Sunset Field
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sunset Field clear sky chart from 2005-11-05 to 2017-09-14.

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
45%
15708
21%
47082
14%
15670
54%
15670
27%
29518

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
28%
718
24%
2327
11%
716
44%
716
20%
1427
January16th to endNight
27%
768
23%
2496
10%
768
44%
768
23%
1525
February1st to 15thNight
25%
701
22%
2287
8%
701
41%
701
23%
1365
February16th to endNight
25%
631
25%
1886
10%
631
42%
631
24%
1161
March1st to 15thNight
36%
720
24%
1980
12%
720
46%
720
26%
1271
March16th to endNight
35%
768
20%
2112
11%
768
42%
768
26%
1388
April1st to 15thNight
35%
718
21%
1853
8%
718
44%
718
30%
1172
April16th to endNight
44%
672
20%
1752
9%
672
50%
672
30%
1157
May1st to 15thNight
46%
540
15%
1620
9%
540
51%
540
24%
1079
May16th to endNight
61%
561
16%
1684
12%
561
63%
561
28%
1084
June1st to 15thNight
68%
451
17%
1531
17%
451
70%
451
29%
894
June16th to endNight
72%
509
17%
1589
16%
509
74%
509
32%
956
July1st to 15thNight
65%
510
12%
1530
11%
510
67%
510
28%
999
July16th to endNight
73%
564
18%
1595
16%
531
75%
531
35%
969
August1st to 15thNight
66%
539
19%
1609
15%
536
67%
536
28%
1054
August16th to endNight
65%
693
19%
1839
14%
693
66%
693
29%
1236
September1st to 15thNight
63%
716
24%
1837
17%
716
65%
716
33%
1202
September16th to endNight
51%
657
18%
1823
15%
657
54%
657
23%
1274
October1st to 15thNight
51%
660
27%
1980
24%
660
58%
660
29%
1222
October16th to endNight
47%
704
31%
2112
21%
704
61%
704
35%
1193
November1st to 15thNight
46%
700
28%
2116
19%
700
57%
700
32%
1228
November16th to endNight
41%
720
24%
2445
17%
720
53%
720
26%
1401
December1st to 15thNight
31%
720
20%
2520
12%
720
43%
720
19%
1589
December16th to endNight
29%
768
22%
2559
11%
768
43%
768
18%
1672

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
14%5%25%5%35%45%7%39%
47588
Night
14%5%25%42445%7%44%
47275
Cloud CoverDay
14%5%25%5%35%5%5%7%39%
47598
Night
14%5%2442445%7%44%
47279
TransparencyDay
40%5%12%22%15%3
47299
Night
38%5%11%23%17%3
47082
SeeingDay
18%7%19%24%19%10%
5598
Night
17%7%21%32%18%2
15715

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
15%6%25%5%3446%6%40%
1611
16th to endDay
15%6%24435%445%43%
1728
February1st to 15thDay
11%7%26%445%446%40%
1575
16th to endDay
15%5%35%43435%7%39%
1584
March1st to 15thDay
15%5%25%43345%6%45%
1969
16th to endDay
17%6%36%423347%38%
2112
April1st to 15thDay
12%5%24423447%47%
2095
16th to endDay
17%5%25%42445%5%41%
2218
May1st to 15thDay
19%5%246%45%46%7%32%
2331
16th to endDay
13%5%25%6%35%5%6%8%36%
2431
June1st to 15thDay
11%4245%37%5%6%9%40%
2415
16th to endDay
9%425%5%35%6%7%10%38%
2357
July1st to 15thDay
13%5%36%6%47%5%7%8%31%
2340
16th to endDay
8%5%36%6%48%6%7%9%32%
2465
August1st to 15thDay
15%5%25%6%45%6%7%10%30%
2340
16th to endDay
12%6%26%6%47%6%6%9%32%
2351
September1st to 15thDay
13%5%25%5%345%46%43%
2096
16th to endDay
23%6%25%5%2444434%
1807
October1st to 15thDay
18%5%13322348%47%
1650
16th to endDay
14%6%24314345%49%
1760
November1st to 15thDay
12%423323436%53%
1739
16th to endDay
16%5%24323446%46%
1512
December1st to 15thDay
16%425%42445%6%42%
1440
16th to endDay
20%5%35%32335%5%39%
1662
January1st to 15thNight
16%42442435%6%44%
2327
16th to endNight
15%6%23435%446%42%
2496
February1st to 15thNight
14%6%24423446%45%
2285
16th to endNight
12%5%35%5%25%447%42%
1886
March1st to 15thNight
16%4244245%5%6%44%
1968
16th to endNight
16%5%25%424435%44%
2112
April1st to 15thNight
13%435%42445%7%45%
1853
16th to endNight
16%5%13424447%43%
1752
May1st to 15thNight
17%5%35%333448%39%
1620
16th to endNight
13%425%42446%9%40%
1682
June1st to 15thNight
8%325%4245%7%11%42%
1531
16th to endNight
7%3145%35%5%6%9%48%
1589
July1st to 15thNight
11%5%245%35%5%6%8%41%
1620
16th to endNight
5%315%5%35%6%7%12%42%
1703
August1st to 15thNight
12%5%25%425%47%8%41%
1620
16th to endNight
9%5%26%6%35%5%6%8%39%
1839
September1st to 15thNight
11%5%25%42445%6%46%
1837
16th to endNight
20%5%15%6%3435%6%37%
1823
October1st to 15thNight
15%5%25%423335%48%
1980
16th to endNight
14%313313346%52%
2112
November1st to 15thNight
14%5%2431244453%
2116
16th to endNight
16%423323446%48%
2445
December1st to 15thNight
17%7%35%42334441%
2520
16th to endNight
17%6%36%5%24446%37%
2559

