Hythe Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hythe Observatory clear sky chart from 2005-11-05 to 2017-09-20.

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
35%
15019
9%
46723
5%
14992
39%
14992
16%
34000

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
27%
925
8%
2865
4%
925
30%
925
11%
2234
January16th to endNight
26%
834
12%
2892
7%
834
32%
834
12%
2126
February1st to 15thNight
32%
698
8%
2464
7%
696
36%
696
12%
1816
February16th to endNight
43%
632
11%
2028
9%
632
47%
632
16%
1486
March1st to 15thNight
31%
720
12%
2160
7%
720
36%
720
15%
1627
March16th to endNight
39%
768
12%
2003
6%
767
41%
767
19%
1528
April1st to 15thNight
34%
703
10%
1783
4%
703
38%
703
17%
1369
April16th to endNight
36%
369
9%
1449
11%
369
40%
369
13%
1021
May1st to 15thNight
39%
359
3%
1388
2%
359
41%
359
16%
922
May16th to endNight
41%
374
0%
1147
0%
374
41%
374
18%
824
June1st to 15thNight
42%
360
0%
1080
0%
360
42%
360
20%
757
June16th to endNight
44%
360
0%
1080
0%
360
44%
360
22%
746
July1st to 15thNight
50%
340
0%
1020
0%
340
50%
340
26%
658
July16th to endNight
52%
376
0%
1123
0%
354
54%
354
24%
728
August1st to 15thNight
60%
360
5%
1432
6%
358
61%
358
23%
841
August16th to endNight
43%
478
12%
1624
11%
478
49%
478
21%
1050
September1st to 15thNight
49%
720
12%
1800
7%
720
51%
720
31%
1210
September16th to endNight
39%
675
15%
1840
8%
675
43%
675
21%
1310
October1st to 15thNight
32%
660
12%
2002
6%
660
39%
660
18%
1446
October16th to endNight
26%
704
9%
2324
3%
704
35%
704
12%
1734
November1st to 15thNight
27%
775
13%
2525
7%
775
35%
775
14%
1842
November16th to endNight
26%
907
10%
2742
5%
907
31%
907
13%
2113
December1st to 15thNight
28%
930
10%
2880
6%
930
32%
930
12%
2252
December16th to endNight
32%
992
12%
3072
5%
992
38%
992
12%
2360

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
11%9%47%6%35%5%5%7%31%
48174
Night
10%10%47%7%35%5%5%7%30%
46856
TransparencyDay
49%8%16%18%5%
47807
Night
51%8%14%18%6%
46728
SeeingDay
16%8%26%28%16%3
6934
Night
15%8%28%30%15%2
15032

