Ambersweet Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ambersweet Observatory clear sky chart from 2005-11-05 to 2017-09-10.

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%
15906
20%
46857
16%
15866
63%
15866
29%
29648

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
42%
719
20%
2327
15%
716
50%
716
25%
1446
January16th to endNight
40%
768
23%
2463
16%
768
51%
768
27%
1487
February1st to 15thNight
42%
701
24%
2106
15%
700
52%
700
31%
1266
February16th to endNight
42%
631
24%
1833
13%
631
52%
631
31%
1119
March1st to 15thNight
49%
720
28%
1980
15%
720
60%
720
40%
1118
March16th to endNight
53%
768
26%
2112
19%
768
58%
768
40%
1215
April1st to 15thNight
53%
718
24%
1976
16%
718
60%
718
40%
1119
April16th to endNight
58%
720
27%
1833
18%
720
62%
720
42%
1082
May1st to 15thNight
71%
561
25%
1641
17%
561
76%
561
41%
913
May16th to endNight
73%
561
22%
1682
19%
561
74%
561
33%
1025
June1st to 15thNight
67%
540
13%
1620
10%
540
68%
540
22%
1141
June16th to endNight
71%
540
7%
1620
6%
540
71%
540
21%
1187
July1st to 15thNight
71%
510
7%
1530
6%
510
71%
510
21%
1121
July16th to endNight
75%
564
7%
1595
7%
531
76%
531
20%
1172
August1st to 15thNight
78%
539
7%
1609
7%
536
78%
536
22%
1148
August16th to endNight
65%
717
9%
2022
9%
717
65%
717
20%
1460
September1st to 15thNight
65%
700
9%
1925
8%
700
65%
700
20%
1402
September16th to endNight
61%
657
12%
1815
12%
657
61%
657
17%
1363
October1st to 15thNight
66%
660
25%
1881
26%
660
68%
660
32%
1152
October16th to endNight
61%
704
27%
2112
26%
704
66%
704
32%
1255
November1st to 15thNight
56%
700
27%
2101
23%
700
64%
700
34%
1227
November16th to endNight
50%
720
28%
2238
20%
720
61%
720
33%
1316
December1st to 15thNight
50%
720
26%
2340
23%
720
57%
720
28%
1410
December16th to endNight
52%
768
23%
2496
20%
768
59%
768
28%
1504

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
8%5%26%6%46%6%6%8%37%
47750
Night
8%425%5%35%5%6%8%44%
47063
TransparencyDay
42%9%13%16%12%5%
47451
Night
34%9%15%19%14%6%
46866
SeeingDay
9%314%22%25%24%
5753
Night
9%319%32%26%7%
15913

By Month

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
11%6%35%4345%5%7%41%
1611
16th to endDay
10%425%4245%5%7%46%
1759
February1st to 15thDay
12%425%5%35%446%45%
1750
16th to endDay
9%425%5%35%347%47%
1638
March1st to 15thDay
7%315%335%45%7%51%
1980
16th to endDay
7%4245%3445%6%50%
2111
April1st to 15thDay
6%3235%35%46%9%48%
1972
16th to endDay
5%3245%35%5%6%8%48%
2124
May1st to 15thDay
5%2145%26%5%5%9%49%
2317
16th to endDay
6%325%7%36%6%8%9%38%
2431
June1st to 15thDay
10%5%26%8%5%7%8%8%9%27%
2340
16th to endDay
8%5%47%8%5%9%8%7%9%25%
2340
July1st to 15thDay
9%7%37%8%6%8%8%7%9%23%
2340
16th to endDay
9%6%49%8%6%8%8%7%8%21%
2465
August1st to 15thDay
7%6%39%8%5%8%8%9%11%20%
2340
16th to endDay
11%7%38%8%5%8%8%7%9%21%
2164
September1st to 15thDay
9%5%39%9%5%8%8%6%9%23%
1923
16th to endDay
11%8%38%9%5%8%6%7%8%22%
1815
October1st to 15thDay
7%5%36%7%46%5%5%8%38%
1746
16th to endDay
9%5%245%35%45%8%46%
1760
November1st to 15thDay
6%425%425%45%7%50%
1757
16th to endDay
8%5%25%5%36%447%45%
1719
December1st to 15thDay
11%5%345%35%45%7%42%
1620
16th to endDay
7%415%5%35%46%8%44%
1728
January1st to 15thNight
10%6%25%5%3445%7%42%
2327
16th to endNight
12%5%3442345%7%44%
2463
February1st to 15thNight
11%434423446%49%
2103
16th to endNight
8%5%25%5%2445%8%48%
1833
March1st to 15thNight
6%31342446%7%56%
1980
16th to endNight
6%32432345%6%57%
2112
April1st to 15thNight
6%31431435%9%55%
1976
16th to endNight
6%414424448%55%
1833
May1st to 15thNight
5%223325%46%9%55%
1641
16th to endNight
6%3144345%6%8%49%
1682
June1st to 15thNight
9%5%25%7%36%5%8%9%35%
1620
16th to endNight
6%6%36%6%38%7%9%11%29%
1620
July1st to 15thNight
7%425%8%46%6%9%10%33%
1620
16th to endNight
45%36%7%5%8%7%8%10%32%
1703
August1st to 15thNight
4326%7%47%7%8%13%33%
1620
16th to endNight
9%5%36%5%46%6%7%12%32%
2022
September1st to 15thNight
8%5%36%6%46%7%7%11%32%
1925
16th to endNight
10%7%37%6%5%8%8%6%9%25%
1815
October1st to 15thNight
6%425%4335%6%9%46%
1881
16th to endNight
9%5%1442435%7%50%
2112
November1st to 15thNight
6%425%4345%5%6%50%
2101
16th to endNight
8%424435%5%47%49%
2238
December1st to 15thNight
9%5%24435%45%8%46%
2340
16th to endNight
7%5%25%5%35%5%5%9%45%
2496

