Sterling
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sterling clear sky chart from 2005-11-05 to 2017-12-02.

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
39%
16295
18%
47804
11%
16252
45%
16252
25%
31654

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
25%
900
13%
2506
5%
895
33%
895
20%
1802
January16th to endNight
23%
960
12%
2595
5%
960
28%
960
17%
1947
February1st to 15thNight
24%
852
14%
2264
4%
852
31%
852
20%
1610
February16th to endNight
28%
631
18%
1893
8%
631
37%
631
20%
1288
March1st to 15thNight
31%
701
15%
2141
9%
701
36%
701
20%
1446
March16th to endNight
28%
576
14%
2010
9%
576
36%
576
16%
1415
April1st to 15thNight
29%
539
16%
1797
11%
539
38%
539
20%
1200
April16th to endNight
35%
540
18%
1791
14%
540
43%
540
20%
1219
May1st to 15thNight
37%
540
15%
1526
8%
540
44%
540
23%
1069
May16th to endNight
47%
563
18%
1497
10%
561
53%
561
32%
976
June1st to 15thNight
58%
540
17%
1440
11%
540
60%
540
35%
901
June16th to endNight
50%
540
17%
1440
9%
540
53%
540
32%
938
July1st to 15thNight
67%
510
17%
1360
11%
510
69%
510
41%
794
July16th to endNight
71%
564
22%
1417
17%
531
73%
531
42%
840
August1st to 15thNight
75%
539
21%
1594
22%
536
76%
536
40%
894
August16th to endNight
67%
573
21%
1910
22%
573
70%
573
33%
1080
September1st to 15thNight
66%
540
28%
1800
29%
540
70%
540
37%
953
September16th to endNight
55%
678
27%
1941
19%
678
62%
678
36%
1131
October1st to 15thNight
44%
720
25%
2139
18%
720
50%
720
32%
1273
October16th to endNight
33%
768
20%
2391
12%
768
42%
768
22%
1552
November1st to 15thNight
35%
760
23%
2471
16%
760
45%
760
26%
1511
November16th to endNight
28%
891
18%
2646
9%
891
37%
891
22%
1774
December1st to 15thNight
23%
910
13%
2547
5%
910
29%
910
18%
1887
December16th to endNight
21%
960
11%
2688
4%
960
27%
960
12%
2154

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
13%7%35%5%3445%7%37%
48658
Night
14%7%35%424446%41%
47973
Cloud CoverDay
13%7%35%5%3445%7%37%
48666
Night
14%7%35%424446%41%
47978
TransparencyDay
44%6%13%21%11%1
48344
Night
43%5%12%22%14%2
47805
SeeingDay
15%6%26%26%18%6%
6238
Night
17%6%29%31%12%1
16298

