CAS Starfield Observatory Dark Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the CAS Starfield Observatory Dark Site clear sky chart from 2005-11-05 to 2018-02-13.

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
40%
16016
19%
48537
13%
15973
46%
15973
23%
31973

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
17%
780
13%
2522
6%
776
26%
776
11%
1897
January16th to endNight
17%
832
16%
2704
6%
832
28%
832
13%
1954
February1st to 15thNight
17%
752
12%
2319
4%
750
25%
750
14%
1713
February16th to endNight
15%
631
14%
1893
6%
631
23%
631
14%
1386
March1st to 15thNight
22%
720
17%
2079
9%
720
29%
720
17%
1472
March16th to endNight
28%
768
15%
2112
7%
768
35%
768
21%
1477
April1st to 15thNight
31%
593
19%
1851
11%
593
41%
593
23%
1185
April16th to endNight
36%
540
22%
1641
11%
540
47%
540
25%
1087
May1st to 15thNight
37%
540
15%
1620
9%
540
42%
540
19%
1144
May16th to endNight
55%
562
18%
1684
13%
561
59%
561
30%
1050
June1st to 15thNight
65%
540
19%
1620
17%
540
68%
540
40%
927
June16th to endNight
60%
540
18%
1469
13%
540
65%
540
37%
897
July1st to 15thNight
58%
510
16%
1432
12%
510
61%
510
29%
933
July16th to endNight
72%
564
20%
1595
18%
531
75%
531
36%
920
August1st to 15thNight
69%
539
23%
1609
20%
536
71%
536
35%
958
August16th to endNight
73%
573
26%
1831
25%
573
76%
573
41%
965
September1st to 15thNight
66%
675
26%
1935
22%
675
69%
675
36%
1147
September16th to endNight
58%
717
30%
1980
22%
717
62%
717
36%
1181
October1st to 15thNight
52%
720
29%
2026
23%
720
59%
720
36%
1190
October16th to endNight
36%
768
25%
2370
19%
768
47%
768
25%
1507
November1st to 15thNight
41%
760
27%
2471
21%
760
51%
760
28%
1453
November16th to endNight
32%
780
22%
2535
15%
780
42%
780
21%
1654
December1st to 15thNight
24%
780
13%
2535
8%
780
30%
780
14%
1831
December16th to endNight
18%
832
14%
2704
5%
832
28%
832
12%
2045

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
15%7%35%5%3445%7%37%
49485
Night
15%7%35%424447%39%
48726
Cloud CoverDay
15%7%35%5%3445%7%37%
49495
Night
15%7%35%424447%39%
48730
TransparencyDay
46%410%21%14%2
49192
Night
44%410%21%15%2
48537
SeeingDay
19%9%24%21%14%8%
6009
Night
19%9%24%26%16%2
16018

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
20%10%5%10%5%3444426%
1746
16th to endDay
18%13%5%7%5%33345%30%
1872
February1st to 15thDay
18%11%5%7%5%3344431%
1807
16th to endDay
16%12%47%5%35%45%429%
1580
March1st to 15thDay
24%9%35%423435%32%
1868
16th to endDay
20%9%36%6%33446%32%
2112
April1st to 15thDay
19%7%33323446%39%
2106
16th to endDay
17%6%25%5%2435%7%38%
2318
May1st to 15thDay
23%7%25%425%5%5%6%31%
2331
16th to endDay
11%5%35%6%35%6%6%9%37%
2431
June1st to 15thDay
10%425%5%36%6%6%8%40%
2340
16th to endDay
8%436%5%47%6%6%9%37%
2485
July1st to 15thDay
15%5%25%445%5%6%8%35%
2439
16th to endDay
10%325%6%46%6%6%9%37%
2465
August1st to 15thDay
8%425%5%35%5%7%9%40%
2340
16th to endDay
7%5%245%36%5%7%10%42%
2369
September1st to 15thDay
14%5%13434446%44%
2013
16th to endDay
14%5%24424346%47%
1980
October1st to 15thDay
13%41442335%6%48%
1932
16th to endDay
20%6%25%312336%44%
1852
November1st to 15thDay
13%7%24423345%48%
1717
16th to endDay
17%9%45%313346%40%
1755
December1st to 15thDay
23%11%35%6%2434429%
1755
16th to endDay
21%13%5%7%5%34235%27%
1872
January1st to 15thNight
18%12%5%10%6%3343426%
2522
16th to endNight
19%12%5%7%42333431%
2704
February1st to 15thNight
22%12%46%5%23335%30%
2317
16th to endNight
19%13%46%5%34436%28%
1893
March1st to 15thNight
18%8%47%5%24346%33%
2067
16th to endNight
17%8%36%424447%35%
2112
April1st to 15thNight
14%6%35%5%33447%41%
1851
16th to endNight
15%6%345%3345%7%40%
1641
May1st to 15thNight
17%6%35%5%25%5%6%8%33%
1620
16th to endNight
9%425%425%5%6%11%41%
1682
June1st to 15thNight
5%2134245%7%9%51%
1620
16th to endNight
6%323435%6%8%10%45%
1469
July1st to 15thNight
10%5%3443446%8%44%
1518
16th to endNight
6%4144245%7%9%48%
1703
August1st to 15thNight
6%415%3346%6%8%48%
1620
16th to endNight
5%31332446%10%54%
1831
September1st to 15thNight
12%41322346%7%51%
1935
16th to endNight
11%424423337%51%
1980
October1st to 15thNight
10%41332445%8%50%
2026
16th to endNight
16%6%245%2344444%
2370
November1st to 15thNight
15%5%23423346%48%
2471
16th to endNight
19%8%34423345%39%
2535
December1st to 15thNight
23%10%5%6%423336%29%
2535
16th to endNight
22%14%5%6%5%34435%25%
2704

