SRAF
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the SRAF clear sky chart from 2005-11-05 to 2017-09-20.

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
58%
14785
19%
46860
17%
14760
61%
14760
28%
29153

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
43%
716
7%
2506
8%
716
45%
716
11%
1957
January16th to endNight
49%
768
8%
2688
8%
768
50%
768
15%
1992
February1st to 15thNight
48%
697
8%
2254
8%
696
51%
696
17%
1627
February16th to endNight
44%
632
12%
1895
12%
632
46%
632
17%
1388
March1st to 15thNight
45%
720
10%
2157
8%
720
48%
720
18%
1567
March16th to endNight
42%
768
15%
2036
10%
768
46%
768
23%
1439
April1st to 15thNight
50%
719
18%
1799
9%
719
53%
719
29%
1212
April16th to endNight
53%
576
24%
1656
16%
576
57%
576
35%
974
May1st to 15thNight
57%
536
22%
1616
17%
536
62%
536
39%
883
May16th to endNight
63%
374
18%
1496
24%
374
67%
374
25%
825
June1st to 15thNight
60%
360
16%
1440
21%
360
66%
360
26%
789
June16th to endNight
71%
360
25%
1440
36%
360
77%
360
44%
613
July1st to 15thNight
80%
340
23%
1360
35%
340
85%
340
55%
522
July16th to endNight
80%
376
33%
1416
44%
354
84%
354
58%
505
August1st to 15thNight
80%
476
31%
1549
31%
474
82%
474
54%
686
August16th to endNight
80%
700
37%
1846
24%
700
82%
700
65%
876
September1st to 15thNight
82%
720
35%
1845
24%
720
85%
720
67%
901
September16th to endNight
71%
675
34%
1869
29%
675
73%
675
45%
1041
October1st to 15thNight
66%
660
27%
1854
23%
660
70%
660
39%
1078
October16th to endNight
63%
704
23%
2288
23%
704
67%
704
30%
1353
November1st to 15thNight
56%
700
21%
2275
22%
700
59%
700
25%
1449
November16th to endNight
51%
720
13%
2367
11%
720
54%
720
20%
1610
December1st to 15thNight
50%
720
9%
2520
8%
720
52%
720
15%
1828
December16th to endNight
39%
768
10%
2688
9%
768
42%
768
13%
2038

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
9%5%24423446%50%
47996
Night
12%6%24424446%46%
47033
TransparencyDay
33%7%12%19%16%10%
47667
Night
37%6%12%18%15%8%
46861
SeeingDay
10%8%23%29%21%6%
5392
Night
14%416%35%25%4
14798

