Stellafane
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stellafane clear sky chart from 2005-11-05 to 2017-08-12.

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%
14673
16%
46468
8%
14641
40%
14641
18%
31269

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
21%
720
16%
2506
7%
716
33%
716
12%
1722
January16th to endNight
19%
768
15%
2688
5%
768
33%
768
14%
1793
February1st to 15thNight
14%
704
12%
2231
3%
701
26%
701
12%
1603
February16th to endNight
19%
631
17%
1893
5%
631
34%
631
15%
1318
March1st to 15thNight
19%
720
16%
2160
6%
720
31%
720
15%
1495
March16th to endNight
25%
768
20%
2010
6%
768
36%
768
20%
1351
April1st to 15thNight
24%
718
16%
1796
4%
718
31%
718
20%
1277
April16th to endNight
26%
617
17%
1697
5%
617
35%
617
20%
1175
May1st to 15thNight
26%
502
16%
1582
9%
502
33%
502
16%
1110
May16th to endNight
40%
375
12%
1497
11%
374
46%
374
15%
999
June1st to 15thNight
35%
360
11%
1440
9%
360
46%
360
14%
956
June16th to endNight
45%
360
10%
1440
13%
360
51%
360
19%
906
July1st to 15thNight
55%
340
12%
1360
17%
340
59%
340
23%
812
July16th to endNight
55%
376
15%
1418
17%
354
61%
354
25%
826
August1st to 15thNight
53%
432
15%
1481
12%
430
57%
430
25%
896
August16th to endNight
54%
693
18%
1743
10%
693
57%
693
33%
1137
September1st to 15thNight
50%
660
20%
1675
10%
660
54%
660
33%
1087
September16th to endNight
49%
657
24%
1815
16%
657
55%
657
35%
1081
October1st to 15thNight
37%
660
19%
1885
11%
660
45%
660
21%
1298
October16th to endNight
27%
704
13%
2269
6%
704
37%
704
15%
1596
November1st to 15thNight
31%
700
18%
2277
10%
700
42%
700
19%
1497
November16th to endNight
29%
720
17%
2397
10%
720
39%
720
16%
1600
December1st to 15thNight
20%
720
13%
2520
4%
720
31%
720
12%
1782
December16th to endNight
16%
768
13%
2688
4%
768
27%
768
11%
1952

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%6%36%6%35%45%7%35%
47514
Night
15%6%35%5%345%5%6%38%
46638
Cloud CoverDay
16%7%36%5%35%45%7%35%
47524
Night
15%6%25%5%25%45%7%38%
46643
TransparencyDay
47%7%12%19%11%1
47202
Night
44%7%13%21%12%1
46468
SeeingDay
21%14%27%20%11%4
5615
Night
20%14%28%26%9%
14673