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
20%10%6%9%5%2344426%
1746
16th to endDay
18%13%5%7%5%33345%30%
1872
February1st to 15thDay
18%11%47%6%24345%30%
1807
16th to endDay
16%12%47%5%35%445%29%
1580
March1st to 15thDay
23%10%35%5%23335%32%
1879
16th to endDay
20%8%36%6%33446%32%
2111
April1st to 15thDay
19%7%34324346%39%
2106
16th to endDay
17%6%25%42435%7%38%
2318
May1st to 15thDay
23%6%35%425%5%5%7%31%
2331
16th to endDay
11%5%26%6%35%5%6%9%37%
2431
June1st to 15thDay
11%325%5%36%6%6%8%40%
2340
16th to endDay
8%435%6%46%6%6%8%37%
2485
July1st to 15thDay
15%5%25%5%35%5%6%8%35%
2439
16th to endDay
10%325%6%36%6%7%10%37%
2465
August1st to 15thDay
8%426%5%35%5%7%10%40%
2340
16th to endDay
8%5%245%26%6%7%10%42%
2369
September1st to 15thDay
14%5%14425%446%44%
2013
16th to endDay
14%5%24423446%47%
1980
October1st to 15thDay
13%414433346%48%
1932
16th to endDay
20%6%24413335%44%
1852
November1st to 15thDay
13%7%24414345%47%
1717
16th to endDay
17%9%45%323345%40%
1755
December1st to 15thDay
23%10%46%5%3434429%
1755
16th to endDay
21%13%5%6%5%24235%27%
1872
January1st to 15thNight
18%11%5%10%6%3343426%
2522
16th to endNight
19%11%5%7%42433431%
2704
February1st to 15thNight
22%11%47%5%2333430%
2310
16th to endNight
19%13%47%5%33446%28%
1893
March1st to 15thNight
18%8%47%5%24345%33%
2079
16th to endNight
17%9%36%5%2435%7%35%
2112
April1st to 15thNight
14%6%25%5%33447%41%
1851
16th to endNight
15%6%35%5%3435%6%41%
1641
May1st to 15thNight
17%6%35%6%245%6%8%33%
1619
16th to endNight
9%5%24435%5%7%11%41%
1682
June1st to 15thNight
5%2143345%7%10%50%
1620
16th to endNight
6%323435%5%8%10%45%
1469
July1st to 15thNight
10%5%25%5%3346%7%44%
1518
16th to endNight
6%3234245%7%9%48%
1703
August1st to 15thNight
6%315%4346%6%9%47%
1620
16th to endNight
6%31332346%10%54%
1831
September1st to 15thNight
12%41322345%7%50%
1935
16th to endNight
11%424323337%51%
1980
October1st to 15thNight
10%41342345%9%49%
2026
16th to endNight
16%6%25%424335%44%
2370
November1st to 15thNight
15%6%13423346%48%
2471
16th to endNight
19%8%34423435%39%
2535
December1st to 15thNight
22%10%5%6%5%23346%29%
2535
16th to endNight
22%14%5%6%434335%25%
2704