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%6%9%18%16%7%
1612
16th to endDay
36%5%9%17%21%10%
1759
February1st to 15thDay
39%6%7%12%19%14%
1752
16th to endDay
36%5%11%14%20%11%
1638
March1st to 15thDay
31%6%10%22%19%8%
1980
16th to endDay
34%6%12%19%18%9%
2112
April1st to 15thDay
31%7%12%19%21%7%
1972
16th to endDay
31%6%12%22%18%8%
2124
May1st to 15thDay
31%7%13%21%18%8%
2317
16th to endDay
38%10%15%19%12%3
2435
June1st to 15thDay
50%12%14%17%4
2340
16th to endDay
52%13%19%11%2
2340
July1st to 15thDay
53%14%19%10%1
2201
16th to endDay
53%14%19%11%1
2310
August1st to 15thDay
49%16%22%8%1
2327
16th to endDay
53%16%17%11%
2164
September1st to 15thDay
53%15%17%10%3
1923
16th to endDay
56%11%12%11%42
1815
October1st to 15thDay
43%8%9%14%14%10%
1746
16th to endDay
36%5%9%15%22%11%
1760
November1st to 15thDay
31%5%11%20%21%10%
1757
16th to endDay
38%5%9%16%18%11%
1719
December1st to 15thDay
40%6%12%18%16%5%
1620
16th to endDay
35%7%13%20%14%8%
1728
January1st to 15thNight
38%6%10%19%15%8%
2327
16th to endNight
37%5%9%16%21%9%
2463
February1st to 15thNight
34%5%9%15%18%16%
2112
16th to endNight
34%6%13%16%20%9%
1833
March1st to 15thNight
25%5%13%26%20%7%
1980
16th to endNight
27%6%12%24%20%9%
2112
April1st to 15thNight
25%7%14%24%20%8%
1976
16th to endNight
26%6%13%24%21%7%
1833
May1st to 15thNight
25%6%16%25%17%7%
1642
16th to endNight
30%9%15%24%17%2
1684
June1st to 15thNight
40%13%17%23%4
1620
16th to endNight
42%15%22%15%3
1620
July1st to 15thNight
42%15%27%12%2
1530
16th to endNight
42%16%25%13%2
1595
August1st to 15thNight
35%20%32%11%
1609
16th to endNight
42%14%25%15%1
2022
September1st to 15thNight
41%16%22%14%4
1925
16th to endNight
48%12%16%15%5%1
1815
October1st to 15thNight
32%8%13%19%18%8%
1881
16th to endNight
33%6%10%14%25%10%
2112
November1st to 15thNight
31%6%11%21%20%8%
2101
16th to endNight
32%6%10%19%17%12%
2238
December1st to 15thNight
35%6%12%24%13%6%
2340
16th to endNight
35%7%13%21%13%8%
2496

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
16%8%34%21%13%5%
90
16th to endDay
14%14%35%20%12%2
96
February1st to 15thDay
8%20%28%20%17%4
90
16th to endDay
14%10%32%30%10%
139
March1st to 15thDay
7%8%29%34%16%3
270
16th to endDay
10%426%25%28%5%
288
April1st to 15thDay
8%8%20%30%25%7%
270
16th to endDay
5%220%25%28%16%
270
May1st to 15thDay
5%313%27%29%19%
288
16th to endDay
6%6%23%32%28%
331
June1st to 15thDay
12%19%19%23%33%
315
16th to endDay
6%413%26%49%
315
July1st to 15thDay
5%10%22%60%
305
16th to endDay
9%6%11%25%46%
326
August1st to 15thDay
6%7%12%27%45%
313
16th to endDay
11%1315%20%47%
332
September1st to 15thDay
11%6%15%30%36%
294
16th to endDay
15%5%14%29%34%
254
October1st to 15thDay
9%113%30%33%11%
255
16th to endDay
8%320%29%27%8%
272
November1st to 15thDay
7%318%30%31%9%
265
16th to endDay
9%426%33%20%5%
189
December1st to 15thDay
7%8%40%35%7%
90
16th to endDay
6%414%47%19%7%
96
January1st to 15thNight
12%8%31%29%16%
720
16th to endNight
15%10%29%33%10%
768
February1st to 15thNight
13%6%33%34%11%
704
16th to endNight
9%9%34%39%6%
631
March1st to 15thNight
8%7%30%38%14%
720
16th to endNight
8%5%28%39%17%1
768
April1st to 15thNight
7%329%39%17%
718
16th to endNight
8%325%40%20%
720
May1st to 15thNight
4115%48%29%1
562
16th to endNight
6%10%34%39%7%
563
June1st to 15thNight
11%17%28%38%12%
540
16th to endNight
7%220%45%22%
540
July1st to 15thNight
9%313%42%30%
510
16th to endNight
4215%51%24%
564
August1st to 15thNight
4314%50%26%
539
16th to endNight
11%6%17%39%23%
717
September1st to 15thNight
12%5%24%37%19%
700
16th to endNight
14%8%26%38%11%
657
October1st to 15thNight
9%111%36%35%5%
660
16th to endNight
11%415%36%28%4
704
November1st to 15thNight
7%223%39%24%2
700
16th to endNight
9%329%37%19%1
720
December1st to 15thNight
11%427%34%20%1
720
16th to endNight
10%6%24%38%18%1
768
Page generated at 2017-09-11 19:35:17. Version ac04

Copyright 2017 A. Danko


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