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 2018-02-22.

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%
16566
21%
48874
16%
16526
63%
16526
29%
30765

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
41%
779
20%
2522
14%
776
50%
776
24%
1574
January16th to endNight
40%
832
24%
2668
17%
832
51%
832
27%
1605
February1st to 15thNight
42%
761
22%
2286
14%
760
52%
760
31%
1388
February16th to endNight
44%
659
26%
1917
16%
659
54%
659
33%
1149
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
64%
720
9%
1980
8%
720
65%
720
20%
1441
September16th to endNight
63%
717
13%
1980
14%
717
64%
717
19%
1447
October1st to 15thNight
66%
720
24%
2052
25%
720
67%
720
32%
1269
October16th to endNight
60%
768
28%
2304
26%
768
66%
768
33%
1359
November1st to 15thNight
58%
760
27%
2281
22%
760
66%
760
36%
1307
November16th to endNight
52%
780
29%
2425
21%
780
62%
780
33%
1412
December1st to 15thNight
52%
780
26%
2535
23%
780
59%
780
29%
1509
December16th to endNight
54%
832
24%
2704
21%
832
60%
832
29%
1604

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%
49358
Night
8%425%5%35%5%6%8%45%
49080
TransparencyDay
41%9%13%16%12%5%
49059
Night
34%9%15%19%14%6%
48883
SeeingDay
9%315%23%25%23%
6321
Night
9%319%32%27%7%
16573

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
12%6%35%4345%5%7%41%
1746
16th to endDay
10%425%4245%5%7%46%
1906
February1st to 15thDay
11%425%5%35%5%5%6%44%
1900
16th to endDay
9%425%5%34347%49%
1701
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%7%6%9%24%
1980
16th to endDay
11%8%37%9%5%8%6%7%8%24%
1980
October1st to 15thDay
7%6%37%7%46%5%5%8%36%
1905
16th to endDay
9%424435%448%47%
1920
November1st to 15thDay
6%425%435%45%7%51%
1907
16th to endDay
9%5%25%5%35%447%46%
1862
December1st to 15thDay
10%5%35%5%35%45%7%44%
1755
16th to endDay
7%415%5%35%46%8%45%
1872
January1st to 15thNight
10%6%26%5%3445%7%42%
2522
16th to endNight
12%5%2442445%7%45%
2668
February1st to 15thNight
11%4345%34446%48%
2283
16th to endNight
7%5%2442445%8%50%
1917
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
9%5%36%6%46%7%7%11%33%
1980
16th to endNight
9%7%26%6%5%8%8%6%9%28%
1980
October1st to 15thNight
6%5%25%4335%6%9%46%
2052
16th to endNight
9%5%1442435%7%50%
2304
November1st to 15thNight
5%4244345%5%7%52%
2281
16th to endNight
8%424435%448%50%
2425
December1st to 15thNight
9%5%24435%35%8%47%
2535
16th to endNight
7%5%25%5%345%5%8%46%
2704

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
41%6%9%17%17%7%
1747
16th to endDay
36%5%8%18%21%9%
1906
February1st to 15thDay
39%7%8%12%18%13%
1902
16th to endDay
35%411%14%22%10%
1701
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%14%17%10%3
1980
16th to endDay
54%11%13%13%5%2
1980
October1st to 15thDay
44%8%9%14%13%9%
1905
16th to endDay
35%5%8%14%22%12%
1920
November1st to 15thDay
31%5%11%21%20%9%
1907
16th to endDay
38%5%8%17%18%10%
1862
December1st to 15thDay
39%6%13%19%15%6%
1755
16th to endDay
34%7%13%21%14%7%
1872
January1st to 15thNight
39%6%10%19%15%8%
2522
16th to endNight
37%5%9%17%21%9%
2668
February1st to 15thNight
35%5%11%15%17%14%
2292
16th to endNight
32%6%13%17%22%8%
1917
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%21%15%5%
1980
16th to endNight
46%12%18%16%5%1
1980
October1st to 15thNight
32%8%13%20%17%7%
2052
16th to endNight
32%5%10%15%24%11%
2304
November1st to 15thNight
29%6%12%22%21%7%
2281
16th to endNight
31%6%10%20%19%11%
2425
December1st to 15thNight
34%6%13%23%13%8%
2535
16th to endNight
34%6%14%23%13%7%
2704

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
19%11%40%17%8%3
135
16th to endDay
13%13%38%22%10%1
144
February1st to 15thDay
8%14%30%26%16%4
135
16th to endDay
12%9%29%31%16%1
158
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%15%15%31%34%
315
16th to endDay
14%416%31%32%
314
October1st to 15thDay
9%213%30%32%11%
315
16th to endDay
10%5%21%31%24%7%
336
November1st to 15thDay
8%218%31%31%7%
325
16th to endDay
11%323%35%21%4
242
December1st to 15thDay
8%8%40%29%11%2
135
16th to endDay
6%316%47%20%6%
144
January1st to 15thNight
12%8%32%29%15%
780
16th to endNight
15%10%29%34%10%
832
February1st to 15thNight
13%6%32%34%11%1
764
16th to endNight
9%8%32%39%8%
659
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%
720
16th to endNight
13%7%27%39%11%
717
October1st to 15thNight
9%111%37%34%5%
720
16th to endNight
10%416%36%27%4
768
November1st to 15thNight
7%223%39%25%2
760
16th to endNight
9%328%37%20%1
780
December1st to 15thNight
10%5%26%34%21%1
780
16th to endNight
10%6%23%37%20%1
832
Page generated at 2018-02-23 11:21:35. Version ac04

Copyright 2018 A. Danko


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