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
13%8%36%8%345%7%8%29%
1432
16th to endDay
11%7%36%6%35%46%9%35%
1536
February1st to 15thDay
12%9%5%8%6%47%5%5%7%28%
1629
16th to endDay
13%10%48%6%345%46%32%
1580
March1st to 15thDay
17%9%47%5%345%5%6%30%
1790
16th to endDay
14%7%47%6%2335%6%38%
2211
April1st to 15thDay
17%7%36%5%43446%36%
2152
16th to endDay
17%6%35%5%245%46%37%
2262
May1st to 15thDay
22%7%35%6%2445%5%31%
2379
16th to endDay
18%6%35%5%3445%7%36%
2618
June1st to 15thDay
23%6%345%3445%6%30%
2520
16th to endDay
16%6%36%6%46%6%5%7%32%
2520
July1st to 15thDay
12%5%35%7%46%5%6%9%34%
2520
16th to endDay
12%425%6%36%5%6%8%37%
2654
August1st to 15thDay
12%426%6%45%6%6%8%35%
2372
16th to endDay
10%435%6%35%46%8%41%
2105
September1st to 15thDay
14%425%5%3435%8%41%
1955
16th to endDay
13%424424336%51%
1815
October1st to 15thDay
20%7%35%5%24345%37%
1744
16th to endDay
18%7%37%5%3445%7%32%
1603
November1st to 15thDay
14%6%26%42445%7%40%
1581
16th to endDay
17%7%36%32445%6%38%
1560
December1st to 15thDay
17%9%37%6%34346%32%
1440
16th to endDay
19%13%46%6%35%44426%
1536
January1st to 15thNight
12%8%27%6%35%6%5%6%34%
2506
16th to endNight
13%7%47%5%35%5%6%7%35%
2688
February1st to 15thNight
11%9%37%8%36%6%6%7%29%
2230
16th to endNight
13%8%36%6%35%6%6%7%33%
1893
March1st to 15thNight
17%7%26%5%345%5%6%35%
2147
16th to endNight
13%6%34425%45%6%41%
2010
April1st to 15thNight
17%6%35%4246%5%6%37%
1796
16th to endNight
18%5%25%5%33346%40%
1697
May1st to 15thNight
20%6%36%6%25%345%35%
1582
16th to endNight
17%5%25%6%3345%8%36%
1495
June1st to 15thNight
22%5%25%41436%6%35%
1440
16th to endNight
14%424425%6%6%7%40%
1440
July1st to 15thNight
11%3235%36%6%5%9%42%
1440
16th to endNight
11%4235%245%6%10%43%
1514
August1st to 15thNight
9%5%24435%5%5%8%45%
1491
16th to endNight
11%5%23325%45%9%46%
1743
September1st to 15thNight
13%41332445%7%49%
1675
16th to endNight
12%414323336%53%
1815
October1st to 15thNight
19%6%25%5%24345%40%
1885
16th to endNight
18%6%35%5%35%5%6%5%34%
2269
November1st to 15thNight
13%7%36%6%34446%40%
2277
16th to endNight
16%7%35%5%35%445%39%
2397
December1st to 15thNight
19%7%36%5%35%45%6%32%
2520
16th to endNight
19%9%36%6%25%45%6%28%
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
13%8%36%7%445%6%8%30%
1432
16th to endDay
11%7%46%5%35%45%9%36%
1536
February1st to 15thDay
11%10%5%8%7%37%45%7%28%
1629
16th to endDay
13%9%5%7%6%34446%32%
1580
March1st to 15thDay
17%9%5%7%5%35%45%6%30%
1800
16th to endDay
13%8%46%5%34346%38%
2211
April1st to 15thDay
17%7%36%6%34446%36%
2152
16th to endDay
17%6%26%5%2445%6%37%
2262
May1st to 15thDay
23%8%36%5%33446%31%
2379
16th to endDay
18%6%25%5%25%447%36%
2618
June1st to 15thDay
23%6%35%5%4445%6%30%
2520
16th to endDay
16%5%26%6%46%5%6%6%32%
2520
July1st to 15thDay
12%425%6%37%6%5%9%34%
2520
16th to endDay
12%5%25%6%36%6%6%7%37%
2654
August1st to 15thDay
12%5%26%6%36%6%6%8%35%
2372
16th to endDay
11%435%6%2446%9%41%
2105
September1st to 15thDay
13%5%25%5%25%45%8%41%
1955
16th to endDay
13%414433236%50%
1815
October1st to 15thDay
20%6%26%5%24345%37%
1744
16th to endDay
18%7%36%5%45%447%32%
1603
November1st to 15thDay
15%7%26%424447%40%
1581
16th to endDay
17%6%46%42445%6%38%
1560
December1st to 15thDay
18%9%47%5%44345%32%
1440
16th to endDay
20%13%46%6%26%45%426%
1536
January1st to 15thNight
12%8%36%6%35%5%6%6%34%
2506
16th to endNight
13%7%46%5%25%5%5%7%35%
2688
February1st to 15thNight
11%9%37%7%36%6%6%7%30%
2223
16th to endNight
13%8%36%5%36%5%6%8%33%
1893
March1st to 15thNight
17%7%36%5%3445%6%36%
2160
16th to endNight
13%7%24435%45%6%41%
2009
April1st to 15thNight
17%6%35%4245%6%7%37%
1796
16th to endNight
19%5%245%23346%40%
1697
May1st to 15thNight
20%6%36%5%35%345%35%
1582
16th to endNight
17%6%25%6%3445%8%36%
1495
June1st to 15thNight
23%5%25%42445%7%35%
1440
16th to endNight
13%425%425%6%6%8%40%
1440
July1st to 15thNight
11%314436%6%6%8%42%
1440
16th to endNight
12%4144246%6%10%43%
1514
August1st to 15thNight
9%5%246%25%45%8%45%
1491
16th to endNight
11%5%243245%48%47%
1743
September1st to 15thNight
14%41331445%7%48%
1675
16th to endNight
12%413223346%53%
1815
October1st to 15thNight
19%7%245%24345%40%
1885