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
19%9%47%7%35%6%6%6%23%
1432
16th to endDay
17%9%5%10%7%45%5%47%22%
1536
February1st to 15thDay
14%9%37%6%34446%34%
1604
16th to endDay
12%9%36%6%35%46%8%32%
1579
March1st to 15thDay
15%9%35%5%35%5%5%7%32%
1802
16th to endDay
14%10%445%3445%7%35%
2187
April1st to 15thDay
10%6%25%5%35%5%6%7%40%
2149
16th to endDay
9%6%24323347%50%
2304
May1st to 15thDay
7%32343345%7%55%
2331
16th to endDay
8%4244345%5%9%47%
2615
June1st to 15thDay
10%424435%5%6%7%46%
2520
16th to endDay
4212212235%70%
2520
July1st to 15thDay
3211113335%71%
2520
16th to endDay
11121223377%
2657
August1st to 15thDay
312222235%71%
2403
16th to endDay
21221223475%
2354
September1st to 15thDay
32121223475%
2115
16th to endDay
7%412313246%62%
1860
October1st to 15thDay
9%41332345%7%53%
1774
16th to endDay
10%5%26%5%2335%7%45%
1584
November1st to 15thDay
15%6%244235%48%41%
1584
16th to endDay
17%7%36%6%35%5%47%31%
1590
December1st to 15thDay
18%10%36%5%345%47%29%
1440
16th to endDay
23%12%36%6%3345%6%22%
1536
January1st to 15thNight
19%12%39%6%43446%25%
2506
16th to endNight
18%9%38%5%2435%6%32%
2688
February1st to 15thNight
17%8%45%5%345%46%33%
2243
16th to endNight
16%8%46%6%35%5%46%30%
1895
March1st to 15thNight
17%9%46%5%35%436%33%
2157
16th to endNight
15%8%36%5%24446%37%
2036
April1st to 15thNight
12%5%34435%5%6%6%42%
1799
16th to endNight
10%41342445%6%52%
1656
May1st to 15thNight
6%41432445%5%58%
1616
16th to endNight
6%425%5%35%47%9%45%
1496
June1st to 15thNight
10%41442435%7%50%
1440
16th to endNight
322334346%65%
1440
July1st to 15thNight
11121325%8%68%
1440
16th to endNight
21112333475%
1512
August1st to 15thNight
312222346%68%
1557
16th to endNight
21111322475%
1846
September1st to 15thNight
21121224474%
1845
16th to endNight
9%313323335%61%
1869
October1st to 15thNight
8%423334345%56%
1854
16th to endNight
12%42443345%7%46%
2288
November1st to 15thNight
18%5%23423438%42%
2275
16th to endNight
18%7%25%424445%39%
2367
December1st to 15thNight
19%8%26%5%3445%7%33%
2520
16th to endNight
24%10%46%5%23445%27%
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
58%14%17%9%
1432
16th to endDay
62%11%15%9%
1536
February1st to 15thDay
51%12%18%14%3
1604
16th to endDay
49%9%19%17%4
1579
March1st to 15thDay
48%10%17%18%4
1802
16th to endDay
46%8%16%20%7%
2187
April1st to 15thDay
40%8%16%22%10%1
2149
16th to endDay
32%6%13%27%16%3
2304
May1st to 15thDay
26%6%11%29%22%4
2331
16th to endDay
31%7%15%25%16%3
2619
June1st to 15thDay
33%7%10%22%20%4
2520
16th to endDay
16%37%21%32%18%
2520
July1st to 15thDay
14%37%14%29%31%
2371
16th to endDay
11%239%26%46%
2490
August1st to 15thDay
16%36%16%25%31%
2386
16th to endDay
12%25%17%35%26%
2354
September1st to 15thDay
13%36%18%33%25%
2115
16th to endDay
23%310%26%26%9%
1860
October1st to 15thDay
29%5%15%25%20%3
1774
16th to endDay
37%8%14%26%13%
1584
November1st to 15thDay
40%9%20%23%6%
1584
16th to endDay
51%10%19%15%3
1590
December1st to 15thDay
53%12%20%11%2
1440
16th to endDay
61%9%15%11%2
1536
January1st to 15thNight
59%9%14%13%2
2506
16th to endNight
53%9%18%15%3
2688
February1st to 15thNight
50%9%17%18%4
2254
16th to endNight
51%8%16%17%4
1895
March1st to 15thNight
51%7%12%20%6%1
2157
16th to endNight
45%7%13%21%10%
2036
April1st to 15thNight
39%7%13%24%14%1
1799
16th to endNight
31%5%11%26%22%2
1656
May1st to 15thNight
25%6%11%21%31%3
1617
16th to endNight
32%7%12%26%15%6%
1496
June1st to 15thNight
33%6%10%22%21%5%
1440
16th to endNight
18%47%19%29%20%
1440
July1st to 15thNight
14%27%14%26%34%
1360
16th to endNight
12%248%25%47%
1416
August1st to 15thNight
15%47%13%23%34%
1549
16th to endNight
12%35%14%27%36%
1846
September1st to 15thNight
12%36%15%31%31%
1845
16th to endNight
26%35%17%28%17%
1869
October1st to 15thNight
28%6%10%26%20%7%
1854
16th to endNight
35%5%14%22%20%1
2288
November1st to 15thNight
40%6%14%22%15%
2275
16th to endNight
45%7%16%21%7%
2367
December1st to 15thNight
50%10%18%15%4
2520
16th to endNight
58%6%16%15%2
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
31%5%125%25%11%
60
16th to endDay
25%415%34%12%7%
64
February1st to 15thDay
21%5%21%20%25%5%
174
16th to endDay
18%15%23%27%10%3
238
March1st to 15thDay
21%11%30%22%12%1
270
16th to endDay
15%16%32%26%7%1
288
April1st to 15thDay
9%17%30%18%15%7%
269
16th to endDay
10%17%32%22%13%2
270
May1st to 15thDay
7%12%31%29%14%3
288
16th to endDay
9%7%19%32%20%10%
330
June1st to 15thDay
9%10%26%28%19%5%
315
16th to endDay
47%23%33%26%5%
315
July1st to 15thDay
4218%34%30%8%
305
16th to endDay
222%44%24%5%
327
August1st to 15thDay
4124%35%29%4
315
16th to endDay
2315%34%32%11%
332
September1st to 15thDay
6%315%27%32%14%
315
16th to endDay
8%5%15%31%31%8%
272
October1st to 15thDay
12%6%21%23%27%9%
250
16th to endDay
19%5%23%27%17%6%
96
November1st to 15thDay
14%18%26%40%
90
16th to endDay
23%12%28%25%8%1
85
December1st to 15thDay
36%6%28%23%13
60
16th to endDay
35%417%21%15%4
64
January1st to 15thNight
20%6%15%30%23%3
720
16th to endNight
20%213%29%28%4
768
February1st to 15thNight
21%316%32%22%3
704
16th to endNight
16%6%21%32%19%2
632
March1st to 15thNight
19%6%21%31%17%3
720
16th to endNight
17%7%26%33%12%2
768
April1st to 15thNight
12%6%22%35%19%3
719
16th to endNight
12%7%21%35%19%3
576
May1st to 15thNight
8%7%23%34%23%3
537
16th to endNight
8%415%32%34%5%
375
June1st to 15thNight
11%418%36%25%3
360
16th to endNight
4217%36%36%2
360
July1st to 15thNight
2111%42%40%2
340
16th to endNight
211%45%38%1
376
August1st to 15thNight
310%43%39%1
476
16th to endNight
3110%42%36%5%
700
September1st to 15thNight
39%36%41%9%
720
16th to endNight
10%211%31%33%11%
675
October1st to 15thNight
9%216%37%26%7%
660
16th to endNight
13%213%35%28%6%
704
November1st to 15thNight
17%416%34%25%2
700
16th to endNight
21%317%32%19%5%
720
December1st to 15thNight
22%413%37%19%3
720
16th to endNight
28%5%16%33%15%1
768
Page generated at 2017-09-21 05:18:14. Version ac04

Copyright 2017 A. Danko


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