STAR
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the STAR clear sky chart from 2005-11-05 to 2017-10-31.

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
60%
16073
21%
47459
16%
16032
65%
16032
30%
29933

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
46%
719
19%
2327
15%
716
54%
716
24%
1458
January16th to endNight
44%
768
24%
2403
18%
768
53%
768
29%
1461
February1st to 15thNight
47%
701
24%
2104
17%
699
55%
699
34%
1244
February16th to endNight
47%
631
24%
1853
15%
631
56%
631
34%
1091
March1st to 15thNight
50%
720
30%
1980
17%
720
61%
720
40%
1127
March16th to endNight
54%
768
26%
2112
19%
768
59%
768
40%
1222
April1st to 15thNight
58%
718
23%
1976
18%
718
62%
718
43%
1105
April16th to endNight
59%
720
27%
1875
18%
720
64%
720
40%
1102
May1st to 15thNight
73%
540
28%
1620
22%
540
77%
540
44%
873
May16th to endNight
76%
561
24%
1683
20%
561
78%
561
37%
1000
June1st to 15thNight
70%
540
11%
1620
11%
540
70%
540
23%
1132
June16th to endNight
73%
540
7%
1620
7%
540
73%
540
23%
1161
July1st to 15thNight
76%
510
5%
1530
5%
510
76%
510
21%
1155
July16th to endNight
75%
564
6%
1595
6%
531
76%
531
19%
1185
August1st to 15thNight
79%
539
5%
1658
5%
536
79%
536
23%
1167
August16th to endNight
67%
701
8%
2038
8%
701
67%
701
19%
1504
September1st to 15thNight
64%
720
7%
1980
7%
720
64%
720
18%
1490
September16th to endNight
65%
717
14%
1980
14%
717
66%
717
20%
1442
October1st to 15thNight
69%
720
25%
2020
24%
720
71%
720
32%
1262
October16th to endNight
56%
768
28%
2303
25%
768
63%
768
34%
1363
November1st to 15thNight
62%
700
31%
2101
25%
700
69%
700
39%
1160
November16th to endNight
52%
720
29%
2245
22%
720
61%
720
33%
1325
December1st to 15thNight
50%
720
25%
2340
21%
720
58%
720
28%
1415
December16th to endNight
55%
768
24%
2496
24%
768
60%
768
29%
1489

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
8%5%26%6%46%6%6%8%36%
48271
Night
7%425%5%35%5%6%9%44%
47666
TransparencyDay
41%9%13%15%13%5%
47972
Night
34%9%16%19%15%5%
47469
SeeingDay
9%313%22%25%26%
5933
Night
9%218%33%27%9%
16080

