Watson Starview Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Watson Starview Observatory clear sky chart from 2005-11-05 to 2019-07-16.

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
49%
17883
27%
54239
18%
17836
58%
17836
36%
30829

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
38%
1049
28%
2717
12%
1045
48%
1045
36%
1666
January16th to endNight
33%
1061
30%
2853
11%
1061
46%
1061
35%
1731
February1st to 15thNight
32%
824
27%
2466
12%
818
44%
818
29%
1468
February16th to endNight
23%
736
27%
2206
8%
736
39%
736
29%
1313
March1st to 15thNight
33%
652
27%
2332
14%
652
48%
652
25%
1360
March16th to endNight
34%
672
24%
2464
15%
672
48%
672
28%
1354
April1st to 15thNight
30%
629
25%
2307
12%
629
47%
629
27%
1275
April16th to endNight
31%
624
25%
2007
14%
624
48%
624
31%
1183
May1st to 15thNight
37%
629
24%
1890
17%
629
49%
629
33%
1135
May16th to endNight
47%
658
24%
1972
18%
657
59%
657
37%
1121
June1st to 15thNight
67%
630
24%
1890
23%
630
74%
630
50%
932
June16th to endNight
68%
630
23%
1890
25%
630
72%
630
41%
1050
July1st to 15thNight
79%
600
21%
1800
24%
600
81%
600
44%
961
July16th to endNight
85%
615
29%
1747
33%
582
88%
582
53%
852
August1st to 15thNight
89%
575
33%
1746
38%
572
90%
572
58%
799
August16th to endNight
78%
621
22%
2135
27%
621
78%
621
35%
1158
September1st to 15thNight
73%
585
19%
2145
23%
585
74%
585
29%
1234
September16th to endNight
69%
582
27%
2145
28%
582
71%
582
31%
1186
October1st to 15thNight
69%
604
33%
2164
31%
604
74%
604
39%
1082
October16th to endNight
55%
832
35%
2496
22%
832
63%
832
45%
1290
November1st to 15thNight
50%
855
29%
2495
18%
855
57%
855
37%
1438
November16th to endNight
46%
1050
32%
2730
16%
1050
55%
1050
40%
1611
December1st to 15thNight
40%
1050
29%
2730
15%
1050
48%
1050
33%
1755
December16th to endNight
37%
1120
24%
2912
10%
1120
45%
1120
32%
1875

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
10%42442445%7%49%
55065
Night
9%323323347%54%
54441
Cloud CoverDay
10%42442445%7%49%
55063
Night
9%313323347%54%
54441
TransparencyDay
34%6%10%20%19%8%
54763
Night
29%5%11%21%20%11%
54246
SeeingDay
12%5%21%31%23%6%
7826
Night
11%6%27%36%16%1
17886

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
15%5%13323245%51%
1881
16th to endDay
12%413413435%54%
2086
February1st to 15thDay
13%6%24312345%52%
2050
16th to endDay
17%5%13324246%47%
1840
March1st to 15thDay
16%5%25%323336%45%
2286
16th to endDay
11%5%34423346%50%
2464
April1st to 15thDay
10%5%35%424347%47%
2301
16th to endDay
12%5%25%5%2433449%
2553
May1st to 15thDay
12%6%36%4345%5%7%39%
2721
16th to endDay
10%5%35%6%35%6%6%7%39%
2846
June1st to 15thDay
4213425%5%6%9%55%
2730
16th to endDay
7%3246%25%5%6%10%43%
2730
July1st to 15thDay
6%2235%36%5%7%8%46%
2730
16th to endDay
5%323425%5%6%9%51%
2677
August1st to 15thDay
21134345%48%61%
2453
16th to endDay
7%3146%36%6%6%8%44%
2419
September1st to 15thDay
11%5%25%5%345%5%6%42%
2145
16th to endDay
9%415%5%3445%8%46%
2145
October1st to 15thDay
9%5%14424336%55%
2113
16th to endDay
10%21221223464%
2080
November1st to 15thDay
11%5%245%33246%49%
2019
16th to endDay
10%423313335%57%
1890
December1st to 15thDay
13%7%24413336%48%
1890
16th to endDay
14%7%35%423345%46%
2016
January1st to 15thNight
15%413312325%54%
2717
16th to endNight
12%423323236%53%
2853
February1st to 15thNight
12%5%2431323453%
2462
16th to endNight
14%424323436%50%
2206
March1st to 15thNight
14%424324447%47%
2332
16th to endNight
8%323433447%52%
2464
April1st to 15thNight
8%324424447%51%
2307
16th to endNight
9%42442335%7%51%
2007
May1st to 15thNight
9%42432445%9%49%
1889
16th to endNight
6%4133235%7%10%51%
1971
June1st to 15thNight
211232345%9%63%
1890
16th to endNight
5%312325%5%6%9%55%
1890
July1st to 15thNight
411332346%10%57%
1890
16th to endNight
211232435%11%60%
1855
August1st to 15thNight
211213349%69%
1756
16th to endNight
6%3145%233412%51%
2135
September1st to 15thNight
10%3144345%5%8%48%
2145
16th to endNight
9%32442345%6%51%
2145
October1st to 15thNight
8%213213347%60%
2164
16th to endNight
10%21221334463%
2496
November1st to 15thNight
9%324323336%57%
2495
16th to endNight
9%413313335%58%
2730
December1st to 15thNight
12%6%24323336%50%
2730
16th to endNight
14%6%24323335%49%
2912

