This page made possible by the sponsorship of: Charles S Morris.

Dreamweaver Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dreamweaver Observatory clear sky chart from 2005-11-05 to 2019-09-17.

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
76%
18431
36%
54745
31%
18381
80%
18381
55%
25941

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
59%
839
30%
2847
27%
836
68%
836
39%
1439
January16th to endNight
59%
896
34%
2844
27%
896
70%
896
40%
1466
February1st to 15thNight
66%
820
37%
2461
32%
816
75%
816
47%
1246
February16th to endNight
61%
736
30%
2207
29%
736
67%
736
41%
1187
March1st to 15thNight
65%
840
27%
2514
25%
840
72%
840
44%
1308
March16th to endNight
72%
896
30%
2323
24%
896
76%
896
50%
1275
April1st to 15thNight
69%
839
33%
2099
20%
839
73%
839
51%
1154
April16th to endNight
75%
832
32%
2080
17%
832
79%
832
61%
1076
May1st to 15thNight
75%
766
29%
2026
20%
766
76%
766
51%
1087
May16th to endNight
80%
657
31%
1973
26%
657
81%
657
59%
901
June1st to 15thNight
90%
443
36%
1703
41%
443
91%
443
59%
636
June16th to endNight
96%
420
39%
1680
48%
420
96%
420
74%
532
July1st to 15thNight
92%
400
38%
1600
45%
400
92%
400
65%
539
July16th to endNight
91%
702
35%
1917
28%
663
92%
663
67%
842
August1st to 15thNight
93%
825
38%
2060
26%
821
93%
821
78%
937
August16th to endNight
96%
892
45%
2230
30%
892
96%
892
83%
985
September1st to 15thNight
92%
840
44%
2100
35%
840
92%
840
73%
997
September16th to endNight
93%
780
46%
2157
44%
780
95%
780
80%
886
October1st to 15thNight
78%
780
37%
2216
36%
780
83%
780
60%
1050
October16th to endNight
77%
832
42%
2496
42%
832
82%
832
60%
1118
November1st to 15thNight
75%
820
37%
2655
35%
820
84%
820
58%
1142
November16th to endNight
71%
840
37%
2730
37%
840
77%
840
52%
1244
December1st to 15thNight
63%
840
37%
2730
32%
840
72%
840
42%
1359
December16th to endNight
59%
896
33%
3097
29%
896
70%
896
38%
1535

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
4212212236%68%
55923
Night
4212212235%70%
54947
TransparencyDay
18%37%17%28%25%
55613
Night
17%36%17%28%26%
54757
SeeingDay
6%7%28%37%15%5%
8639
Night
5%111%34%36%9%
18439

By Month

Percentage Cloud Cover SW (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
8%314423335%59%
1749
16th to endDay
11%312322235%60%
2082
February1st to 15thDay
8%312312346%59%
2051
16th to endDay
9%313323346%56%
1839
March1st to 15thDay
6%214424447%56%
2104
16th to endDay
5%214314348%58%
2604
April1st to 15thDay
5%324312348%60%
2509
16th to endDay
3313212237%67%
2485
May1st to 15thDay
5%323212337%63%
2582
16th to endDay
3313312246%66%
2845
June1st to 15thDay
2313212247%67%
2913
16th to endDay
11211225%79%
2940
July1st to 15thDay
112212246%74%
2940
16th to endDay
212212235%75%
2836
August1st to 15thDay
1111123481%
2473
16th to endDay
111222483%
2676
September1st to 15thDay
111222381%
2520
16th to endDay
1111112482%
2157
October1st to 15thDay
321221323471%
2070
16th to endDay
221121233473%
2080
November1st to 15thDay
222222345%71%
1861
16th to endDay
4312323338%64%
1890
December1st to 15thDay
6%31322335%8%60%
1890
16th to endDay
8%31232335%6%58%
1827
January1st to 15thNight
7%314323347%58%
2847
16th to endNight
8%322222335%61%
2844
February1st to 15thNight
7%313212337%63%
2461
16th to endNight
11%313313235%59%
2207
March1st to 15thNight
5%413323347%59%
2514
16th to endNight
431332335%6%62%
2323
April1st to 15thNight
5%413213246%64%
2099
16th to endNight
2212213246%71%
2080
May1st to 15thNight
2413322236%67%
2026
16th to endNight
2112212235%73%
1972
June1st to 15thNight
11221236%75%
1703
16th to endNight
11112385%
1680
July1st to 15thNight
11121122479%
1680
16th to endNight
1111212235%77%
2030
August1st to 15thNight
11111112483%
2070
16th to endNight
11212484%
2230
September1st to 15thNight
111111221381%
2100
16th to endNight
1112484%
2157
October1st to 15thNight
421221224472%
2216
16th to endNight
231211123475%
2496
November1st to 15thNight
2212212235%72%
2655
16th to endNight
4211222346%67%
2730
December1st to 15thNight
6%22322335%6%61%
2730
16th to endNight
9%312212346%62%
3097

