st to 10thDay
10%5%36%7%5%7%7%8%10%31%
2340
11th to 20thDay
8%5%26%7%5%7%8%9%12%30%
2340
21st to endDay
7%5%47%8%5%8%8%9%12%29%
2547
August1st to 10thDay
7%425%6%5%8%8%10%12%31%
2306
11th to 20thDay
10%5%27%7%5%7%7%7%10%33%
2125
21st to endDay
13%6%36%7%5%7%6%7%9%30%
2376
September1st to 10thDay
9%6%36%6%46%6%6%10%38%
2030
11th to 20thDay
15%6%25%5%45%5%7%6%41%
1980
21st to endDay
13%5%245%3445%7%48%
1980
October1st to 10thDay
11%5%25%5%33435%54%
1980
11th to 20thDay
12%5%3442345%6%54%
1919
21st to endDay
15%5%2342334454%
1928
November1st to 10thDay
13%5%24423335%57%
1672
11th to 20thDay
13%5%34434445%51%
1710
21st to endDay
16%6%245%2445%7%46%
1710
December1st to 10thDay
22%7%26%4345%5%6%38%
1710
11th to 20thDay
18%8%25%6%23446%42%
2153
21st to endDay
21%8%25%5%35%5%5%7%35%
3124
January1st to 10thNight
20%7%245%34445%43%
2459
11th to 20thNight
19%9%35%5%3445%6%38%
2391
21st to endNight
18%7%35%423436%46%
2458
February1st to 10thNight
17%7%25%5%24346%43%
2160
11th to 20thNight
22%7%35%42434442%
2098
21st to endNight
23%7%35%443447%37%
1776
March1st to 10thNight
15%6%244345%47%46%
2150
11th to 20thNight
15%7%25%5%3446%7%41%
1980
21st to endNight
14%8%36%5%345%46%43%
2178
April1st to 10thNight
11%4245%245%6%8%49%
1868
11th to 20thNight
14%6%2442435%7%50%
1775
21st to endNight
10%4344245%6%6%52%
1695
May1st to 10thNight
9%4245%35%45%7%52%
1620
11th to 20thNight
11%5%35%6%446%6%9%42%
1592
21st to endNight
8%5%25%6%36%6%7%9%45%
1744
June1st to 10thNight
6%5%36%5%46%6%8%12%38%
1620
11th to 20thNight
4325%5%35%5%6%11%50%
1620
21st to endNight
6%425%445%5%8%12%46%
1620
July1st to 10thNight
8%5%26%5%45%7%10%11%36%
1620
11th to 20thNight
6%425%5%5%6%7%8%13%38%
1620
21st to endNight
5%6%35%6%48%6%8%12%36%
1771
August1st to 10thNight
6%425%7%45%7%7%13%38%
1627
11th to 20thNight
8%6%36%6%446%7%11%40%
1776
21st to endNight
13%6%36%6%246%7%10%37%
1980
September1st to 10thNight
9%5%26%6%46%5%6%8%44%
1912
11th to 20thNight
12%5%25%5%35%5%5%8%43%
1980
21st to endNight
11%42342446%7%53%
1980
October1st to 10thNight
9%5%23413346%59%
1980
11th to 20thNight
12%5%24434336%54%
2038
21st to endNight
13%5%245%33435%54%
2425
November1st to 10thNight
12%424424346%55%
2406
11th to 20thNight
13%6%24423346%54%
2470
21st to endNight
17%5%244345%5%7%45%
2470
December1st to 10thNight
20%7%37%5%2345%6%38%
2470
11th to 20thNight
18%8%24323435%47%
3042
21st to endNight
20%9%36%5%3445%8%33%
4532

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 10thDay
44%28%20%21%4
1707
11th to 20thDay
48%37%19%21%3
1647
21st to endDay
44%25%24%21%5%
1894
February1st to 10thDay
48%27%19%20%3
1800
11th to 20thDay
49%25%21%18%4
1758
21st to endDay
51%26%15%20%6%
1480
March1st to 10thDay
40%38%17%23%8%
1808
11th to 20thDay
