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 2018-03-21.

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
46%
16460
22%
49424
14%
16422
54%
16422
27%
30925

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
29%
778
24%
2522
11%
776
45%
776
21%
1531
January16th to endNight
28%
832
24%
2704
11%
832
45%
832
23%
1639
February1st to 15thNight
26%
761
21%
2482
9%
761
41%
761
22%
1498
February16th to endNight
27%
683
25%
2042
10%
683
42%
683
24%
1264
March1st to 15thNight
35%
780
24%
2145
12%
780
46%
780
26%
1376
March16th to endNight
34%
792
20%
2178
11%
792
42%
792
26%
1439
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%
720
24%
1848
17%
720
65%
720
33%
1208
September16th to endNight
54%
717
20%
1989
18%
717
56%
717
25%
1363
October1st to 15thNight
53%
720
26%
2160
23%
720
59%
720
29%
1330
October16th to endNight
47%
768
32%
2304
23%
768
61%
768
35%
1297
November1st to 15thNight
46%
760
27%
2297
19%
760
57%
760
31%
1365
November16th to endNight
42%
780
26%
2649
19%
780
55%
780
28%
1483
December1st to 15thNight
31%
780
20%
2730
12%
780
44%
780
19%
1720
December16th to endNight
29%
832
22%
2772
12%
832
44%
832
18%
1812

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%
49379
Night
14%5%25%42445%7%44%
49617
Cloud CoverDay
14%5%25%5%35%5%5%7%39%
49389
Night
14%5%2442445%7%44%
49621
TransparencyDay
40%5%12%22%15%3
49090
Night
38%5%11%23%17%3
49424
SeeingDay
19%7%20%24%18%9%
6219
Night
17%7%21%32%18%2
16467

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%5%25%5%3446%6%40%
1746
16th to endDay
15%7%25%435%345%44%
1872
February1st to 15thDay
13%7%26%435%447%39%
1710
16th to endDay
17%5%35%43435%6%38%
1714
March1st to 15thDay
15%5%25%42345%6%45%
2134
16th to endDay
18%6%36%423347%38%
2174
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%
2109
16th to endDay
21%6%25%5%2445%5%36%
1971
October1st to 15thDay
18%5%13322347%47%
1800
16th to endDay
14%6%1421434450%
1920
November1st to 15thDay
14%423323436%50%
1887
16th to endDay
15%424323446%48%
1638
December1st to 15thDay
16%5%345%2445%5%42%
1560
16th to endDay
20%5%35%42335%5%39%
1801
January1st to 15thNight
16%42442435%6%45%
2522
16th to endNight
15%6%23425%446%43%
2704
February1st to 15thNight
14%7%25%423446%44%
2480
16th to endNight
13%6%35%424447%41%
2042
March1st to 15thNight
15%4144245%5%5%45%
2133
16th to endNight
17%5%25%424435%43%
2178
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%
1848
16th to endNight
18%5%25%5%3445%6%38%
1989
October1st to 15thNight
16%425%423345%48%
2160
16th to endNight
14%313313346%53%
2304
November1st to 15thNight
15%5%2431243452%
2297
16th to endNight
15%423323446%50%
2649
December1st to 15thNight
17%8%35%5%2334441%
2730
16th to endNight
16%6%36%5%24446%37%
2772

