Starflower Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starflower Observatory clear sky chart from 2005-11-05 to 2017-10-16.

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
31%
14771
14%
47191
9%
14740
38%
14740
18%
32883

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
16%
720
7%
2506
4%
716
21%
716
8%
1999
January16th to endNight
21%
768
12%
2631
7%
768
29%
768
12%
1927
February1st to 15thNight
19%
703
11%
2287
5%
701
27%
701
12%
1714
February16th to endNight
23%
631
14%
1958
6%
631
34%
631
14%
1433
March1st to 15thNight
22%
720
13%
2089
7%
720
29%
720
16%
1549
March16th to endNight
31%
768
19%
2041
10%
768
39%
768
23%
1378
April1st to 15thNight
23%
718
16%
1796
6%
718
28%
718
20%
1304
April16th to endNight
31%
643
18%
1723
9%
643
37%
643
23%
1191
May1st to 15thNight
35%
360
17%
1440
17%
360
44%
360
18%
924
May16th to endNight
36%
375
14%
1497
11%
374
49%
374
20%
939
June1st to 15thNight
39%
360
10%
1440
9%
360
48%
360
17%
929
June16th to endNight
45%
360
9%
1440
12%
360
50%
360
20%
882
July1st to 15thNight
52%
340
15%
1360
21%
340
59%
340
29%
727
July16th to endNight
56%
376
15%
1418
18%
354
60%
354
28%
775
August1st to 15thNight
56%
454
16%
1525
14%
452
61%
452
28%
907
August16th to endNight
53%
702
21%
1848
11%
702
57%
702
38%
1127
September1st to 15thNight
48%
720
16%
1800
9%
720
50%
720
31%
1211
September16th to endNight
50%
717
24%
1961
16%
717
55%
717
33%
1234
October1st to 15thNight
36%
720
18%
2160
12%
720
45%
720
22%
1458
October16th to endNight
25%
708
12%
2203
6%
708
33%
708
14%
1649
November1st to 15thNight
29%
700
17%
2340
13%
700
37%
700
17%
1616
November16th to endNight
20%
720
11%
2520
7%
720
27%
720
10%
1904
December1st to 15thNight
18%
720
8%
2520
4%
720
24%
720
9%
1974
December16th to endNight
15%
768
10%
2688
4%
768
22%
768
9%
2132

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
17%8%36%5%3445%6%33%
48240
Night
17%9%46%5%34446%32%
47360
Cloud CoverDay
21%7%35%5%34446%33%
48249
Night
20%8%36%5%34445%34%
47366
TransparencyDay
50%312%21%10%1
47927
Night
52%311%21%10%1
47191
SeeingDay
21%10%27%23%12%4
5578
Night
22%9%27%28%11%
14772

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%13%5%9%7%35%345%20%
1432
16th to endDay
14%15%48%8%43446%23%
1591
February1st to 15thDay
13%13%6%12%6%445%4423%
1575
16th to endDay
18%12%48%6%3444427%
1515
March1st to 15thDay
18%10%5%6%8%45%5%4427%
1859
16th to endDay
15%8%35%5%34345%40%
2182
April1st to 15thDay
23%9%36%423245%34%
2152
16th to endDay
21%7%25%42344437%
2247
May1st to 15thDay
19%7%36%5%34446%33%
2511
16th to endDay
17%6%25%6%345%5%6%36%
2618
June1st to 15thDay
20%6%345%35%5%5%8%30%
2520
16th to endDay
17%6%25%5%36%6%6%7%32%
2520
July1st to 15thDay
12%4345%36%6%6%9%38%
2520
16th to endDay
11%5%25%5%36%5%7%9%38%
2654
August1st to 15thDay
10%5%26%6%46%5%6%7%38%
2424
16th to endDay
11%5%245%35%5%6%9%40%
2342
September1st to 15thDay
15%5%24435%447%41%
2160
16th to endDay
13%6%1442345%7%45%
1997
October1st to 15thDay
20%6%36%424446%33%
1800
16th to endDay
26%9%36%6%34335%25%
1690
November1st to 15thDay
15%8%5%5%5%45%5%5%6%33%
1515
16th to endDay
23%11%5%8%5%34345%23%
1440
December1st to 15thDay
20%15%5%9%8%35%5%45%16%
1440
16th to endDay
24%14%5%9%6%2433421%
1536
January1st to 15thNight
18%15%6%11%7%34445%18%
2506
16th to endNight
13%16%6%7%6%35%345%26%
2631
February1st to 15thNight
13%13%6%10%8%35%445%23%
2285
16th to endNight
17%11%48%7%3445%428%
1958
March1st to 15thNight
17%11%6%7%7%24335%30%
2076
16th to endNight
15%6%45%5%25%34441%
2041
April1st to 15thNight
22%8%345%24335%34%
1796
16th to endNight
18%8%36%5%23345%37%
1723
May1st to 15thNight
22%6%25%414346%36%
1440
16th to endNight
15%6%26%5%34447%38%
1495
June1st to 15thNight
18%5%27%6%2446%8%34%
1440
16th to endNight
16%5%245%245%7%7%37%
1440
July1st to 15thNight
10%314425%5%5%10%46%
1440
16th to endNight
9%5%135%245%7%8%45%
1514
August1st to 15thNight
9%5%36%43446%10%42%
1535
16th to endNight
9%32442445%8%49%
1848
September1st to 15thNight
14%5%25%5%34446%43%
1800
16th to endNight
16%424423345%49%
1961
October1st to 15thNight
18%6%345%24446%37%
2160
16th to endNight
24%10%36%5%34445%25%
2203
November1st to 15thNight
19%9%46%5%24346%32%
2340
16th to endNight
23%10%5%8%6%34445%23%
2520
December1st to 15thNight
22%15%5%7%6%35%5%45%19%
2520
16th to endNight
24%15%5%8%6%2433419%
2688