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
27%29%13%25%22%
1749
16th to endDay
28%27%17%19%24%
2082
February1st to 15thDay
25%36%15%25%24%
2051
16th to endDay
28%47%19%28%11%
1839
March1st to 15thDay
26%311%19%20%18%
2104
16th to endDay
24%5%11%21%22%14%
2604
April1st to 15thDay
22%5%13%23%22%12%
2509
16th to endDay
18%39%22%30%15%
2485
May1st to 15thDay
21%311%20%25%17%
2582
16th to endDay
18%410%27%28%10%
2848
June1st to 15thDay
17%29%19%31%18%
2913
16th to endDay
9%1412%36%35%
2940
July1st to 15thDay
12%2413%30%36%
2791
16th to endDay
12%27%22%29%25%
2686
August1st to 15thDay
8%1313%36%36%
2459
16th to endDay
6%1311%43%33%
2676
September1st to 15thDay
8%2411%30%42%
2520
16th to endDay
8%314%35%37%
2157
October1st to 15thDay
17%26%19%25%28%
2070
16th to endDay
15%3411%26%38%
2080
November1st to 15thDay
16%35%15%28%30%
1861
16th to endDay
20%37%15%22%29%
1890
December1st to 15thDay
23%48%17%22%24%
1890
16th to endDay
26%47%19%23%17%
1827
January1st to 15thNight
26%37%16%24%21%
2847
16th to endNight
25%37%14%19%28%
2844
February1st to 15thNight
22%36%16%25%26%
2472
16th to endNight
28%17%17%28%15%
2207
March1st to 15thNight
24%410%19%22%18%
2514
16th to endNight
21%5%10%23%23%15%
2323
April1st to 15thNight
22%310%26%24%12%
2099
16th to endNight
15%38%24%31%17%
2080
May1st to 15thNight
20%49%22%26%15%
2027
16th to endNight
14%311%28%30%11%
1973
June1st to 15thNight
11%311%19%35%17%
1703
16th to endNight
6%15%14%37%34%
1680
July1st to 15thNight
9%2414%27%41%
1600
16th to endNight
11%36%21%29%27%
1917
August1st to 15thNight
8%1310%37%38%
2060
16th to endNight
6%211%44%34%
2230
September1st to 15thNight
10%239%32%41%
2100
16th to endNight
6%1213%37%38%
2157
October1st to 15thNight
15%25%17%29%29%
2216
16th to endNight
15%2412%23%42%
2496
November1st to 15thNight
14%26%14%28%32%
2655
16th to endNight
18%36%17%23%30%
2730
December1st to 15thNight
23%37%17%21%26%
2730
16th to endNight
24%47%17%25%19%
3097

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%10%38%27%6%
197
16th to endDay
13%12%39%25%8%
371
February1st to 15thDay
12%12%33%29%9%3
386
16th to endDay
11%16%34%28%8%
342
March1st to 15thDay
11%17%35%26%8%
390
16th to endDay
7%10%40%31%9%1
416
April1st to 15thDay
8%13%37%27%9%3
389
16th to endDay
414%42%25%9%3
378
May1st to 15thDay
11%9%28%34%11%4
408
16th to endDay
8%10%34%31%13%2
458
June1st to 15thDay
5%423%38%21%6%
435
16th to endDay
217%46%25%8%
435
July1st to 15thDay
1111%45%27%12%
425
16th to endDay
310%47%24%13%
455
August1st to 15thDay
1117%52%15%11%
419
16th to endDay
14%51%20%12%
460
September1st to 15thDay
2224%47%15%6%
435
16th to endDay
2325%48%15%4
380
October1st to 15thDay
49%37%37%10%1
375
16th to endDay
36%31%39%17%3
400
November1st to 15thDay
2427%36%24%4
187
16th to endDay
5%11%28%35%17%1
180
December1st to 15thDay
7%8%26%36%18%1
180
16th to endDay
5%12%31%32%15%2
138
January1st to 15thNight
9%221%43%17%5%
840
16th to endNight
11%5%18%42%18%4
896
February1st to 15thNight
8%216%43%22%6%
824
16th to endNight
13%117%39%23%4
736
March1st to 15thNight
7%317%44%23%4
840
16th to endNight
5%213%45%29%4
896
April1st to 15thNight
5%214%42%29%4
839
16th to endNight
3313%40%31%8%
832
May1st to 15thNight
5%111%35%40%6%
767
16th to endNight
319%39%40%5%
659
June1st to 15thNight
332%51%11%
443
16th to endNight
21%65%11%
420
July1st to 15thNight
216%69%20%
400
16th to endNight
29%64%23%
702
August1st to 15thNight
117%61%18%
825
16th to endNight
111%63%23%
892
September1st to 15thNight
2222%54%18%
840
16th to endNight
231%46%17%
780
October1st to 15thNight
419%41%36%6%
780
16th to endNight
411%35%34%12%
832
November1st to 15thNight
3115%41%30%8%
820
16th to endNight
6%116%39%29%7%
840
December1st to 15thNight
8%317%43%22%4
840
16th to endNight
12%5%17%40%20%3
896
Page generated at 2019-09-17 18:12:19. Version ac04

Copyright 2019 A. Danko


Dreamweaver Observatory Clear Sky Chart |Charts Home