49%310%17%18%4
1980
21st to endDay
46%210%23%16%3
2178
April1st to 10thDay
38%311%22%20%6%
2106
11th to 20thDay
40%36%19%25%7%
2134
21st to endDay
35%49%28%20%3
2263
May1st to 10thDay
36%411%26%19%4
2340
11th to 20thDay
41%6%15%22%15%2
2305
21st to endDay
37%5%14%25%16%3
2531
June1st to 10thDay
44%6%15%22%12%1
2340
11th to 20thDay
33%6%19%27%13%2
2340
21st to endDay
40%6%17%23%12%3
2340
July1st to 10thDay
44%7%18%19%10%2
2275
11th to 20thDay
42%8%20%16%10%3
2271
21st to endDay
43%7%21%19%9%
2405
August1st to 10thDay
40%8%20%23%8%1
2293
11th to 20thDay
45%6%17%20%10%2
2125
21st to endDay
49%7%14%16%11%4
2376
September1st to 10thDay
41%5%15%18%16%5%
2030
11th to 20thDay
42%5%10%21%19%3
1980
21st to endDay
37%49%18%24%7%
1980
October1st to 10thDay
33%48%19%27%8%
1980
11th to 20thDay
33%37%24%24%9%
1919
21st to endDay
36%2420%30%9%
1928
November1st to 10thDay
33%26%19%32%8%
1672
11th to 20thDay
37%26%19%27%9%
1710
21st to endDay
40%27%19%27%5%
1710
December1st to 10thDay
49%27%20%18%5%
1710
11th to 20thDay
46%25%20%22%5%
2150
21st to endDay
50%27%22%17%2
3124
January1st to 10thNight
45%36%21%21%4
2459
11th to 20thNight
48%38%19%18%3
2391
21st to endNight
43%2424%23%5%
2458
February1st to 10thNight
43%27%21%21%5%
2160
11th to 20thNight
49%25%20%19%6%
2099
21st to endNight
49%27%17%19%6%
1776
March1st to 10thNight
39%37%19%22%10%
2150
11th to 20thNight
43%310%19%19%5%
1980
21st to endNight
43%37%25%19%3
2178
April1st to 10thNight
34%411%22%23%7%
1868
11th to 20thNight
36%26%23%24%9%
1775
21st to endNight
33%310%30%20%5%
1695
May1st to 10thNight
34%312%24%23%4
1620
11th to 20thNight
38%5%19%22%16%1
1593
21st to endNight
35%5%13%26%18%3
1745
June1st to 10thNight
37%7%18%22%14%2
1620
11th to 20thNight
28%5%22%29%15%1
1620
21st to endNight
31%6%22%23%14%5%
1620
July1st to 10thNight
38%8%18%22%12%2
1575
11th to 20thNight
35%10%23%19%11%3
1566
21st to endNight
39%9%20%21%10%2
1672
August1st to 10thNight
36%8%20%25%9%1
1616
11th to 20thNight
37%9%20%18%14%2
1776
21st to endNight
42%7%16%19%13%3
1980
September1st to 10thNight
37%6%17%19%16%6%
1912
11th to 20thNight
38%6%12%22%19%2
1980
21st to endNight
30%411%23%23%9%
1980
October1st to 10thNight
28%38%22%29%9%
1980
11th to 20thNight
33%27%22%25%10%
2038
21st to endNight
34%2420%29%11%
2425
November1st to 10thNight
32%37%20%27%11%
2406
11th to 20thNight
34%25%21%28%11%
2470
21st to endNight
39%36%22%25%5%
2470
December1st to 10thNight
47%37%20%19%3
2470
11th to 20thNight
41%26%19%27%4
3044
21st to endNight
51%26%23%16%2
4532

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 10thDay
29%22%35%11%2
270
11th to 20thDay
30%20%29%14%5%1
249
21st to endDay
26%25%35%11%31
264
February1st to 10thDay
32%19%32%16%2
240
11th to 20thDay
