Lancaster
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lancaster clear sky chart from 2005-11-06 to 2024-01-11.

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
67%
24224
38%
74324
29%
24175
76%
24175
60%
32813

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 10thNight
57%
756
29%
2646
25%
756
66%
756
41%
1285
January11th to 20thNight
61%
724
36%
2418
31%
724
73%
724
48%
1119
January21st to endNight
56%
792
39%
2396
28%
792
69%
792
47%
1197
February1st to 10thNight
60%
720
37%
2160
29%
720
71%
720
51%
1057
February11th to 20thNight
57%
700
37%
2098
28%
700
71%
700
51%
1024
February21st to endNight
52%
592
34%
1776
27%
592
65%
592
52%
846
March1st to 10thNight
53%
720
30%
2160
23%
720
66%
720
48%
1079
March11th to 20thNight
58%
720
30%
2108
24%
720
67%
720
51%
1036
March21st to endNight
53%
792
36%
1980
18%
792
65%
792
57%
1042
April1st to 10thNight
51%
720
36%
1800
15%
720
64%
720
59%
935
April11th to 20thNight
53%
711
39%
1779
17%
711
64%
711
67%
860
April21st to endNight
56%
720
38%
1800
16%
720
65%
720
71%
848
May1st to 10thNight
55%
640
36%
1720
18%
640
64%
640
76%
744
May11th to 20thNight
61%
531
42%
1595
26%
531
71%
531
72%
629
May21st to endNight
54%
582
37%
1746
21%
582
65%
582
73%
674
June1st to 10thNight
66%
470
38%
1550
28%
470
76%
470
77%
552
June11th to 20thNight
76%
360
44%
1440
42%
360
87%
360
87%
397
June21st to endNight
78%
360
43%
1440
46%
360
86%
360
82%
411
July1st to 10thNight
92%
350
41%
1400
48%
350
95%
350
78%
418
July11th to 20thNight
90%
348
41%
1392
48%
348
91%
348
65%
469
July21st to endNight
86%
703
39%
1780
28%
664
87%
664
74%
795
August1st to 10thNight
84%
716
38%
1780
24%
712
85%
712
80%
812
August11th to 20thNight
90%
712
43%
1780
25%
712
91%
712
86%
775
August21st to endNight
89%
792
46%
1980
30%
792
90%
792
85%
866
September1st to 10thNight
85%
720
46%
1800
33%
720
89%
720
84%
794
September11th to 20thNight
83%
720
49%
1929
39%
720
90%
720
88%
768
September21st to endNight
79%
720
48%
1980
37%
720
89%
720
83%
802
October1st to 10thNight
74%
720
42%
1980
32%
720
85%
720
70%
881
October11th to 20thNight
74%
720
46%
2101
39%
720
85%
720
74%
859
October21st to endNight
70%
792
45%
2428
40%
792
81%
792
71%
969
November1st to 10thNight
74%
740
39%
2405
37%
740
83%
740
67%
947
November11th to 20thNight
78%
760
40%
2470
39%
760
86%
760
64%
1000
November21st to endNight
67%
760
38%
2470
36%
760
75%
760
52%
1123
December1st to 10thNight
61%
760
35%
2470
29%
760
71%
760
48%
1170
December11th to 20thNight
62%
758
30%
2944
29%
758
71%
758
35%
1490
December21st to endNight
53%
823
20%
4623
26%
817
65%
817
26%
2140

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
2212222346%75%
74931
Night
2212223346%74%
74778
TransparencyDay
12%46%16%29%34%
74653
Night
12%46%17%29%30%
74577
SeeingDay
39%24%31%22%12%
14361
Night
2324%42%26%3
24249