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%14%49%8%34245%21%
1432
16th to endDay
14%15%48%8%44445%24%
1591
February1st to 15thDay
15%12%5%11%7%45%44324%
1575
16th to endDay
18%12%47%6%26%44427%
1515
March1st to 15thDay
26%9%35%6%2433331%
1869
16th to endDay
24%7%3432333439%
2181
April1st to 15thDay
26%8%35%413245%33%
2152
16th to endDay
25%7%145%23335%36%
2247
May1st to 15thDay
29%6%25%5%33245%31%
2511
16th to endDay
27%4245%34345%34%
2618
June1st to 15thDay
25%5%34435%446%32%
2520
16th to endDay
21%5%25%5%35%5%5%6%33%
2520
July1st to 15thDay
13%425%5%35%5%6%9%39%
2520
16th to endDay
11%5%25%436%5%7%9%38%
2654
August1st to 15thDay
22%324425%45%6%37%
2424
16th to endDay
21%414324446%40%
2342
September1st to 15thDay
16%5%245%3345%6%42%
2160
16th to endDay
14%5%23433447%45%
1997
October1st to 15thDay
20%7%346%34445%34%
1800
16th to endDay
26%9%36%6%34435%26%
1690
November1st to 15thDay
19%7%35%5%3435%6%33%
1515
16th to endDay
24%11%47%5%35%335%25%
1440
December1st to 15thDay
21%14%48%7%36%45%5%18%
1440
16th to endDay
23%15%5%8%5%2433422%
1536
January1st to 15thNight
18%14%5%11%8%35%445%19%
2506
16th to endNight
14%16%5%8%6%34345%27%
2631
February1st to 15thNight
14%13%5%10%6%35%445%26%
2278
16th to endNight
18%11%38%6%3435%6%29%
1958
March1st to 15thNight
29%8%36%423225%32%
2089
16th to endNight
25%5%25%42423342%
2041
April1st to 15thNight
25%8%25%423335%35%
1796
16th to endNight
20%7%25%434346%37%
1723
May1st to 15thNight
27%6%23423435%35%
1440
16th to endNight
21%4345%23446%37%
1495
June1st to 15thNight
20%426%5%245%5%7%34%
1440
16th to endNight
18%5%15%425%5%47%38%
1440
July1st to 15thNight
11%2234345%6%9%46%
1440
16th to endNight
9%4245%345%6%8%46%
1514
August1st to 15thNight
14%425%324448%46%
1535
16th to endNight
16%313323345%50%
1848
September1st to 15thNight
15%425%434445%43%
1800
16th to endNight
16%414423435%49%
1961
October1st to 15thNight
19%6%3442445%6%37%
2160
16th to endNight
25%10%26%6%43445%27%
2203
November1st to 15thNight
24%8%25%5%3433434%
2340
16th to endNight
26%10%37%433345%27%
2520
December1st to 15thNight
24%14%46%5%35%5%45%21%
2520
16th to endNight
25%14%5%7%6%3333421%
2688