41%23%27%8%1
240
21st to endDay
35%20%35%9%1
198
March1st to 10thDay
28%20%31%15%42
248
11th to 20thDay
27%19%30%18%6%1
420
21st to endDay
24%16%36%18%6%1
462
April1st to 10thDay
23%15%31%16%13%2
420
11th to 20thDay
18%17%31%20%13%2
412
21st to endDay
18%10%31%23%15%3
420
May1st to 10thDay
17%10%28%26%12%7%
423
11th to 20thDay
13%5%19%36%15%12%
447
21st to endDay
11%419%31%22%13%
485
June1st to 10thDay
12%321%28%24%12%
450
11th to 20thDay
7%414%26%25%24%
450
21st to endDay
13%416%26%23%18%
450
July1st to 10thDay
12%26%27%29%24%
445
11th to 20thDay
8%5%8%23%28%28%
444
21st to endDay
10%37%22%37%21%
488
August1st to 10thDay
11%311%25%32%20%
446
11th to 20thDay
13%38%32%27%18%
439
21st to endDay
14%37%25%29%21%
495
September1st to 10thDay
10%311%29%30%18%
450
11th to 20thDay
18%212%26%28%13%
450
21st to endDay
11%318%32%27%9%
450
October1st to 10thDay
15%5%22%28%21%9%
450
11th to 20thDay
16%10%24%30%18%3
450
21st to endDay
21%10%26%25%16%3
443
November1st to 10thDay
22%12%29%24%11%3
270
11th to 20thDay
19%16%36%22%7%1
270
21st to endDay
17%17%37%17%10%1
270
December1st to 10thDay
32%17%29%16%42
270
11th to 20thDay
26%17%31%20%5%1
270
21st to endDay
31%18%28%17%41
297
January1st to 10thNight
24%18%30%22%6%
760
11th to 20thNight
25%14%29%25%7%
736
21st to endNight
23%16%33%25%3
792
February1st to 10thNight
22%14%33%27%5%
720
11th to 20thNight
28%16%32%23%1
703
21st to endNight
27%18%35%17%3
592
March1st to 10thNight
20%14%33%29%4
720
11th to 20thNight
20%15%32%24%9%1
720
21st to endNight
19%13%30%28%9%
792
April1st to 10thNight
15%12%30%29%13%
608
11th to 20thNight
16%12%32%26%13%1
533
21st to endNight
12%8%26%36%16%1
540
May1st to 10thNight
12%6%25%36%20%1
540
11th to 20thNight
14%5%19%34%24%5%
531
21st to endNight
10%212%35%33%8%
584
June1st to 10thNight
9%211%38%34%6%
540
11th to 20thNight
4212%31%37%14%
540
21st to endNight
8%28%33%40%9%
540
July1st to 10thNight
10%45%23%43%15%
525
11th to 20thNight
8%1427%46%15%
522
21st to endNight
8%26%24%47%12%
591
August1st to 10thNight
9%15%31%42%12%
537
11th to 20thNight
11%2433%40%9%
534
21st to endNight
15%35%27%39%11%
594
September1st to 10thNight
10%38%29%41%10%
652
11th to 20thNight
16%312%29%37%3
720
21st to endNight
13%214%34%33%3
720
October1st to 10thNight
12%5%21%33%23%7%
720
11th to 20thNight
14%6%27%31%20%2
720
21st to endNight
16%9%20%35%17%2
792
November1st to 10thNight
16%7%23%33%19%2
740
11th to 20thNight
15%10%32%29%13%1
760
21st to endNight
19%12%29%29%11%
760
December1st to 10thNight
23%16%29%24%9%
760
11th to 20thNight
25%11%28%27%7%1
760
21st to endNight
27%12%28%26%7%
836
Page generated at 2024-01-11 13:32:01. Version ac07

Copyright 2024 Attilla Danko


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