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
60%28%16%11%
1747
16th to endDay
56%210%22%6%
1872
February1st to 15thDay
56%210%20%8%1
1809
16th to endDay
56%310%20%8%
1580
March1st to 15thDay
54%311%18%10%1
1879
16th to endDay
53%310%21%9%
2112
April1st to 15thDay
46%38%24%14%2
2106
16th to endDay
44%49%22%14%4
2318
May1st to 15thDay
51%5%12%17%10%1
2331
16th to endDay
41%7%15%22%11%1
2435
June1st to 15thDay
38%6%12%23%16%1
2340
16th to endDay
41%7%12%19%16%3
2485
July1st to 15thDay
45%6%11%16%16%2
2296
16th to endDay
40%7%14%22%13%2
2310
August1st to 15thDay
37%7%12%24%15%1
2327
16th to endDay
35%7%12%23%16%4
2369
September1st to 15thDay
39%5%11%18%19%5%
2013
16th to endDay
38%39%22%23%2
1980
October1st to 15thDay
36%310%25%20%3
1932
16th to endDay
43%29%26%15%2
1852
November1st to 15thDay
39%37%25%19%5%
1717
16th to endDay
46%38%23%17%1
1755
December1st to 15thDay
58%310%16%9%1
1755
16th to endDay
59%49%17%7%
1872
January1st to 15thNight
62%27%14%11%1
2522
16th to endNight
57%29%20%8%1
2704
February1st to 15thNight
58%210%19%7%1
2319
16th to endNight
57%211%19%8%
1893
March1st to 15thNight
52%38%21%11%1
2079
16th to endNight
48%412%22%10%
2112
April1st to 15thNight
42%49%21%19%2
1851
16th to endNight
44%48%21%14%7%
1641
May1st to 15thNight
47%8%10%21%9%2
1620
16th to endNight
35%7%15%20%17%3
1684
June1st to 15thNight
27%6%14%28%18%3
1620
16th to endNight
30%7%17%21%19%3
1469
July1st to 15thNight
39%6%11%20%17%5%
1432
16th to endNight
29%7%14%27%18%2
1595
August1st to 15thNight
31%6%13%25%19%3
1609
16th to endNight
24%6%14%28%21%4
1831
September1st to 15thNight
32%5%12%22%21%6%
1935
16th to endNight
33%38%22%28%2
1980
October1st to 15thNight
31%410%27%20%4
2026
16th to endNight
42%27%25%18%2
2370
November1st to 15thNight
37%28%22%24%5%
2471
16th to endNight
46%39%23%14%1
2535
December1st to 15thNight
56%310%18%9%1
2535
16th to endNight
62%210%16%7%
2704

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
29%21%32%10%5%
135
16th to endDay
33%22%36%6%
144
February1st to 15thDay
27%35%29%6%
126
16th to endDay
30%18%38%12%
81
March1st to 15thDay
33%18%32%14%
169
16th to endDay
25%17%31%18%7%
288
April1st to 15thDay
27%13%25%21%10%2
270
16th to endDay
21%12%31%16%12%5%
270
May1st to 15thDay
31%10%27%14%11%5%
288
16th to endDay
16%7%26%23%13%12%
331
June1st to 15thDay
12%5%20%31%20%10%
315
16th to endDay
13%6%25%28%16%8%
460
July1st to 15thDay
21%5%22%22%17%11%
400
16th to endDay
8%115%29%21%22%
326
August1st to 15thDay
13%112%30%22%20%
313
16th to endDay
11%213%30%24%16%
332
September1st to 15thDay
17%213%25%27%13%
315
16th to endDay
16%420%17%27%14%
314
October1st to 15thDay
14%8%23%26%18%7%
315
16th to endDay
20%8%32%23%13%1
268
November1st to 15thDay
21%12%29%24%8%3
135
16th to endDay
22%14%40%17%41
135
December1st to 15thDay
25%19%35%11%7%
135
16th to endDay
35%25%34%4
144
January1st to 15thNight
27%18%32%17%4
780
16th to endNight
28%18%32%19%1
832
February1st to 15thNight
31%15%30%21%1
753
16th to endNight
29%16%34%18%1
631
March1st to 15thNight
26%15%30%22%4
720
16th to endNight
21%13%30%24%8%
768
April1st to 15thNight
19%13%32%24%8%
593
16th to endNight
18%8%32%26%11%1
540
May1st to 15thNight
20%9%28%26%13%2
540
16th to endNight
12%322%31%23%5%
563
June1st to 15thNight
7%120%42%26%2
540
16th to endNight
7%122%38%27%2
540
July1st to 15thNight
14%116%31%30%4
510
16th to endNight
7%112%32%38%7%
564
August1st to 15thNight
7%12%33%40%5%
539
16th to endNight
6%12%33%40%6%
573
September1st to 15thNight
13%312%31%33%5%
675
16th to endNight
13%5%16%27%31%5%
717
October1st to 15thNight
14%7%20%28%23%4
720
16th to endNight
20%10%27%25%13%1
768
November1st to 15thNight
18%9%26%23%18%2
760
16th to endNight
25%13%25%25%9%
780
December1st to 15thNight
30%14%24%23%6%1
780
16th to endNight
31%17%28%19%3
832
Page generated at 2018-02-13 20:46:08. Version ac04

Copyright 2018 A. Danko


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