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
11%5%25%435%46%10%39%
1611
16th to endDay
10%5%344245%5%7%46%
1818
February1st to 15thDay
12%5%244145%5%6%46%
1750
16th to endDay
7%5%25%42445%8%49%
1619
March1st to 15thDay
5%3134246%5%7%52%
1980
16th to endDay
8%424435%5%5%7%48%
2111
April1st to 15thDay
7%315%5%36%5%6%9%45%
1972
16th to endDay
5%5%245%35%5%6%8%47%
2090
May1st to 15thDay
5%324435%6%6%8%49%
2331
16th to endDay
6%436%7%6%7%7%7%9%34%
2431
June1st to 15thDay
12%7%37%7%5%7%7%8%10%23%
2340
16th to endDay
8%6%48%9%5%8%7%9%9%22%
2340
July1st to 15thDay
9%6%39%10%6%9%8%7%9%20%
2340
16th to endDay
8%7%39%10%5%9%8%7%10%19%
2465
August1st to 15thDay
6%6%37%11%6%8%9%8%10%20%
2286
16th to endDay
10%7%39%9%48%7%7%9%22%
2151
September1st to 15thDay
9%7%38%8%48%8%8%9%22%
1980
16th to endDay
10%8%37%8%47%7%7%9%24%
1980
October1st to 15thDay
6%6%26%8%47%6%6%7%36%
1938
16th to endDay
9%5%25%5%35%45%7%47%
1920
November1st to 15thDay
6%325%425%45%7%51%
1757
16th to endDay
8%4245%245%6%7%47%
1713
December1st to 15thDay
10%6%25%5%245%6%8%42%
1620
16th to endDay
8%5%24425%6%5%9%45%
1728
January1st to 15thNight
9%6%36%5%35%45%8%41%
2327
16th to endNight
12%5%245%245%5%7%43%
2403
February1st to 15thNight
11%6%2432445%7%49%
2103
16th to endNight
8%435%43335%7%50%
1853
March1st to 15thNight
5%224433448%55%
1980
16th to endNight
6%3134245%5%7%54%
2112
April1st to 15thNight
5%21432346%10%54%
1976
16th to endNight
6%414324448%54%
1875
May1st to 15thNight
431243346%8%57%
1620
16th to endNight
5%314435%45%9%51%
1682
June1st to 15thNight
9%7%35%5%35%6%8%11%33%
1620
16th to endNight
6%426%7%36%7%8%14%32%
1620
July1st to 15thNight
5%5%35%5%48%8%8%12%31%
1620
16th to endNight
45%36%7%48%7%11%12%28%
1703
August1st to 15thNight
35%16%7%46%9%8%11%34%
1669
16th to endNight
8%437%7%36%7%8%13%30%
2038
September1st to 15thNight
7%6%26%8%5%5%8%8%12%27%
1980
16th to endNight
7%7%37%6%46%6%7%10%31%
1980
October1st to 15thNight
5%425%5%345%6%8%47%
2020
16th to endNight
8%5%25%42335%7%50%
2303
November1st to 15thNight
5%313435%447%54%
2101
16th to endNight
7%425%5%245%5%8%48%
2245
December1st to 15thNight
10%425%5%3435%8%46%
2340
16th to endNight
7%425%436%5%5%8%46%
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
39%7%9%19%18%5%
1612
16th to endDay
35%49%17%24%8%
1818
February1st to 15thDay
36%5%7%15%21%14%
1752
16th to endDay
32%6%11%15%23%10%
1619
March1st to 15thDay
28%6%10%23%21%9%
1980
16th to endDay
32%5%11%20%20%9%
2112
April1st to 15thDay
32%8%12%18%20%7%
1972
16th to endDay
32%6%10%18%23%7%
2090
May1st to 15thDay
29%7%11%22%19%8%
2331
16th to endDay
41%10%12%18%14%2
2435
June1st to 15thDay
52%10%16%16%3
2340
16th to endDay
52%13%19%12%2
2340
July1st to 15thDay
56%15%20%6%1
2201
16th to endDay
54%15%19%9%1
2310
August1st to 15thDay
52%16%23%7%
2273
16th to endDay
54%14%18%10%
2151
September1st to 15thDay
52%16%18%9%2
1980
16th to endDay
51%12%14%12%7%1
1980
October1st to 15thDay
42%8%9%15%14%8%
1938
16th to endDay
36%6%8%14%20%13%
1920
November1st to 15thDay
30%5%8%22%23%10%
1757
16th to endDay
35%6%8%18%17%13%
1713
December1st to 15thDay
39%7%9%20%16%6%
1620
16th to endDay
34%6%12%19%20%7%
1728
January1st to 15thNight
40%5%11%20%16%5%
2327
16th to endNight
38%310%18%19%8%
2403
February1st to 15thNight
33%48%17%22%13%
2112
16th to endNight
32%5%14%17%22%7%
1853
March1st to 15thNight
27%5%10%27%20%7%
1980
16th to endNight
27%5%12%24%21%8%
2112
April1st to 15thNight
25%5%17%23%21%6%
1976
16th to endNight
28%6%12%24%22%6%
1875
May1st to 15thNight
23%5%14%27%20%7%
1621
16th to endNight
28%9%18%24%17%2
1684
June1st to 15thNight
41%12%21%18%6%
1620
16th to endNight
39%15%25%15%4
1620
July1st to 15thNight
41%18%30%8%1
1530
16th to endNight
40%19%28%11%
1595
August1st to 15thNight
35%18%35%10%
1658
16th to endNight
42%17%24%13%1
2038
September1st to 15thNight
44%16%23%13%2
1980
16th to endNight
44%13%18%16%42
1980
October1st to 15thNight
32%9%12%20%19%6%
2020
16th to endNight
33%49%16%24%11%
2303
November1st to 15thNight
28%411%21%23%9%
2101
16th to endNight
33%5%9%20%17%12%
2245
December1st to 15thNight
36%6%11%23%16%5%
2340
16th to endNight
33%7%12%20%17%7%
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
13%15%31%23%15%1
90
16th to endDay
14%16%30%25%11%2
96
February1st to 15thDay
14%13%24%24%16%6%
90
16th to endDay
11%6%38%29%14%
120
March1st to 15thDay
46%32%35%18%2
270
16th to endDay
11%5%20%31%26%4
288
April1st to 15thDay
6%422%31%27%7%
270
16th to endDay
8%415%27%31%12%
270
May1st to 15thDay
6%213%26%32%17%
288
16th to endDay
6%19%20%29%33%
331
June1st to 15thDay
16%25%12%25%37%
315
16th to endDay
6%29%27%53%
315
July1st to 15thDay
6%6%19%67%
305
16th to endDay
10%2212%20%50%
326
August1st to 15thDay
8%210%21%55%
313
16th to endDay
11%15%11%23%47%
332
September1st to 15thDay
14%1417%23%39%
315
16th to endDay
9%318%33%34%
314
October1st to 15thDay
6%112%32%34%12%
315
16th to endDay
11%223%30%23%8%
336
November1st to 15thDay
9%116%33%29%9%
265
16th to endDay
6%230%33%21%4
183
December1st to 15thDay
8%5%36%33%15%
90
16th to endDay
5%8%12%47%22%3
96
January1st to 15thNight
11%7%25%38%16%
720
16th to endNight
14%6%28%35%13%
768
February1st to 15thNight
14%430%35%13%
704
16th to endNight
9%5%30%43%10%
631
March1st to 15thNight
5%434%42%12%
720
16th to endNight
7%428%41%17%
768
April1st to 15thNight
6%326%44%19%
718
16th to endNight
8%323%44%20%
720
May1st to 15thNight
5%16%44%29%3
541
16th to endNight
5%110%40%35%6%
563
June1st to 15thNight
10%15%23%44%15%
540
16th to endNight
5%315%41%32%
540
July1st to 15thNight
8%18%46%34%
510
16th to endNight
5%29%42%39%
564
August1st to 15thNight
417%47%38%
539
16th to endNight
11%415%38%28%
701
September1st to 15thNight
10%7%22%40%18%
720
16th to endNight
11%6%28%39%13%
717
October1st to 15thNight
7%111%41%33%5%
720
16th to endNight
11%121%34%28%1
768
November1st to 15thNight
6%222%42%22%3
700
16th to endNight
8%327%42%17%1
720
December1st to 15thNight
11%426%36%21%
720
16th to endNight
8%323%42%20%1
768
Page generated at 2017-11-01 17:23:31. Version ac04

Copyright 2017 A. Danko


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