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%12%48%6%36%5%5%6%27%
1432
16th to endDay
14%13%6%10%6%34446%25%
1629
February1st to 15thDay
13%12%5%7%5%35%445%30%
1598
16th to endDay
13%9%47%5%45%5%37%32%
1580
March1st to 15thDay
16%9%35%5%3445%7%34%
1820
16th to endDay
17%9%35%6%4445%6%31%
2214
April1st to 15thDay
17%10%46%5%34346%32%
2151
16th to endDay
21%7%35%5%34346%33%
2169
May1st to 15thDay
18%8%36%5%345%5%7%29%
2424
16th to endDay
14%5%25%6%35%5%5%8%35%
2617
June1st to 15thDay
11%5%245%25%5%6%7%42%
2520
16th to endDay
9%425%5%35%6%6%10%40%
2520
July1st to 15thDay
6%415%5%35%5%6%9%45%
2520
16th to endDay
7%5%245%36%5%7%10%42%
2655
August1st to 15thDay
5%3246%35%6%8%9%43%
2355
16th to endDay
10%5%145%3445%8%45%
2292
September1st to 15thDay
12%313333447%50%
2160
16th to endDay
8%5%2444446%6%48%
2007
October1st to 15thDay
17%5%25%423337%44%
1818
16th to endDay
18%7%24423346%40%
1833
November1st to 15thDay
15%7%345%2445%6%39%
1717
16th to endDay
17%10%35%5%2234438%
1641
December1st to 15thDay
18%14%47%5%35%435%27%
1450
16th to endDay
21%13%6%7%7%24336%23%
1536
January1st to 15thNight
14%11%47%5%34445%35%
2506
16th to endNight
12%11%6%8%5%345%5%7%29%
2595
February1st to 15thNight
13%11%5%6%5%3433438%
2262
16th to endNight
14%9%37%5%23336%38%
1893
March1st to 15thNight
17%8%34425%346%38%
2128
16th to endNight
17%8%46%5%3445%6%32%
2010
April1st to 15thNight
18%7%44424445%38%
1797
16th to endNight
20%7%25%433446%36%
1791
May1st to 15thNight
17%6%245%35%5%5%7%36%
1526
16th to endNight
10%5%245%245%6%9%42%
1496
June1st to 15thNight
9%424424447%50%
1440
16th to endNight
9%3345%25%6%7%9%43%
1440
July1st to 15thNight
6%42431446%7%53%
1440
16th to endNight
5%2134245%7%10%49%
1513
August1st to 15thNight
432442445%9%54%
1603
16th to endNight
9%41442445%7%51%
1910
September1st to 15thNight
10%313213346%57%
1800
16th to endNight
7%324435%448%51%
1941
October1st to 15thNight
12%5%25%422336%50%
2139
16th to endNight
17%8%25%323336%42%
2391
November1st to 15thNight
13%7%34323336%48%
2471
16th to endNight
17%7%36%423346%40%
2646
December1st to 15thNight
19%11%48%5%23345%32%
2547
16th to endNight
23%12%5%7%6%3444424%
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%12%6%7%6%446%46%27%
1432
16th to endDay
14%13%6%10%6%3445%6%25%
1629
February1st to 15thDay
13%12%6%7%5%35%446%30%
1598
16th to endDay
13%9%47%5%35%5%47%32%
1580
March1st to 15thDay
16%9%35%5%24447%34%
1830
16th to endDay
17%9%35%6%3445%7%31%
2212
April1st to 15thDay
17%10%47%5%2445%6%31%
2151
16th to endDay
21%8%26%5%24446%33%
2169
May1st to 15thDay
18%8%46%5%3446%7%28%
2424
16th to endDay
14%5%35%6%35%5%5%8%35%
2617
June1st to 15thDay
11%5%25%5%35%5%5%7%42%
2520
16th to endDay
9%4245%35%6%6%10%40%
2520
July1st to 15thDay
6%415%5%35%5%6%10%45%
2520
16th to endDay
7%5%245%36%5%7%9%43%
2655
August1st to 15thDay
6%3145%35%6%7%10%44%
2355
16th to endDay
10%5%245%3446%7%45%
2292
September1st to 15thDay
13%313333448%50%
2160
16th to endDay
8%5%15%5%3445%7%48%
2007
October1st to 15thDay
17%5%25%413336%44%
1818
16th to endDay
18%8%25%423346%40%
1833
November1st to 15thDay
15%7%245%2445%6%39%
1717
16th to endDay
17%10%45%423345%38%
1641
December1st to 15thDay
18%14%48%6%34436%27%
1450
16th to endDay
21%13%6%7%6%24335%23%
1536
January1st to 15thNight
14%10%5%7%6%24445%35%
2506
16th to endNight
12%11%6%8%5%345%5%7%29%
2595
February1st to 15thNight
12%12%5%5%5%2443438%
2255
16th to endNight
15%9%46%423345%38%
1893
March1st to 15thNight
16%10%33425%35%6%37%
2141
16th to endNight
18%9%35%6%35%35%6%32%
2010
April1st to 15thNight
19%7%34425%345%38%
1797
16th to endNight
20%7%24423445%37%
1791
May1st to 15thNight
17%6%24435%5%5%8%36%
1525
16th to endNight
10%5%15%4345%6%9%43%
1496
June1st to 15thNight
10%41442445%7%50%
1440
16th to endNight
9%3245%35%6%7%9%42%
1440
July1st to 15thNight
6%41432346%8%53%
1440
16th to endNight
5%2145%246%7%10%50%
1513
August1st to 15thNight
432442445%9%54%
1603
16th to endNight
9%42442345%8%51%
1910
September1st to 15thNight
9%4331335%6%57%
1800
16th to endNight
7%324425%45%8%50%
1941
October1st to 15thNight
12%5%14322346%50%
2139
16th to endNight