By Month

Percentage Cloud Cover NW (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
7%13%7%10%7%346%5%7%26%
1074
16th to endDay
9%13%5%8%7%45%45%5%28%
1344
February1st to 15thDay
8%11%5%10%8%345%5%9%27%
1400
16th to endDay
5%15%6%10%7%37%5%6%6%23%
1446
March1st to 15thDay
8%12%5%9%7%46%5%6%7%25%
1800
16th to endDay
10%15%6%8%6%35%5%6%8%24%
2214
April1st to 15thDay
6%11%5%8%7%36%6%5%8%29%
2164
16th to endDay
11%10%5%8%7%36%5%6%7%27%
2511
May1st to 15thDay
10%7%36%7%46%6%5%7%34%
2561
16th to endDay
16%7%36%6%46%5%6%7%28%
2962
June1st to 15thDay
15%7%37%7%35%6%5%7%30%
2880
16th to endDay
14%7%25%6%35%6%6%7%32%
2880
July1st to 15thDay
13%5%35%5%36%5%6%7%37%
2880
16th to endDay
9%435%6%35%6%7%9%39%
2966
August1st to 15thDay
10%425%6%35%5%6%8%40%
2520
16th to endDay
11%6%26%6%25%6%6%7%35%
2578
September1st to 15thDay
12%5%35%6%34447%42%
2160
16th to endDay
12%6%25%5%35%5%6%7%39%
1889
October1st to 15thDay
13%10%38%7%35%46%6%29%
1628
16th to endDay
14%12%37%5%35%5%6%6%28%
1546
November1st to 15thDay
14%13%47%5%345%5%6%29%
1321
16th to endDay
9%13%5%10%9%45%446%26%
1218
December1st to 15thDay
13%13%48%8%36%6%5%424%
1080
16th to endDay
10%13%411%8%35%448%24%
1152
January1st to 15thNight
7%13%6%11%9%46%45%6%25%
2865
16th to endNight
10%14%5%7%6%35%45%7%28%
2892
February1st to 15thNight
8%14%49%7%45%5%5%7%27%
2452
16th to endNight
5%10%6%10%7%5%7%5%6%8%27%
2028
March1st to 15thNight
8%12%5%10%7%44447%27%
2160
16th to endNight
8%13%5%7%7%35%46%7%28%
2003
April1st to 15thNight
7%9%5%9%8%47%6%6%7%27%
1783
16th to endNight
12%10%5%6%6%35%6%5%6%31%
1449
May1st to 15thNight
11%9%45%6%36%45%7%35%
1388
16th to endNight
14%8%37%6%35%5%5%6%31%
1147
June1st to 15thNight
14%6%47%6%35%46%6%34%
1080
16th to endNight
16%6%25%5%26%45%8%34%
1080
July1st to 15thNight
13%4235%25%6%8%9%37%
1080
16th to endNight
7%5%35%6%35%7%7%7%39%
1200
August1st to 15thNight
7%3145%35%6%7%9%44%
1440
16th to endNight
11%5%35%5%35%6%7%8%37%
1624
September1st to 15thNight
10%5%26%43346%7%45%
1800
16th to endNight
13%7%25%5%35%5%6%7%36%
1840
October1st to 15thNight
15%9%37%5%35%45%7%32%
2002
16th to endNight
13%13%48%7%35%5%5%5%28%
2324
November1st to 15thNight
13%12%47%6%35%5%46%31%
2525
16th to endNight
10%16%6%8%8%3435%6%27%
2742
December1st to 15thNight
9%13%6%8%8%46%5%46%25%
2880
16th to endNight
7%14%5%10%8%46%5%6%6%24%
3072

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
55%8%15%16%31
1074
16th to endDay
55%7%11%17%6%1
1344
February1st to 15thDay
53%10%15%13%7%
1400
16th to endDay
60%7%13%12%5%
1446
March1st to 15thDay
55%9%11%17%5%
1800
16th to endDay
56%9%16%14%3
2214
April1st to 15thDay
51%8%14%17%6%
2164
16th to endDay
54%8%13%17%6%
2511
May1st to 15thDay
46%8%14%19%10%
2561
16th to endDay
51%8%14%18%6%
2967
June1st to 15thDay
52%7%14%19%5%
2880
16th to endDay
47%8%14%20%8%
2880
July1st to 15thDay
42%9%15%23%7%
2711
16th to endDay
37%11%26%19%5%
2780
August1st to 15thDay
38%10%23%23%4
2503
16th to endDay
43%10%20%21%4
2578
September1st to 15thDay
40%8%22%20%6%
2160
16th to endDay
42%9%17%22%6%
1889
October1st to 15thDay
54%6%17%18%1
1628
16th to endDay
53%6%17%18%3
1546
November1st to 15thDay
54%7%13%19%5%
1321
16th to endDay
59%6%13%13%41
1218
December1st to 15thDay
62%8%11%13%3
1080
16th to endDay
58%7%12%15%6%
1152
January1st to 15thNight
60%7%14%14%21
2865
16th to endNight
54%7%14%14%6%1
2892
February1st to 15thNight
55%7%15%15%6%
2464
16th to endNight
52%8%15%18%4
2028
March1st to 15thNight
55%6%13%18%5%
2160
16th to endNight
53%6%13%17%7%
2007
April1st to 15thNight
54%7%12%18%7%
1783
16th to endNight
51%9%12%17%9%
1449
May1st to 15thNight
46%8%11%20%12%1
1389
16th to endNight
50%7%13%19%9%
1147
June1st to 15thNight
48%6%14%23%6%
1080
16th to endNight
46%7%16%20%9%
1080
July1st to 15thNight
36%10%17%26%8%
1020
16th to endNight
37%10%24%21%4
1123
August1st to 15thNight
32%12%20%27%6%
1432
16th to endNight
40%9%21%22%5%
1624
September1st to 15thNight
37%7%21%23%8%1
1800
16th to endNight
45%9%14%22%7%
1840
October1st to 15thNight
50%7%16%20%4
2002
16th to endNight
55%8%15%17%2
2324
November1st to 15thNight
53%7%12%19%6%
2525
16th to endNight
58%7%11%15%41
2742
December1st to 15thNight
59%8%13%14%4
2880
16th to endNight
57%7%11%16%5%
3072