16th to endNight
18%6%35%425%6%5%6%34%
2269
November1st to 15thNight
14%7%26%6%34436%40%
2277
16th to endNight
16%7%345%35%445%39%
2397
December1st to 15thNight
19%7%35%5%25%45%6%32%
2520
16th to endNight
20%10%36%5%2445%6%28%
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
49%7%12%20%9%1
1433
16th to endDay
44%7%16%21%9%1
1536
February1st to 15thDay
55%7%12%16%8%
1632
16th to endDay
52%5%10%16%12%2
1580
March1st to 15thDay
53%6%11%14%10%2
1800
16th to endDay
47%5%10%18%14%4
2211
April1st to 15thDay
49%6%10%19%12%2
2152
16th to endDay
46%6%9%19%14%3
2262
May1st to 15thDay
54%5%7%18%12%1
2379
16th to endDay
47%7%12%18%11%1
2622
June1st to 15thDay
52%6%13%16%9%
2520
16th to endDay
49%9%13%15%11%
2520
July1st to 15thDay
44%9%12%19%12%
2371
16th to endDay
42%7%16%22%10%
2487
August1st to 15thDay
43%9%15%22%8%1
2358
16th to endDay
38%7%16%24%11%1
2105
September1st to 15thDay
41%7%12%23%15%
1955
16th to endDay
35%411%27%19%1
1815
October1st to 15thDay
49%6%8%22%10%2
1744
16th to endDay
51%6%14%18%8%1
1603
November1st to 15thDay
43%8%14%20%12%1
1581
16th to endDay
46%5%14%18%12%1
1560
December1st to 15thDay
53%6%13%16%9%
1440
16th to endDay
60%6%12%12%8%
1536
January1st to 15thNight
47%8%12%18%10%1
2506
16th to endNight
46%6%12%19%12%1
2688
February1st to 15thNight
50%8%14%16%9%
2231
16th to endNight
47%6%12%21%9%2
1893
March1st to 15thNight
48%5%12%20%10%2
2160
16th to endNight
41%5%13%17%17%4
2010
April1st to 15thNight
44%6%12%19%15%1
1796
16th to endNight
45%6%9%19%16%2
1697
May1st to 15thNight
51%48%17%15%2
1582
16th to endNight
46%8%13%19%10%1
1497
June1st to 15thNight
48%6%14%21%8%
1440
16th to endNight
40%10%15%22%11%
1440
July1st to 15thNight
35%10%15%26%11%
1360
16th to endNight
34%8%15%27%11%1
1418
August1st to 15thNight
35%9%15%25%13%1
1481
16th to endNight
34%8%14%29%13%
1743
September1st to 15thNight
34%8%13%28%15%
1675
16th to endNight
31%5%11%30%20%1
1815
October1st to 15thNight
45%5%12%20%12%2
1885
16th to endNight
48%8%13%21%8%
2269
November1st to 15thNight
44%5%14%18%14%1
2277
16th to endNight
46%6%14%21%10%2
2397
December1st to 15thNight
51%7%14%19%6%
2520
16th to endNight
54%6%13%16%7%
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
25%23%25%21%5%
60
16th to endDay
26%21%31%15%4
64
February1st to 15thDay
22%28%26%17%4
163
16th to endDay
21%20%32%20%4
239
March1st to 15thDay
29%17%31%18%3
270
16th to endDay
24%22%27%13%8%3
288
April1st to 15thDay
28%19%26%14%9%1
270
16th to endDay
24%14%28%18%9%4
270
May1st to 15thDay
31%17%23%15%7%3
288
16th to endDay
19%13%32%25%7%1
331
June1st to 15thDay
25%14%29%19%10%1
315
16th to endDay
16%14%33%20%12%2
315
July1st to 15thDay
16%7%32%24%15%3
305
16th to endDay
12%5%36%27%14%3
326
August1st to 15thDay
12%11%27%23%17%7%
297
16th to endDay
13%5%20%26%19%14%
268
September1st to 15thDay
16%6%20%22%22%11%
255
16th to endDay
15%9%25%19%13%16%
254
October1st to 15thDay
24%12%18%23%15%5%
255
16th to endDay
23%16%25%24%9%
243
November1st to 15thDay
21%13%22%29%11%1
235
16th to endDay
25%19%27%15%10%2
180
December1st to 15thDay
23%30%23%18%5%
60
16th to endDay
37%20%31%10%
64
January1st to 15thNight
20%20%32%23%2
720
16th to endNight
21%17%36%22%2
768
February1st to 15thNight
18%19%38%21%1
704
16th to endNight
21%22%32%22%2
631
March1st to 15thNight
25%19%31%21%1
720
16th to endNight
21%19%29%21%7%
768
April1st to 15thNight
22%20%29%22%5%
718
16th to endNight
23%16%30%21%8%
617
May1st to 15thNight
23%13%30%26%6%
502
16th to endNight
18%8%27%30%13%1
375
June1st to 15thNight
24%9%24%30%11%
360
16th to endNight
13%430%41%10%
360
July1st to 15thNight
12%5%21%43%15%1
340
16th to endNight
12%224%37%21%1
376
August1st to 15thNight
11%324%42%16%1
432
16th to endNight
14%5%20%33%23%3
693
September1st to 15thNight
14%6%24%33%20%1
660
16th to endNight
15%7%22%28%20%4
657
October1st to 15thNight
25%13%18%28%12%1
660
16th to endNight
23%16%27%25%6%
704
November1st to 15thNight
18%15%26%28%10%1
700
16th to endNight
22%16%27%22%9%1
720
December1st to 15thNight
24%18%32%19%4
720
16th to endNight
27%19%33%18%1
768
Page generated at 2017-08-13 14:16:19. Version ac04

Copyright 2017 A. Danko


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