18%8%34323336%42%
2391
November1st to 15thNight
13%7%35%323336%47%
2471
16th to endNight
18%7%45%423346%40%
2646
December1st to 15thNight
19%11%48%5%23345%31%
2547
16th to endNight
23%11%5%7%6%3444324%
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
56%6%13%13%9%
1433
16th to endDay
59%413%13%6%
1629
February1st to 15thDay
55%5%12%18%6%
1600
16th to endDay
50%7%11%21%8%
1580
March1st to 15thDay
49%6%15%19%8%
1830
16th to endDay
52%6%13%20%5%
2214
April1st to 15thDay
52%5%12%20%8%
2151
16th to endDay
51%6%11%16%12%1
2169
May1st to 15thDay
53%6%13%20%6%
2424
16th to endDay
45%8%12%19%13%
2621
June1st to 15thDay
39%6%13%25%15%
2520
16th to endDay
36%9%13%23%15%1
2520
July1st to 15thDay
33%8%15%25%14%2
2371
16th to endDay
33%9%18%22%13%2
2488
August1st to 15thDay
31%10%15%25%14%1
2340
16th to endDay
35%7%12%26%14%2
2292
September1st to 15thDay
32%6%10%27%20%3
2160
16th to endDay
34%5%12%27%18%1
2007
October1st to 15thDay
41%410%26%15%
1818
16th to endDay
45%414%22%11%1
1833
November1st to 15thDay
43%5%13%22%11%2
1717
16th to endDay
48%416%23%6%
1641
December1st to 15thDay
58%5%12%15%6%
1450
16th to endDay
64%5%11%9%8%
1536
January1st to 15thNight
51%414%17%11%
2506
16th to endNight
54%6%15%14%8%
2595
February1st to 15thNight
49%411%21%11%
2264
16th to endNight
47%5%13%22%9%1
1893
March1st to 15thNight
47%5%14%19%10%2
2141
16th to endNight
51%6%12%19%9%
2010
April1st to 15thNight
47%410%20%14%2
1797
16th to endNight
47%6%9%21%11%3
1791
May1st to 15thNight
44%7%13%20%12%1
1526
16th to endNight
35%8%15%21%17%2
1498
June1st to 15thNight
32%7%12%25%20%2
1440
16th to endNight
34%8%12%20%19%3
1440
July1st to 15thNight
28%5%13%30%19%2
1360
16th to endNight
26%7%17%26%18%4
1417
August1st to 15thNight
26%6%14%31%17%2
1594
16th to endNight
30%7%12%26%18%4
1910
September1st to 15thNight
27%5%9%27%27%3
1800
16th to endNight
30%5%11%29%19%2
1941
October1st to 15thNight
35%410%25%21%3
2139
16th to endNight
44%410%25%13%1
2391
November1st to 15thNight
38%5%11%23%17%3
2471
16th to endNight
45%412%25%11%
2646
December1st to 15thNight
55%412%20%7%
2547
16th to endNight
64%410%13%6%
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
27%8%36%20%6%
90
16th to endDay
22%7%36%19%11%2
96
February1st to 15thDay
20%16%45%11%6%
90
16th to endDay
18%18%29%22%11%
81
March1st to 15thDay
30%14%34%15%32
90
16th to endDay
29%5%30%24%7%2
198
April1st to 15thDay
18%13%31%24%10%1
270
16th to endDay
25%9%27%21%12%3
270
May1st to 15thDay
22%8%32%24%8%3
381
16th to endDay
17%10%28%22%16%5%
517
June1st to 15thDay
11%428%32%18%5%
495
16th to endDay
11%6%31%28%16%5%
495
July1st to 15thDay
9%222%31%22%12%
475
16th to endDay
8%20%31%28%10%
515
August1st to 15thDay
7%116%33%30%10%
457
16th to endDay
11%314%28%29%12%
332
September1st to 15thDay
10%217%27%32%8%
315
16th to endDay
7%424%29%26%6%
314
October1st to 15thDay
20%10%23%26%15%3
153
16th to endDay
26%8%34%23%6%
144
November1st to 15thDay
17%8%26%25%14%7%
135
16th to endDay
31%9%29%22%6%
135
December1st to 15thDay
23%12%24%29%9%
94
16th to endDay
29%12%48%7%2
96
January1st to 15thNight
19%11%38%24%6%
900
16th to endNight
17%10%36%30%4
960
February1st to 15thNight
20%8%38%25%6%
855
16th to endNight
19%9%36%27%7%
631
March1st to 15thNight
22%8%33%26%8%
701
16th to endNight
20%8%36%25%8%1
576
April1st to 15thNight
22%10%33%27%5%
539
16th to endNight
24%7%29%27%9%1
540
May1st to 15thNight
19%433%32%9%
540
16th to endNight
12%330%40%13%
563
June1st to 15thNight
11%321%49%12%
540
16th to endNight
10%132%40%14%1
540
July1st to 15thNight
10%113%43%28%2
510
16th to endNight
6%112%46%30%2
564
August1st to 15thNight
49%46%32%5%
539
16th to endNight
11%113%38%31%3
573
September1st to 15thNight
11%215%35%31%3
540
16th to endNight
10%5%23%34%24%3
678
October1st to 15thNight
16%5%28%30%17%1
720
16th to endNight
23%10%29%26%9%
768
November1st to 15thNight
17%7%37%27%10%
760
16th to endNight
21%10%34%26%7%
891
December1st to 15thNight
24%10%33%26%5%
910
16th to endNight
28%8%33%25%3
960
Page generated at 2017-12-03 10:16:40. Version ac04

Copyright 2017 A. Danko


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