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
13%5%30%28%15%8%
60
16th to endDay
15%6%25%29%18%4
64
February1st to 15thDay
6%13%25%36%15%3
60
16th to endDay
11%6%35%26%18%1
209
March1st to 15thDay
17%11%30%28%11%1
270
16th to endDay
15%6%33%31%12%
288
April1st to 15thDay
14%17%30%26%9%1
269
16th to endDay
20%11%30%25%11%1
270
May1st to 15thDay
13%12%29%29%14%
338
16th to endDay
19%6%21%28%18%5%
677
June1st to 15thDay
18%8%25%26%17%3
675
16th to endDay
19%6%22%25%19%5%
675
July1st to 15thDay
14%7%25%30%18%4
645
16th to endDay
10%8%22%34%20%3
634
August1st to 15thDay
13%5%20%27%24%8%
315
16th to endDay
15%12%34%26%10%
332
September1st to 15thDay
17%9%27%25%14%4
315
16th to endDay
16%15%27%26%12%2
272
October1st to 15thDay
24%10%29%19%14%1
233
16th to endDay
29%5%15%24%21%3
89
November1st to 15thDay
20%6%45%21%6%
60
16th to endDay
21%320%31%10%13%
60
December1st to 15thDay
10%6%16%38%25%3
60
16th to endDay
17%10%23%29%10%7%
64
January1st to 15thNight
13%11%30%29%12%3
930
16th to endNight
17%13%30%29%9%
834
February1st to 15thNight
16%12%26%24%15%3
704
16th to endNight
10%5%23%35%20%3
632
March1st to 15thNight
13%10%31%31%12%1
720
16th to endNight
15%5%25%35%17%1
768
April1st to 15thNight
12%6%33%30%14%2
703
16th to endNight
14%9%30%26%16%2
369
May1st to 15thNight
13%8%27%35%12%2
360
16th to endNight
16%5%24%32%20%1
375
June1st to 15thNight
14%6%24%30%23%1
360
16th to endNight
19%322%34%18%3
360
July1st to 15thNight
14%227%36%16%2
340
16th to endNight
10%223%35%24%2
376
August1st to 15thNight
9%120%33%30%4
360
16th to endNight
13%429%30%20%1
478
September1st to 15thNight
13%424%33%21%2
720
16th to endNight
16%9%28%29%13%2
675
October1st to 15thNight
19%8%31%30%9%
660
16th to endNight
18%11%29%28%10%1
704
November1st to 15thNight
16%11%34%27%9%
775
16th to endNight
17%11%29%26%12%2
907
December1st to 15thNight
15%11%28%30%12%2
930
16th to endNight
13%11%26%29%16%2
992
Page generated at 2017-09-21 05:18:10. Version ac04

Copyright 2017 A. Danko


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