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
14%6%13323335%52%
1881
16th to endDay
13%323323345%54%
2086
February1st to 15thDay
13%6%14312345%52%
2050
16th to endDay
17%5%13323345%47%
1840
March1st to 15thDay
16%6%25%423435%45%
2286
16th to endDay
11%5%34324346%50%
2462
April1st to 15thDay
10%5%25%43345%6%47%
2301
16th to endDay
12%5%245%24335%49%
2553
May1st to 15thDay
13%6%26%5%345%5%7%39%
2721
16th to endDay
10%5%35%6%45%5%6%7%39%
2846
June1st to 15thDay
4213425%5%6%8%55%
2730
16th to endDay
8%3245%35%5%6%10%43%
2730
July1st to 15thDay
6%2235%36%6%6%8%46%
2730
16th to endDay
6%2143245%6%9%50%
2677
August1st to 15thDay
2133345%6%8%61%
2453
16th to endDay
7%3246%36%6%6%8%43%
2419
September1st to 15thDay
11%425%5%45%5%6%6%42%
2145
16th to endDay
9%3245%3445%8%46%
2145
October1st to 15thDay
9%5%14324346%54%
2113
16th to endDay
10%21321222465%
2080
November1st to 15thDay
11%5%25%43325%6%49%
2019
16th to endDay
10%423313335%58%
1890
December1st to 15thDay
14%7%24413345%48%
1890
16th to endDay
14%7%25%423345%46%
2016
January1st to 15thNight
14%413312335%55%
2717
16th to endNight
12%414323237%53%
2853
February1st to 15thNight
12%6%2432223453%
2462
16th to endNight
14%423323346%50%
2206
March1st to 15thNight
13%424314447%47%
2332
16th to endNight
8%324433447%53%
2464
April1st to 15thNight
8%42443445%7%51%
2307
16th to endNight
9%424423347%51%
2007
May1st to 15thNight
9%324415%45%9%49%
1889
16th to endNight
6%31332348%10%51%
1971
June1st to 15thNight
211232345%9%63%
1890
16th to endNight
4222225%46%10%55%
1890
July1st to 15thNight
421322346%10%57%
1890
16th to endNight
21232435%11%61%
1855
August1st to 15thNight
211212349%69%
1756
16th to endNight
6%31442435%11%51%
2135
September1st to 15thNight
10%314425%5%6%8%48%
2145
16th to endNight
9%32442445%7%51%
2145
October1st to 15thNight
7%212323347%60%
2164
16th to endNight
9%213212335%63%
2496
November1st to 15thNight
9%314323336%57%
2495
16th to endNight
9%414313345%58%
2730
December1st to 15thNight
12%5%24323336%50%
2730
16th to endNight
14%6%34323335%49%
2912