By Month

Percentage Cloud Cover SW (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 10thDay
34244245%6%9%58%
1519
11th to 20thDay
441333445%7%62%
1552
21st to endDay
45%2433346%8%60%
1955
February1st to 10thDay
322342435%6%66%
1800
11th to 20thDay
3212323449%67%
1750
21st to endDay
2313434447%65%
1480
March1st to 10thDay
23134346%6%10%59%
1800
11th to 20thDay
23123235%6%9%64%
1846
21st to endDay
11123245%5%7%69%
2376
April1st to 10thDay
221222345%7%69%
2160
11th to 20thDay
1212212236%78%
2129
21st to endDay
11212347%78%
2160
May1st to 10thDay
111212237%79%
2238
11th to 20thDay
1111112236%82%
2301
21st to endDay
1112111236%80%
2530
June1st to 10thDay
11112336%82%
2403
11th to 20thDay
1113390%
2520
21st to endDay
11111112388%
2520
July1st to 10thDay
11111122485%
2520
11th to 20thDay
111222123481%
2520
21st to endDay
2211112236%79%
2426
August1st to 10thDay
111121112485%
2149
11th to 20thDay
111222487%
2122
21st to endDay
1111222484%
2376
September1st to 10thDay
11111232484%
2160
11th to 20thDay
111122390%
2030
21st to endDay
111222486%
1980
October1st to 10thDay
1111212246%79%
1980
11th to 20thDay
1111223484%
1854
21st to endDay
11211335%83%
1926
November1st to 10thDay
1112212337%77%
1674
11th to 20thDay
1213233446%72%
1710
21st to endDay
2213325%449%66%
1710
December1st to 10thDay
34245%3345%7%61%
1710
11th to 20thDay
5%5%25%5%45%6%6%9%49%
2169
21st to endDay
7%6%35%6%46%6%5%7%45%
2876
January1st to 10thNight
332442347%8%59%
2646
11th to 20thNight
4313423348%66%
2418
21st to endNight
3324423347%65%
2396
February1st to 10thNight
2413323346%69%
2160
11th to 20thNight
3213323446%69%
2098
21st to endNight
3313424346%67%
1776
March1st to 10thNight
22233345%6%9%61%
2160
11th to 20thNight
321333335%8%66%
2108
21st to endNight
221332445%7%69%
1980
April1st to 10thNight
221222335%8%70%
1800
11th to 20thNight
112212246%78%
1779
21st to endNight
1111112246%80%
1800
May1st to 10thNight
111225%7%80%
1720
11th to 20thNight
11111235%84%
1594
21st to endNight
111111235%84%
1746
June1st to 10thNight
11112226%85%
1550
11th to 20thNight
112492%
1440
21st to endNight
1111111391%
1440
July1st to 10thNight
111112488%
1440
11th to 20thNight
11121224481%
1440
21st to endNight
111213226%80%
1885
August1st to 10thNight
21111133385%
1790
11th to 20thNight
111112489%
1780
21st to endNight
1111123387%
1980
September1st to 10thNight
11111111388%
1800
11th to 20thNight
11122291%
1929
21st to endNight
111112389%
1980
October1st to 10thNight
111212345%80%
1980
11th to 20thNight
111212235%83%
2101
21st to endNight
111211235%82%
2428
November1st to 10thNight
111221235%6%77%
2405
11th to 20thNight
1212213337%75%
2470
21st to endNight
321322345%7%68%
2470
December1st to 10thNight
3323323448%66%
2470
11th to 20thNight
5%315%435%6%6%9%54%
3041
21st to endNight
4425%6%36%6%6%8%49%
4778

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 10thDay
21%6%9%24%27%12%
1519
11th to 20thDay
21%49%18%30%18%
1552
21st to endDay
23%6%8%21%24%18%
1955
February1st to 10thDay
19%46%21%28%22%
1800
11th to 20thDay
16%45%19%36%20%
1760
21st to endDay
19%5%8%20%31%16%
1480
March1st to 10thDay
19%7%10%23%23%18%
1800
11th to 20thDay
16%7%11%21%28%18%
1846
21st to endDay
14%6%10%28%30%13%
2376
April1st to 10thDay
15%5%10%25%28%17%
2160
11th to 20thDay
10%37%23%35%22%
2132
21st to endDay
8%49%23%38%18%
2160
May1st to 10thDay
8%48%22%34%24%
2238
11th to 20thDay
8%36%18%40%25%
2304
21st to endDay
9%36%20%41%20%
2530
June1st to 10thDay
6%46%15%31%38%
2403
11th to 20thDay
21313%25%56%
2520
21st to endDay
6%23320%68%
2520
July1st to 10thDay
5%226%16%68%
2451
11th to 20thDay
9%2311%27%48%
2445
21st to endDay
10%3415%29%39%
2291
August1st to 10thDay
7%227%19%63%
2135
11th to 20thDay
5%226%29%57%
2122
21st to endDay
7%226%25%58%
2376
September1st to 10thDay
7%246%24%57%
2160
11th to 20thDay
4127%31%54%
2030
21st to endDay
6%228%37%45%
1980
October1st to 10thDay
9%3414%27%42%
1980
11th to 20thDay
5%4412%33%42%
1854
21st to endDay
6%3411%31%44%
1926
November1st to 10thDay
9%45%16%37%28%
1674
11th to 20thDay
13%47%17%31%29%
1710
21st to endDay
16%6%7%16%28%26%
1710
December1st to 10thDay
21%5%8%21%25%20%
1710
11th to 20thDay
27%9%10%20%23%11%
2168
21st to endDay
33%6%8%22%22%8%
2876
January1st to 10thNight
21%7%8%20%30%14%
2646
11th to 20thNight
18%5%7%20%30%19%
2418
21st to endNight
19%6%9%20%26%20%
2396
February1st to 10thNight
18%5%7%18%27%25%
2160
11th to 20thNight
17%6%6%17%30%24%
2099
21st to endNight
16%5%10%22%29%18%
1776
March1st to 10thNight
18%7%10%25%24%17%
2160
11th to 20thNight
17%6%10%20%29%18%
2108
21st to endNight
14%7%10%30%28%12%
1980
April1st to 10thNight
14%5%10%30%23%17%
1800
11th to 20thNight
11%47%29%30%20%
1779
21st to endNight
8%48%24%42%14%
1800
May1st to 10thNight
5%5%9%27%33%21%
1720
11th to 20thNight
6%35%21%43%21%
1595
21st to endNight
6%28%27%40%18%
1746
June1st to 10thNight
5%37%19%33%34%
1550
11th to 20thNight
21413%31%49%
1440
21st to endNight
412426%63%
1440
July1st to 10thNight
5%226%19%67%
1400
11th to 20thNight
8%3311%27%47%
1392
21st to endNight
8%3414%32%39%
1780
August1st to 10thNight
7%227%23%59%
1780
11th to 20thNight
4217%30%57%
1780
21st to endNight
5%136%28%56%
1980
September1st to 10thNight
5%235%27%58%
1800
11th to 20thNight
2238%35%51%
1929
21st to endNight
5%129%36%47%
1980
October1st to 10thNight
9%3315%28%42%
1980
11th to 20thNight
6%4411%34%41%
2101
21st to endNight
7%3410%27%48%
2428
November1st to 10thNight
9%45%17%34%32%
2405
11th to 20thNight
10%46%16%30%33%
2470
21st to endNight
16%5%7%19%26%28%
2470
December1st to 10thNight
19%5%7%18%27%24%
2470
11th to 20thNight
22%9%14%18%25%12%
3041
21st to endNight
26%7%8%25%25%9%
4778