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
15%5%25%5%3445%7%40%
1611
16th to endDay
15%6%345%24445%43%
1728
February1st to 15thDay
12%5%36%5%36%5%47%41%
1575
16th to endDay
15%5%36%43445%6%40%
1584
March1st to 15thDay
14%42443445%6%45%
1980
16th to endDay
17%6%26%424348%38%
2111
April1st to 15thDay
12%5%24423447%47%
2095
16th to endDay
17%5%2443445%6%41%
2218
May1st to 15thDay
18%5%345%36%5%5%8%32%
2331
16th to endDay
12%5%25%6%46%5%6%8%36%
2431
June1st to 15thDay
10%3245%46%6%6%9%39%
2415
16th to endDay
8%426%6%35%7%7%9%38%
2357
July1st to 15thDay
12%6%46%6%47%6%7%8%31%
2340
16th to endDay
7%5%36%6%5%7%7%7%9%31%
2465
August1st to 15thDay
14%5%26%6%35%7%7%9%30%
2340
16th to endDay
11%5%26%7%46%5%7%9%32%
2351
September1st to 15thDay
12%5%25%5%44447%43%
2096
16th to endDay
23%7%25%5%2445%434%
1807
October1st to 15thDay
17%5%23322247%48%
1650
16th to endDay
15%5%24323345%49%
1760
November1st to 15thDay
12%413423436%53%
1739
16th to endDay
16%423423446%46%
1512
December1st to 15thDay
15%425%4235%5%7%42%
1440
16th to endDay
20%6%35%423445%39%
1662
January1st to 15thNight
15%425%43345%5%45%
2327
16th to endNight
15%5%23435%446%43%
2496
February1st to 15thNight
14%6%25%42345%5%46%
2278
16th to endNight
12%6%25%5%24447%42%
1886
March1st to 15thNight
16%4145%2345%6%44%
1980
16th to endNight
16%5%24434345%44%
2112
April1st to 15thNight
13%5%25%42435%7%45%
1853
16th to endNight
15%5%23425%45%7%43%
1752
May1st to 15thNight
17%5%24434448%39%
1619
16th to endNight
13%5%25%43446%9%40%
1682
June1st to 15thNight
8%3344345%7%11%42%
1531
16th to endNight
7%3145%45%5%6%10%47%
1589
July1st to 15thNight
10%5%245%45%5%6%9%41%
1620
16th to endNight
44245%36%5%7%11%42%
1703
August1st to 15thNight
12%5%16%4345%6%8%41%
1620
16th to endNight
9%5%25%6%35%5%7%8%39%
1839
September1st to 15thNight
11%435%5%2345%6%46%
1837
16th to endNight
20%6%25%5%3435%6%36%
1823
October1st to 15thNight
14%5%25%422335%48%
1980
16th to endNight
14%41332325%5%53%
2112
November1st to 15thNight
13%5%2431343453%
2116
16th to endNight
16%423323446%48%
2445
December1st to 15thNight
17%8%35%42334441%
2520
16th to endNight
17%7%35%42445%6%37%
2559