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
65%29%14%6%
1433
16th to endDay
61%211%15%8%
1591
February1st to 15thDay
62%311%17%4
1577
16th to endDay
58%310%16%9%1
1515
March1st to 15thDay
58%311%17%7%1
1869
16th to endDay
45%29%20%16%6%
2182
April1st to 15thDay
53%17%20%14%2
2152
16th to endDay
49%26%20%17%3
2247
May1st to 15thDay
51%27%21%14%2
2511
16th to endDay
47%411%21%12%2
2622
June1st to 15thDay
51%410%22%9%
2520
16th to endDay
47%313%22%11%1
2520
July1st to 15thDay
38%414%29%12%
2371
16th to endDay
40%5%16%27%10%
2487
August1st to 15thDay
41%418%23%11%
2410
16th to endDay
38%415%30%11%
2342
September1st to 15thDay
41%312%29%11%
2160
16th to endDay
37%413%34%9%
1997
October1st to 15thDay
50%312%23%9%
1800
16th to endDay
61%312%15%6%
1690
November1st to 15thDay
49%414%22%8%
1515
16th to endDay
62%312%13%6%1
1440
December1st to 15thDay
68%411%13%2
1440
16th to endDay
66%311%12%5%
1536
January1st to 15thNight
67%49%12%5%
2506
16th to endNight
59%39%18%8%
2631
February1st to 15thNight
61%311%17%5%
2287
16th to endNight
57%210%19%9%
1958
March1st to 15thNight
57%29%20%8%
2089
16th to endNight
46%29%20%16%4
2041
April1st to 15thNight
52%27%20%16%1
1796
16th to endNight
48%26%20%17%3
1723
May1st to 15thNight
49%27%20%15%4
1440
16th to endNight
45%411%22%14%2
1497
June1st to 15thNight
47%412%23%10%1
1440
16th to endNight
43%5%12%22%15%
1440
July1st to 15thNight
32%5%12%32%15%1
1360
16th to endNight
34%415%29%15%
1418
August1st to 15thNight
37%419%25%12%1
1525
16th to endNight
33%315%34%12%
1848
September1st to 15thNight
41%411%30%11%1
1800
16th to endNight
37%310%36%11%
1961
October1st to 15thNight
47%310%25%12%
2160
16th to endNight
59%312%17%6%
2203
November1st to 15thNight
52%313%19%10%
2340
16th to endNight
61%411%17%5%
2520
December1st to 15thNight
65%312%14%3
2520
16th to endNight
68%29%13%5%
2688

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
28%26%21%20%11
60
16th to endDay
27%17%31%19%4
73
February1st to 15thDay
28%24%28%17%
90
16th to endDay
33%18%25%15%6%
174
March1st to 15thDay
25%13%30%26%4
270
16th to endDay
23%15%29%19%9%2
288
April1st to 15thDay
27%18%27%18%6%1
270
16th to endDay
25%13%27%17%12%3
270
May1st to 15thDay
28%9%30%18%8%4
288
16th to endDay
20%11%32%22%11%1
331
June1st to 15thDay
24%7%31%23%10%2
315
16th to endDay
16%8%32%26%13%2
315
July1st to 15thDay
14%428%30%14%6%
305
16th to endDay
13%328%26%21%6%
326
August1st to 15thDay
12%322%35%17%8%
313
16th to endDay
13%325%26%18%12%
332
September1st to 15thDay
19%6%19%18%23%12%
315
16th to endDay
14%6%23%22%21%10%
314
October1st to 15thDay
21%9%26%24%14%3
315
16th to endDay
31%14%23%21%8%
261
November1st to 15thDay
18%11%28%26%13%1
169
16th to endDay
33%13%31%15%6%
60
December1st to 15thDay
26%11%40%18%3
60
16th to endDay
37%18%37%41
64
January1st to 15thNight
25%14%32%21%5%
720
16th to endNight
22%12%30%27%6%
768
February1st to 15thNight
20%13%36%23%5%
704
16th to endNight
24%14%29%25%5%
631
March1st to 15thNight
25%12%31%27%3
720
16th to endNight
20%14%25%28%10%
768
April1st to 15thNight
27%12%28%24%5%
718
16th to endNight
23%11%28%27%8%
643
May1st to 15thNight
25%6%25%30%10%1
360
16th to endNight
18%5%33%28%13%
375
June1st to 15thNight
19%5%27%34%13%
360
16th to endNight
18%323%39%13%1
360
July1st to 15thNight
10%125%43%17%1
340
16th to endNight
10%321%45%17%2
376
August1st to 15thNight
13%218%40%23%1
454
16th to endNight
10%420%38%23%2
702
September1st to 15thNight
17%423%30%20%2
720
16th to endNight
17%5%22%27%24%3
717
October1st to 15thNight
23%8%23%29%13%1
720
16th to endNight
30%11%24%26%7%
708
November1st to 15thNight
25%8%27%24%12%
700
16th to endNight
30%13%25%20%9%
720
December1st to 15thNight
30%13%29%22%4
720
16th to endNight
33%11%28%19%41
768
Page generated at 2017-10-17 16:35:17. Version ac04

Copyright 2017 A. Danko


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