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 10thDay
410%23%33%26%3
180
11th to 20thDay
10%12%20%24%22%11%
272
21st to endDay
5%15%23%25%23%8%
452
February1st to 10thDay
413%24%30%18%10%
420
11th to 20thDay
5%16%30%26%14%9%
415
21st to endDay
5%17%28%28%17%5%
346
March1st to 10thDay
7%21%28%25%14%6%
420
11th to 20thDay
416%32%25%16%6%
420
21st to endDay
418%35%26%13%3
462
April1st to 10thDay
5%14%30%27%17%7%
420
11th to 20thDay
418%34%26%11%7%
412
21st to endDay
214%34%22%16%12%
420
May1st to 10thDay
213%32%28%17%9%
423
11th to 20thDay
212%32%30%15%9%
448
21st to endDay
311%33%25%16%12%
485
June1st to 10thDay
18%27%32%19%13%
450
11th to 20thDay
6%28%30%21%15%
450
21st to endDay
1426%36%20%14%
450
July1st to 10thDay
222%42%21%13%
446
11th to 20thDay
213%42%27%16%
444
21st to endDay
2112%39%25%20%
487
August1st to 10thDay
2220%43%22%13%
447
11th to 20thDay
2212%41%23%20%
437
21st to endDay
117%40%26%16%
495
September1st to 10thDay
2218%33%29%17%
450
11th to 20thDay
1427%31%24%14%
450
21st to endDay
16%21%30%27%16%
450
October1st to 10thDay
18%25%26%27%13%
450
11th to 20thDay
16%20%28%32%14%
450
21st to endDay
28%22%24%27%16%
441
November1st to 10thDay
26%23%27%29%14%
270
11th to 20thDay
4415%34%31%11%
270
21st to endDay
38%24%24%32%9%
270
December1st to 10thDay
5%5%23%34%26%7%
270
11th to 20thDay
47%22%27%30%10%
270
21st to endDay
12%11%21%28%22%5%
219
January1st to 10thNight
5%6%25%40%21%3
760
11th to 20thNight
4425%46%19%1
724
21st to endNight
5%5%29%42%18%2
792
February1st to 10thNight
3428%39%23%2
720
11th to 20thNight
4432%37%19%4
704
21st to endNight
5%5%35%39%15%1
592
March1st to 10thNight
37%33%40%15%1
720
11th to 20thNight
4429%39%21%2
720
21st to endNight
37%35%39%15%1
792
April1st to 10thNight
45%37%33%19%2
720
11th to 20thNight
16%38%37%17%1
711
21st to endNight
16%35%34%20%3
720
May1st to 10thNight
340%41%14%2
640
11th to 20thNight
6%31%41%21%1
531
21st to endNight
8%36%41%14%
584
June1st to 10thNight
428%52%16%
470
11th to 20thNight
23%54%23%
360
21st to endNight
119%54%26%
360
July1st to 10thNight
5%56%39%1
350
11th to 20thNight
15%50%42%1
348
21st to endNight
18%48%39%3
703
August1st to 10thNight
111%49%34%4
716
11th to 20thNight
17%45%41%6%
712
21st to endNight
18%40%45%6%
792
September1st to 10thNight
111%38%44%6%
720
11th to 20thNight
114%44%35%5%
720
21st to endNight
118%40%35%6%
720
October1st to 10thNight
1221%44%29%4
720
11th to 20thNight
1220%40%33%4
720
21st to endNight
1224%35%30%7%
792
November1st to 10thNight
1321%41%30%5%
740
11th to 20thNight
1216%49%27%5%
760
21st to endNight
5%221%43%26%2
760
December1st to 10thNight
5%325%41%24%2
760
11th to 20thNight
6%422%45%22%2
760
21st to endNight
6%5%30%39%18%2
836
Page generated at 2024-01-08 08:14:20. Version ac07

Copyright 2024 Attilla Danko


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