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
35%27%18%23%12%
1882
16th to endDay
33%35%14%27%14%
2086
February1st to 15thDay
35%47%15%20%16%
2051
16th to endDay
38%46%16%20%13%
1840
March1st to 15thDay
40%5%7%12%21%11%
2286
16th to endDay
35%5%9%17%22%9%
2464
April1st to 15thDay
36%5%8%18%18%12%
2301
16th to endDay
38%46%18%22%9%
2553
May1st to 15thDay
43%6%9%15%16%7%
2721
16th to endDay
41%8%10%18%17%3
2850
June1st to 15thDay
25%7%13%26%22%4
2730
16th to endDay
34%8%13%22%17%3
2730
July1st to 15thDay
30%9%18%25%13%2
2591
16th to endDay
24%9%17%30%16%1
2522
August1st to 15thDay
19%6%15%35%19%2
2439
16th to endDay
34%9%15%25%12%3
2419
September1st to 15thDay
40%7%11%19%15%5%
2145
16th to endDay
34%8%10%18%18%8%
2145
October1st to 15thDay
31%5%10%21%17%13%
2113
16th to endDay
25%3415%30%20%
2080
November1st to 15thDay
36%49%20%18%9%
2019
16th to endDay
29%46%15%23%19%
1890
December1st to 15thDay
39%48%16%21%10%
1890
16th to endDay
39%48%15%21%9%
2016
January1st to 15thNight
33%36%17%21%17%
2717
16th to endNight
33%35%14%24%18%
2853
February1st to 15thNight
35%46%14%21%19%
2472
16th to endNight
35%47%16%19%16%
2206
March1st to 15thNight
36%5%9%12%22%13%
2332
16th to endNight
32%5%11%19%21%9%
2464
April1st to 15thNight
32%6%8%17%19%15%
2307
16th to endNight
34%5%10%18%20%10%
2007
May1st to 15thNight
31%7%12%22%17%8%
1890
16th to endNight
27%7%16%29%16%3
1973
June1st to 15thNight
17%6%16%29%24%5%
1890
16th to endNight
23%9%14%30%18%3
1890
July1st to 15thNight
20%9%22%31%15%1
1800
16th to endNight
16%6%22%37%17%1
1747
August1st to 15thNight
13%5%19%37%21%3
1746
16th to endNight
27%7%20%28%12%4
2135
September1st to 15thNight
33%7%15%22%15%6%
2145
16th to endNight
31%6%12%23%16%9%
2145
October1st to 15thNight
25%5%13%24%17%14%
2164
16th to endNight
24%36%15%26%23%
2496
November1st to 15thNight
30%49%22%20%12%
2495
16th to endNight
29%36%16%24%19%
2730
December1st to 15thNight
36%47%16%21%12%
2730
16th to endNight
38%47%14%23%13%
2912

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
19%10%34%28%6%1
180
16th to endDay
16%14%39%20%9%
192
February1st to 15thDay
18%16%36%25%4
180
16th to endDay
29%8%37%22%1
159
March1st to 15thDay
22%14%39%17%5%
180
16th to endDay
9%9%43%28%8%
192
April1st to 15thDay
17%10%43%24%3
180
16th to endDay
14%12%40%21%10%
445
May1st to 15thDay
14%10%35%29%10%
618
16th to endDay
14%5%29%31%15%2
677
June1st to 15thDay
5%15%48%23%5%
645
16th to endDay
9%113%40%28%6%
645
July1st to 15thDay
5%8%37%37%10%
625
16th to endDay
3432%45%12%
597
August1st to 15thDay
2433%47%12%
516
16th to endDay
10%1230%36%18%
331
September1st to 15thDay
12%220%41%24%
180
16th to endDay
11%8%28%35%15%
180
October1st to 15thDay
7%112%30%35%13%
180
16th to endDay
23%416%28%23%2
192
November1st to 15thDay
27%5%28%26%10%2
180
16th to endDay
14%12%28%27%13%3
180
December1st to 15thDay
22%7%32%21%11%4
180
16th to endDay
25%14%33%21%5%
192
January1st to 15thNight
17%8%31%32%9%
1050
16th to endNight
15%9%37%29%7%
1061
February1st to 15thNight
17%13%34%30%4
824
16th to endNight
18%11%45%23%1
736
March1st to 15thNight
15%9%37%32%4
652
16th to endNight
8%10%43%31%4
672
April1st to 15thNight
10%10%47%29%2
629
16th to endNight
10%9%45%26%7%
624
May1st to 15thNight
12%6%41%31%7%
630
16th to endNight
7%436%36%13%1
659
June1st to 15thNight
324%48%22%1
630
16th to endNight
5%18%50%21%2
630
July1st to 15thNight
49%49%33%3
600
16th to endNight
25%51%35%4
615
August1st to 15thNight
2446%40%5%
575
16th to endNight
7%444%37%5%
621
September1st to 15thNight
11%16%38%37%4
585
16th to endNight
10%19%36%37%4
582
October1st to 15thNight
9%115%42%26%4
604
16th to endNight
11%425%34%22%1
832
November1st to 15thNight
11%428%36%16%1
855
16th to endNight
12%8%29%33%15%
1050
December1st to 15thNight
17%8%30%34%8%
1050
16th to endNight
20%8%31%32%7%
1120
Page generated at 2019-07-17 07:53:05. Version ac04

Copyright 2019 A. Danko


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