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%6%41%
1746
16th to endDay
14%6%345%24445%44%
1872
February1st to 15thDay
13%5%36%5%35%5%47%40%
1710
16th to endDay
16%5%36%43445%6%39%
1714
March1st to 15thDay
15%42443445%6%45%
2145
16th to endDay
18%6%26%424347%38%
2173
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%
2109
16th to endDay
21%6%25%5%3445%5%35%
1971
October1st to 15thDay
17%5%23322347%47%
1800
16th to endDay
14%5%14323345%51%
1920
November1st to 15thDay
13%413423336%50%
1887
16th to endDay
15%423423446%48%
1638
December1st to 15thDay
15%5%25%5%2345%7%41%
1560
16th to endDay
20%6%25%423445%39%
1801
January1st to 15thNight
15%42442345%5%46%
2522
16th to endNight
15%5%23434446%43%
2704
February1st to 15thNight
13%6%25%42345%6%44%
2473
16th to endNight
12%6%25%5%24447%42%
2042
March1st to 15thNight
15%41442445%5%45%
2145
16th to endNight
17%5%24434345%44%
2178
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%
1848
16th to endNight
18%5%25%5%2435%6%38%
1989
October1st to 15thNight
15%5%25%422336%48%
2160
16th to endNight
13%41332325%5%53%
2304
November1st to 15thNight
14%5%2432343452%
2297
16th to endNight
15%323323446%50%
2649
December1st to 15thNight
16%8%35%5%3334441%
2730
16th to endNight
16%7%35%5%2445%6%37%
2772

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%411%21%18%3
1747
16th to endDay
40%49%24%17%3
1872
February1st to 15thDay
41%411%22%17%2
1712
16th to endDay
45%310%22%15%2
1714
March1st to 15thDay
37%411%22%18%5%
2145
16th to endDay
45%5%9%21%14%3
2174
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
2109
16th to endDay
47%47%21%17%1
1971
October1st to 15thDay
36%310%28%16%4
1800
16th to endDay
35%28%28%20%4
1920
November1st to 15thDay
34%39%20%24%6%
1887
16th to endDay
35%48%26%23%2
1638
December1st to 15thDay
40%5%12%20%16%4
1560
16th to endDay
45%410%23%13%1
1801
January1st to 15thNight
38%49%20%18%7%
2522
16th to endNight
39%310%24%18%3
2704
February1st to 15thNight
39%310%23%18%4
2482
16th to endNight
38%411%25%17%2
2042
March1st to 15thNight
38%5%9%25%16%4
2145
16th to endNight
42%410%22%18%2
2178
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%20%19%5%
1848
16th to endNight
45%5%8%20%17%2
1989
October1st to 15thNight
38%37%27%18%3
2160
16th to endNight
31%27%27%25%4
2304
November1st to 15thNight
36%37%20%23%8%
2297
16th to endNight
34%39%25%23%4
2649
December1st to 15thNight
45%39%23%15%3
2730
16th to endNight
45%410%20%15%2
2772

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
22%20%36%17%21
135
16th to endDay
31%21%27%14%4
144
February1st to 15thDay
25%21%45%5%1
135
16th to endDay
24%17%30%22%4
188
March1st to 15thDay
24%16%26%26%6%
330
16th to endDay
25%10%24%27%10%1
311
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%
315
16th to endDay
27%310%18%26%14%
314
October1st to 15thDay
23%314%27%23%6%
315
16th to endDay
15%9%20%33%17%3
336
November1st to 15thDay
21%7%17%33%17%2
305
16th to endDay
17%15%23%25%13%4
108
December1st to 15thDay
23%14%31%20%11%
90
16th to endDay
30%15%32%17%3
128
January1st to 15thNight
20%16%27%30%5%
780
16th to endNight
20%12%33%30%2
832
February1st to 15thNight
20%12%34%31%2
764
16th to endNight
19%14%33%29%2
683
March1st to 15thNight
19%11%27%35%5%
780
16th to endNight
20%8%29%31%9%1
792
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%
720
16th to endNight
22%211%29%30%4
717
October1st to 15thNight
18%5%15%30%25%4
720
16th to endNight
15%6%22%34%17%2
768
November1st to 15thNight
18%6%21%35%15%2
760
16th to endNight
18%11%22%32%14%1
780
December1st to 15thNight
21%9%28%31%8%
780
16th to endNight
20%11%29%34%3
832
Page generated at 2018-03-22 11:34:20. Version ac04

Copyright 2018 A. Danko


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