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
40%412%22%17%2
1612
16th to endDay
41%49%24%17%3
1728
February1st to 15thDay
40%411%22%17%2
1577
16th to endDay
43%311%23%15%2
1584
March1st to 15thDay
37%411%23%18%4
1980
16th to endDay
44%5%9%22%13%3
2112
April1st to 15thDay
34%412%26%16%6%
2095
16th to endDay
41%411%20%15%6%
2218
May1st to 15thDay
47%7%13%18%10%2
2331
16th to endDay
41%6%17%22%9%1
2435
June1st to 15thDay
35%8%18%24%12%
2415
16th to endDay
35%10%15%20%14%2
2357
July1st to 15thDay
45%9%13%15%12%3
2201
16th to endDay
41%9%16%19%12%1
2310
August1st to 15thDay
45%7%13%21%10%
2327
16th to endDay
44%7%15%19%11%1
2351
September1st to 15thDay
38%6%11%20%20%3
2096
16th to endDay
50%47%19%17%1
1807
October1st to 15thDay
36%210%29%16%4
1650
16th to endDay
36%29%27%19%5%
1760
November1st to 15thDay
32%39%20%26%7%
1739
16th to endDay
37%48%25%21%2
1512
December1st to 15thDay
39%5%12%20%17%5%
1440
16th to endDay
45%410%22%14%2
1662
January1st to 15thNight
39%410%21%18%6%
2327
16th to endNight
40%310%24%17%3
2496
February1st to 15thNight
38%39%23%19%4
2287
16th to endNight
38%411%25%18%2
1886
March1st to 15thNight
38%5%10%27%15%3
1980
16th to endNight
41%410%22%18%2
2112
April1st to 15thNight
36%412%22%18%5%
1853
16th to endNight
38%5%12%19%17%6%
1752
May1st to 15thNight
42%6%15%18%14%1
1620
16th to endNight
38%7%16%26%9%2
1684
June1st to 15thNight
32%8%18%24%13%1
1531
16th to endNight
30%10%15%21%18%3
1589
July1st to 15thNight
38%8%16%18%12%5%
1530
16th to endNight
32%6%17%27%14%
1595
August1st to 15thNight
38%8%13%22%16%1
1609
16th to endNight
38%8%14%23%12%1
1839
September1st to 15thNight
36%6%11%19%19%5%
1837
16th to endNight
47%5%8%18%17%2
1823
October1st to 15thNight
39%37%26%18%3
1980
16th to endNight
32%27%27%24%4
2112
November1st to 15thNight
34%37%20%25%9%
2116
16th to endNight
36%39%24%21%4
2445
December1st to 15thNight
45%39%22%16%3
2520
16th to endNight
46%410%20%15%2
2559

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
23%18%37%15%22
90
16th to endDay
32%25%26%13%3
96
February1st to 15thDay
18%26%48%32
90
16th to endDay
24%15%29%25%3
144
March1st to 15thDay
22%14%25%29%7%
270
16th to endDay
23%10%24%28%11%2
288
April1st to 15thDay
17%14%22%26%16%2
270
16th to endDay
23%421%22%18%8%
270
May1st to 15thDay
25%10%26%18%12%6%
288
16th to endDay
19%319%21%22%12%
331
June1st to 15thDay
11%417%28%26%13%
315
16th to endDay
10%421%30%20%12%
315
July1st to 15thDay
16%16%31%24%9%
305
16th to endDay
8%112%24%32%21%
326
August1st to 15thDay
17%115%20%25%19%
313
16th to endDay
13%9%22%25%29%
332
September1st to 15thDay
13%411%20%27%22%
310
16th to endDay
33%310%17%24%11%
254
October1st to 15thDay
24%416%27%21%5%
255
16th to endDay
16%8%19%36%16%2
272
November1st to 15thDay
17%8%17%33%19%3
247
16th to endDay
23%12%22%23%15%2
72
December1st to 15thDay
21%15%31%18%13%
60
16th to endDay
34%14%30%18%2
85
January1st to 15thNight
20%16%27%29%5%
720
16th to endNight
20%12%34%29%2
768
February1st to 15thNight
20%12%34%30%2
704
16th to endNight
18%15%35%28%2
631
March1st to 15thNight
19%11%26%35%5%
720
16th to endNight
19%8%29%31%9%1
768
April1st to 15thNight
16%15%28%29%9%
718
16th to endNight
19%5%23%33%17%1
672
May1st to 15thNight
20%5%20%35%15%2
540
16th to endNight
16%211%32%31%6%
563
June1st to 15thNight
8%110%41%34%3
451
16th to endNight
7%17%41%36%4
509
July1st to 15thNight
11%19%33%39%4
510
16th to endNight
6%17%30%45%9%
564
August1st to 15thNight
15%6%34%36%6%
539
16th to endNight
12%16%29%43%6%
693
September1st to 15thNight
14%110%30%36%7%
716
16th to endNight
24%212%29%28%2
657
October1st to 15thNight
18%5%16%31%23%4
660
16th to endNight
15%7%22%35%16%1
704
November1st to 15thNight
17%7%22%35%15%2
700
16th to endNight
19%12%22%31%13%1
720
December1st to 15thNight
21%9%28%31%8%
720
16th to endNight
20%11%29%33%3
768
Page generated at 2017-09-15 10:29:58. Version ac04

Copyright 2017 A. Danko


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